Heat wave

While we are on the subject of weather, just prior to the record-breaking rain storms, we had a brief heat wave with heat indexes climbing to 105 to 110 degrees – which got me thinking about freezing (being cold).

I don’t know about you, but I hate being frozen stiff on hot summer days the moment you walk into a grocery store, office, bank, or restaurant. When running errands, I go three or four times in and out of a store, from hot and humid to freezing cold, and I am worn out for the rest of the day.

During one of our heat wave days, I visited friends in their house that felt freezing too. I commented on it and was surprised to hear that their thermostat was set to 80 degrees. This reminded me that thermal comfort levels are a moving target.

What currently guides the level of air conditioning we are exposed to is the ASHRAE Standard 55-2004 (Thermal Environmental Conditions for Human Occupancy).

The recommended temperature ranges depend on a number of factors, including how much clothing we wear, which in turn depends on the exterior weather conditions.

The core range (meaning the least possible thermal discomfort) is at 77 to 79 degrees at low humidity levels and 74 to 75 degrees at higher humidity levels. Accepting some level of thermal discomfort, the range can be expanded from 71 to 83 degrees at low humidity levels and 67 to 80 degrees at higher humidity levels.

This always seemed to me to be an overly static approach to recommending thermal comfort levels, considering that we have a natural adaptation capacity to heat; i.e. 80 degrees can feel freezing during a hot summer day, whereas it can feel hot during a cool spring day.

Even the ASHRAE Standard acknowledges this limitation:

“… this standard only addresses thermal comfort in a steady state […]. As a result, people entering a space that meets the requirements of this standard may not immediately find the conditions comfortable if they have experienced different environmental conditions just prior to entering the space. The effect of prior exposure or activity may affect comfort perceptions for approximately one hour.”

Why not develop a more adaptive approach to thermal comfort levels, one that is based on a sliding scale acknowledging the relationship between outdoor and indoor temperatures?

That way we may be able to create more comfortable indoor environments (i.e. stop the freezing in mid-summer), which would be easier on our health and ultimately lead to less energy consumption because we are not air conditioning in excess any more.


About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

2 thoughts on “Heat wave

  1. I like your thinking. On a recent steamy day, I went into our neighborhood CVS, which was so overchilled that my sunglasses instantly fogged up. Of course, it felt doubly miserable to go back outside and readjust to the steam.

    On a similar note, I’m tired of needing to take a long sleeve shirt or jacket if I’m going out to the movies in summer or to a restaurant that may be overchilled. Even with that precaution, I sometimes end up freezing long before it’s time to leave. For years, I’ve been in the habit of keeping an office sweater, because office temperatures are set for guys in suits and I’m not wearing a suit.

    I have to wonder what the net effect would be on the environment and our health if controlled indoor temps were actually set to healthy temperatures, not extremes.

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