In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.
Towards a Brazilian standard for naturally ventilated buildings: guidelines for thermal and air movement acceptability.
The Brazilian Federal Government has been recently promoting energy-conservation initiatives, most notably the ‘Thermal Performance in Buildings – Brazilian Bioclimatic Zones and Building Guidelines for Low-Cost Housing’ and the ‘Federal Regulation for Voluntary Labelling of Energy Efficiency Levels in Commercial, Public and Service Buildings’. These new regulations provide information for designers based on Brazil's climate requirements, with specific advice related to lighting systems, HVAC and the thermal envelope of buildings. Nevertheless, requirements for naturally ventilated indoor environments appear as an open category without clear criteria. To address this, the paper proposes guidelines for naturally ventilated environments in which specific thermal and air movement acceptability goals must be achieved. The guidelines are based on results from field experiments in non-residential naturally ventilated buildings in different climatic zones as well as drawing on other studies. The proposed guidelines consider occupants' adaptive potential as well as thermal and air movement acceptability. Combining thermal acceptability with air movement acceptability is a key design challenge. Permissible operative temperature ranges are based on the ASHRAE 55 adaptive comfort standard, and minimum air velocity requirements within the occupied zone are specified. Considerations also included ‘active’ occupants and specific control over openings and fans.
In the ASHRAE comfort database , underpinning the North American naturally ventilated adaptive comfort standard , the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ , . These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.
O efeito da utilização de ventiladores de teto no conforto térmico em salas de aulas com condicionamento híbrido em um local de clima quente e úmido
Em climas quentes e úmidos, é sabido que a velocidade do ar exerce um papel importante no conforto, promovendo as trocas térmicas entre nossa pele e o ambiente. Com isso em mente, o objetivo principal deste trabalho é avaliar o efeito de valores elevados de velocidade do ar (0,20-1,35 m/s) no conforto térmico de ocupantes em salas de aula com sistema de condicionamento híbrido (ar condicionado + ventiladores de teto), localizadas em uma região de clima quente e úmido. Para esse fim, questionários foram aplicados em alunos de graduação, simultaneamente às medições instrumentais ambientais (temperatura do ar, umidade relativa, temperatura de globo e velocidade do ar). Os resultados sugerem que, para as condições do experimento e em ambientes condicionados artificialmente, os usuários podem aceitar, e até preferir, a velocidade do ar acima de 0,90 m/s, se associada a valores de temperatura mais elevados (25 a 28 ºC) em climas quentes e úmidos.
What is the most adequate method to assess thermal comfort in hybrid commercial buildings located in hot-humid summer climate?
The aim of this paper is to identify which method to assess thermal comfort is the most appropriate to be used in hybrid commercial buildings located in hot and humid summer climate. Three methods to assess thermal comfort were analysed: (1) ASHRAE 55 for determining acceptable thermal conditions in occupied spaces, (2) ASHRAE 55 for determining acceptable thermal conditions in naturally ventilated spaces and (3) Givoni's chart for hot and humid climates. Models with two geometries, two room sizes per geometry, two solar orientations and three window areas per model were analysed. Simulations were performed using the EnergyPlus programme, with the TRY climate file of Florianópolis. Thermal comfort was evaluated applying the simulations output data into the three methods. Thus, the amount of time (number of hours per year) in which the use of air-conditioning is necessary to bring thermal comfort for the users throughout the year was determined using each method. Such number of hours of use of air-conditioning was also compared with the pattern of use of air-conditioning observed in Florianópolis. The main conclusion is that the most suitable method for use in hot and humid summer climates is the method proposed by Givoni.
ASHRAE Standard 55 is widely used to assess thermal comfort in buildings worldwide. The main purpose of this paper is to evaluate the adaptive method application proposed by ASHRAE 55 in two different climates in Brazil. This method relates the conditions for comfort to the “prevailing mean outdoor air temperature”. The currently available version of the Standard allows for linear and exponential methods to calculate the “prevailing mean”, and both are tested to establish the acceptability zones. The results indicate that choosing any of the methods to calculate the prevailing mean outdoor air temperature gives similar results when the temperature amplitudes are small; but it can lead to different limits of acceptability, and consequently sum of discomfort hours, when significant day-to-day temperature variations are present. In addition, the results indicate that it is possible to find significant percentages of thermal acceptability from previous studies below the lower limit of acceptability proposed by the Standard. As a result, a “clo adjustment zone” is suggested.
The aim of this paper is to review the literature on human thermal comfort in the built environment. First an overview about the subject area is presented. This is followed by a review of papers published in the last 10 years that examine the various sub-areas of research related to human thermal comfort. Some remarkable works about both the Fanger's and adaptive thermal comfort models are also discussed. This review does not contain simulation works and/or experimental studies without subjective results of people. As a result of the literature review, 466 articles were classified and grouped to form the body of this article. The article examines standards, indoor experiments in controlled environments (climate chamber) and semi-controlled environments, indoor field studies in educational, office, residential and other building types, productivity, human physiological models, outdoor and semi-outdoor field studies. Several research topics are also addressed involving naturally ventilated, air-conditioned and mixed-mode buildings, personalized conditioning systems and the influence of personal (age, weight, gender, thermal history) and environmental (controls, layout, air movement, humidity, among others) variables on thermal comfort.
Currently, there is a rising trend for commercial buildings to use air conditioning to provide indoor thermal comfort. This paper focuses on the impact of prolonged exposure to indoor air-conditioned environments on occupants’ thermal acceptability and preferences in a mixed-mode building in Brazil. Questionnaires were administered while indoor microclimatic measurements were carried out (i.e., air temperature, radiant air temperature, air speed and humidity). Results suggest significant differences in occupants’ thermal acceptability and cooling preferences based on thermal history; differences were found between groups based on different physical characteristics (i.e., different gender and body condition). The findings also indicated a significant potential to implement temperature fluctuations indoors when occupants are exposed to air conditioning environments in warm and humid climates.
Conforto térmico humano em escritórios com sistema central de condicionamento artificial em clima subtropical úmido: estudos de campo vs. abordagem analítica
Quando se trata de conforto térmico em edificações condicionadas artificialmente, o modelo predicted mean vote/predicted percentage of dissatisfied (PMV/PPD) de Fanger, publicado em 1970, é o mais utilizado para prever e avaliar as condições térmicas internas. Este artigo apresenta dados de conforto térmico levantados em uma edificação de escritórios com sistema central de condicionamento de ar, localizada em Florianópolis, uma cidade de clima subtropical úmido. O objetivo da pesquisa é analisar e comparar os resultados de sensação térmica obtidos em estudos de campo (284 participantes) com os valores calculados de PMV/PPD provenientes do método analítico adotado pela ASHRAE 55 (2013). Questionários eletrônicos foram aplicados simultaneamente às medições das variáveis ambientais (temperatura do ar, umidade relativa, temperatura radiante média e velocidade do ar) durante 2014. Observou-se que, embora 91% dos ocupantes tenham avaliado o ambiente como confortável termicamente, o PPD médio apontou 16% de insatisfeitos termicamente. Constatou-se certa inadequação do modelo ao clima em questão, principalmente quando se considera o restrito intervalo de PMV entre ± 0,50 delimitado como confortável pela ASHRAE 55 (2013).
Predicting thermal comfort in office buildings in a Brazilian temperate and humid climate. Energy and Buildings
This paper aims to compare thermal comfort responses from office workers in both fully air-conditioned and mixed-mode buildings against both the analytical and adaptive models of thermal comfort of ASHRAE 55-2013. Occupants were asked to record their thermal perception in questionnaires delivered online while instantaneous instrumental measurements were taken in situ (air temperature, radiant temperature, air velocity and humidity). Three buildings were investigated in a temperate and humid climate, i.e., in Florianópolis, southern Brazil. Two buildings have mixed-mode operation and one building has central air-conditioning. Almost two thousand six hundred questionnaires were collected during field studies. Actual thermal sensation and acceptability votes were compared against two predictive models of thermal comfort: the analytical model and the adaptive model. The 80% and 90% acceptability limits of indoor operative temperature used in the adaptive model were calculated using the prevailing mean outdoor air temperature. The analytical model overestimated the cold sensation of users, mainly for natural ventilation mode, and did not properly predict the percentage of thermal dissatisfaction of users. The analytical model could be used only when air-conditioning is operating; and a wider range of indoor thermal conditions than recommended by ASHRAE 55-2013 is recommended to be adopted during air-conditioning operation. The application of the adaptive model seems to be inappropriate for fully air-conditioned buildings. This work was not conclusive about the use of the adaptive model when the air-conditioning is on in mixed-mode buildings due to few data collected in this mode of operation. Under natural ventilation operation in mixed-mode buildings, occupants adapted to temperature fluctuations as predicted by the adaptive model, however, occupants appear to be more tolerant to cool conditions. The adaptive model may be used in mixed-mode buildings, when the air-conditioning is not on.