Research On The Calculation Method Of Conduction Heat Gain Of Exterior Wall Based On Radiant Time Series Method In Radiant Cooled Room

Because of good thermal comfort and great energy saving potential,radiant cooling system has been widely concerned by scholars in related fields,and has a broad application prospect.However,there is a lack of a simplified cooling load calculation method for radiant cooling system,which impedes its further spread and application.One of the key factors to improve the accuracy of cooling load calculation is to accurately calculate the heat transfer through the exterior envelope.Based on Radiant Time Series Method（RTSM）,a simplified cooling load calculation method proposed by ASHRAE,this paper focuses on the calculation of conduction heat transfer rate through the exterior wall in radiant cooled room,and mainly carries out the following research work:Firstly,the simplified process of RTSM relative to the heat balance method（HBM）was analyzed theoretically combined with the external wall heat transfer node network diagram,and explored the causes of calculation errors of conduction heat gain through exterior walls by RTSM.It is concluded that RTSM uses air temperature as the temperature node of radiation heat transfer,when there is disturbance radiation heat and long wave radiation heat transfer with the interior surfaces of other envelopes on the interior surface of the exterior wall,errors may be caused.Secondly,sensitivity analysis was carried out for the influence of six factors on the error of RTSM calculating conduction heat gain through exterior wall in radiant cooled room.A total of 2772 models were simulated by Energy Plus,and the error of RTSM fluctuation range under the influence of each factor was given quantitatively.Based on this,the influence degree of each factor was sorted.The results from large to small is the ratio of window to wall are the type of the ratio of windows to walls,the type of windows,the type of internal disturbance,the schedule of internal disturbances,the shortwave radiation absorption rate of interior surface,the position of radiant cooling surface.And the relative errors of RTSM fluctuates by 87.51%,60.09%,52.06%,40.16%,10.28%and 9.77%,respectively.Thirdly,the"hourly correction of heat conduction"Δq_cond was introduced to improve the RTSM calculation.The proportional relationship betweenΔq_cond and‘compound heat transfer’q is determined by theoretical derivation.It is found that the ratio coefficient is only related to the composite heat transfer coefficient H_out and the convective heat transfer coefficient h_c on the interior surfaces of the exterior walls.And then on the basis of 2772 models,the regression empirical formula between the compound heat transfer q and the disturbance short wave and long wave radiation heat absorbed on the interior surfaces of the exterior walls q_radis obtained by means of the Marquardt algorithm and the general global optimization algorithm with the help of 1st Opt software.The improved formula was applied to the whole model.By comparing the hourly relative error of RTSM before and after the improvement is found that the upper and lower limits of RTSM relative error are improved from 391.50%,-63.94%to 235.07%,-53.05%respectively.Finally,based on all the models,the analysis shows that the relationship among interior surface temperature of wall,mean radiant temperature and indoor air temperature determines the proportion value of the radiation and convection part of the heat conduction.The influence of various sensitive factors on the radiation proportion of heat conduction was explored,and the range of radiation and convection proportion of heat conduction gain through external walls under different internal disturbance radiation proportion in the radiant cooled room was obtained.The results show that when the radiation proportions of internal disturbances are0～0.4,the air temperature is higher than the interior surface temperature of the wall,and the direction of convection heat transfer is negative.At this time the radiation proportion of conduction heat gain is basically more than 1.when the radiation proportions of internal disturbances are 0.5～1,the radiation proportion gradually decreases and changes in a certain range,and the corresponding basis for determination of value is given as a reference.