'A black shingled roof was used as a collector/regenerator for the evaporation of water to obtain a strong solution of lithium chloride absorbent. In the house, water (the refrigerant) is sprayed into an evaporator and this was evacuated to a pressure of about 5mm of mercury where the water immediately flashes into vapour. Cold water pumped from the bottom of the evaporator then flowed through a fan coil unit which blew cold air into the area requiring cooling. (Fan coil units are usually used with chilled water in the HVAC industry). Water vapour from the evaporator flows over the absorber where it is absorbed by the concentrated absorbent (lithium chloride). The continuous absorption of water vapour maintained a low pressure in the system and permitted flashing of water in the evaporator. The product of the absorption process which was a weak absorbent solution collected at the bottom of the absorber to be pumped over the roof for concentration.

'The dilute lithium chloride solution was delivered to the collector surface through a spray header spanning the top of the roof and made from 2 inch PVC pipe fitted with 35 evenly spaced nozzles. The concentrated solution collected at the bottom in a PVC rain gutter and returned via gravity to a 425 gallon tank'.

The Authors demonstrated a regeneration efficiency of between 38 and 67% which corresponds to a cooling capacity range of from 31kW to 72kW (8.8-20 tons of refrigeration). This is about 3.5kW per 10 metres square or 1 ton per 100 foot squared of roof area.

Reference to the original paper:
Unglazed collector/ regenerator performance for a solar assisted open cycle absorption cooling system - by M.N.A. Hawlader, K.S. Novak and B. D. Wood of the Center for Energy System Research, College of Engineering and Applied Sciences, Arizona State University, Tempe. Published in Solar Energy Vol. 50 pp59 - 73 1993

Source of this explanation: http://www.ambthair.com/coolingandlowenergy.html
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