Study On Operation Characteristics And Control Scheme Of Radiant Air-conditioning System For Household Utilization

With the rise of people’s living standard and the increasing demand for indoor thermal comfort,radiant heating/cooling system has become an active research topic and been gradually applied in residential buildings.Compared with traditional air conditioning system,the radiant heating&cooling system possesses unique superiority in high comfort performance,energy conservation,high energy efficiency,low cost of initial installation,et al.In this paper,a radiant heating/cooling system for household utilization has been introduced for the residential buildings in hot-summer and cold-winter regions.In detail,the content and the results of this study were presented as follows.Firstly,according to the different positions of the air outlet and the radiant panel,six models of the proposed system are constructed by using Airpak software to ensure that the various needs of residential buildings are basically covered: bottom supply wall laying,bottom supply top laying,bottom supply combination laying,upper supply wall laying,upper supply top laying and upper supply combination laying.Secondly,in order to avoid or reduce the condensation on the radiant panel,a pre-dehumidification scheme is introduced: the system operation is divided into two phases,the start-up stage and the stable stage.In the start-up stage,dry fresh air is introduced into the room in advance to reduce the indoor moisture content to below the saturation moisture content corresponding to the surface temperature of the radiant panel,so as to achieve the purpose of preventing condensation.In this stage,the four influence factors on the moisture content,including the volume and the moisture content of supply air,the location of the air supply outlet and the radiant panel,and the pre-dehumidification time required by the six models are simulated.The results show that when the pre-dehumidification time was 1 h,the moisture content of the air attached to the radiation panels decreased from 11 g/kg to 10 g/kg with the air volume increasing from 75 m~3/h to 105 m~3/h and that can be significantly reduced from about 14 g/kg to about 11 g/kg when the moisture content of the supply air is reduced from 11 g/kg to 8 g/kg.The decreasing rate of air moisture content when the air supply outlet is at the bottom part is greater than that when the air supply outlet is at the upper part,and the maximum is about 3%.The decreasing rate of air moisture content is the slowest when the radiant panels are laid in combination,and the fastest when wall surface laying.When the moisture content of the supply air is from 10 g/kg to 8 g/kg,the time of pre-dehumidification process can be descreased from 55 min to 30 min.The six simulation results show that the pre-dehumidification time required by bottom supply wall laying is the shortest and is 7.5 min faster than that of upper supply combination laying which is the biggest.Thirdly,the room is supplied with chilled water to cool and dehumidify at the same time which is called the stable stage.In this stage,the indoor temperature field,humidity field and condensation were analyzed under six working conditions.The indoor thermal comfort was analyzed by PMV-PPD index.The results show that with the initial indoor temperature of32 ℃ and the relative humidity of 60 %,the indoor horizontal and vertical temperature difference is respectively less than 0.25 ℃ and 0.4 ℃.What’s more,the indoor horizontal and vertical relative humidity difference is respectively around 0.7 % and 0.5 %.In terms of thermal comfort,human body feels most and least comfortable seperately in the room of upper supply top laying and bottom supply combination laying attributing to the lowest and highest indoor PPD value.In addition,after pre-dehumidification process,the moisture content of the air attached to the radiant panels is about 10.5 g/kg,which is far lower than the corresponding saturated moisture content of 14.2 g/kg of the radiant surface when water supply temperature is 18 ℃.Finally,the operating modes were proposed for the annual working conditions in hot-summer and cold-winter regions,including cooling mode,dehumidification mode,cooling & dehumidification mode,heating mode and heating & humidification mode.In the cooling mode,dehumidification mode and cooling & dehumidification mode,the water and air supply only need to be last for 9～18 min,and the indoor temperature and humidity can be maintained within the set range for 12～30 min.Under the six working conditions in the cooling&dehumidification mode,the response time difference of reaching the set indoor air moisture content in the start-up stage is about 2.5 min,and the upper supply top laying is the fastest,which is 52.5 min.The response time difference of reaching the set indoor air temperature in the start-up stage is 15 min,the bottom supply combination laying is the fastest,which is 20 min,while the upper supply wall laying is the slowest.When the regulation enters the stable stage,the dynamic variation period of the temperature of the upper supply wall laying is the longest,and the bottom supply top laying is the shortest.The dynamic change period of moisture content is similar,and the closing time of air valve is longer than the opening time in terms of dehumidification function,which demonstrates that the regulation scheme is energy-saving.