PROJECT > Background information
The project essentially concerns the cooling of public buildings (hospitals, universities, care centers, etc.). Developing solar cooling installations is important from the standpoint of reducing the consumption of primary energy in buildings, and their dependence on energy from the power grid rather than energy produced on-site using renewable sources. Decarbonizing buildings is critical for achieving the targets set by the Paris Agreement. Space cooling demand rose by more than 33% between 2010-18 and by 5% in 2017-18. Although heating provision is still the main end energy demand in the building sector, space cooling remains the fastest growing end use. The issue of solar-powered air-conditioning is extremely important when considering technical, living and social conditions. Every year, there is an increased demand for air-conditioning devices, which are no longer a luxury but rather a daily requirement resulting from progressive climate change.
The innovativeness of the proposed COOLSPACES prototype manifests itself mainly in the refrigerants used. The prototype will use either a binary or a ternary mixture, the main component of which will be hydrocarbons (HC). By applying the above solution, it will be possible to obtain a low refrigerant impact on the environment (a GWP below 150), which is consistent with the provisions of Regulation (EU) No 517/2014. At the same time, it will be possible to improve the efficiency of the cooling cycle by improving the thermodynamic properties of the substances in relation to pure HC. Secondly, the prototype will use two refrigerant compression stages with full intercooling, which significantly reduces the amount of work necessary to implement the compression process, hence a high EER will be obtained. The prototype design also assumes that the evaporator is fed through a liquid separator, which allows the heat exchanger to operate with zero superheat. Thirdly, operating the system in tandem with short-term energy storage extends the scope of operation beyond the hours of solar radiation necessary to start the air-conditioning system. This improves the building’s energy performance by pre-cooling in the morning and improves overall system efficiency. Another innovation of the system is the use of phase-change materials (PCMs) in the form of replaceable energy storage inserts. Combining the possibility of smooth refrigerant evaporation temperature adjustment, it will allow for optimal phase-change temperature adjustment and increase the possibility of cold accumulation for initial building cooling using latent heat, without the need for extensive technical interventions in the storage tank. Last, but not least, using PV panels as a power source for the inverter compressors and the autonomous operating control system will make it possible to use the harvested energy optimally and distribute it between cooling the building directly and energy storage. A further advantage of the solution is the reduction in energy losses from using the condensation heat discharge for water heating (pre-heating water for household use, etc.).
Overall concept and approach
The entire solar-powered BC system is divided into four subsystem: a newly designed CFR-based cooling prototype (SCD) driven by photovoltaic panels; short-term cold energy storage subsystem in the form of phase change materials and cooling and domestic hot water (DHW) subsystems. During summer running, the studied building’s cooling demand will be covered by the cold PCM tank, operating at 1°C-6°C, and coupled to the prototype SCD working in tandem with the hot water tank (25°C-45°C, used to cover DHW demand). When there is a low cooling demand, chilled water will circulate from the SCD through the cold PCM tank to store this surplus energy. Therefore, on cloudy days, when the incident solar energy is insufficient to drive the SCD, the cooling demand will be covered by the chilled water retrieved from cold PCM tank, which will be charged the day before. Using the PV modules coupled with batteries as the main energy source to supply the SCD will permit operation with no additional fuel deliveries. The operation of the entire system will be controlled completely automatically – managing all key monitoring variables, choosing optimal system control, matching the instantaneous production of the PV modules to the SCD’s power needs and allowing the surplus energy to be stored in batteries or in the form of PCM wherever possible. In this way, we can ensure summer-round cover of the building’s cooling and DHW demand. COOLSPACES for the first time will study a solar-powered system that employs a newly designed CFR-based cooling prototype, a photovoltaic electricity production system and PCM-based tanks working in tandem. Such an approach has not yet been attempted in construction sector applications and it constitutes a major technological challenge, surpassing the performance of existing solutions, thereby advancing the state of the art. The underlying idea of the presented proposal is to drive the newly designed CFR-based cooling prototype using solar energy captured in the photovoltaic panels during the cooling season at two selected EU locations (Poland and Spain) – the main aim being to study the applicability of such systems under different climatic conditions. In particular, we will focus on demonstrating the technical and cost reliability and performance of both pilot systems. COOLSPACES aspires to being a prototype system that can be implemented in numerous European locations and that will form the basis of a highly exploitable product.
Actions and means involved
1) Determining the refrigerant composition, its flammability and safety classes for an innovative solar cooling device
The flammability issue is one of the key aspects when using substances in refrigeration and when constructing refrigeration equipment. This affects the amount of substance that can be used in the thermodynamic cycle, and thus affects its efficiency. It imposes restrictions on refrigeration system design and operation as well as various safety considerations that must be observed.
2) Design of the innovatice solar-powered CFRs-based cooling device coupled with short term cold energy storage system
The newly designed solar-driven cooling device based on CFRs will comprise the main part of the system providing the building’s cooling. The designed prototype will utilize blends that have a negligible impact on the greenhouse effect, the main components of which will be hydrocarbons, providing high efficiency and low system filling. The prototype device will be powered by solar energy coming from PV panels. The amount of generated electrical power needed to drive the refrigeration system, as well as the automation and hydraulic elements, is estimated to be 15 kW. This energy will be harvested from 65 PV panels connected to a set of batteries; this will allow an autonomous power supply of the control elements and system security around the clock. The cold storage system will be based on a selected PCM, which will store and release energy when they transition between their solid and liquid states. Our solution will allow solar energy to be stored in the form of cold, and then releasing it when it is most cost effective.
3) Transfer of technology to other European countries
After validating the device’s operation under Polish climate conditions, the device will be replicated and installed at the UAL site in order to check how effectively it works under hot climate conditions and to compare the performance characteristics with the two, already tested and continuously operating CIESOL cooling systems.
4) Dissemination campaign
The project envisages reaching the widest possible audience, using various methods of communication, both live and online. These activities will be of key importance for the effective development of the innovative BC system, raising awareness in the industry and society regarding the the use of renewable energy sources in cooling sector and geographic replication of the installation concerned.