Research On Human Thermal Comfort In Non-uniform Cold Radiant Environments From External Wall And Window In Winter

It is freezing outdoors in the north part of China and the duration of winter lasts for a long time.There are cold radiations from internal surfaces of external window and wall and people indoors feel thermally uncomfortable.Therefore,the purpose of this paper is to study human thermal comfort for whole body and local body parts in non-uniform asymmetric environments,thus providing reference for designing of indoor thermal environment.Firstly,a field survey was conducted during the coldest month in Harbin,which is the typical city of the severe cold region.Thermal environmental parameters,local and overall thermal responses of occupants were obtained.It is found that the temperatures of internal surfaces of exterior walls and windows were around 4°C and 10°C respectively lower than the indoor air temperature,causing cold radiations to indoor climates and local discomfort of subjects.The lower limbs of subjects were more sensitive to coldness than the rest parts of human body.The relationship between clothing insulation and indoor air temperature was established to study the adaptive behaviors of occupants in the severe cold region.The evaluation model for local thermal comfort in field environments was built when the whole-body thermal comfort was satisfied.Secondly,an experiment was conducted in a controlled climate chamber to investigate the effects of heating mode and exposure distance from cold vertical surfaces on personal thermal comfort.Radiator heating and floor radiant heating were adopted respectively.Moreover,representatives were invited to sit at distances of 1m,2m,and 3m from the external wall separately.R esults show thermal sensation of legs was warmer in floor heating rooms than that in radiator heating rooms.The horizontal radiant asymmetry from the cold wall and window played a significant role in the thermal comfort of occupants in the radiator heating rooms.When subjects sat closer to the external wall,their non-uniformity of skin temperature became larger and their thermal sensations were colder.Thirdly,an experiment with subjects was conducted to study the acceptable limits of radiant asymmetry caused by a cold wall at a room temperature of18°C,which is the lower limit of the room temperature for heating design in Chinese Building Regulations.The body center of the subject was 1.0m away from the cold panel,which is considered as the unfavorable environment in heated rooms.The regression between the percentage of the dissatisfied(PD)and radiant temperature asymmetry was established and the allowable radiant temperature asymmetry of 4.2K was obtained to satisfy the local thermal comfort in neutral-cool environments.Fourthly,the data from the laboratory studies at Technical University of Denmark with subjects exposed to different types of radiant asymmetry were analysed.A comfort chart for local equivalent temperature was developed for the evaluation of indoor built environments,which identifies the source of discomfort and predicts the observed subjective evaluations.It was found that a neutral thermal sensation does not guarantee thermal comfort and thermal preference varied among each body part.Finally,applications for the research results were illustrated.The lower limit of radiant temperature asymmetry was applied to derive the lower limit of the interior surface temperature of the external wall,which is the basic parameter for building insulation design.Moreover,the limit value of inner surface temperature integrating external wall and window was induced.Therefore,the result could be served for parameter set of building insulation design.Applications of the new comfort chart were also illustrated at aspects of creating and evaluating thermal environments.Moreover,local thermal comfort chart was applied to evaluate the cold radiant asymmetric environments and provide a reference of thermal design of exte rnal wall.The comfort chart identifies the source of discomfort and is compatible with the subjective results.The thermal parameters obtained from the local comfort chart are identical with the experimental results conducted in neutral-cool chamber.In general,the evaluation model for local thermal comfort in field environments,the lower limit of radiant temperature asymmetry and the new comfort chart were proposed in this study,which could provide theoretical basis of building energy-saving standards and information on the sensitivity of different body parts to heat loss that can be used to optimise the personal control system to improve indoor environments.