The Truth About Thermal Comfort: Why Windows Matter
Now that summer will soon be upon us, a great war will be waged in office buildings across the country. Some will say the building is too cold, some will say it’s too hot, but both will agree they’re uncomfortable. The issue of thermal comfort (and lack thereof) continues to be a factor when designing and building new construction.
Thermal comfort is key for productivity, energy, and performance. In the March 2018 Edition of USGlass, Metal & Glazing Magazine, Mark Silverberg and Helen Sanders laid out key facts about thermal comfort. Check out the full article by subscribing to the USGlass Magazine, but here are the key takeaways:
Assessing Thermal Comfort
Thermal comfort is highly subjective. There are many factors that contribute to thermal comfort, including:
- Air speed
- Level of Activity
- Clothing Weight
- Temperature of Surrounding Surfaces (Radiant Temperature).
ASHRAE Standard 55 “Thermal Environment Conditions for Human Occupancy” specifies conditions for acceptable thermal environments in buildings and considers all these factors. However, thermal comfort is judged by the percentage of the population that’s predicted to be uncomfortable – “acceptable” comfort is generally when 80 percent of the population is predicted to be comfortable.
The Impact of Windows
Silverberg and Sanders go on to emphasize the importance of windows in thermal comfort. They argue that connective currents near cold windows are a key factor in thermal comfort:
The cold window surfaces cool adjacent air. This cooled air then falls downward and is replaced by warmer air, which is also then cooled by the window and falls, and so on. These currents (downdrafts) manifest themselves to occupants as cold drafts and are often mistake for air infiltration.”
However, there are ways to combat this effect. High-performance windows can drastically improve thermal comfort to bring it into that acceptable 80% comfort range mentioned earlier. Architectural firm Payette recently developed an online calculator to determine thermal comfort and discovered that high-performance windows faired significantly better. A person would have to move more than 7 feet away from the poorest poor-performing window to be comfortable, but they would only need to move 2 feet away from the highest-performing window.
Clearly, thermal comfort is still an important consideration for architects and builders alike.