ASHRAE-Standard-55 - Page 062
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All surveys should strive for a representative sample size and a high response rate across the occupied space in the building. If the objective of the survey is to assess an entire building or installation, an adequate sample size and response rate help lower the risks of generalizing a limited observation to the entire occupant population. Section 7.3.1 prescribes minimum response rates for surveys. It is possible that in operating buildings, the perceptions of nonrespondents may be less important than those of respondents who take the time to answer the questions.
Thermal environment surveys are invaluable tools for diagnostic purposes in existing buildings and facilities. As a diagnostic tool, the goal is not a broad-brush assessment of environmental quality but rather a detailed insight into the building’s day-to-day operation through occupant feedback. For such purposes, each response is valuable, regardless of the size or response rate of the survey.
There are two types of thermal environment surveys. In either type of survey, the essential questions relate to thermal comfort, but additional questions can help identify problems and formulate possible responses.
L2.1 Point-in-Time Surveys. Point-in-time (“right-now”) surveys are used to evaluate occupants’ thermal experience at a single point in time. Thermal comfort researchers have used these surveys to correlate thermal comfort with environmental factors such as those included in the PMV model: metabolic rate, clothing insulation, air temperature, radiant temperature, air speed, and humidity.
A sample point-in-time survey is included in Figure L-1. It includes a thermal sensation survey that asks occupants to rate their sensation (from “hot” to “cold”) on the ASHRAE seven-point thermal sensation scale. The scale units are sometimes designated “TSENS.”
It also asks, “How satisfied are you with the thermal environment?” with a scale of “very dissatisfied” to “very satisfied.” The satisfaction scale is a standard psychometric test in other disciplines and is best divided into seven scale units.
Sometimes, preference scales for temperature and air movement are also used (e.g., these scales are common in the comfort field study database found in ASHRAE RP-884, Towards an Adaptive Model of Thermal Comfort and Preference ):
“Prefer to be:” “cooler/no change/warmer” “Prefer”: “less air movement/no change/more air movement”
In order to use the results of a point-in-time survey to assess satisfaction with the thermal environment over time, the survey must be implemented under multiple thermal conditions and in multiple building operating modes. The difficulty of arranging multiple surveys in workplace environments usually limits the feasibility of using the point-in-time survey approach for assessing comfort over time. This limitation may diminish with the use of Web-based and mobile applications oriented toward building operation.
L2.2 Satisfaction Surveys. A second form of thermal environment survey, a satisfaction survey, is used to evaluate thermal comfort response of the building occupants in a certain span of time. Instead of evaluating thermal sensations and environmental variables indirectly to assess percentage dissatisfied, this type of survey directly asks occupants to provide satisfaction responses.
An example thermal satisfaction survey is included in Figure L-2. It asks occupants to rate their satisfaction with their thermal environment (from “very dissatisfied” to “very satisfied”) on a seven-point satisfaction scale. The percentage of occupants satisfied is calculated from seven-point satisfaction survey scores by dividing the number of votes falling between +1 and +3, inclusive, by the total number of votes. The percentage of occupants dissatisfied is calculated from seven-point satisfaction survey scores by dividing the number of votes falling between –1 and –3, inclusive, by the total number of votes.
The premise of the satisfaction survey is that occupants can recall instances or periods of thermal discomfort, identify patterns in building operation, and provide “overall” or “average” comfort votes on their environment. The surveyor may identify a span of time for the respondents to consider, and the occupants provide the time integration. Questions to identify the nature (causes) of dissatisfaction may be included in satisfaction surveys (e.g., source-of-discomfort questions in Figure L-2).
As the thermal satisfaction survey assesses a long time frame, it should be administered every six months or repeated in heating and/or cooling seasons. In a new building, the first thermal satisfaction survey may be performed approximately six months after occupancy, late enough to avoid assessing the effects of building commissioning but early enough to help identify long-term building problems that have escaped detection in the commissioning process.
The thermal satisfaction survey can be used by researchers, building operators, and facility managers to assess building system performance in new buildings, and to perform periodic postoccupancy evaluation in existing facilities.
60 ANSI/ASHRAE Standard 55-2023