Study On The Performance Of Direct Expansion Air Source Heat Pump Coupled Capillary Floor Radiation Heating System

A direct expansion air source heat pump coupled with capillary floor radiant heating system was proposed.Different from the conventional air source heat pump heating system,the direct expansion air source heat pump uses liquid refrigerant as the heating medium,which can effectively reduce the heat loss in the intermediate heat exchange process.The numerical simulation and experimental test were adopted in the study.Firstly,the temperature distribution on the floor surface and the indoor air temperature distribution under different capillary tube layout,different coil spacing,and different heat medium temperature in the coil were simulated by FLUENT,and the optimal coil spacing meeting the uniform distribution of the floor surface temperature and the indoor air temperature was obtained.Then,an experimental prototype was built to study the temperature distribution on the floor surface and the heating performance of the heat pump system under different outdoor ambient temperatures in the artificial environment room.According to the FLUENT numerical simulation results,the capillary arrangement has little influence on the temperature distribution;that capillary arrangement has little influence on temperature distribution.Capillary spacing has a significant influence on the uniformity of temperature distribution.the maximum surface temperature of the floor is 32℃,which is far higher than the standard range of indoor heating,causing great discomfort to human body.With the increase of capillary spacing,the floor surface temperature and indoor temperature decrease,the maximum temperature difference increases,and the temperature unevenness is high;The condensation temperature also has a significant influence on the floor surface temperature and indoor vertical temperature.When the capillary spacing is 10 cm and the condensation temperature is40℃,the indoor temperature is maintained at 24.5℃ and the temperature difference is0.7℃.An experimental device was built to study the variation characteristics of capillary wall temperature distribution,1cm cement filling layer temperature distribution,floor surface temperature distribution and unit heating performance under different outdoor temperatures with capillary spacing of 10 cm in the artificial environment room.The experimental results show that after stable operation,the temperature difference between different filling layer thicknesses is within 2 ℃,and the temperature fluctuation at the same position is within 1 ℃;At different positions on the same capillary tube,the temperature difference from the inlet side to the outlet side of the refrigerant is between 1 ℃-2.2 ℃;The temperature difference at the same position of different capillaries is within 0.5 ℃.When the system operates stably under different operating conditions,at the end of the capillary tube and after laying a 2cm cement filling layer,the heating capacity of the heat pump unit reached 2.31 k W and 1.86 k W respectively,and the heating COP reached 5.21 and 4.61,the energy-saving performance of the system is significant.