Handbook of air conditioning and refrigeration / Shan K

28.2 CHAPTER TWENTY-EIGHT
● Four-pipe fan-coil air conditioning systems, or simply four-pipe fan-coil systems
● Two-pipe fan-coil air conditioning systems, or simply two-pipe fan-coil systems
● Water-source heat pump systems
Advantages and Disadvantages
Space conditioning systems have the following advantages compared to central and packaged systems:
● Both heating and cooling devices in the form of terminals, such as fan coils or water-source heat
pumps, are installed directly above or within the conditioned space, or very near to it. There is no
return duct in a space conditioning system except the large core water-source heat pumps. Only a
delivery outlet or a short recirculating duct supplies conditioned air to the perimeter zone.
● As discussed in Sec. 20.9, a separately dedicated outdoor ventilation system is always required to
provide ventilation air for occupants as well as the necessary exhaust air. At the same time, a
space recirculating system is used to condition the recirculating air for fan-coil and water-source
heat pump systems. The required amount of ventilation is always guaranteed, and a dedicated outdoor
air ventilation system facilitates the adoption of demand-controlled ventilation. The air economizer
cycle for free cooling is only limited to the volume flow of the outdoor ventilation air.
In space conditioning systems except the large core water-source heat pumps, the outdoor ventilation
air duct is probably the only main duct with comparatively less headroom required than in
the supply duct that crosses under the beams in the ceiling plenum.
● Both four-pipe fan coils and console water-source heat pumps provide individual zone control
with each fan coil or each console water-source heat pump serving an individual zone. There is
often an additional high-low speed or high-medium-low speed control on the volume flow of the
supply fan. The four-pipe fan coil or the water-source heat pump can be changed from cooling
mode to heating mode and vice versa automatically or manually, and it adjusts its capacity to
meet the variation of the zone load during part-load operation.
● There is less cross-contamination between rooms and control zones.
● According to Zaidi and Howell (1993), the energy use of a four-pipe fan-coil system was only 73
percent compared with a VAV reheat system, and the energy use of a water-source heat pump was
only 63 percent that of a VAV system. Anantapantula and Sauer (1994) found that the energy use
of a four-pipe fan-coil system compared to a VAV reheat system was even lower. Lower energy
use in fan-coil and water-source heat pump systems is due to the following:
First, there is far less energy required to transport the conditioned air and the recirculating air;
also, no energy is needed to transport the return air.
Second, a fan-coil system can transfer excess heat from the interior zone of a building to the
perimeter zone through a heat recovery system, as discussed in Sec. 13.3. A water-source heat
pump operated in heating mode can absorb the heat rejected by another water-source heat pump
that is operated in cooling mode and recovers it for heating in the perimeter zone.
Space conditioning systems have the following disadvantages:
● Only low-efficiency filters are used in fan coils and water-source heat pumps. Low efficiency air
filters are unable to remove particulates of size � 3 �m and are ineffective at proving an acceptable
IAQ for occupants as well as protecting the coils and components in the air distribution system
from dust and contaminants.
● Fan-coil systems reduce the chilled water flow rate to decrease their cooling capacity during part
load. Therefore, this results in a significantly higher zone relative humidity at part-load operation.
The zone relative humidity may increase to 70 percent at part load, especially when the fan coil is
oversized.
● Because fan coils and water source heat pumps are often mounted directly above or near to the
conditioned space, they may create a noise problem, as discussed in Sec. 26.2, which is always