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 maximize the tank temperature and minimize heat losses. A cost model was also developed in order to calculate operating and capital costs. Then, 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 maximize 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 SC area and of the volume of the storage tank TK1 are mandatory: PES is positive in case of high solar field area, the optimal thermo-economic volume of storage tank was found at 75 L/m2. The parametric optimization also showed that it is important to lower the SC and AH set-point temperatures, as much as possible.