An investigation into thermal comfort in the summer season of Ghadames,Libya

This paper reviews the results from a field survey of thermal comfort within two types of buildings; old (traditional) and new (contemporary), in Ghadames oasis in Libya. The survey was undertaken in the summer seasons 1997 and 1998, which were typical of the hot–dry climate of North Africa. It shows how the 237 residents responded to the environmental conditions. Questionnaires were collected from the residents of 51 buildings: 24 old buildings that employ natural ventilation systems with courtyards and 27 new buildings that employ air-conditioning systems. In addition the environmental parameters were measured in 11 buildings (5 old, 6 new) representing 50 subjects, to calculate the predicted mean vote value of the subject using Fanger’s model as presented in ISO 7730 standard 1995. The survey has shown that the measurements of predicted mean vote (PMV) in new air-conditioned buildings provide satisfactory comfort conditions according to ISO 7730 and the occupants agree by indicating a satisfactory actual mean vote (AMV). The equivalent measurements and survey results in old traditional buildings indicated that although the PMV, based on measurements and ISO 7730, implied discomfort (hot), the occupants expressed their thermal satisfaction with the indoor comfort conditions. The field study also investigated occupants’ overall impression of the indoor thermal environments; the results suggest that people have an overall impression of higher standard of thermal comfort in old buildings than in new buildings.     

Introduction to thermal comfort standards and to the proposed new version of EN ISO 7730

This paper describes existing International Standards Organization (ISO) standards and current activity concerned with thermal comfort. It describes how an ISO standard is produced from a new work item proposal to publication as an International Standard. ISO Standards should be valid, reliable, useable, and with sufficient scope for practical application. The existing thermal comfort standard—EN ISO 7730—is considered in terms of these criteria as well as ISO 8996 (metabolic rate) and ISO 9920 (clothing). The work of ISO/TC 159 SC5, ‘ergonomics of the physical environment’, is presented in Appendix A. The proposed revision of EN ISO 7730 is presented in detail. The revised standard will be based on requirements for general thermal comfort (predicted mean vote (PMV), operative temperature) and local thermal discomfort (radiant temperature asymmetry, draught, vertical air temperature differences, floor surface temperatures). One critical issue is the effect of air velocity. Increased air velocity has a beneficial effect at warm temperatures, but it may result in draught sensation in cooler temperatures. Another issue is the extent to which requirements of humidity need to be included in a standard for thermal comfort. Several recent research projects dealing with adaptation, influence of air velocity and the effect of humidity have been responsible for keeping the standards up to date.     

Spot Monitoring: Thermal comfort evaluation in 25 office buildings in winter

In Germany, the optimization of energy uses in buildings demands a strict compliance with the requirements for thermal comfort as proposed by the Norm DIN EN ISO 7730:2006 (originated in ISO 7730), regardless of the diagnosis the building users may state. In the present field study, a survey on thermal comfort is made for winter periods, covering 345 measurements in 148 work spaces belonging to 25 office buildings. The survey method consists on sensed measurements and simultaneously gathered questionnaire data given by office users. For measurements, a mobile unit equipped with temperature, air humidity and airflow speed sensors was employed; the questionnaire inquired on thermal aspects of the close environment within the office. The main objective of the survey is to define an optimal operative temperature that can be attained by assessing the relationship between the measured data and the subjective data given by the users. The evaluation of the thermal comfort takes on the basis of the Norms’ criteria and on the average rating (vote) on thermal sensation chosen by the users, namely, the Comfort Vote or CV. As a relevant result, it can be stated that the users express acceptance to pre-established thermal conditions, even though the thermal prediction index as proposed by the Norm (PMV, Predicted Mean Vote) indicates that said thermal conditions are not good.     

Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate

The current design standard BS EN ISO7730 [Moderate thermal environments—determination of the PMV and PPD indices and specification of the conditions for thermal comfort, International Standards Organisation (1995)] is based upon the work of Fanger, and essentially comprises a steady-state human heat balance model that leads to a prediction of the sensation of human thermal comfort for a given set of thermal conditions. The model was derived from laboratory-based measurements conducted in the mid-1960s in relatively ‘conventional’ environments. However, a chilled ceiling operated in combination with displacement ventilation represents a more sophisticated environment as compared with the original conditions in which the Fanger model was derived. This raised a question about the applicability of the current standard when designing for thermal comfort in offices equipped with chilled ceiling/displacement ventilation systems. This paper presents findings from an EPSRC-funded study that sought to answer the above question. Human test subjects (184 in total) carried out sedentary office-type work in a well-controlled environmental test room that simulated an office fitted with the above system. Measurements of environmental variables were taken at a number of locations near the subjects, each of whom wore a typical office clothing ensemble. The reported thermal comfort sensations were compared with values predicted from BS EN ISO7730 over a range of system operating conditions. It was shown that the current standard BS EN ISO7730 may be used, without modification, when designing for the thermal comfort of sedentary workers in offices equipped with chilled ceiling/displacement ventilation systems. These findings are interpreted within the context of a proposed modification to thermal comfort design standards that includes adaptive effects, and the influence of BS EN ISO7730 on the development of other radiant surface/displacement ventilation configurations is discussed.     

Thermal perceptions,general adaptation methods and occupant's idea about the trade-off between thermal comfort and energy saving in hot–humid regions

A field study conducted in workplaces and residences in Taiwan is carried out to clarify two questions in detail: (1) do people in the tropical climate regions demonstrate a correlation between thermal sensation and thermal dissatisfaction the same as the PMV–PPD formula in the ISO 7730; and (2) does the difference in opportunities to choose from a variety of methods to achieve thermal comfort affects thermal perceptions of occupants? A new predicted formula of percentage of dissatisfied (PD) relating to mean thermal sensation votes (TSVs) is proposed for hot and humid regions. Besides an increase in minimum rate of dissatisfied from 5% to 9%, a shift of the TSV with minimum PD to the cool side of sensation scale is suggested by the new proposed formula. It also reveals that the limits of TSV corresponding to 80% acceptability for hot and humid regions are −1.45 and +0.65 rather than −0.85 and +0.85 suggested by ISO 7730. It is revealed in the findings that the effectiveness, availability and cost of a thermal adaptation method can affect the interviewees' thermal adaptation behaviour. According to the discussion of interviewees' idea about the trade-off between thermal comfort and energy saving, it is found that an energy-saving approach at the cost of sacrificing occupant's thermal comfort is difficult to set into action, but those ensure the occupant's comfort are more acceptable and can be easily popularized.     

The validity of ISO-PMV for predicting comfort votes in every-day thermal environments

One of the uses of ISO 7730 (predicted mean vote, PMV) is to predict the thermal sensations of people in buildings. This application is examined, using the ASHRAE database of field-studies. Taking these world-wide data as a single distribution, PMV is free from serious bias. There exist, however, underlying biases in relation to all contributing variables, and a further bias related to the outdoor temperature. These biases often combine to produce a substantial bias in PMV. In surveys of individual buildings, PMV often differs markedly and systematically from the actual mean vote, both for naturally ventilated (NV) and for air-conditioned (AC) spaces. Possible origins of the biases are discussed, and it is shown that it would be possible to modify PMV substantially to reduce them. Environmental consequences of the use of PMV are discussed. It is concluded that ISO 7730 in its present form can be seriously misleading when used to estimate thermal comfort conditions in buildings.     

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.     

The effect of air-conditioning on worker productivity in office buildings: A case study in Thailand

This paper presents findings from a study of the impact of indoor thermal conditions on the productivity of office workers in Thailand. The experiment simulating office working conditions was carried out with a completely randomized design under a variety of indoor thermal conditions over different time periods. In the experiment, subjects performed five simulated tasks: calculation, typing, proof-reading, simple quick reaction, and concentration-needed reaction. Normalized changes in worker productivity associated with those five tasks were measured and analyzed using the analysis of variance technique. In this study, the ranges of thermal conditions resulting in the greatest productivity were calculated by the predicted mean votes (PMVs). The results of this study suggest that the general appropriate PMV value recommended by ISO 7730 is suitable for Thais only in afternoon and evening periods. In addition, it was found that a satisfactory thermal comfort condition for office workers can be achieved by setting the temperatures of air-conditioning systems at 26 °C–28 °C for morning periods and at 24.5 °C–26 °C for afternoon and evening periods. These ranges of temperature settings help maintain and improve the productivity of office workers during morning, afternoon, and evening periods by 18%, 1% to 15%, and 7%, respectively.     

Thermal comfort in air-conditioned mosques in the dry desert climate

In Kuwait, as in most countries with a typical dry desert climate, the summer season is long with a mean daily maximum temperature of 45 °C. Centralized air-conditioning, which is generally deployed from the beginning of April to the end of October, can have tremendous impact on the amount of electrical energy utilized to mechanically control the internal environment in mosque buildings. The indoor air temperature settings for all types of air-conditioned buildings and mosque buildings in particular, are often calculated based on the analytical model of ASHRAE 55-2004 and ISO 7730. However, a field study was conducted in six air-conditioned mosque buildings during the summers of 2007 to investigate indoor climate and prayers thermal comfort in state of Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait mosque buildings, together with an analysis of prayer thermal comfort sensations for a total of 140 subjects providing 140 sets of physical measurements and subjective questionnaires were used to collect data. Results show that the neutral temperature (T_n) of the prayers is found to be 26.1 °C, while that for PMV is 23.3 °C. Discrepancy of these values is in fact about 2.8 °C higher than those predicted by PMV model. Therefore, thermal comfort temperature in Kuwait cannot directly correlate with ISO 7730 and ASHRAE 55-2004 standards. Findings from this study should be considered when designing air conditioning for mosque buildings. This knowledge can contribute towards the development of future energy-related design codes for Kuwait.     

建筑环境热舒适性研究进展与趋势分析

重点从研究方法和研究内容的角度,系统地阐述了建筑环境热舒适性实验室研究和现场测试调查研究的国内外研究进展.大量的国内外研究表明,基于热平衡和严格实验室试验的ASHRAE55和ISO7730热舒适性标准,因实验室研究方法的缺陷而使得其规定值与实际测试调研结果存在较大的差别.不同种族人体热舒适性差异、人体热感觉环境适应性、...     

Predicted and reported thermal sensation in climate chambers,offices and homes

Past thermal comfort research has shown differences in the thermal sensation votes given in field and laboratory settings. However, such research tends to compare the votes of different groups of people in different environments rather than comparing the same people in each environment. Therefore, a two-phase study was conducted of the thermal comfort of 30 BRE employees in their home, in their office, and in a climate chamber. In the first phase each subject spent two 3 h sessions in each environment and the temperature was adjusted between sessions within the range 18–26°C. Data loggers were used to record the air and mean radiant temperature, air velocity and relative humidity; subjective ratings of thermal sensation were obtained using questionnaires. The subjects wore the same clothing in each session and were allowed to conduct only sedentary activities. The reported thermal sensation votes were compared with those predicted using ISO 7730. The observed neutral temperatures for each of the three environments differed by up to 2°C and were up to 1°C different to those predicted. This finding has implications for energy use. In the second phase, the subjects were studied in their home and office only. No restrictions were imposed on clothing, previous or current activities, or environmental conditions. The observed thermal sensation votes were very poorly correlated with those predicted and with operative temperature.     

Energy saving and improved comfort by increased air movement

In this study, the potential saving of cooling energy by elevated air speed which can offset the impact of increased room air temperature on occupants’ comfort, as recommended in the present standards (ASHRAE 55 2004, ISO 7730 2005 and EN 15251 2007), was quantified by means of simulations with EnergyPlus software. Fifty-four cases covering six cities (Helsinki, Berlin, Bordeaux, Rome, Jerusalem and Athens), three indoor environment categories I, II and III (according to standard EN 15251 2007) and three air velocities (<0.2, 0.5 and 0.8 m/s) were simulated. The required cooling/heating energy was calculated assuming a perfectly efficient HVAC system. A cooling energy saving between 17 and 48% and a reduction of the maximum cooling power in the range 10–28% has been obtained. The results reveal that the required power input of the fan is a critical factor for achieving energy saving at elevated room temperature. Under the assumptions of this study, the energy saving may not be achieved with the methods for air speed increase, such as ceiling, standing, tower and desk fans widely used today when the power consumption of the fan is higher than 20 W.     

Impact of adaptive thermal comfort criteria on building energy use and cooling equipment size using a multi-objective optimization scheme

Recently adaptive thermal-comfort criteria have been introduced in the international indoor-climate standards to reduce the heating/cooling energy requirements. In 2008, the Finnish Society of Indoor Air Quality (FiSIAQ) developed the national adaptive thermal-comfort criteria of Finland. The current study evaluates the impact of the Finnish Criteria on energy performance in an office building. Two fully mechanically air-conditioned single offices are taken as representative zones. A simulation-based optimization scheme (a combination of IDA-ICE 4.0 and a multi-objective genetic-algorithm from MATLAB-2008a) is employed to determine the minimum primary energy use and the minimum room cooling-equipment size required for different thermal comfort levels. The applicability of implementing energy-saving measures such as night ventilation, night set-back temperature, day lighting as well as optimal building envelope and optimal HVAC settings are addressed by investigating 24 design variables. The results show that, on average, an additional 10 kWh/(m² a) primary energy demand and a larger 10 W/m² room cooling-equipment size are required to improve the thermal comfort from medium (S2) to high-quality (S1) class; higher thermal comfort levels limit the use of night ventilation and water radiator night-set back options. Compared with the ISO EN 7730-2005 standard, the Finnish criterion could slightly decrease the heating/cooling equipment size. However, it significantly increases both the heating and cooling energy demand; the results show 32.8% increase in the primary energy demand. It is concluded that the Finnish criterion-2008 is strict and does not allow for energy-efficient solutions in standard office buildings.     

Building envelope regulations on thermal comfort in glass facade buildings and energy-saving potential for PMV-based comfort control

This paper presents an investigation of the effect of building envelope regulation on thermal comfort and on the energy-saving potential for PMV-based comfort control in glass facade buildings. Occurrences and severity of overheating, based on the PMV-PPD model contained in ISO 7730, were used for the thermal comfort assessment. Parametric study simulations for an actual building with a large glass facade were carried out to predict the changes in thermal comfort levels in a space due to different glazing types, depths of overhang and glazing areas, which are the key parameters of the building envelope regulation index, named ENVLOAD, in Taiwan. The result demonstrates that the ENVLOAD has significant effect on thermal comfort. Additionally, comparative simulations between PMV-based comfort control and conventional thermostatic control were performed to investigate the changes in the energy-saving potential of a thermal comfort-controlled space due to changes of its ENVLOAD. The results demonstrate that the energy-saving potential in a PMV-based controlled space increases with low ENVLOAD conditions.     

寒冷地区居室热舒适设计温度的研究

根据寒冷地区人类居住特点,利用VB语言编程,以ISO7730为理论依据,通过PMV和PPD模拟计算了寒冷地区室内热环境,给出了寒冷地区人体不同代谢率条件下常规采暖和地板辐射采暖的舒适性温度。结果表明,在PPD≤20%的前提下,寒冷地区满足人体热舒适的室内常规采暖设计温度推荐值为20℃,地板辐射采暖设计温度推荐值为19℃,明显高于我国现行的设计温度。     

低温送风室内气流组织模拟及热舒适评价

采用三维紊流k-ε模型,应用FLUENT软件对低温送风房间的气流组织和热环境进行了模拟。按照ISO7730标准,采用有效吹风感温度T_(ed),空气分布特性指标ADPI等指标对室内热舒适度进行评价。验证采用常规的送风末端和低温送风相结合的气流组织模式的可行性,同时为空调室内气流组织形式的优化设计及舒适性提供依据。     

Survey of thermal comfort in residential buildings under natural conditions in hot humid and cold wet seasons in Nanjing

Comfort standards (ISO 7730, ASHRAE 55) specify the exact physical criteria for producing acceptable thermal environments, such as temperature, air movement, and humidity limits. These, however, are often difficult to comply with, particularly in hot humid and cold wet seasons in Nanjing, China. Changing expectations of comfort is important in evaluating comfort, since naturally conditioned buildings in Nanjing are not typically air-conditioned. For this objective, a field study was conducted during the summer of 2000 and the winter of 2001. A total of 600 participants each answered a subjective questionnaire. Analyzing these field data shows that in natural conditions, the influence of gender and age on people’s thermal sensations is insignificant compared with six main variables. In addition, people’s thermal discomfort rapidly increases along with growth in relative humidity. Further, the variation of people’s hot or cold sensations is in proportion to that of air movement, and the effect in winter is greater than that in summer. The range of acceptable temperatures in hot humid and cold wet Nanjing is between 14.14°C and 29.42°C.     

Influence of the ventilation system on thermal comfort of the chilled panel system in heating mode

In heating mode, fresh air is still essential for a chilled panel system in order to ensure the indoor air quality. In this paper, a chilled ceiling panel system was designed and built in a typical office room. The thermal environment and thermal comfort in the room were fully measured and evaluated by using the Fanger's PMV-PPD model and the standard of ISO 7730 respectively, when room was heated in two modes, one of which is the chilled panel heating mode and the other of which is the combined heating mode of chilled panel and supply air. The research results indicate that in the combined mode, ceiling ventilation improves the general thermal comfort and reduces the risk of local discomfort. Under the condition of same general thermal comfort, the heating supply upper limit of chilled panel can be increased by 12.3% because of air mixing effect caused by introduction of air ventilation.     

Evaluation of adaptive thermal comfort models in moderate climates and their impact on energy use in office buildings

Thermally Activated Building Systems (TABS) are regarded as top-cooling systems rather than full air-conditioning systems. Therefore, adaptive thermal comfort models (ASHRAE55, ISSO74 or EN15251) are supposed to be applicable to TABS buildings, although the comfort model conditions are not necessarily satisfied. This paper investigates whether, for a moderate climate and with the heating and cooling set points chosen according to the adaptive models, the building’s energy use reduces. After all, applying adaptive models, if appropriate, is thought to lower energy use because higher maximum operative zone temperatures T_op,max are allowed, compared to the conventional ISO7730 model. For purpose of generality, a building with an ideal heating and cooling system is considered. Analysis of moderate climate weather data reveals a low energy reducing potential for the ASHRAE55 and ISSO74 model, because high reference outdoor temperatures hardly occur. EN15251 on the other hand, allows very high T_op,max and will lower the cooling need.A 2-zone building simulation demonstrates a higher cooling need for ASHRAE55 and ISSO74, compared to ISO7730. Because cooling is needed during the whole year, the lower winter T_op,max of these adaptive models causes these unexpected results. With real data of warmer years or varying gains, this conclusion holds.