Ask any building facility manager what the number one complaint is among building occupants and they will tell you that people are either too hot or too cold. Both LEED and Green Globes offer points for designing buildings that
address thermal comfort. Both rely on ASHRAE Standard 55 in establishing thermal comfort requirements. The standard outlines “the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space.” Designing a building that satisfies a majority of occupants the majority of the time is an elusive, if not an impossible, task. Some suggest that designing sealed buildings (necessary for control over a building’s thermal environment) results in a loss of connection with the outdoor environment. In a paper titled Thermal Boredom by Alison Kwok, one survey respondent writes:
“Occupants of some of the early passive solar houses experienced temperature variations that “were in tune with nature. I remember being in David Wright’s passive solar Sea Ranch house in California and it was colder than 50 degrees Fahrenheit (10 degrees Celsius inside) and we had to do jumping jacks to bring up the room temperature (and ours) to something approaching comfort and he was ecstatic about the variation in temperature.”
THERMAL BEIGE-STATE OF THE ART IN THERMAL COMFORT?
The ASHRAE 55 Committee has been tweaking the standard in acknowledgment that human beings are not all the same with regard to indoor conditioning preferences and that “the pursuit of uniformity” must give way to a more adaptive model. Factors such as gender, metabolic rate, clothing, and physical activity all contribute toward an individual’s thermal comfort in buildings. Incorporating “natural” ventilation and cooling strategies into buildings makes it even more difficult for designers to please the majority of occupants a majority of the time.
The term “majority” in LEED is defined as at least 80 percent but this definition has been removed from ASHRAE 55 in recently proposed addendum. The standard simply states that a majority of occupants must be addressed, and does not assign a numerical value (which means that now, I assume, “majority” means 51 percent or more). The standard now also recognizes air speed as a variable used to enhance thermal comfort, in addition to simply changing the air temperature.
In a 1980 publication Indoor Climate, author D.A. McIntyre introduces the term “thermal boredom” to describe what happens to people in indoor spaces that are designed to meet the requirements of standards, such as ASHRAE 55 and ISO 7730. He argues that people need sensory and physical stimulation and makes a case for counteracting thermal boredom with fluctuating interior temperatures.
“It can be argued that achieving a steady optimum temperature is akin to finding the most popular meal at the canteen and then serving it every day,” he says. “The canteen user wants not only variety but choice, and the two cannot be entirely separated.”
McIntyre suggests that we desire variations in our thermal environment, a concept that is often at odds with strategies traditionally employed in meeting requirements of ASHRAE 55.
GREEN BUILDINGS AND THERMAL COMFORT
The latest versions of LEED and Green Globes offer points for designing for occupant’s thermal comfort. LEED gives one point for meeting requirements of ASHRAE 55 and an additional point if the owner promises to conduct an occupant survey to verify that 80 percent of occupants are satisfied with thermal comfort of the building. Green Globes offers 10 points for meeting ASHRAE 55 requirements and an additional 10 points for incorporating Thermal Control Zones based on building type.
Designing a building to meet requirements stipulated in ASHRAE 55 is relatively straightforward, but verifying that a majority of the occupants are satisfied may not be. LEED attempts to solve this problem by offering a “verification” component for thermal comfort design with IEQ Credit 7.2 Thermal Comfort-Verification. This is a gimme point requiring only that an owner promise to conduct an occupant survey six to 18 months after the building has been occupied. The survey requires collection of “anonymous responses about thermal comfort in the building, including an assessment of overall satisfaction with thermal performance and identification of thermal comfort-related problems.” The owner must also “agree to develop a plan for corrective action if the survey results indicate that more than 20 percent of occupants are dissatisfied with thermal comfort in the building.”
The LEED Reference Guide directs users to the Center for the Built Environment for a sample survey that can be used to satisfy, according to the CBE Web site, IEQ 7.2 credit requirements. (To view the CBE sample survey, go to www.cbe.berkeley.edu/RESEARCH/survey.htm and click on “Demo the IEQ Survey.”) There are pages of questions for the respondent to answer, including:
To which direction do the windows closest to your workspace face?
Are you near a window (within 15 feet)?
Overall, does the office layout enhance or interfere with your ability to get your job done?
How satisfied are you with the colors and textures of flooring, furniture and surface finishes?
Overall, does your thermal comfort in your workspace enhance or interfere with your ability to get your job done?
But the only question that is asked that has anything to do with meeting the credit requirement, according to the LEED reference guide, is: How satisfied are you with the temperature in your workspace?
Respondents are presented with a seven-point scale from “very satisfied” (+3) to “very dissatisfied” (-3) with the center (0) signifying the neutral point. The total dissatisfied percentage is based on the number respondents who answer “dissatisfied” (any of the lower three point of the seven point scale, i.e., <0).
The corrective action plan triggered by a 20 percent dissatisfied survey result may include things such as control adjustments (e.g., temperature set points, schedules, operating modes), diffuser airflow adjustments, and solar control.
THE PLACEBO EFFECT
It’s been said that thermal comfort is 90 percent mental and 10 percent physical. Building owners and facility managers have known since the advent of HVAC that people’s minds can be the most powerful determinant of thermal comfort in buildings. So much so, in fact, that it is not uncommon to find nonfunctional thermostats, known as “dummy stats,” mounted on the walls of many commercial buildings. In a 2003 Internet survey conducted by Air-Conditioning, Heating & Refrigeration News (sister publication of Walls & Ceilings), 51 of 70 respondents answered yes to the question “Have you installed ‘dummy thermostats’?”
In an article titled “Top Low-Cost & No-Cost Energy Efficiency Tactics for Buildings,” 21 tips are provided to facilities managers which include things such as reducing after hours usage of HVAC and lighting, installing lighting occupancy sensors, and lowering the thermostat set point in winter months. Coming in at number 18 on the list is:
Providing a few dummy thermostats is good for allowing the perception of control for the tenant, which has been shown to improve productivity along with providing a comfortable working environment.
Designing buildings that are thermally comfortable for the majority of occupants is an ever-evolving pursuit. But is it a worthy pursuit? Are thermal comfort standards like ASHRAE 55 and ISO 7730 trying to do too much? Or the impossible? Should the pursuit of uniformity be the goal? Will corrective measures such as calisthenics and dummy stats be acceptable to the USGBC in satisfying IEQ Credit 7.2? If not, why not? Is it really necessary for a building to be designed in accordance with ASHRAE 55 or ISO 7730 in order to be thermally comfortable to building occupants?
Meeting prescriptive requirements for thermal comfort in buildings often requires solutions that cause excessive energy and resources use. Green buildings of the future will need better, more flexible standards. W&C