| Air source heat pump(ASHP)is a clean and sustainable heating technology.The air conditioner and the water-heated device,such as the radiator,floor and ceil,are coupled with the ASHP heating system for space heating.However,the draft sensation and noise caused by the fan of the air conditioner will reduce indoor comfort.The secondary heat exchange in the ASHP heating system with water-heated devices enhances the system condensation temperature,which will reduce the system efficiency.Besides,the equipment,such as water pumps and tanks,enhances the complexity of the system,which also leads to the proliferation of the system operation and maintenance cost.Therefore,a novel direct-condensation radiant heating panel with higher thermal comfort is proposed.A combination of the theoretical model and experimental research is used to study the thermal performances and to optimize the geometry of the novel device.The main completed work of the study is summarized as follows:(i)A novel direct-condensation radiant heating panel is proposed for the ASHP heating system.The device relies on natural convection and radiation to exchange heat with the indoor chamber.The composite straight-and-circular fins are used to enhance the thermal performance of the novel device.In this paper,the analytical solutions of temperature distribution,heat dissipation and efficiency of the composite straight-and-circular fins are derived.To maximize the heat dissipation per unit fin length,the ratio of straight fin length to composite fin length is optimized with analytical solutions.(ii)The mathematical model considering the condensation and pressure drop of the refrigerant flow is established for the direct-condensation radiant heating panel.The test method for the thermal performance of the direct-condensation radiant heating panel is proposed,and the experimental platform was established.The mathematical model is validated to be reliable and effective with experimental data.The average deviations between the simulated heat dissipation,total pressure drop and surface temperature and the experimental values are 2.02%,7.37%and 2.1%.Under the typical heating condition with condensation temperature of 44.4℃and indoor temperature of18℃,the heat dissipation per unit apparent area of the novel device is as high as 1290W/m~2.Meanwhile,the lowest temperature of the direct-condensation radiant heating panel is higher than the indoor air temperature during the defrosting condition for the heat storage material of the device.The indoor comfort is guaranteed with the novel device.(iii)Based on the mathematical model,the variation characteristics of temperatures and pressure drop of the direct-condensation radiant heating panel are analyzed.The effects of the refrigerant flow rate,inlet condensation temperature,superheat of inlet refrigerant,indoor air temperature and enclosure temperatures on thermal performances of the novel device are performed.Meanwhile,the standard characteristic equation of heat dissipation of the direct-condensation radiant heating panel is proposed to promote the development and application of the novel device.(iv)Based on the mathematical model and the particle swarm optimization-gradient descent algorithm,the structure optimization of the direct-condensation radiant heating panel is investigated.Under three heat dissipation requirements,the diameter of the copper tube,the length of the copper tube,the vertical channel spacing and the length of the composite fin are optimized to maximize the heating capacity under per unit cost. |
