| Radiation air conditioning system originated in Europe,radiation cooling system is a kind of air conditioning systems that has one or more cold surfaces by putting cold water pipe network in the building structure.The heat transfer of radiation ceiling cooling system is radiation mainly,coupling with convective heat transfer.Radiation cooling system has been gaining much popularity due to its high thermal comfort and energy saving properties.But because of the low temperature of the radiation surface,it's easier to occur condensation on the surface when air moisture content is high,which may not only prevent the normal running of the air conditioner,but also cause some hygiene issues.Therefore,condensation become one major problem that limits the widely use of radiation cooling system.Condensation is caused when the radiation surface temperature is lower than dew point temperature of attach air,then research on the dynamic variation characteristics of radiant panel surface temperature and research on the dynamic variation characteristics of dew point temperature of attach layer are two necessary stage to study condensation prevention of radiation cooling system.This paper mainly studied the dynamic variation characteristics of dew point temperature of attach layer based on the result of the dynamic variation characteristics of radiant panel surface temperature which has been finished before.The impact factors of dew point temperature of attach layer are studied and the dynamic variation characteristics when occupation indoor increased is obtained.The impact of attach layer temperature when indoor heat source increased is studied experimentally first,the result shows that the impact of heat source on dew point temperature is not significant and can be ignored.Then the variation characteristics of dew point temperature of attach layer when occupation indoor increased.And based on the experiment,physical model was set and some further study has been done using FLUENT,and the relationship formula between impact factors and dew point temperature was obtained.Based on this,the optimum temperature difference prediction model was obtained.The conclusions of this study are as follows:(1)The temperature impact factors have little effect on the dew point temperature of attach layer and can be ignored in the formula,such as radiant panel surface temperature,inside envelope surface temperature and indoor heat source etc..The humidity impact factors has obvious effect on dew point temperature of attach layer,such as wet source strength and distance between wet source and the attached layer;(2)When indoor occupation increased,dew point temperature of attach layer increases first as negative exponential form,then gets steady.With the difference of increased number,the dew point temperature increasing rate and final steady temperature are different.(3)The dew point temperature increasing rate is less than radiant surface temperature increasing rate when water temperature is increased,only if indoor wet source strength is strong enough that panel surface temperature and dew point temperature increasing rates come close.And the optimum temperature difference prediction model under these conditions are obtained.(4)The key factor to find the optimum temperature difference is the increasing slope of panel surface temperature and dew point temperature.Decreasing water volume has little effect on preventing condensation.This paper studied the dynamic variation characteristics of dew point temperature of attach layer coupling the dynamic variation characteristics of radiant panel surface temperature,proposed the optimum temperature difference and adjusting time under different conditions.The results of this study provide theoretical support for the popularization and application of radiation cooling air-conditioning system.The research method also provides reference for anti-condensation of radiation cooling air-conditioning system. |
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