Showing papers on "Thermal comfort published in 1998"

Developing an adaptive model of thermal comfort and preference - eScholarship

Abstract: The adaptive hypothesis predicts that contextual factors and past thermal history modify building occupants' thermal expectations and preferences. One of the predictions of the adaptive hypothesis is that people in warm climate zones prefer warmer indoor temperatures than people living in cold climate zones. This is contrary to the static assumptions underlying the current ASHRAE comfort standard 55-92. To examine the adaptive hypothesis and its implications for Standard 55-92, the ASHRAE RP-884 project assembled a quality-controlled database from thermal comfort field experiments worldwide (circa 21,000 observations from 160 buildings). Our statistical analysis examined the semantics of thermal comfort in terms of thermal sensation, acceptability, and preference, as a function of both indoor and outdoor temperature. Optimum indoor temperatures tracked both prevailing indoor and outdoor temperatures, as predicted by the adaptive hypothesis. The static predicted means vote (PMV) model was shown to be partially adaptive by accounting for behavioral adjustments, and fully explained adaptation occurring in HVAC buildings. Occupants in naturally ventilated buildings were tolerant of a significantly wider range of temperatures, explained by a combination of both behavioral adjustment and psychological adaptation. These results formed the basis of a proposal for a variable indoor temperature standard.

Developing an adaptive model of thermal comfort and preference

Abstract: The adaptive hypothesis predicts that contextual factors and past thermal history modify building occupants' thermal expectations and preferences. One of the predictions of the adaptive hypothesis is that people in warm climate zones prefer warmer indoor temperatures than people living in cold climate zones. This is contrary to the static assumptions underlying the current ASHRAE comfort standard 55-92. To examine the adaptive hypothesis and its implications for Standard 55-92, the ASHRAE RP-884 project assembled a quality-controlled database from thermal comfort field experiments worldwide (circa 21,000 observations from 160 buildings). Our statistical analysis examined the semantics of thermal comfort in terms of thermal sensation,

Understanding the adaptive approach to thermal comfort

Abstract: This paper explains the adaptive approach to thermal comfort, and an adaptive model for thermal comfort is presented. The model is an example of a complex adaptive system (Casti 1996) whose equilibria are determined by the restrictions acting upon it. People`s adaptive actions are generally effective in securing comfort, which occurs at a wide variety of indoor temperatures. These comfort temperatures depend upon the circumstances in which people live, such as the climate and the heating or cooling regime. The temperatures may be estimated from the mean outdoor temperature and the availability of a heating or cooling plant. The evaluation of the parameters of the adaptive model requires cross-sectional surveys to establish current norms and sequential surveys (with and without intervention) to evaluate the rapidity of people`s adaptive actions. Standards for thermal comfort will need revision in the light of the adaptive approach. Implications of the adaptive model for the HVAC industry are noted.

Indoor climate and air quality. Review of current and future topics in the field of ISB study group 10.

Abstract: In industrialized countries about 90% of the time is spent indoors. The ambient parameters affecting indoor thermal comfort are air temperature and humidity, air velocity, and radiant heat exchange within an enclosure. In assessing the thermal environment, one needs to consider all ambient parameters, the insulating properties of the occupants' clothing, and the activity level of the occupants by means of heat balance models of the human body. Apart from thermal parameters, air quality (measured and perceived) is also of importance for well-being and health in indoor environments. Pollutant levels are influenced by both outdoor concentrations and by indoor emissions. Indoor levels can thus be lower (e.g. in the case of ozone and SO2) or higher (e.g. for CO2 and formaldehyde) than outdoor levels. Emissions from cooking play an important role, especially in developing countries. The humidity of the ambient air has a wide range of effects on the energy and water balance of the body as well as on elasticity, air quality perception, build-up of electrostatic charge and the formation or mould. However, its effect on the indoor climate is often overestimated. While air-handling systems are commonly used for achieving comfortable indoor climates, their use has also been linked to a variety of problems, some of which have received attention within the context of "sick building syndrome".

A fuzzy control system based on the human sensation of thermal comfort

Abstract: Unlike the majority of the existing residential heating, ventilating and air conditioning (HVAC) control systems which are considered as temperature control problems, this paper presents a new HVAC control technique that is based on the human sensation of thermal comfort. The proposed HVAC control strategy goal is not to maintain a constant indoor air temperature but a constant indoor thermal comfort. This is realized by the implementation of a fuzzy reasoning that takes into account the vagueness and the subjectivity of the human sensation of thermal comfort in the formulation of the control action that should be applied to the HVAC system in order to bring the indoor climate into comfort conditions. Simulation results show that the proposed control strategy makes it possible to maximize both thermal comfort of the occupants and the energy economy of HVAC systems.

Architecture : comfort and energy

Abstract: Introduction (A. Sayigh). Thermal Comfort and the Development of Bioclimatic Concept in Building Design. Introduction. Thermal comfort. Degree day method for estimating heating and cooling requirements for Qatar. Building bioclimatic charts. Problems impairing the use of the bioclimatic charts. Mahony tables. Conclusions. References (A. Sayigh, A. Hamid Marafia). Vernacular and Contemporary Buildings in Qatar. Introduction. Vernacular architecture. Contemporary buildings in Qatar. Conclusions. References (A. Sayigh, A. Hamid Marafia). Principles of Thermal Comfort. Introduction. Heat exchanges man-environment. Comfort indexes. The adaptation model. References. Appendix - A. Appendix - B (F.M. Butera). Bioclimatism in Vernacular Architecture. Vernacular architecture vs representative architecture: the role of energy. General principles of the relationship between form and climate. The richness of vernacular architecture. A singular solution - changes of location. Typologies depending on the climate (H. Coch). The Utilization of Microclimate Elements. Introduction. The wind. The sun. Thermal mass. The vegetation. Shading devices. References (C. Gallo). Daylighting. Condition of the sky. On natural lighting. Basic physical principles. The physiology of vision. Daylighting in architecture. Daylighting improvement in buildings. Daylighting evaluation in architecture (R. Serra). Ventilation. Introduction. Indoor pollutants. Ventilation strategies. Air flow principles. Building air leakage and natural ventilation. Solar induced ventilation. Mechanical ventilation. References (H. Awbi). Technology for Modern Architecture. Ventilated roofs. Active curtain wall. Greenhouses. Movable shading devices. Light ducts. Integrated ventilation. Cooling technology. Outdoor spaces. References (M. Sala).

Designing for thermal comfort in combined chilled ceiling/displacement ventilation environments

Abstract: This paper presents general guidance on designing for thermal comfort in combined chilled ceiling/displacement ventilation environments. Thermal comfort measurements involving 184 human subjects were carried out in a laboratory-based test room, constructed to resemble a normal office and equipped with a combined chilled ceiling and wall-mounted displacement ventilation system. Room characterization tests revealed that the chilled ceiling has a detrimental effect upon displacement flow, suppressing the stratified boundary layer at ceiling temperatures of 18 C--21 C and destroying displacement flow all together at low ceiling temperatures (14 C--16 C). Reduction in ceiling temperature was found to increase local air velocities at heights of 0.1 m and 1.1 m above the floor, showing further evidence of mixing, though there was an insignificant effect on local discomfort due to draft, as measured by subjective responses and by draft rating assessment. ISO Standard 7730 (1995) is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants performing office work in combined chilled ceiling/displacement ventilation environments. The vertical radiant asymmetry induced by a cooled ceiling does not significantly affect the thermal comfort of desk-seated occupants; this, together with relative humidity, is shown to require no additional comfort-related design limitations beyondmore » those already in the literature and beyond the prevention of ceiling surface condensation.« less

Thermal comfort in transitional spaces in the cool season of Bangkok

Abstract: A field survey of 593 subjects occupying both indoor (air-conditioned and naturally ventilated) and outdoor environments was carried out. The focus of the survey dealt with experience of transitional spaces of buildings in the cool season of Bangkok, Thailand. This paper presents the results of the survey, which were compiled and analyzed in the following order: expectation, sensation, preference, and adaptation. The data are also compared with previous research of office environments in Bangkok. The results from the analysis show two important aspects. First, the neutral temperature for the whole sample is 27.1 C (80.8 F) and thermal acceptability is between 25.5 C (77.9 F) and 31.5 C (88.7 F), whereas the expected temperature is 26.7 C (80.1 F). As might be expected, the majority would prefer a cooler environment. The results are in good agreement with those of previous research but are beyond the upper limit of International Standard ISO 7730. Second, it is shown that the thermal responses of each group are influenced by the acclimatized characteristics of their environmental conditions. The work described here is part of a larger thermal comfort study and program to optimize comfort in buildings in warm climates.

An investigation of the thermal comfort adaptive model in a tropical upland climate

Abstract: The results of two thermal comfort surveys performed in Zambia, which has a tropical upland climate, are presented and analyzed with special reference to the adaptive model. The main forms of adaptation and adjustment analyzed are: clothing, skin moisture, activity level, and environmental controls. Results show that in the cool season the main methods of adaptation used by the subjects were clothing and environmental controls, while in the warm season only environmental controls were used. It proved difficult to establish the impact of the various levels of adaptivity on thermal comfort standards. It would be useful if the adaptive model could be factored into thermal comfort to produce adaptive thermal comfort standards that would allow for differences in culture and climate across the globe.

Cooled ceilings/displacement ventilation hybrid air conditioning system : Design criteria design criteria

Abstract: For realizing comfort and ventilation efficiency simultaneously using a cooled ceiling (CC)/ displacement ventilation (DV) hybrid air conditioning system (CC/DV), Vertical distribution of temperature, local ventilation efficiency, and thermal comfort were studied by conducting a series of experiments to determine the design conditions. The characteristics of the thermal environment were measured in a laboratory, which was set up to simulate an office room in summer. The local air change efficiency was measured by tracer gases method and a subjective experiment was also carried out. The interaction between the major system parameters of room cooling load (P), CC cooling output ratio (η), ventilation airflow rate (Q), temperature gradient (dt) and the relevant constraints were studied. The results of these experiments showed the temperature gradient in the occupied zone, an important factor of DV, adversely affects thermal comfort. As a result, the temperature gradient in the occupied zone should be in a range of 2-2.5 deg. C to realize comfort and ventilation efficiency simultaneously. A diagram for the system design was developed using the relationship among the above factors, which provides a useful and practical design tool.

Human response to local heating for use in connection with low enthalpy ventilation

Abstract: This paper presents results on the human response to individually controlled radiant local heating of the body which can be used together with low enthalpy ventilation based on low room air temperature and humidity. Experiments were performed with 18 human subjects to identify the optimum combination and location of local radiant heating panels designed to compensate for cooling of the body at room air temperatures in the range 14-23 °C. The subjects were instructed to change the heating power of the panels and to select the optimum condition that would provide them with thermal comfort. Questionnaires were used to register subjects' satisfaction with the thermal environment. Most of the subjects were able to control the local heating panels and were able to achieve thermal comfort for the body at a room air temperature of 20 °C. Half of the subjects, however, complained of cold discomfort on one or more body parts at room air temperatures of 17 and 14 °C. The thermal comfort reported by the subjects for the whole body and for the different body parts was influenced significantly by the number and location of the heating panels. Recommendations for the design of local radiant heating are suggested in this paper.

Requirements and guidelines for low-velocity measurements

Abstract: In this paper, new requirements for the characteristics of anemometers used for low-velocity measurements indoors, as well as requirements for the signal processing, are presented. The static calibration, dynamic response, and temperature compensation of the anemometers, as well as the directional sensitivity and the design of the velocity transducer, are considered, together with the period and the sampling rate of the measurements. The requirements in ASHRAE Standard 55 (1992), ASHRAE Standard 113 (1990), and ISO Standard 7726 (1985) are modified, and new requirements not considered in the current standards are developed and suggested for inclusion in future standards.

Perception of comfort in relation to weather and indoor adaptive opportunities

Abstract: This paper compares conditions on three floors of a building that use different environmental control strategies. The first floor uses night ventilation and thermal mass to keep the interior cool, the third floor was fitted with mechanical cooling units, and the second floor consists of standard cellular offices with 50% glazing. This paper discusses the results of staff satisfaction surveys conducted in three consecutive months, August, September, and October 1995, among the occupants of the three floors of the building. The results show a clear change in the perception of comfort and adaptive opportunities on each floor as the weather cools down from an exceptionally hot summer. Lessons are drawn for the design of passively cooled buildings and for future research in this important area.

Simplified thermal comfort evaluation of MRT gradients and power consumption predicted with the BCAP methodology

Abstract: Accurately predicting the thermal comfort in a room requires careful consideration of the energy balance in a room. Not only does an accurate thermal comfort analysis include conductive, convective, and radiative heat exchanges, but also wall properties, heating system data, and room geometry. Since these calculations are often complex, thermal comfort calculations are not readily done without the aid of a computer. The thermal comfort algorithm employed for this analysis was the Building Comfort Analysis Program (BCAP) methodology initially developed under Jones and Chapman (1994) and modified under Chapman and DeGreef (1997). This thermal comfort evaluation focuses on the mean radiant temperature gradients and power consumption for two different room geometries using three different heating systems. The results from the analysis are presented with detailed discussion. This simplified thermal comfort evaluation provides the design engineer with an additional tool for determining the appropriate type of heating system in a room.

Natural ventilation: Impact of wall material and windows on thermal comfort:

Abstract: Thermal comfort in a naturally ventilated test room is investigated. The test room is a lightweight portable cabin located in a sheltered area at Loughborough University, UK. Thermal comfort simulations were carried out for various sizes of openings and glazing. Medium and high thermal mass were added to the test room and their effects on thermal comfort were investigated. The results suggested that thermal mass has significant effect on thermal comfort parameters. Adding a 200 mm thick layer of medium-density concrete to the walls improved the thermal comfort over the summer by 40%.