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

Periodic Reporting for period 2 - ZEOSOL (Integrated solar heating and cooling unit based on a novel zeolite chiller and heat pump)

Reporting period: 2018-09-01 to 2020-02-29

The ZEOSOL concept is mainly based in the coupling of two innovative components (a) a hybrid adsorption chiller using zeolite-water as working pair with heating option 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 hybridization of adsorption chillers with heat pumps 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. 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.
The demo site was evaluated for operation on both cooling and heating mode in the period August 2019-February 2020. The results of the measurements came in agreement with the preliminary results of the design simulations. During August, the system was driven continuously within the day solely on solar adsorption module with COPs close to the nominal of the sorption chiller and daily EERs as high as 10, reducing thus significantly the need for the use of the conventional heat pump. Similarly, on heating mode capacities as high as 30 kW were reported, however, the reduced solar availability resulted in the conclusion that the industrial design of the system should have a slight increase in the solar field per produced from the chiller cooling kW. The respective economic analysis that used the results from the demo site concluded that the system can be economically competitive in regions with high solar irradiance as in the southern Mediterranean, a performance which can be further improved by taking advantage of the different financial instruments provided per country for renewable heating and cooling applications.
The first results for the zeolite chiller indicate a performance in the range of the predicted values. The EERs reported from the demo site are very high based on Eurovent standards, especially for part load operation. In particular, testing revealed a maximum COP of 0.54 for the adsorption module, and part load EERs of up to 45 for a driving temperature of 85 oC. The optimization procedure continued throughout the entire period of the project in parallel to the testing of the demo site 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 months of the project.
As proven by the experimental results within August the solar fraction was close to 100% within the day and with the assistance of the storage tank sufficient cooling was provided to fully cover the thermal needs of the laboratory’s offices. Based on this and the feedback from the manufacturing partners, the LCA of the system was analyzed. 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, namely components that make excessive use of copper and copper based materials such as the pipelines and the solar field. Indicative results regarding the LCA of the system are given in figure.
The experimental results of the demo unit installed at NTUA regarding hot summer days (first week of August) indicated a maximum COP of approximately 0.575 for a maximum driving temperature of 79 oC with a corresponding EER of as high as 12 and an average operation at approximately 5.8. In addition he system was able to cool down the water to 7.5 oC despite the driving temperature being below 80 oC in all cases. 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.