A Simplified Cooling Load Calculation Method In The Radiant Cooling Room

With the continuous progress of society,people have increasingly higher demands on the indoor environment.The radiation cooling system is favored by people because of its comfort.However,at present there is no method that can accurately calculate the load of a radiant conditioning room.The radiant time series(RTS)method is a simplified load calculation method based on the heat balance(HB)method which is introduced by ASHRAE Handbook.It divides internal heat gain into convection heat gain and radiant heat gain.The convection heat gain is directly converted into instantaneous cooling load,and the radiant heat gain is converted into radiant cooling load by using radiant time factors.It is a method that is rigorous yet does not require the iterative calculations,it replaces other load calculation methods effectively.However,the radiant time series method is aimed at the air conditioning system when calculating the room load,this article attempts to improve and apply the radiant time series method to calculate the room load of the radiant conditioning system.There are some difficulties and key points in applying the radiant time series method in the radiant conditioning system: Compared with the air conditioning system,due to the existence of the radiant plate in the radiant conditioning system,the radiative/convective splits for internal heat gains will be changed.This paper used EnergyPlus which is an energy consumption simulation software to simulate the indoor thermal environment and calculated the radiative/convective splits for internal heat gains through the heat balance equations.On the other hand,because of radiant heat exchange between the radiant plate and the walls,the characteristics of heat storage in the walls will change,so the radiant time factors of the two conditioning systems are different.First,the relationship between the radiant time factors and the room transfer function coefficients could be established using the transfer function.Then the radiant heat gains and the radiant cooling loads of the room could be calculated by the data of the software simulation,so it was possible to calculate the room transfer function coefficients through the least squares method,and the radiant time factors could be calculated.In this paper,the radiant time series method had been applied in the radiant conditioning comparing with the air system.The main conclusions are as follows:(1)Different kinds of internal heat gains in different conditioning systems have different radiative/convective splits.For the heat conduction of the walls,instantaneous cooling load accounts for 64.1% of the total heat gain,radiation heat accounts for 35.9% of the total heat gain in the air conditioning system;and in the radiant conditioning system,instantaneous cooling load accounts for up to 80.2% of the total heat gain,radiant heat gain only accounts for 18.2% of the total heat gain.For the solar radiant heat gain that enters the room through the window,the instantaneous cooling load accounts for 48.3% of the total heat gain,and the radiant heat gain accounts for 51.7% in the air conditioning system,In the radiant conditioning system,the instantaneous cooling load accounts for 67.2% of the total heat gain,the radiant heat gain accounts for 32.8% of the total heat gain.(2)For different kinds of heat gains,the radiant time factors calculated by the two conditioning systems are different.In comparison,the first few items of the radiant time factors are quite different,especially the first item,and the first radiant time factor has a great influence on the calculation of the hourly radiant cooling load.(3)The radiation time series method was used to calculate the cooling load of the two room models in the two conditioning systems,and compared with the cooling load simulated by Energyplus.The first room in the air conditioning system,the relative error of calculated cooling load is 1.6% than the simulated cooling load,and the relative error in the second room model is 2.8%;while in the radiant conditioning system,the error of calculated cooling load in the first room model relative to the simulated cooling load is 6.5%,the relative error of the second room model is as high as 8.3%.