Design, monitoring and dynamic model development of a solar heating and cooling system

This paper presents the design and performance analysis of a solar thermal heating and cooling (SHC) system. Apart from year-round domestic hot water (DHW) heating and space cooling, the specific system design provides the possibility to utilize waste heat of absorption chiller (ACH) during cooling operation for DHW preheating. This system was designed and set up as a first pilot plant on northern Adriatic coast of Croatia to ensure better assessment of technical and economic feasibility of SHC systems in that area through monitoring during operation. Following the system configuration design with original control system parameters, a detailed TRNSYS dynamic simulation model is developed. A methodology for validation of simulation model on a level of complete SHC system is proposed. The presented approach comprises simulation of the control system and interaction between system components, thus enabling reliable application of simulation model for further improvements of a particular system. Monitoring and simulation data showed satisfactory performance of SHC system. 55% of total irradiated solar energy is utilized at solar collectors, measured seasonal chiller efficiency ratio is 0.68 and running costs are 0.0225 € per kWh of produced cooling energy. Monitoring data also indicated that, due to unexpected low DHW consumption of the particular system compared to design guidelines, only 8% of heat from condenser and absorber is recovered, while the rest of the heat is rejected to surroundings at the cooling tower. Using the simulation model, a set of scenarios with increased DHW consumption and improved heat exchanger parameters were investigated in order to overcome the issue of low heat recovery efficiency. Preliminary analysis for analyzed period showed possibility for recovery up to 53% of waste condenser and absorber heat, reduction of cooling energy price by 15% and reduction of total system running costs when heating and cooling are both considered. The developed simulation model has been proven as valuable tool for evaluation of energy balances and feasibility analysis as well as for system configuration analysis and performance enhancement and it will be used for further research in order to achieve optimal efficiency in year-round operation.