Study Of An Integrated Radiant Heating/Cooling Air-Conditioning System With Fresh Air Supply For Household Utilization

With the increasing demand for indoor thermal comfort in recent years,radiant heating&cooling systems have been popular in China.However,for the residential buildings in hot-summer and cold-winter regions,there lack effective methods for indoor humidity control,consequently restricting the utilization of radiant heating/cooling systems.In this paper,an integrated air-conditioning system was introduced,in which the heating or cooling source is supplied for radiant heating/cooling,meanwhile the fresh air is treated and supplied to control the indoor humidity.Under winter conditions,the heating water is supplied for radiant panels,and the fresh air is pre-heated and humidified for the humidification of indoor space.Under summer conditions,the chilling water is supplied for radiant panels,and the fresh air is pre-cooled and dehumidified for the dehumidification of indoor space.In detail,the content and the results of this study were presented as follows.Firstly,the system was schematically introduced.The desiccant solution in the system can be sufficiently regenerated for fresh air dehumidification.The mass transfer process during the two-stage dehumidification was presented,and the hot-cold offset in liquid desiccant loop was also demonstrated.Secondly,the mathematical model of the system was introduced and then validated with experimental results.Both dehumidification capacity and energy-saving performance of the system were evaluated under summer conditions in Nanjing.With the outdoor temperature of 35℃ and relative humidity of 65%,the fresh air can be sufficiently dehumidified to the humidity ratio of 9.67 g/kg for indoor humidity control.The chilling water flow rate in the pre-cooling coil(mw,coil)and the solution flow rate from regenerator to dehumidifier(ms,ss)can be regulated to adjust the humidity ratio of supply air.A COP improvement of 22.6-25.7%was revealed compared to the conventional household air-conditioners,and suffered insignificant change under different load ratios of indoor sensible heat to indoor latent heat.The loss of cooling capacity resulting from hot-cold offset kept a negligible value of 0.6%of the total cooling capacity.Thirdly,the operating modes were proposed for the annual working conditions in hot-summer and cold-winter regions,including cooling&dehumidification mode,cooling mode,dehumidification mode,heating mode and heating&humidification mode.The desiccant solution loop was developed into intermittent solution delivery to alleviate both hot-cold offset and concentrated-diluted offset.During the 24-hour quasi-dynamic simulation in cooling&dehumidification mode,the fresh air can be dehumidified to maintain the indoor relative humidity of around 60%,meanwhile the COP revealed an improvement of 25.5%-29.8%compared to conventional air-conditioners.In dehumidification mode,the indoor relative humidity can also be controlled below 65%and 70%under normal conditions and extremely humid conditions,respectively.The dehumidification capacity can be further strengthened with higher chilling water flow rate in pre-cooling coil(mw,coil)or lower chilling water temperature(tw).The temperature of supply air was lower than indoor temperature,while had no significant impact on indoor thermal environment.Finally,a novel liquid desiccant dehumidifier with no film flow was introduced for household air-conditioning.A mathematical model was established to numerically evaluate the dehumidification performance.The influence of the stage number,the immersion depth of the disks,the rotate speed of the disks and the air and solution parameters on dehumidification performance have been investigated.The increase in stage number can decrease the air outlet humidity ratio and increase the dehumidification performance.The outdoor fresh air can be dehumidified to the humidity ratio of below 10 g/kg with 4 stages.The dehumidification efficiency increased with the increase in stage amount,while changed insignificantly with varied air inlet temperature,solution inlet temperature and solution inlet concentration.The rotate speed of the disks can significantly influence the dehumidification performance and can be adjusted to control the indoor humidity in practical air-conditioning.