"The reason for creating thermal
comfort is first and foremost to satisfy man’s desire to
feel thermal comfortable, in line with his desire for
comfort in other directions." Fanger, P.O., Thermal Comfort:
Analysis and Applications in Environmental Engineering,
McGraw-Hill Book Company, 1970
“The most commonly used indicator of
thermal comfort is air temperature – it is easy to use and most
people can relate to it. But although it is an important
indicator to take into account, air temperature alone is neither
a valid nor an accurate indicator of thermal comfort or thermal
stress.” Source: The Health & Safety Executive (UK.gov)
So you think you know what thermal comfort is?: Discussion on the Thermal Comfort
the terms mean? (For
a detailed overview on thermal comfort
Predicted Mean Vote(PMV): is a scale used by your
indoor climate engineer to predict comfort. Ideal
range is between -0.5 and +0.5 (Neutral).
Predicted Percentage Dissatisfied (PPD): If 85% of the occupants are
satisfied (or 15% dissatisfied) with their thermal environments,
then the Building/HVAC
system is generally considered acceptable. Some things like
floor surface temperature, and stratification can influence comfort more than other metrics.
Statistically over 50% of
home owners and 70% of occupants in commercial spaces are dissatisfied for one reason or another – but you can
see why by using the comfort calculator.
Air Temperature: is
the dry ambient temperature reading or what an ordinary thermometer
shielded from radiation and moisture would measure.
Did you notice what happened when you raised or lowered the
air temperature? In thermal comfort analysis, air
temperature must be incorporated with the mean radiant
temperature for the combined effect known as the
operative temperature. It is the operative
temperature (not air temperature) shown on the x-axis of
the psychrometric chart in the ASHRAE 55 and ISO Thermal
comfort standards. Having said that,
air temperature and more specifically temperature stratification, is
an important factor. Temperature stratification is
the difference between your ankles and head - as a
localized factor it plays a role in discomfort.
At rest the human body exchanges between 50% and 60% of its
sensible heat via radiation
Table 1). Notice the sensitivity of
radiant on comfort. Also note the temperature you are controlling is not the surface temperature of a radiant floor for example but the
mean radiant temperature of the space. Other radiant
elements which affect comfort include
radiant asymmetry and
floor surface temperatures.
Learn more about radiant systems and
Relative Humidity:is the ratio of
partial pressure of the water vapor in a sample of
the saturation pressure at the same temperature...or for
a simpler explanation it is the amount of water in the air
compared to what the air could hold at saturation for
the same temperature. Humidity does play a moderate role
in thermal comfort in most controlled environments, but
having a more greater affect on how dry or clammy you would feel.
Dry and clammy are more physical discomforts than
thermal discomforts. (Learn More)
Air Velocity: is how fast the air is moving through the room.
Air can move naturally through convection or is forced by fans. What
is the relationship
between air temperature and air velocity - play with the
indicators and find out. (Learn More)
Activity Rate: describes what you are doing ...afternoon nap,
or playing tennis perhaps? (Learn More)
Clothing Level: describes what you might be wearing while doing an activity.
thermal comfort determined: Ask the medical doctors...
comfort mediates behavioral modification of heat loss, the most
important thermoregulatory response in humans.
is determined by skin-surface temperature, not by tissue heat
content, cutaneous heat flux, or central temperature.[27-29]
However, comfort produced by a local thermal stimulus depends
both on the location of the stimulated skin and the rate of
temperature change. For example, facial skin is five times as
sensitive as other skin surfaces; furthermore, rapid changes in
skin temperature produce approximately five times the response
of slow changes. " Source: Sessler (M.D.),
D., Moayeri, A., Skin-Surface Warming: Heat Flux and Central
Temperature, Anesthesiology, 73:218-224, 1990
understand now why we say thermal comfort isn't a boiler or a
furnace or a thermostat? Comfort is sensed by your body and
perceived by your brain. That's why we state the science of
indoor climate engineering
HVAC engineering...as you might have grasped - they
definitely not the same thing. The former
the occupant the
latter focuses on the building. In fact, passing an HVAC system
doesn't even require the occupant input - all it requires is an
HVAC inspector; i.e. HVAC design doesn't have to meet your own
personal requirements only the
minimum requirements of the building code.
approach makes better
sense to you?
support visit our
visitor services page.
For consumers or general interest
For the architect, engineer, contractor, wholesaler and
those interested in the business side of the industry
Do I need an
engineer? A Guide to HVAC/Indoor Climate Design Service
HVAC does not equal IEQ
will your indoor climate system score?
How to "ball park" your budget for
indoor climate control.
Indoor environments: Self assessment
Built to code: What does it mean for consumer thermal comfort?
The Total Comfort System -
The "Un-minimum" System
Comfort: A 40 grit perspective for consumers
Comfort: A Condition of Mind
Do-It-Yourself HVAC - Should you do it?
The Cost of HVAC Systems - Are You Paying Too Much for Downgrades?
Radiant Installations - The Good, Bad
Thermal Comfort Surveys - Post Occupancy, Part I
Thermal Comfort Surveys - Post Occupancy, Part II
support on this topic visit our
Be sure to check out
design validation software tools for radiant cooling
and heating systems.
Sample set of blueprints for residential
indoor climate systems: A competent professional should
be able to prepare documents such as these - but only
after a thorough review of the clients needs and wants.
Self Assessment Form,
Ranking Your Indoor Climate System and
How to Ball Park the Cost of Indoor Climate Systems.