Method For Improving Radiant Cooling Capacity By Double-skin Infrared Membranes

Compared with traditional convective cooling,radiant cooling has attracted extensive attention because of its potential to save energy,improve thermal comfort and air quality.However,there are two problems in radiant cooling(i.e.condensation risk and insufficient cooling capacity),especially in humid and hot climate areas.In order to improve the cooling capacity of radiant cooling and avoid condensation,an condensation-free radiant cooling with double-skin infrared membranes(DIMs)is proposed in this paper.By adding DIMs on the cooling source to separate the air contact surface from the radiant cooling surface,the cooling capacity can be improved by reducing the radiant cooling temperature while keeping the air-contact surface higher than the dew point temperature.DIMs were made of cheap and commercial low-density polyethylene membranes,and infrared parameters of the material were measured.A reduced-scale radiant cooling experiment was built to measure the performance of condensation-free radiant cooling.By comparing with the full-scale building radiant cooling measurement in the literature,it is proved that the reduced-scale radiant cooling experiment is operable.The comprehensive heat transfer process of condensation-free radiant cooling with DIMs is analyzed theoretically,the influence mechanism of the separation of radiant cooling surface temperature and air contact surface temperature on the cooling performance is studied,and the comprehensive heat transfer model of condensation-free radiant cooling with DIMs is established.The predicted value of the model is compared with the experimental value,and the error is no more than ± 5%,which verifies the reliability of the calculation model.By further analyzing the comprehensive heat transfer model,the effects of cooling surface temperature and thermal radiation parameters of DIMs on the cooling performance of condensation-free radiant cooling are studied.The results show that with the decrease of cooling surface temperature,the temperature of air contact surface decreases and the cooling capacity increases.Therefore,under the limitation of dew point,there is a minimum cooling surface temperature,in which the maximum cooling capacity can be obtained.For example,the cooling capacity with DIMs at cooling source temperature of 7℃ was 104.0W/㎡,48%improved compared to conventional radiant cooling.On the premise of condensation-free,aiming at obtaining the maximum cooling capacity,the thermal radiation parameters of DIMs are optimized for the radiant cooling ceiling with different surface emissivity in practical application,and the performance of condensation-free radiant cooling with DIMs in different humidity environment is analyzed.The research results can provide theoretical and experimental data reference for condensation-free radiant cooling with DIMs.