Research On Cooling Performance And Thermal Comfort Of Decoupled Radiant Cooling System Using Low Temperature Source

Radiant cooling is a promising space cooling technology for the built environment,with high energy efficiency and thermal comfort.However,there are technical bottlenecks of condensation and insufficient cooling capacity in hot and humid areas,making large-scale commercial applications difficult.The use of double-skin infrared transparent membranes to separate the cooling surface from the air-contact surface is a good means,which can increase cooling capacity while preventing condensation.However,the experimental verification of full-scale prototype needs to be investigated.In addition,the use of low temperature source may lead to increase inhomogeneity in the indoor thermal environment.How to evaluate the influence mechanism of this unevenness on human thermal comfort has become a major scientific issue affecting the thermal comfort of new decoupled radiant cooling.Firstly,two full-scale chambers with same size(4.50m×3.88m×2.70m)were constructed,one is a new decoupled radiant cooling chamber and the other is a conventional co-planar radiant cooling chamber,to investigate the influence mechanism of temperature decoupling between the radiant cooling surface and the air-contact surface on the radiant cooling performance.By testing the temperature of each surface,condensation and cooling capacity in the chambers,the effect of the double-skin infrared transparent membranes on preventing condensation and enhancing cooling capacity were investigated.The results show that the cooling capacity of the decoupled radiant cooling panel at lower water supply temperature of8°C was 105.5W/m~2,which can achieve a performance improvement of 24.4%compared with the maximum cooling capacity of the conventional co-planar radiant cooling panel of84.9W/m~2.Secondly,the steady-state heat transfer model was established for decoupled radiant cooling using double-skin infrared transparent membranes based on Kirchhoff’s current law and Nusselt’s criterion by analysing the comprehensive indoor heat transfer process.At the same time,the model predictions were compared with experimental test data to verify the reliability of theoretical calculation model.The results show a good agreement between the data,with the error of air-contact surface temperature was less than±5%and the error of cooling capacity was within±10%.In addition,the model sensitivity analysis was carried out to explore the effect of interlayer air thickness and membrane infrared transmittance on the air-contact surface temperature and cooling capacity.Finally,32 subjects were recruited to carry out human thermal comfort experiments at different indoor operative temperatures(22.5°C,24°C,26°C and 28°C)under decoupling mode,in order to study the issue that the indoor radiation inhomogeneity was aggravated due to low temperature source,which affected human thermal comfort.The thermal comfort characteristics and related indexes were studied by recording thermal environment parameters,monitoring the changes of physiological indexes of subjects and subjective questionnaire surveys.The results show that the decoupled radiant cooling system using low temperature source can create a good thermal comfort environment.The measured thermal neutral operative temperature is 24.8°C,the thermal expected operative temperature is 24.2°C,and the acceptable operative temperature range is 22.1～26.7°C.Based on the linear fitting results,the PMV model predicts that the thermal neutral operative temperature is 24.4°C,which is0.5°C lower than the measured average thermal sensation voting AMV.The actual thermal sensation of the subjects is colder than predicted,and the indoor operative temperature can be appropriately increased by 0.5°C to improve satisfaction with the thermal environment.This study provides prototype experimental verification for the new technology of using double-skin infrared transparent membranes to improve the radiant cooling performance and provides experimental data reference for related theoretical and model research.Meanwhile,the influence mechanism of temperature decoupling between the radiant cooling surface and the air-contact surface on the radiant cooling performance was revealed.The establishment of steady-state heat transfer model can be used to regulate the design of decoupling components,and lay foundation for the practical application of new technology.In addition,the thermal environment and thermal comfort created by decoupled radiant cooling system using low temperature source are analyzed to provide a theoretical basis for the design of indoor thermal environment parameters in this field.