Optimization of performance of Combined Solar Collector-Geothermal Heat Pump Systems to supply thermal load needed for heating greenhouses

In this research, optimum design of the combined solar collector and geothermal heat pump system is studied. The aforementioned system should meet the heat load of a greenhouse as a sample. Our main purpose is analyzing the system from economical and technical points of view simultaneously. In order to optimize the system from technical point of view, operation of the controllers, diverters and mixers are adjusted with some control strategies to preheat the entering fluid into the evaporator of the heat pump and regulation of this temperature up to our ideal temperature was done successfully to increase heat recovery of the ground in maximum heat extraction periods, maximum outlet temperature of the ground source heat exchanger and coefficient of performance of heat pump and to decrease minimum auxiliary energy required for heating the greenhouse and heat recovery during summer season. Furthermore, from economical point of view the optimum condition calculated and the corresponding final optimized design is determined with the aim of balancing between economical and technical issues. Meanwhile, payback time of the system is calculated accordingly. The selected model has mean seasonal coefficient of performance of 4.14, borehole length and number of boreholes of 50 m and 3, correspondingly. Moreover, total collector area of the gained model is 9.42 m(2). At the end, a comparison between the final optimized system with an exchanger using the best working fluid for each loop and the same system with one single fluid is done. (C) 2015 Elsevier Ltd. All rights reserved.