Research On Characteristics Of Thermal Comfort And Energy-use Behaviors Of Occupants With Personal Comfort Systems

A comfortable environment is important for people's mental and physical health: it can reduce the incidence of various diseases,maintain people's well-being and improve work productivity.In modern society,a comfortable built environment is usually achieved by air-conditioning systems which,however,are impossible to fulfill all individuals' requirements.Simultaneously,air-conditioning systems consume a lot of energy.Therefore,how to both improve people's thermal comfort and save building energy is one of the largest challenges in the HVAC field.The use of personal comfort systems(PCSs)provides a potential solution to this problem: PCSs enhance comfort and energy efficiency by optimizing local thermal states of human body parts to meet individuals' comfort needs over a wider range of ambient temperatures.However,current studies did not fully explore the comfort mechanism of PCSs,and a suitable thermal comfort model for different personal comfort systems remains blank.Besides,fixed-temperature environments in current studies cannot prove whether PCSs fully meet comfort needs of occupants.And the behaviors of people using air-conditioning systems under the influence of PCSs remain unclear.In addition,existing evaluation methods are difficult to simultaneously evaluate the comfort and energy consumption characteristics of different PCSs.In this study,the cooling-type PCSs include a radiant cooling workstation,desktop fans and a combination of the two,while the heating-type PCSs include electric heating chairs,electric heating chairs+leg-warmers and Huoxiang.Through three stages of work,subjects' thermal comfort and energy-use behaviors under the influence of PCSs were analyzed.In the first stage,the comfort and energy consumption characteristics of various PCSs in non-adjustable environments were studied experimentally.In the second stage,the comfort requirements and energy-use behaviors of subjects with various PCSs in adjustable environments were studied experimentally.In the third stage,on the basis of the experimental results of the first two stages,thermal comfort models,air-conditioning-related energy-use behavior models and evaluation indexes for PCSs were established.It was found that PCSs mainly reduced extreme conditions of the upper body parts of the human body and the lower body parts of the human body in warm and cool environments,respectively,and therefore improved the whole-body thermal comfort.PCSs allowed the extension of the acceptable temperature ranges to 32°C and 14°C in summer and winter,respectively,while the equivalent electric power of a single PCS was usually lower than 50 W.In adjustable environments,regardless of whether PCSs or which kind of PCSs was used,subjects finally chose a similar condition with the neutral overall thermal sensation and the "Slightly comfortable" level of overall thermal comfort,while nearly 100% of subjects felt their ambient environments acceptable.With initial indoor temperatures of 26°C,28°C,and 30°C,subjects without PCSs eventually decreased the indoor temperature to 25.6°C,and when subjects had PCSs,the final temperature was at most 3°C higher than when without PCSs.With initial indoor temperatures of 18°C,14°C and 16°C,subjects without PCSs eventually raised the room temperature to 19°C~20°C.And when subjects had PCSs,the final temperature was 2°C~3°C lower than when without PCSs.The local-overall thermal sensation model shows that the overall thermal sensation is equal to half the sum of the local thermal sensation votes of the two coolest body parts on the cool side and the two warmest body parts on the warm side.The local-overall thermal comfort model shows that(1)when most of body parts are on the uncomfortable side,the overall thermal comfort is equal to half the sum of local thermal comfort votes of the two most uncomfortable body parts on the uncomfortable side and the most comfortable body part on the comfort side;and(2)when most of body parts are on the comfortable side,the overall thermal comfort is equal to half the sum of the two most comfortable body parts on the comfort side a nd the most uncomfortable body part on the uncomfortable side.The root mean square error s of the two models for predicting the actual thermal sensation and thermal comfort are less than 0.2 scale.The comfort mechanism of PCSs is to make local thermal sensations of body parts fall in the comfort zone or to bring the local thermal sensations closer to the ideal local thermal sensation point.By doing so,the actual thermal-comfort-ski-line is closer to the ideal thermal-comfort-ski-line,thereby improving the overall thermal comfort.The comprehensive energy-use behavior model shows that in adjustable environments,when the overall thermal sensation of occupants increases/decreases by one scale,occupants would use air-conditioning systems to increase/decrease indoor temperatures by about 2.5°C and 2°C,respectively.According to the energy-use behavior model,the energy-saving mechanism of PCSs is to fully or partially reduce the deviation of the overall thermal sensation from the neutral level by local heating or cooling,which fully or partially meets the comfort requirements of occupants.As a result,occupants less use air-conditioner systems,or reduce the change of indoor temperatures by using air-conditioning systems,thus achieving energy savings.In addition,this study proposed the effective corrective power(CPe)and the corrective efficiency of PCSs(CEP)indexes.Through the CEP-CPe index,it is easy and fast to determine and compare the energy consumption and the extension of comfortable temperature ranges of different PCSs.PCSs which heat or cool fewer body parts have the higher energy efficiency,but the narrower comfortable temperature range.While if PCSs heat or cool more body parts,they have the stronger ability to extend the comfort temperature range,but with the lower energy efficiency.This study provides reference for studies on thermal comfort characteristics in non-uniform environments,air-conditioning-related energy-use behaviors,the development of intelligent air-conditioning systems,and evaluation methods of PCSs.