In the PA video under Section 4.1, “Effect of Building Design on Occupants,” and in the 1st PA mock exam question, the comfort zone boundary is delineated based on wet-bulb temperature. The PA mock exam explanation states that the comfort zone should be between 67°F and 75°F, but the correct answer on the chart indicates that this boundary is based on wet-bulb temperature. However, as per online references and the Mechanical and Electrical Equipment references, comfort zone delineation is typically based on dry-bulb temperature between 68°F and 80°F, as shown below.
Could you clarify how to properly delineate the comfort zone on a psychrometric chart as per ASHRAE, considering all chart parameters such as wet/dry-bulb temperature, relative humidity, and clothing insulation (Clo)?
Hey @elie! ASHRAE does not delineate the comfort zone using wet-bulb temperature. On a psychrometric chart, the ASHRAE 55 comfort zone is defined by dry-bulb (or operative) temperature and humidity, with clothing level, metabolic rate, and air speed determining the exact shape. Wet-bulb lines only intersect the chart and may appear near the comfort polygon, but they do not control the boundary.
For typical sedentary occupants wearing standard indoor clothing (about 1.0 clo), the ASHRAE comfort region generally falls in the high-60s to mid-70s°F range on the dry-bulb axis. That’s why the practice exam simplifies it as 67–75°F. Textbook ranges like 68–80°F are broader design guidelines, not the strict ASHRAE polygons.
So even if part of the shaded zone on the chart aligns with a wet-bulb line, the correct way to interpret the comfort zone—per ASHRAE—is still by dry-bulb temperature + humidity, adjusted for clo/met conditions. The practice exam is just presenting a simplified slice of that ASHRAE comfort zone.
Hope this helps!
Kiara Galicinao, AIA, NCARB
Product Coordinator Black Spectacles
Thank you, Kiara, for the explanation. However, in the mock exam, the comfort zone shown in green on the chart indicates a range of 75°F to 85°F on the dry-bulb vertical axis, which differs from the stated answer of 67°F to 75°F.
@elie Sorry for the delayed follow-up. I checked with our subject matter expert and he confirmed that the correct answer area in this question is based off of Building Construction Illustrated not MEEB, so we have updated the reference accordingly. Wet bulb is a better indicator of a comfort zone because it takes into account humidity, so it’s more akin to the ‘feels like’ temperature versus the actual temperature (which is the dry bulb temp).
