Ensure that steel and ductile iron piping has a factory-applied
extruded polyethylene covering or is tape wrapped and cathodically protected.
Do not use aluminum pipe in aviation fueling systems in alkaline
soils with pH greater than 8.5 due to accelerated corrosion.
Plumbing Fixtures. Use non-corrosive fixtures such as vitreous
fixtures are also suitable when other alternatives are not practical. The use
of enamelled pressed steel fixtures is not recommended.
Ductwork. Use stainless steel for weather hoods, exhaust stacks,
and vent caps. Paint galvanized steel or aluminum sheetmetal ductwork for
outdoor use with one coat of polyamide epoxy primer and one coat of polyamide
epoxy exterior top coat.
system. The system may be a central air handling type with chilled water
coils or a unitary (single or multiple) direct expansion type unit capable of
controlling the dew point of the supply air for all conditions of load. When
required, apply reheat centrally using recovered heat or solar. Heat recovery
may be double-bundle condensers or separate, auxiliary condensers; run-around
closed-loop; or refrigerant hot gas. Use electric reheat only when critical
space conditions must be maintained or in variable air volume terminal units
to prevent over cooling of space.
Small Systems. For systems up to 35 tons, use single compressors
with a minimum of three-step capacity.
Packaged Units. Use packaged unitary units with multiple
reciprocating compressors (not to exceed four) for systems between 35 and 100
tons. Ensure that each compressor has separate and independent refrigerant
Chilled Water Systems. Divide the cooling capacity of chilled
water systems of 100 tons and greater between two chillers to ensure
reliability and constant chilled water supply without temperature fluctuations
and to prevent short cycling. Ensure that the combined capacity of the two
chillers does not exceed the total requirement including diversity. Consider
temperature rise in supply pipe to the most remote coil to ensure proper coil
dewpoint in selection of chilled water supply temperature.
Direct-Expansion Systems. Provide the compressor, evaporator, and
condenser of direct-expansion systems with necessary accessories to ensure
proper oil return and uniform circuit distribution at minimum coil load. Give
consideration to the need for unloading, vertical split-row coils, back
pressure regulators, and hot gas bypass.