Heat Transfer Characteristics Of Water-cooled PVT Envelope

The building integrated solar technology has good application prospects because of its high heat recovery, aesthetic advantages, rapid economic returns et al. In addition, the water-cooled BIPVT system has obvious advantages and applications with its higher overall thermal efficiency. From the existing research we can see that the one-dimensional heat transfer model can ensure the accuracy requirements with the assumption of uniform flow distribution tubes while a two-dimensional or three-dimensional heat transfer model still need to be built for the purpose of structural optimization. Therefore, the two-dimensional heat transfer model (quasi-three-dimensional heat transfer model) will be established on the basis of one-dimensional heat transfer model of water-cooled PVT envelope and heat transfer properties of the water-cooled type PVT envelope will be studied under the background of BIPVT. The study not only has important academic value for scientific and rational design of BIPVT system, but also has important social development significance for BIPVT technology promotion.Firstly, the structure optimization of water-cooled absorber PVT envelope is studied with the use numerical simulation methods. The impacts of header pipe cross-sectional area and the aspect ratio of the absorber on fluid flow distribution are analyzed. Results show that the model of Amanifold/Ariser=3should be chosen and1.23-1.51is the optimum range of absorber aspect ratio in order to obtain a more uniform flow distribution.Secondly, two-dimensional heat transfer model of water-cooled PVT envelope is established under the non-uniform flow distribution。Two-dimensional heat transfer equations are discreted by the control volume method, with algebraic equations solved by ADI-TDMA and the correctness of the developed calculation program is verified a numerical example.Finally, the heat transfer characteristics of water-cooled PVT envelope structure are studied. The effects of intensity of solar radiation, inlet temperature of cooling water, uneven distribution of fluid flow, mass flux of imports et al. on the heat transfer characteristics of water-cooled PVT envelope are respectively analyzed and the maximum inlet temperature of cooling water is determined. The results show that compared with the one-dimensional heat transfer model calculations, the two-dimensional heat transfer model has higher precision, relative deviation of wall heat transfer using one-dimensional and two-dimensional heat transfer model is the largest, the maximum value is about146%. Uneven distribution of fluid flowand mass flux of imports have greater impact on the wall heat transfer and heat loss compareed with cooling water heat and solar cell generating capacity. The maximum inlet temperature of the cooling water is45℃in summer while the maximum inlet temperature is35℃in winter in Beijing.