Performance testing and evaluation of solid absorption solar cooling unit

Abstract

Based on solid-vapour intermittent absorption system, DORNIER a German Firm designed and fabricated a solar cooling unit, which utilizes thermal energy supplied by heat pipe vacuum tube solar collectors through thermosyphonic flow of water. The unit of 1.5 kWh/day cooling capacity uses ammonia as a refrigerant and IMPEX material as absorbent and does not have any moving part requiring no auxiliary energy. The IMPEX material (80% SrCl 2 and 20% Graphite) has high heat and mass transfer coefficient as well as high absorption capacity. Detailed experiments were performed on a unit in Delhi under real field conditions followed by theoretical analysis. Theoretical maximum overall COP of the unit is 0.143, and it depends upon the climatic conditions. Under field conditions, it was found that if the maximum daytime ambient temperature was 30°C and night time temperature 20°C, it took three sunny days to freeze water in the cooling box. After the second day, the temperature inside the cooling box remained 1°C. The overall COP was found to be 0.081 only. The automatic control valve based on mechanical/thermal principles however has defects and the problem of corrosion of the sealings needs to be solved. In climates where day time temperatures are high (Delhi summer 43°C–47°C during the day, 30°C–35°C during the night) and solar radiation relatively low (4–5 kWh/m 2d) because of pollution and sand in the atmosphere, it is most unlikely that pressure in the ammonia circuit can reach values at which ammonia vapours start to condense. The unit, needs to be redesigned for such conditions.