thermal comfort
indoor environmental quality Bookmark and Share
residential heating design

 

Here's where and how you can participate in our fall educational programs. Also - time is running out to register for our  Integrated HVAC Engineering: Mastering Comfort, Health, and Efficiency. September 22 - November 28, 2014

Solutions: For additional support visit our visitor services page.
For consumers or general interest
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For those interested in the business side of the industry


Do you really know what thermal comfort is? Have some fun:
Some of the interactive solution tools you'll find here at www.healthyheating.com are like the thermal comfort calculator below.
 Have some fun and see if you can create a neutral zone where you would be comfortable at home or at work. Courtesy of  Dr. Marsh and Caroline Raines
 

Instructions: Place your cursor over the grey sliders to experiment with different values. (If the graphic does not appear you will need to download a free flash program from Adobe - click here).


"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
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“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)
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So you think you know what thermal comfort is?: Discussion on the Thermal Comfort Calculator

What do the terms mean? (For a detailed overview on thermal comfort click here)

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 and ISO Thermal comfort standards. Having said that, air temperature stratification, is important and is the difference between your ankles and head - as a localized factor it plays a role in discomfort.

Radiant Temperature: At rest the human body exchanges between 50% and 60% of its sensible heat via radiation (see 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 radiant theory.

Relative Humidity :is the ratio of partial pressure of the water vapor in a sample to the saturation pressure at the same temperature...or for a simpler explanation its 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 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.


How is thermal comfort determined: Ask the medical doctors...

"Thermal comfort mediates behavioral modification of heat loss, the most important thermoregulatory response in humans. Thermal comfort 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. [35]" Source: Sessler (M.D.), D., Moayeri, A., Skin-Surface Warming: Heat Flux and Central Temperature, Anesthesiology, 73:218-224, 1990

Do you 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 comes before HVAC engineering...as you might have grasped - they are most definitely not the same thing. The former focuses on 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.

Which approach makes better sense to you?

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Related reading:

Do I need an engineer? A Guide to HVAC/Indoor Climate Design Service Providers
HVAC does not equal IEQ
Where 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
Thermal Comfort: A 40 grit perspective for consumers
Thermal 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 and Ugly
Thermal Comfort Surveys - Post Occupancy, Part I
Thermal Comfort Surveys - Post Occupancy, Part II

For additional support on this topic visit our visitor services page.

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Be sure to check out our new 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. See our Self Assessment Form, Ranking Your Indoor Climate System and How to Ball Park the Cost of Indoor Climate Systems.

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