A solar-assisted double absorption heat transformer: Off-design performance and optimum control strategy

Using solar-assisted absorption heat transformers to provide high-temperature process heat over 100 degrees C has raised increasing concern in recent years for its energy saving and environmentally friendly characteristics. In this study, a solar-assisted double absorption heat transformer is proposed and analyzed theoretically. The optimum off-design performance is investigated to develop high-efficient control strategies under various climatic conditions (solar radiation intensity I and ambient temperature t(amb)). In order to maximize the heating capacity and overall system thermal efficiency ((Q) over dot(h) and eta(sys)), the conjugate directions method is applied for searching the optimum operation parameters including the strong solution mass flow rate and bypass ratio ((m) over dot(sol) and BP). The results show that the eta(sys )can reach 20.3% with the heating temperature at 130 degrees C under typical climatic conditions (I = 600 W.m(-2) and t(amb) = 25 degrees C). Under off-design conditions, the (m) over dot(sol) and BP exist optimum values, at which the (Q) over dot(h) reaches the maximum value. Specifically, under typical operation conditions, the maximum (Q) over dot(h) can be obtained as the m(sol) = 90kg.h(-1) and BP = 0.8. Under higher I and t(amb) conditions, the control strategies of increasing the collector temperature and (m) over dot(sol) are very practical to enhance the system performance.