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

Tune into the Edifice Complex Podcast by host Adam Muggleton and Robert Bean

Essay: How Can Auditors Use the ASHRAE 55 Standard? Part 1 Fundamentals

Copyright (C) 2018 Robert Bean, R.E.T., P.L. (Eng.)

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For a background study see: Which Comes First: Comfort vs Efficiency?

I’m sitting here on the balcony enjoying the summer evening, having just read a brochure from a major utility flogging the most current version of shiny new thermostats. Like most anglers, they’re fishing for new customers using these devices as bait. The brochure essentially reads, switch to our ‘comfort and control’ plan and receive your very own wiz-bang thermostat. The implication is for under a few hundred dollars the user might achieve…wait for it…both ’comfort’ and ‘control’. Just let that smokin’ hot deal reside in your head while I explain how these kinds of promotions have contributed to nationwide thermal comfort illiteracy. I’ve also just received from a colleague an article headline which essentially reads, “What are the recommended air temperature settings and what rights do you have if you’re uncomfortable?” Well let’s consider space air temperatures of 72F (22C)+/- are required by Codes and according to manufacturers you could achieve that with their Energy Star ‘comfort equipment’. But here’s the rub, where I’m from Codes say, “an objective of this Code is to limit the probability that, “…a person in the building will be exposed to an unacceptable risk of illness due to inadequate air quality, thermal comfort, and contact with moisture.” The operative phrase is, “risk of illness”, that’s Code talk for saying, if you’re uncomfortable but not ill as a result of (ala Jerry Seinfeld’s soup Nazi)…there is no complaint department for you. Which is why I’m about to share with you, (in my opinion) that all of this hyperbole involving free zippy stats and ‘comfort equipment’ and utility comfort programs and air temperature set points in Codes flies directly in the face of thermal comfort science.

Yes I just drew a big fat line in the sand. It is time we called industry to the mat on comfort because all the fancy utility leaflets and smooth talking wooers of warmth have only one objective (again in my opinion) - to sell equipment and services under the guise of ‘comfort’. Before you explode - follow along. Since the first of countless brochure started to show up in my mailbox not one, zilch, zero, notta a single sales pitch has focused on correctly establishing the indoor climate conditions necessary for people to sense and perceive the comfort the purveyors are promoting. If that were a false statement, the people behind these schemes would be incorporating into their glossy advertisements the ethos of ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy. At the very least they would have taken a class or two on the building and health sciences to understand what Prof. Bomberg et al meant when they said , “physics does not tell us how to integrate people with their environment."

So how can I be so cocky about this stuff? My position in this debate is founded in 15 years of public polling of professionals across North America. Here are the conclusions; 97% of those claiming to participate one way or another in the comfort industry either don’t know comfort Standards exists or can’t name them, and of the 3% that do only half of them are proficient in their application. It’s an incredibly shocking statistic when you consider what business we’re in. It’s even more alarming when one considers the statistics holds true for building scientists, architects, interior designers, engineers, energy auditors, HVAC equipment and building material manufacturers, distributors, builders, tradespersons, code officials and those employed by building programs, utilities and governments. If you want proof just ask any one of the thousands of people that have born witness to my polling techniques at lectures across the continent.

The short strokes are, the thermal comfort industry is illiterate about thermal comfort…full stop. Pretty bold statement you say…yes it is - but we, as a comfort collective, ethically shouldn’t move forward harvesting consumer dollars if our direction is based on naivety and falsehoods. It’s time we dealt in realities.
This is where Energy Auditors and the world of HVAC service providers come in. First you need to know one critical component to thermal comfort and this usually comes as a complete shock to those raised on the Holy Grail of regulating air temperature in spaces. In fact it’s an error in many industry training manuals. Here it is…when it comes to heat transfer from the human body, the medical textbooks, ASHRAE Handbooks and environmental ergonomic manuals are congruent - radiant heat transfer is the dominant function. According to the referenced medical textbook, radiant exceeds evaporation and convection by a factor of 3 and 4 respectively (Figure 2). So where is the epicenter of this absorption and release of heat? Why of course from the largest organ on the body, the skin. Coincidence? I think not considering the absorptivity (0.70+), and emissivity and of skin at 0.97 is greater than almost any other known substance, matte-black metals included. Our bodies have been engineered to have an intimate radiant relationship with our environments. So setting aside academic interests, let’s just say we don’t sense and perceive thermal comfort through our lungs and we don’t respire through our skin. Our thermal systems and air systems have separate physiological systems just as we have separate ASHRAE Standards for comfort (ASHRAE 55) and ventilation/air quality (ASHRAE 62.1/2, CSA F326). So let me ask a rhetorical question, who elected air temperature as the all-encompassing spokesperson for IEQ and the air based thermostat as the ambassador to the HVAC system? Both are legacy wrongs that need to be righted.

Figure 1 Air temperature and indoor air quality is not a proxy for indoor environmental quality (IEQ). The quality of the indoor environment is based on (from left to right) vibrations, odours, lighting quality, sound quality, air quality and thermal comfort.

Next big message…the myopic focus on air based equipment and controls which contributes and solely regulates air temperature might comply with the minimum requirements of Codes but as the default representative it is technically flawed through the lens of thermal comfort. As noted by the highly respected Rocky Mountain Institute, “comfort is incredibly important to building occupants, but the traditional air temperature-centric design approach used in buildings for decades is ineffective, inefficient, and expensive.”

If you still don’t get it…just ask yourself, how could air temperature adequately serve as a sole surrogate for thermal comfort when radiant represents approximately 60% of the body’s sensible heat loss?

Figure 2 when it comes to heat transfer from the human body, the medical textbooks, ASHRAE Handbooks and environmental ergonomic manuals are congruent - radiant heat transfer is the dominant function (60% of sensible). According to the referenced medical textbook, radiant exceeds evaporation/respiration and convection by a factor of 3 and 4 respectively.

If you’re still skeptical, this is currently what the UK’s Health and Safety Executive has to say on the matter, “…air temperature alone is neither a valid nor an accurate indicator of thermal comfort or thermal stress.” Furthermore using air temperature as the proxy for comfort sustains the ignorance when practitioners ought to know there are in fact four general factors, four localized factors and two personal factors that must be considered in thermal comfort analysis. These ten factors outlined in ASHRAE Standard 55 are like ingredients in a cake and when you get the fixings correct you will mostly get the correct results. To put brackets around this discussion let’s just say, using 72F (22C)+/- air temperature as the benchmark for comfort is like calling baking soda a muffin.

This is not a trivial matter for those promoting energy efficiency and enclosure and HVAC upgrades. Why? Because study after study show society isn’t doing upgrades exclusively to reduce energy consumption. Many if not the majority do them to improve comfort. For example, the 2015 Healthy Homes Barometer, stated, “Comfort is more appealing to people than energy efficiency”. In the same year, the Rocky Mountain Institute reported that, “70% of whole home performance customers cited comfort as a reason for their upgrade.” To put a third nail in the message, these reports were echoed by a recent 2017 study in Europe which stated, “…an increase in comfort was selected by the largest number of people as a renovation trigger (70%) “. To be fair there are studies which suggest energy is the reason people do upgrades. But even the most current study by ACEEE which has this implication also states that most household purchases are not made to, “save money” and cited ‘comfort’ and ‘health’ and “sustainability/environment” as the top non-saving benefits of upgrades.

Improving comfort means that discomfort was a pre-existing condition and where do you think that discomfort came from? I’m putting my two cents on poor enclosures that were conditioned by furnaces controlled exclusively by air based thermostats. Why? Because that describes the majority of homes built to Code in Canada and the United States. Homes being perceived as too hot in the summer and too cold in the winter is the subjective nature and genesis of discomfort. What we ought to be doing is educating industry and the public why and how this happens rather than implying that spanky air based thermostats or energy efficient equipment are the solutions to comfort and control.

Now go back and read that paragraph again. Ask, what do bad enclosures have in common? If all the energy auditors in North America contributed their thermographic images to a data base I could guarantee one would find the images support bad buildings have cold interior surfaces in winter and hot surfaces in summer even when the ‘smart thermostat’ says 72F (22C)+/- and the furnace is running at 97% efficiency. So let’s go back to that radiant thing because in comfort radiant is the big deal. What drives radiant transfer? Why of course the difference between surface temperatures and optical surface characteristics (emissivity, absorptivity, reflectivity). Specifically we are talking about the temperature differences between the skin and clothing on the human body and all the enclosure surfaces surrounding that person. With radiant transfer, winter time differentials extract body heat; it is the heat leaving the body which results in a cooling sensation. Summer time differentials supress body heat rejection; it is the heat retention which results in an overheating sensation. So how can we control radiant transfer between the occupant and enclosure? Well the core temperature of the human body and skin characteristics are essentially a fixed value, the only option (sans discussion on adaptive behaviour) is to control the interior surface temperatures of the enclosure. So how do we control room side surface temperatures? With appropriate window to wall ratios, window upgrades, external shading, reduced thermal bridging and increased insulation levels. Throw in the reduction in leakage which affects drafts, stratifications and humidity and what you have is the DNA for home performance. Cool eh?

Whether you realized it or not, efforts by auditors and HVAC service providers to reduce energy is actually rooted in human physiology and thermal comfort. If you truly care about reducing energy then this connection should make you ecstatic because the vocabulary of thermal comfort is accessible to everyone, way more so than the vocabulary of energy efficiency. In fact people are born with the vocabulary of discomfort whereas the language around energy is an academic exercise most people dread to take on. Message: improve for comfort and energy efficiency will follow.

So let’s set that discussion aside and get back to the mechanics of comfort and introduce the occupants into the study because people drive the basis for the very important term of, “Mean Radiant Temperature” or MRT. MRT describes the radiant experience an individual has as a result of all the inside surface temperatures in the room collectively affecting the body’s heat loss or retention. This next part is significant. Unlike air temperature (which will be measured by the thermostat usually at a fixed location), comfort analysis follows the person, ergo where the person goes so goes the MRT.

Consider a person in Northern Canada sitting with lighter clothing in a kitchen nook with their back to large triple pane argon filled windows in a home in Yellowknife, NWT. At -40F/C there is a high probability they would experience a chill even if the thermostat reads 72F (22C)+/-. This is because the inside surface temperature of the glass is likely 30F to 35F (17C to 19C) colder than mean skin temperature. This differential drives the negative effects of radiant transfer and radiant asymmetry. Cold interior surfaces also drive downdrafts and temperature stratification. Consider also the glass temperature is likely 15F (8C) lower than the minimum air temperature required by Codes! This will drag down the MRT and begs me once again to ask, why do we find it acceptable to have 72F (22C)+/- air temperature as minimum and yet ignore MRT’s colder than minimum? Yes, colder than minimum! The result is colder than Code intended homes exists where Codes are enforced and that by definition is a fail.

Here’s what the history books teach us on this subject, “…the Commissioners of the General Board of Health advocated in 1857 that for comfort the temperature of the walls of a room should be at least as high as the general temperature of the room, and included cold walls or floors amongst the conditions which make for discomfort.” From the appendix of the National Building Code of Canada, “In addition to controlling condensation, interior surface temperatures must be warm enough to avoid occupant discomfort due to excessive heat loss by radiation.” Over 150 years have lapsed and all we can do is get the radiant effects into the appendix of a National Code. The illiteracy on this one metric borders on absurdity. Read the above paragraph again if you think Codes represent comfort.

Ok stepping off my soap box lets now move our northern resident away from the glass and the MRT will change and so will their perception of comfort. So consider again that air based stats don’t recognize the effects of radiant nor the occupant’s position in the room and you now see how flaws around air temperature as a proxy for comfort multiply when we incorporate the human factors.

Figure 3 Codes ignore the effects of inside surface temperatures (T1) and this omission is propagated by thermostats that only sense air temperature (Tdb) (left graphic). In comfort analysis surface temperatures are dynamic and different (T1-T7) and change with the suns position and outdoor ambient temperature (right graphic). The radiant effect on the body is described by the Mean Radiant Temperature (MRT). MRT combined with Dry-bulb temperatures (Tdb) defines the operative temperature (TO).

Now comes another key piece of information. In most homes with basic geometries we can average out the MRT with the air temperature to obtain what is called, “Operative Temperature”. So it is also true that where the person goes, so goes the operative temperature. Operative temperature or TO is what people actually thermally experience and is what thermostats should measure if they were truly a ‘comfort and control’ device. Well that’s not entirely correct. We should add in humidity and air velocity and that would cover the four general factors in ASHRAE Standard 55. So let’s summarize;

The general factors for thermal comfort are:
1. Mean radiant temperature
2. Air temperature
3. Humidity
4. Air velocity.

The first three are closely tied into the enclosure performance and choice in HVAC systems. The last is exclusive to air system design; combined they have a consequential effect on energy use. Why? Because in a poorly designed and built house, especially in extreme climates the owners have only a handful of practical choices to compensate for discomfort. They can adjust air velocity up (or down) up is good in summer but bad in winter (item 4 above); and/or increase or decrease the setting on the thermostat (1 and 2 above); both have direct energy consequences. They could also add or remove clothes (Clo value) and or change their activity (met rate). The latter two personal metrics bring the basic ingredients list up to six factors.

Personal Factors
5. Metabolic rate
6. Clo value (Clothing)

Now anyone who does the discomfort dance with house mates around these first six factors have entered the mosh pit affectionately known in my practice as the ‘Thermal Thunderdome’ and have become fodder for the now infamous ‘thermostat wars’.

Alright we’re almost done. Because comfort is subjective, circumstantial and relative it’s not enough to imply that getting these six factors right is going to deliver the comfort cake everyone covets. That would be too easy. You see other factors come into play when people are lounging around at home in their skivvies.

Regardless if it’s 1857 or 2017 by far one of the most popular complaints people have, even in better built homes in warmer climates, is cool to cold floors. It doesn’t matter if you’re in Ft. Lauderdale or Fairbanks any floor temperature lower than foot temperature (appx. 77F (25C) +/-) is going to cause some people some degree of foot discomfort (pun intended). This is especially true for conductive floors assembled with masonry like materials. Cold floors are why carpet, wool socks and slippers exists. These solutions work if you are an able bodied person. However consider in the real world some people don’t like carpet - I know a shocking statement. Some people such as infants and the infirm can’t slip on wool socks or slippers without assistance. Many others especially the elderly have circulatory concerns that carpets, socks and slippers can’t fix. Ignoring these constituents by assuming everyone is the same; or have the same capacity to adapt or have the same capabilities to manipulate windows, fans and thermostats is just another element in thermal comfort illiteracy.

Now let’s go back to our friends in the north next to the cold window. The differential between the glass and the occupant, other room surfaces and room air temperature drives radiant asymmetry, downdrafts and to some extent temperature stratification. So what is radiant asymmetry? Recall the last time you were down at the beach in front of the bonfire roasting a marshmallow sipping your favorite brew. Remember how your front felt warm and your backside felt cold? So what did you do? You rotated like pork on a spit roast. That sensation of hot on one side and cold on the other is radiant asymmetry and it happens all the time in poorly designed and constructed buildings. Drafts and temperature stratification occur because of changes in air buoyancy frequently caused by temperature and pressure differentials that occur at cold and hot surfaces, through enclosure leaks, from stack effects and effects from mechanical systems.

From a comfort perspective the latter factors don’t normally require attention if the occupants have met rates exceeding 1.3 Btu/hft (doing more than light standing activities) and clo values exceeding 0.7 Ffth/Btu (sweat pants and long sleeve shirt). But they become important if they are seated or lying down doing light activates such as reading, watching TV or working on the computer whilst wearing lighter clothing.

So the four local factors to consider are;
7. floor temperatures
8. drafts
9. temperature stratification
10. radiant asymmetry

Figure 4 Reality (left) versus codes (right). There are ten major metrics to consider in thermal comfort (left), air temperature (right) is just one. When we deal in realities we can formulate real soutions. We can't do that if Codes permit the least acceptable environment before someone becomes ill.

So that covers the essential ten ingredients in thermal comfort analysis. If you and yours are going to say that one way or another you affect your clients thermal comfort through your products and services, then at the very least you need to know what goes into the comfort cake. Ask, “who would buy a cake from a baker if they only cooked with one ingredient?” No one. So why do we expect our clients to buy comfort systems based on one element?

You should now also appreciate that air temperature and indoor air quality as a proxy for thermal comfort and indoor environmental quality is false and one of the stubborn lies we must expose and bring to truth. Finally we need to treat thermostats for what they are…a switch. Ok maybe they have some creative algorithms associated with their points of measurement to engage the relays; but they don’t entirely sense what humans sense and they don’t follow the occupant around, ergo there is no way they can accurately and completely serve as the ambassador to the building and HVAC system as a sole ‘comfort and control device’.

So what’s next? Well we know the ingredients for thermal comfort so next is to establish the quantities or the combination of ranges and we’ll do that in part II so stay tuned.



70F in the USA, 72F (22C) in Canada…don’t ask me why the difference.

Bomberg, M., Furtak, M., Yarbrough, D. (2017) Buildings with environmental quality management, part 1: Designing multifunctional construction materials. Journal of Building Physics, June-19-2017

Anatomy & Physiology, Rice University, Texas, 2016, ISBN-10 1938168135

Sessler (M.D.), D., Moayeri, A., Skin-Surface Warming: Heat Flux and Central Temperature, Anesthesiology, 73:218-224, 1990

Villaseor-Mora, Carlos & Sanchez-Marin, Francisco & S, Calixto-Carrera. (2009). An indirect skin emissivity measurement in the infrared thermal range through reflection of a CO2 laser beam. Revista Mexicana de Fsica. 55. accessed Nov. 2017

Rocky Mountain Institute, Re-Defining and Delivering Thermal Comfort In Buildings, 2016

Table 1, Representative Rates at Which Heat and Moisture Are Given Off by Human Beings in Different States of Activity, section 18.4, 2009 ASHRAE Fundamentals Handbook

Fig. 3.1, Achieving the Desired Indoor Climate, Energy Efficiency Aspects of System Design. Editor Per Erik Nilsson, Studentlitteratur, The Commtech Group. 2003

<> accessed Oct 2017

<> accessed Oct. 2017

Kapedan, E., Herssens, J., Nuyts, E., Verbeeck, G., (2017) The Importance of Comfort Indicators in Home Renovations: A Merger of Energy Efficiency and Universal Design. Proceedings, Plea 2017. Edinburgh

Sussman, R., Chikumbo, M., 2017. How to Talk about Home Energy Upgrades (webinar). Based on Report Number B1701. American Council for an Energy-Efficient Economy. <> accessed Nov. 2017

Skin temperatures on different parts of a nude person measured at different ambient temperatures.

Adapted from: Olesen, B.W., 1982, Thermal Comfort, Technical Review, Bruel & Kjaer

Munro, A.F., Chrenko, F.A. The Effect of Radiation from the Surroundings on Subjective Impressions of Freshness. Medical Research Council's Group For Research In Industrial Physiology, London School of Hygiene and Tropical Medicine, Epidemiology & Infection, Volume 47, Issue 3 November 1949 , pp. 288-296 <> accessed Oct. 2017

Skin temperatures on different parts of a nude person measured at different ambient temperatures

Adapted from: Olesen, B.W., 1982, Thermal Comfort, Technical Review, Bruel & Kjaer


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