Imagine two houses on the same street: one built in the 1950s and the other in the 1990s. There are no trees or other shade. The air conditioning units are identical, recently replaced and working perfectly. Identical thermostats are set to 82°F (27.8°C).
When the temperature outside is 110 F (43.3 C), a home in the 50s will likely feel at least 10 F (5.6 C) warmer indoors, even with the same air temperature.
Why?
The answer has to do with radiant heat. Radiant heat is what keeps you toasty at a campfire on a cold winter night. Fire does not warm the air much; Instead, like the sun, most of a fire’s heat is transmitted via invisible waves directly from the campfire to your body.
In the radiant heat of the Arizona sun, the surface temperature of the uninsulated beam roofs in my house, which is one of… 41,000 were built In Tucson during the post-World War II era, it could reach over 100 degrees Fahrenheit. Single-pane steel windows register 122 F, and uninsulated concrete walls are no cooler.
Inside my house on triple-digit days, it can feel like I’m standing near a campfire, even with the air conditioner roaring to maintain 75 degrees. When the system collapses, as it did during… Long-lasting heat wave of 2023When the temperature in Phoenix reaches 110 degrees Fahrenheit every day for weeks, temperatures rise dangerously quickly. Without air conditioning, hot surfaces plus the swirling air from the ceiling fan become like home Feels like an air fryer.
Air temperature: an incomplete indicator of comfort
While people used to think about how to dress, air movement, temperature, and… moisture On comfort, there are two lesser-known metrics that help explain how comfortable they feel inside a home:
- Average radiant temperature. This is the average temperature of all the surfaces surrounding us: ceiling, windows, walls, floor. For radiant heat to transfer between an object and a human body, it needs an uninterrupted line of sight, so open ceilings and windows have a significant impact on the radiant temperature that occurs in a particular location in the home.
- Operating temperature. This can be approximated by calculating the average radiant temperature and the average air temperature in the room. Other operating temperature calculations take into account the effects of air movement, humidity, and additional variables. severely Describe how comfortable you feel It is determined by Radioactive environment.
Unfortunately, as a construction world Robert Bean (No relationship) “An entire industry of manufacturers, suppliers, builders and dealers incorrectly equates thermal comfort with air temperatures,” he says. The result is that most people are completely oblivious to what makes a space feel uncomfortable or uncomfortably hot.
On a hot, sunny day, good insulation and double-paned windows slow heat transfer enough for air conditioning to keep the average radiant temperature inside the building within a few degrees of the air temperature.
However, in an uninsulated building, like my house, or in some older public housing projects in Phoenix, the high average radiant temperature can push the operating temperature over 90 degrees, even with the thermostat set to 75. When Surface temperature: If the temperature exceeds our skin temperature, heat will begin to radiate from the hot surface to the body, causing heat Heatstroke is more likely.
While the exact threshold at which overheating becomes dangerous is still debated, most people agree that 90 degrees Fahrenheit is too warm to provide comfort.
Hot roofs are the reason behind small buildings, such as mobile homes, tiny homes, Shipping containersGarages converted into apartments often feel uncomfortable regardless of the thermostat setting. Smaller structures expose occupants to three, four or even six decks with the exterior exposed to the sun and hot outside air. More warm surfaces, more discomfort.
Cooler surfaces, more comfort
If you live in an uninsulated building and don’t mind using more electricity, you can set your thermostat to a lower level. But if the average radiant temperature is high, a two-degree drop in air temperature will feel like only one degree, and those hot surfaces will still make you uncomfortable.
Add insulation to your roof and replace single pane windows with double pane units Low Emissivity (Low E) glass. It can help reduce the average radiant temperature and your energy bills. They’re expensive improvements, but they’re new federalism Tax credits And Upcoming discountswhich would be managed by individual states, could help.
Trees, awnings, and outdoor shade can also reduce average radiant temperatures by blocking direct sunlight. but, Glass is a poor insulatorso in very hot climates, single-pane windows that are completely protected from the sun can become uncomfortably warm.
Adding a curtain inside and keeping it closed can help reduce the average radiant temperature because the curtain will be closer to the air temperature than the glass.
What about tenants in old buildings?
Tenants in older, uninsulated buildings are often less able to afford large energy bills, and landlords may be unable or unwilling to make expensive improvements. To make matters worse, Older air conditioning systems use two to three times more energy As newer units deliver the same amount of cooling.
Because creating a comfortable operating temperature requires setting the thermostat lower, an HVAC system in an uninsulated building must run longer and harder, using more energy and increasing cost. And the costs of discomfort aren’t just financial: hot buildings have that, too Negative effects on health And productivity.
Millions of Americans now live in places where… Cooling is the only thing preventing mass casualties. in phoenix, City code requires rental units cooled by air conditioning To maintain the temperature no higher than 82 F, measure 3 feet above the floor in the center of the room. Unfortunately, the code does not specify whether 82 degrees is the value or not operative temperature or air Temperature.
That one word makes a world of difference.
In an old, uninsulated building similar to my own — or, in what would be a worst-case scenario, a sun-baked southwest unit on the top floor of an uninsulated concrete high-rise — a safe air temperature seems like 82 degrees Celsius. F can easily mask dangerous operating temperatures of 96°F or higher.
The key to better design
As a professor in Architecture and building sciencesI believe the current byzantine building codes and rental rules could be greatly improved for convenience through Regulating the average radiant temperature Instead of air temperature. Large chunks of code can be eliminated by requiring internal surfaces that are easy to scale inexpensively Infrared heatis kept within a comfort range above 60 degrees and below 85 degrees.
For more comfortable buildings, architects and engineers can apply Simple and well-established principlesSuch as natural ventilation, shading, proper insulation and windows suitable for the climate. Keeping the heat out in the first place means we don’t have to spend as much energy cooling. Research shows that these measures can make us safer, too Keeping buildings cooler for longer In summer power outages.
The happy result: homes and other buildings that are not only comfortable, but also safer and more affordable to operate.
Jonathan Bean He is an Associate Professor of Architecture, Sustainable Built Environments and Marketing at the College University of Arizona.
This article was republished from Conversation Under Creative Commons license. Read the Original article.
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