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GBlist: thermal mass / time constants / "diurnal heat capacity"




Jorg Ostrowski wrote:
> I am presenting working out the "Building Time Constant" (BTC) for our
> demonstration project. To do that we need to calculate component and > total 
mass, then the heat storage capacity by using the specific heat for
> each. We then will have to use the heat loss characteristics to arrive at
> a final number in hours.
----------------------------------------
A building's total heat capacity may be interesting in terms of calculating
a thermal time constant, but the effective -- diurnal heat capacity -- 

    the amount of heat that flows into and out of intentional thermal     
storage (not including third order, very indirect mass) during a 
      24 hour period --

may have the greatest effect upon building energy consumption for heating
and cooling, after thermal protection, fenestration energy balance, and 
air-leakage rates are considered.

A plethora of information on thermal mass particularly in passive
solar buildings is available in a library-reference volume called
the "Solar Documentation Project" managed by Rockwell International
and published by BrickHouse, several years ago. I do not have a copy
to cite page numbers, but Bion Howard and Harrison Fraker, AIA
developed the thermal mass chapter based largely on monitored passive
solar building performance results.

Doug Balcomb now Senior Scientist at NREL, developed a Basic/DOS program
called DHC at one point, which calculated the diurnal heat capacity
effects in passive solar buildings. This may still be available somewhere.

The ASHRAE "Red Book" for design and analysis of passive solar buildings has a 
companion update volume (supplement) that contains discussion of diurnal heat 
capacity and why it is important for good performance in passive solar 
buildings.

Also, check with Jeff Christian at ORNL (I think -- jeff@ornl.gov) to 
see if copies of various reports done during the DOE Thermal Mass Assessment 
project might still be available.  During part of this study 
estimates of the internal heat capacity of home furnishings were made by NIST 
researchers (Prin. Doug Burch); which was part of several published papers in 
the ASHRAE transactions 1983-1988 time frame.

Finally, you may wish to repost your energy inquiry on the Energy 
efficient buildings list (a sister list to "greenbuilding@crest.org")\
where you may get additional input.
.........................................

I hope these leads are helpful. (ps: check the publications listing
on my web site to see if there is anything there of possible interest)

--------------- Contact Information------------------
        Mr. Bion D. Howard, Principal          
  Building Environmental Science & Technology   
  P. O. Box 1007, Upper Marlboro, Maryland 20773 USA
  bdhoward@ix.netcom.com <--> http://nrg-builder.com
     Voice#  410-867-8000  fax#  301-889-0889
-------------------------------------------------------          
 
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