Occupant Response Measures Must Figure in Building Evaluation
Research, new metrics show the often overlooked relationship between energy efficiency and occupant comfort helps to define a truly high-performance building. Part 2 of a 5-part article.
To evaluate how well a building is achieving or sustaining its fundamental purpose, functional metrics of building performance must include measures of tenant or occupant responses to indoor environmental exposures. These metrics may be characterized as: 1) objective measures, which are obtained through clinical testing; and 2) perceptual and affective measures, which are obtained through surveys, questionnaires, and interviews.
Measures of occupant performance are also essential in evaluating how well a building is achieving or sustaining its fundamental purpose. Occupant performance is typically expressed in terms of measurable and controllable parameters and values related to the function provided in the indoor environment. Examples of these metrics are: number of phone calls processed per unit of time, number or frequency of absences from the workspace, frequency or percentage of nosocomial infection rates, and percentage of increase in student achievement. Occupant performance data are obtained either through occupant interviews and surveys (i.e., self-reporting) or by independent measures of performance.
Traditional measures of facility productivity are often confused with measures of occupant performance. Whereas occupant performance assesses functional action or occupant behavior in the indoor environment, productivity is a transformed economic metric of occupant performance. It includes metrics such as cost of salaries and wages for substitute workers due to sick leave; lost revenue due to absence of workers; or direct and indirect health-care costs due to worker illnesses.
Fundamentally, these metrics do not provide information on the effectiveness of the energy consumed in buildings to provide for acceptable human responses, occupant performance, or productivity. Occupant acceptability is a primary attribute that is independent of the building's function. However, this measurable attribute can also be correlated with exposure attributes that vary for specific building functions. The measured values of occupant acceptability can also be compared with design criteria, building codes, and design standards.
The effectiveness of the energy used to provide for the fundamental purpose of the building can be evaluated by establishing a "Figure of Merit" (FOM), which combines energy use and occupant response data. An example of such an FOM is the ratio of the EUI to the percentage of occupants whose average response is that the overall indoor environment in their workplaces is "acceptable" (i.e., OA).
Another similar example is the ratio of the EUI to the percentage of occupants whose average response is that the temperature (or illumination level, sound level, or odor perception level) at their workplaces is acceptable. Of these FOMs, the overall "Acceptability Index Value" (AIV), defined as EUI/OA, offers an opportunity to increase the sensitivity of building performance metrics by evaluating the effectiveness of the annual energy used per percentage of overall occupant acceptability results. A lower AIV indicates that energy is being used more effectively to achieve occupant satisfaction. Similar and incrementally more sensitive AIVs can also be derived for other specific attributes (e.g., thermal, lighting, air quality, and acoustics).