General. Select air cooled equipment on the basis of
entering air at 5 degrees F above the design temperature as given
in NAVFAC P-89 for roof mounted equipment and for equipment in
Packaged DX Equipment. Multiple packaged DX equipment
should only be used when it is shown to be life cycle cost
effective for the application.
Central Chilled Water Equipment
a) Use only one chiller for comfort cooling
applications unless it becomes economical to split capacity.
Mission requirements may dictate the use of multiple units with
capacities determined by critical loads. Obtain approval for the
use of multiple units from the engineering field division (EFD)
or engineering field activity (EFA).
b) Size units on the basis of acceptable refrigerants
specified in NAVFAC guide specification (NFGS)-15652, Central
Refrigeration Equipment for Air Conditioning. Do not use
refrigerants with an ozone depletion potential (ODP) greater than
0.05 or a global warming potential (GWP) greater than 0.34.
c) Use centrifugal or rotary screw compressor chillers
for capacities greater than 120 tons.
d) Though air cooled chillers are less efficient than
water cooled chillers, air cooled chillers require less
maintenance; this should be a consideration in the selection.
e) Water treatment of cooling towers and evaporative
or dumping of water treated with chemicals to the sanitary or
storm sewer may be prohibited. Check with the local
environmental program manager for use of wastewater and sanitary
Auxiliary Equipment - Cooling
a) Condenser Heat Rejection. Heat can be rejected
from a condensing refrigerant to atmosphere with an evaporative
condenser, with a water-cooled condenser and a cooling tower,
with an air-cooled condenser, or with closed ground-loop water
rejection. Do not use potable water for condenser heat
rejection. Provide a three-way diverter valve to control
condenser cooling water supply temperature. Cooling with pond,
stream, or lake water should only be considered after evaluating
environmental impact of returning heated water and additional