Off-grade Home / Enclosing Under Space

I am considering enclosing,with styrofoam/polystyrene board,the under space(from the bottom of the home to the earth, approx 36") in an attempt to trap in the earth temp. and thereby create a passive radiant heat source (the earth) based on the premise that the earth is a nearly constant 68 deg F.My son is concerned that,having noticed that nearly all structures he has seen has had vents intalled,there exists some reason not to totally enclose this space.Our home is a doubewide built in '87 and set on a mound of hard pan earth.We live in NE Florida.Can anyone address this issue?

Thanks in advance,Nate.

Foundation crawl spaces are typically ventilated because moisture buildup there will cause problems. Check with local contractors about practice in your area. Sometimes a vapor barrier is placed on the ground, but I don't know if this would eliminate the need to ventilate the crawl space.

not an expert on this, but will tell you what i know.

if you enclose the space while leaving closeable / openable ventilation, you'll have something that works with seasonal variations in temperaure. It'll keep out cold winter air and / or the hottest heat wave air -- but only for temporary cold spells and heat waves.

Long-term average temperatures are still going to seep in and establish another average temperature inside the enclosure, which is still better than before. Even with ventilation open, the temperature inside will be better than before, since air (ventilation) does not equalize temperature immediately.

Extreme swings in temperature get dampened, and a new average temperature gets created inside your foundation space belwo your floor.

Two seasons out of four, you can close the vents for a certain length of time, which you manage and control. Most of the time, you'll have to leave the ventilation open. I don't know the answer to jimbo's question, but I think a vapor barrier won't work well enough to do what is required over a "long" period of time being enclosed, because there is no or little air circulation if you have a 99% airtight space.

Humidity eventually gets through or around any barrier. Ventilation removes the ever-higher humidity.

Foam hung under the floor is good too. It's heat insulation applied at the right place. If the house enclosure is not made totally of foam but is made airtight, it will do the job.

David

I have worked in quite a few crawl spaces and the ones that have insulated walls have, by far, more stable year round temps.

A vapor barrier on the ground will reduce the amount of moisture in the crawl space by slowing it's transfer from the ground to the air.

Ventilation is a must.

I had considered the humidity issue.Like Cass I too have worked in many crawl spaces with and without vents and have found two conditions common to most; a)During the summer they are cooler by far than the ambient temp.and b) They are usually powder dry.
David mentioned managed ventilation.I was thinking that could be managed automatically by using motorized dampers and fans controlled by two humidistats.One in the controlled space and one outside.When humidity in the controlled space exceeds a preset "and" the outside humidity is lower then vent until controlled space is lower.Otherwise venting could take place say during a rain and actually increase the humidity of the controlled space.
Two issues I have with insulating the underside of the floor are;a)this negates any radiation from the earth and b) it is three times as much insulation.Which I would do if earth radiation is not a meaningful consideration.
The ventilation issue being handled; the remaining question becomes; Would the earth temp be a viable asset?
Here in Florida we don't really have four seasons.We have summer,a little cooler summer where spring is supposed to be,a little cooler summer where fall is supposed to be and a little cooler summer where winter is supposed to be.So cooling costs are of most importance.
Be back later,gotta take my daughter to church.Nate.

you're right

nate i think it's a correct analysis, to leave the floor and let the earth temp temper, and to work out some method manual or semiautomated to let crossventilation air go through the space, assuming it needs it. A $20 hygrometer will tell you.

david

David,to coin a British phrase,you are "spot on" when you say "if you need it.I've just been doing more research and found some studies by the DOE (Department of Energy) and EERE ( Energy Efficientcy and Renwable Energy)
I found one article that bsically said that in the past vents were code because it was believed that they would de-humidify the space.Now however industry professionals backed up by gov. studies have found that vents make it colder in the winter and in summer rather than de-humidifying the space it actually tends to humidify it.I'll try to include some of the links I have found.

http://www.energycodes.gov/news/2003_workshop/pdfs/warren.pdf

http://search.nrel.gov/query.html?q...k=1&rf=0&oq=&col=eren&qt=crawl+space&x=20&y=7

http://www.eere.energy.gov/

The first site I found,and by far the most clear,dissapeared when I tried to return to it.I keep getting a 502 ERROR Bad Gateway.Just my luck!
Here's the link anyway.Maybe it'll clear up.

http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11480
Thanks guys.I'll keep digging and keep everyone updated.I'm not on an environmental mission,just trying to keep te energy bill from swallowing me up.
Nate

Nate. I'll throw in my 2 cents. In my area when a home(with a crawl space) is sold, if it doesn't have a vapor barrier on the ground it will not pass inspection for a loan. The vapor issue is one of the reasons and the other is more concerned with termites. There are probably also concerns with radon. For many years mobile homes have been manufactured with very good insulation under the floor and some kind of vapor barrier (thick black plastic or what we call black board). Especially if the floor insulation has been torn out or compromised the underpinning you describe will be a great help, not so much as a source for hot/cold but to inhibit the fluctuation of temp of the floor. I would surmize that putting vents in would worsen any vapor problems as there have been studies in attics where sprayed on insulation was used against the underside of roofs and the conclusions were that these houses fared much better without attic ventilation. Whereas, with the insulation only above the ceiling ventilation was necessary to remove the extreme temperatures as well as the humid air. Not sure where the research was done but it was done in Florida. My opinion/conclusion: cover the dirt with plastic, install the styrofoam underpinning, and seal it up tight.

I think you need to rethink the radiant heat thing. Assuming you are correct that the earth is 68º, which may be true in your area, and you want the house to be warmer than 68, heat moves from a warmer area to a cooler area. Unless the house is below 68, where does the radiant heat action take place.

Now, you may have heard of ground source heat pumps. That is a different situation, because you are using a mechanical device ( heat pump, with refrigerant medium) to cause heat transfer to take place.

Thanks for the responses guys.What Randyj siad about a vapor barrier I believe is true.The first study did say that a barrier had to installed(plastic glued at the seams and held down by sand or concrete or concrete slab).
To the 68 deg. issue.Here in Florida I have long been told (I haven't proven it myself) that the ground is a constant 68 deg.If that turns out to be true (I will check) then that would be great inasmuch as 68 deg. is the winter target for heating.Summer taret being 72 deg. then the cooling shouldn't fall under the home for the same reason (cooler air moves to warmer).In all honesty though guys I didn't get to read all the data.My wife is going into surgery tomorrow (today now) for a hysterectomy so I'll be very scarce this week.Should anyone find time to crunch through some of the data that would be great.You could then enlighten us all. That's the most wonderful aspect of this and other forums.In answering someone elses question we all become more informed. Thank a lot everyone,Nate.

Good luck to the wife on the hysterectomy... you'll appreciate it as much as she will... fewer mood swings is a big bonus! Expect some weight change in her. She will probably fight to control it.

I've never heard the 68 degree earth temp... it might be different in FL but around here it's 55. Maybe you should investigate geothermal systems for more study on the idea. If you're considering just using the earth for a heat exchange then my mind tells me that once the area is heated then it will tend to be like a heat bank. If you can drill down to an underground stream or other replenishing source then you can get a serious replenishing replacement of heat/cold. As for just pulling heat/cold out of dirt...hmmmmm.... that sounds a bit like stretching it.... if you could suck cool air out of a cave then you'd be in great shape.