15 May 2003
CHAPTER 2 FUNDAMENTALS
CALCULATIONS. Perform multiple load calculations where suggested by
ASHRAE in order to determine HVAC system requirements. One example where at
least two load calculations are required is in order to verify comfort (including both
indoor temperature and humidity levels) at the most challenging "low ambient sensible
peak ambient latent" design conditions for systems installed in humid areas as specified
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.
Cooling Load Calculations. 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 the sensible, the latent, and the total cooling 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
Outdoor Design Conditions. Outdoor design conditions will be obtained at
2-2.1.1 Cooling. The outdoor design temperature for comfort cooling will be the 1.0
percent dry bulb and the corresponding mean coincident wet bulb temperature. Base
the selection of evaporative equipment on the 1.0 percent wet bulb temperature. For
applications where maintaining indoor temperature or humidity conditions is critical, the
designer may use the corresponding 0.4 percent temperatures. For the selection of
gain, add 5 degrees F (3 degrees C) to the dry bulb temperature specified above.
2-2.1.2 Heating. The outdoor design temperature for comfort heating will be the 99
percent dry bulb temperature. For applications where maintaining indoor temperature
or humidity conditions is critical, the designer may substitute the 99.6 percent
temperature for the 99 percent temperature.