Impact of radiant temperature on people comfort

[ICanHas]

Warm blooded creatures like us are thermally regulated unlike cold blooded animals or objects.

So, how we perceive comfort is affected by many factors.
Obviously there's the air temperature (dry bulb).

Other factors are:
Humidity (RH%, dew point, wet bulb).
Air movement and the characteristics (db and wb) of the air stream.
Evaporation rate from a constant temperature surface such as swimming pool or people is a function of air flow and dew point, however it seems like mold growth and decay are more closely tied to RH%.

Something that I know that affects comfort, but I don't have a good understand of the effect on comfort is the radiant temperature. I understand being near very hot objects like a pot of molten steel feels very hot, but I don't really have a good idea of how it relates to indoor comfort.

I've been playing around a bit, but want to hear from someone who's an expert on it.
Even if the indoor air temp is kept the same, it sometimes feels chilly or hot. So, I looked around the room with an IR thermometer and I can clearly see a significant temperature difference on window facing sides and these differences reflect how I feel.

When it feels chilly with indoor temp at 75F, IR thermometer shows about 5-10F lower towards the window. When it feels hot such as facing the east during sunrise, I read 90s. So, using a fan, I cooled off the blinds and got it down to low 80s and it seems less uncomfortable.

Does 10F or so change in radiant temp make a difference or is it psychological effect?

[snupytcb]

i think it is physical. we just converted a customer from an oil fired low boy forced air with a hw coil to a wall hung lp knight with staple up radiant. he is a lineman and likes it warm so the stat hasn't been below 72 in 10 years according to the owner. after using the radiant for 2 days he had to drop the stat to 66 because it was too hot. he commented how the objects in the house are consistent temps and feels this makes the most difference. even walking around the house he doesn't feel "cold pockets" as he did with the old system. I have never had a customer be able to describe radiant heat as he does and like that. it teaches me where and what to improve. every radiant job we have done has resulted in the customer commenting about lowering the stat 5-8 degrees and still be more comfy than before, even when they had baseboard before radiant. just baseboard can make a noticeable different if it can be operated right. I guess some could be psychological but i believe it is mostly physical. another quick analogy could be a metal row boat. when we are fishing for steelhead in December the drift boat seats will wick the heat out of our bodies because it feels so cold. now drifting for when it's warm out is much more comfortable.

[earlburnermann]

I remember studying this, but not sure if it was in college or a bpi class I took. Sounds like your talking about the effect of the mean radiant temperature of a space. To be comfortable we need to be able to shed the excess btus our bodies produce.

Heat goes to cold, so as long as the area around us is cool enough to absorb our extra btus we will be comfortable. If the area is too cold we will loose too much heat, if it's not cold enough we will not be able to shed enough heat. Sitting near a window during the the winter may be uncomfortable even if the room temp is perfect. That's because the temperature of the glass may be so much lower than us that we are radiating more heat to that spot than is comfortable.

Here's a link from Wikipedia on the subject:


http://en.wikipedia.org/wiki/Mean_radiant_temperature

[Sicofthis]

Earl, Our bodys will radiate a certain amount of heat based on our body temp. Not based on the surrounding surfaces. The surrounding surfaces will affect our radiant heat absorption.

[jimj]

I've been playing around a bit, but want to hear from someone who's an expert on it.
Even if the indoor air temp is kept the same, it sometimes feels chilly or hot. So, I looked around the room with an IR thermometer and I can clearly see a significant temperature difference on window facing sides and these differences reflect how I feel.

The first chapter, first page of Manual "RS" (Comfort , Air Quality, and Efficiency by Design) does a great job of answering your question. But in essence states That when occupant comfort is evaluated, the temperature of indoor surfaces are as important as the room temperature . Tests have shown that increasing or decreasing surface temperatures by one degree will have the same effect as increasing or decreasing room air temperature by one degree.

[ICanHas]

Earl, Our bodys will radiate a certain amount of heat based on our body temp. Not based on the surrounding surfaces. The surrounding surfaces will affect our radiant heat absorption.

The surrounding surface definite affects the amount of radiant emission. If you're outside on a clear night, you will definitely feel cool. We get frost on objects overnight even if the temperature does not drop below freezing. If you take an IR thermometer and point at the sky on a clear night, it will be something like 0-20F even this time of the year. So, I know it affects us... I just wasn't so sure to what degree. If it's like what jimj says and it has the same effect degree for degree as air temp, I think I was on the right track with with a fan blowing at the window to drop the radiant temperature of the window and shades to improve comfort.

[earlburnermann]

Earl, Our bodys will radiate a certain amount of heat based on our body temp. Not based on the surrounding surfaces. The surrounding surfaces will affect our radiant heat absorption.

Depending how close we are to the surrounding surfaces and their temperatures, we will either radiate heat to those surfaces, or they will radiate heat to us.

[ICanHas]

Depending how close we are to the surrounding surfaces and their temperatures, we will either radiate heat to those surfaces, or they will radiate heat to us.

Regardless of distance, I think temperature as read on IR thermometer is the radiant temperature.

So, if the sky reads 15F and air temp is 50F, it would be like having a ceiling panel that is at 15F.

IR thermometer is such an awesome toy..

[Sicofthis]

So, I know it affects us... I just wasn't so sure to what degree. If it's like what jimj says and it has the same effect degree for degree as air temp, I think I was on the right track with with a fan blowing at the window to drop the radiant temperature of the window and shades to improve comfort.

Never said it didn't.

[Sicofthis]

Depending how close we are to the surrounding surfaces and their temperatures, we will either radiate heat to those surfaces, or they will radiate heat to us.

Incorrect.

All objects above absolute zero radiate heat, based on emissivity, surface area, and temperature. Our surroundings will radiate heat to us and we will radiate heat out to our surroundings.

Hotter surroundings will radiate more heat onto us and colder surroundings will radiate less. The amount of heat radiated by an object is determined by its surface temp.

[jimj]

Regardless of distance, I think temperature as read on IR thermometer is the radiant temperature.

So, if the sky reads 15F and air temp is 50F, it would be like having a ceiling panel that is at 15F.

IR thermometer is such an awesome toy..

Yup I agree. Hank Rutkowski the author of many of the ACCA Manuals ( J,D,S,T,RS P and a lot more) says it his way. For radiant heat to occur, the surface of the skin must "see" the radiating surface. If a sight-line is established, exposed skin receives heat energy from any surface that is warmer then the skin and lose heat to any surface that is cooler than the skin.

[travlinjohn]

The term "mean radiant temperature" is derived from experiments with passive solar homes. Simply stated, the mean radiant temperature is the average of the air temperature and surrounding object temperature. If the walls are 80 degrees and the air is 60 degrees then the body thinks it is 70 degrees. The body must, of course, be exposed to the 80 degree wall. Radiant ceiling heat works on the same principle. when it is first turn on, your feet legs and feet will be cold if the are hidden under a table. however, as time goes on all parts of the home will become warm due to convection caused by gradually heated furniture, walls, carpet, etc.