1 February 1999
a. Heating Load Calculations. Exclude anticipated internal and solar heat gains from
heating load calculations. Increase the calculated size of equipment and distribution system by
up to 30 percent where necessary to compensate for morning recovery due to night setback.
b. Cooling Load Calculations. Prepare cooling load calculations using either the transfer
function method (TFM) or the CLTD/SCL/CLF Method, which is based on the cooling load
temperature differences (CLTD), the solar cooling load factors (SCL), and the cooling load
factors (CLF). These methods are described in the ASHRAE Handbook Fundamentals. If
necessary, increase the calculated size of equipment and distribution system(s) by up to 10
percent to compensate for morning recovery due to night set forward or by up to 10 percent to
compensate for unanticipated loads or changes in space usage. Limit the total combined
increase above the size calculated of equipment and distribution system(s) to 15 percent total.
Submit a psychometric plot of each air-conditioning system along with the calculations. Clearly
identify all points in the conditioning process on the psychrometric chart and verify both
sensible, latent, and total capacity using the appropriate data from the chart. List the sensible,
latent, and total capacity requirements for each cooling coil specified. For applications where
reheat is required for humidity control, the capacity of the reheat will be equal to the total
internal sensible heat generated in the area served.
2-2. DESIGN CONDITIONS.
a. Outdoor Design Conditions.
(1) The outdoor design temperature for comfort cooling will be the 2.5 percent dry bulb
and the corresponding mean coincident wet bulb temperature as listed in TM 5-785. Base the
selection of evaporative equipment on the 2.5 percent wet bulb temperature. For applications
where maintaining indoor temperature or humidity conditions is critical, the designer may use
the corresponding 1.0 percent temperatures. For the selection of condensers and condensing
units that will be subjected to unusually high radiation heat grain, add 3 degrees C (5 degrees F)
to the dry bulb temperature specified above.
(2) The outdoor design temperature for comfort heating will be the 97.5 percent dry
bulb temperature as listed in TM 5-785. For applications where maintaining indoor temperature
or humidity conditions is critical, the designer may substitute the 99.0 percent temperature for
the 97.5 percent temperature.
b. Indoor Design Conditions.
(1) The indoor design temperature for comfort cooling will be 8.3 degrees. C (15
degrees. F) less than the 2.5 percent outdoor design temperature, but will not be lower than
23.9 degrees C (75 degrees F) or higher than 25.6 degrees C (78 degrees F). The indoor
design specific humidity will not exceed the outdoor design specific humidity; otherwise, the