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In the last week or so I learned about a fascinating modern version of a millennia old technology.
I'm
talking about thermal mass...this is a very popular technology among
the passive solar crowd--stretching back to the dawn of
civilization--and it involves building your home (or castle) with
"thick" walls that absorb heat during the heat of the day (cooling the
home) and release that heat during the cool night (heating the home).
Of
course most modern buildings (with the exception of some "fringe"
passive solar designs) do not call for walls that are multiple feet
thick. Enter the "new material" commonly known as phase change material
(PCM), which is formulated to accomplish the same thermal effect as a
12 inch wall in about a 1 inch package.
The PCM is engineered
to absorb heat by melting at a predetermined temperature. The melting
material absorbs a massive amount of energy (simple thermodynamics) if
the ambient/outside temperature rises above the melting point. And when
temperatures fall below the same predetermined temperature the PCM
reverts to a solid and releases the stored energy. Basically the PCM
acts as a "natural" air conditioner to provide cooling above a set
temperature and heating below it. Once the PCM completes its phase
change in either the up or down temperature direction it offers no
"additional" thermal benefit until the surrounding temperature again
crosses the set temperature. (I just point this out to be as clear as
possible about what the material does.)
Basically the PCMs
behave like ice that can "freeze" at room temperature (or whatever
temperature you design them to work at). We all know that if you put an
ice cube in a glass of room temperature water, the ice cube melts and
the water in the glass gets chilled below room temperature. This is
because the melting ice--the phase change from solid to liquid--absorbs
heat from the surrounding water. Conversely you need to put liquid
water into a freezer for quite some time to convert the liquid back to
a solid--this is slightly harder to conceptualize but the liquid water
gives off heat (to the surrounding freezer) as it solidifies.
There is a company marketing products that contain PCMs to the (home) building industry called BioPCM.
There are other companies that produce PCMs for this and different
applications, but this one offers an interesting "green" spin by using
"bio-based materials" rather than paraffin derived from petroleum. Also
BioPCM has specifically packaged its product for use in buildings (and
it really looks easy to install--check their products page) which seems
sensible, I have no idea about its cost, but the company claims up to
30% energy savings--FYI.
A thermal mass product works in
conjunction with standard insulation (not instead of!), where the
insulation slows the rate of heat transfer either up or down while the
thermal mass stores (and releases) the heat that gets through the
insulation to make a certain desired temperature "sticky".
Assuming
you pick the right temperature for your climate, using a PCM can reduce
both your heating and cooling bills, as well as increase comfort by
providing temperature stability with its natural air conditioning
properties. If you are lucky enough to experience zero climate
variation, a PCM will do you almost no good, but if you experience
frequent (i.e. daily) climate variation you will get the most benefit
from a PCM.
