Mike Woolsey
2021-09-01 02:29

Comfort concepts for the built environment

From an investment standpoint, occupant comfort is valuable, and investors are giving comfort more attention. In “A Surprising Way to Cut Real Estate Costs”, Jones Lang Lasalle (2017) reported that on a per-square-foot basis, companies typically spend 10 times as much on rental costs and 100 times as much on wage costs per year than they do on utilities. The report cites an example, “where a 10% increase in energy efficiency would yield $0.30 savings per square foot and a 10% decrease in rent would save $3.00, a 10% gain in productivity is worth $30.” Comfort, then, should demand the attention of the building design and operating team in order to optimize space occupancy rates and worker productivity. More often, however, design and operating teams are focused on reducing overall first cost, placing little or no value in occupant comfort.

Comfort isn’t just nice to have – it is a condition that humans value yet infrequently experience while indoors. The building type doesn’t matter.

Figure 1 Occupants reporting dissatisfaction with their indoor environment (Huizenga)

According to one study[1], 34,000 building occupants in 215 buildings in US, Canada, and Finland were satisfied with their thermal comfort in only 11% of the buildings surveyed. In the same survey, occupants rated air quality as only somewhat better, with 26% of buildings providing occupant satisfaction. With respect to thermal comfort and air quality performance goals set out by standards, most buildings appear to be falling far short. Occupant surveys offer a means to systematically measure this comfort performance, and also to provide diagnostic information for building designers and operators.

One such comfort study[2] by researchers at University of California’s Center for the Built Environment found that of more than 90,000 respondents from approximately 900 buildings, a “total of 68% of the respondents are satisfied with their workspace. Satisfaction is highest with spaces’ ease of interaction (75% satisfied), amount of light (74%), and cleanliness (71%). Dissatisfaction is highest with sound privacy (54% dissatisfied), temperature (39%), and noise level (34%).” They also found that “roughly two-fifths of building occupants think acoustical quality and temperature interfere with their ability to get their job done.”

Poor thermal comfort can have direct effects on occupants, including nausea, fatigue, headaches, etc. According to European research, the indirect effects of poor thermal comfort can also be measured: “Thermal comfort is ranked by building occupants to be of greater importance compared with visual and acoustic comfort and good air quality. It also seems to influence to a higher degree the overall satisfaction with indoor environmental quality compared with the impact of other indoor environmental conditions.”[3]

Research also shows that comfortable indoor environments can be beneficial to occupants. According to Razjouyan, et al, “Those who spent the majority of their time at the office in conditions of 30%‐60% RH experienced 25% less stress at the office than those who spent the majority of their time in drier conditions. Further, a correlational study of our stress response suggests optimal values for RH may exist within an even narrower range around 45%.”[4]

A traditional benchmark for comfort is the setpoint – the design conditions for the building. A setpoint can be any point that defines dry-bulb temperature and humidity, for example 72 degrees F at 50% relative humidity. At these conditions, comfort may be achieved by people in summer (light) or winter (heavy) clothing. This single setpoint condition is extremely precise, therefore would be expensive to control in most indoor spaces. And in reality, different people are comfortable in different conditions. Occupied spaces therefore are best defined to operate within a controllable range of temperatures and humidities.

[1] Huizenga, Charlie & Abbaszadeh, Sohiel & Zagreus, L & Arens, Edward. (2006). Air quality and thermal comfort in office buildings: Results of a large indoor environmental quality survey. HB 2006 – Healthy Buildings: Creating a Healthy Indoor Environment for People, Proceedings.

[2] 2. Graham, L. T., Parkinson, T., & Schiavon, S. (2021). Lessons learned from 20 years of CBE’s occupant surveys. Buildings and Cities, 2(1), 166–184. DOI: http://doi.org/10.5334/bc.76

[3] 1. Frontczak M, Wargocki P. Literature survey on how different factors influence human comfort in indoor environments. Build Environ. 2011;46(4):922-937.

[4] Razjouyan J, Lee H, Gilligan B, et al. Wellbuilt for wellbeing: Controlling relative humidity in the workplace matters for our health. Indoor Air. 2020;30(1):167-179. doi:10.1111/ina.12618

Occupant Comfort Control using demand-control ventilation and boost mode

ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy defines Thermal Comfort as that condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation. ASHRAE 55 provides building designers with a range of target values for temperature, thermal radiation, humidity and air speed. Buildings designed to operate within these ranges are expected to operate so that most occupants will experience thermal comfort. The chart nearby shows comfort conditions for a range of temperatures, humidity levels, and type of clothing worn by the occupants. Some generalizations from the chart include a maximum comfortable indoor relative humidity of over 80% when temperatures are low and 50% when temperatures are high. Air speed introduces another dimension not shown on this chart but discussed further below. Occupant health and building resilience are not part of the stated purpose of ASHRAE 55, however, so project specifiers must inform comfort design conditions with other industry guidance.

Cover Photo: Photo of Betances Residence, source https://cookfox.com/news/nyrej-breaking-ground-begins-100-million-passive-house-project-betances-residence-designed-by-cookfox-architects/

Figure 2 ASHRAE Standard 55 target comfort range

ANSI/ASHRAE Standard 160-2016 (Criteria for Moisture-Control Design Analysis in Buildings) specifies a maximum indoor relative humidity of 70%. But this value can be as low 50% or lower, depending on a number of variables including outside air and exposure conditions and type of mechanical equipment specified.

Design teams must then consider current industry recommendations when selecting upper and lower limits on indoor humidity, to support human health, building resilience and comfort.

An additional consideration when designing for occupant comfort is the air speed. The reader has probably experienced discomfort when inside a building with excess air velocity. The author has! Buildings designed for temperature and humidity control can still be deemed uncomfortable if the air speed is too high. ASHRAE 55 provides for analysis tools to understand this relationship. Usually, lower air speed is better. [1]

When occupant comfort is a design goal, specifiers must then consider and establish the comfort range which provides the desired building resilience and occupant health.

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[1] A convenient tool for evaluating indoor comfort is the CBE Thermal Comfort Tool, found online.

AHRI, balanced flow, casing leakage, continuous ventilation, cross-contamination, ERV, heat recovery effectiveness, Passive House, PHI, and specific power