Abstract
In dairy farming, much hot water are used for washing, heating, milking and refrigeration.
Paying attention to the quality and quantity of heat demand in dairy farming, a solar energy system to supply hot water which consists of high temperature and low temperature system is devised. A border of temperature between two systems is considered about 70-80°C.
In this paper, characteristics of a concentrating collector manufactured by way of trial for high temperature system are reported. Finally, collection of heat till 130-140°C will be held by the concentrating collector, but this paper described the case in which temperature of collection of heat was limited below 100°C using water as heat transfer medium to compare with a flat plate collector on a market for low temperature system.
The main results were as follows:
1) The concentrating collector could collect about 1800kcal (7540kJ) per day and maximum temperature of water in a storage tank was about 80-90°C in summer, and about 1300kcal (5400kJ) and 60-70°C in winter. The flat plate collector could collect about 70-80% of the concentrating collector at the temperature 50-55°C in winter.
2) Introducing the concept of exergy, the concentrating collector could collect about 80kcal (330kJ) per day both in summer and winter, and this quantity is about two times as much as that of the flat plate collector.
3) Collector efficiency of the concentrating collector takes the value about 60% at the maximum, and decreases according to conditions of solar radiation, ambient temperature and collecting temperature.
4) Collector efficiency of the concentrating collector was calculated theoretically by classifying the heat flow in the cross section into conduction, convection and radiation, and compared with experimental results.
5) Converting heat flow mentioned above into exergy flow, exergy efficiency of the concentrating collector was calculated theoretically. Exergy efficiency was about 10% and some differences between collector and exergy efficiency were appeared clearly.
