EVALUATION OF A SOLAR-DRIVEN ABSORPTION CYCLE HEAT-PUMP .1. DESIGN THEORY, DEVELOPMENT, AND BASIC EVOLUTION

A commercially available lithium bromide-water absorption cycle air conditioner was developed into a solar-driven heat-pump system for grain drying. Energy obtained from water heating flat-plate solar collectors was used as the driving force for the heat-pump system. The system was evaluated under both clear and partly cloudy weather conditions. The coefficients of performance obtained followed a pattern very similar to the temperature pattern in the hot water loop. In other words, throughout a day's operations, performance coefficients increased to a maximum then decreased until there was insufficient solar energy to operate the system. The effectiveness of the solar collectors was about 77%, but varied with ambient temperature and heat losses to the surroundings. Their effectiveness cut-off point (when not enough energy was captured to operate the heat pump) was 0.46 which was very close to the design point (0.45) for minimum operations. Clouds occurring during operation of the system reduced generator inlet water temperature, lowered capacity and in extreme cases forced suspension of operations. Post-cloud performance sufficiently recovered to follow clear day performance. The system was capable of transferring only 47% of the energy between condensing water and an air stream heat sink. But, the system energy efficiency ratios obtained approached values in the higher part of the range generally stated for commerical air conditioners. The coefficients of performance for heating were much higher than values generally stated for commercial heat pumps. Based on the heat-pump evaporator, the cooling function was less influenced by ambient temperature variations than was the air heating function.