Handbook of air conditioning and refrigeration / Shan K

26.8 CHAPTER TWENTY-SIX
Space Limitations
Maintenance
Initial Costs
systems), a smoke exhaust system of about 6 ach (air changes per hour) should be installed; and the
dedicated outdoor ventilation system can be used to pressurize the adjacent control zones according
to local and federal fire code requirements.
Space limitations specified by the architect or facility owner also influence the selection of the air
conditioning system. For instance, for a high-rise building of more than 30 stories, if rooftop space
is not available for the penthouse of AHUs and other mechanical equipment, or if there is no space
left for supply and return duct shafts, a floor-by-floor AHU central system may be the practical
choice. Because of the available ceiling space, low-velocity duct systems are often used in highceiling
industrial buildings to save air-transporting energy.
A central system with AHUs, a few water-cooled centrifugal chillers, and cooling towers needs less
maintenance work than a packaged system with many rooftop air-cooled reciprocating packaged
units. A VAV reheat central system needs less maintenace work in the fan and plant rooms than a
fan-coil system, which often requires much maintenance work in the ceiling space directly above
the conditioned space.
Initial cost and operating costs (mainly energy cost) are always primary factors that affect the selection
of an air conditioning system, especialy for a developer who sells buildings with installed air
conditioning systems. The initial cost of the air conditioning (HVAC&R) system in a building, expressed
in $/ft 2 ($/m 2 ), depends on the building occupancies, system configurations, size of the
building, and capabilities of specific systems. According to Gladstone and Humphreys (1995), the
initial costs of an HVAC&R system for school buildings are as follows:
Generally, the more complex an air conditioning system becomes and the more features it has, the higher
will be the initial cost. Among all these, the Class 1 clean room central system is the most expensive.
26.3 INDIVIDUAL AIR CONDITIONING SYSTEMS
Basics
System type $/ft 2
Single-zone, constant-volume packaged systems 5.25
Multizone reheat constant-volume central system 6.60
Multizone dual-duct central systems 8.25
As discussed in Sec. 1.3, an individual room air conditioning system or simply an individual system
uses a self-contained, factory-made packaged air conditioner to serve an individual room. It is ready
to use after electric cable and necessary water drainage are connected. Individual systems always
use a DX coil to cool the air directly. Individual systems can be subdivided into the two following
air conditioning systems: