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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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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 72°F (22°C)+/- 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 72°F (22°C)+/- 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 72°F (22°C)+/-
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 -40°F/°C
there is a high probability they would experience a chill even
if the thermostat reads 72°F (22°C)+/-. This is because the
inside surface temperature of the glass is likely 30°F to 35°F
(17°C to 19°C) 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 15°F (8°C) 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
72°F (22°C)+/- 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. 77°F (25°C) +/-) 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/h·ft² (doing more than light standing activities) and clo
values exceeding 0.7 °F·ft²·h/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.
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70F in the USA, 72F (22C) in Canada…don’t ask me
why the difference.
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Table 1, Representative Rates at Which Heat and
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Fig. 3.1, Achieving the Desired Indoor Climate,
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Skin temperatures on different parts of a nude
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Adapted from: Olesen, B.W., 1982, Thermal
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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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