Gail Brager | University of California, Berkeley (original) (raw)

Papers by Gail Brager

Building Research & Information, 2013

The predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) are the most widely ... more The predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) are the most widely used thermal comfort indices. Yet, their performance remains a contested topic. The ASHRAE Global Thermal Comfort Database II, the largest of its kind, was used to evaluate the prediction accuracy of the PMV/PPD model. We focused on: (i) the accuracy of PMV in predicting both observed thermal sensation (OTS) or observed mean vote (OMV) and (ii) comparing the PMV-PPD relationship with binned OTS-observed percentage of unacceptability (OPU). The accuracy of PMV in predicting OTS was only 34%, meaning that the thermal sensation is incorrectly predicted two out of three times. PMV had a mean absolute error of one unit on the thermal sensation scale and its accuracy decreased towards the ends of the thermal sensation scale. The accuracy of PMV was similarly low for air-conditioned , naturally ventilated and mixed-mode buildings. In addition, the PPD was not able to predict the dissatisfaction rate. If the PMV model would perfectly predict thermal sensation, then PPD accuracy is higher close to neutrality but it would overestimate dissatisfaction by approximately 15-25% outside of it. Furthermore, PMV-PPD accuracy varied strongly between ventilation strategies, building types and climate groups. These findings demonstrate the low prediction accuracy of the PMV-PPD model, indicating the need to develop high prediction accuracy thermal comfort models. For demonstration, we developed a simple thermal prediction model just based on air temperature and its accuracy, for this database, was higher than PMV.

International Journal of Biometeorology, 2007

Office workers’ preferences for air movement have been extracted from a database of indoor enviro... more Office workers’ preferences for air movement have been extracted from a database of indoor environmental quality surveys performed in over 200 buildings. Dissatisfaction with the amount of air motion is very common, with too little air movement cited far more commonly than too much air movement. Workers were also surveyed in a detailed two-season study of a single naturally ventilated building. About one-half the building’s population wanted more air movement and only 4% wanted less. This same ratio applied when the air movement in workspaces was higher than 0.2 m/s, the de facto draft limit in the current ASHRAE and ISO thermal environment standards. Preference for “less air motion” exceeded that for “more” only at thermal sensations of −2 (cool) or colder. These results raise questions about the consequences of the ASHRAE and ISO standards’ restrictions on air movement, especially for neutral and warm conditions.

Building Research and Information, 2009

‘Mixed-mode’ refers to a hybrid approach to space conditioning that uses a combination of natural... more ‘Mixed-mode’ refers to a hybrid approach to space conditioning that uses a combination of natural ventilation and some form of mechanical ventilation and/or cooling. This study focuses on mixed-mode in buildings with operable windows (as opposed to natural ventilation through vents). By utilizing active cooling only when and where it is necessary, a well-designed mixed-mode building offers the potential to

Building Research and Information, 2011

Mixed-mode buildings operate along a spectrum from sealed heating, ventilation and air-conditioni... more Mixed-mode buildings operate along a spectrum from sealed heating, ventilation and air-conditioning to 100% naturally ventilated, but little is known about their occupants' comfort expectations and experiences. Exceedance metrics, which quantify the percentage of time that a building's environment falls outside an expected thermal comfort zone, can help address the comfort trade-offs in building design and operation. Practitioners were polled on exceedance use in practice and comfort models and exceedance metrics were analysed: several comfort standards using EnergyPlus simulations of a mixed-mode building with radiant cooling in California's 16 climate zones. Results indicate that comfort model choice significantly influences predicted exceedance. Exceedance using PMV-PPD and the adaptive comfort models from ASHRAE Standard 55, EN 15251, and the Dutch NPR-CR 1752 frequently differed by 10 percentage points, often with 2–4 percentage points across the adaptive models. Yet, recommended exceedance limits often fall between 3% and 5% total. Exceedance predictions are also sensitive to uncertainties in predicted neutral comfort temperatures and variations in building envelope performance, solar heat gain, thermal mass, and control precision. Future work is needed to characterize comfort better in support of improved comfort modelling, exceedance targets, building design and building operation, and the development of related codes and standards.Les immeubles en mode mixte font intervenir un éventail de systèmes allant d'un chauffage, d'une ventilation et d'une climatisation étanches à une ventilation 100 % naturelle, mais l'on sait peu de choses sur ce qu'attendent et ressentent leurs occupants en matière de confort. La métrologie relative aux dépassements de seuils, qui quantifie le pourcentage de temps pendant lequel l'environnement d'un immeuble se situe hors d'une zone de confort thermique attendue, peut aider à traiter les compromis en matière de confort dans la conception et l'exploitation des immeubles. Des professionnels ont été interrogés par sondage sur l'utilisation des dépassements de seuils dans la pratique, et les modèles de confort comme la métrologie relative aux dépassements de seuils ont été analysés pour plusieurs normes de confort en utilisant les simulations EnergyPlus d'un immeuble en mode mixte équipé d'un système de refroidissement par panneaux dans les 16 zones climatiques de la Californie. Les résultats indiquent que le choix du modèle de confort influe considérablement sur les dépassements de seuils prévus. Les dépassements de seuils utilisant les indices PMV-PPD et les modèles de confort adaptatif de la norme ASHRAE 55, de la norme EN 15251 et de la norme néerlandaise NPR-CR 1752 différaient fréquemment de 10 points de pourcentage, avec souvent 2-4 points de pourcentage sur les modèles adaptatifs. Néanmoins, les limites de dépassement recommandées se situent souvent entre 3 % et 5 % du total. Les prévisions de dépassement de seuils sont également sensibles aux incertitudes relatives aux températures de confort neutres prévues et aux variations en termes de performances des enveloppes des immeubles, d'apport de chaleur par insolation, de masse thermique et de précision des contrôles. Des travaux ultérieurs sont nécessaires pour mieux caractériser le confort afin d'appuyer les efforts d'amélioration de la modélisation du confort, des objectifs de dépassement de seuils, de la conception des immeubles et de l'exploitation des immeubles, ainsi que pour appuyer le développement des codes et des normes s'y rapportant. Mots clés: confort adaptatif normes de construction modèles de confort refroidissement dépassement de seuils mode mixte occupants sensibilité confort thermique

Energy and Buildings, 2002

International Journal of Biometeorology, 2001

Current thermal comfort standards and the models underpinning them purport to be equally applic... more Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of building, ventilation, occupancy pattern and climate zone. A recent research project sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, RP-884) critically evaluated these assumptions by statistically analysing a large database of research results in building comfort studies from all over the world (n=22,346). The results reported in this paper indicated a clear dependence of indoor comfort temperatures on outdoor air temperatures (instead of outdoor effective temperature ET* used in RP-884), especially in buildings that were free-running or naturally ventilated. These findings encourage significant revisions of ASHRAE's comfort standard in terms of climatically relevant prescriptions. The paper highlights the potential for reduced cooling energy requirements by designing for natural or hybrid ventilation in many moderate climate zones of the world.

International Journal of Biometeorology, 2001

Current thermal comfort standards and the models underpinning them purport to be equally applicab... more Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of building, ventilation, occupancy pattern and climate zone. A recent research project sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, RP-884) critically evaluated these assumptions by statistically analysing a large database of research results in building comfort studies from all over the world (n=22,346). The results reported in this paper indicated a clear dependence of indoor comfort temperatures on outdoor air temperatures (instead of outdoor effective temperature ET* used in RP-884), especially in buildings that were free-running or naturally ventilated. These findings encourage significant revisions of ASHRAE’s comfort standard in terms of climatically relevant prescriptions. The paper highlights the potential for reduced cooling energy requirements by designing for natural or hybrid ventilation in many moderate climate zones of the world.

Energy and Buildings, 1998

Energy and Buildings, 1994

ABSTRACT This paper describes the logic of a microprocessor-controlled thermostat termed ‘comfort... more ABSTRACT This paper describes the logic of a microprocessor-controlled thermostat termed ‘comfortstat’ to address the needs of temporary room occupants such as hotel guests while reducing energy consumption. The ‘comfortstat’ design grew out of a study of thermal comfort control in a luxury hotel in San Francisco, California, USA. Hotel guests frequently arrive from widely disparate climates and have high expectations of the thermal environment. Their short-term occupancy (for periods ranging from one day to several weeks) provides a unique challenge for thermal comfort control. We examined the hotel complaint log, collected detailed physical measurements of the thermal environment in typical hotel rooms, assessed the HVAC (heating, ventilating and air-conditioning) system capacity and response time, and surveyed 315 hotel guests over a five-month period. The results of this study led to the design of a thermostat control system (the ‘comfortstat’) that would solve the most serious problems. The ‘comfortstat’ integrates an infrared occupancy sensor, door switch, radiant temperature sensor, and control logic to optimize room conditions while ‘learning’ about the occupant's preferred comfort zone. This paper focuses on how the joint requirements of the guests and the hotel management guided the design of the ‘comfortstat’ for increased occupant satisfaction and lower energy use in the hotel. The concepts are completely generic and could be applied to the design of comfort systems for other types of short-term occupancy. We present control logic flowcharts and typical examples of the action of the hotel ‘comfortstat’ in response to data received from the physical environment and/or human input.

Energy and Buildings, 1996

Building Research & Information, 2013

The predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) are the most widely ... more The predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) are the most widely used thermal comfort indices. Yet, their performance remains a contested topic. The ASHRAE Global Thermal Comfort Database II, the largest of its kind, was used to evaluate the prediction accuracy of the PMV/PPD model. We focused on: (i) the accuracy of PMV in predicting both observed thermal sensation (OTS) or observed mean vote (OMV) and (ii) comparing the PMV-PPD relationship with binned OTS-observed percentage of unacceptability (OPU). The accuracy of PMV in predicting OTS was only 34%, meaning that the thermal sensation is incorrectly predicted two out of three times. PMV had a mean absolute error of one unit on the thermal sensation scale and its accuracy decreased towards the ends of the thermal sensation scale. The accuracy of PMV was similarly low for air-conditioned , naturally ventilated and mixed-mode buildings. In addition, the PPD was not able to predict the dissatisfaction rate. If the PMV model would perfectly predict thermal sensation, then PPD accuracy is higher close to neutrality but it would overestimate dissatisfaction by approximately 15-25% outside of it. Furthermore, PMV-PPD accuracy varied strongly between ventilation strategies, building types and climate groups. These findings demonstrate the low prediction accuracy of the PMV-PPD model, indicating the need to develop high prediction accuracy thermal comfort models. For demonstration, we developed a simple thermal prediction model just based on air temperature and its accuracy, for this database, was higher than PMV.

International Journal of Biometeorology, 2007

Office workers’ preferences for air movement have been extracted from a database of indoor enviro... more Office workers’ preferences for air movement have been extracted from a database of indoor environmental quality surveys performed in over 200 buildings. Dissatisfaction with the amount of air motion is very common, with too little air movement cited far more commonly than too much air movement. Workers were also surveyed in a detailed two-season study of a single naturally ventilated building. About one-half the building’s population wanted more air movement and only 4% wanted less. This same ratio applied when the air movement in workspaces was higher than 0.2 m/s, the de facto draft limit in the current ASHRAE and ISO thermal environment standards. Preference for “less air motion” exceeded that for “more” only at thermal sensations of −2 (cool) or colder. These results raise questions about the consequences of the ASHRAE and ISO standards’ restrictions on air movement, especially for neutral and warm conditions.

Building Research and Information, 2009

‘Mixed-mode’ refers to a hybrid approach to space conditioning that uses a combination of natural... more ‘Mixed-mode’ refers to a hybrid approach to space conditioning that uses a combination of natural ventilation and some form of mechanical ventilation and/or cooling. This study focuses on mixed-mode in buildings with operable windows (as opposed to natural ventilation through vents). By utilizing active cooling only when and where it is necessary, a well-designed mixed-mode building offers the potential to

Building Research and Information, 2011

Mixed-mode buildings operate along a spectrum from sealed heating, ventilation and air-conditioni... more Mixed-mode buildings operate along a spectrum from sealed heating, ventilation and air-conditioning to 100% naturally ventilated, but little is known about their occupants' comfort expectations and experiences. Exceedance metrics, which quantify the percentage of time that a building's environment falls outside an expected thermal comfort zone, can help address the comfort trade-offs in building design and operation. Practitioners were polled on exceedance use in practice and comfort models and exceedance metrics were analysed: several comfort standards using EnergyPlus simulations of a mixed-mode building with radiant cooling in California's 16 climate zones. Results indicate that comfort model choice significantly influences predicted exceedance. Exceedance using PMV-PPD and the adaptive comfort models from ASHRAE Standard 55, EN 15251, and the Dutch NPR-CR 1752 frequently differed by 10 percentage points, often with 2–4 percentage points across the adaptive models. Yet, recommended exceedance limits often fall between 3% and 5% total. Exceedance predictions are also sensitive to uncertainties in predicted neutral comfort temperatures and variations in building envelope performance, solar heat gain, thermal mass, and control precision. Future work is needed to characterize comfort better in support of improved comfort modelling, exceedance targets, building design and building operation, and the development of related codes and standards.Les immeubles en mode mixte font intervenir un éventail de systèmes allant d'un chauffage, d'une ventilation et d'une climatisation étanches à une ventilation 100 % naturelle, mais l'on sait peu de choses sur ce qu'attendent et ressentent leurs occupants en matière de confort. La métrologie relative aux dépassements de seuils, qui quantifie le pourcentage de temps pendant lequel l'environnement d'un immeuble se situe hors d'une zone de confort thermique attendue, peut aider à traiter les compromis en matière de confort dans la conception et l'exploitation des immeubles. Des professionnels ont été interrogés par sondage sur l'utilisation des dépassements de seuils dans la pratique, et les modèles de confort comme la métrologie relative aux dépassements de seuils ont été analysés pour plusieurs normes de confort en utilisant les simulations EnergyPlus d'un immeuble en mode mixte équipé d'un système de refroidissement par panneaux dans les 16 zones climatiques de la Californie. Les résultats indiquent que le choix du modèle de confort influe considérablement sur les dépassements de seuils prévus. Les dépassements de seuils utilisant les indices PMV-PPD et les modèles de confort adaptatif de la norme ASHRAE 55, de la norme EN 15251 et de la norme néerlandaise NPR-CR 1752 différaient fréquemment de 10 points de pourcentage, avec souvent 2-4 points de pourcentage sur les modèles adaptatifs. Néanmoins, les limites de dépassement recommandées se situent souvent entre 3 % et 5 % du total. Les prévisions de dépassement de seuils sont également sensibles aux incertitudes relatives aux températures de confort neutres prévues et aux variations en termes de performances des enveloppes des immeubles, d'apport de chaleur par insolation, de masse thermique et de précision des contrôles. Des travaux ultérieurs sont nécessaires pour mieux caractériser le confort afin d'appuyer les efforts d'amélioration de la modélisation du confort, des objectifs de dépassement de seuils, de la conception des immeubles et de l'exploitation des immeubles, ainsi que pour appuyer le développement des codes et des normes s'y rapportant. Mots clés: confort adaptatif normes de construction modèles de confort refroidissement dépassement de seuils mode mixte occupants sensibilité confort thermique

Energy and Buildings, 2002

International Journal of Biometeorology, 2001

Current thermal comfort standards and the models underpinning them purport to be equally applic... more Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of building, ventilation, occupancy pattern and climate zone. A recent research project sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, RP-884) critically evaluated these assumptions by statistically analysing a large database of research results in building comfort studies from all over the world (n=22,346). The results reported in this paper indicated a clear dependence of indoor comfort temperatures on outdoor air temperatures (instead of outdoor effective temperature ET* used in RP-884), especially in buildings that were free-running or naturally ventilated. These findings encourage significant revisions of ASHRAE's comfort standard in terms of climatically relevant prescriptions. The paper highlights the potential for reduced cooling energy requirements by designing for natural or hybrid ventilation in many moderate climate zones of the world.

International Journal of Biometeorology, 2001

Current thermal comfort standards and the models underpinning them purport to be equally applicab... more Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of building, ventilation, occupancy pattern and climate zone. A recent research project sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, RP-884) critically evaluated these assumptions by statistically analysing a large database of research results in building comfort studies from all over the world (n=22,346). The results reported in this paper indicated a clear dependence of indoor comfort temperatures on outdoor air temperatures (instead of outdoor effective temperature ET* used in RP-884), especially in buildings that were free-running or naturally ventilated. These findings encourage significant revisions of ASHRAE’s comfort standard in terms of climatically relevant prescriptions. The paper highlights the potential for reduced cooling energy requirements by designing for natural or hybrid ventilation in many moderate climate zones of the world.

Energy and Buildings, 1998

Energy and Buildings, 1994

ABSTRACT This paper describes the logic of a microprocessor-controlled thermostat termed ‘comfort... more ABSTRACT This paper describes the logic of a microprocessor-controlled thermostat termed ‘comfortstat’ to address the needs of temporary room occupants such as hotel guests while reducing energy consumption. The ‘comfortstat’ design grew out of a study of thermal comfort control in a luxury hotel in San Francisco, California, USA. Hotel guests frequently arrive from widely disparate climates and have high expectations of the thermal environment. Their short-term occupancy (for periods ranging from one day to several weeks) provides a unique challenge for thermal comfort control. We examined the hotel complaint log, collected detailed physical measurements of the thermal environment in typical hotel rooms, assessed the HVAC (heating, ventilating and air-conditioning) system capacity and response time, and surveyed 315 hotel guests over a five-month period. The results of this study led to the design of a thermostat control system (the ‘comfortstat’) that would solve the most serious problems. The ‘comfortstat’ integrates an infrared occupancy sensor, door switch, radiant temperature sensor, and control logic to optimize room conditions while ‘learning’ about the occupant's preferred comfort zone. This paper focuses on how the joint requirements of the guests and the hotel management guided the design of the ‘comfortstat’ for increased occupant satisfaction and lower energy use in the hotel. The concepts are completely generic and could be applied to the design of comfort systems for other types of short-term occupancy. We present control logic flowcharts and typical examples of the action of the hotel ‘comfortstat’ in response to data received from the physical environment and/or human input.

Energy and Buildings, 1996