Modeling and Experimental Verification of a Straight-Through Evacuated Tube Installed on a Façade for Solar Space Heating

Abstract

Using solar energy for space heating is a promising technology to offset buildings’ energy consumption and reduce environmental pollution. Solar air heating system is free of freezing and inexpensive owing to its inherent simplicity in many circumstances. In this paper, the performance of a straight-through evacuated tube (ST tube) which opens on both ends for space heating, is studied. A thermal model for a single ST tube installed on a building façade for solar space heating using hot air was developed and an experimental measurement was conducted. The results predicted by the thermal model and experimental measurement agreed well, which confirms the validity of the thermal model. The performance and some aspects for practical application of the ST tubes for solar space heating are studied and discussed. The daily average efficiency of the ST tube was approximately 55% under the experimental conditions. The radiative thermal resistance from the absorber tube to the cover tube was almost equal to the total resistance, and the emissivity of coating on the outside surface of absorber tube had great effect on total heat loss. The cost and useful heat gains for a single room in a building in Beijing was studied. The payback period of this solar space heating system is approximately 8 years. The performance of solar collectors, including multiple ST tubes, will be studied in the next research.