Marc:
>From the paper "The Embodiment of Embodied Energy", 1994, G. Baird et.
al.:
Embodied energy for: Insitu concrete: 3160 MJ/m3 (+/- 15%)
200 cu m. concrete would be 632,000 MJ
For comparison, 2 cords of hardwood fuel burned at 100% efficiency would
yield 50,000 MJ
So, if this were the average fuel saving or consumption, the embodied
energy in the concrete would represent 12.5 year's worth. The only
energy gain realizable from the thermal mass of the concrete would be to
even out solar gain fluctuations, since the concrete itself has
(virtually) no insulating value, so does not contribute to energy
efficiency (heating fuel consumption) in any other way except perhaps to
reduce infiltration. As a wild guess, I'd ballpark the passive solar
energy "contribution" of the concrete in the building I mentioned at 10%
- 20% that value, or 5 - 10 MJ annually, or roughly 1 to 2% of the
embodied energy. Just some back-of-envelope doodlings, something we need
to get better at.
Also, any masonry over 4" in thickness does not participate in a 24 hour
thermal cycle.
In a superinsulated building with HRV and a sufficiently large area of
high tech windows, this begins to look a little different, since the
concrete could carry the building through multi-day solar cycles. We
recently built a masonry heating system in another concrete building,
north of Toronto, designed by Greg Allen's company. It has an
uninsulated floor to provide earth coupling, and their modelling
indicates that the unoccupied building (it is a secondary residence)
will never drop below 10C, with no backup heat. I guess the lesson is,
if you're gonna use a lot of concrete, you better invest in some serious
passive solar design as well, and be ready to spend a lot for windows.
Best.....Norbert
-- -------------------------------------------------------- Norbert Senf email: mheat@mha-net.org Masonry Stove Builders mheat@hookup.net RR 5, Shawville website: http://mha-net.org/msb Quebec J0X 2Y0 fax: 819.647.6082 voice: 819.647.5092 __________________________________________________________________ This greenbuilding dialogue is sponsored by Oikos (www.oikos.com) and Environmental Building News (www.ebuild.com). For instructions send e-mail to greenbuilding-request@crest.org. __________________________________________________________________