| Radiant floor systems have been widely applied in buildings to meet heating/cooling demand due to their advantages of high comfort and energy saving.For the purpose of peak shifting,these systems were usually coupled with phase change materials(PCM)for storing energy during the daytime and release energy at nighttime in previous studies.However,these studies mainly focused on the system for the heating/cooling demand during a single season(i.e.winter or summer).Though some researchers proposed a double-layer radiant floor system integrated with PCM which can work in both summer and winter,their performance is still limited due to the significant thermal interference between these two PCM layers,long response time and a lack of fresh air.To address this issue,a new PCM radiant floor system coupled with fresh air handling system was developed in this study.This system would avoid the direct contact between the PCM with high and low melting temperature due to its single-layer structure with horizontally arranged PCM,thereby reducing the thermal interference between these two PCM and energy waste during the operation.Meanwhile,with such a structure,thermal energy would be allowed to directly transfer to the floor through the leveling layer.This would reduce the heat transfer resistance between the PCM and floor,and consequently decrease the time required for the system reaching a comfortable temperature.Moreover,the fresh air handling system could meet the requirements of indoor air quality in winter and summer,and also form an air layer with low dew points on the floor surface to avoid condensation.In order to study the thermal performance of this system,a laboratory experimental platform(1.3 m *1.1 m * 2 m)was built in Changsha(hot summer and cold winter regions)and used to examine the system performance in summer and winter.On the basis of that,a numerical model was developed and calibrated via COMSOL,and a parametric analysis was conducted to investigate the system performance of the system agains different factors.The main results and conclusions of this study are as follows:(1)Compared with the radiant floor system with double-layer PCM vertically arranged,the system proposed in this paper effectively reduced the thermal interference between the PCM with high and low melting temperature during the operation.Specifically,as the heat source temperature was set at 45℃,the temperature of the PCM with low melting temperature was always below 19℃ during the operation in the winter,which was lower than its melting temperature.Moreover,as the cold source temperature was set at 14℃,the temperature of the PCM with high melting temperature was less than 24.2℃ during the operation in the summer.(2)Compared with the radiant floor system with double-layer PCM vertically arranged,this system reached the user’s comfortable temperature faster.As the heat source temperature was set at 45℃,50℃ and 55℃,the system’s thermal response time were 1.25 h,1.5 h and 1.75 h,respectively.As the cold source temperature was set at10℃ and 12℃,the system’s thermal response time were 3h and 3.5 h,respectively.(3)The fresh air handling system not only improves the indoor air quality,but also can effectively prevents condensation at the floor surface under cooling conditions by adjusting the supply temperature and humidity of the fresh air.(4)The selection of cold and heat source temperature significantly affects the heat storing and releasing characteristics of the PCM and indoor temperature.For heating conditions in winter,its temperature should not be too high for avoiding phase change of the PCM with low melting temperature.Low-grade heat sources with temperature ranging from 45℃ to 45℃ are recommended in actual applications.For cooling conditions in summer,its temperature should not be too low for reducing the risk of condensation on the floor surface and improving energy efficiency.Cold sources with temperature ranging from 12℃ to 14℃ are recommended in practical applications.(5)Increasing the thermal conductivity of PCM can help to reduce the thermal response time of the system and increase the charging rate of PCM and the fresh air temperature.However,overly high thermal conductivity of the PCM can lead to very high/low floor surface temperature at the end of charge processes in winter/summer conditions,as well as very low/high floor surface temperature at the end of discharge process,thereby reducing the comfort of the residents.In addition,it would also strengthen the thermal interference between the PCM with low and high melting temperature.For the system proposed in this study,the thermal conductivity of the PCM with high melting temperature should not exceed 0.8 W/(m·K),and the thermal conductivity of the PCM with low melting temperature should not exceed 0.2 W/(m·K).(6)Increasing the phase change temperature of the PCM with high melting temperature would lead to the increase of the average and maximum temperature at the floor surface in winter conditions,while they would decrease by decreasing the phase change temperature of the PCM with low melting temperature in summer conditions,thereby improving indoor comfort.However,overly high phase change temperature of the PCM would lead to the melting of the PCM with low melting temperature and overly high floor surface temperature in winter conditions.While overly low phase change temperature of the PCM would lead to condensation at the floor surface in summer conditions.Therefore,the phase change temperature of these two PCM should be appropriately selected.In this article,the optimal temperature of these two PCM are38℃ and 17℃,respectively.(7)Although the decrease in the width of phase change modules increases the thermal interference between the PCM with high and low melting temperature,it also increases/decreases the maximum and average temperature at the floor surface in winter/summer conditions,thereby improving the indoor comfort.Therefore,with the consideration of meeting the thermal interference between these two PCM,such a width can be appropriately reduced in practical designs.Based on this study,further research should focus on optimizing the system’s operating modes,control strategies,economic efficiency and parameters.Moreover,indoor thermal comfort of a room should be evaluated when the system is applied for heating and cooling. |
PDF Full Text Request