Dynamic simulation and parametric optimisation of a solar-assisted heating and cooling system

In this paper, a complete transient simulation model of a solar heating and cooling plant is presented. The system under analysis is based on the coupling of evacuated solar collectors with a single-stage LiBr-H2O absorption chiller. An auxiliary heater, circulation pumps, storage tanks, feedback controller, mixers, diverters, ON/OFF hysteresis controller, single lumped capacitance building and controllers are also included. The simulation was performed using the TRNSYS environment. This software also includes a detailed database with weather parameters for several cities all over the world. The system was simulated using specially designed control strategies and varying the main design variables. In particular, a variable speed pump on the solar collector was implemented, in order to maximise the tank temperature and minimise heat losses. A cost model was also developed in order to calculate operating and capital costs. A case study is presented and discussed, aiming at determining the performance of the system, from both energetic and economic viewpoints, in a specific application. A thermoeconomic objective function was also introduced, and finally a sensitivity analysis was performed, in order to calculate the set of synthesis/design parameters that maximise the global efficiency of the system or the above-mentioned objective function, for the case under analysis. The results of the case study showed that a good selection of the solar collector (SC) area and of the volume of the storage tank (TK1) are mandatory. The Primary Energy Saving (PES) is positive in the case of high solar field area, while the optimal thermo-economic volume of the storage tank was found to be 75 l/m(2). The parametric optimisation also showed that it is important to lower the SC and auxiliary heater (AH) set-point temperatures, as much as possible.