Energy Vanguard Blog

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

Posted by Allison Bailes on Wed, Mar 28, 2012

GUEST POST: As the Affordable Comfort conference kicks off today, it's appropriate to take a look at what comfort is and how we construct buildings to have the best shot at getting it. Robert Bean is an engineer in Calgary who's full of knowledge and wisdom on the topics of building science and HVAC, especially radiant heating. In addition to having all kinds of credentials and honors, he's the editor of a great website called Healthy Heating, which you really should check out. In this guest post for the Energy Vanguard Blog, he discusses the ASHRAE standard on thermal comfort. Pay attention, because he makes a statement toward the end that, I believe, could lead to a great shift in our thinking about buildings.

thermal comfort ashrae standard 55 robert bean recliner

Let me start by suggesting that one would think that an industry with its roots grounded in thermal comfort, could roll the definition of thermal comfort right off its tongue like an old Frank Sinatra classic. I mean this should not be difficult to do right? It seems almost obvious that someone who sells comfort equipment or designs HVAC systems for comfort or repairs buildings to be more comfortable should not have to think about what it takes to be comfortable right?

Unfortunately, if you assembled a thousand people from the professions of HVAC contracting, energy auditing, construction, engineering, interior design, architectural, and manufacturing in an exam hall and asked them only one question, that being to list the 10 key elements of an industry thermal comfort standard, approximately 30 individuals would pass. How do I know that? Because I’ve been asking that question in classes for over a decade and typically only 3% get it right and of these only half of them own a copy of ANSI/ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy.

The purpose statement from this standard is, “to specify the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space.” This standard is as equally resourceful as other ASHRAE standards and was first published 1966 – that would be almost 37 years before ANSI/ASHRAE Standard 62.2 (Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings) came unto its own. 

So let me take this moment to ask a few basic questions: Do you provide products or services related to thermal comfort? If so, could you right now explain ten key elements of thermal comfort? If you do promote thermal comfort, do you own a copy of ASHRAE Standard 55? If not, why not? I’m always intrigued by the answers I get. Most people don’t even know the document exists.

Along this line of questioning, how many consumers and their service providers believe comfort is defined by a numerical thermostat setting? If so, why do we have color-coded temperature controls in cars and on plumbing fixtures? Is comfort provided by high efficiency furnaces? If so why do people still complain about discomfort with the newest of appliances, especially in origami homes constructed essentially of glass? Is indoor air quality a requirement of thermal comfort or thermal comfort a requirement of indoor air quality? If so, can you explain all the thermal comfort complaints in leaky homes or how it is that you can sitthermal comfort in an easy chair back in your granddad’s La-Z-Boy™, tipping back your favorite brew, feeling all warm and cozy inside whilst inhaling radon gas, VOCs, or carbon monoxide?

The latter of these questions are definitively rhetorical and stated only to point out that neither air quality nor thermal comfort serve as proxies for each other. In fact, ASHRAE 62.2 states the standard does not address thermal comfort, referring users to ASHRAE Standard 55. Likewise, ASHRAE Standard 55 states that the standard does not address indoor air quality.

These questions should get you to start thinking about what thermal comfort really is. Now here’s mind-blowing part: According to indoor environmental ergonomic definitions, thermal comfort is (wait for it) a “condition of mind.” That’s right – it’s in your head and your client’s head and because all heads are not alike (unless you’re in the club of medicinal marijuana licensees), thermal comfort is and always will be a subjective perception.

Ultimately one of the difficulties in discussing thermal comfort is that this definition of “condition of mind” sits, "at the crossroads of physics, physiology, psychology, culture, and climate (Solomon, 2011);" and as I like to point out, it does so amongst a competitive industry driven by public relations, marketing, and sales teams all offering products and services related to a term that it doesn’t really understand nor can it accurately define.

In the space allotted I’ve not gone into the exhaustive details of thermal comfort but I have provided in the reference section below numerous free resources for you to study at your leisure, including a link where one can purchase the ASHRAE standard; in a nutshell the ten elements for consideration when addressing thermal comfort are shown in the accompanying table.

thermal comfort ten factors robert bean ashrae standard 55

Most are familiar with “dry bulb temperature,” that being what 99.99% of all thermostats measure and readers of the Energy Vanguard Blog should now be familiar with “mean radiant temperature” from Allison’s infamous article, Naked People Need Building Science, but the others are equally imperative to understand when establishing conditions for thermal comfort. When all are considered, it points out why the typical thermostat is a poor “thermal ambassador” to an HVAC system since most fail to perceive what the occupants perceive.

As I wind down this post, I want to point out one of the principles that indoor climate engineers understand full well – there exists an intimate relationship between building performance and that “condition of mind” and ultimately HVAC must start with the choice in architectural systems where energy consumption and system complexity is inversely proportionate to the performance of the enclosure. As David Butler pointed out in his excellent guest post, the enclosure should do the bulk of the thermal comfort work.

In support of this principle, I have stated on several occasions that if building codes dropped the reference to controlling air temperatures and switched the requirements to controlling mean radiant temperature, building performance specifications would have to change overnight. Bad buildings have low MRT’s in winter and high MRT’s in summer; this contributes to large differences in the vertical air temperature; creates excessive drafts and increased radiant asymmetry. Bad buildings also have uncomfortable floor temperatures and are challenged to maintain reasonable levels of humidity.

I believe once you read and digest the content below (linked for convenience), you will be motivated to purchase the ASHRAE standard and embrace its messaging as it relates to improving building enclosures and reducing energy demands for conditioning people…because at the end of the day people don’t feel the heat loss or heat gain of the building, they feel the heat loss and heat gain within their bodies and this will effect a “condition of mind”, that being our individual perceptions of thermal comfort.


Copyright © Robert Bean, R.E.T., P.L.(Eng.)

The views and opinions expressed in this post are strictly those of the author and do not necessarily reflect the views of The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE).


Photo by stevendepolo from, used under a Creative Commons license.

Tags: comfort, building science, heating & cooling