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Integrated solar heating and cooling unit based on a novel zeolite chiller and heat pump

Periodic Reporting for period 1 - ZEOSOL (Integrated solar heating and cooling unit based on a novel zeolite chiller and heat pump)

Reporting period: 2017-06-01 to 2018-08-31

The ZEOSOL concept is mainly based in the coupling of two innovative components (a) an adsorption chiller using zeolite-water as working pair and (b) evacuated tube collectors. The system is designed to operate under intermittent heat supply of low-temperature solar thermal energy (< 90 °C). The innovation offers a complete solution for covering both heating (space heating and domestic hot water-DHW) and cooling without requiring any additional system (e.g. boiler or air-conditioning). The combination of adsorption chillers with heat pumps in a single unit is one main innovative aspect of the new product. This integration reduces the number of collectors and chiller capacity, and provides an excellent part-load operation. The nominal cooling power of the new product is 20 kW, combining a solar driven adsorption chiller with an electrically driven back-up chiller/heat pump. Herein, the adsorption part is designed to cover the base load of 10 kW.
The overall objective of the ZEOSOL project is to further develop and validate an affordable cooling and heating product for small-sized superior energy performance buildings, and bringing this innovation within a timeframe of 24 months to the market. Initial focus is on south and central Europe markets.The key objectives of the project are listed below:
• Improve the existing technologies regarding the involved heat exchangers and the dry heat rejection unit
• Enhance system performance by integrating a backup heat pump
• Couple all components into a compact single unit design powered by the vacuum tube solar collectors
• Enhancing solar collectors efficiency to allow for continuous thermal comfort in the building
• Improving the control strategy to enhance system’s ESEER
• Reduce system costs down to 2000 €/kW
• Fully cover the thermal loads of a building
• Develop and test prototypes for various scenarios
• Validate the first demo units
• Identify the profile of installers
• Increase directed market promotion to enhance system sales
Until the end of the midterm period the main conducted work involved the modelling, sizing, development and testing of the separate components by the respective partners and the preparation of the site for the experiments of the coupled system in the premises of the National Technical University of Athens (NTUA). The adsorption chiller, developed by Fahrenheit GmbH, was sized in such a way to deliver 10 kW cooling power at the 50% load point based on the Eurovent standard RS/6/C/003-2015. In terms of the sorption material, the results of a series of comparative studies revealed that the optimal performance, by means of higher SEER, for the considered application was achieved with zeolite AIPO-5 as the adsorptive material, which enhanced significantly system’s performance in respect to other conventional types of zeolite or silica gel.
In terms of the dry cooler, a V shape configuration was selected as it reduces the footprint, while maximizing at the same time the capacity. In order to realize the compact all-in-one design, the backup heat pump was decided to be installed on the interior of the dry cooler. Thus, the system’s size would be significantly reduced, while the implementation of the compressor, in particular, within the dry cooler would allow for its cooling and consequently would result in a more durable and efficient compressor’s operation.
Conventional equipment was selected for the back-up heat pump to ensure stable low cost operation. The experiments conducted by CNR ITAE revealed that backup heat pump was achieving higher rates than the respective commercial ones, reaching a COP of up to almost 8. The overall system will be driven by vacuum tube collectors that were manufactured by AkoTec GmbH. Based on the experimental results, the vacuum tube collectors’ efficiency was significantly higher than other commercial products.
In parallel to the manufacturing process, a Life Cycle Analysis has been conducted to assess the impact of the system in comparison to a conventional heat pump.
Concerning the dissemination of the project, although main activities will take place over the last period of the project, with the planned workshops, already some preliminary activities have been conducted. The first act towards the publishing of the work to be conducted in ZEOSOL was the development of the project’s website and logo. The project has been introduced to scientific and industrial community by presentations in events and workshops (e.g. Deutsche Zeolithtagung, Chillventa 2018 etc).
At this point the results already assessed by the project’s partners involve the separate operation of ZEOSOL’s components, thus only preliminary conclusions can be extracted.
The first results for the zeolite chiller indicate a performance in the range of the predicted values. The EERs achieved in calculations are very high based on Eurovent standards, especially for part load operation.
These investigations showed that a class of adsorption material with working at lower desorption temperature show a high potential for reaching higher SEER values. The optimization procedure will be ongoing throughout the entire period of the project in parallel to the testing of the first prototypes by Fahrenheit GmbH to further enhance system’s performance and reliability.
The new vacuum tube collectors developed by AkoTec GmbH resulted in a significant enhancement (>5%) on the optical efficiency and a power increase of >25%/m². Further improvement is currently being conducted by AkoTec to allow for new durable connections and easier installation of the O-rings.
In terms of the backup heat pump, the experimental results indicated that the overall performance was 30% higher than the respective commercial products’ performance and 27% higher in respect to the ones considered during the modelling activity carried out in the early month of the project.
Early system’s simulation for the cooling period in Athens revealed a very efficient performance achieving solar fractions as high as 60-65% for a solar field of 40 m². Based on this and the feedback from the manufacturing partners, the LCA of the system was analysed. The results indicated a very positive impact of the system in respect to a conventional heat pump, especially for the case of global warming in which a reduction in the impact of more than 50% was achieved. Furthermore, the key fields for further improvement of the system towards its environmental impact have been identified.
The main results of the demo unit installed at NTUA will start in spring 2019 and will reveal the actual performance of the coupled system, as well as identify the key risks and challenges introduced by the coupling of the sub-systems. Based on the test results, all system components will be optimized, to achieve the best cost performance-ratios with reference to the objectives given in ZEOSOL project description. Finally, having resolved all maintenance, installation and operation issues the product industrial design will be finalized for commercial application.
At the end phase of the project, a joint venture will be created for the commercialization of the new product, in which Fahrenheit and AkoTec participate with Diadikasia being their strategic partner in south Europe. The initial target markets are in Italy, Greece and Germany, with the next expansion stage including Turkey and Cyprus, where Diadikasia has a strong network of collaborators.
Efficiency curve of ZEOSOL vacuum tube collectors developed by Akotec
Schematic of ZEOSOL system