Research On The Performance Of Gravity Self-circulating Radiator And Air Source Heat Pump Combined Heating System

Air source heat pump heating has the advantages of simple system form,high heating efficiency and no direct emission of pollutants.Air source heat pump heating as a distributed heating method has a broad application prospect in China’s Yangtze River valley and rural areas without central heating conditions.The traditional air source heat pump heating takes indoor air as the heat carrying medium and realizes the purpose of heating by sending hot air to the room.Although this hot air heating method has the advantage of fast heating output,it also has some shortcomings.First of all,under the action of buoyancy,hot air tends to gather at the top of the heating room,resulting in a low temperature in the activity area.The resulting temperature gradient is generally above 1 ^oC·m^-1.In some measurements,the temperature difference in the direction of room height can reach 6 ^oC～8 ^oC.In order to raise the temperature of the active area,the heat supply of the heat pump can be increased to raise the average indoor temperature,but this will increase the building heat consumption and the energy consumption of the heat pump operation.At the same time,the thermal radiation effect induced by hot air heating is almost zero,so in practice,it is easy to appear the phenomenon of low average indoor radiation temperature and serious"cold radiation".In order to improve the comfort and energy saving of heat pump heating,this paper proposes a new type of gravity self-circulating radiator as the indoor heating end of air source heat pump.In view of the operation characteristics of the new heat pump system,the thermal response of the gravity self-circulating radiator during the system startup and the performance of the system during startup and stable operation are analyzed.It is found that the heat response of the new radiator is rapid in the system start-up stage,and the average temperature rise rate can reach 21.3 ^oC·h^-1.At the same time,the new heat pump heating system can create a more stable and uniform indoor thermal environment,better overcome the shortcomings of hot air heating caused by large indoor vertical temperature difference.In terms of energy efficiency,the average COP of the system was 2.51 during the test period.Under low temperature conditions,the compressor exhaust temperature of the new heat pump heating system is always controlled below 80 ^oC,and the COP of the system is always maintained above 2,which has good low temperature operation stability.At the same time,based on the actual measured data of office buildings,TRNSYS simulation software was used to build four kinds of conventional heat pump heating systems with different heating ends（gravity self-circulating radiator,conventional radiator,radiant floor and hot air coil）,and comparative analysis was conducted.The results show that gravity self-circulating radiator heating can meet the requirements of indoor thermal comfort on the coldest day,and the COP of the heat pump heating system is always above 2.In the whole heating season,gravity self-circulating radiator heating can improve system performance by13.6%-36%and save total heating costs by 18%-50%compared to the other three conventional heat pump heating methods.