Beijing Solar Energy Research Institute, No.3 Huayuan Road ,100083 Beijing, China

Tel: 86 (10) 62351066, Fax: 86 (10) 62012880, E-mail: solarthe@public.bta.net.cn

A solar-powered absorption air-conditioning plant with 100 kW cooling capacity has been successfully designed and constructed in Rushan, Shandong Province, China. The plant consists of evacuated tubular collector array, absorption chiller, cooling tower, water storage tanks, circulating pumps, fan-coil units, auxiliary oil-burned boiler and control system.

The solar air-conditioning plant was installed in the Solar Energy Hall of the Chinese Scientific Popularization Park on Renewable Energy. The Hall is a two-storey building with a construction area over 1000 m² and was architecturally designed to meet requirements of solar collector placement.

The collector array using 2160 heat-pipe evacuated tubes, manufactured by Beijing Sunda Solar Energy Technology Co., has an aperture area of 540 m² and an absorber area of 363 m². The collectors were arranged in nine rows, in which seven rows were installed on an inclined south-facing roof and two rows on a flat roof. In order to obtain more solar irradiation over a day, evacuated tubes with a semicylindric absorber plate were selected.

The air-conditioning plant applies a Sanyo lithium-bromide absorption chiller with a maximum cooling capacity of 176 kW. The solar collectors supply hot water of 88to the inlet of the chiller, and the water leaves the chiller at 83. The chiller produces cold water of 8and the chilled-water returns to the chiller at 13. The cooling water temperature through the cooling tower is 31and 37respectively.

In addition to space cooling in summer, the plant also can be used for space heating in winter and for domestic hot water supply in the other seasons. For this multifunctional purpose, there are totally four water storage tanks in the plant. Two of them store the hot water produced by solar collectors, in which the smaller one aims to reach the specified temperature for the chiller in the early morning. The third one stores the cold water produced by the chiller. These three tanks are also applied to store the hot water for space heating when required in winter. The largest tank supplies the domestic hot water and rescues the plant from overheating in summer.

The control system serves to open / close valves and switch on / off circulating pumps to operate the plant for either space cooling or space heating or domestic hot water supply, as well as to prevent overheating in summertime and to prevent freezing in wintertime, and serves to light up / off the auxiliary oil-burned boiler to compensate the heat provided by solar collectors when water temperature is below the required level.

Through operation of the solar air-conditioning plant at different seasons, measuring results have shown following performance characteristics:

• As one smaller storage tank is specially adopted, hot water temperature can be raised from 70to 88before 9:30 am in summer to meet the requirements of the chiller, and from 40to 55before 9:30 am in winter for space heating.
• Under normal operating conditions in a clear day, the maximum collector outlet temperature can reach 95in summer and 85in winter respectively, that means more energy obtained from the sun can be stored for use after sunset.
• Thermal efficiencies of the evacuated tubular collector array for space cooling, space heating and hot water supply are respectively 40%, 35% and 50%.
• The COP of the chiller is approximately 0.71 under the solar-powered condition, and the cooling efficiency of the entire system is around 30%.
• There is obvious thermal stratification inside storage tanks owe to special design. Water temperature at upper part is 8-12higher than that at lower part, so that solar energy can be fully utilized by the collector array.

Keywords: solar, air-conditioning, heat-pipe evacuated tubular collector, absorption chiller, lithium-bromide, space heating, domestic hot water supply.