ASHRAE-Standard-55 - Page 068

Extracted Content

b. Long-Term Analyses (Representing Time Periods Such as Season or Year): In an occupant satisfaction

survey, thermal environment questions apply over time (three to six months or more). The survey includes diagnostic questions to identify sources of dissatisfaction. Point-in-time surveys may be repeated over time to obtain a long-term record of comfort. Because occupants have other responsibilities and limited time, repeated surveys must be very short and quickly completed.

1. Measures from Occupant Satisfaction Surveys i. Thermal satisfaction scale (“very satisfied” to “very dissatisfied”)
2. Criteria for Passing i. From neutral (0 scale unit) to +3 (Votes below this range generally comprise 40% of a building’s total votes in the CBE survey benchmark database.) ii. Scale units –1 to +3 (Votes below this range generally comprise 20% of a building’s total votes in

the CBE survey benchmark database.) 3. Branching Dissatisfaction Questions (Count Responses and Tally by Category) i. Used to identify and correct problems. Analysis involves documenting the improvements made, resurveying the areas in which the problem occurred, and tallying the differences in responses obtained before and after the improvements. 4. Accumulated Scores from Repeated Point-in-Time Surveys i. If point-in-time surveys can be repeated sufficiently, the distribution of accumulated votes can be used to evaluate long-term comfort in the building. Such repetition becomes feasible, with short computer applications available to occupants via desktop and mobile devices.

L3.2 Analysis Based on Measurements of Environmental Variables. Environmental measurements are linked to occupant comfort through comfort models. Two comfort models, PMV and adaptive, are specific to mechanically conditioned and naturally ventilated buildings, respectively. Some mixed-mode buildings include a combination of both comfort model types. Active investigation is underway into how the two models apply in these cases.

The following measures and criteria underlie the documentation of comfort performance based on physical environmental measurements.

L3.2.1 Point-in-Time (Short-Term) Analyses

a. PMV Model

1. Measures: PMV heat-balance model prediction of thermal sensation and satisfaction from environmental measurements are described in Section 5.3 (including air movement extension in Section 5.3.4). Limits to local thermal discomfort are described in Section 5.3.5, and rates of temperature change are described in Section 5.3.6.
2. Criteria for Passing: –0.5 to +0.5 on the PMV scale, inclusive. This represents an estimated 90% satisfied with the thermal environment. Expressed as a comfort zone on a psychrometric chart, this represents a temperature range of 3 K to 5 K (5°F to 8°F), depending on clothing level and humidity. b. Local Thermal Discomfort Limits: Local thermal should, by itself, not exceed the limits prescribed in

Section 5.3.5. At a minimum, an assumed 10% dissatisfaction caused by local discomfort is added to PMV-predicted discomfort to obtain the overall thermal dissatisfaction of an environment. Solar radiation on occupants in neutral or warm conditions should not exceed 10% of outdoor solar radiation incident on the window. The best-practice upper limit is 5%. c. Adaptive Model (Section 5.4): The adaptive model is an empirical model of adaptive human responses

to environments offering operable window control. The comfort zone on a given day is dependent on a running mean of previous outdoor air temperatures to which people continuously adapt over time.

1. Measures i. Air temperature indoors ii. Running mean of outdoor air temperature, defined in Section 3 as the prevailing mean outdoor air

temperature tpma  out  2. Criteria for Passing i. An environmental condition passes if it is within the 80% boundaries predicted by the adaptive model. d. Limits to Rate of Environmental Change

1. Measures i. Operative temperature to rate of change ii. Instances of rate-of-change exceedance within a defined time period

66 ANSI/ASHRAE Standard 55-2023