A new predictive thermal sensation index of human response

The purpose of this paper is to investigate the problem of determining a human thermal sensation index that can be used in feedback control of HVAC systems. We present a new approach based on fuzzy logic to estimate the thermal comfort level depending on the state of the following six variables: the air temperature, the mean radiant temperature, the relative humidity, the air velocity, the activity level of occupants and their clothing insulation. The new fuzzy thermal sensation index is calculated implicitly as the consequence of linguistic rules that describe human's comfort level as the result of the interaction of the environmental variables with the occupant's personal parameters. The fuzzy comfort model is deduced on the basis of learning Fanger's `Predicted Mean Vote' (PMV) equation. Unlike Fanger's PMV, the new fuzzy PMV calculation does not require an iterative solution and can be easily adjusted depending on the specific thermal sensation of users. These characteristics make it an attractive index for feedback control of HVAC systems. The simulation results show that the new fuzzy PMV is as accurate as Fanger's PMV.     

Improving thermal comfort conditions by accounting for the mean radiant temperature

The environment in many air conditioned spaces is often determined by the air dry bulb temperature alone. However, in certain circumstances, ignoring the consequences of the mean radiant temperature is not acceptable. A strategy is proposed, therefore, in which the operative temperature, which accounts for radiant effects, is employed as the parameter for control purposes. It is based primarily upon the ASHRAE comfort chart and results in improved thermal comfort.     

Analysis on the impact of mean radiant temperature for the thermal comfort of underfloor air distribution systems

Despite the potentially significant advantages of underfloor air distribution (UFAD) systems, the shortcomings in fundamental understanding have impeded the use of UFAD systems. A study has been carried out on the thermal stratification which is crucial to system design, energy efficient operation and comfort performance of UFAD systems with an aim of examining impact of mean radiant temperature (MRT) on thermal comfort. Clear elucidation of the benefit of UFAD systems has been shown by comparing it to the traditional overhead air distribution systems. Keeping the same level of comfortable environment in the occupied zone, UFAD systems require much higher temperature of supply air, which represents significant energy savings. The benefit of UFAD systems is more pronounced at the condition of high ceiling height building. Considerable discrepancies in thermal comfort are found on the assumption that air temperature rather than MRT is used for the evaluation of PMV. However, more rigorous analysis including the full radiation simulation does not show any significant difference in PMV distribution. The result of the full radiation simulations requires much longer simulation time but gives similar air temperature distribution and only slightly higher averaged temperature than present approaches.     

Numerical Method for a Full Assessment of Indoor Thermal Comfort

Heat, mass and momentum transfer takes place simultaneously in ventilated rooms. For accurate predictions of the indoor environment, all the environmental parameters that influence these transport phenomena should be taken into consideration. This paper introduces a method for a full assessment of indoor thermal comfort using computational fluid dynamics in conjunction with comfort models. A computer program has been developed which can be used for predicting thermal comfort indices such as thermal sensation and draught risk. The sensitivity of predicted comfort indices to environmental parameters is analysed for a mechanically ventilated office. It was found that when the mean radiant temperature was considered uniform in the office, the error in the predicted percentage of dissatisfied (PPD) could be as high as 7.5%. The prediction became worse when the mean radiant temperature was taken to be the same as air temperature point by point in the space. Moreover, disregarding the variation of vapour pressure in the space resulted in an error in PPD of abour 4% near the source of moisture generation. The importance of evaluating both thermal sensation and draught risk is also examined. It is concluded that in spaces with little air movement only the thermal sensation is needed for evaluation of indoor thermal comfort whereas in spaces with air movement induced by mechanical vantilation or air-conditioning systems both thermal sensation and draught risk should be evaluated.     

日较差对居住建筑夜间通风室内热环境的影响

为了研究不同日较差情况下,夜间通风对室内热环境的影响,采用Energyplus软件对西安地区某公寓室内空气温度、平均辐射温度进行了模拟研究。结果表明,与无夜间通风相比,夜间通风时室内最高气温、最高平均辐射温度分别降低了0.32℃、0.34℃。室内空气温度、平均辐射温度随日较差的增大而降低,且机械通风时段比渗透通风时段降低显著。当日较差为4℃、6℃、8℃、10℃、12℃时,室内处于热舒适时段的比例分别为0,16.11%,28.06%,32.01%和34.86%。     

Evaluation and comparison of thermal comfort of convective and radiant heating terminals in office buildings

Radiant heating systems are increasingly widely utilized in buildings for its energy conservation potential and enhanced thermal comfort. This paper presented an experiment to compare the thermal comfort performance of radiant heating system with convective heating system through objective measurement and subjective survey. Six physical parameters which might influence occupants' thermal satisfaction, including the Mean Radiant Temperature(MRT), humidity, air movement, A-weighted sound level,temperature fluctuation and vertical temperature difference, were measured. In addition, 97 subjects participated in the subjective survey part of this experiment, experiencing all the three environments heated by air source heat pump, radiator and floor heating.And they were asked to vote in six thermal comfort related aspects, i.e. thermal sensation, humidity, draught, local discomfort,overall thermal satisfaction and overall preferences, plus the acoustic environment, since the operation noise of heating system might lead to complains of the occupants. It was found that in continuous heating, no significant difference between radiant and convective heating system was observed in the Mean Radiant Temperature(MRT), indoor humidity and noise issue. Though radiant heating systems resulted in lower draught risk and less local discomfort complains in the feet region due to the less significant temperature fluctuations and vertical temperature gradients, radiant heating did not have significantly higher overall thermal satisfaction votes and was not significantly more preferred by occupants.     

Analytical solution for heat transfer in a multilayer floor of a radiant floor system

In radiant floor systems, the distribution of the floor surface temperature, which can be used to determine the mean temperature and the lowest/highest temperature of the floor surface, is an important parameter. The mean temperature of the floor surface determines cooling/heating capacity and indoor thermal comfort. The lowest surface temperature, which considers the dew point in an indoor environment, is a crucial factor in the prevention of condensation on a floor surface. The highest surface temperature is typically considered for local thermal comfort. In this paper, an analytical solution for heat transfer in a multilayer floor structure of a radiant floor system is proposed based on the analysis of the heat transfer process of a multilayer floor, equivalent thermal resistance and separation of variables method. The corresponding formulas are derived to estimate the distribution of floor surface temperature. The calculation results are validated by experiments. The calculation and experimental results show good accordance. The absolute error between the calculation and experimental results for floor surface temperature is within 0.3°C. A method for the calculation of the dimensionless temperature of the floor surface, which can be used for radiant heating and cooling systems, is provided. Using this proposed method, the distribution of floor surface temperature and the influence of floor structure parameters on the thermal performance of floors can be estimated and analyzed.     

An experimental technique for thermal comfort comparison in a transient pull down

Various types of spaces are controlled for maintaining a desired comfort-condition level. Examples include buildings, automobiles, airplanes, and trains. The steady-state or longer-duration HVAC control is well established. However, situations are encountered where a rapid march towards a thermal space comfort level is required such as in the parked automobiles or in buildings where thermal mass is utilized for conserving energy. Many times design changes are proposed to improve the transient pull down in one zone but that could significantly affect the transient pull down in another zone. Further, in addition to the temperature, other parameters such as air velocity, mean radiant temperature, humidity need to be considered for assessing space comfort level. In our work we have developed an experimental technique for the multi-zone or comparative assessment of thermal comfort in a transient pull-down situations. First, the fan and system curves were developed for the competing designs. The predicted mean vote (PMV) methodology was employed for determining perceived comfort level. PMV is an ideal technique since it accounts for all of the above-mentioned parameters that are needed to assess space comfort level. Using an indoor climate analyzer, the transient PMV response at various locations was obtained. Conclusions are drawn to illustrate how this technique can be utilized for the simultaneous assessment of thermal comfort level in multiple zones, especially when transient pull downs are encountered.     

Experimentally-determined characteristics of radiant systems for office buildings

Radiant heating and cooling systems have significant energy-saving potential and are gaining popularity in commercial buildings. The main aim of the experimental study reported here was to characterize the behavior of radiant cooling systems in a typical office environment,including the effect of ceiling fans on stratification,the variation in comfort conditions from perimeter to core,control on operative temperature vs. air temperature and the effect of carpet on cooling capacity. The goal was to limit both the first cost and the perceived risk associated with such systems. Two types of radiant systems,the radiant ceiling panel( RCP) system and the radiant slab( RS) system,were investigated. The experiments were carried out in one of the test cells that constitute the FLEXLAB test facility at the Law rence Berkeley National Laboratory in March and April 2016. In total,tentest cases( five for RCP and five for RS) were performed,covering a range of operational conditions. In cooling mode,the air temperature stratification is relatively small in the RCP,with a maximum value of 1. 6 K. The observed stratification effect was significantly greater in the RS,tw ice as much as that in the RCP.The maximum increase in dry bulb temperature in the perimeter zone due to solar radiation was 1. 2 K for RCP and 0. 9 K for RS-too small to have a significant impact on thermal comfort. The use of ceiling fans was able to reduce any excess stratification and provide better indoor comfort,if required. The use of thin carpet requires a 1 K low er supply chilled water temperature to compensate for the added thermal resistance,somew hat reducing the opportunities for water-side free cooling and increasing the risk of condensation. In both systems,the difference betw een the room operative temperature and the room air temperature is small when the cooling loads are met by the radiant systems. This makes it possible to use the air temperature to control the radiant systems in lieu of the operative temperature,reducing both first cost and maintenance costs.     

佛山某文化综合体室外热环境模拟分析

采用ENVI-met对佛山某城市文化综合体的室外热环境进行了数值模拟计算。模拟结果表明:在14:00地块内绿地、水体和遮阳棚可明显降低世纪大街的地表表面温度;空气温度受空气风速和风向的影响较大;天蓬对世纪大街的热环境改善明显,显著降低了平均辐射温度和SET*值,保证世纪大街60%以上区域热环境在最热时段仍处于可接受范围。19:00模拟结果表明,热环境舒适区域覆盖大部分的公共文化体的室外活动区域,为傍晚时分市民活动提供了舒适的空间。对现状建筑设计和景观设计方案提出热环境优化措施,以求构建更加良好的室外热环境。     

室内气流组织和空气品质的数值研究

分析了气流分布性能的评价指标、热舒适性评价指标和室内空气品质的评价指标。将通风方式分为置换通风和混合通风,利用暖通空调专用模拟软件Airpak对室内气流进行模拟。模拟某小型会议室的温度、速度、CO2浓度、平均空气龄、PMV值和PPD值,并依据模拟结果分析不同气流组织下的室内空气品质、人体热舒适性和空调能耗情况。指出不同气流组织对室内空气品质、人体热舒适性和空调能耗的影响不同,置换通风和上侧送上回送风方式能得到较好的空气品质和有效的能量利用。     

Draught,Radiant Temperature Asymmetry and Air Temperature – a Comparison between Measured and Estimated Thermal Parameters

Thermal comfort measurements were taken in 17 enterprises at 129 work sites in shops, stores and offices. The measurements included air temperature, air velocity, relative humidity and radiant temperature asymmetry according to ISO 7726 and ISO 7730 standards. The workers also answered a questionnaire dealing with thermal comfort. Predicted mean vote (PMV) and the percentages of workers complaining of draught (“percentage dissatisfied”, PD) were determined and compared with the workers' assessments of thermal conditions. The estimations of air temperature were always too low, and the estimated PMV indicated that the thermal environment was too warm. The calculated PMVs were usually lower than the estimated ones. Most of the workers complained of draught, even though, according to the PD index, fewer than 17% of the workers should have felt discomfort due to draught. The radiant temperature asymmetry was always small and did not explain complaints of draught on the basis of the reference value. Judged by the present reference values, and the measurement of the thermal environment, the workers overestimated the sensation of thermal discomfort.     

Thermal comfort and energy consumption of the radiant ceiling panel system.: Comparison with the conventional all-air system

The purpose of this study is to investigate the various characteristics of a radiant ceiling panel system and their practical application to office buildings. The radiant ceiling panel system and conventional air-conditioning system were compared in terms of thermal comfort, energy consumption, and cost. Thermal environment, along with human response, was tested by using a small meeting room equipped with radiant ceiling panels. The responses were collected by questionnaires given to the male subjects in the room. The experiment for the female subjects was conducted separately. Results show that the radiant ceiling panel system is capable of creating smaller vertical variation of air temperature and a more comfortable environment than conventional systems. When using a cooled ceiling, a small volume of supplied air creates a less draught environment, which reduced the discomfort of feeling cold in the lower part of the body. Numerical simulation of yearly energy consumption and cost estimation were conducted. Typical office rooms located on the 3rd, 4th, and 5th floor of a six-floor building in the Tokyo area were simulated. Since part of the sensible heat load is handled by radiant ceiling panels, the volume of supplied air can be reduced, leading to lower energy consumption for air transport. By using the radiant ceiling panel system in one of the three floors of the simulated building, energy consumption can be reduced by 10%. Estimated pay back time was from 1 to 17 years depending on the market price of the radiant ceiling panel.     

Experimental and numerical analysis of air and radiant cooling systems in offices

This paper analyses office cooling systems based on all air mixing ventilation systems alone or coupled with radiant ceiling panels. This last solution may be effectively applied to retrofit all air systems that are no longer able to maintain a suitable thermal comfort in the indoor environment, for example in offices with high thermal loads.     

Effect of MRT variation on the energy consumption in a PMV-controlled office

This paper investigates the energy-saving potential of a thermal comfort-controlled office building. A comparative simulation study between the thermal comfort control and conventional thermostatic control is conducted on a building with glass façades where changes in the outdoor temperature and solar radiation over the course of a day affect radiant temperature and thus thermal comfort. To evaluate the thermal performance in the comfort-controlled space, a PMV-based thermal comfort controller, which adjusts the set-point room temperature of the existing thermostatic controller according to the changes of environmental variables, is assumed. The results demonstrate that thermal comfort competes with energy saving in a conventional thermostatic-controlled space. However, it is suggested that thermal comfort control provides consistent thermal comfort as well as energy-saving effect. The results show that energy consumption in a thermal comfort-controlled space is more affected by a change in the mean radiant temperature than in the conventional thermostatic-controlled space. The energy-saving potential in the thermal comfort-controlled space increases with low mean radiant temperature conditions. Although the energy-saving potential is reduced under high mean radiant temperature conditions, it is suggested that thermal comfort control is still a reasonable strategy to achieve both thermal comfort and energy savings simultaneously.     

Effect of building interface form on thermal comfort in gymnasiums in hot and humid climates

The thermal environment and thermal comfort of a building are greatly affected by the design of the building interface form. Most contemporary architectural designs consider only the relations between architectural form and architectural beauty. Few studies on the correlation of architectural form and thermal comfort address the influence of architectural form on thermal comfort and thermal environment. These studies are particularly important for gymnasium architectures located in hot and humid areas, which have high requirements for thermal comfort. This paper presents an experimental investigation and an analysis of the effect of the building interface form of gymnasiums on thermal comfort in hot and humid subtropical regions durings ummer. Results showed that the influence of the top interface forms on thermal comfort is mainly dominated by the mean radiant temperature, which could be controlled to improve thermal comfort. The influence of side interface forms on thermal comfort is mainly dominated by air velocity, and thermal comfort could be improved by promoting natural ventilation on the side interface form design to reduce indoor heat. This research enhanced our understanding of the relation between the interface form and the thermal comfort of gymnasiums. In addition, this paper provides a theoretical reference for the sustainable design of gymnasiums in hot and humid climates.     

Predictions of thermal comfort in stratified room environment

Studies of thermal comfort of occupants started in the early part of the 20th century to describe the comfort level in terms of environmental variables. Field studies have indicated that many of the complaints about unsatisfactory indoor environment can be attributed to the thermal environment. Hence, heating, ventilation, and air conditioning (HVAC) systems are used in buildings to create thermal environments that are capable of providing comfort to the occupants. Among different ventilation systems, displacement ventilation (DV) systems have become popular as more energy efficient room air distribution systems compared with the other more common forms of air distribution systems, such as mixing ventilation. However, local cold discomfort at the lower extremities due to vertical temperature gradient is often reported with DV systems. Although many studies are reported in the literature that compare the performance of the DV systems with the other more conventional types of ventilation systems, the performance of different displacement ventilation types in providing thermal comfort need further investigation. The aim of the current work is to compare the ventilation performance, as predicted by an advanced thermal comfort model, of three commonly used DV air terminal devices (ATDs) for room ventilation: a flat wall diffuser (ATD1), semi-cylindrical wall diffuser (ATD2) and floor swirl diffusers (ATD3). The CBE (Center for the Built Environment at Berkeley) comfort model has been implemented in this study to compare the thermal comfort provided by the three ATDs due to its good performance in non-uniform thermal environments. Based on the test conditions and the results obtained from the comfort model, the predicted occupant’s local sensations for the case of ATD2 were better than those for ATD1 and ATD3 and it showed better overall thermal sensation. Since the local comfort of the CBE model is a function of both local and overall thermal sensations, the predicted occupant’s local comfort values for ATD2 were better than those for ATD1 and ATD3 and consequently it provided better overall thermal comfort.     

车站高大空间空调系统气流组织与热舒适性分析

兼顾人体热舒适和建筑节能的要求,对目前车站高大空间空调气流组织的数值模拟研究报道进行对比分析。分析结果显示,人们对高大空间建筑室内热舒适要求高于居住建筑和办公建筑;从满足人体热舒适角度出发,空调送风加地板辐射供冷方案适于夏季满员工况,地板辐射供热加空调加湿方案适用于冬季满员工况;高大空间的空调系统适宜采用上送上回的送风方式,其温度场和速度场均优于上送下回的空调送风方式;在高大空间内设置分层空调系统将在一定程度上降低空调能耗,且分层空调中送风速度对分层界面的位置影响较大,送风温差对高大空间分层空调的温度分布和流场分布有较大影响。     

Effect of humidity and small air movement on thermal comfort under a radiant cooling ceiling by subjective experiments

Radiant air-conditioning systems are expected to be more comfortable and superior energy-saving systems than convective air conditioning ones generally used. There are some studies on radiant cooling systems. However, they were seldom put to practical use because of dew point problem in Japan. The objective of this study is to investigate the thermal comfort of local parts of the body and the whole body, in particular, including the effects of humidity (45% rh, 65% rh, 85% rh) and small air movements, by subjective experiments under a radiant cooling system. The experiments have been performed by using radiant cooling panels in a climate chamber. Subjects were seated on a chair under the radiant cooling panels, and voted their thermal sensation and comfortable sensation. The following results were obtained. Even in the radiant cooling system, the influence of humidity and small air movement on thermal sensation votes of the whole body could be correctly estimated by using a standard new effective temperature (SET*) within one scale error of thermal sensation. Small air movement with the radiant cooling system had a possibility of improving the comfortable sensation votes in the radiant cooling.     

Research on seasonal indoor thermal environment and residents' control behavior of cooling and heating systems in Korea

Indoor thermal environments and residents' control behavior of cooling and heating systems were investigated in Seoul, Korea and compared with the results of previous studies. Twenty-four houses in summer, six houses in autumn and 36 houses in winter were used in this study. The measurement of temperature, humidity and air conditioner usage behavior was carried out. The clo-value, thermal comfort, sensation and basic data of the houses were also investigated. The indoor thermal environment in the summer had a high temperature and a high humidity ratio compare to standard comfort zone. Most of the indoor thermal environments at the time of starting the air conditioner in the summer were out of the comfort zone. Some of the data recorded while the air conditioner was stopped were in the comfort zone, but in many cases the temperature was relatively higher than comfort zone. Most indoor climate distributions in the winter were in the comfort zone and the indoor climate in autumn coincided well with the criteria of the comfort zone. Compared with results of previous studies in these 25 years, indoor ambient average temperature in winter has increased and the comfort temperature has increased in the heating period and decreased in the cooling period. This result indicates that the development of an HVAC system has created an expectation of comfort for residents and has shifted their thermal comfort zone warmer in winter and cooler in summer.