Energy-exergy analysis of a direct-expansion solar-assisted heat pump floor heating system

The set-up of a direct-expansion solar-assisted heat pump (DX-ASHP) floor heating system is introduced. The DX-ASHP floor heating system uses a 1.86m² bare plate solar collector as the evaporator, while the refrigerant is chosen to be R134a. The system provides 40~50°C low temperature hot water for a resident in Shanghai during the heating season. The energy analysis and exergy analysis mathematical models of the DX-ASHP floor heating system are given simulating the climatic conditions of Shanghai. The rate of irreversibility in each component of the whole system is evaluated. Focused on the influence of the layout of solar collector on the performance of the whole system, it is found that the rate of irreversibility of the solar collector decrease significantly with the increase of the number of solar collectors in parallel because the pressure drop passing through the solar collector decrease significantly. When the number is 1, the relative irreversibility of the solar collector is about 20% or so; the rank of the irreversibility in the solar collector is 2, after the compressor, the number is 2 or 3, the rank of the solar collector is 3. Accordingly, the coefficient of performance (COP) and exergy efficiency ^ε of the whole system increase with the increase of the number of solar collectors in parallel. When the number of solar collectors is 1, the average COP and the exergy efficiency of the whole system are 2.78 and 26.48% respectively. When the number is 2, the average COP and the exergy efficiency of the whole system increase to 3.00 and 30.66% respectively, which are very close to those of the system where the number is 3.