Final Report Summary - NXTHPG (Next Generation of Heat Pumps working with Natural fluids.)
Executive Summary:
For heat pumps to become broadly accepted, an important effort is still required to increase their efficiency, reduce their environmental impact and become more economical. In regard to their environmental performance, one very important issue must still be solved, i.e. the use of refrigerants with 0 Ozone Depletion Potential and very low Global Warming Potential. HFC refrigerants, nowadays massively employed, have a very high GWP and consequently they were declared as Greenhouse Gases in the recent GHG European regulation.
The NxtHPG project strived to give a definitive step forward to overcome the barriers impeding the spread of natural refrigerants and usher in a new generation of heat pumps based on Hydrocarbons and CO2. In order to do so, NxtHPG project decided to concentrate on the development of a few selected applications in which it is feasible to develop a safe and cost effective solution and at the same time offer good prospects for commercial exploitation.
With this aim, the main objective of the NxtHPG project has been the development of a set of 5 reliable, safe, high efficiency and high capacity heat pumps (prototypes capacity around 50kW) working with the two most promising natural refrigerants: HCs and CO2. The finally selected case were:
• CASE 1 is a 40kW air to water heat pump (HP) for the production of hot water for heating also covering a low demand of domestic hot water (DHW) with the use of a de-superheater. The unit is reversible on the refrigerant circuit, so providing either heating in winter and cooling in summer.
• CASE 2 is a 60kW geothermal HP for hot water production for heating also covering a low demand of DHW with the use of a de-superheater. The unit is reversible on the refrigerant circuit, so providing either heating in winter and cooling in summer.
• CASE 3 consists of a 50kW HP booster from a neutral water loop, (10-30 ºC) (e.g. recovery of waste heat from condensation (25-30ºC) or sewage water (10-15ºC)) up to 60ºC for DHW production.
• CASE 4 is a 30kW air to water HP for sanitary water production at 60ºC or up to 80ºC for high temperature applications.
• CASE 5 is a 50kW air to water HP for heating applications. It targets the replacement of old gas boiler heating systems (5-6 families house) with old high temperature radiators as terminal units and high water return temperature. It provides DHW all over the year.
The project has been able to develop an optimized solution for each selected case (case1, 2 and 3 with propane, and case 4 and 5 with CO2) reaching the specified targets:
- High efficiency: 10 to 20% increase on Seasonal Performance Factor (SPF) compared to current HFC’s and HFO’s equivalent equipment.
- Very Low CO2 emission.
- Efficient and flexible capacity modulation.
- Tight containment and minimum charge. Design incorporating all the necessary safety measures and high reliability.
- Affordable cost: similar to that of equivalent HFC’s or HFO’s solution or slightly higher (10%).
The most important result of the project is the compilation of a set of design guidelines for the optimal design of each of this kind of heat pumps working with natural refrigerants, and a number of innovation and knowhow results acquired both for the heat pumps and their components: compressors, evaporators, condensers, and auxiliaries, optimized for the use of each of the selected refrigerants: propane and CO2.
NxtHPG project has proven that safe, reliable and cost effective heat pumps employing natural refrigerants are perfectly feasible and cost effective.
Project Context and Objectives:
Project context and motivation: Natural Refrigerants technology
Electrical Heat pumps (HPs) based on the vapor compression cycle have considerably improved in the last decades in terms of efficiency, flexibility and reliability and nowadays they constitute one of the pillars with the highest potential for the reduction of primary energy consumption in all heating/cooling applications on buildings but also on industrial processes. Notably, the cleanest alternative energy is that energy which is never consumed! In fact, energy never consumed by its efficient use has the highest potential for broad industrial application.
Environmental impact is another strong point of heat pumps. HPs are able to produce heat from the ambient air or ground heat, and they need little electricity consumption to pump that heat to the required supply temperature. For moderate temperature lifts, as modern heating systems now employ, the heat pump is a very efficient solution with a minimum carbon total footprint. Additionally, in recent years the technology of CO2 heat pumps working under a transcritical cycle has also shown high efficiency at high temperature lifts, as for instance in heating city water from 10 ºC to 60ºC or even higher temperatures.
However, there is still a significant margin for further improvement. For heat pumps to become broadly accepted, an important effort is still required to increase their efficiency, reduce their environmental impact and become more economical. Efficiency is essential to reduce energy consumption and global CO2 emissions but also to reduce annual operation costs, by being able to reasonably compensate a higher first cost of investment when compared with other conventional technologies, such as a gas boiler.
In regard to their environmental performance, one very important issue must still be solved, i.e. the use of a 0 ODP and very low GWP refrigerants. In fact, the HFC refrigerants, nowadays massively employed, have a very high Global Warming Potential, and consequently they were declared as Greenhouse Gases in the recent GHG European regulation.
After several failed trials, the reaction of the Chemical Industry to the public concern on HFCs and their high Global Warming Potential has been the development of a new family of synthetic fluids: HFOs which have a very low global warming potential. However, first they are again ‘synthetic’, and second they are flammable. It is true that the risk of ignition of a mixture of these fluids with air is lower than that with hydrocarbons, but still they are flammable and will require careful design of the equipment to insure their intrinsic safety, which of course may be equally done for hydrocarbons at a slightly higher cost. Furthermore, HFO producers have been recently investigated by the European Commission, who has opened antitrust proceedings concerning agreements between Honeywell and DuPont for the development of the new HFO-1234yf refrigerants.
It is very important to point out that these artificial chemical substances may be found in a longer perspective to have unexpected negative consequences on the environment (history is full of such stories), so does it make sense to substitute HFCs once again by synthetic fluids which are ‘very’ recent, when both Hydrocarbons and CO2 can provide superior total environmental performance for Refrigeration, A/C and Heat pumps? We strongly believe that the answer is: No!
Natural fluids present 4 very important advantages as refrigerants:
• 0 Ozone depletion potential
• Almost negligible Global Warming Potential
• They are not synthetic so that we are 100% sure they are not harmful for the environment.
• Some natural fluids possess very good thermodynamic properties to be employed as refrigerants. Development of equipment specifically designed for them will lead to higher efficiencies than the ones obtained with synthetic refrigerants, contributing to the reduction of the global environmental impact of the future heat pumps and refrigeration equipment.
Regarding the capacity of the units, up to now and after two decades of considerable Research on Natural Refrigerants, only small capacity refrigeration and heat pump equipment are commercially available at present, and there is almost no commercially available heat pump equipment of commercial size (20 kWthermal to hundreds of kW) employing natural refrigerants. This has in practice prevented the implementation of natural fluids for heating and cooling in the building sector and Industry.
This project strived to give a definitive step forward to overcome the barriers impeding the spread of natural refrigerants and usher in a new generation of heat pumps based on HCs and CO2 that are perfectly feasible and commercially competitive.
Project Objectives
The project targets the development of the next generation of heat pumps of high capacity working with Natural fluids. However, the development of improved components and optimization of the unit design and its control strategy cannot be made in “general”, and doing it for each specific application is of course not affordable. Consequently, manufacturers optimize the design of components and equipment only for the applications with the largest market. This means that the components and equipment available for heat pumps are obliged to employ components and designs which have been optimized for Air Conditioning, since the A/C market is much larger than the heat pump market. This constitutes a very important barrier for the future improvement of the heat pumps.
Therefore, the only way to produce a significant boost of this heat pump technology is by concentrating on the development on a few selected applications...those whose aggregation of all the small improvements leads to a product with superior performance and affordable cost.
The first objective of the project is therefore the identification of the cases in which the development of a new generation of heat pumps employing Natural refrigerants can lead to a fast commercial exploitation of the first series of heat pumps developed here, and later to the successful deployment of the technology to other sizes, ranges and applications.
Regarding the targeted market, for rapid deployment of a natural refrigerants technology, it is much better to first target the development of applications with a large potential market, and at least moderate production series where the cost can be sufficiently minimized. Therefore, the applications will very probably belong to the Sector of heating and sanitary hot water production of large buildings, in which, on the one side the installation of this kind of equipment is perfectly feasible, the new technology could lead to a significant reduction on both energy consumption and CO2 total emissions, and in which, on the other hand, the European HVAC industry still has the majority of the market, in contrast with the domestic sector in which the low cost equipment coming from Asia dominates the market. This potential market is large since it includes both systems in new buildings and renovation of HVAC systems in existing buildings.
Taking into account the above mentioned requirements, the following cases have already been identified as of high potential interest:
• Hydrocarbons (HCs) will be employed for the development of a small family of heat pumps supplying hot water at (40-50 ºC) for heating applications as well as to produce sanitary hot water at 60ºC. For this last case, several solutions will be explored: (i) an eventual direct production of sanitary hot water by the same unit also producing hot water for heating, (ii) a combination with storage and hot water production by batch heating, (iii) a high temperature stage provided by a hydrocarbon with high critical point (for instance butane).
Given the hazardous characteristics of HCs, the systems must be indirect: the heat pump will heat water, and this water (heat transfer medium) is then distributed to the terminal systems. This solution is also the best for coupling with other sources and for storage, maximizing the capabilities for integration and optimal operation.
• CO2 will be employed for the development of a heat pump of high capacity being able to produce sanitary hot water at 60 ºC directly from city water (10-15 ºC). Designs for simultaneous production of hot water for heating purposes and sanitary hot water, and applications with higher temperatures: 70-90 ºC will be also explored.
In regard to the heat source for the HPs, water (or a brine in geothermal applications) will lead to the best performance and the greatest potential for integration with other systems so it will be the choice for most of the solutions to be developed. In any case, at least one prototype will also be based on air, since Air to water units also constitute an important part of the market and minimization of charge in that sort of equipment is an important issue.
The general objective of the project is the development of a set of safe, reliable, and high efficiency heat pumps working with natural refrigerants of high capacity > 40 kW (probably ranging from 40 to 100 kW) together with a set of improved components and auxiliary devices adequate for the efficient and safe use of the two considered refrigerants: Hydrocarbons and CO2; the project will also provide the necessary know-how to key European companies of the Sector to bring to market the newly developed technology.
The project aims at reaching higher efficiency (10 - 20% SPF improvement) and lower Carbon footprint (20% lower TEWI) than the current state of the art of HFCs/HFOs or Sorption heat pump technologies while keeping the cost very similar or only a bit higher (10%) in a way that the better environmental performance clearly compensates for the extra cost; and additionally, the project aims to achieve efficient capacity modulation and the highest capabilities for combination and integration with other renewable sources in the energy systems of Buildings and Industry.
The final aim of the project is for the new heat pump designs to become the seeds for a future generation of heat pumps working with natural fluids manufactured by European companies and commercially available over a wide range of applications and capacities.
Project Results:
The first result of the project was the identification of the cases in which the use of Natural refrigerants could lead to cost effective and high efficient solutions with potential fast commercial exploitation. As a result of the market analysis and the safety and technical requirements for both refrigerants, 5 different application cases were identified which have the following characteristics:
CASE 1 is an air to water heat pump for the production of hot water for heating applications also covering a low demand of domestic hot water with the use of a de-superheater. The unit will be reversible on the refrigerant circuit, so providing heating and cooling. The range for outdoor temperature variation is approximately: -10 to 35 ºC. The supply temperature for the heating water should range between 40 and 50 ºC, while the supply temperature for the domestic hot water should be 60 ºC. Unit size should be around 50 kW (targeted for the prototype: 40 kW). This is a good case for employing a hydrocarbon as refrigerant, since it is an outdoor unit so there is practically no limit on the refrigerant charge and safety measures, if any is required, are simple.
CASE 2 is a geothermal heat pump for the production of hot water for heating applications also covering a low demand of domestic hot water with the use of a de-superheater. It will be reversible on the refrigerant circuit, so providing heating and cooling. The range for brine temperature variation is approximately: -5 to 15 ºC. The supply temperature for the heating water should range between 40 and 50 ºC, while the supply temperature for the domestic hot water should be 60 ºC. Unit size should be around 50 kW (targeted for the prototype: 60 kW). This is a good case for employing a hydrocarbon as refrigerant if the unit is installed in some machinery room (with the exception of installation below ground level) or in open air. Again, in this case there will be practically no limit on the refrigerant charge and safety measures, if any is required, are simple.
CASE 3 is a very innovative case consisting of a heat pump booster which pumps the heat from a neutral water loop, (10-30 ºC) (recovery of waste heat from condensation (25-30ºC) or sewage water (10-15ºC)), pumping it up to 60ºC for sanitary hot water use. The supply temperature for the sanitary hot water should be 60 ºC. Unit size should be around 50 kW (targeted for the prototype: 50 kW). Again, this is a good case for employing a hydrocarbon as refrigerant because the mentioned conditions the discharge temperature is going to high, and hydrocarbons, typically have a reduced discharge temperature when compared with synthetic refrigerants. The unit should be installed in some machinery room (with the exception of installation below ground level) or in open air. Again, in this case there will be practically no limit on the refrigerant charge and safety measures, if any is required, are simple.
CASE 4 is an air to water heat pump for hot water production at 60ºC or up to 80ºC for high temperature applications. The range for outdoor temperature variation is approximately: -10 to 35 ºC. The supply temperature for sanitary hot water use should be 60 ºC. However, thanks to the special characteristics of CO2 higher temperatures can be reached, e.g. 80ªC, with still good efficiency. Unit size should be around 50 kW (targeted for the prototype: 30 kW). This is a good case for employing CO2 as refrigerant since the production of high temperature hot water from city water is very well suited to this refrigerant due to the high refrigerant glide obtained at the gas cooler.
CASE 5 is an air to water heat pump for ‘heating applications’. It targets the renovation market for the replacement of old gas boiler heating systems (5-6 families houses) with high temperature old radiators as terminal units. Main role is hot water production for heating but it must also provide DHW all along the year. The development should be targeted for winter operation, although the unit will be also used during summer for DHW production.. The range for outdoor temperature variation is approximately: -10 to 35 ºC. The supply temperature for the old radiators should be 80ºC with the return temperature from the heating network being 40ºC. Unit size should be around 50 kW (targeted for the prototype: 50 kW). This is a good case for employing CO2 as refrigerant because this will decrease to a minimum direct Global Warming impact. Indirect emissions due to the electricity consumption will depend on the achievable efficiency.
As explained above, given the application it was decided that CASES 1 to 3 will be developed for use with a hydrocarbon refrigerant, while CASES 4 and 5 were adequate for CO2. Therefore, the development of five different HP prototypes was targeted in the project, 3 with hydrocarbons and 2 with CO2.
Once the case studies and the design and operation requirements were defined, heat pump mathematical models were developed for each case, and employed to design the prototypes. The modelling allowed the optimization of each HP design to the selected refrigerant and the given application. For the prototypes 1 to 3 propane was selected as the most suitable hydrocarbon refrigerant. Butane also seem to have good properties for prototype 3, however its low volumetric capacity requires a too large compressor resulting in a too expensive solution. In regard to other components, the following special characteristics should be highlighted:
• Prototype 1 should count with a variable speed scroll compressor in order to get a good SPF taking into account the wide range of variation of the outdoor conditions for air to water HPs.
• Prototype 2 should count with two scroll compressors working in tandem. In this way, partial load capacity of this geothermal unit could be enhanced.
• Prototype 3 should incorporate a system to produce a high subcooling in order to take advantage of the high temperature lift of the water in sanitary hot water production to produce a high COP. Two designs were identified: mode A, incorporating a subcooler after the condenser, and mode B, incorporating an innovative liquid throttling valve in order to control the flooding of the condenser and thus the refrigerant subcooling.
• Prototype 4 should concentrate in reaching the highest SPF for hot water production at 60 or higher temperature, especially concentrating on the components, efficiency, the internal heat exchanger design and the unit control.
• Prototype 5 should concentrate on the optimization of the design for the very peculiar operating conditions, production of heating hot water at 80 ºC for old high temperature radiators with a relatively high return water temperature of 40ºC. A two stage special CO2 cycle was considered the best solution for this prototype.
Once the design was defined, the 5 different prototypes were constructed.
DCC provided the adequate scroll compressors adapted for the use of propane, DORIN provided the suitable compressors for the CO2 prototypes, ALFA LAVAL provided all water to refrigerant heat exchangers for the 5 prototypes, including the desuperheaters for prototypes 1 and 2, the subcooler for prototype 3, and the gas coolers and internal heat exchangers for prototypes 4 and 5. LUVE provided all air to water heat exchangers, i.e. the outdoor coil for prototype 1, and the evaporators for prototypes 4 and 5. Finally, CIATESA constructed the three propane prototypes (1 to 3) while ENEX constructed the two CO2 prototypes (4 and 5).
The prototypes were then tested along a 1st experimental campaign at: KTH (prototypes 1 and 2), UPVLC (prototype 3), and ENEA (prototypes 4 and 5). This test campaign allowed first the solution of some initial design problems and the tuning up of the prototypes. Second, it allowed the study and optimization of the HP controllers. And finally, it allowed the check of the reliability of the operation and the characterization of the performance of each prototype. The analysis of the results of this 1st experimental campaign allowed the optimization of the design of the different prototypes. The results were analyzed in detail, and the mathematical models were adjusted. This allowed to determine a series of changes that could lead to improvements in their performance.
Once the experiments from the first campaign were analyzed, the heat pump models were adjusted in IMST-ART software and polynomial correlations were created by means of parametric studies carried out in IMST-ART software. These polynomial correlations were programmed in a model in TRNSYS jointly with the rest of the system components in the framework of WP6. The updated lumped parameter models for each case study were provided to all RTD partners and explained by UNINA in deliverable D6.1’Updated lumped parameter models for each case study’. The models were employed by UNINA in order to study the operation of the heat pumps for each case study, and an estimation of the seasonal performance factor for each case study was carried out. This allowed to make a first assessment of the project results which was presented in deliverable D6.5 ’First assessment of the project results’.
Regarding this first generation of heat pump prototypes developed, the required modifications were identified by each of the heat pump and component manufacturers in collaboration with the rest of the RTD partners of the project, and they were implemented in the framework of WP7 ‘Improvement of HP prototypes design and construction’ in order to improve the heat pump prototypes and produce a second generation of very high efficient heat pumps. A second experimental campaign took then place in the corresponding labs in the framework of WP8 ‘2nd experimental campaign and control optimization’.
Once the new experimental measurements from the second experimental campaign were available, both the heat pump models and the integrated system lumped parameter models were updated by UPVLC and UNINA respectively. Finally, UNINA carried out a final analysis and optimisation of the heat pump control for each case study and presented the final estimation of the seasonal performance factor for each case study in deliverable D8.4 ’Analysis and optimisation of the heat pump control for each case study’.
Taking into consideration the new updated information, a final assessment of the project results was presented in deliverable D9.2 ‘Assessment of the developed heat pump solutions’ with a critical review of the objectives: higher efficiency (10 - 20% SPF improvement) and lower Carbon footprint (20% lower TEWI) than current state of the art HFCs/HFOs or Sorption heat pump technologies while keeping the cost very similar or only a bit higher (10%).
The main final results about the performance of the developed prototypes are described in the following:
RESULTS OF THE 2ND EXPERIMENTAL CAMPAIGN. NOMINAL POINT AND FINAL ASSESSMENT.
Hydrocarbon heat pump prototypes
CASE 1
The nominal conditions selected for the design of the HP correspond to winter operation. According to EUROVENT operating conditions for standard rating, the external ambient temperature would correspond to 7ºC (6ºC wet bulb) for the outdoor circuit. For the indoor circuit, the water temperatures would be 40/45 ºC (Return (heat pump inlet)/ Supply) according to medium temperature application (fan-coil) as indicated in the norm EN 14511-2).
The target of the project was to reach at least the EUROVENT classification of class A, and reach a 20% higher efficiency than the reference unit provided by CIATESA which was: 2.96. The COP including auxiliaries finally obtained for the nominal point was 3.43 what represents a 15.9% increase in COP respect the reference unit. On the other hand the Eurovent Class A tresshold is COP 3.2 so prototype 1 exceeds Class A by 7.2%.
In regard to the heat pump capacity, it should be noted that the capacity of the unit was around 36.6 kW for a nominal frequency of the compressor of 50Hz, as it was expected from the specified design of the HP.
CASE 2
The nominal conditions selected for the design of the HP correspond to winter operation. According to EUROVENT operating conditions for standard rating, brine temperatures existing in the outdoor circuit would correspond to 0/(-3ºC) (inlet/outlet of evaporator); for the indoor circuit, the water temperatures would be 40/45 ºC (Return (heat pump inlet)/ Supply) according to medium temperature application (fan-coil) as indicated in the norm EN 14511-2).
The COP of the reference unit provided by CIATESA was: 4.02. The COP including auxiliaries finally obtained for the nominal point was 4.47 what represents an 11.1% increase in COP respect the reference unit.
In regard to the comparison with EUROVENT, data appearing in EUROVENT for the classification of this kind of units only exists for the water cooled case which is a different application, as CASE 2 is a geothermal heat pump for heating of buildings. Therefore the comparison is not possible for this prototype.
In regard to the heat pump capacity, it should be noted that the capacity of the unit was around 63.11 kW at the nominal point, which is close to the initially targeted value of 60 kW.
CASE 3
The nominal conditions selected for the design of the HP correspond to hot water production with 20ºC inlet temperature in the outdoor circuit (evaporator) and 10/60ºC (return temperature/supply) for the indoor circuit (condenser). At this conditions, the measured COP is 5.7.
As this case is very innovative, there is no existing reference unit, neither in EUROVENT classification nor in the manufacturer catalogue. However, it will be compared with those units available in the market for sanitary hot water production which work with a transcritical CO2 cycle. In particular, Q-ton unit produced by Mitsubishi has been selected for this purpose. Although Q-ton is not the same type of heat pump as CASE 3 (heat pump booster), it has been chosen because it is a high efficiency air to water CO2 heat pump for the production of hot water. So, the application is the same, and they differ in the type of source considered (waste heat recovery water versus ambient air).
If one compare the measured COP with the Q-ton unit working at 25ºC of ambient air temperature, for different condenser inlet water temperatures, the measured COP is always higher than the one provided by the Q-ton unit, with differences ranging from 5% to 30% depending on the condenser inlet temperature. The higher this temperature the higher the difference in COP.
Regarding the heat pump capacity, experimental measurements carried out at UPVLC for the nominal working conditions, conclude that the heat pump capacity is around 47 kW, which is very close to the design heat pump capacity (50kW).
In regard to the layout of the heat pump, it has been proved that both developed and analyzed cases (mode A and B) can lead to the same high performance. In the tests, Mode A has a slightly higher COP, but one should realize that it also has more heat transfer area (subcooler). On the other hand, mode B has one heat exchanger less, but it needs an extra valve, the throttling valve to control subcooling, and a more sophisticated control. Long duration tests, as well as a detailed economical study, should be carried out before making a final decision about which of both modes is the most cost-effective.
Finally, just comment that the refrigerant charge of the final industrial product, which for the case of refrigerant propane is an important issue, could be reduced from the one needed in the developed prototype, since the lab prototype included components and refrigerant circuit providing the possibility of testing both modes in the same prototype. This is of course not necessary in the final product and a considerable reduction of around 2 kg is expected for mode B, and 1.5 kg for mode A. The final propane charge could be around:
Charge Mode A = 4.8 kg
Charge mode B = 4.3 kg
CO2 heat pump prototypes
CASE 4
The nominal conditions selected for the design of the HP correspond to winter operation, that is to say an ambient temperature of 7ºC, and a water inlet temperature in the gas cooler of 10ºC, for a supply temperature (outlet of the gas cooler) of 60ºC. At this conditions, the measured COP was 3.76 including auxiliaries. The reference COP established by ENEX for this case under those operating conditions was 3.4. Therefore, the increase in performance in this case has been of 10.6%.
In any case, we must state that the reference value for the COP in this case was a target value stated by ENEX because at the beginning of the project the company did not have any unit with similar size and characteristics to the one which was going to be developed.
On the other hand, regarding the heat pump capacity, it should be noted that the capacity of the unit is around 30 kW, as it was expected from the design of the HP.
Additionally, an assessment was carried out considering an already existing product in the market manufactured by Mitsubishi (model ‘Q-ton’). The comparison of results shows that the developed prototype provides significant higher COP then the Q-ton unit (from 10 to 20% higher) at low ambient temperatures (from -7ºC to 5ºC). Only at high ambient temperatures (e.g. 16ºC) the COP of the Q-ton unit becomes higher by 11%. This is probably due to the technology used for the compressor in the ‘Q-ton’ unit whichi is totally different, as it combines two different types of compressor working in series (two stages of compression): a rotary compressor and a scroll compressor, whereas CASE 4 employs a piston compressor with one single stage of compression. It should be noted that, using the compressor technology considered in the ‘Q-ton’ unit, would mean a much higher cost and not reaching the threshold of 10% extra cost at much according to the targets of the NxtHPG project.
This difference in COP at low temperatures will lead to a great advantage in terms of seasonal COP since the dominant temperatures along the winter season are always low.
CASE 5
The nominal conditions selected for the design of the HP correspond to winter operation, it is to say an ambient temperature of 7ºC, and a water inlet temperature in the gas cooler of 40ºC (return temperature from the radiators in the building), for a supply temperature (outlet of the gas cooler) of 80ºC (supply temperature to radiators in the building). The measured COP including auxiliaries at this point is 2.46 and the heating capacity 45.6 kW which is in line with the targeted design.
There is no reference value for the COP of this unit since there is no commercial unit available for this application in the market. The reference unit considered in deliverable ‘D1.3 Description of the selected case studies’ corresponds to old gas boilers installed over 15 years ago which are less efficient than the new condensing boilers. These old boilers commonly convert 80% of their fuel into heat. In order to make a fair assessment for CASE 5 in this context, a comparison in terms of primary energy consumption was be carried out and it is described in the next section.
In order to get a comparison with some existing unit a single point test was carried out in conditions for which there was information of the ‘Q-ton’ unit mentioned above. The results showed an advantage of 5.4% on COP including auxiliaries for prototype 5.
ANALYSIS OF THE OPERATION OF THE HEAT PUMP FOR EACH CASE STUDY: FINAL ESTIMATION OF THE SEASONAL PERFORMANCE FACTOR (SPF).
An analysis of the operation of the heat pump for each case study and application was carried out by UNINA by means of the updated lumped parameter models developed in the framework of WP2 and WP6. These models were updated in WP8 and a final analysis was carried out by UNINA.
In order to have an assessment of the performance updated to the current development of the prototypes of the HPs, the models of the HPs were programmed using IMST-ART adjusted to experimental measurements, and polynomial correlations were implemented as black-box models for the HP and integrated into a global model of the system developed for each case study and application. In order to estimate the performance of the units under the most real operating conditions, different types of weathers, load profiles...etc were considered as explained in deliverable D8.4 ’Analysis and optimisation of the heat pump control for each case study’.
In order to make an assessment of the heat pump units, the Seasonal Performance Factor including auxiliaries’ consumption, SPF, which accounts for the seasonal operation (heating or cooling mode) was selected. For the cases 3, 4 and 5 the Yearly PF has been employed since they must provide domestic hot water all along the year.
SPF results are summed up for what concerns heating and cooling season performance in an average climate conditions according to EN 14825 regulation (Strasbourg) for all the cases. Terminal units considered in the results, correspond to fan coils (water temperature setting 40ºC; deaband=4K; demand profile=office building) for CASE 1 and CASE 2, which are the ones already specified on deliverable D1.3 ‘Description of the selected case studies’ and presented also in the previous sections for each case study. In the case of heat pump units for domestic hot water production, (CASE 3 and CASE 4), only the Yearly Performance Factor (YPF) will be considered since the production of domestic how water is carried out all over the year. For CASE 3 the SHW demand profile of a hotel has been considered; and for CASE 4, the profile considered corresponds to a school, as specified in deliverable D8.4 ‘Analysis and optimisation of the heat pump control for each case study’.
In order to assess the efficiency of CASE 3 and CASE 4 according to the Ecodesign 812/2013 regulation, two performance parameters were considered: AEC (annual energy consumption) and the water heating efficiency ηwh.
The Ecodesign testing procedure is based around a schedule of DHW draw-offs. The text of the regulation proposes different schedules intended to test water heaters of different sizes: from 3XS to XXL. For each schedule, the following variables are set: draw-offs from 7 to 22 h, amount of energy associated with each draw-off, the minimum flow rate of DHW that needs to be provided, the temperature at which the DHW starts to contribute to the useful energy, and the minimum temperature at which the domestic hot water needs to be delivered during the draw-offs. The regulation leaves the choice of the schedule to the tester. From a preliminary estimation, it was concluded that CASE 3 heat pump could be simulated with the XXL draw-off schedule, and CASE 4 could be simulated with the XL draw-off schedule. The testing procedure and the calculation of AEC and ηwh must be repeated at three different ambient temperatures: 2, 7 and 14°C.
Finally, regarding CASE 5, and according to deliverable D8.4 ‘Analysis and optimisation of the heat pump control for each case study’, the SHW demand profile corresponds to a 5-6 family houses demand, and the terminal units considered are radiators for heating mode, being the temperature setting equal to 70ºC for the water temperature supply to the radiators in heating mode.
The obtained results, all for the Strasbourg (EN Average climate), are the following:
CASE1. SPFwinter = 3.09 SPFsummer= 5.31
CASE2. SPFwinter = 4.57 SPFsummer= 8.65
CASE3. Yearly PF = 5.59 corresponding to: XXL draw-offs schedule, AEC = 1127 kWh; and Efficiency of water heater: ηwh = 191%. This leads to a Classification: A++ (170 < ηwh < 213)
CASE4. Yearly PF = 3.72 corresponding to: XL draw-offs schedule, AEC = 1338 kWh; and Efficiency of water heater: ηwh = 125%. This leads to a Classification: A+ (123 < ηwh < 160)
CASE5. Yearly PF = 2.45
As it can be observed, for CASE 1 and CASE 2 the values of the estimated SPF are very high (above 6) during the summer operation, mainly due to the more convenient source temperatures in this type of climate for both the air and the ground source. Regarding winter operation, the SPF values observed are close or above 4, which are high for the considered climate.
For those cases which are focused on domestic hot water production such as CASE 3 and CASE 4, both turn out to be very efficient according to the Ecodesign 812/2013 regulation, being class A++ and class A+ respectively.
Regarding CASE 5, as it was already stated in a previous section, an assessment should be done comparing it with the reference unit defined in deliverable D1.3 which is an old gas boiler without condensation. As this case is not standard, the assessment needs to be done in terms of primary energy consumption.
Considering an energy conversion factor of 2.35 (MWh of primary energy)/(MWh electrical energy consumption) according to the Spanish ministry in energy, the primary energy (i.e gas consumption) that would be needed by the heat pump will be compared to the gas consumption of an old gas boiler without condensation. Now, considering that the heat pump has a yearly performance factor of 2.45 the ratio between the primary energy consumed by the heat pump and the one consumed by the gas boiler for the same application results in 0.75 which means that the heat pump would consume 25% less gas than the old gas boiler.
Considering that the CO2 emissions are directly proportional to the gas consumption, a reduction of 25% in gas consumption and the cancellation of CO2 local emissions at the city. Finally, depending on the energy mix of each country, the obtained COP would lead to a reduction of 25% in the associated CO2 total emissions in the case of Spain for instance. Of course, this analysis depends on the energetic scenario existing at each country. Therefore, the developed heat pump is a very interesting solution for the substitution of old gas boilers without any reform of the actual indoor heat distribution system or the radiators in the dwellings.
CONCLUSIONS
From the obtained results, it can be finally concluded that the objectives initially set in the project in terms of efficiency and costs have been successfully reached, as the heat pumps are very efficient and the components considered for their development are standard components or their modification just imply minor extra costs.
In summary, the main features of the developed heat pump units are:
- Employ natural refrigerants, either propane or CO2.
- High efficiency: 10 to 20% increase on Seasonal Performance Factor (SPF) compared to current HFC’s and HFO’s equivalent equipment.
- Very Low CO2 emission.
- Efficient and flexible capacity modulation.
- Tight containment and minimum charge. Design incorporating all the necessary safety measures and high reliability.
- Affordable cost: similar to that of equivalent HFC’s or HFO’s solution or slightly higher (10%).
Apart from the developed prototypes, a whole set of other important results are:
- The complete experimental assessment of the performance of the developed heat pumps.
- Accurate estimation of the seasonal performance for each application, working alone or in combination with other components of the overall energy system.
- Assessment of performance improvement in comparison with current state of the art conventional equipment.
- Guidelines for the optimal design of components and the heat pumps for each of the refrigerants.
- Guidelines for the safe design of the systems and for the selection of the necessary extra safety devices.
- Guidelines for the adequate and safe operation of this kind of technologies.
There has also been an important development at component level and at the optimization of the control of the units. All the design and control characteristics, as well as the measured performance, for each prototype have been compiled in deliverable D9.1 ‘Design guidelines for each heat pump/application’.
All partners have tried to disseminate as much as possible the results of the project with participation in a number of events (see the corresponding section on this report). Particular details of the Scientific and Technological results of the project can be found in the published journal papers or conference papers which has been presented along the project. A full list of them is given in the corresponding section of this report.
A number of results have been identified as foregrounds of the project. They are described in detail in: Deliverable D9.1 ‘Design guidelines for each heat pump/application’, Deliverable D10.8 ‘Final exploitation plan’, and Deliverable D10.9 ‘Description of products requiring IPR, and corresponding protection plan’. They are listed and briefly described in next Section.
In the attachments the reader can find the presentations which were made at the final project Workshop, held in Milan, at March 16th 2016, containing pictures and design schemes of the prototypes, as well as the final obtained performance, including also the special features and improvements carried out at component level.
Potential Impact:
POTENTIAL IMPACT AND MAIN DISSEMINATION ACTIVITIES
Apart from the detailed design of the developed prototypes, there has also been an important progress on the heat pump components: compressors, evaporators, condensers, and auxiliaries, which have been optimized for the use of each of the selected refrigerants: HCs and CO2. This is a very important result since the available commercial components have been designed instead for the conventional refrigerants and there is an important margin for improvement if the designs are optimized for the new fluids, which have particular properties. All these results have been compiled in a set of design guidelines which has been issued as deliverable D9.1 ‘Design guidelines for each heat pump/application’ where the detailed of the important information compiled all along the project has been summarized.
All the progress done in terms of the heat pumps design and new components should contribute to open up a new market for the heat pump applications targeted by the project, but it also has a good potential for exploitation for other applications in the cooling, refrigeration or industrial sectors, hence boosting the future development of HVAC and refrigeration technology employing hydrocarbons and CO2 as working fluids.
But, apart from the hardware and the know-how, NxtHPG project has tried to also contribute with some important results in non-technological issues to overcome both the technical and non-technical barriers to start the deployment of the heat pump technologies working with natural fluids, namely by:
- Involving key European industrial partners
- Bringing the developed heat pumps to the market. Prototype 4 is already in field testing, prototype 5 is going to start that phase, and given the good performance achieved it is expected a successful commercialization. Prototypes 1, 2 and 3 are still in phase of detailed market and business analysis but prospects are good.
- Disseminating the availability of the technology and its potentiality through their important distribution channels. As we will explain below all partners have done a big effort in dissemination all the S&T results of the project and in particular the feasibility and good performance of the developed technology.
- And last but not least, by proving that the technology is feasible, safe, efficient and cost effective. This is essential to overcome the common skepticism about the existence of safe and cost effective solutions.
Regarding the socio-economic impact of the results, NxtHPG project has proven that safe, reliable and cost effective heat pumps employing natural refrigerants are perfectly feasible, and will do its best in contributing to spreading the news of the advantages of a natural refrigerants technology. This will contribute to the general acceptance of the technology, overcoming psychological barriers for their penetration in the market. Last but not least, bringing to the market a Natural Refrigerants Technology will in parallel require specialized training and new servicing and installation techniques, which will open new business opportunities for SMEs, with the corresponding impact on creation of new qualified jobs.
Regarding the Dissemination of results, results were disseminated to the Scientific and Industrial community from the beginning of the project in collaboration with EHPA through the development of the project website, and newsletters where project results were presented. All along the project, all project partners have done an important effort in disseminating the results of the project and performed a considerable high number of dissemination actions. It should be pointed out that the project has included a total around 100 dissemination acts, 70 papers on workshops, conferences... with presentations on 50 different events.
A compilation of presentations and publications, result of the project, has been prepared in form of report as D10.5 which is public. A summary of publications is included in a followind section.
The main scientific results of the project have been presented in the most specialized scientific conferences, including the latest edition of the Gustav Lorentzen Conference, very recently held:
CYTEF 2014 (V Congreso Iberoamericano de Ciencias y Técnicas del Frío), 18-6-2014, Tarragona, Spain.
2014 International Compressor Engineering, Refrigeration and Air Conditioning, and High Performance Buildings Conference, 14-7-2014, Purdue University, West Lafayette, Indiana, (USA).
11th IIR-Gustav Lorentzen Conference on Natural Refrigerants - GL2014, 31-8-2014, Hangzhou, China.
ATMOsphere Europe 2015, 16-3-2015, Brussels (Belgium)
6th IIR Conference “Ammonia and CO2 Refrigeration Technologies”, 16-4-2015, Ohrid, Republic of Macedonia.
ASME-ATI-UIT 2015 Conference on Thermal Energy Systems: Production, Storage, Utilization and the Environment, 17-5-2015, Naples (Italy).
24th International Congress of Refrigeration ICR 2015, 16-8-2015, Yokohama, Japan.
ATMOsphere Europe 2016, 19-4-2016, Barcelona (Spain)
CYTEF 2016 − VIII Iberian Congress | VI Ibero-American Refrigeration Sciences and Technologies, 3-5-2016, Coimbra-Portugal
ATMOsphere Australia 2016, 16-5-2016, Melbourne (Australia)
33rd AICARR National Conference New frontiers for saving energy with an integrated approach to air conditioning: control aspects, thermal storage, new refrigerants and natural ventilation, 9-6-2016, Padua, Italy.
22nd International Compressor Engineering Conference, 14-7-2016, Purdue University, West Lafayette, Indiana, (USA).
12th IIR Gustav Lorentzen Conference on Natural Refrigerants, 2016, 21-8-2016, Edinburgh, United Kingdom,
Apart from this, it is important to highlight that, the results of the project have been presented in the most important European technical forums related with heat pumps. To be especially highlighted, the following ones:
EHPA European Heat Pump Forums, Brussels: editions 2013, 14, 15 and 2016.
Fairs:
ISH 2013, 12-3-2013, Frankfurt, Germany
ISH 2015, 10-3-2015, Frankfurt, Germany
European Heat Pump Summit, 14-10-2013, Nurenberg, Germany
European Heat Pump Summit, 24-10-2015, Nurenberg, Germany
Mostra Convegno Expocomfort, 16-3-2016, Milan, Italy
Finally, as a special dissemination activity the Final Technical workshop, titled: Breaking out the barriers of natural refrigerant, should be highlighted. It was organized by ENEA in cooperation with EHPA, in Milan, on March 16th 2016, inside the Mostra Convegno Expocomfort, March 15th-18th. This trade-fair, covering Refrigeration, Heating, ventilation and plumbing is one of the largest world events in the Sector. 2016 edition reached 2018 exhibitors and 155.332 visitors. The workshop was attended by approximately 80 representatives of the HP industry who showed a great interest on the project results.
EXPLOITATION OF RESULTS
The exploitation plan developed by industrial partners of NxtHPG project includes a market research with an assessment of the potential demand for the developed prototypes. Within the Market Analysis, the industrial partners determined the industry’s dominant economic traits, the strength of the competitive forces, the causes for changes in industry, the companies with the strongest competitiveness position and the key factors to achieve the expected success in the industry environment. Thereafter, the industrial partners developed a Business plan, aimed at ensuring the project results are quickly and efficiently exploited from a commercial standpoint. The main topics of the Business plan are the estimate of the market chances in terms of sales volumes, the study of the technological proposal developed (within the NxtHPG project) vs. demand (use, acceptation by customer of new technologies, comparative tests, formats, dimensions, etc.) and the follow-up of the regulatory and standardization issues at European and global level.
During the NxtHPG project five innovative heat pumps working with natural refrigerants, propane and carbon dioxide, have been built and tested. The project industrial partners agreed that the final exploitation plan, that is to bring these final products to the market, depends primarily on the expected trend for the heat pump market (which in turn is dependent on global economic trends, legislation, national energetic policies, etc.) and on national and international normative that limits the use of refrigerants not eco-friendly.
Despite the unfavorable global economic conditions of recent years, the heat pump market registered a trend constant or in slight increase (+ 3% in 2013 and 2014). Moreover, in the UE zone, the market experienced in the last years a considerable increment of sales of heat pumps for domestic hot water production.
Regarding the refrigerant market, the promulgation of Regulation 517/2014 opened scenarios not necessarily favorable to natural refrigerants. According to CIATESA, this Regulation postpones to 2020 the problem of the substitution of HFC in the HVACs, reducing the urgency of finding a solution for HFO and HFO+HFC blends flammability. Furthermore, this new Regulation seems to increase the time for the development and the introduction on the market of new synthetic refrigerants with mild GWP, as R-32 (~600) or HFO R1234ze (~7).
About the previous points, ENEX thinks that the regulatory issues will not influence the exploitation plan developed for Cases 4 and 5 products. Indeed, these products (Case 4, water heating to high temperatures, up to 85°C for sanitary use and with water storage; Case 5, water heating between 40°C and 70°C for the retrofit market) involve applications not suitable for HFCs or their possible substitutes.
As for products using propane and carbon dioxide as refrigerants, it should be noted that propane experienced 3 digits growth in the 2014 in light commercial equipment (vending machines, remote display cabinets – 3kW). Regarding carbon dioxide, in the year 2015, about 1600 new systems were installed and an annual growth rate of approx. 25% is foreseen by 2020.
Along the project a number of innovations and designs have been developed. Each industrial partner of NxtHPG project has developed its own exploitation plan which has been compiled in deliverable D10.8 ‘Final exploitation plan’. In the following, a very brief description is given:
DANFOSS Cooling (DCC) is evaluating the qualification of a full range of reciprocating and scroll compressors for R290 for a variety of applications. Various compressor qualification / optimisation projects will be carefully evaluated in terms of market opportunity and market need in order to provide the best solution compliant with current and in-development safety regulations at product and building level. Furthermore, Danfoss Cooling has already invested in a series of compressor / component / system testing labs compliant with the current safety regulations related to A2/A3.
DORIN has a long tradition with CO2, and it is very active on this field to support engineers in developing “improved solutions”. In the web site is available a calculation software which permits to simulate special and sophisticate solutions and to calculate the relevant energy efficiency. The heat pump developed for the case study 5 it is an example of a special economized refrigerating system that, thanks to a special dedicated solution and components (the compressor CDHP2500), permits to increase the energy efficiency of a CO2 system which works in conditions not favorable (temperature of water return from radiators equal to 40°C). The properties of the refrigerant R744 induces operating conditions characterized by high operating pressure level accomplished by high discharge temperature; furthermore the high miscibility of CO2 with oil reduce the viscosity of the oil. With such peculiarity, the technology of reciprocating compressors has particularly advantages compared to the volumetric compressors, scroll or screw; the high differential pressure, the high thermal level and the low viscosity has a dramatic influence on the volumetric efficiency and on the reliability of volumetric compressors. In the contrary the presence of dedicate sealing elements (suction / discharge valves and piston rings) and the lower operating speed give to piston compressors decisive advantages in terms of performance and reliability.
LUVE has developed a fin and tube coil technology with 5mm tube diameter, with enhanced fins and design, which is excellent for both propane and CO2, increasing efficiency and at the same time reducing the refrigerant charge, what it is especially important for hydrocarbons. Additionally, they have found some innovations in the manufacturing of this kind of small diameter tube fin and tube coils. They are already able to give full support to heat pump manufacturers on the design of the heat exchangers for natural refrigerants.
ALFA LAVAL already had in their catalogue BPHE solutions for both propane and CO2 but they have considerably increased their knowledge for their application in heat pumps of commercial size. Apart from this, interesting innovations and know how on control and production of the subcooling in case 3 prototype working with propane, and on the design of the internal superheat and gas cooler on prototypes 4 and 5 have been found. They are also already able to give support to heat pump manufacturers on the design of the heat exchangers for natural refrigerants.
CIATESA has found a number of innovations on the optimization of the design in order to get the maximum efficiency from propane as refrigerant, and important knowhow in the design of desurperheaters, and subcooling control. Regarding the exploitation of results, unfortunately CIATESA sees competition with HFO R1234ze becoming very tough (this fluid has just a GWP of 7). Important European manufacturers of water chillers and heat pumps seems to be driving their effort to developing units with that new fluid since for this case, manufacturing and maintenance costs could be lower. Since its integration in United Technology Corporation, CIATESA is abandoning the production of water chillers and heat pumps in favor of more experienced factories of its mother company. Research work is conducted in the field of leak detection; this is of particular interest for indoor installations as machine rooms (case 2 and 3 of NxtHPG project).
ENEX has found a number of innovations on the optimization of the design and control of the two developed prototypes. According to ENEX, the adoption of Regulation 517/2014 stimulated the demand for cheaper refrigerants, so new synthetic refrigerants (HFO and HFO+HFC mixtures) have been developed. Some of these fluids have a low GWP, which enables them to meet the mentioned regulatory requirements, while requiring minor re-engineering costs. Fortunately, the products developed for Cases 4 and 5 involve features which make their prospect good for commercialization. The product developed for Case 4 has features which are not obtainable using conventional HFCs – i.e. it allows to heat water to high temperatures, up to 85°C for sanitary use and with water storage. This is not possible using the techniques existing up to this moment. The product under development in relation to Case 5 is meant for the retrofit market, i.e. to satisfy the market niche requiring heating with water between 40°C and 70°C. This is also not possible using conventional refrigerants. ENEX has already passed to the ‘field testing’ phase for the heat pump corresponding to prototype 4 and will do the same with prototype 5 in the immediate future.
List of Websites:
Web site of the project: http://www.nxthpg.eu/
Contact Details:
UPVLC: José Miguel Corberán, corberan@iie.upv.es;
KTH: Björn E Palm, Bjorn.Palm@energy.kth.se;
ENEA: Raniero Trinchieri, raniero.trinchieri@enea.it;
UNINA: Rita Mastrullo, rita.mastrullo@unina.it>;
EPFL: John Richard Thome, john.thome@epfl.ch;
NTNU: Trygve Magne Eikevik, trygve.m.eikevik@ntnu.no;
DANFOSS CC: Ginies Pierre, p.ginies@danfoss.com;
CIATESA: Miguel Zamora, Miguel.Zamora@utc.com;
DORIN: Mauro Dallai, m.dallai@dorin.com;
ENEX: Sergio Girotto, sergio.girotto@enex-ref.com;
LU-VE: Stefano Filippini, stefano.filippini@luvegroup.com;
ALFA-LAVAL: Rolf Christensen, rolf.christensen@alfalaval.com;
EHPA: Thomas Nowak, thomas.nowak@ehpa.org
For heat pumps to become broadly accepted, an important effort is still required to increase their efficiency, reduce their environmental impact and become more economical. In regard to their environmental performance, one very important issue must still be solved, i.e. the use of refrigerants with 0 Ozone Depletion Potential and very low Global Warming Potential. HFC refrigerants, nowadays massively employed, have a very high GWP and consequently they were declared as Greenhouse Gases in the recent GHG European regulation.
The NxtHPG project strived to give a definitive step forward to overcome the barriers impeding the spread of natural refrigerants and usher in a new generation of heat pumps based on Hydrocarbons and CO2. In order to do so, NxtHPG project decided to concentrate on the development of a few selected applications in which it is feasible to develop a safe and cost effective solution and at the same time offer good prospects for commercial exploitation.
With this aim, the main objective of the NxtHPG project has been the development of a set of 5 reliable, safe, high efficiency and high capacity heat pumps (prototypes capacity around 50kW) working with the two most promising natural refrigerants: HCs and CO2. The finally selected case were:
• CASE 1 is a 40kW air to water heat pump (HP) for the production of hot water for heating also covering a low demand of domestic hot water (DHW) with the use of a de-superheater. The unit is reversible on the refrigerant circuit, so providing either heating in winter and cooling in summer.
• CASE 2 is a 60kW geothermal HP for hot water production for heating also covering a low demand of DHW with the use of a de-superheater. The unit is reversible on the refrigerant circuit, so providing either heating in winter and cooling in summer.
• CASE 3 consists of a 50kW HP booster from a neutral water loop, (10-30 ºC) (e.g. recovery of waste heat from condensation (25-30ºC) or sewage water (10-15ºC)) up to 60ºC for DHW production.
• CASE 4 is a 30kW air to water HP for sanitary water production at 60ºC or up to 80ºC for high temperature applications.
• CASE 5 is a 50kW air to water HP for heating applications. It targets the replacement of old gas boiler heating systems (5-6 families house) with old high temperature radiators as terminal units and high water return temperature. It provides DHW all over the year.
The project has been able to develop an optimized solution for each selected case (case1, 2 and 3 with propane, and case 4 and 5 with CO2) reaching the specified targets:
- High efficiency: 10 to 20% increase on Seasonal Performance Factor (SPF) compared to current HFC’s and HFO’s equivalent equipment.
- Very Low CO2 emission.
- Efficient and flexible capacity modulation.
- Tight containment and minimum charge. Design incorporating all the necessary safety measures and high reliability.
- Affordable cost: similar to that of equivalent HFC’s or HFO’s solution or slightly higher (10%).
The most important result of the project is the compilation of a set of design guidelines for the optimal design of each of this kind of heat pumps working with natural refrigerants, and a number of innovation and knowhow results acquired both for the heat pumps and their components: compressors, evaporators, condensers, and auxiliaries, optimized for the use of each of the selected refrigerants: propane and CO2.
NxtHPG project has proven that safe, reliable and cost effective heat pumps employing natural refrigerants are perfectly feasible and cost effective.
Project Context and Objectives:
Project context and motivation: Natural Refrigerants technology
Electrical Heat pumps (HPs) based on the vapor compression cycle have considerably improved in the last decades in terms of efficiency, flexibility and reliability and nowadays they constitute one of the pillars with the highest potential for the reduction of primary energy consumption in all heating/cooling applications on buildings but also on industrial processes. Notably, the cleanest alternative energy is that energy which is never consumed! In fact, energy never consumed by its efficient use has the highest potential for broad industrial application.
Environmental impact is another strong point of heat pumps. HPs are able to produce heat from the ambient air or ground heat, and they need little electricity consumption to pump that heat to the required supply temperature. For moderate temperature lifts, as modern heating systems now employ, the heat pump is a very efficient solution with a minimum carbon total footprint. Additionally, in recent years the technology of CO2 heat pumps working under a transcritical cycle has also shown high efficiency at high temperature lifts, as for instance in heating city water from 10 ºC to 60ºC or even higher temperatures.
However, there is still a significant margin for further improvement. For heat pumps to become broadly accepted, an important effort is still required to increase their efficiency, reduce their environmental impact and become more economical. Efficiency is essential to reduce energy consumption and global CO2 emissions but also to reduce annual operation costs, by being able to reasonably compensate a higher first cost of investment when compared with other conventional technologies, such as a gas boiler.
In regard to their environmental performance, one very important issue must still be solved, i.e. the use of a 0 ODP and very low GWP refrigerants. In fact, the HFC refrigerants, nowadays massively employed, have a very high Global Warming Potential, and consequently they were declared as Greenhouse Gases in the recent GHG European regulation.
After several failed trials, the reaction of the Chemical Industry to the public concern on HFCs and their high Global Warming Potential has been the development of a new family of synthetic fluids: HFOs which have a very low global warming potential. However, first they are again ‘synthetic’, and second they are flammable. It is true that the risk of ignition of a mixture of these fluids with air is lower than that with hydrocarbons, but still they are flammable and will require careful design of the equipment to insure their intrinsic safety, which of course may be equally done for hydrocarbons at a slightly higher cost. Furthermore, HFO producers have been recently investigated by the European Commission, who has opened antitrust proceedings concerning agreements between Honeywell and DuPont for the development of the new HFO-1234yf refrigerants.
It is very important to point out that these artificial chemical substances may be found in a longer perspective to have unexpected negative consequences on the environment (history is full of such stories), so does it make sense to substitute HFCs once again by synthetic fluids which are ‘very’ recent, when both Hydrocarbons and CO2 can provide superior total environmental performance for Refrigeration, A/C and Heat pumps? We strongly believe that the answer is: No!
Natural fluids present 4 very important advantages as refrigerants:
• 0 Ozone depletion potential
• Almost negligible Global Warming Potential
• They are not synthetic so that we are 100% sure they are not harmful for the environment.
• Some natural fluids possess very good thermodynamic properties to be employed as refrigerants. Development of equipment specifically designed for them will lead to higher efficiencies than the ones obtained with synthetic refrigerants, contributing to the reduction of the global environmental impact of the future heat pumps and refrigeration equipment.
Regarding the capacity of the units, up to now and after two decades of considerable Research on Natural Refrigerants, only small capacity refrigeration and heat pump equipment are commercially available at present, and there is almost no commercially available heat pump equipment of commercial size (20 kWthermal to hundreds of kW) employing natural refrigerants. This has in practice prevented the implementation of natural fluids for heating and cooling in the building sector and Industry.
This project strived to give a definitive step forward to overcome the barriers impeding the spread of natural refrigerants and usher in a new generation of heat pumps based on HCs and CO2 that are perfectly feasible and commercially competitive.
Project Objectives
The project targets the development of the next generation of heat pumps of high capacity working with Natural fluids. However, the development of improved components and optimization of the unit design and its control strategy cannot be made in “general”, and doing it for each specific application is of course not affordable. Consequently, manufacturers optimize the design of components and equipment only for the applications with the largest market. This means that the components and equipment available for heat pumps are obliged to employ components and designs which have been optimized for Air Conditioning, since the A/C market is much larger than the heat pump market. This constitutes a very important barrier for the future improvement of the heat pumps.
Therefore, the only way to produce a significant boost of this heat pump technology is by concentrating on the development on a few selected applications...those whose aggregation of all the small improvements leads to a product with superior performance and affordable cost.
The first objective of the project is therefore the identification of the cases in which the development of a new generation of heat pumps employing Natural refrigerants can lead to a fast commercial exploitation of the first series of heat pumps developed here, and later to the successful deployment of the technology to other sizes, ranges and applications.
Regarding the targeted market, for rapid deployment of a natural refrigerants technology, it is much better to first target the development of applications with a large potential market, and at least moderate production series where the cost can be sufficiently minimized. Therefore, the applications will very probably belong to the Sector of heating and sanitary hot water production of large buildings, in which, on the one side the installation of this kind of equipment is perfectly feasible, the new technology could lead to a significant reduction on both energy consumption and CO2 total emissions, and in which, on the other hand, the European HVAC industry still has the majority of the market, in contrast with the domestic sector in which the low cost equipment coming from Asia dominates the market. This potential market is large since it includes both systems in new buildings and renovation of HVAC systems in existing buildings.
Taking into account the above mentioned requirements, the following cases have already been identified as of high potential interest:
• Hydrocarbons (HCs) will be employed for the development of a small family of heat pumps supplying hot water at (40-50 ºC) for heating applications as well as to produce sanitary hot water at 60ºC. For this last case, several solutions will be explored: (i) an eventual direct production of sanitary hot water by the same unit also producing hot water for heating, (ii) a combination with storage and hot water production by batch heating, (iii) a high temperature stage provided by a hydrocarbon with high critical point (for instance butane).
Given the hazardous characteristics of HCs, the systems must be indirect: the heat pump will heat water, and this water (heat transfer medium) is then distributed to the terminal systems. This solution is also the best for coupling with other sources and for storage, maximizing the capabilities for integration and optimal operation.
• CO2 will be employed for the development of a heat pump of high capacity being able to produce sanitary hot water at 60 ºC directly from city water (10-15 ºC). Designs for simultaneous production of hot water for heating purposes and sanitary hot water, and applications with higher temperatures: 70-90 ºC will be also explored.
In regard to the heat source for the HPs, water (or a brine in geothermal applications) will lead to the best performance and the greatest potential for integration with other systems so it will be the choice for most of the solutions to be developed. In any case, at least one prototype will also be based on air, since Air to water units also constitute an important part of the market and minimization of charge in that sort of equipment is an important issue.
The general objective of the project is the development of a set of safe, reliable, and high efficiency heat pumps working with natural refrigerants of high capacity > 40 kW (probably ranging from 40 to 100 kW) together with a set of improved components and auxiliary devices adequate for the efficient and safe use of the two considered refrigerants: Hydrocarbons and CO2; the project will also provide the necessary know-how to key European companies of the Sector to bring to market the newly developed technology.
The project aims at reaching higher efficiency (10 - 20% SPF improvement) and lower Carbon footprint (20% lower TEWI) than the current state of the art of HFCs/HFOs or Sorption heat pump technologies while keeping the cost very similar or only a bit higher (10%) in a way that the better environmental performance clearly compensates for the extra cost; and additionally, the project aims to achieve efficient capacity modulation and the highest capabilities for combination and integration with other renewable sources in the energy systems of Buildings and Industry.
The final aim of the project is for the new heat pump designs to become the seeds for a future generation of heat pumps working with natural fluids manufactured by European companies and commercially available over a wide range of applications and capacities.
Project Results:
The first result of the project was the identification of the cases in which the use of Natural refrigerants could lead to cost effective and high efficient solutions with potential fast commercial exploitation. As a result of the market analysis and the safety and technical requirements for both refrigerants, 5 different application cases were identified which have the following characteristics:
CASE 1 is an air to water heat pump for the production of hot water for heating applications also covering a low demand of domestic hot water with the use of a de-superheater. The unit will be reversible on the refrigerant circuit, so providing heating and cooling. The range for outdoor temperature variation is approximately: -10 to 35 ºC. The supply temperature for the heating water should range between 40 and 50 ºC, while the supply temperature for the domestic hot water should be 60 ºC. Unit size should be around 50 kW (targeted for the prototype: 40 kW). This is a good case for employing a hydrocarbon as refrigerant, since it is an outdoor unit so there is practically no limit on the refrigerant charge and safety measures, if any is required, are simple.
CASE 2 is a geothermal heat pump for the production of hot water for heating applications also covering a low demand of domestic hot water with the use of a de-superheater. It will be reversible on the refrigerant circuit, so providing heating and cooling. The range for brine temperature variation is approximately: -5 to 15 ºC. The supply temperature for the heating water should range between 40 and 50 ºC, while the supply temperature for the domestic hot water should be 60 ºC. Unit size should be around 50 kW (targeted for the prototype: 60 kW). This is a good case for employing a hydrocarbon as refrigerant if the unit is installed in some machinery room (with the exception of installation below ground level) or in open air. Again, in this case there will be practically no limit on the refrigerant charge and safety measures, if any is required, are simple.
CASE 3 is a very innovative case consisting of a heat pump booster which pumps the heat from a neutral water loop, (10-30 ºC) (recovery of waste heat from condensation (25-30ºC) or sewage water (10-15ºC)), pumping it up to 60ºC for sanitary hot water use. The supply temperature for the sanitary hot water should be 60 ºC. Unit size should be around 50 kW (targeted for the prototype: 50 kW). Again, this is a good case for employing a hydrocarbon as refrigerant because the mentioned conditions the discharge temperature is going to high, and hydrocarbons, typically have a reduced discharge temperature when compared with synthetic refrigerants. The unit should be installed in some machinery room (with the exception of installation below ground level) or in open air. Again, in this case there will be practically no limit on the refrigerant charge and safety measures, if any is required, are simple.
CASE 4 is an air to water heat pump for hot water production at 60ºC or up to 80ºC for high temperature applications. The range for outdoor temperature variation is approximately: -10 to 35 ºC. The supply temperature for sanitary hot water use should be 60 ºC. However, thanks to the special characteristics of CO2 higher temperatures can be reached, e.g. 80ªC, with still good efficiency. Unit size should be around 50 kW (targeted for the prototype: 30 kW). This is a good case for employing CO2 as refrigerant since the production of high temperature hot water from city water is very well suited to this refrigerant due to the high refrigerant glide obtained at the gas cooler.
CASE 5 is an air to water heat pump for ‘heating applications’. It targets the renovation market for the replacement of old gas boiler heating systems (5-6 families houses) with high temperature old radiators as terminal units. Main role is hot water production for heating but it must also provide DHW all along the year. The development should be targeted for winter operation, although the unit will be also used during summer for DHW production.. The range for outdoor temperature variation is approximately: -10 to 35 ºC. The supply temperature for the old radiators should be 80ºC with the return temperature from the heating network being 40ºC. Unit size should be around 50 kW (targeted for the prototype: 50 kW). This is a good case for employing CO2 as refrigerant because this will decrease to a minimum direct Global Warming impact. Indirect emissions due to the electricity consumption will depend on the achievable efficiency.
As explained above, given the application it was decided that CASES 1 to 3 will be developed for use with a hydrocarbon refrigerant, while CASES 4 and 5 were adequate for CO2. Therefore, the development of five different HP prototypes was targeted in the project, 3 with hydrocarbons and 2 with CO2.
Once the case studies and the design and operation requirements were defined, heat pump mathematical models were developed for each case, and employed to design the prototypes. The modelling allowed the optimization of each HP design to the selected refrigerant and the given application. For the prototypes 1 to 3 propane was selected as the most suitable hydrocarbon refrigerant. Butane also seem to have good properties for prototype 3, however its low volumetric capacity requires a too large compressor resulting in a too expensive solution. In regard to other components, the following special characteristics should be highlighted:
• Prototype 1 should count with a variable speed scroll compressor in order to get a good SPF taking into account the wide range of variation of the outdoor conditions for air to water HPs.
• Prototype 2 should count with two scroll compressors working in tandem. In this way, partial load capacity of this geothermal unit could be enhanced.
• Prototype 3 should incorporate a system to produce a high subcooling in order to take advantage of the high temperature lift of the water in sanitary hot water production to produce a high COP. Two designs were identified: mode A, incorporating a subcooler after the condenser, and mode B, incorporating an innovative liquid throttling valve in order to control the flooding of the condenser and thus the refrigerant subcooling.
• Prototype 4 should concentrate in reaching the highest SPF for hot water production at 60 or higher temperature, especially concentrating on the components, efficiency, the internal heat exchanger design and the unit control.
• Prototype 5 should concentrate on the optimization of the design for the very peculiar operating conditions, production of heating hot water at 80 ºC for old high temperature radiators with a relatively high return water temperature of 40ºC. A two stage special CO2 cycle was considered the best solution for this prototype.
Once the design was defined, the 5 different prototypes were constructed.
DCC provided the adequate scroll compressors adapted for the use of propane, DORIN provided the suitable compressors for the CO2 prototypes, ALFA LAVAL provided all water to refrigerant heat exchangers for the 5 prototypes, including the desuperheaters for prototypes 1 and 2, the subcooler for prototype 3, and the gas coolers and internal heat exchangers for prototypes 4 and 5. LUVE provided all air to water heat exchangers, i.e. the outdoor coil for prototype 1, and the evaporators for prototypes 4 and 5. Finally, CIATESA constructed the three propane prototypes (1 to 3) while ENEX constructed the two CO2 prototypes (4 and 5).
The prototypes were then tested along a 1st experimental campaign at: KTH (prototypes 1 and 2), UPVLC (prototype 3), and ENEA (prototypes 4 and 5). This test campaign allowed first the solution of some initial design problems and the tuning up of the prototypes. Second, it allowed the study and optimization of the HP controllers. And finally, it allowed the check of the reliability of the operation and the characterization of the performance of each prototype. The analysis of the results of this 1st experimental campaign allowed the optimization of the design of the different prototypes. The results were analyzed in detail, and the mathematical models were adjusted. This allowed to determine a series of changes that could lead to improvements in their performance.
Once the experiments from the first campaign were analyzed, the heat pump models were adjusted in IMST-ART software and polynomial correlations were created by means of parametric studies carried out in IMST-ART software. These polynomial correlations were programmed in a model in TRNSYS jointly with the rest of the system components in the framework of WP6. The updated lumped parameter models for each case study were provided to all RTD partners and explained by UNINA in deliverable D6.1’Updated lumped parameter models for each case study’. The models were employed by UNINA in order to study the operation of the heat pumps for each case study, and an estimation of the seasonal performance factor for each case study was carried out. This allowed to make a first assessment of the project results which was presented in deliverable D6.5 ’First assessment of the project results’.
Regarding this first generation of heat pump prototypes developed, the required modifications were identified by each of the heat pump and component manufacturers in collaboration with the rest of the RTD partners of the project, and they were implemented in the framework of WP7 ‘Improvement of HP prototypes design and construction’ in order to improve the heat pump prototypes and produce a second generation of very high efficient heat pumps. A second experimental campaign took then place in the corresponding labs in the framework of WP8 ‘2nd experimental campaign and control optimization’.
Once the new experimental measurements from the second experimental campaign were available, both the heat pump models and the integrated system lumped parameter models were updated by UPVLC and UNINA respectively. Finally, UNINA carried out a final analysis and optimisation of the heat pump control for each case study and presented the final estimation of the seasonal performance factor for each case study in deliverable D8.4 ’Analysis and optimisation of the heat pump control for each case study’.
Taking into consideration the new updated information, a final assessment of the project results was presented in deliverable D9.2 ‘Assessment of the developed heat pump solutions’ with a critical review of the objectives: higher efficiency (10 - 20% SPF improvement) and lower Carbon footprint (20% lower TEWI) than current state of the art HFCs/HFOs or Sorption heat pump technologies while keeping the cost very similar or only a bit higher (10%).
The main final results about the performance of the developed prototypes are described in the following:
RESULTS OF THE 2ND EXPERIMENTAL CAMPAIGN. NOMINAL POINT AND FINAL ASSESSMENT.
Hydrocarbon heat pump prototypes
CASE 1
The nominal conditions selected for the design of the HP correspond to winter operation. According to EUROVENT operating conditions for standard rating, the external ambient temperature would correspond to 7ºC (6ºC wet bulb) for the outdoor circuit. For the indoor circuit, the water temperatures would be 40/45 ºC (Return (heat pump inlet)/ Supply) according to medium temperature application (fan-coil) as indicated in the norm EN 14511-2).
The target of the project was to reach at least the EUROVENT classification of class A, and reach a 20% higher efficiency than the reference unit provided by CIATESA which was: 2.96. The COP including auxiliaries finally obtained for the nominal point was 3.43 what represents a 15.9% increase in COP respect the reference unit. On the other hand the Eurovent Class A tresshold is COP 3.2 so prototype 1 exceeds Class A by 7.2%.
In regard to the heat pump capacity, it should be noted that the capacity of the unit was around 36.6 kW for a nominal frequency of the compressor of 50Hz, as it was expected from the specified design of the HP.
CASE 2
The nominal conditions selected for the design of the HP correspond to winter operation. According to EUROVENT operating conditions for standard rating, brine temperatures existing in the outdoor circuit would correspond to 0/(-3ºC) (inlet/outlet of evaporator); for the indoor circuit, the water temperatures would be 40/45 ºC (Return (heat pump inlet)/ Supply) according to medium temperature application (fan-coil) as indicated in the norm EN 14511-2).
The COP of the reference unit provided by CIATESA was: 4.02. The COP including auxiliaries finally obtained for the nominal point was 4.47 what represents an 11.1% increase in COP respect the reference unit.
In regard to the comparison with EUROVENT, data appearing in EUROVENT for the classification of this kind of units only exists for the water cooled case which is a different application, as CASE 2 is a geothermal heat pump for heating of buildings. Therefore the comparison is not possible for this prototype.
In regard to the heat pump capacity, it should be noted that the capacity of the unit was around 63.11 kW at the nominal point, which is close to the initially targeted value of 60 kW.
CASE 3
The nominal conditions selected for the design of the HP correspond to hot water production with 20ºC inlet temperature in the outdoor circuit (evaporator) and 10/60ºC (return temperature/supply) for the indoor circuit (condenser). At this conditions, the measured COP is 5.7.
As this case is very innovative, there is no existing reference unit, neither in EUROVENT classification nor in the manufacturer catalogue. However, it will be compared with those units available in the market for sanitary hot water production which work with a transcritical CO2 cycle. In particular, Q-ton unit produced by Mitsubishi has been selected for this purpose. Although Q-ton is not the same type of heat pump as CASE 3 (heat pump booster), it has been chosen because it is a high efficiency air to water CO2 heat pump for the production of hot water. So, the application is the same, and they differ in the type of source considered (waste heat recovery water versus ambient air).
If one compare the measured COP with the Q-ton unit working at 25ºC of ambient air temperature, for different condenser inlet water temperatures, the measured COP is always higher than the one provided by the Q-ton unit, with differences ranging from 5% to 30% depending on the condenser inlet temperature. The higher this temperature the higher the difference in COP.
Regarding the heat pump capacity, experimental measurements carried out at UPVLC for the nominal working conditions, conclude that the heat pump capacity is around 47 kW, which is very close to the design heat pump capacity (50kW).
In regard to the layout of the heat pump, it has been proved that both developed and analyzed cases (mode A and B) can lead to the same high performance. In the tests, Mode A has a slightly higher COP, but one should realize that it also has more heat transfer area (subcooler). On the other hand, mode B has one heat exchanger less, but it needs an extra valve, the throttling valve to control subcooling, and a more sophisticated control. Long duration tests, as well as a detailed economical study, should be carried out before making a final decision about which of both modes is the most cost-effective.
Finally, just comment that the refrigerant charge of the final industrial product, which for the case of refrigerant propane is an important issue, could be reduced from the one needed in the developed prototype, since the lab prototype included components and refrigerant circuit providing the possibility of testing both modes in the same prototype. This is of course not necessary in the final product and a considerable reduction of around 2 kg is expected for mode B, and 1.5 kg for mode A. The final propane charge could be around:
Charge Mode A = 4.8 kg
Charge mode B = 4.3 kg
CO2 heat pump prototypes
CASE 4
The nominal conditions selected for the design of the HP correspond to winter operation, that is to say an ambient temperature of 7ºC, and a water inlet temperature in the gas cooler of 10ºC, for a supply temperature (outlet of the gas cooler) of 60ºC. At this conditions, the measured COP was 3.76 including auxiliaries. The reference COP established by ENEX for this case under those operating conditions was 3.4. Therefore, the increase in performance in this case has been of 10.6%.
In any case, we must state that the reference value for the COP in this case was a target value stated by ENEX because at the beginning of the project the company did not have any unit with similar size and characteristics to the one which was going to be developed.
On the other hand, regarding the heat pump capacity, it should be noted that the capacity of the unit is around 30 kW, as it was expected from the design of the HP.
Additionally, an assessment was carried out considering an already existing product in the market manufactured by Mitsubishi (model ‘Q-ton’). The comparison of results shows that the developed prototype provides significant higher COP then the Q-ton unit (from 10 to 20% higher) at low ambient temperatures (from -7ºC to 5ºC). Only at high ambient temperatures (e.g. 16ºC) the COP of the Q-ton unit becomes higher by 11%. This is probably due to the technology used for the compressor in the ‘Q-ton’ unit whichi is totally different, as it combines two different types of compressor working in series (two stages of compression): a rotary compressor and a scroll compressor, whereas CASE 4 employs a piston compressor with one single stage of compression. It should be noted that, using the compressor technology considered in the ‘Q-ton’ unit, would mean a much higher cost and not reaching the threshold of 10% extra cost at much according to the targets of the NxtHPG project.
This difference in COP at low temperatures will lead to a great advantage in terms of seasonal COP since the dominant temperatures along the winter season are always low.
CASE 5
The nominal conditions selected for the design of the HP correspond to winter operation, it is to say an ambient temperature of 7ºC, and a water inlet temperature in the gas cooler of 40ºC (return temperature from the radiators in the building), for a supply temperature (outlet of the gas cooler) of 80ºC (supply temperature to radiators in the building). The measured COP including auxiliaries at this point is 2.46 and the heating capacity 45.6 kW which is in line with the targeted design.
There is no reference value for the COP of this unit since there is no commercial unit available for this application in the market. The reference unit considered in deliverable ‘D1.3 Description of the selected case studies’ corresponds to old gas boilers installed over 15 years ago which are less efficient than the new condensing boilers. These old boilers commonly convert 80% of their fuel into heat. In order to make a fair assessment for CASE 5 in this context, a comparison in terms of primary energy consumption was be carried out and it is described in the next section.
In order to get a comparison with some existing unit a single point test was carried out in conditions for which there was information of the ‘Q-ton’ unit mentioned above. The results showed an advantage of 5.4% on COP including auxiliaries for prototype 5.
ANALYSIS OF THE OPERATION OF THE HEAT PUMP FOR EACH CASE STUDY: FINAL ESTIMATION OF THE SEASONAL PERFORMANCE FACTOR (SPF).
An analysis of the operation of the heat pump for each case study and application was carried out by UNINA by means of the updated lumped parameter models developed in the framework of WP2 and WP6. These models were updated in WP8 and a final analysis was carried out by UNINA.
In order to have an assessment of the performance updated to the current development of the prototypes of the HPs, the models of the HPs were programmed using IMST-ART adjusted to experimental measurements, and polynomial correlations were implemented as black-box models for the HP and integrated into a global model of the system developed for each case study and application. In order to estimate the performance of the units under the most real operating conditions, different types of weathers, load profiles...etc were considered as explained in deliverable D8.4 ’Analysis and optimisation of the heat pump control for each case study’.
In order to make an assessment of the heat pump units, the Seasonal Performance Factor including auxiliaries’ consumption, SPF, which accounts for the seasonal operation (heating or cooling mode) was selected. For the cases 3, 4 and 5 the Yearly PF has been employed since they must provide domestic hot water all along the year.
SPF results are summed up for what concerns heating and cooling season performance in an average climate conditions according to EN 14825 regulation (Strasbourg) for all the cases. Terminal units considered in the results, correspond to fan coils (water temperature setting 40ºC; deaband=4K; demand profile=office building) for CASE 1 and CASE 2, which are the ones already specified on deliverable D1.3 ‘Description of the selected case studies’ and presented also in the previous sections for each case study. In the case of heat pump units for domestic hot water production, (CASE 3 and CASE 4), only the Yearly Performance Factor (YPF) will be considered since the production of domestic how water is carried out all over the year. For CASE 3 the SHW demand profile of a hotel has been considered; and for CASE 4, the profile considered corresponds to a school, as specified in deliverable D8.4 ‘Analysis and optimisation of the heat pump control for each case study’.
In order to assess the efficiency of CASE 3 and CASE 4 according to the Ecodesign 812/2013 regulation, two performance parameters were considered: AEC (annual energy consumption) and the water heating efficiency ηwh.
The Ecodesign testing procedure is based around a schedule of DHW draw-offs. The text of the regulation proposes different schedules intended to test water heaters of different sizes: from 3XS to XXL. For each schedule, the following variables are set: draw-offs from 7 to 22 h, amount of energy associated with each draw-off, the minimum flow rate of DHW that needs to be provided, the temperature at which the DHW starts to contribute to the useful energy, and the minimum temperature at which the domestic hot water needs to be delivered during the draw-offs. The regulation leaves the choice of the schedule to the tester. From a preliminary estimation, it was concluded that CASE 3 heat pump could be simulated with the XXL draw-off schedule, and CASE 4 could be simulated with the XL draw-off schedule. The testing procedure and the calculation of AEC and ηwh must be repeated at three different ambient temperatures: 2, 7 and 14°C.
Finally, regarding CASE 5, and according to deliverable D8.4 ‘Analysis and optimisation of the heat pump control for each case study’, the SHW demand profile corresponds to a 5-6 family houses demand, and the terminal units considered are radiators for heating mode, being the temperature setting equal to 70ºC for the water temperature supply to the radiators in heating mode.
The obtained results, all for the Strasbourg (EN Average climate), are the following:
CASE1. SPFwinter = 3.09 SPFsummer= 5.31
CASE2. SPFwinter = 4.57 SPFsummer= 8.65
CASE3. Yearly PF = 5.59 corresponding to: XXL draw-offs schedule, AEC = 1127 kWh; and Efficiency of water heater: ηwh = 191%. This leads to a Classification: A++ (170 < ηwh < 213)
CASE4. Yearly PF = 3.72 corresponding to: XL draw-offs schedule, AEC = 1338 kWh; and Efficiency of water heater: ηwh = 125%. This leads to a Classification: A+ (123 < ηwh < 160)
CASE5. Yearly PF = 2.45
As it can be observed, for CASE 1 and CASE 2 the values of the estimated SPF are very high (above 6) during the summer operation, mainly due to the more convenient source temperatures in this type of climate for both the air and the ground source. Regarding winter operation, the SPF values observed are close or above 4, which are high for the considered climate.
For those cases which are focused on domestic hot water production such as CASE 3 and CASE 4, both turn out to be very efficient according to the Ecodesign 812/2013 regulation, being class A++ and class A+ respectively.
Regarding CASE 5, as it was already stated in a previous section, an assessment should be done comparing it with the reference unit defined in deliverable D1.3 which is an old gas boiler without condensation. As this case is not standard, the assessment needs to be done in terms of primary energy consumption.
Considering an energy conversion factor of 2.35 (MWh of primary energy)/(MWh electrical energy consumption) according to the Spanish ministry in energy, the primary energy (i.e gas consumption) that would be needed by the heat pump will be compared to the gas consumption of an old gas boiler without condensation. Now, considering that the heat pump has a yearly performance factor of 2.45 the ratio between the primary energy consumed by the heat pump and the one consumed by the gas boiler for the same application results in 0.75 which means that the heat pump would consume 25% less gas than the old gas boiler.
Considering that the CO2 emissions are directly proportional to the gas consumption, a reduction of 25% in gas consumption and the cancellation of CO2 local emissions at the city. Finally, depending on the energy mix of each country, the obtained COP would lead to a reduction of 25% in the associated CO2 total emissions in the case of Spain for instance. Of course, this analysis depends on the energetic scenario existing at each country. Therefore, the developed heat pump is a very interesting solution for the substitution of old gas boilers without any reform of the actual indoor heat distribution system or the radiators in the dwellings.
CONCLUSIONS
From the obtained results, it can be finally concluded that the objectives initially set in the project in terms of efficiency and costs have been successfully reached, as the heat pumps are very efficient and the components considered for their development are standard components or their modification just imply minor extra costs.
In summary, the main features of the developed heat pump units are:
- Employ natural refrigerants, either propane or CO2.
- High efficiency: 10 to 20% increase on Seasonal Performance Factor (SPF) compared to current HFC’s and HFO’s equivalent equipment.
- Very Low CO2 emission.
- Efficient and flexible capacity modulation.
- Tight containment and minimum charge. Design incorporating all the necessary safety measures and high reliability.
- Affordable cost: similar to that of equivalent HFC’s or HFO’s solution or slightly higher (10%).
Apart from the developed prototypes, a whole set of other important results are:
- The complete experimental assessment of the performance of the developed heat pumps.
- Accurate estimation of the seasonal performance for each application, working alone or in combination with other components of the overall energy system.
- Assessment of performance improvement in comparison with current state of the art conventional equipment.
- Guidelines for the optimal design of components and the heat pumps for each of the refrigerants.
- Guidelines for the safe design of the systems and for the selection of the necessary extra safety devices.
- Guidelines for the adequate and safe operation of this kind of technologies.
There has also been an important development at component level and at the optimization of the control of the units. All the design and control characteristics, as well as the measured performance, for each prototype have been compiled in deliverable D9.1 ‘Design guidelines for each heat pump/application’.
All partners have tried to disseminate as much as possible the results of the project with participation in a number of events (see the corresponding section on this report). Particular details of the Scientific and Technological results of the project can be found in the published journal papers or conference papers which has been presented along the project. A full list of them is given in the corresponding section of this report.
A number of results have been identified as foregrounds of the project. They are described in detail in: Deliverable D9.1 ‘Design guidelines for each heat pump/application’, Deliverable D10.8 ‘Final exploitation plan’, and Deliverable D10.9 ‘Description of products requiring IPR, and corresponding protection plan’. They are listed and briefly described in next Section.
In the attachments the reader can find the presentations which were made at the final project Workshop, held in Milan, at March 16th 2016, containing pictures and design schemes of the prototypes, as well as the final obtained performance, including also the special features and improvements carried out at component level.
Potential Impact:
POTENTIAL IMPACT AND MAIN DISSEMINATION ACTIVITIES
Apart from the detailed design of the developed prototypes, there has also been an important progress on the heat pump components: compressors, evaporators, condensers, and auxiliaries, which have been optimized for the use of each of the selected refrigerants: HCs and CO2. This is a very important result since the available commercial components have been designed instead for the conventional refrigerants and there is an important margin for improvement if the designs are optimized for the new fluids, which have particular properties. All these results have been compiled in a set of design guidelines which has been issued as deliverable D9.1 ‘Design guidelines for each heat pump/application’ where the detailed of the important information compiled all along the project has been summarized.
All the progress done in terms of the heat pumps design and new components should contribute to open up a new market for the heat pump applications targeted by the project, but it also has a good potential for exploitation for other applications in the cooling, refrigeration or industrial sectors, hence boosting the future development of HVAC and refrigeration technology employing hydrocarbons and CO2 as working fluids.
But, apart from the hardware and the know-how, NxtHPG project has tried to also contribute with some important results in non-technological issues to overcome both the technical and non-technical barriers to start the deployment of the heat pump technologies working with natural fluids, namely by:
- Involving key European industrial partners
- Bringing the developed heat pumps to the market. Prototype 4 is already in field testing, prototype 5 is going to start that phase, and given the good performance achieved it is expected a successful commercialization. Prototypes 1, 2 and 3 are still in phase of detailed market and business analysis but prospects are good.
- Disseminating the availability of the technology and its potentiality through their important distribution channels. As we will explain below all partners have done a big effort in dissemination all the S&T results of the project and in particular the feasibility and good performance of the developed technology.
- And last but not least, by proving that the technology is feasible, safe, efficient and cost effective. This is essential to overcome the common skepticism about the existence of safe and cost effective solutions.
Regarding the socio-economic impact of the results, NxtHPG project has proven that safe, reliable and cost effective heat pumps employing natural refrigerants are perfectly feasible, and will do its best in contributing to spreading the news of the advantages of a natural refrigerants technology. This will contribute to the general acceptance of the technology, overcoming psychological barriers for their penetration in the market. Last but not least, bringing to the market a Natural Refrigerants Technology will in parallel require specialized training and new servicing and installation techniques, which will open new business opportunities for SMEs, with the corresponding impact on creation of new qualified jobs.
Regarding the Dissemination of results, results were disseminated to the Scientific and Industrial community from the beginning of the project in collaboration with EHPA through the development of the project website, and newsletters where project results were presented. All along the project, all project partners have done an important effort in disseminating the results of the project and performed a considerable high number of dissemination actions. It should be pointed out that the project has included a total around 100 dissemination acts, 70 papers on workshops, conferences... with presentations on 50 different events.
A compilation of presentations and publications, result of the project, has been prepared in form of report as D10.5 which is public. A summary of publications is included in a followind section.
The main scientific results of the project have been presented in the most specialized scientific conferences, including the latest edition of the Gustav Lorentzen Conference, very recently held:
CYTEF 2014 (V Congreso Iberoamericano de Ciencias y Técnicas del Frío), 18-6-2014, Tarragona, Spain.
2014 International Compressor Engineering, Refrigeration and Air Conditioning, and High Performance Buildings Conference, 14-7-2014, Purdue University, West Lafayette, Indiana, (USA).
11th IIR-Gustav Lorentzen Conference on Natural Refrigerants - GL2014, 31-8-2014, Hangzhou, China.
ATMOsphere Europe 2015, 16-3-2015, Brussels (Belgium)
6th IIR Conference “Ammonia and CO2 Refrigeration Technologies”, 16-4-2015, Ohrid, Republic of Macedonia.
ASME-ATI-UIT 2015 Conference on Thermal Energy Systems: Production, Storage, Utilization and the Environment, 17-5-2015, Naples (Italy).
24th International Congress of Refrigeration ICR 2015, 16-8-2015, Yokohama, Japan.
ATMOsphere Europe 2016, 19-4-2016, Barcelona (Spain)
CYTEF 2016 − VIII Iberian Congress | VI Ibero-American Refrigeration Sciences and Technologies, 3-5-2016, Coimbra-Portugal
ATMOsphere Australia 2016, 16-5-2016, Melbourne (Australia)
33rd AICARR National Conference New frontiers for saving energy with an integrated approach to air conditioning: control aspects, thermal storage, new refrigerants and natural ventilation, 9-6-2016, Padua, Italy.
22nd International Compressor Engineering Conference, 14-7-2016, Purdue University, West Lafayette, Indiana, (USA).
12th IIR Gustav Lorentzen Conference on Natural Refrigerants, 2016, 21-8-2016, Edinburgh, United Kingdom,
Apart from this, it is important to highlight that, the results of the project have been presented in the most important European technical forums related with heat pumps. To be especially highlighted, the following ones:
EHPA European Heat Pump Forums, Brussels: editions 2013, 14, 15 and 2016.
Fairs:
ISH 2013, 12-3-2013, Frankfurt, Germany
ISH 2015, 10-3-2015, Frankfurt, Germany
European Heat Pump Summit, 14-10-2013, Nurenberg, Germany
European Heat Pump Summit, 24-10-2015, Nurenberg, Germany
Mostra Convegno Expocomfort, 16-3-2016, Milan, Italy
Finally, as a special dissemination activity the Final Technical workshop, titled: Breaking out the barriers of natural refrigerant, should be highlighted. It was organized by ENEA in cooperation with EHPA, in Milan, on March 16th 2016, inside the Mostra Convegno Expocomfort, March 15th-18th. This trade-fair, covering Refrigeration, Heating, ventilation and plumbing is one of the largest world events in the Sector. 2016 edition reached 2018 exhibitors and 155.332 visitors. The workshop was attended by approximately 80 representatives of the HP industry who showed a great interest on the project results.
EXPLOITATION OF RESULTS
The exploitation plan developed by industrial partners of NxtHPG project includes a market research with an assessment of the potential demand for the developed prototypes. Within the Market Analysis, the industrial partners determined the industry’s dominant economic traits, the strength of the competitive forces, the causes for changes in industry, the companies with the strongest competitiveness position and the key factors to achieve the expected success in the industry environment. Thereafter, the industrial partners developed a Business plan, aimed at ensuring the project results are quickly and efficiently exploited from a commercial standpoint. The main topics of the Business plan are the estimate of the market chances in terms of sales volumes, the study of the technological proposal developed (within the NxtHPG project) vs. demand (use, acceptation by customer of new technologies, comparative tests, formats, dimensions, etc.) and the follow-up of the regulatory and standardization issues at European and global level.
During the NxtHPG project five innovative heat pumps working with natural refrigerants, propane and carbon dioxide, have been built and tested. The project industrial partners agreed that the final exploitation plan, that is to bring these final products to the market, depends primarily on the expected trend for the heat pump market (which in turn is dependent on global economic trends, legislation, national energetic policies, etc.) and on national and international normative that limits the use of refrigerants not eco-friendly.
Despite the unfavorable global economic conditions of recent years, the heat pump market registered a trend constant or in slight increase (+ 3% in 2013 and 2014). Moreover, in the UE zone, the market experienced in the last years a considerable increment of sales of heat pumps for domestic hot water production.
Regarding the refrigerant market, the promulgation of Regulation 517/2014 opened scenarios not necessarily favorable to natural refrigerants. According to CIATESA, this Regulation postpones to 2020 the problem of the substitution of HFC in the HVACs, reducing the urgency of finding a solution for HFO and HFO+HFC blends flammability. Furthermore, this new Regulation seems to increase the time for the development and the introduction on the market of new synthetic refrigerants with mild GWP, as R-32 (~600) or HFO R1234ze (~7).
About the previous points, ENEX thinks that the regulatory issues will not influence the exploitation plan developed for Cases 4 and 5 products. Indeed, these products (Case 4, water heating to high temperatures, up to 85°C for sanitary use and with water storage; Case 5, water heating between 40°C and 70°C for the retrofit market) involve applications not suitable for HFCs or their possible substitutes.
As for products using propane and carbon dioxide as refrigerants, it should be noted that propane experienced 3 digits growth in the 2014 in light commercial equipment (vending machines, remote display cabinets – 3kW). Regarding carbon dioxide, in the year 2015, about 1600 new systems were installed and an annual growth rate of approx. 25% is foreseen by 2020.
Along the project a number of innovations and designs have been developed. Each industrial partner of NxtHPG project has developed its own exploitation plan which has been compiled in deliverable D10.8 ‘Final exploitation plan’. In the following, a very brief description is given:
DANFOSS Cooling (DCC) is evaluating the qualification of a full range of reciprocating and scroll compressors for R290 for a variety of applications. Various compressor qualification / optimisation projects will be carefully evaluated in terms of market opportunity and market need in order to provide the best solution compliant with current and in-development safety regulations at product and building level. Furthermore, Danfoss Cooling has already invested in a series of compressor / component / system testing labs compliant with the current safety regulations related to A2/A3.
DORIN has a long tradition with CO2, and it is very active on this field to support engineers in developing “improved solutions”. In the web site is available a calculation software which permits to simulate special and sophisticate solutions and to calculate the relevant energy efficiency. The heat pump developed for the case study 5 it is an example of a special economized refrigerating system that, thanks to a special dedicated solution and components (the compressor CDHP2500), permits to increase the energy efficiency of a CO2 system which works in conditions not favorable (temperature of water return from radiators equal to 40°C). The properties of the refrigerant R744 induces operating conditions characterized by high operating pressure level accomplished by high discharge temperature; furthermore the high miscibility of CO2 with oil reduce the viscosity of the oil. With such peculiarity, the technology of reciprocating compressors has particularly advantages compared to the volumetric compressors, scroll or screw; the high differential pressure, the high thermal level and the low viscosity has a dramatic influence on the volumetric efficiency and on the reliability of volumetric compressors. In the contrary the presence of dedicate sealing elements (suction / discharge valves and piston rings) and the lower operating speed give to piston compressors decisive advantages in terms of performance and reliability.
LUVE has developed a fin and tube coil technology with 5mm tube diameter, with enhanced fins and design, which is excellent for both propane and CO2, increasing efficiency and at the same time reducing the refrigerant charge, what it is especially important for hydrocarbons. Additionally, they have found some innovations in the manufacturing of this kind of small diameter tube fin and tube coils. They are already able to give full support to heat pump manufacturers on the design of the heat exchangers for natural refrigerants.
ALFA LAVAL already had in their catalogue BPHE solutions for both propane and CO2 but they have considerably increased their knowledge for their application in heat pumps of commercial size. Apart from this, interesting innovations and know how on control and production of the subcooling in case 3 prototype working with propane, and on the design of the internal superheat and gas cooler on prototypes 4 and 5 have been found. They are also already able to give support to heat pump manufacturers on the design of the heat exchangers for natural refrigerants.
CIATESA has found a number of innovations on the optimization of the design in order to get the maximum efficiency from propane as refrigerant, and important knowhow in the design of desurperheaters, and subcooling control. Regarding the exploitation of results, unfortunately CIATESA sees competition with HFO R1234ze becoming very tough (this fluid has just a GWP of 7). Important European manufacturers of water chillers and heat pumps seems to be driving their effort to developing units with that new fluid since for this case, manufacturing and maintenance costs could be lower. Since its integration in United Technology Corporation, CIATESA is abandoning the production of water chillers and heat pumps in favor of more experienced factories of its mother company. Research work is conducted in the field of leak detection; this is of particular interest for indoor installations as machine rooms (case 2 and 3 of NxtHPG project).
ENEX has found a number of innovations on the optimization of the design and control of the two developed prototypes. According to ENEX, the adoption of Regulation 517/2014 stimulated the demand for cheaper refrigerants, so new synthetic refrigerants (HFO and HFO+HFC mixtures) have been developed. Some of these fluids have a low GWP, which enables them to meet the mentioned regulatory requirements, while requiring minor re-engineering costs. Fortunately, the products developed for Cases 4 and 5 involve features which make their prospect good for commercialization. The product developed for Case 4 has features which are not obtainable using conventional HFCs – i.e. it allows to heat water to high temperatures, up to 85°C for sanitary use and with water storage. This is not possible using the techniques existing up to this moment. The product under development in relation to Case 5 is meant for the retrofit market, i.e. to satisfy the market niche requiring heating with water between 40°C and 70°C. This is also not possible using conventional refrigerants. ENEX has already passed to the ‘field testing’ phase for the heat pump corresponding to prototype 4 and will do the same with prototype 5 in the immediate future.
List of Websites:
Web site of the project: http://www.nxthpg.eu/
Contact Details:
UPVLC: José Miguel Corberán, corberan@iie.upv.es;
KTH: Björn E Palm, Bjorn.Palm@energy.kth.se;
ENEA: Raniero Trinchieri, raniero.trinchieri@enea.it;
UNINA: Rita Mastrullo, rita.mastrullo@unina.it>;
EPFL: John Richard Thome, john.thome@epfl.ch;
NTNU: Trygve Magne Eikevik, trygve.m.eikevik@ntnu.no;
DANFOSS CC: Ginies Pierre, p.ginies@danfoss.com;
CIATESA: Miguel Zamora, Miguel.Zamora@utc.com;
DORIN: Mauro Dallai, m.dallai@dorin.com;
ENEX: Sergio Girotto, sergio.girotto@enex-ref.com;
LU-VE: Stefano Filippini, stefano.filippini@luvegroup.com;
ALFA-LAVAL: Rolf Christensen, rolf.christensen@alfalaval.com;
EHPA: Thomas Nowak, thomas.nowak@ehpa.org
