Face
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Face
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November 4th, 2011 at 6:11:46 PM permalink
This was mentioned before, so I figured I'd give it a whirl and see if it takes off. Science and math is like peas and carrots, no?

I thought Wiz's Spanish WoD format was very clean, the way he posted a topic, allowed a few days of comments, then posted another. Maybe this one can be as organized. In any case, feel free to join in or pose questions of your own. I'm in no way claiming this thread since I'm not exactly an expert in these matters, I only wanted to get it started because I have a high interest. There's been a number of discoveries these past years and I only expect them to continue; now there's a place to discuss them.

I'll pose the first question to get things started. Just bear with my absurdity. You're not likely to hear something profound from me and my first topic is no exception, I just have a number of questions I feel would better my understanding of my world around me. If nothing else, I might get a giggle or two =)

Stand by for my first lighthearted, elementary question....
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Face
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Face
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November 4th, 2011 at 6:28:31 PM permalink
TOPIC: Why Isn't 70*F Always 70*F?

This time of the year always begs this question from me. My house, depending on a few variables, is always maintained at a temp ranging from 70*F to 74*F. My basement is even more stable, ranging only from 68*F to 70*F. I have central heat and air, so no matter if it's -9*F or 95*F outside, the house stays in the above range.

So why does it FEEL so bloody different? In summer, I hop out of the shower, dripping wet, into my 72* house and it feels like heaven, absolute bliss. Yet in winter, even though my house is still 72*, I have on sweatpants, thermal shirts, wrapped in a blanket, and I'm STILL cold. The basement in summer is a blessed retreat, somewhere I wish I could stay for hours, yet in winter, it's an icy dungeon not fit for Russian criminals. What gives?

Stupid as it sounds, this is a dead serious question, one I've pondered for years yet can't solve. 72* should always be 72*, right?

The only possible answer I've ever had is the evaporation factor. Winter house heat is a dry heat, which allows faster evaporation of your body surface's moisture, which would cause the feeling of being colder. But I can't believe that such a slight change in evaporation could cause such an extreme difference - on one hand I can be stark naked, dripping wet and loving it, on the other hand I can have on 3 layers and still be cold.

Thoughts?
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Scotty71
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November 4th, 2011 at 7:09:04 PM permalink
Damn good question IMO. I think you might be right, it might have to do with humidity, is it ever bitter cold and humid? Always the chance too that you brain is tricking you because of you're aware that is much colder or hotter outside your home.
when man determined to destroy himself he picked the was of shall and finding only why smashed it into because." — E.E. Cummings
Doc
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November 4th, 2011 at 7:29:56 PM permalink
I don't know that evaporation rate is the key here, but the humidity is an important factor. First, to confirm a part of what you have already said:

In the winter, when it is cold outside, there is little water content in the outside air, even at rather high relative humidity levels (as heard on the TV weather report). The cold air just cannot maintain as much water vapor as the warm/hot summer air. Since your house is not air-tight, you have some of this dry, cold air finding its way indoors. Once your furnace heats it to 70F, its relative humidity is very low. You have already acknowledged that in your post, and this very low humidity is the key reason that static electricity tends to be more of a problem in the winter -- it is difficult to dissipate the charge without the moisture.

The energy content of the atmosphere in your house is a combination of the energy of the air (Nitrogen, Oxygen, Carbon dioxide, etc) and the energy content of the water vapor (humidity). Think of this water vapor as steam that has been added to the otherwise dry air. At the same temperature, a room atmosphere that has higher humidity has greater energy content than a room atmosphere with low humidity. Thus, you typically have more energy in the room (air energy plus water vapor energy) in the summer than in the winter, even if you maintain the same temperature.

You can adjust that by adding a humidifier and running it in the winter. It will cost you money to evaporate the water that is added to the room atmosphere, but then the air will feel warmer at the same temperature. I cannot recommend a residential humidifier without also offering a bit of a warning: most of them involve moistening some sort of porous material that your air is circulated through (which initially cools the air) relying on the furnace to maintain the desired temperature. Unfortunately, these damp, porous fabrics tend to be fertile breeding grounds for various biological growths (Legionaire's disease, anyone?). In commercial buildings, the winter humidity level is typically raised by direct injection of steam from the boiler into the duct work.
MrV
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November 4th, 2011 at 9:09:29 PM permalink
Humidity.

A wet cold can feel "bone chilling," and a dry cold much less intrusive.
"What, me worry?"
pacomartin
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November 4th, 2011 at 9:18:28 PM permalink
Quote: Doc

I don't know that evaporation rate is the key here, but the humidity is an important factor.



As a general rule high humidity makes it seem colder when the temperature is below 53 degrees F and warmer when the temperature is above 53 degrees F.

A heat index chart is only concerned about temperatures above 80 degrees F where high humidity makes it seem warmer.
Doc
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November 4th, 2011 at 9:59:35 PM permalink
Quote: pacomartin

As a general rule high humidity makes it seem colder when the temperature is below 53 degrees F and warmer when the temperature is above 53 degrees F.

A heat index chart is only concerned about temperatures above 80 degrees F where high humidity makes it seem warmer.

I think this particular question relates to the temperature, or temperature range, at which Face maintains his house or basement, nominally 70F, rather than the outdoor temperatures we are likely to encounter.

The HVAC folks often talk about comfort zones, which reflect a combination of temperature and humidity and indicate the conditions that are considered acceptable or comfortable to most people for their work environments. This may not be the best illustration, but it is one that I found conveniently posted on the web. You may see that for any particular room temperature (such as Face's 70F) as the humidity increases, people are less likely to consider the room too cold. Similarly, at 82F, increased humidity is more likely to have people feeling too hot.

The comfort vs. humidity relationship may be quite different if you are far outside of this range of typical indoor temperatures.
TheNightfly
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November 4th, 2011 at 11:36:11 PM permalink
Quote: Doc

Unfortunately, these damp, porous fabrics tend to be fertile breeding grounds for various biological growths (Legionaire's disease, anyone?).

Doc is exactly right. Moist air retains heat longer so if you have low humidity in your home your heating system will have to work harder (longer) to maintain the desired temperature. As far as his comment about humidifiers being a breeding ground for bacteria and the like, get a flow-through humidifier and you won't have standing water, eliminating (almost completely) this issue.
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Face
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November 5th, 2011 at 12:06:27 AM permalink
Thanks all for playing along, especially Doc, who's seemingly willing to forsake his nap to rescue me from my own absurdity. ;)

I must admit I'm embarrassed, almost to the point of shame, that I came far enough in thought to realize humidity was the cause, but not far enough to realize why. I reckon this also explains why 110* air from a blowdryer feels kind of nice, while 110* water from a hot cocoa burns like hell. Same concept, correct? The air has the same temp, but "not as much", as it were, so it disperses rapidly, while the cocoa has the energy and can kind of keep it there longer. To make an analogy, you could cup your hand and open a lighter into it, filling it with gaseous butane and lighting it in a fireball, and not get burned. But if you just light a lighter in your hand, you go to the hospital. They're both the same temp, but the fireball (air) releases all it's energy quick, whereas the lighter (water) keeps that energy on you longer.

God, so simple ><

I'm cooking up another temperature question that actually has real world application. I'll let this simmer for now and probably post it tomorrow. It starts strange (like all my stuff) but there is a point to it. Promise ;)
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odiousgambit
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November 5th, 2011 at 12:44:58 AM permalink
I think there is a third factor, seldom mentioned: ambient radiant infared heat. This is one reason systems with heat pumps tend to disappoint.
the next time Dame Fortune toys with your heart, your soul and your wallet, raise your glass and praise her thus: “Thanks for nothing, you cold-hearted, evil, damnable, nefarious, low-life, malicious monster from Hell!” She is, after all, stone deaf. ... Arnold Snyder

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