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Energy recovery in new and retrofitted heat pumps using a dedicated expander concept

Final Report Summary - EXP-HEAT (Energy recovery in new and retrofitted heat pumps using a dedicated expander concept)

Executive Summary:
The main concept of the EXP-HEAT project is to replace the throttle or expansion valve used in common vapour-compression units with an expansion machine. Its purpose is to recover energy from the high-pressure liquid (condensed) refrigerant and provide it to the compressor, reducing its electricity consumption. In the first year , according to the schedule of the project, a prototype expander has been designed starting from a commercial hydraulic motor of Italgroup SRL. The modification compared to the original hydraulic motor considered the inlet distribution system and timing, the machine bearings, the reduction of the dead volume and the design of a ventilation system to ensure stable expander operation. An overview of the evolution of the design of the expander and its main features as well as the achieved performance can be seen in Figure 2. The manufactured expander prototype (version 1.1 – Figure 3) was then tested at a dedicated test-rig. These first tests with R314a and CO2 served to measure the performance of the expander and to solve the first major technical issues. The efficiency of the first version of the expander was poor and a dedicated test campaign was subsequently launched in order to identify the different inefficiency sources (mainly internal leakages and friction losses) and define the best available lubrication options. Further modifications were designed to be implemented to the expander in order to solve these issues. Accordingly, the prototype expander was modified leading to the expander version 1.2. The performance of the new machine was indeed enhanced, but a new optimized expander was finally designed taking into consideration the latter analysis and tests. The new expander features are in particular: increased expansion ratio, reduced dead volume and number of cylinders, and a lubrication system. The final version 2.0 of the expander (Figure 4) was manufactured in two copies, and a second test campaign was run with R404a and R410a in reaching a maximum shaft isentropic efficiency of 26%, while the indicated isentropic efficiency was at 52%. This value for the shaft isentropic efficiency has been extrapolated to more favourable conditions reaching the threshold value of 30%.
The two expander prototypes of the latest version of the expander (version 2.0) were then tested in two dedicated test rigs: in a new heat pump system (Figure 5) and in a retrofitted commercial heat pump according to the project schedule (Figure 6). The achieved performance was in all cases lower than the efficiency values measured during the tests dedicated to the stand-alone expander. The reason is that the whole heat pump’s unit cycle induces further pressure losses (mainly due to the currently used evaporator heat exchangers) and as a result the performance of the expander is poorer. However it was proved that it’s fairly easy to integrate the expander in new and existing heat pump units with very low costs. to At the same time, the start-up, operation, lubrication and control of both units proved also to be simple, meaning that there is no need for sophisticated (for new units) or tailor/made (retrofitting of existing units) expensive control and lubrication systems that could hamper the viability of such projects. A modification of the control unit in new heat pumps and the installation of an additional simple independent control system are the most suitable solutions for the materialization of final commercial products.
During these tests some further reliability and maintenance issues of the new expander prototypes were identified and further modifications in view of enhanced reliability and performance are planned to be implemented after the project end.
Finally, the different options to use the produced mechanical energy were evaluated concluding in the installation of an asynchronous generator driven by the expander in order to generate electricity. In this way, the generated electricity will be fed to the heat pump unit, reducing the amount of electricity absorbed by the grid, thus enhancing the energetic performance of the heat pump unit. This low-cost but efficient configuration was experimentally tested proving a mostly suitable technical solution.

Project Context and Objectives:
The main concept of the EXP-HEAT project is to replace the throttle or expansion valve used in common vapour-compression units with an expansion machine. Its purpose is to recover energy from the high-pressure liquid (condensed) refrigerant and provide it to the compressor, reducing its electricity consumption. The recovered mechanical energy can either be directly fed via mechanical coupling or it can be converted to electricity. The expansion machine can then be integrated both in new heat pump units (Figure 1a) or retrofitted to existing units (Figure 1b).
The strategic technical objective of the project is to improve the performance of heat pump units, by integrating a new hydraulic piston type expander, leading to performance increase, while keeping the cost of the expander low. As a result, the overall objective of the project is to open new markets for the participating SMEs, and further develop new products and services, in order to magnify their business cycle. Specific S&T objectives are:
Development of a dedicated liquid expander: The project partners have investigated the different existing approaches and propose two very promising technologies that are ideal for the application of work-recovery in heat pumps: a hydraulic piston expander or a reciprocating expander, with max. capacity of 1-2 kW. The final selection will be carried in the very beginning of the project, when all boundary conditions, operational characteristics of heat pumps, and some additional data are evaluated.
Subsequently, the expander will be designed, focusing on the inlet/outlet flows from the valves/ports (of critical importance for part load operation), the dead volume and the mechanical efficiency of the machine. Then, a prototype will be manufactured, focusing on the reduction of leakages, its dead volume and over/under-expansion phenomena. A dedicated test-rig will be developed in the laboratory of FIR for the testing of this expander. Special focus will be given on its expansion efficiency (including the isentropic, mechanical, and volumetric efficiency) at various operating conditions. An isentropic efficiency of 40% is considered as a great technological breakthrough.
Integration of the expander in a re-designed commercial heat pump unit. The integration of the developed expander into a new heat pump unit requires a slightly different design, since the compressor/motor should have lower capacity and the evaporator should be larger to handle the higher heat flows. The use of the recovered energy (e.g. mechanical coupling, electricity generation etc) will also be investigated . Regarding the control unit, it will be modified in order to adjust the operation of the motor and the heat exchangers conditions (e.g. fans, flow rates of air/water) and finally to optimize the combined system efficiency (at partial and full load), achieving higher COP values. This combined concept will be installed in the laboratory of KTH and extensively tested under variable conditions. The operation of the expander in real conditions will be monitored, while the coupling of expander/compressor/motor will be evaluated.
The retrofitting of an installed heat pump, using the developed expander, in order to boost its performance will also be investigated during the project. The relevant know-how that will be gained will result in a retrofit kit capable to be used in a wide range of heat pumps. The retrofitting of such a unit requires the replacement of a few parts while keeping the initial compressor/motor. The retrofitted unit will be installed in the NTUA laboratory, at a dedicated test-rig for its experimental evaluation. Special effort will be given on the operation optimization and the control system, while keeping the necessary modifications at a minimum level in order to minimize the related costs.

Project Results:
Specific S&T objectives achieved during the research activities within the EXP-HEAT project were:

1. Development of a dedicated liquid expander

The project partners had initially investigated the different existing approaches and proposed two very promising technologies that are ideal for the application of work-recovery in heat pumps: a hydraulic piston expander or a reciprocating expander, with max. capacity of 1-2 kW. The final selection had to be carried in the very beginning of the project, when all boundary conditions, operational characteristics of heat pumps, and some additional data would have been evaluated. Subsequently, the expander would be designed, focusing on the inlet/outlet flows from the valves/ports (of critical importance for part load operation), the dead volume and the mechanical efficiency of the machine. Then, a prototype had to be manufactured, focusing on the reduction of leakages, its dead volume and over/under-expansion phenomena. A dedicated test-rig would then be developed in the laboratory of FIR for the testing of this expander. Special focus was planned to be given on its expansion efficiency (including the isentropic, mechanical, and volumetric efficiency) at various operating conditions. An isentropic efficiency of 40% would at that point considered as a great technological breakthrough.
As already discussed, the main technical objectives for the first reporting period of the project were related to the development and testing of the dedicated liquid piston expander prototype (WP2 and WP3). Accordingly, at the first phase of the project a dedicated liquid expander has been designed, manufactured and tested. This was version 1.1 as it was characterised later. Actually a hydraulic piston motor has been re-designed and a prototype has been manufactured to serve this purpose . At first, the technology of hydraulic piston expander was selected over the reciprocating one and was then studied, starting from the boundary conditions determined by the heat pump thermodynamic cycle (WP2). Through a dedicated simulation model, the technical data of the heat pump units (capacity, temperatures, pressures, etc) have been defined. Then, appropriate tools have been developed to simulate the operation of the expander, and to estimate its performance. The tools have been used to suggest the main modifications on the expander. According to the design modifications carried out, the expander has been manufactured. A test-rig equipped with all necessary measurement instruments has been designed; it has been installed first in the FIR laboratory, in order to calibrate the measurement system and to test the expander with compressed air. Then, the test-rig has been moved to DORIN premises, where a high-pressure rig operating with R134a is available. At DORIN, various tests have been performed to assess the performance of the expander in various conditions. Tests and optimization are still on going on the expander; however, first tests have shown interesting performance of the expander. The results of the first set of tests have been shown to the partners in the technical meeting held in Florence at the end of October 2014 and subsequently presented to the scientific community through two international conferences.
These first tests with R314a and CO2 served to measure the performance of the expander and to solve the first major technical issues. The efficiency of the first version of the expander was poor and a dedicated test campaign was subsequently launched in order to identify the different inefficiency sources (mainly internal leakages and friction losses) and define the best available lubrication options. Further modifications were designed to be implemented to the expander in order to solve these issues. Accordingly, the prototype expander was modified leading to the expander version 1.2. The performance of the new machine was indeed enhanced, but a new optimized expander was finally designed taking into consideration the latter analysis and tests. The new expander features are in particular: increased expansion ratio, reduced dead volume and number of cylinders, and a lubrication system. The final version 2.0 of the expander (Figure 4) was manufactured in two copies, and a second test campaign was run with R404a and R410a in reaching a maximum shaft isentropic efficiency of 26%, while the indicated isentropic efficiency was at 52%. This value for the shaft isentropic efficiency has been extrapolated to more favourable conditions reaching the threshold value of 30%.
With the completion of these activities, three core milestones of the project were successfully reached: Milestone No1 – Simulation of expander ,Milestone No2 - Expander manufactured and Milestone No3 - Expander tested.

2. Thermodynamic investigation of the combined process and optimization

In the meantime, in WP4 dedicated modelling and simulation tools were developed.
The work within WP4 regarded two parts: a) the development of a semi-empirical model for the simulation of the expander operation and b) the development of a dedicated model for the simulation of a heat pump unit equipped with an integrated expander and the estimation of the energetic benefits for different scenarios. The purpose of the first part of the work was the development of a semi-empirical thermodynamic model for simulating the operation of the developed hydraulic piston liquid expander. Semi-empirical models involve a limited number of physically meaningful parameters that can easily be identified from experimental measurements, while deterministic models require an exact knowledge of the geometry of all the components. Semi-empirical models are usually numerically more robust than deterministic models and allow a sharp decrease of the computational expenses.
The development of this model was based on several semi-empirical thermodynamic models available in the literature. Desired objective was the ability to simulate, “on the spot”, the expander of the test bench used within the EXP-HEAT project. The only required data for the simulation were the experimental results of the test campaign of the expander with R134a that took place during WP3 and its main technical specifications. Simultaneously the results of the simulation needed to be in convergence with the actual experimental results. In the context of this work, a complete semi-empirical model was developed. Significant part of this investigation was the determination of the actual internal leakages of the expander and of the actual supply density at the suction phase, when the pistons are charged with the high pressure two-phase refrigerant. With the use of the model and the elaboration of the experimental results the main causes of inefficiency were identified, showing the direction for further modifications that were to be implemented to the expander machine. The first results were generally in agreement with the results of other researches of the international literature, while the comparison procedure over its precision and accuracy with the actual measurements showed similar agreement.
The next steps included the simulation of the integration of the expander in a re-designed and a retrofitted heat pump. The aim of this second part of the work was to compare the seasonal performance factors (SPF) of a brine/water heat pump with the compressor frequency of 50 Hz in two different component configurations; First, the heat pump with an expansion valve with an isenthalpic process. Second, the heat pump with an expander instead of the normal expansion valve in different cases with different isentropic efficiencies including 10 %, 20 %, 40 %, 60%, 80 % and 100 %. The comparison was done for three different cases; First, with propane (R290) as the refrigerant and with the theoretical swept volume of 0.07 (L), for the climatic conditions of Stockholm and for a single-family house with the area of 265 (m2). Second and third, with R134a and R410A as the refrigerants and with the theoretical swept volumes of 0.23 (L) and 0.1 (L) respectively, for the climatic conditions of Strasbourg and for a multi-family house with 5 floors with the area of 140 (m2) in each floor.
In the first place, a system model of a brine/water heat pump was developed in EES (Engineering Equation Solver) software. The system model included models of the evaporator, the compressor, the condenser and the expansion valve or expander. Next, a system model of a ground-source heat pump was developed in TRNSYS simulation program. It included models of a ground-source heat pump, a ground heat exchanger installed in a borehole, a thermal storage tank, an electrical auxiliary heater, a house, a heating distribution system in the house (radiator), control units and climatic conditions. The heat pump performance maps, resulted from the developed model in EES, were used in the developed model in TRNSYS and the seasonal performance factors (SPF) for all heat pump component configurations were determined in the simulation results in TRNSYS.


3. Integration of the expander in a re-designed commercial heat pump unit.

Assembly and installation of the heat pump in the lab/ Operation of the heat exchangers, control and instrumentation:
A commercial heat pump unit, designed and manufactured by EURE, has been re-designed and fitted with the second level redesigned expander (version 2.0) developed within the project. The heat pump was installed at the laboratory of the Division of Applied Thermodynamics and Refrigeration at The Royal Institute of Technology, KTH. The aim of the installation was to test the expander in a typical Swedish heat pump for single family, or small multifamily house, designed for and located in the Nordic countries. The evaluation was focusing on the difference in performance of the heat pump with and without the expander integrated. The system performance in terms of efficiency at part load and full load was verified in typical Nordic climate conditions. Temperature, pressure, condenser water flow and compressor power was measured as well as the power generated by the expander. Out of the measured data, the COP and the isentropic efficiencies were calculated.
The heat pump, using R410A as a refrigerant, was equipped with the expander in such a way that it, in the future, it could easily be integrated into a final product. The compressor was capacity controlled and the condenser heat output of the system could be varied between 10 and 35 kW at running conditions -4/45°C. The condenser was selected assuming a 6K temperature difference of the heat sink fluid when the sub cooling is 4K at 45°C condensing temperature and a heating capacity of 30 kW.
The evaporator was designed for a suction super heat of 3,5K, inlet temperature of 4°C and a temperature change of 4K of the heat source at 23 kW cooling capacity. Finally, the condenser was cooled by water, circulated from a 1 m3 tank. To decrease the condenser inlet temperature, excess heat was rejected to the ambient by a fan coil with an inverter controlled fan, regulating the condenser inlet temperature. As an option it was also possible to use tap water as coolant. By use of a three way valve it is possible to regulate the condenser inlet water temperature. The evaporator temperature was controlled by two circuits. The circuit directly connected to the evaporator used a mixture of water and ethanol as heat transfer fluid and got its heat indirectly supplied from the water tank via a heat exchanger. By adjusting a three way valve it was possible to change the evaporator inlet temperature. To be able to perform tests with and without the expander, a throttling valve (EEV) was mounted in parallel. This also simplified the start-up process.
When the expander was running, a servo motor system measured the torque and the rotational speed, by which the power produced by the expander could be calculated. The power consumed by the heat pump was measured with a power meter and temperatures and pressures were measured at vital positions. A flow meter measured the water flow rate through the condenser, so that heat balance calculations could be carried out. Thermocouples, type T, were inserted into the circuit so that the temperatures where measured in direct contact with the fluid and refrigerant.

3.1 Solving lubrication issues of the new heat pump:
One of the most important issues addressed in the final redesign of the expander (version 2.0) was related to the lubrication. In the previous version, the lubrication of the components inside the expander was assured by putting an amount of oil in the bottom drain chamber to be spread by the eccentric rotating shaft and by injecting a small amount of oil in the cycle working fluid upstream the expander. In the modified expander, it was expected to inject oil in two different parts of the machine. In particular, a duct in the shaft from the outlet of the expander to the internal part of the case is present to lubricate the bearings and the pistons. Moreover, a modification was implemented to lubricate the plates through a duct from the external part of the case to the distributor, in order to reduce both the friction losses between the rotating and the stationary plates and the leakages through these components.
The heart of the lubrication system consisted of an oil tank. The tank was pressurized by the compressor discharge line with a check valve to ensure that no oil is sucked by the expander in case of under-pressure in the discharge line. Subsequently, the pressurized oil tank was connected with the expander lubrication ports with a regulating oil valve. When the valve opened the oil flowed in the expander. It is remarked that the oil tank pressure was always higher than the pressure at the expander’s distribution plates, shaft and pistons. The lubrication procedure involved a flash opening of this valve at regular intervals to allow the injection of a small amount of oil.
Ann identical lubrication system was also used in the NTUA laboratory where the retrofitted heat pump was tested. The system is thoroughly analysed in D 7.3- Report on tested retrofitted system durability and final optimisation aspects, and therefore no further analysis was included in the deliverables of WP5. All tests showed that this lubrication procedure was sufficient to ensure trouble-free operation of the expander. Actually, up to now the initial amount of oil that was injected in the expander was enough to lubricate the expander. At this point it should be noted that the refrigerant mixture of heat pumps contains dissolved oil which also contributes in the expander lubrication. The expander was inspected regarding its lubrication after 4 hour intervals of operation and all parts were found to be very well lubricated.
Further conclusions can be drawn after a specific real test case that is planned to run on a long-term basis after the project end. In this case, two scenarios will be tested. In the first scenario an automated lubrication system will be installed. The control system will be programmed to inject a small amount of oil at specific time intervals (e.g. 12 hours of operation – parameter to be optimized) by opening an electromagnetic oil valve at the tank outlet. The excess oil will be collected at the sump guard of the compressor where the oil is separated from the refrigerant mixture due to increased temperatures and flashing procedures. This strategy is commonly used in commercial heat pump units. Having collected a handful of data the possibility to return the oil from the sump guard to the oil tank will be evaluated if necessary. The second scenario regards the operation of the expander without additional lubrication in order to evaluate the necessity of adding further oil during the operation of the expander or if the initial amount of oil and the dissolved oil in the circulating refrigerant are sufficient.

3.2 Combined system start-up and operation:
To be able to run tests with and without expander the expander was connected in parallel to the main cycle throttling valve (EEV). This parallel connection was also useful during the start-up process. To control the amount of refrigerant flowing into the expander a needle valve located after the expander was used. This needle valve was gradually opened while the EEV was closing. Meanwhile, the expander was started at a low rotational speed and thereby the refrigerant flow was gradually re-directed from the throttling valve to the expander. All measurements where conducted with fully closed EEV.

3.3 Testing and evaluation of performance and components durability:
The main results obtained by the experimental process are summarized next.
a) It was found that, as could be expected, the performance of the expander was highly dependent on the pressure difference,
b) Under the best conditions, the power of the expander could reach 150 W,
c) The power of the expander was small compared to the power of the compressor (in the range 0.6% to 1.8%.) , and
d) The isentropic efficiency of the expander has been determined to a maximum of 16% on the basis of the heat pump low and high pressure conditions and not on the conditions at the inlet and outlet of the expander as in the standalone expander tests. This means that the real heat pump cycle induces important pressure losses at the heat exchangers and especially at the distributor of the evaporator where a pressure drop of even 3 to 4 bar is usual for most commercial heat pumps. The main conclusion was that in order to enhance the performance of the expander fitted in a complete heat pump unit it is imperative to first proceed in an exclusive redesign of the heat exchangers in order to deal with the above mentioned issues. Moreover, the reliability issues described in D 7.2 Report on tested combined system durability and final optimisation aspects it was not possible to run as many expander test as it was initially desirable.
Overall, the tests were evaluated by all partners as pretty successful regarding expander installation and integration in the combined system as well as control, start-up and operation of the whole system. However, the performance of the expander in terms of the whole system conditions proved to be lower than expected for the reasons explained above and therefore in terms of performance it has been considered that the WP activities have achieved most of the project objectives and technical goals for the period with relatively minor deviations.
With the completion of these research activities two more core milestones of the project were successfully reached: Milestone No4 - Integration of expander in a re-designed heat pump and Milestone No5 - Tested the combined concept.

4. The retrofitting of an installed heat pump

A main goal for this part of research activities was to make as few changes to a commercial heat pump unit as possible in order to retrofit it with the developed expander, while still increasing its performance. An on/off heating only commercial unit (NIBE F2300-20) was selected for the retrofitting of the expander. The choice was made upon the commercial plans of THERMO. For the reasons that have already been discussed in Deliverable 9.2 (Market Strategy) THERMO plans to focus more on the retrofitting of larger capacity on/off commercial units (e.g. hotel chillers) with low COP rather than domestic heat pump units. Moreover, the ON/OFF unit was more suitable for retrofitting the expander compared to an inverter driven unit as it did not require any changes to the control unit, keeping the retrofitting costs low.
The installed heat pump was subsequently retrofitted with the expander prototype coupled to an asynchronous generator. The generator was driven by a regenerative frequency drive (inverter) in order to control its rotational speed. Moreover, some additional measuring sensors were added: a torque-meter to measure the produced mechanical power of the expander and two energy-meters to measure the consumed electric power of the heat pump unit and the produced electric power of the generator. Additionally, a flow meter of the closed hot water circuit was also installed.
Most importantly, the retrofitting of such a unit did not require the replacement of any of its components including the compressor/motor, heat exchangers, automation and safety system, throttling valves etc. Nevertheless, it was proved that the performance improvement can be significant, considering the few additional resources required, and therefore fully justifying the effort of the research teams and the SMEs personnel. The retrofitted unit, installed in the NTUA laboratory, was tested in a dedicated test-rig that was constructed for its experimental evaluation, focusing more on its testing at various operating conditions, and on the components’ coupling rather than pure performance.

4.1 Control system and measuring equipment
The control system and data acquisition system was materialised with ADAM ADVANTECH input/output modules. The computer interface was done in DASYLAB software. The operation of the heat pump is controlled by its original control unit which has not been modified.
The main input variables were the values obtained by the measuring equipment:Temperature and pressure sensors, Energy meters, Torque-meter, Water flow-meter.
The main control (output) variables were: Electromagnetic valves, Expander rotational speed (inverter output frequency).
Additional manually controlled variables were: Needle valve at the expander output (refrigerant mass flow regulation),Oil valve (ON/OFF), How water circuit adjustment valve (hot water mass flow regulation).
The experience of the test campaign of the retrofitted commercial heat pump showed that the ontrol procedures described above can be fully automated, which is an absolutely necessary step towards the development of a commercial retrofit kit product. Actually, in the final product, the expander/generator speed will not be controlled as there will be no frequency inverter. An optimal speed of the motor will be chosen according to the unit’s refrigerant and nominal mass flow so that in full load the expander rotational speed ensures the nominal mass flow rate and the needle valve can remain fully open.

4.2 Retrofitted system start-up and control
The start-up process was very smooth and did not indicate any malfunctions that should be resolved. The operation of the unit followed the procedure described in the following steps:
1. Start of the heat pump at normal mode with all the valves that lead to the expander closed. The unit is kept running until it gradually reaches its full output thermal load. The maximum flow in the hot water circuit is ensured so that the condensation temperature and thus pressure are as low as possible in order to achieve a smooth expander start-up. Once at full load operation, the heat pump is let running for several minutes in order to stabilize its operation.
2. After the heat pump's operation at full load is stabilized, the expander's outlet valve is opened, while the inlet valve still remains closed. This allows the system to recover any remaining liquid refrigerant in the expander back to the heat pump's circuit. In that way, a smooth start-up of the expander is ensured, once it is connected to the rest of the system.
3. The expander's desired smooth start-up requires low rotating speeds. For that reason, the electric motor/generator coupled to the expander's shaft is set at a low rotational speed through the inverter drive.
4. After the expander's start-up, the inlet valve is opened. As a result, a limited amount of refrigerant flows through the expander, while the majority of the flow continues to flow through the main expansion valve. It is intentional that the expander is not instantly driven into full load operation, as a rapid liquid refrigerant mass flow could cause a hydraulic pressure shock wave. Moreover, the needle valve is kept half-opened to ensure a quite low mass flow rate at the first moments of the expander operation. The importance of the needle valve is further analyzed next.
5. After stability under these conditions is achieved, the by-pass electromagnetic valve is closed and the main expansion valve QN1 is isolated leading to full expander mode operation. At that point, all the circulating refrigerant mass flow passes through the expander. Further adjustments to the mass flow rate can be done through the needle valve and the expander rotational speed, while the expander inlet pressure can be adjusted by the control of the flow in the hot water circuit.
An important point that needs to be highlighted and explains the importance of controlling the circulating refrigerant mixture mass flow rate is the superheating degree at the outlet of the evaporator, which was monitored by the Superheating Indicator. It is very important to maintain the superheating degree more than 2 K in order to prevent the suction of two phase refrigerant by the compressor that would eventual lead to its damage and failure. The superheating degree of the refrigerant is closely linked to the mass flow through the evaporator. In other words it must be ensured that the evaporator can cope with the circulating mass flow, which can be adjusted either by the needle valve at the expander outlet by the expander rotational speed. Generally it is preferred to operate the unit with the needle valve fully open so that no pressure losses are induced in the system. Indicatively, in the NTUA lab, stable conditions under low inlet pressure (13bars) were ensured at around 150rpm with the needle valve fully open. This value may vary according to the ambient conditions (due to the use of air to refrigerant evaporator) and the condensation temperature which affects both the high and the low pressure of the system. Most importantly, the adjustments ensure a sufficient superheating degree while at the same time the unit continued to deliver its nominal thermal power.
Overall, the retrofitted system at expander operation mode run in a very satisfying way without any major issues and its control proved quite easy.
To sum up, even though certain operational problems were expected especially during the expander start-up, no particular issues were encountered during the start-up and operation of the unit at expander mode. As a result, a start-up and operation procedure as well as some safety and monitoring parameters have been fully defined. Moreover, without modifying the original control unit of the heat pump mother-unit it was possible to control the whole system without any interference issues and without affecting the heat pump thermal power output. Therefore it was concluded that it’s possible to install an independent additional control unit for a fully automated operation, control and monitoring of the final commercial retrofit kit product. In this context, a detailed analysis of the control and operation strategy was presented.
Overall, the expander installation and modifications for the retrofitting of a commercial ON/OFF heat pump unit proved to be quite an easy task with fewer problems than initially expected. The same holds also for the start-up, operation, control, and monitoring of the unit. It was therefore concluded that the retrofit kit can indeed develop into a fully commercial product given a reliable expander unit, which was actually the goal of a successful completion of WP6 tasks.

4.3: Testing and evaluation of performance and components durability
The main results obtained by the experimental tests are summarized next:
a) It was found that, as could be expected, the performance of the expander was highly dependent on the pressure difference and expander rotational speed
b) Under the best conditions, the power of the expander could reach 140 W,
c) The isentropic efficiency of the expander has been determined to a maximum of 17% on the basis of the conditions at the inlet and outlet of the expander similarly to the standalone expander tests.
The abovementioned results refer to a maximum pressure of 16 bar. This was due to limitations of the commercial heat pump unit. High ambient temperatures during the final experimental test campaign caused high discharge temperatures at the compressor outlet, not allowing ot further increase the expander inlet pressure. Interpolation of the experimental results to higher pressure provided an isentropic efficiency of 19% at 20bar and 21% at 25 bar.
Similarly to the research activities for the new redesigned heat pump, overall it has been evaluated by all project partners that the tests were pretty successful regarding expander installation and integration in the retrofitted commercial heat pump unit as well as control, start-up and operation of the whole system. This was anyhow the main goal of this WP rather than outright performance. However, the performance of the expander in terms of the whole system conditions proved to be lower than expected and therefore in terms of performance it has been considered that the WP activities have achieved most of the project objectives and technical goals for the period with relatively minor deviations.
With the completion of these research activities one more core milestone of the project was successfully reached: Milestone No6 - Tested the retrofitted heat pump.

5 Further optimization of the expander version 2.0 towards a future version 3.0 – Optimization of combined systems

Further optimisation of the combined process was planned to be done, after recording and processing the first series of measured data, concerning the combined operation of the re-designed and the retrofitted heat pump describe above.
The operation of the original control unit as well as the operation and optimization of the additional one and its evolution towards fully automated operation, the operation and the sufficiency of the lubrication as well as a detailed analysis of reliability issues encountered with the expander version 2.0 in the redesigned and the retrofitted heat pump test bench of KTH and NTUA have also been presented.
Specifically, several problems arose during the experimental tests such as: debris presence in the interior of the expander, bearings damage, O-ring faults, piston rods damage due to their discontinuous contact with the crankshaft bearing, and insufficient spring force on the pistons. Each issue along with the identified cause has been presented and explained in detail, giving an even more insight to the expander’s design and operation. The implemented technical solutions or modifications to be made in the next expander version have also been included in a dedicated report.

6 Technoeconomic assessment of project concepts’ viability and achievement of target costs

The aim of this work was the techno-economic assessment of the integration of the dedicated expander into domestic and commercial heat pumps and chillers. For this purpose, two main scenarios were distinguished, following the innovation work conducted in the project and the developed market strategy according to the commercial plans of the involved SMEs. The first scenario includes the integration of the expander into a new heat pump, as a complete commercial product. In the second scenario, an existing commercial chiller is retrofitted with the dedicated expander. The aim was to provide reliable calculations and comparisons of the economic viability of these two scenarios under a wide range of operating conditions that covered the whole addressable market.
In the first section, the main technical characteristics, as well as a cost breakdown of the heat pump products to be evaluated were presented. The base case assessment scenarios were defined, according to the technical/operational characteristics of each heat pump product and additional economic assumptions. The main parameters (technical/operational and financial ones) that influence the economic performance of the expander integration concept are identified, while their variation ranges are specified. Subsequently, the implemented techno-economic evaluation methodology were presented. This methodology was used for calculating major economic performance indicators, such as the net present value (NPV), the internal rate of return (IRR) and the discounted payback period (DPBP) for different input values of the main evaluation parameters. For each one of the base cases, a calculation of the economic performance of the heat pump products was initially carried out. Then, a series of sensitivity analyses were conducted, in order to estimate the influence of the main independent technical/operation and economic parameters and assumptions on the profitability of the expander integration concepts. Focus as given on the discounted PBP, which was selected as the most representative indicator, and on the evaluation of the business cases. The most important result of this study was the achievement of a PBP below 5 years for all base cases which actually means that Milestone No7 - Target cost achieved was successfully completed.
Potential Impact:
Potential Impact:

The overall objective of the project was to open new markets for the participating SMEs, and further develop new products and services, in order to magnify their business cycle. The new expander produces work through the expansion of a high-pressure liquid fluid to a low-pressure wet vapour state. For this reason, the expander can have several applications such as refrigeration systems, heat pumps, air-conditioning units, and ORC systems.
Apart from the expander, two more commercial products are expected to be launched by the SMEs. Firstly, an improved re-designed heat pump unit of higher efficiency offered at slightly higher cost will be introduced by EURE. In parallel, a retrofit kit, with the capability to be installed in a variety of heat pumps (mostly old ones with low COP) and boost their performance with limited cost, will be introduced by THERMO,, putting the company in a leading position as it will be the first company to introduce such a kit in the market. Except from that, DORIN and ITAL can distribute the developed expander to other heat pump manufacturers as well.
The developed technology finds potential applications in the following markets:
• The heat pump market. The study of the potential development of heat pump sales in the capacity range from 12 to 30 kW showed that annual sales in Europe is about 800 000 units, 10% of which are units larger than 20 kW. Even though the number of sold heat pumps is large, there is a very large potential for increasing. Moreover, the increase in sales of larger heat pumps, which is already visible in the statistics, increases the market possibilities for an expander of the type developed in the EXP-HEAT project.
• The refrigeration market. The same component can also be used in refrigeration units, increasing their COP values. Probably in such units, the increase in performance is higher, since the temperature/pressure ratio is larger and the running hours higher. For example, in supermarket refrigeration the systems are literally running all year around. Additionally, the market for refrigeration systems of different types is much larger than for heat pumps. Applications with CO2 are the most promising for DORIN activities. In fact, DORIN is a market leader for CO2 compressors used in refrigeration, and it is active in proposing and doing research for the optimal use of these refrigerants within compression refrigerators.
• The air-conditioning market: it is huge, considering that the estimated sales of AC equipment in Europe 2013 was about 7.6 million units. A similar concept could be also used in this case, since there is higher work-recovery potential, due to the larger pressure ratios.
The high-performance heat pump units and the developed expander will further help the SME partners to offer high efficiency innovative products, with slightly increased cost. At the same time it will be a much needed boost for the strongly positioned European heat pump and refrigeration industry that is under pressure internationally with hi-tech products at much lower costs, from large international companies with well organized R&D departments.
Apart from that, the final products are ideal to be used in the commercial/residential sector to reach the goals concerning decreased energy use, and CO2 emissions and increased use of renewable energy. The already present state support (e.g. subsidies) for the further growth of heat pumps can therefore be expected to expand, including larger capacity systems for larger buildings. For example, they can contribute to the nearly zero-energy building, which is a priority of EC (EC Directive 2010/31/EU) for decreasing the energy footprint of buildings. In addition, the increasing constraints induced by the energy efficiency labelling, can raise the interests by many heat pumps manufacturers in the proposed products, even with the small but important COP increase given by the expander.

Dissemination activities:

Dissemination provides important networking opportunities for obtaining feedback about the followed course of work and the project results, which can fine-tune the research process. Synergies with other research teams can be identified and the foundations for future partnerships can be set.
An important aspect of the EXP-HEAT project was the exploitation of the results by the involved SMEs, supporting them to clearly pave the way to bring the improved technology to the market. Regarding the academic partners, dissemination provided the basis for exploiting the project results, as it provided the means for access and communication with a wide variety of stakeholders from academia and industry including SMEs.
All project partners were involved in dissemination, awareness raising activities and exploitation of the results actions. SMEs used their numerous industrial contacts to maximize the market penetration of the products. RTD performers promoted the RTD work in national and international events, such as conferences and seminars and through publications, press conferences and daily press. All partners had the skills to implement an ambitious dissemination plan, since they were recognizable as leading organizations in the industrial and scientific community on the technologies of concern.
A wide range of dissemination activities has been carried out. All dissemination activities aimed on the promotion of the EXP-HEAT project and are mentioned next:

• Project Website. Internet was the main dissemination tool, as it constitutes a means of wide access and communication. Therefore, first of all, the project website was developed (www.expheat.eu) in the beginning of the project and since then it has been regularly updated with relevant material, news and upcoming events. Special attention was given to the development of a user-friendly environment with easy access to project information and contact details of project partners. An internal password-protected area has been also included for internal communication between the consortium members for sharing documents and electronic material .The web-site informs its visitors of the project concept, the involved technologies and the project progress and results. The consortium members and the coordinator are also listed with their brief description. Moreover a project video has been created and is available both on the project website and on YouTube (https://www.youtube.com/watch?v=dO7PqChBK18).
• Promotional material and publication activities: creation of the project poster and leaflet (Figure 7 and Figure 8), as a means of raising interest and receiving feedback from the international research community. A project leaflet has been produced giving an overview of the project concept and objectives and raising awareness of the project and its web-site, where more and up-to-date information was available. The leaflets have been produced by the coordinator and handed out to all partners, in order to distribute them to their colleagues and contacts as well as to be handed out in public events such as conferences, exhibitions and workshops. In addition, a project poster has been produced with similar content, providing more detailed information about the project. Leaflets and posters were used in all public events (e.g. conferences, workshops, exhibitions, etc) where project partners participated. The use of printed material provides an easy way of communicating a summary of the projects’ objectives and activities.

• The RTD partners of the consortium took part in international conferences and made novel publications in scientific journal using the project results. In all publications, the contribution of the EU towards the implementation of the project is stressed.

• The SMEs partners took part in various international exhibitions where they presented the research and development activities and the project results. In these exhinbitions project goals and the developed expander were presented both for dissemination and informative reasons, as well as to showcase the difficulties of implementing such an innovation and at the same time to measure the interest of the market. The leading partner of the consortium in this field was DORIN which regularly participates in refrigeration-related international exhibitions which is of great interest for the dissemination of the project goals and results. ITAL cycle of business on the other hand is not so closely related to the developed expander and the new and retrofitted heat pump products. However, the marine sector showed remarkable interest towards the developed expander for possible applications on-board ships (for both refrigeration and chilling units). Moreover, the presentation of R&D activities at such a level had a positive feedback on the company’s profile.
THERMO is a much smaller company, almost entirely oriented to the Greek market and for this reason it participated only in one international exhibition, where the domestic market attitude for the developed retrofit kit was explored and different potential customers were informed about the EXP-HEAT project and specifically for the activities of THERMO and NTUA.

• A workshop was organized by FIR in Florence, where the project results and activities were presented to some Italian companies and to the research groups that deal with energy systems. In addition, the aim of this event was the exchange of views and feedback to the project’s impact, and the networking for promoting further research activities. The workshop took place on March 13th, 2017 at the School of Engineering of the University of Florence (FIR).

• Technicians and engineers from the involved SMEs were planned be trained in the development, operation, retrofitting and maintenance of the expander and the combined processes. The training activities were designed and planned according to the specific needs of each SME partner in regard to the R&D activities and the respective product. Accordingly, DORIN and ITAL concentrated on the design, modification and manufacturing of the expander while obtaining additional knowledge from the installation, operation, lubrication and maintenance of the expander from the standalone expander testing as well as from the integrated testing at the new heat pump unit performed by EURE and KTH and at the retrofitted unit performed by THERMO and NTUA. EURE on the other hand concentrated on the installation, operation, lubrication and maintenance of the expander in new heat pump units while THERMO focused on the development, design and installation of the retrofit kit as well as on the respective operation, lubrication and maintenance of the expander in retrofitted heat pump units. This Task is thoroughly presented in D 9.5 - Report on the training activities.

• Development of market penetration strategy: Firstly, a thorough market analysis of heat pumps was conducted in order to showcase the potential for the developed expander. This analysis was based on the request to carry out a robust analysis of the size of the market for high-priced heat pumps with a somewhat higher energy efficiency compared to standard heat pumps. It included an analysis of the European heat pump market, including statistics, government and EU policies and initiatives for heat pump growth, and cost analyses. Moreover, the market of other heat pump technologies including supermarket refrigeration, commercial chillers and air conditioning was also analysed. In the last part, the profile of each SME product as well as the envisaged EXP-HEAT products have been correlated and the targeted market for each SME has also been determined.

• Another task within the dissemination activities of the project regarded the management of knowledge and intellectual property, the plan for the use of results (e.g. exploitation plan) and for the dissemination of the foreground among the consortium both during the lifetime of the project and afterwards, information relating to all press releases, publications, and all dissemination actions. An interim exploitation plan of the project was developed for the first reporting period (months 1-12), and concerned the use of the research results and how these could help the participating SMEs to improve their products and expand their activities to new highly-competitive markets. The dissemination activities had to do not only with the promotion of the project concept within the industry sector (highly relevant to the SMEs activities), but also with the presentation of the results to the scientific community for further elaboration. Close to the project end, when the final experimental results as well as the conclusions from the techno-economical analyses were available. A final exploitation plan for the use and dissemination of the foreground as well as the knowledge management has been developed.

Exploitation plan and market penetration strategy:

After the project end, the two installed prototype heat pumps (the new one and the retrofitted one) and the developed expander will continue to operate, in order to expand the know-how gained from the project and acquire further experience. At the same time, as previously said, the involved SMEs will be looking for early adopters of the new technology. These first installations will allow the involved SMEs to gain valuable experience in producing and installing this concept and dealing with the customers, by also offering after sales service, maintenance and updated and improved components. Additionally, the involved SMEs will be further adjusting the basic design of the prototype systems, in order to up-scale and downscale the size of the expander and of the heat pumps. In this way, various end-users demand will be met; a preliminary list of possible expander capacity versions is the following: 1 kW, 2 kW, 5 kW, 10 kW, and 20 kW; while a possible list of new heat pump versions could be: 10 kW, 20 kW, 60 kW, 100 kW, 150 kW. In addition, the expander could be used with natural refrigerants, even at trans-critical conditions, aiming the CO2 heat pump and refrigeration market. The focus will be to establish a number of successful running units that will serve as shining examples for future prospective customers. In parallel with that, the production process of the expander, heat pumps and retrofit kits will become standardized with increased sales, driving the costs further down and achieving low pay-back-periods, as mentioned previously.
The vision is that within a period of 2-3 years after the project end several systems (mainly of small-scale) will be installed in different sites, mainly for residential/commercial applications, to build customer confidence. In the meantime, in terms of cost the products will be very competitive, with a pay-back-period lower than 2-5 years, as described previously. At that point, the break-through is expected, with the expansion machine, the re-designed heat pump and the retrofit kit to be established in Italy, Sweden and Greece, while the expansion in new target markets will be on going with negotiation of licensing agreements.
The exploitation plan of DORIN relevant to the EXP-HEAT project results is to apply the new developed expander directly to its compressors designed for heat pumps and chillers, possibly using natural refrigerants as well (such as CO2). In fact, this is one of the main DORIN’s market oriented strategies, which should place the SME into a very interesting international position in the field of innovative heat pumps’ and chillers’ cycles with high efficiency. The investigation of similar concepts with natural refrigerants is one-step further in the research activities of DORIN and FIR with expected future collaborations as well.
Starting from the developed expander, further commercial collaboration between ITAL and DORIN are planned, jointly developing additional versions of the developed expander and promoting them to the market. In this way, the two involved SMEs will build a sort of profitable consortium to exploit the outcomes of EXP-HEAT project applied to heat pumps and chillers operating with conventional refrigerants or even CO2.
EURE on the other hand manufactures custom made small and medium size variable speed heat pumps, (water to water and air to water) and currently its target markets are the ones of Sweden and Finland. To be able to compete with the major heat-pump manufacturers EURE has to make even higher performance heat pumps, being one-step ahead of the competition. Variable speed (frequency controlled electrical motors) has been one-step in this direction, giving superior capacity control abilities with high seasonal performance factors (SPF).
Another step is the integration of an affordable expander in EURE’s heat pumps, which can increase the COP/SPF values significantly, making EURE to market its products even more aggressively as high performance products. By improving the COP by at least 3%, will lead to a major increase of the SPF value with lower power consumption and without power-peaks during the cold winter months. For this reason, the first target markets will be in countries with cold climates (such as Norway, Denmark, Germany and Austria), and then expanding to southern countries as well.
Finally, THERMO can directly include the developed expander in the heat pumps it has already installed in Greece, providing upgrade services, or even being the official representative of EURE products. In general, the Greek heat pumps market is in a very early stage. An estimation of the number of the domestic heat pumps installed in Greece is 12.000 units, half of which are equipped with one stage compressor, i.e. applicable to EXP-HEAT project, while a conservative number of installed chillers is approximately 100.000 units, almost all of them equipped with one stage compressor. THERMO have also considered the fact that most of the domestic heat pumps are still in their Pay-Back-Period, which leaves very little space for any additional investment. This is, probably, the biggest challenge that THERMO will be facing, during its exploitation plan and one of the main reasons THERMO plans to reach out to a more promising market such as the commercial installations (i.e. Hotels). In the initial exploitation phase after the project end, THERMO plans to apply such a kit to commercial sector (retail or hotels), where heat pumps with low COP, high maintenance and operating costs in addition to high energy demand, due to high running hours per year. In such applications, where the COP enhancement could be higher than the 5% above calculated, THERMO has estimated Pay-back-Period in the range of 3 to 5 years, so leading to greater economic savings. A point of consideration raised by the reviewers regards the selection of 20kWth capacity domestic heat pumps as target units. As correctly mentioned in the Assessment Report, modern single-family houses require about 5-7kWth capacity heat pumps for the cover of their needs. However, as shown in the market analysis presented in the first part of this report, sales statistics in many countries (e.g. Italy, the Netherlands, Slovakia) show that a great share of the sold domestic heat pumps is in the 20kWth range. This is due to the fact that these heat pumps are installed for renovating older single-family houses with insufficient thermal insulation as well as for the hybridization of existing burner/boiler central heating systems in multi-store apartment buildings, where the needs are considerably higher compared to a single house. Finally, as already mentioned, commercial applications show greater potential for getting retrofitted with the developed kit. These units have generally higher installed capacities (in the range of 20-80 kWth). For this reason, the main consideration for the retrofit kits would be the commercial applications. Naturally, large capacity domestic units (20-30 kWth) will not be excluded. Anyway, the one already installed at the laboratory of NTUA, which will be subsequently retrofitted with the expander and experimentally tested is a standard on/off 20kWth domestic heat pump.
After the successful penetration of the Greek market and the acquaintance of the respective knowhow, THERMO plans to expand its business in commercial applications of the European market. A breakthrough achievement for the standards of the European market will then be the release of a retrofit kit product in co-operation with Vailant and /or NIBE. Both companies have a wide sales network as well as extended customers’ networks and invaluable experience in these markets. Taking into account this undoubted advantage over the competition, the retrofit kit is expected to be a great product both in terms of energy efficiency and sales.

Specific market issues:
The SMEs partners already constitute a complementary group of experts with distinguished roles in the realisation and commercialisation of relevant products. Consequently, the consortium as already formed can guarantee the implementation of the technology and has the infrastructure to produce a certain number of units in yearly basis. However, since the participating SMEs come from different EU member states (Greece, Italy, and Sweden), it is absolutely necessary in the future to seek for licensed partners and distributors of the technology in other countries as well, starting from European ones and gradually expanding the commercial network to non-European countries.
The SMEs partners currently own the necessary financial and human resources to support the technology in both the development stage and the first commercialisation steps. Further on, there will be a need to improve the level of their infrastructure few years after that (i.e. venues, equipment, labour) to increase the production and meet the demand, under the condition that the target market is enlarged according to the preliminary strategic market plan. This can be done by applying for subsidies, being available in both national and European level and through further participation in RTD projects (e.g. demonstration projects) along with the use of their existing resources.

List of Websites:
www.expheat.eu

Contact Person: Assoc. Prof. Sotirios Karellas (NTUA) E-mail address: sotokar@mail.ntua.gr Tel: +30-210-7722810