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Re: Calculating "Ideal" Thermal Mass for Residence

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Posted by Michael Dewolf on August 14, 2003, 1:51 am

I'm not sure what you mean by a "setback".

I will say that SIPs don't seem to have a lot of thermal mass.  Personally,
I would look at Earthblock, and sandwich-style concrete walls.  The
sandwich-style concrete walls are very similar to SIPs, only they have
concrete as their outer shell.

Is Eco-Tierra the patented building method developed by Tierra homes?

Check out http://www3.telus.net/TDGC/earthblock/commercial/


Posted by Michael Dewolf on August 14, 2003, 2:31 am
There's another building system.  It's another concrete-foam-concrete
Apparently, home depot has built over 70 stores with this method.


Michael D

Posted by Nick Pine on August 14, 2003, 5:00 am

A thermostat setback. An R24 SIP house with 1/2" drywall (0.5 Btu/F-ft^2)
might have a 12 hour time constant. You might go to bed when the house
is 70 F on a 30 F night with the thermostat set for 40 F and wake up to
a 30+(70-30)e^-(12h/12h) = 45 F house 12 hours later, saving lots of heating
energy. With 8" concrete (17 Btu/F-ft^2) walls, RC becomes 400 hours, so
you might wake up to a 30+(70-30)e^-(12/400) = 68.8 F house with almost
no overnight energy savings.

Exactly. I suggested SIP walls, with enough thermal mass in the ceiling
(eg 2 layers of drywall with some low-emissivity paint or a poly film duct
with a few inches of water over a dropped ceiling) to store overnight heat,
heated to 90 F or so with warm air from a low-thermal-mass sunspace. A
thermostat and a slow ceiling fan might control the room air temp and
allow large setbacks when the fan isn't running.

A shelfbox inside the sunspace might provide hot water and heat for five
cloudy days in a row.


Posted by Michael Dewolf on August 14, 2003, 5:23 pm
 I think I know what you're saying.  Since heat loss is dependant on the
temperature difference, more heat will be lost between the 68 degree
concrete and the outside than between the colder 45 degree inside wall and
the outside.

In tropical areas, there isn't a setback, so it wouldn't really apply.

In the case of a Canadian climate, where the heating season is longer, *but
there is a cooling season*, you would have to calculate the difference
between the advantages of larger thermal mass to carry a house through the
entire day during the cooling season, as well as it's ability to remove the
need for any cooling or heating during some of the fall and spring (when the
average heat loss would be equal to the internal energy generation), versus
the setback savings of less thermal mass during the heating season.

Michael Dewolf





Posted by News on August 26, 2003, 9:59 am

Thermal mass only stores heat, it does not produce it.  The thermal mass
inside a house in winter is heated via the occupants and the heating system,
then it gives heat out at night.   You are getting nothing for nothing
unless solar is used somehow.  However it does prevent temperature swings,
absorbing excess heat, adding to comfort conditions.  It contributes to the
Mean Radiant Temperature.  MRT is controversial.


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