Study On The Suitable Surface Temperature Of Floor Radiant Heating Based On Comfort

With the frequent occurrence of extreme weather in the southern part of China and the significant improvement in the quality of life of the residents,people in the hot summer and cold winter climate areas are increasingly calling for heating in winter.In order to improve the cold and humid indoor environment in this area in winter,the research team has conducted a lot of research on the performance improvement of the radiant heating terminal in the early stage.By comparing the comfort performance of three different radiant wall surfaces:roof,side wall and floor.When the indoor temperature is low,the comfort of radiant floor heating is the best.The formulation of domestic standards for floor radiant heating mainly refers to the parameter values in European,American and international standards.Lacking of a large amount of basic data that can be referenced to meet the living habits and thermal comfort needs of the Chinese people.Therefore,in this article,a floor radiation heating experiment platform was built in a residential building in Chongqing,recruited local residents who lived in Chongqing for many years as subjects,and then investigated the thermal environment,air quality status and thermal comfort of the floor radiant heating system.Firstly,introduced the experimental platform and experimental design method of the experiment on the comfort of floor heating.And summarized the wall structure materials and thermal performance of the residential building where the experimental room is located,the working principle of the floor heating system,and the measuring instruments and methods of various parameters in the experimental environment.Clarified the basic principles of human experimental research,recruiting a total of 45 subjects,aged from 16to 47 years old.The thermal comfort questionnaire included the content of thermal sensation,thermal comfort,freshness of the air,thermal expectations and behavioral adjustment expectations,and discomfort symptoms.Designed six different floor surface temperature(t_f):25℃,27℃,29℃,31℃,33℃and 35℃.The duration of the experiment is 2 hours to compare the different thermal comfort requirements of instantaneous and long-term exposure.Objective parameter measurement included thermal environment parameters,air quality parameters,and physiological parameters.The data analysis mainly uses the Kolmogorov-Smirnov(KS)test,Spearman rank correlation test,repeated measures analysis of variance,single-factor analysis of variance and univariate regression analysis method to connect the objective parameters with the subjective evaluation results,to comprehensively discuss the comfort conditions at different floor surface temperatures.Secondly,the objective thermal environment measurement results and subjective questionnaire evaluation results were discussed and analyzed separately.From the analysis of the thermal environment,it was found that the floor heating could create a thermal stratification phenomenon of head warming and foot cooling at vertical height.The higher the horizontal surface temperature in the horizontal direction,the greater the temperature decreasing gradient,from-0.539℃/m(t_f=25℃)to-0.692℃/m(t_f=31℃)increased,and the air temperature was lower the closer to the outer wall area.In general,the temperature uniformity of the whole room was the best when t_f=31℃.In addition to the floor surface,the surface temperature of the remaining non-heated walls will also increased with the increased of the floor temperature.The heating effect of the surface of the envelope structure with t_f between 27℃and 31℃was most obvious.Among them,the temperature increase rate of the inner surface of the outer wall was the fastest,from 0.528℃/1℃to 0.592℃/1℃.Among the physiological parameters,the upper body skin temperature was less affected by the floor temperature,the lower body skin temperature was more affected by the floor temperature,and the longer the residence time,the stronger the correlation.In the subjective evaluation results,the thermal sensation of the foot changes significantly with the floor temperature,and the overall thermal sensation was basically in the range of neutral to slightly warm.The local thermal dissatisfaction rate of the foot was the highest,exceeding 25%at t_f=33℃and 35℃,and the rest of the foot was no more than 15%.Perceived air quality did not change significantly with floor temperature,while air freshness was affected by both floor temperature and residence time.Air freshness at t_f=25℃was better than that at t_f=35℃.When the floor is too hot(t_f=33℃and 35℃),the longer the residence time was,the more depressing the air perception would be.When the thermal sensation was too hot,people expected to lower the floor temperature and air temperature,and increase the indoor wind speed to improve thermal comfort.And people’s acceptability of partial hot floor temperature was higher than that of partial hot air temperature.Finally,the correlation between subjective evaluation and objective physical parameters was analyzed,the average skin temperature range that meet the thermal sensation evaluation criteria was 30.5℃～33.9℃,and the acceptable instep skin temperature range was 23.9℃～28.9℃.In the regression curve of the percentage of thermal dissatisfaction of the feet,the freshness of the air and the temperature of the floor surface,it is obtained by superposing the temperature interval:when radiant floor heating is used,the optimal floor surface temperature range for short and frequent stays of barefoot and tile flooring materials is 25℃～29.5℃and 25℃～30.6℃,respectively.The upper limit of frequent stays is 30.6℃,which is higher than the 28/29℃given by domestic standards,which is closer to 31℃in Japanese literature.