An evaluation of three biometeorological indices for human thermal comfort in urban outdoor areas under real climatic conditions

Three biometeorological indices were examined in terms of their potential to describe the actual thermal sensation as this is experienced by humans at areas with different climatological characteristics. The thermal comfort scales, as derived from using Physiological Equivalent Temperature (PET), the Temperature-Humidity Index (THI) and the wind chill index (K), were compared to Actual thermal Sensation Votes (ASV) data as expressed on a 5-point scale. These data were collected by surveys that covered all four seasons of the year and were conducted in seven European cities (Athens, Thessaloniki, Milan, Fribourg, Cambridge, Sheffield and Kassel). Results show that, for any given ASV class, the corresponding classes calculated according to PET, THI and K, present a strong correlation with the climatic mean temperature of the survey site, which in turn leads to misclassification of the thermal sensation. Accordingly, an effort was made to apply an adjustment to the indices based on climatic mean temperature. Only small improvements were observed on the performance of the indices.     

Modeling urban microclimate to ameliorate thermal sensation conditions in outdoor areas in Athens (Greece)

Previous research that conducted in three typical public areas in Athens showed that the acceptable air temperature range that determines thermal comfort varies among 17.0–21.0 °C and 26.0–32.0 °C for the cool and the warm period of the year, respectively. The present research goes further and determines the acceptable environmental conditions via two wide acknowledged thermal indices, which are PET and UTCI, in order to evaluate, whether or not, thermal comfort conditions are presented in three typical outdoor urban areas of a Mediterranean city, like Athens. Thus, environmental model ENVI-met 3.1 was applied to calculate the daily microclimatic variation of the three examined areas for the same dates, one typical for the warm period and one typical for the cool period. Thermal sensation conditions were then assessed by the indices. Results showed that the examined areas approach the acceptable environmental conditions only for the cool day, whereas an assumed urban design scenario was able only to ameliorate thermal discomfort but not to reach thermal comfort during a hot day.     

Three-year measurements of ambient and indoor air temperatures in Solar Village-3, Athens,Greece

This paper presents the results of ambient and indoor air temperature measurements in the dwellings of Solar Village-3, Athens. The temperatures were monitored centrally using a Data Acquisition System and the measurements cover a 37 continuous month period, from 1/12/88 to 31/12/91. The main effort in this paper was given to the appropriate elaboration and presentation of indoor air temperature measurements in all buildings of Solar Village-3 for all the evaluation period as well as detailed data for representative dwellings. The elaborated data are average, maximum and minimum daily values for buildings, apartments and rooms, as well as daily variation of half hourly values. The daily average temperatures of each apartment are weighted average of the daily mean temperatures of each room, which in turn is the mean value of 48 measurements/day (every 30 min). Analysis shows that indoor temperatures measured during the evaluation period contributed to prevail thermal comfort conditions in winter as well in summer days. Analysis also shows that buildings of high thermal capacity and proper insulation have no need for air conditioning.     

Investigation of indoor thermal comfort under transient conditions

In industrialized countries about 90% of the time is spent indoors. In indoor, thermal comfort can be basically predicted by the environmental parameters such as temperature, humidity, air velocity and by the personal parameters as activity and clothing resistance. In this study, a mathematical model of thermal interaction between human body and environment was established and the effect of clothing and air velocity was examined under transient conditions. By the developed model, human body has been separated to 16 segments and possible local discomforts are taken into consideration. Using the model, changes in the sensible and latent heat losses, skin temperature and wettedness, thermal comfort indices were calculated. In a hot environment latent heat loss increases by means of sweating. Because of over wetted skin, comfort sense goes worse. Especially, at feet and pelvis skin wettedness reaches maximum level. Sensible and latent heat losses rise and the skin temperature and wettedness decrease with increasing air velocity.     

Improved indoor thermal comfort during defrost with a novel reverse-cycle defrosting method for air source heat pumps

When an air-source heat pump (ASHP) unit is used for space heating at a low ambient temperature in winter, frost may be formed on its outdoor coil surface. Frosting affects its operational performance and energy efficiency, and therefore periodic defrosting is necessary. Currently, the most widely used standard defrosting method for ASHP units is reverse-cycle defrost. During a standard reverse-cycle defrosting process, the indoor coil in an ASHP unit actually acts as an evaporator, therefore, no heating is provided and hence indoor air temperature in a heated space can drop. Furthermore, a longer period of time is needed before space heating can become available immediately after the completion of defrosting. Consequently, occupants’ thermal comfort may be adversely affected. To improve the indoor thermal comfort for occupants during reverse-cycle defrosting, a novel thermal energy storage (TES) based reverse-cycle defrosting method has been developed and the improvement to occupants’ thermal comfort experimentally evaluated and is reported in this paper. Comparative experiments using both the novel TES based reverse-cycle defrosting method and the standard reverse-cycle defrosting method were carried out. Experimental results and the evaluated indoor thermal comfort indexes clearly suggested that when compared to the use of standard reverse-cycle defrost, the use of the novel reverse-cycle defrosting method can help achieve improved indoor thermal comfort, with a shorter defrosting period and a higher indoor supply air temperature during defrosting.     

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.     

校园行道树对夏季室外行人热舒适的 影响研究

道路绿地作为城市绿地的重要组成部分,在缓解城市热岛和改善行人热舒适等方面起着重要作用。通过监测大学校园内7种典型行道树树荫和阳光下的空气温度(T_a)、相对湿度(RH)、风速(V_a)、黑球温度(T_g)和太阳辐射(G)等气象参数以及行道树的叶表面温度(T_(1s),运用通用热气候指数(Universal Thermal Climate Index,UTCI)分析不同行道树对道路空间热环境的影响和行人热舒适的改善效果。结论如下:1)行道树改善道路空间行人热舒适作用明显,对T_a和平均辐射温度(Mean Radiant Temperature,T_(mrt)降低能力最强的树种分别为悬铃木和银杏;2)天空可视因子(Sky View Factor,SVF)是影响道路空间行人热舒适的主要因素;3)T_(1s)与UTCI呈强线性正相关(R~2=0.8083),夏季T_(1s)越高,道路空间行人热舒适度越差。研究结果从室外热舒适评价的角度为行道树设计提供了理论基础和量化指导。     

Thermal effect of temperature gradient in a field environment chamber served by displacement ventilation system in the tropics

The effect of vertical air temperature gradient on overall and local thermal comfort at different overall thermal sensations and room air temperatures (at 0.6 m height) was investigated in a room served by displacement ventilation system. Sixty tropically acclimatized subjects performed sedentary office work for a period of 3 h during each session of the experiment. Nominal vertical air temperature gradients between 0.1 and 1.1 m heights were 1, 3 and 5 K/m while nominal room air temperatures at 0.6 m height were 20, 23 and 26 °C. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative humidity at 0.6 m height was maintained at 50%. It was found that temperature gradient had different influences on thermal comfort at different overall thermal sensations. At overall thermal sensation close to neutral, only when room air temperature was substantially low, such as 20 °C, percentage dissatisfied of overall body increased with the increase of temperature gradient. At overall cold and slightly warm sensations, percentage dissatisfied of overall body was non-significantly affected by temperature gradient. Overall thermal sensation had significant impact on overall thermal comfort. Local thermal comfort of body segment was affected by both overall and local thermal sensations.     

强化室内空气流动以改善热舒适的节能研究

基于热舒适实验，研究了提高室内空气流速对人体热舒适的改善程度以及空气流速的合理取值。研究结果表明，可以通过提高空气流速保持室内标准有效温度SET*不变，从而可适当提高室内温度、相对湿度的设定值，达到节能的目的。以天津地区为例，分析结果表明，空调运行时间大大缩短，直接蒸发冷却方式的利用率得到提高。     

Comparison of physical performances of the ventilation systems in low-energy residential houses

The paper presents experimental results of the effect of ventilation systems in modern residential low-energy houses on thermal and humid conditions, heat consumption and perception of thermal comfort and air quality by their residents. Practical projects of modern residential houses with various ventilation systems which realize thermal, humid and psycho-physical comfort were worked out. To analyze the influence of ventilation systems on human comfort, results of questionnaires and comprehensive experimental measurements were taken into account. For measurements, 22 identical residential houses in Germany were chosen where 4 various ventilation systems were installed: gravitational (natural) ventilation, air heating system, mechanical ventilation with in- and out-leading air elements and a function of heat recovery and mechanical ventilation with single ventilators. The following parameters were measured in test units: relative air humidity, concentration of CO₂ in the air, air temperature, consumption of electricity, gas and heat, working time of the window opening, working time of the mechanical ventilation and number of residents. Advantages and disadvantages of ventilation systems were outlined. Experimental results were evaluated. Relationships between ventilation systems and thermal comfort were discussed by taking into account opinions of house residents.     

New index indicating the universal and separate effects on human comfort under outdoor and non-uniform thermal conditions

The purpose of this study is to propose new thermal index for outdoor and non-uniform environments with heat conduction, such as when a person sits on a bench at a park. This paper describes mathematically the theory of how solar radiation and heat conduction, as well as air temperature, humidity, air velocity and longwave radiation, are incorporated into the new index and how these thermal factors that may not be uniform are treated. Another important feature is that separate indices are generated for each factor while the new index is derived. It is expected that the new index will help us to understand how much each factor affects the human thermal comfort in outdoor and non-uniform environments with heat conduction.     

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.     

On the use of bioclimatic architecture principles in order to improve thermal comfort conditions in outdoor spaces

The present paper describes a process for designing and applying several techniques based on bioclimatic architecture criteria and on passive cooling and energy conservation principles in order to improve the thermal comfort conditions in an outdoor space location located in the Great Athens area. For that reason, the thermal comfort conditions in 12 different outdoor space points in the experimented location have been calculated using two different thermal comfort bioclimatic indices developed to be used for outdoor spaces. The used indices were the following: (a) “Comfa”, which is based on estimating the energy budget of a person in an outdoor environment and (b) “thermal sensation”, based on the satisfaction or dissatisfaction sensation under the prevailing climatic conditions of the outdoor spaces. Calculations were performed during the summer period and two different scenarios of the constructed space parameters have been considered. The first scenario consists of a conventionally constructed space, while the second one includes various architectural improvements according to the bioclimatic design principles. The two bioclimatic indicators were used for calculating the outdoor thermal comfort conditions in the above-mentioned outdoor space locations for both scenarios and the effect of the bioclimatic design architectural improvements on the human thermal comfort sensation was presented and analysed.     

Pedestrian level winds and outdoor human comfort

Outdoor human comfort in an urban climate may be affected by a wide range of parameters, including wind speed, air temperature, relative humidity, solar radiation, air quality, human activity, clothing level, age, etc. Several criteria have been developed in the wind engineering community for evaluating only the wind-induced mechanical forces on the human body and the resulting pedestrian comfort and safety. There are significant differences among the criteria used by various countries and institutions to establish threshold values for tolerable and unacceptable wind conditions even if a single parameter, such as the wind speed is used as criterion. These differences range from the speed averaging period (mean or gust) and its probability of exceedance (frequency of occurrence) to the evaluation of its magnitude (experimental or computational). The paper addresses the progress made towards the computational evaluation of pedestrian level winds. All existing criteria for wind and thermal comfort are absolute criteria, which specify the threshold values or comfort ranges for respective weather parameters. The paper will outline an approach towards the establishment of an overall comfort index taking into account, in addition to wind speed, the temperature and relative humidity in the area.     

Design considerations with ventilation-radiators: Comparisons to traditional two-panel radiators

Performance of heat emitters in a room is affected by their interaction with the ventilation system. A radiator gives more heat output with increased air flow along its heat transferring surface, and with increased thermal difference to surrounding air. Radiator heat output and comfort temperatures in a small one-person office were studied using different positions for the ventilation air inlet. In two of the four test cases the air inlet was placed between radiator panels to form ventilation-radiator systems. Investigations were made by CFD (Computational Fluid Dynamics) simulations, and included visualisation of thermal comfort conditions, as well as radiator heat output comparisons. The room model was exhaust-ventilated, with an air exchange rate equal to what is recommended for Swedish offices (7 l s⁻¹ per person) and cold infiltration air (−5 °C) typical of a winter day in Stockholm.Results showed that under these conditions ventilation-radiators were able to create a more stable thermal climate than the traditional radiator ventilation arrangements. In addition, when using ventilation-radiators the desired thermal climate could be achieved with a radiator surface temperature as much as 7.8 °C lower. It was concluded that in exhaust-ventilated office rooms, ventilation-radiators can provide energy and environmental savings.     

Experimental investigation of thermal and ventilation performances of stratum ventilation

Stratum ventilation has been proposed to cope for elevated indoor temperatures. Air speed, temperature and CO₂ concentration of a stratum ventilated office are investigated experimentally. The data obtained under well defined conditions and therefore can be used for validating numerical models. Thermal comfort conditions and ventilation efficiency are studied based on the experimental results of four experimental cases. Thermal comfort indices, i.e. PMV, PPD and PD are calculated from measured data. The values of these indices are found to satisfy the requirements of ISO 7730, CR 1752-1998 and ASHRAE 55-2010. In terms of thermal comfort, the two cases with supply air temperature of 21 °C are found to perform better compared with the two cases with supply air temperature of 19 °C. For all the cases, the ventilation effectiveness is close to 1.5. This ventilation method could therefore be expected to provide indoor air quality in an efficient way.     

载人航天器舱内通风空调特性和数值模拟

由于载人航天器这一密闭狭小空间及其微重力这一特殊环境,舱内通风空调问题和热舒适环境与地面的HVAC问题不同,微重力效应特别是自然对流大为减弱影响着通风换热效果。本文首先分析了舱内通风空调问题的特殊性,通过无量纲分析和计算微重力的流体力学效应,然后利用FLUENT软件对两种集中通风方式进行数值模拟。模拟结果表明：微重力下几乎不存在“冷风下坠”或者“热羽”现象;集中斜进风在一定的进风角度和Re数下出现分岔解现象;与常重力相同通风条件下,微重力下自然对流的减弱使得舱内温度降低,换热减少,因此满足常重力热舒适要求的通风条件不一定满足微重力下热舒适性的要求。     

Displacement Ventilation - the Influence of the Characteristics of the Supply Air Terminal Device on the Airflow Pattern

Displacement ventilation is acknowledged to be an efficient system for the removal of contaminants and excess heat from occupied zones of rooms. However, airflow rates, temperature and the design of the air supply device strongly influence the parameters which determine thermal comfort. This paper reviews experiments and theoretical models which show the connection between these parameters. The width and shape of the air supply device have been varied, and a porous media has been used on the inlet area of the air supply device. The velocity and temperature profiles have been measured. The results presented show also that the flow can be described with respect to width and form of the profiles for temperature and velocity. The flow does not operate like a turbulent jet due to thermal stratification. It is shown that the Archimedes number of the supply air is the parameter which determines the air velocity in the area close to the floor. (The Archimedes number is here defined as the ratio between buoyancy and inertia forces.) The results show that it is possible to remove considerable amounts of excess heat from a room, typically 40-50 W/m², without exceeding the limits for thermal comfort. However, this requires relatively high airflow rates and supply air terminal units at least along one of the walls.     

Indoor air quality and thermal comfort studies of an under-floor air-conditioning system in the tropics

This paper reports thermal comfort and indoor air quality (IAQ) studies of an under-floor air-conditioning (UFAC) system in hot and humid climate. Thermal comfort parameters were measured at predetermined grid points within an imaginary plane to predict the airflow pattern of the supply air jet as well as to determine the occurrence of thermal stratification in the office space. Fanger’s [Thermal Comfort Analysis and Applications in Environmental Engineering, McGraw-Hill, New York, 1970] thermal comfort index was also computed to detect the occupants’ thermal sensation. Besides, the concentration levels of dust and carbon dioxide were recorded with the intention to examine the quality of the indoor air. Statistical methods were applied to derive the relationship between air velocity and the other parameters as mentioned earlier. The main findings from the study revealed reasonable level of acceptability of IAQ associated with the UFAC system. However, occupants are likely to experience localised thermal discomfort near the supply diffusers due to the existence of large temperature gradients. In addition, a stagnant zone is discovered at sedentary level, which is caused by the parabolic airflow nature of the primary air jet.     

我国湿热地区自然通风建筑夏季热舒适研究——以广州为例

2008年夏季对广州某高校学生在自然通风建筑中进行了501人次的热舒适现场调查,调查内容包括热感觉、热舒适度、热可接受度及潮湿感,并对相应的室内干球温度、相对湿度、黑球温度和风速等热环境参数进行了测试记录。通过对数据的整理分析发现,自然通风建筑的夏季室内温湿度均高于ASHRAE标准的舒适区域,但人们对该环境有较好的适应性。调查结果表明,我国湿热地区自然通风建筑的热中性温度为28.1℃(ET*=29.3℃),可接受的热环境温度的上限为29.7℃(ET*=30.9℃),相对湿度上限为78%。