[GSBN] [nbne] no Timber frame for Alberta house

[Derek Roff]

I had a friend who used to describe an unsatisfying alternative with words like, "This is much better than something that isn't as good."  This was usually good for a smile, and a little further reflection.  I'm a big fan of Kelly Lerner and her work, and her words below remind me of the comparison above.  Kelly says that "ground coupling...is clearly a more energy efficient choice...", and I am left wondering, more efficient than what?  Certainly, coupling a house to moderately cold ground is way more efficient than coupling it to very cold, moving air.  

I wanted to thank Robert for his response last week on this topic, and for posting the graphic on thermoclines.  (I apologize for being slow to respond.)  I look at the same data, and come to a contrasting conclusion.  I agree that a building designer can allow energy to flow from the living space into the earth below a house, and create a bubble of warmer soil, that can help prevent freezing, if the house is unheated for some period.  And I agree that passive survivability (non-freezing) of this sort is important.  However, I'm bothered by two aspects of this approach.  In the normal case, heat is continually drained from the house into the soil, which increases energy consumption and decreases comfort.  Not only are cold floors a common homeowner complaint, but they also cause people to turn up the thermostat, thereby magnifying the energy waste.  This energy drain is continuous, and is therefore poorly matched as a remedy to the rare situation of trying to keep the pipes from freezing when the home is unoccupied or experiences a prolonged power failure.  

On the other hand, when a building experiences a long period with no power input, its sub-floor thermal battery of warmed soil has a limited capacity.  This kind of earth coupling runs the risk of not offering sufficient protection in the rare cases when passive survivability is really needed.  The pipes in our house may freeze in a severe weather/power event, and the constant energy drain over the years may not provide the anticipated protection from catastrophic events.  I prefer the solution that Rob Tom already mentioned.  We can design our building so that it is not earth coupled, and leaks only a very small amount of energy into the surrounding soil.  Frost protected foundations can be designed, so that the house and pipes will not freeze, even if the house is never occupied, and never has any power input.  Such designs will be more energy efficient, will be more comfortable, and will offer much more reliable passive survivability.  Oh yeah, I'm supposed to say more efficient than what.  More efficient than earth coupling, as the term is being used in this discussion.  In most climates, even during severe weather/power events, intelligent solar design (sun coupling?) combined with excellent insulation can provide not only passive survivability for water pipes, but tolerable human habitation temperatures (50˚F or more) with no power input, beyond the suns rays.  

Best wishes,
Derelict

On Sep 19, 2011, at 10:08 AM, Kelly Lerner wrote:

> HI all,
> Just chiming in to say that ground coupling (with insulated crawlspace OR slab on grade with excellent perimeter insulation and insulation below based on climate, soil conditions and heating system) is clearly a more energy efficient choice in a cold climate, because the delta-T at the soil is always going to be less in the winter. That means less heat loss at the floor/foundation. Ground coupling also helps with summer cooling if that is an issue in your climate. 


Derek Roff
derek at unm.edu




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