Handbook of air conditioning and refrigeration / Shan K

● A packaged system always has a cooling system that uses the DX coil to cool air directly. A desiccant-based
system usually uses the DX coil as supplementary cooling. An individual system
also uses a small, self-contained, factory-assembled refrigeration system that has a DX coil to
cool air.
● A central system has a cooling system that uses chilled water as a cooling medium to cool air indirectly.
A thermal storage system is always a central system that uses chilled water or brine as
the cooling medium.
● As discussed in Sec. 9.18, for DX coils in individual systems, rotary compressors are the most
widely used. For DX coils in packaged systems, reciprocating and scroll compressors are most
widely used. Scroll compressors are gradually replacing the reciprocating compressors in packaged
systems because of their higher energy efficiency. For chillers in central and space systems,
centrifugal and screw compressors are widely used in large chillers whose cooling capacities are
greater than 75 tons (264 kW); and screw, scroll, and reciprocating compressors are widely used
in medium-size and small chillers. Screw and scroll types are also gradually replacing the reciprocating
compressors in small and medium-size chillers.
● As discussed in Sec. 8.1, hot water, heat pump, and direct-fired warm air furnace heating systems
were installed in commercial and residential buildings with a floor area of both about 75 percent
in the early 1990s. In packaged systems, direct-fired warm air furnaces and heat pumps are often
used. For individual systems, either heat pumps or electric resistance heaters are often used. In
central and clean space systems, hot water heating systems are most widely used.
● As discussed in Sec. 20.9, air systems can be classified into three categories:
Constant-volume (CV) outdoor recirculating air mixing systems
Variable-air-volume (VAV) outdoor recirculating air mixing systems
Dedicated ventilation and space recirculating systems
Only air systems of the space air conditioning systems are dedicated ventilation and space circulating
systems. Individual, packaged systems in residentials and clean room air conditioning systems
are mostly CV air systems. All the other air conditioning systems may be either CV or VAV
systems and will be so designated.
26.2 AIR CONDITIONING SYSTEM, SUBSYSTEM,
AND MAIN COMPONENTS SELECTION
Selection Levels
AC SYSTEMS: SYSTEM CLASSIFICATION, SELECTION 26.3
During the design of a new or retrofit system, air conditioning system, subsystems, and main components
selection is performed mainly on three levels:
● Air conditioning system level. This level deals with such aspects as whether a VAV packaged air
conditioning system or a fan-coil air conditioning system should be selected.
● Air system, water system, central plant cooling and heating system, and control system level. For
a VAV packaged system, it must be determined whether the system is to be a single-zone VAV
air mixing system, a multizone VAV reheat air mixing system, or a fan-powered VAV air mixing
system. In a packaged system, its cooling system is always a DX system with either reciprocating
or scroll compressors. Its heating system is either a direct-fired warm air heating system or, in locations
where the unit electric rate is low, a heat pump system or an electric heating system.
For a space air conditioning system, its air system is always a dedicated ventilation and space
recirculating system. For the water system, the choice is between a plant-building loop with
variable flow in the building loop and a plant-through-building loop. Either a hot water heating
system or an electric heating system can be selected for a fan-coil system. A fan-coil system