APPENDIX C (continued)
that comfort is exceeded can be rapidly determined on the annual psychrometric
summary by counting the percentage of time between the original boundary and
the new interior temperature line. If the total percentage of time exceeds
the acceptable percentage, either Qinternal should be reduced or Qvent
should be increased.
Thus, to determine the required air changes per hour to keep the
interior temperature below the top of the comfort zone at the 0.5 m/sec
boundary, solve for ACH.
ACH = (Qinternal) / (0.018) (Bldg Vol.) (delta T)
Qinternal is an assumed (estimated or calculated) value,
Bldg Vol is known (from the preliminary design), and
delta T = Tout - Ttop
of 0.5 m/sec boundary
Computer Models of Interior Temperatures. The use of a computer
allows a much more detailed analysis of the interior environment of buildings.
Currently available computer programs for thermal analysis include: DOE-2,
BLAST, CALPAS3 and TRACE. These can perform hour-by-hour analysis of the
detailed loads imposed on the building by weather, occupancy, lighting,
equipment, and the shape and thermal properties of the building envelope.
The mechanical engineer should evaluate the expected internal loads
and determine whether they cause the comfort zone to be substantially
exceeded. If so, he should consider computer simulation for more precise
Program Inputs and Outputs. Program inputs include a detailed
description of the physical parameters of the building, its expected
occupancy, and an appropriate weather tape. Outputs include expected
temperatures and humidities on an hourly basis and as summaries.
Program Limitations. To date, such programs do not predict the
airflow patterns or velocities within buildings. They are generally unable to
predict even the bulk ventilation rate through spaces caused by wind
the interior. These limitations severely affect the utility of such models
for design of naturally ventilated buildings.
Computer Programs for Thermal Analysis. Currently available
National Technical Information Service (NTIS)
U.S. Department of Commerce
5285 Port Royal Road
Springfield, Virginia 22161