Thermal comfort in office buildings: Findings from a field study in mixed-mode and fully-air conditioning environments under humid subtropical conditions

Autores:
De Vecchi, R.; Candido, C.; de Dear, R.; Lamberts, R.
Evento:
Building and Environment
Resumo:

This paper addresses thermal comfort conditions in office buildings with rudimentary mixed-mode environments controlled by occupants compared to fully air-conditioning in a humid subtropical climate in Brazil. Occupants from three office buildings with two different environmental control strategies (two with mixed-mode ventilation and one with permanent air-conditioning) assessed their thermal environment via “right-here-right-now” online questionnaires, while indoor climatic measurements were simultaneously carried out in situ. 2688 questionnaires from 617 occupants were collected. The results indicated that air-conditioning in mixed-mode (MM) buildings controlled by occupants was used permanently throughout the year without any season pattern, being specially connected to the peak outdoor air temperature. In addition, there was a strong tendency toward thermal discomfort due to excessive cold in MM buildings at times when air-conditioning mode was under operation, and hot discomfort during the naturally ventilated mode. When compared to fully-air conditioning buildings, there were similarities in terms of occupant thermal sensation and acceptability levels within the same intervals of Standard Effective Temperature (SET). The results obtained in this study could be useful as a framework for future studies, as well as a baseline for a Brazilian thermal comfort standard.

Ano:

The role of clothing in thermal comfort: how people dress in a temperate and humid climate in Brazil

Autores:
De Vecchi, R.; Lamberts, R.; Candido, C.
Evento:
Ambiente Construído
Resumo:

Thermal insulation from clothing is one of the most important input variables used to predict the thermal comfort of a building’s occupants. This paper investigates the clothing pattern in buildings with different configurations located in a temperate and humid climate in Brazil. Occupants of two kinds of buildings (three offices and two university classrooms) assessed their thermal environment through ‘right-here-right-now’ questionnaires, while at the same time indoor climatic measurements were carried out in situ (air temperature and radiant temperature, air speed and humidity). A total of 5,036 votes from 1,161 occupants were collected. Results suggest that the clothing values adopted by occupants inside buildings were influenced by: 1) climate and seasons of the year; 2) different configurations and indoor thermal conditions; and 3) occupants’ age and gender. Significant intergenerational and gender differences were found, which might be explained by differences in metabolic rates and fashion. The results also indicate that there is a great opportunity to exceed the clothing interval of the thermal comfort zones proposed by international standards such as ASHRAE 55 (2013) - 0.5 to 1.0 clo - and thereby save energy from cooling and heating systems, without compromising the occupants’ indoor thermal comfort.

Ano:

A field study about gender and thermal comfort temperatures in office buildings

Autores:
Maykot, J. K.; Rupp, R. F.; Ghisi, E.
Evento:
Energy and Buildings
Resumo:

The aim of this paper is to determine the comfort temperature for men and women in two office buildings, one operating under mixed-mode strategy (naturally ventilated and/or air-conditioned) and one fully air-conditioned. Thus, 116 field studies were performed from March 2014 to March 2016 involving 584 participants in two office buildings. In order to collect temperature, relative humidity and air velocity data, microclimate stations were installed in the offices. Data collected were submitted to statistical analysis: they were initially separated according to the type of building (mixed-mode or fully air-conditioned) and operating system, and then they were distributed according to gender. The comfort temperatures were estimated by means of linear regression and by using the Griffiths method. Results show that the Griffiths method is more suitable to express the comfort temperature for men and women. Overall, the comfort temperature was 24.0°C for females, and 23.2°C for males. In the mixed-mode building, comfort temperature was statistically higher for females than that for males (23.7°C and 23.0°C, respectively). In the fully air-conditioned building, significant differences were found for comfort temperature for females and males (24.2°C and 23.4°C, respectively). Furthermore, when the mixed-mode building operated under natural ventilation the comfort temperatures tended to be lower for both men and women when compared to the comfort temperature found in the same building during air-conditioning operation.

Ano:

Influência do índice de massa corpórea e frequência de atividades físicas no conforto térmico humano: análise estatística de dados de estudo de campo com usuários de escritórios em Florianópolis, SC

Autores:
Menegatti, M. C.; Rupp, R. F.; Ghisi, E.
Evento:
Ambiente Construído
Resumo:

O objetivo deste trabalho é verificar a influência do índice de massa corpórea (IMC) e da frequência de atividades físicas na sensação, preferência, conforto e aceitabilidade térmica de pessoas que trabalham em escritórios com ventilação híbrida ou que operam com sistema de ar-condicionado central em Florianópolis, SC. Analisaram-se os resultados de 85 estudos de campo (medições ambientais e aplicação de questionários) em três edificações. Os dados foram separados conforme cada modo de operação e subdivididos em dois subgrupos, um de IMC e outro de frequência de atividades físicas; e submetidos a análises estatísticas com as variáveis de conforto térmico. Observou-se uma tendência de os valores de isolamento da vestimenta diminuírem conforme se aumentam os valores de IMC. Sensação, preferência e conforto térmico mostraram relação significativa com os dois modos de operação, quando levados em consideração os valores de IMC. Em geral, indivíduos com maiores IMCs sentem o ambiente mais aquecido, tendem a preferir ambientes mais resfriados e sentem-se mais confortáveis termicamente do que usuários com menores valores de IMC. Os resultados relacionados à frequência de atividades físicas não se mostraram conclusivos.

Ano:

Associations of occupant demographics, thermal history and obesity variables with their thermal comfort in air-conditioned and mixed-mode ventilation office buildings

Autores:
Rupp, R. F.; Kim, J. ; de Dear, R.; Ghisi, E.
Evento:
Building and Environment
Resumo:

Building occupants' perception of thermal comfort can be influenced by a number of contextual factors, such as their demographic and anthropometric characteristics, behavioural patterns and cultural aspects. The objective of this work is to investigate the relationship between various contextual factors and the perception of thermal comfort in workplaces, by examining the gap between the current thermal comfort criteria and the actual requirements observed for different groups of occupants. The classic thermal comfort field research design i.e. simultaneous measurements of physical environmental parameters and questionnaire surveys, was implemented for two years in both centralised HVAC and mixed-mode office buildings located in Southern Brazil. Over 7500 questionnaires were completed by occupants of the buildings. Key variables including the participants' gender, age, body mass index, prior exposure to air-conditioning and building ventilation type were investigated in order to identify their association with thermal discomfort in the office workplace. Our results suggest that males, overweight occupants and those who are more frequently exposed to air-conditioning are more likely to express thermal discomfort due to feeling ‘warm’, compared to females, non-overweight occupants and those who were exposed to air-conditioning less frequently. In comparison, females, non-overweight occupants, air-conditioning light users, and occupants of centralised HVAC buildings were more likely to declare ‘cold’ discomfort. We also investigated how those variables were related to the width of thermal comfort zone. The analysis indicates that different groups of occupants require different comfort zones, suggesting that group differences should be considered when designing/operating spaces for diverse groups of occupants.

Ano:

Field study of mixed-mode office buildings in Southern Brazil using an adaptive thermal comfort framework

Autores:
Rupp, R. F.; de Dear, R.; Ghisi, E.
Evento:
Energy and Buildings
Resumo:

Studies about thermal comfort in mixed-mode buildings have been performed in order to better understand this type of building and its influence on occupants’ thermal perception. However, there is still no consensus amongst researchers regarding whether mixed-mode buildings should be evaluated separating each mode of operation (natural ventilation or air-conditioning) and whether adaptive thermal comfort theory applies to both modes of operation. Does the mode of operation of a mixed-mode building, ceteris paribus, influence occupant thermal comfort perception? Trying to answer such questions, field studies on thermal comfort were conducted in three mixed-mode office buildings in the city of Florianópolis (a temperate and humid climate), Southern Brazil. Buildings were equipped with mechanical cooling systems and operable windows, both controlled by occupants. Thermal comfort questionnaires were collected at the same time and location that environmental variables were measured by microclimate instruments. Almost 5500 questionnaires were answered by occupants of the three buildings in both modes of operation over the four seasons. Analysis of the results indicated that occupants’ thermal perception was influenced by the mode of operation. Adaptive thermal comfort models were developed for natural ventilation and air-conditioning mode of mixed-mode buildings. This work found no evidence to support a single adaptive model for mixed-mode buildings. During natural ventilation mode, occupants adapted to indoor temperature fluctuations as predicted by the adaptive thermal comfort theory. On the other hand, during air-conditioning operation a weak adaptive relation (indoor comfort temperature vs. outdoor climate) was observed – a range of about 4 °C of indoor temperature fluctuation may be used for the operation of the air-conditioning system without compromising thermal comfort, which could help saving energy. This work is a first step towards building an adaptive model of thermal comfort for Brazilian subtropical climate.

Ano:

Assessment of gender on requirements for thermal comfort in office buildings located in the Brazilian humid subtropical climate

Autores:
Maykot, J. K. ; Rupp, R. F.; Ghisi, E.
Evento:
Energy and Buildings
Resumo:

This article aims to assess the effects of gender on requirements for thermal comfort in office buildings. Data were obtained from 83 field studies conducted over 2014 in three office buildings located in Florianópolis, southern Brazil. One of the buildings is fully air-conditioned and the other two operate under mixed-mode strategy, i.e., alternating from air-conditioning to natural ventilation. Data were measured by means of microclimate stations, and the occupants opinions were obtained through a questionnaire. There was no significant difference of clothing insulation for male and female subjects. Significant differences were found for thermal sensation, thermal preference, thermal acceptability and thermal comfort in the central air-conditioned building. In mixed-mode buildings, significant differences were found for thermal sensation and thermal preference responses of male and female subjects. However, during air-conditioning operation in mixed-mode buildings, significant differences were found for thermal preference and thermal acceptability responses of male and female subjects; and during natural ventilation operation, significant differences were found for thermal sensation and thermal preference. In contrast to what some previous studies have found this work indicates the existence of significant differences in the thermal comfort responses of male and female subjects.

Ano:

Influence of relative air humidity and movement on human thermal perception in classrooms in a hot and humid climate

Autores:
Buonocore, C.; De Vecchi, R.; Scalco, V.; Lamberts, R.
Evento:
Building and Environment
Resumo:

In equatorial, hot-humid tropical climates, users of naturally ventilated environments are commonly susceptible to heat discomfort caused by high air temperatures and thus require more air movement to improve thermal comfort. To evaluate the influence of relative humidity and air speed on the occupant's thermal perception, field studies were conducted in naturally ventilated and fan-assisted classrooms in São Luis City, North-Eastern Brazil. Indoor environmental variables were measured alongside questionnaires, focusing on thermal environment and air movement evaluation. The results indicated that relative humidity had a significant negative impact on thermal perception when the operative temperature was above 30 °C, while airspeed played a key role in reducing thermal discomfort. Despite the contribution of internal air movement, it was concluded that, when the indoor operative temperature exceeded 31 °C, mechanical cooling is required to achieve thermal comfort. The results also indicated the great acceptability of indoor conditions, as well as the influence of environmental variables on student's thermal perception in naturally ventilated spaces.

Ano:

Development of the ASHRAE Global Thermal Comfort Database II. Building and Environment.

Autores:
Földváry, V.; Cheung, L.T.; Zhang, H.; de Dear, R.; Parkinson, T.; Arens, E.; Chun, C.; Schiavon, S.; Luo, M.; Brager, G.; Li, P.; Cândido, C.; Lamberts, R.; De Vecchi, R.; ... Zhou, X.
Evento:
Building and Environment
Resumo:

Recognizing the value of open-source research databases in advancing the art and science of HVAC, in 2014 the ASHRAE Global Thermal Comfort Database II project was launched under the leadership of University of California at Berkeley's Center for the Built Environment and The University of Sydney's Indoor Environmental Quality (IEQ) Laboratory. The exercise began with a systematic collection and harmonization of raw data from the last two decades of thermal comfort field studies around the world. The ASHRAE Global Thermal Comfort Database II (Comfort Database), now an online, open-source database, includes approximately 81,846 complete sets of objective indoor climatic observations with accompanying “right-here-right-now” subjective evaluations by the building occupants who were exposed to them. The database is intended to support diverse inquiries about thermal comfort in field settings. A simple web-based interface to the database enables filtering on multiple criteria, including building typology, occupancy type, subjects' demographic variables, subjective thermal comfort states, indoor thermal environmental criteria, calculated comfort indices, environmental control criteria and outdoor meteorological information. Furthermore, a web-based interactive thermal comfort visualization tool has been developed that allows end-users to quickly and interactively explore the data.

Ano:

Thermal sensitivity of occupants in different building typologies: the Griffiths Constant is a Variable

Autores:
Rupp, R. F.; Kim, J.; Ghisi, E.; de Dear, R.
Evento:
Energy and Buildings
Resumo:

The Griffiths method is widely used in thermal comfort studies to derive building users’ comfort temperature, or thermal neutrality as it is sometimes known. A single value (so called the Griffiths Constant, typically 0.5/°C) is prescribed as a representation of thermal sensitivity of building occupants to indoor temperature variations, which in turn is used to estimate indoor thermal neutrality from a subject's actual thermal sensation vote at a measured room temperature. Despite the Griffiths Constant of 0.5/°C having been used widely across the thermal comfort research literature and in some generic standards, the constant was derived exclusively from office building data and its applicability across different typologies is yet to be rigorously validated. The objective of this study is to quantify how sensitive people are to temperature variations inside a building, and to investigate if thermal sensitivity differs between different contexts (including building typologies, modes of ventilation, outdoor climatic types, and genders). A collection of thermal comfort field studies in different building typologies containing around 11,500 datasets was used to statistically derive building users’ thermal sensitivity, i.e. the rate of change in thermal sensation per unit change in indoor temperature within a day. Our results suggest that occupant thermal sensitivity does vary depending on building typologies and building ventilation mode. In naturally ventilated spaces users are about half as sensitive to temperature variations as in air-conditioned spaces. Age, gender and climate are found to be factors that can also influence thermal sensitivity of building occupants. Our findings imply that reliance on a universal thermal sensitivity value, the Griffiths Constant, in comfort temperature (neutrality) calculations should be avoided because it is in fact a variable.

Ano:
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