Thermal Comfort Standards: Myth #1 "Flat-line"
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
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.
Thermal Comfort: Indeed a Condition of Mind (in simple
Thermal Comfort: Everyone Wants It but Few Know the ASHRAE
Titles, Purposes and Scope of ASHRAE 55 Thermal
Environmental Conditions for Human Occupancy
Residential Buildings Resources
Thermal Comfort Standards: "Flat-line"
Myth #2 ASHRAE 55 Thermal Environmental Conditions for Human
Occupancy is for commercial spaces only.
Myth #3 ASHRAE 55 Thermal Environmental
Conditions for Human Occupancy is too complicated for
findings, conclusions, or recommendations expressed in this
post are those of the author and do not necessarily reflect the
views of ASHRAE.