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Fundamentals of indoor environmental quality / thermal comfort and air quality solutions using radiant based HVAC

Myth #1
Myth #2
Myth #3

Thermal Comfort Standards: Myth #1 "Flat-line" Environments
Copyright (C) 2015, Robert Bean, R.E.T., P.L.(Eng.) All world rights reserved.

Thermal comfort has been getting a lot of press lately and though ASHRAE Standard 55 has been around since 1966 there is no shortage of people who are part of the “comfort business” who still, “just-don’t-get-it”.

One of the most sustained myths about comfort Standards is that they require a steady state “flat-line” environment. This mistaken perception goes against the science that the Standards are based upon and just illustrates the ignorance surrounding an industry based on keeping people thermally satisfied.

As I’ve noted at the 2015 Westford Symposium on Building Science and in a recent post on Green Building Advisor, “ASHRAE Standard 55 and ISO 7730 do not require a static monotonous environment”. There is in fact incredible flexibility as demonstrated in the “Graphical Method” which allows an operative temperature range between appx. 67F and 83F and up to 0.012 moisture ratio with no minimum; and air speeds up to 20 fpm again with no minimum. Plus the operative temperature can swing up to 6F over a four hour period. If that isn’t enough “give and take” for you, then users can employ the, "Naturally Ventilated Space Method" which allows occupants to open windows and doors or otherwise condition the space to their satisfaction with the outdoors - so long as you don’t try it in a February Fairbanks or a Phoenix summer. Nor can you use the outdoors if the building has a mechanical cooling system (an area under discussion within SSPC 55).  For total flexibility designers can apply the, "Analytical Method" where there are no maximums or minimums only combinations of 10 factors which results in ranges of comfort.

The operative word for all compliance paths is “range”, it is not and never has been a requirement for stagnant indoor thermal environments. I don’t know where this misconception comes from but it is a false understanding that has developed into a myth.  I’m going to be spending some more time busting thermal comfort folklore so if you have one that needs to be exposed – let me know.

Myth #1 busted.

Additional reading: 

  1. Thermal Comfort: Indeed a Condition of Mind (in simple terms) 

  2. Thermal Comfort: Everyone Wants It but Few Know the ASHRAE Standard 

  3. Titles, Purposes and Scope of ASHRAE 55 Thermal Environmental Conditions for Human Occupancy

  4. Residential Buildings Resources

  5. Myth #1 Thermal Comfort Standards: "Flat-line" Environments

  6. Myth #2 ASHRAE 55 Thermal Environmental Conditions for Human Occupancy is for commercial spaces only.

  7. Myth #3 ASHRAE 55 Thermal Environmental Conditions for Human Occupancy is too complicated for residential buildings

Note: Opinions, findings, conclusions, or recommendations expressed in this post are those of the author and do not necessarily reflect the views of ASHRAE.

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