Substantial progress in our understanding of human response to thermal environments has been made since Standard 55- 1992, including the amendment 55-95a. Incorporating many of these advances, Standard 55-2004, Thermal Environmental Conditions for Human Occupancy, was recently published after completingfour public reviews and receiving approval by both ASHRAEand the American National Standards Institute (ANSI).

The standard specifies conditions of the indoor thermal environment that occupants will find acceptable. It is intended for use in design, commissioning, and testing of buildings and other occupied spaces and their HVAC systems, and for the evaluation of existing thermal environments. Because of the inherent variations in occupants’ metabolic rates and clothing levels, and because it is not possible to prescribe or enforce what these should be, this standard cannot practically mandate operating setpoints for buildings.

The two most important additions included in this new standard are an analytical method based on the PMV-PPD indices and introduction of the concept of adaptation with a separate method for naturally conditioned buildings. The adaptive model and several other changes are based on various ASHRAE sponsored research projects. This article provides an overview of the key features and limits of applicability of Standard 55-2004.

This paper discusses reassessment of indoor climate control in the context of current thermal comfort practice and research. We review the limitations of comfort models and standards with several examples. We examine how people's thermal sensation and preferences may be influenced by culture and climate and associated issues of thermal expectations and adaptation. Finally, we discuss how incorporating these factors into future comfort standards might yield more 'effective' indoor climate control.

This paper presents the results of an extensive literature review on the topic of thermal adaptations in the built environment. The adaptive approach to modeling thermal comfort acknowledges the thermal perception in 'real world' settings is influenced by the complexities of past thermal history and cultural and technical practices. An important premise of the adaptive model is that the person is no longer a passive recipient of the given thermal environment, but instead is an active agent interacting with the person-environment systems via multiple feedback loops. The thermal adaptation can be attributed to three different processes--behavioral adjustment, physiological acclimatization and psychological habituation or expectation. Both climate chamber and field evidence indicates that the slower process of acclimatization is not so relevant to thermal adaptation in the relatively moderate conditions found in buildings, whereas behavioral adjustments and expectations have a much greater influence. One of the most important findings from our review of field evidence was the distinction between thermal comfort responses in air-conditioned vs. naturally ventilated buildings, most likely resulting from a combination of past thermal history in the buildings and differences in levels of perceived control.

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.

Recently proposed revisions to ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, include a new adaptive comfort standard (ACS) that allows warmer indoor temperatures for naturally ventilated buildings during summer. The ACS is based on the analysis of 21,000 sets of raw data compiled from field studies in 160 buildings, both airconditioned and naturally ventilated, located on four continents in varied climatic zones. This paper summarizes this earlier research, presents some of its findings for naturally ventilated buildings, and discusses the process of getting the ACS incorporated into Std. 55. We suggest ways the ACS could be used for the design, operation, or evaluation of buildings, and for research applications. We also use GIS mapping technology to examine the energy-savings potential of the ACS on a regional scale. Finally, we discuss related new directions for researchers and practitioners involved in the design of buildings and their environmental control systems.

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 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.

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 control in a luxury hotel in San Francisco, California, USA. Hotel guests frequently arrive from widely disparate climates and have high expectation so 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, venting 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 'thermostat') what would solve the most serious problems. The 'comfortstat' integrates an infrared occupancy sensor, door switch, radiant temperature sensor, and control logical 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 hotel 'comfortstat' in response to data received from the physical environment and/or human input.