Analysis, Design, and Preliminary Testing of Solar Chimney for Residential Air-conditioning Applications

A solar chimney is designed and tested to pump outside air through an underground cooling tube during summer for building cooling. Both theoretical analysis and experimental results show that the solar chimney can be used to power the underground cooling system during daytime without use of electricity. This paper presents the theoretical design principals of the solar chimney, detailed experimental facilities, and the experiments results. The impacts of other related parameters, such as building tightness and tube design on the system airflow are also discussed in the paper. INTRODUCTION A motor-driven compressor and a motor-driven fan are normally used in residential air conditioning systems [1]. Both of them consume electricity. Electricity is the primary power for building cooling. The electricity bill may be several times higher during summer months due to the electricity consumption of the building cooling system. The electrical motor makes noise. The heat rejected to the outside pollutes the environment as well. Renewable energy, such as solar and geothermal energy, may provide solutions to our modern society problems. The geothermal energy may be used to provide cooling to building without use of electrical compressor. In fact underground soil temperature is much closed to supply air temperature for the building cooling. For example, the average soil temperature is about 12 oC (53 oF) while the cooling design outside air temperature is about 33 oC (92 oF) in Omaha, Nebraska [2, 3]. To use underground soil as the cooling source, a cooling tube can be buried underground as a soil-air heat exchanger. The air is cooled down when it passes through the tube. A theoretical model of the cooling tube thermal performance was developed and tested using the small scale cooling tube in the University of Nebraska in 1983 [4, 5]. In 1990, a 57 m (188 ft) long full scale cooling tube with a diameter of 0.457m (18 inch) was installed and the thermal performance was evaluated in the Passive Solar Energy Research Test Facility of the University of Nebraska. An axial fan was installed at outlet of the tube to draft warm outside air through the cooling tube. The measurement shows that the cooling capacity of the cooling tube can reach to 5 kW (18,000 Btu/h) with an airflow of 0.76 m3/s (1,600 CFM). On the other hand, solar energy may be used to replace the electrical fan power. The total solar irradiation normal to the sun’s rays is up to 30MJ/day.m2 (2,600Btu/day.ft2) during summer [6]. Solar cookers have been developed to cook food and simple reflector cookers can offer the equivalent of a 500W (1700Btu/h) hot plate in bright sun [7]. Solar energy is also used for space heating and cooling, domestic water heating, power generation, distillation, and process heating through solar collector [6]. A 50 kW demonstration solar chimney plant with a 195-meter (656-foot) high chimney and a 240-meter (800-foot) diameter solar collector has been built in Spain. The solar collector warms up the ambient air and the warm air generates draft by the chimney, finally the air drives the turbine to produce electricity. After the demonstration, one 200 MW full scale solar chimney plant has been scheduled to be built in Australia in 2006. Obviously, the solar chimney can generate enough draft for the air conditioning system. An electricity energy free air conditioning system, solar chimney driven earth tube cooling system, was created by integrating the cooling tube and the solar chimney. This paper focuses on the contribution of the solar chimney to the cooling tube system. The paper presents the theoretical airflow model and design principals of the solar chimney, detailed experiments facilities, and the experiments results.