| Radiation air conditioning system is a kind of air conditioning system which provides indoor cooling by radiation heat transfer combined with convective heat transfer.It has excellent performance in energy saving and thermal comfort.The main disadvantage of radiant air conditioning is the risk of condensation on the surface of the radiant panel.Most of the existing anti-condensation measures for radiant air conditioners are to control the temperature of the control radiant panel is always 1-3 ° C higher than the indoor real-time dew point temperature.However,in engineering practice,condensation does not occur immediately after the temperature of radiation plate is lower than the dew point temperature,but requires a certain degree of supercooling and a certain delay time.Considering the dew delay time in the dew prevention measures of radiation air conditioning can delay the time of increasing the temperature of radiation plate and improve the cooling capacity of radiation air conditioning.However,there are few studies on the sub-cooled degree and delay time of condensation in radiation air conditioning.In this paper,the effects of indoor hot and humid state and fresh air state on the sub-cooled and delay time of condensation in radiation air conditioning are studied by combining experimental research with numerical simulation.In this paper,the effect of indoor thermal and humid environment on the sub-cooled and delay time of dew on the surface of radiation plate was studied experimentally.The experimental results show that:(1)After the condensation occurs,the condensed water on the surface of the radiant panel is distributed in a ring shape directly above the indoor wet source,and the condensation on the center and the periphery of the wet source is less;(2)The process of condensation on the surface of radiation plate is that fog is generated first on the surface of radiation plate,and granular dew droplets are produced after 30 minutes or so,and then dripping begins after about 4 hours;(3)With the increase of the speed of humidification,the degree of supercooling increases gradually,and the time of condensation delay decreases gradually.When the speed of humidification doubles,the degree of condensation supercooling increases by about 0.084 ° C,and the delay time decreases by about 2.8 min.(4)With the decrease of the surface temperature of the radiation panel,the condensation supercooling degree increases and the delay time decreases.When the surface temperature of the radiation panel rises by 1 °C,the condensation supercooling degree decreases by about 0.53 °C,and the delay time increase by about 4 minutes;(5)With the increase of indoor temperature,the condensation supercooling and delay time of radiation plate surface decrease gradually.For every 1 °C increase in indoor temperature,the condensation reduction is reduced by about 0.078 °C,and the delay time is reduced by about 0.8 min.(6)With the increase of indoor humidity,the change of condensation supercooling degree on the surface of radiation panel is small and the delay time decreases gradually.The condensation supercooling degree decreases by about 0.112 ° C and the delay time decreases by about 1.2 min for every 5% increase of indoor relative humidity.The above experimental results show that when the indoor temperature and humidity are constant,the higher the supercooling degree,the lower the delay time;the dew delay time of radiation panel surface in radiation air conditioning room decreases with the increase of humidification speed,the decrease of radiation panel temperature,the increase of indoor temperature and the increase of indoor humidity.The change of humidification speed and radiation plate temperature will change the supercooling degree and affect the delay time;indoor temperature and humidity will change the energy required for condensation,thus affecting the condensation delay time.On the basis of the experimental results,the same small radiant air-conditioned room model as the experiment was established,and the accuracy of the model was verified and improved.On this basis,in order to expand the research,the physical model and mathematical model of the actual application space are established.When the air supply mode includes no fresh air,radiation flow and displacement ventilation,and the air speed includes 0.5m/s,1m/s,1.5m/s and 2m/s,the effects of three factors of fresh air supply mode,air speed and relative humidity(45%-65%)on condensation supercooling and delay time are studied.The simulation results show that:(1)Compared with the non-ventilated working conditions,the way of attaching the jet and replacing the ventilation reduces the degree of sub-cooled of the condensation and increases the delay of dew condensation;(2)In the room with displacement ventilation,when the wind speed increases by 0.5 m/s,the sub-cooled degree decreases by 0.72°C,and the delay time is increased by about 1.056 min.The attached jet can also reduce the sub-cooled but can not increase the delay time of condensation,however,it can reduce the area of condensation on the surface of the radiant panel.(3)Both the attached jet and the replacement ventilation can reduce the average moisture content of the attached layer air,and the lower the moisture content of the air in the attached layer when the wind speed is higher.Both the attached jet and the displacement ventilation can reduce the moisture content of the attached layer air and the effect of attaching the jet is more remarkable.At the same wind speed,the humidity content of the air attached to the jet layer is 5-7% less than that in displacement ventilation;(4)With the increase of fresh air humidity,the condensation supercooling will increase and the delay time will decrease.For every 5% reduction of fresh air humidity,the condensation delay time will increase by 0.14 minutes on average.The above simulation study shows that the effect of attaching jet to prevent condensation is better,but the displacement ventilation has a better effect on reducing the condensation rate in the condition that condensation has occurred.Higher wind speed and lower supply air humidity can increase the condensation delay time in a ventilated room.In this paper,the effects of room temperature,humidity and fresh air condition on condensation supercooling and delay time of radiation air conditioning are studied by combining experiment and simulation.The variation rule of condensation delay time with various influencing factors is obtained,which provides a technical basis for further improving the cooling capacity of radiation air conditioning system and the accuracy of dew prevention technology. |
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