Author Topic: Heat loss through concrete slab foundations  (Read 6778 times)

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tjm73

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Heat loss through concrete slab foundations
« on: December 21, 2005, 07:26:51 AM »
Is there a way to prevent heat loss through concrete slab foundations?  If you built a slab foundation that had the proper construction to extend down past the frostline (as required in my area) how do you keep the slab from sucking the heat in the home and exchanging it into the cooler ground under the house/slab?

Daddymem

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #1 on: December 21, 2005, 08:07:24 AM »

jraabe

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Re: Heat loss through concrete slab foundations
« Reply #2 on: December 21, 2005, 09:04:29 AM »
Daddymem's article is a good one and shows the same insulation techniques I have detailed in the Victoria and 20' wide plans - both the mono pour and the floating slab.


Mono pour Slab


Floating Slab

Note that three things help keep the floors warm and heating costs down: edge insulation, moisture control, and uncoupling radiation downward with a gravel bed under the slab.

In very cold climates and heavy clay soils I spec out full insulation under the interior of the slab at 1/2 the R-value of the edge insulation. This is especially cost effective for heated radiant slabs or if you are using the slab for solar heat storage.
« Last Edit: December 27, 2005, 11:59:50 AM by jraabe »

tjm73

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #3 on: December 21, 2005, 09:14:11 AM »
Quote
Insulated it:
http://www.southface.org/web/resources&services/publications/technical_bulletins/SI-Slab%20Insulation%2000-775.pdf
RIH in the slab would make nice warm floors too.

Thanks for the link.

RIH?  Is that radiant induction heating?

RAB

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #4 on: December 21, 2005, 09:28:37 AM »
Washington State has a very comprehensive guide that will meet your situation. The enclosed image is one of approximately 20 different types that you might have.
Link:  
http://www.energy.wsu.edu/code/code_support.cfm
Scroll down to -Field guide-
Then down to –Foundation-
All PDF files - dialups beware

tjm73

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #5 on: December 21, 2005, 09:34:41 AM »
Quote
Washington State has a very comprehensive guide that will meet your situation. The enclosed image is one of approximately 20 different types that you might have.
Link:  
http://www.energy.wsu.edu/code/code_support.cfm
Scroll down to -Field guide-
Then down to –Foundation-
All PDF files - dialups beware


I get a page can not be displayed message.  I'll try again later.

Also this probably belongs in the Refference section now.   :-?
« Last Edit: December 21, 2005, 09:35:39 AM by tjm73 »

Daddymem

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #6 on: December 21, 2005, 02:48:44 PM »
Decent site explaining radiant floor heating.
http://www.radiantec.com/

tjm73

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #7 on: December 22, 2005, 09:00:38 AM »
Quote
Washington State has a very comprehensive guide that will meet your situation. The enclosed image is one of approximately 20 different types that you might have.
Link:  
http://www.energy.wsu.edu/code/code_support.cfm
Scroll down to -Field guide-
Then down to –Foundation-
All PDF files - dialups beware

I still can't access any of these PDF's.  I get page can not be displayed messages on any page I try to open.  :(

Daddymem

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #8 on: December 22, 2005, 10:40:35 AM »
Work fine here...runing Firefox 1.5 and Acrobat 7.0 if that helps at all.

tjm73

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #9 on: December 22, 2005, 11:23:06 AM »
Hmmm...I'm using Internet Exploder at work.

I'll try from home on MAC with Safari.

Daddymem

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #10 on: December 22, 2005, 12:11:45 PM »
There ya go, native support is always nicer. :D

jraabe

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #11 on: December 23, 2005, 05:29:39 AM »
Thanks for that link Ryan. I've used the Feild Guide for years. I'll add a listing in the Reference section.

The PDFs don't tell you they are loading. They just start when you click on a link.
If you don't have Acrobat Reader already installed it may just stall out. Also these work best with a
broadband connection. There may well be problems with dial-up service.


tjm73

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #12 on: December 23, 2005, 10:05:36 AM »
When I went to them on my MAC at home they opened just fine.

Amanda_931

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #13 on: December 23, 2005, 05:01:11 PM »
Updating Adobe Acrobat helped me a couple of months ago.  Even the two-month old computer had an earlier version.

There are always PAHS and AGS.  The idea here is that as you circulate air quite slowly from the ground--not all that deep--into your house the heat gradually gets as far as your house through the summer, so that you can use it in the winter, when the outside air is quite cold, so you gradually cool the air as far as your house, so that you have cool air in the summer.  It certainly works in the high desert, but there are links below to houses in the Pacific North West and Virginia.  Know someone who's trying it in (Southern) Ohio. And I believe that JRR or somebody mentioned someplace in North Georgia or Alabama.

Passive Annual Heat Storage (is that right?) and Annualized Geo-Solar.  They work best for earth-bermed/underground houses.  

The AGS is a bit less cumbersome.  


Lots and lots of links about this woman's study for their house:

http://www.axwoodfarm.com/house/index.php?inc=5&PHPSESSID=ed4f2115fc60c696d948b0006a5841a4

Official AGS link--there's a paper linked to at the bottom of the page:

http://www.greenershelter.com/index.php?pg=3


PAHS

This turns up on a search, although he didn't use tubes.  His house is gorgeous.  And apparently works beautifully.

PACCS is yet another acronym "passive annual climate control systems"

http://paccs.fugadeideas.org/tom/index.shtml

same guy, has plenty of links here to classic PAHS (John Hait)

http://paccs.fugadeideas.org/

John Hait and the Rocky Mountain Research Center  (also try coolscience)

http://www.earthshelters.com/sustainable_living.html
« Last Edit: December 23, 2005, 05:12:23 PM by Amanda_931 »

jraabe

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #14 on: December 26, 2005, 12:11:42 AM »
Passive annual heat storage and other long term high mass passive solar strategies do not work well in all climates. They particularly do not work well in climates with little winter sun. Such houses can be energy efficient and therefore have low heating bills but this is not because of the thermal mass and south windows.

Cloudy northern climates are particularly inappropriate for such high mass structures. Yet, many proponents of the system seem to suggest that location makes little difference.

Such houses perform best in southern dry climates with strong seasonal temperature swings but predicable winter sun.

Personally I don't think there is any such thing as true seasonal heat storage without huge expenditures of money. To do it you need high heat density storage and lots of it. Things such as underground highly insulated water tanks fed from hydronic solar panels. Most high mass passive solar buildings are responding to the daily or at best multi-day sun cycles. Masonry and concrete are just too good an insulator to store heat in much more than the first 4" to 6" of the surface area.

That's why such houses perform best in climates where the soil temperature is somewhat close to the interior comfort range. The deep soil or water temperature of an area is actually that - the averaging out of the seasonal temperature swings. This is what you are insulating against when you build an earth tempered solar house.

Take a house that works well in Denver, the California desert or the American Southwest and then move it to central Alaska or northern Manitoba where the soil temp is perhaps 40º and see what happens. (Permafrost happens in a climate where the long term average of winter and summer temperatures is below freezing.) All that soil and thermal mass will now have to be insulated AGAINST. Large window areas will have to be buttoned up in winter to keep heatings costs under control.

A light frame high insulation building generally performs much better in such a climate, especially if the structure is not constantly occupied and kept at the same temperature.

Just like the real estate agent says, it's all about location.
« Last Edit: December 26, 2005, 12:30:42 AM by jraabe »

Amanda_931

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Re: Heat loss through concrete slab foundations
« Reply #15 on: December 26, 2005, 06:19:08 AM »
Probably true, at least as far as Northern Manitoba is concerned.  And to do them right, these houses pretty well have to be underground.

High groundwater levels can be a problem as well.  Although I know someone who is trying to work with them for summer cooling.

If you look at the "Average Annual Temperature" for a given region, that's going to be really close to the ground temperature.  I'd think that you could do some raising, but not lowering of it under a house with the earth tubes.  Air temperature might be more important than sun on the ground, don't know for sure.

The Axwood Farm site does not have much on how the house has been finished (if it has!) but it seems to be in what might be Western Washington State.  I know that there has been some work--house, I think, and a test building--in the Spokane area.

The other house is somewhere in Virginia--piedmont if not mountains.  No idea what the microclimate is there, but probably (winter) USDA zone 7.  This measurement is useless for calculating annual temperature, by the way--there are parts of Alaska (and England, and Denmark) that qualify as zone 7.  Virginia can be quite warm in the summer.

But I'd surely give a lot to have built-in natural air conditioning.  Especially if we get another summer like that of 1980, when the official airport temperature at Nashville was 100 (F) or more every day in July.  No rain either.  Beef prices went way way down, because farmers were selling off their herds or having to buy hay (from Texas, IIRC) by the third week in July.  Especially in the summer we get about a 20oF difference between day and night temperatures.  A friend remembers sitting out on his porch with his morning coffee in early August that year and feeling cold--he looked at the thermometer, 78 (F).  I had the world's clunkiest air conditioner in my apartment that year, think I only used it four or five times (no AC in the car either, or where I was working, so I acclimatized pretty well), but I'm older now, less tolerance for heat in particular.

RAB

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #16 on: December 27, 2005, 09:06:41 AM »
John
I will give you my vote on passive storage not working all that well. Lived in a house for 3 years with large windows and a thick slab floor. The damn slab never did get warm and neither did my feet. I did do some amateur temperature analysis and found the slab temperature followed the outside temperature – My conclusions from this experience are eerily close to yours:

-The slab needed to be insulated as well as the wall – this means R21 on all sides.
-The wall/slab insulation-intersection should overlap so a "cold seam" does not occur.
-The depth of insulation should be proportional to the soil conditions, if you have rocky soil any heat "captured" from the earth is lost through cold air infiltration through the soil regardless of published frost depths.
-Heat gathered by day is quickly loss through the windows unless expensive curtains are deployed as the sun moves.
-The storage area should be separated by an additional insulating wall and door system when weather conditions don’t cooperate.
Solar home builders should definitely do a cost analysis before proceeding.
Ryan B
« Last Edit: December 27, 2005, 09:44:44 AM by RAB »

Neil

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Re: Heat loss through concrete slab foundations
« Reply #17 on: December 27, 2005, 09:48:36 AM »
I'm considering an off-grid, ~1000 sq ft, earth-sheltered house on a south facing slope in the cloudy Pacific Northwest.  What I'm considering is basically a walk-out basement without a first floor :).  The slab and concrete walls would be well insulated and water-proofed.   The primary heating would be radiant floor heating with a wood stove as backup.  Power would be a couple PV panels with a large battery bank.  Backup power would initially be a generator.  The house site is just off a nice long ridge that might be suitable for a wind generator.

An earth-sheltered house is appealing to me because of its low impact on the home site and its low maintenance.  I don't find most house architectures very appealing and putting a house on a beautiful site is a shame.  I want to travel a bit so I want a house that can handle being empty for months without requiring maintenance and not be an easy target for vandalism.

Going off-grid complicates things, but the nearest power is about a 1/4 mile away through a young douglas fir tree farm (mine).  I could run the power up the driveway but that is a longer route.  If a wind generator isn't possible, going on-grid would always be an option.

Does all this sound realistically possible without throwing large sums of money at the problems?

glenn-k

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #18 on: December 27, 2005, 09:54:23 AM »
Depends on how much power you want - a couple panels in the cloudy PNW will give next to nothing when it is cloudy.  Wind may be a better option if you have enough -avg 12 to 25 @ 85 to 100' AGL would be nice--- in combination with some solar panels - but there goes some money.

Ultimately - on grid is still probably your cheapest option unless you get a kick out of playing with it like me.
« Last Edit: December 27, 2005, 09:56:01 AM by glenn-k »

jraabe

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #19 on: December 27, 2005, 11:38:17 AM »
Glenn's right. I have several friends up here who make or have made their own power. During the winter the generator runs a lot. Wind can work if the site is appropriate.

Here's a link to a very dedicated sun and wind power guy in the Northwest.

http://www.whidbeysunwind.com/

Also, thanks to Ryan and his comments.

Passive solar storage slabs can add a thermal flywheel to a house and help store solar and wood stove heat (which often overshoot and are harder to control). However, I would heavily insulate the edges and (less) all the way underneath such a slab, especially if you are in northern wet soils. Even then the slab will not be as warm as a radiant heated floor.

A slab at 75º is storing usable heat for the structure, but your 98.6º bare foot will experience it as COLD :o. A radiant slab at 105º will be much nicer  :)

« Last Edit: December 27, 2005, 12:12:13 PM by jraabe »

Amanda_931

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Re: Heat loss through concrete slab foundations
« Reply #20 on: December 27, 2005, 04:36:42 PM »
75oF slab will feel cold.

Pity, because floors are so much easier to take care of if you are barefoot (or slippered) any time you are inside.

The cheapest of the off-grid electricity is usually one of the micro-hydro systems--some are very simple indeed.  And they do weird things like 24 hours a day, seven days a week, 365 (or 366) days a year.  If you're lucky you almost never need the generator.  If you're like a friend in the next county you spend a lot of time trying to get your system that somebody cobbled together ten years ago to work at all.
« Last Edit: December 27, 2005, 04:41:48 PM by Amanda_931 »

JRR

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #21 on: December 27, 2005, 07:33:30 PM »
A little "heads up" for folks considering pouring slabs atop foam insulation:

The compressive strength of most of the foam panels that can be gathered at the local big box store will be in the neighborhood of 15 psi or so ... only suitable for walls, etc., ... not slabs.

However, higher strength foam panels are available in various compressive strengths up to 100 psi.  You can get info at the Owens Corning ("Formular") website.

Kelly Keilwitz(Guest)

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #22 on: December 28, 2005, 07:56:29 PM »
Hi Neil,
Kelly Keilwitz with Whidbey Sun & Wind, here (thanks for pointing me here, John).
As a geotechnical engineer and renewable energy contractor the house you describe is my dream home that I hope to build some day. I also love the low-profile aesthetics of an earth-sheltered home like you describe.

First, from a geotech viewpoint, understand that a great deal of your budget - maybe 30% to 40% could be in excavation, drainage and concrete (or other appropriate foundation wall) work, and the associated engineering and permitting costs. If you want to go the full-monte you could add on (considerably) more for a reinforced concrete and/or living roof.

Now, solar, passive: You probably already are aware, but your ridge should be facing south with no shading from tall trees

In deciding to go off-grid you need to first consider why you're doing it. If it's to be the most cost-effective, you must consider your energy use and habits, willingness to be actively involved with your energy system, and level of convienience and comfort you want (vs how much you want to spend on the energy system). As a rough guideline it's generally cost effective to go off-grid if you live more than 1/3 mile from power.

Electricity source is the main need for an offgrid home, as thermal needs can be met with fossil fools (oops!)  :)  Solar PV should be your main source, as there are no moving parts, 25 yr warranties and good incentives available. In the wintertime you'll need other production source(s), like fuel genny, wind genny, etc. If you're going to be away a lot in the winter, then a backup fuel genny is the best (most cost-effective) solution. If you have a wind resource, and can put up a tower tall enough to get the wind generator a minimum of 30 feet above the nearest tree within 500 feet (including tree growth for the next 20 years), then wind power is an excellent source to create a "hybrid" system to complement your PV's. As Amanda mentioned the best off-grid resource is micro-hydro, but it is highly site and stream specific.

If your energy requirements are small and you don't mind starting the fuel generator every now and then when it's cloudy for a few days, and do some of the work yourself you should easily be able to install a power system for less than the cost of running power to your site - and have no power bill! You definitely need to think bigger than "a couple of solar panels", though! In considering this cost remember that you're paying up-front for 15 to 20 years of power.

For space-heating, consider solar-thermal and woodstove heat exchanger input into a large water storage tank (usually your domestic water source) with heat exchangers feeding your radiant floor slab. I'm doing exactly this in my (early 70's energy dumb, but sustainably retrofitted) home. Wood IS a renewable resource, as long as you have a woodlot (or live on a tree farm)  :) !

Good luck!

-Kelly





glenn-k

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #23 on: December 28, 2005, 08:08:36 PM »
Thanks for popping in here with that, Kelly.  We hope to see more of you here.

jraabe

  • Guest
Re: Heat loss through concrete slab foundations
« Reply #24 on: December 29, 2005, 09:55:18 AM »
Good to see you here Kelly. Thanks for that thoughtful overview.

Kelly and I have worked together on some past projects including a volunteer effort to solarize and make energy efficient an old community building that was put up by farmers in the 1920's. What was the most cost effective thing we did to an old leaky building that was not occupied and heated all the time? Change out all the lights to CFL and LED bulbs! Really made a difference in the power bill.