Thermal Comfort Science

This is a post I made in about June on thermal comfort science basing on PMV calculations. I actually believe thermal comfort sensation in normal people has changed.

Somehow, an environemnt used to be bearable is now unbearable when people "experience" another environment and want to enjoy an "comfortable" environment at OPM. (other people's money)

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Thermal Comfort Science 熱環境舒適性

Recently, I completed a report related to thermal comfort.

So I think it is beneficial to raise the awareness and boarden the general public about thermal comfort.

Air temperature is related to thermal comfort but it is not the only factor.

ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) has devised a thermal sensation scale as below:

+3 Hot
+2 Warm
+1 Slightly warm
0 Neutral
-1 Slightly cool
-2 Cool
-3 Cold

Extensive research was done in Kansas University by Ole Fanger. His team has found out that there are gerneally six factors that will affect the sensation of thermal comfort in human.

The six factors are:
1. Air temperature
2. Mean radiant tempersture (this is related to the surface temperature of the surrounding environment. It can't be measured but can be calculated by some mathematical formulae)
3. Humidity
4. Air speed
5. Clothing
6. Human activity

A computer software to estimate the PMV can be downloaded from this link:

http://www.freedownloadscenter.c ... fort_Estimator.html

The ASHRAE standard recommends that a PMV range of -0.5 to +0.5 is good for an indoor office environment.

For the project that I work on, currently a PMV range of -1.0 to +1.0 is thought acceptable.

Basing on this, I found that even an air temperature of 30 degree is still acceptable if other factors can compensate for that:

0.3 clo which is equivalent to T-shirt and shorts
1.3 met which is standing or shopping leisurely
1.3 m/s air speed, this is somehow breezy but acceptable in that environment
60% relative humidity
31 deg C mean radiant temperature, that building does not have any large window and radiation is very little.

So if you experience a hot environment, try the following method rather than just turning on the air conditioner:
1. Lower the curtain
2. Take off your clothes, just leave T-shirt and shorts on
3. Turn on you fan(s)
4. Switch off large appliances
5. Keep yourself calm and don't move about
6. You may spray some water over yourself, probably over the arms and legs to cool yourself down by evaporation.