[GBlist] Passive Solar/Thermal Mass Comparison

["Bion D. Howard" <bdhoward@ix.netcom.com>]

Passive Solar/Thermal Mass Comparison

The two topics are inter-related and not mutually exclusive.  It is best to
beware of generalizations about thermal mass where these concepts are mixed
up.

Those of you interested in thermal mass need to differentiate between two
principal issues regarding its deployment:

  1.  the effect of heat capacity upon materials thermal properties of
exterior building envelopes (like concrete block or log-walls in comparison
with wood frame construction and annual energy use; and

  2.  the use of additional heat capacity deployed on surfaces inside a
conditioned space for the purpose of reducing temperature "swings" and
storing collected solar heat for later release.

These are not the same. A building with a thermally massive shell may also
(or not) use larger glazing areas for passive solar heating and
daylighting.  It may or may not require additional heat capacity inside to
control temperatures as a function of its thermal protection, orientation
and the "excess" glazing area which might otherwise create overheated
contritions (mild day, low-sun angle, clear sky).

By the same token, a light frame building (with little heat capacity in its
shell) can behave as if it has insufficient thermal mass -- overshooting
thermostat set points.  Adding interior thermal storage can reduce this
effect.  At a given level of increased equatorial facing glazing area, a
light frame building will need added interior thermal capacity "sooner"
than a heavier structure, all things held equal.

By April 1, 2001 my report to NAHB Log Homes Council will be ready for
"public review," and if you would like to receive an electronic copy,
please send a request in response to this message.  The findings and
background information should be useful to those interested in
understanding heat capacity effects in exterior envelopes of buildings.

For passive solar design, I recommend getting a copy of the excellent
STeven Winter Assoc. book - Passive Solar Design and Construction Handbook.
 Then expect to do some calculations to "tune" your design to the local
climate and occupant comfort needs.

   -- Bion Howard




-
    ||              Contact:  Bion D. Howard, President
=(O) =     Building Environmental Science & Technology
    ||      P.O. Box 1107   Edgewater, MD 21037  USA
         Phone:  410.867.8000   Telefax: 301-889-0889
                   <http://www.energybuilder.com>

______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________