Under Home Treasures

Can you elaborate on your original post?

I have been toying with the idea of sealing my crawlspace with spray-foam insulation and introducing forced air heat into the envelope to create positive pressure. The floor registers would allow the heat to enter the living space. No ductwork, no pipe freeze and no ground ambient. I suppose the earth could be covered with thick plastic to allow heat transfer and storage but would it be better than a sealed envelope of insulation? Likewise, I would do the same in the attic and introduce AC there allowing the cool air to drop down through ceiling vents. I think this would allow me to use a much smaller ac and heater. Your thoughts?

be careful of foam products they out gas. blown in cellouse is best. and remember humidity out all winter, and fresh air in all summer. It's best of course to have a dry stem wall with footers down 4-5 feet R 40 is good , this creates sort of a "battery for the house above it. If you use forced air heating sys., be sure you have good CO detectors in place and "optimize" , not only the forced air gas burners, but also every other gas burner appliance. That allone will save you money, and at any kind of altitude, quite a bit.

This is in reply to #2 and #3; re: the idea of putting down a thick sheet of plastic under your dwelling.

I lived in a tipi one winter and I used 3" rubber sheets (obtained from a local factory that made them for automotive and other uses) which I cut to shape with a kitchen knife (the best knife I've ever had - I want it as part of my grave furniture). But, I first laid down a sheet of heavy plastic to keep moisture from wicking into the rubber. Although I didn't have any crawl space (except for those of small tunneling persons) I'm thinking cellulose would wick moisture also - even though it may not get dripping wet, it may feel colder. That tipi floor was much drier and more comfortable than you might suppose it would have been, throughout four seasons in the temperate rain forest.

I think your idea about your envelope is very good. heat upward and cool downward.

and your right, it would not take much energy to exchange air within the envelope.

the 55 degree mass of your foundation is year round . and most passive solar homes

utilize this effect to kick start a positive convection . Another "battery" you can

use is a 500 gal. solar storrage tank (not pressurized) and humidity control a must

another plus to your idea is the fact that you can employ some air filtration sys. as

the air moves.

"...hot air mass next to cold air mass makes counter clockwize(sic) rotation..."

I presume you are referring to the Coriolis effect. This effect only occurs over distances MUCH larger than any basement or crawl space.

As long as all the vents are at the same level (altitude), there should be no differential temperature in the air at different vents, so no convection. The only thing causing any significant flow through the vents will be differences in pressure due to outside air flow (wind).

I have been in my crawl space many times, and even in a strong storm there is very little circulation. I do live in an area with lots of trees - they keep most of the wind well off the ground. And of course I do live in a place where the lowest temperatures are in the mid to high teens F.

"75 % of all air infiltration into a home is through the rim joist"

That depends on the construction and insulation of the home. Before I had insulation blown into my walls (about 30 years ago), a large amount of infiltration was through the power outlets.

I have a 5 feet "crawl space" with concrete floor. It was very simple: here everyone builds his foundation wall up to floor level and fills it up with :fill. I thought: instead of buying fill, I will get the fill out and spread it around the house. Everything is made with ICF blocks - just too warm inside. I drive around in it in a MERCEDES BENZ driver seat on 4 little wheels. Speaking of class? This is probably the only house of the nation with a expanded crawl basement. Good post.

Hi dymdsc,

I envy the height of your crawlspace.

My house , the builders did the ABSOLUTE minimum of site prep, scratched dirt away from perimeter and left saw palmetto roots under house. But that was 85 years ago, in the first housing bubble in Florida.

If I had 5' & concrete floor, I would take your M B seat idea and invite my neighbor over for rolling desk chair competition.

ratty

builders are doing the same thing today because they can. when I drive around one day there is a back ho on the site and it seems like the next day there is a house there. site preperation including solar oriented foundations and useable crawlspaces and landscaping and irrigation, should be done by a professional. and let the builders frame and sheetrock and paint till there hearts content. most "builders" do not consider passive solar because they don't care.

To my knowledge, cold whatever never flows to hot whatever- hot whatever having more energy flows to cold whatever till equilibrium is reached. An example- sitting in a pub at the bar having a few or more soothing libations- behind the bar is the coldroom where stock is stored- a barmaid opens the coolroom door- at once it feels cold around one-this is NOT cold air spilling out- BUT hot or warmer air around one flowing into the coldroom. Another example is where some say a chest freezer is more efficient than an upright freezer- because when upright door opened- cold air spills out!- whereas chest freezer when lid opened- cold air stays inside!. The facts are that each are as good as each other -insulation,seals being equal.

"...at once it feels cold around one-this is NOT cold air spilling out- BUT hot or warmer air..."

I think you may have had a few too many libations! The pressure in that cold room stays very nearly constant. No warm air can flow into the cold room unless some cold air flows out. Since cold air is heavier that warm air, the outflow is at the bottom and the inflow is at the top. The same is true of your upright refrigerator or freezer.This is known as convection. Place a candle near the top and/or bottom of the door, and watch them/it while you open the door gently.

Craig, this is true in my profession as well and I am thankful that builders continue to build crud or I would be out of work (Foundation Repair). If they paid their money to properly design and install their foundations, I would be seeking a different profession.

DK, I am glad that I wasn't completely clueless about convection and thank all who have contributed their thoughts on my double envelope idea. I would love to hear more! Gary

I think you are splitting hairs!. If what you say was true, no refrigerator would need to run once a certain coldness was reached. But they do- because it is hotter outside than inside- & that heat leaches inside thru the insulation. Or am I confusing conduction between air & materials?. As to coldrooms- yes-they usually have a fan blowing cold air from cooling coils around the room- but an interlock on the cold room door shuts off the fan when the door is opened- but I can now appreciate that yes- the coldroom may have a slightly higher pressure than outside-so yes- some cold air could concievably spill out- but that is not true in the case of an upright freezer or a chest freezer- unless each has an internal fan circulating air inside!(so-called frost-free?). Well mine don't have a fan!. I can open my chest freezer & feel cold air or coldness around me- now this should not happen according to you- cold air does not rise!?. But warmer air- or warmer anything- DOES flow to colder whatever- I was taught this principle many years ago- it is 1 of the 1st things learnt in refrigeration.

I am certainly NOT splitting hairs! I am simply stating standard high school physics!

I did NOT say that no heat could enter the cold room unless some cold air came out. I said that no hot air could enter the room unless some cold air came out. Heat can flow in any direction without requiring a difference in pressure. Hot air can not. I said nothing about conduction or radiation. Of course a refrigerator must run occasionally to compensate for those energy inputs.

Since cold air is more dense than warm air, there is a greater pressure difference between the floor and ceiling (or top and bottom) inside a refrigerator than there is between corresponding levels in a normal room. If the average pressure inside is the same as the average pressure outside, then the pressure near the floor is higher and the pressure near the ceiling is lower inside the refrigerator than in the room. When not blocked by the door, air will flow from regions of higher pressure to regions of lower pressure; into the refrigerator at the top and out of it at the bottom.

When you open the lid of a chest type freezer, this top-to bottom pressure difference can not cause air flow, because the bottom is never open. BUT, the lid IS. Room air near the inside of the lid will be cooled by the lid, and that air will flow DOWN to you, standing near the freezer.

What you were taught (or should have been taught) is that cold does not flow, heat does. That is very different than the incorrect statement that cold air does not flow, hot air does. Cold is simply a lack of energy, while heat is energy. The lack of something can't flow. Cold air is a very real thing, and it certainly does flow (otherwise there would be no wind chill).

Thank you for eddicating me- I left high school the day I turned 14 due to economic reasons- thus I am iggerant of the finer nuances & meanings of things- but i love finding out the truth, & will certainly look at this subject a lot more closely.

And thank you for listening! So many in situations like yours seem totally unwilling to accept new information and explanations thereof.

I live in the mountains and have noticed that there are some pretty crazy pressure differentials. Inside a home with forced air heating and a crawl space , that's one set of differentials, now add a big windy low pressure storm that lasts a few days, the positive pressure in the envelope (not the crawl) moves heat out pretty fast, plus the t-stats are usually turned up during storms. What a waste of gas, I always turn my heat down for the storms and hunker down the hatches till it passes. It is hard to conserve energy in thesE kind of homes because it is moving so much. Like electricty along the wire is heat which is loss. In-floor heating (which is best) only heats what is in contact with it, so I use the 55 earth temp. , now the foundation of my home is in contact with this energy, it does not "move", now my crawl stays at 55 and it is "warm" compaired to the outside temp. which is very cold low pressure and moving. heat stored in radiant floors does not move per sey, although you feel it first at your feet then a couple minutes later your who body, then it stops, you do NOT NEED heat above your head. Radiant floors are not affected by convection, if you have 24 hrs of stored heat in the floors it takes exactly 24 hrs to lose it (unless you poured liquid nitrogen on them).

The builders 0f the past knew how to capture this energy first then anything they built on top of this was good. with out a good foundation , it's very hard to HUNKER DOWN.