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GBlist: Mass Wall time constants, tools, etc.




  Calculation of Mass Wall Time Constants and Performance
  --------------------------------------------------------
Thermal mass can only be effective if it is designed with the
overall building conservation performance and local climate
kept in mind.  Overly thick walls, centralized masses, and mass
that either a.) is not in direct path of admitted solar radiation,
or b.) is not a "secondary" mass open to reflected solar energy
and to convective heat transfer, will be much less effective.

ASHRAE Passive Solar Design Analysis Manual, and the user handbook
which comes with the PSIC "builder-guidelines" workshops are
currently available.  Also, passive solar mass "rules of thumb" 
are contained in Mazria (classic) "The Passive Solar Design Book,"
now sadly out of print.  Another source of thermal storage info
is the set of ASES passive conference proceedings, now in over
20 volumes dating back to the mid-1970's.

Here area some (hopefully) useful tools assisting this thread --

  1.  WINguide, windows embodyment of NREL BuilderGuide first
      produced for PSIC.     ( http://www.solaequis.com )
      Has specific thermal mass performance analysis section.
      Also helps US builders determine if they meet MEC !

  2.  Energy10 -- a simulation tool that can examine the
      role of thermal mass in buildings up to about 10,000 SF
      of floor area.  Initial design for light commercial but
      I have found it does OK on residential (updated version),
      but its major focus is on efficiency and daylighting.

  3.  DHC (MS Basic) diurnal heat capacity program, originally
      available from J. Douglas Balcolm of NREL -- developed while
      Dr. Balcolm was at Los Alamos -- is a calculator of the diurnal
      heat capacity of assemblies.  (not real sure of where to find
      hot program now) A program listing is contained in a DOE
      Los Alamos publication:  LA-9694-MS "Heat Storage and Distrib-
      ution inside Passive Solar Buildings," pages 105-113, May 1983.
      In the same report on pages 24 - 37, the analytical process and
      equations are derived for DHC calculations in the DHC code.

  4.  Other computer programs for energy calculations are reviewed
      at a great DOE site (by energy software expert Dru Crawley): 

          http://www.eren.doe.gov/buildings/tools_directory/

  5.  Discussion of the use and design considerations for thermal
      mass in passive solar buildings -- Balcolm, J.D. 1981, "Heat
      Storage Duration." proc. 6th ASES Passive Solar Conference,
      Portland, OR (c) ASES, Boulder, CO http://www.ases.org/solar/
      This clearly written paper reviews key issues in effective
      climate specific design of thermal mass in buildings (...not
      exterior mass-walls or building codes compliance as in MEC
      or ASHRAE 90.1 or 90.2 standards...)

Since 1982, I have performed about 100 different passive solar building
design analyses for "tuning" thermal mass and providing for good 
performance of such systems as the "air-core" floor and wall masonry
system.  In nearly all cases, our results show that thinner "tuned" layers
of mass distributed in the building as primary and secondary heat
capacity results in much better performance than an equivalent amount
of mass in centralized building features.  One exception has been in 
buildings that are "super-insulated" with very high levels of air-
tightness.  They act as if they have more mass than can be accounted
in typical simulations.  They appear to operate more efficiently as
"sun-tempered" buildings (without larger equatorial facing glazing 
areas).  

***  Balancing conservation, glazing, internal heat gains, and
ventilation strategies to minimize purchased energy and maximize comfort
should be one goal -- look at meeting whole-building design criteria!

*** One whole building design criteria worth taking a look at is from
    EEBA's techncial efforts spanning a 4-year development process:

                http://www.eeba.org/criteria.htm

[Comments always welcome at Building Environmental Science & Technology]

--------------- 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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