Handbook of air conditioning and refrigeration / Shan K

● Room air conditioning (RAC) systems
● Packaged terminal air conditioning (PTAC) systems
As discussed in Sec. 1.3, individual air conditioning systems always use a DX coil for cooling. They
are normally used in perimeter zones for the convenience of local outdoor ventilation air intake.
Advantages and Disadvantages
Individual air conditioning systems have the following advantages:
● There are no supply, return, or exhaust ducts.
● Individual air conditioning systems are the most compact, flexible, and lower in initial cost than
others, except portable air conditioning units.
● Building space is saved for mechanical rooms and duct shafts.
● It is easier to match the requirements of an individual control zone.
● They are quick to install.
Individual systems have the following disadvantages:
● Temperature control is usually on/off, resulting in space temperature swing.
● Air filters are limited to coarse or low-efficiency filters.
● Local outdoor ventilation air intake is often affected by wind speed and wind direction.
● Noise level is not suitable for critical applications.
● More regular maintenance of coils and filters is required than for packaged and central systems.
Individual room and unitary packaged air conditioning systems are both self-contained, factorymade,
packaged systems using DX coils for cooling. However, individual systems are single-zone
units, whereas a packaged system can be either a single-zone or multizone unit. Individual systems
have no supply and return ducts. Also, individual systems provide far smaller heating-cooling capacities,
poorer outdoor ventilation intake, lower-efficiency filters, simpler control system, and far
less ECMs than packaged systems. Room air conditioners are often window-mounted. Most of the
packaged units are rooftop units.
As discussed in Sec. 1.5, individual air conditioning systems were found in about 26 percent of
66 million air conditioned homes and packaged systems in 74 percent in 1991 in the United States.
Also, individual systems were found in 22 percent of commercial buildings and packaged systems
in 48 percent in 1992 in the United States.
26.4 ROOM AIR CONDITIONING SYSTEMS
Equipment Used in Room Air Conditioning Systems
AC SYSTEMS: SYSTEM CLASSIFICATION, SELECTION 26.9
Room air conditioning systems are the most widely used individual air conditioning system in the
United States. Window-mounted or through-the-wall types of room air conditioners; room heat
pumps (RHPs) to provide both heating in winter and cooling in summer; and split air conditioners
(SACs) with an outdoor condensing unit and an indoor air handler, for the sake of greater flexibility
in location of the air handler as well as isolation of compressor noise outdoors are three kinds of
equipment used in room air conditioning systems. A room heat pump has a similar configuration to a
room air conditioner except a four-way reversing valve is added to change from cooling mode to
heating mode, and vice versa. According to Mahoney (1996), annual shipments of window-mounted