Package air conditioner is a bigger version of the window air conditioner. However, unlike window air conditioner or PTAC units, it has a higher cooling or heating capacity and is usually able to cool an entire house or a commercial building. The nominal capacities ranges from 3 tonne to 15 tonne.
The conditioned air are transferred to the space to be conditioned through ducting which is usually hidden in the ceiling and wall of the building. The unit is placed outside the house, a special room in a building or even on top of a roof. This unit is factory assembled and skilled technicians are needed to install this type of unit.
Protection devices such as High/Low pressure switch, overload relays for all motors, water flow and air flow switches are included in the units. The compressor have winding protection thermostat built into the winding to disconnect the circuit in the event of overheating.
There is an interlocking circuit with the evaporator fan motor starter to ensure that the compressor can only start if the fan motor is running.
This self contained unit is assembled in a casing where all the air conditioning componenets are housed. They include:
Rooftop Air-Cooled Package Air Conditioner.
Package Air Conditioner Condenser Type
The condenser used in a package air conditioner can be air-cooled or water-cooled type. Air-cooled type is usually for capacity below 5 tonne and water-cooled for capacity above 5 tonne. The capacity of air-cooled type is lower than that of water-cooled condenser using the same compressor.
The water-cooled type can be completely factory assembled, tested and charged with refrigerant before being installed in the field. This is advantages because less man power is needed in the field to do the installation hence cost saving.
The air-cooled type cannot be factory assembled or charged as the laying of refrigerant piping, pressure testing, charging and evacuation have to be carried out in the field.
In the air distribution, centrifugal fans are usually provided at the evaporator side which can develop higher static pressure. The higher the static pressure, the better the air throw to the room is. Air distribution is done through ducts and grills. The air quantitites are usually in the range of 10-11.3 cubic meter/min (350-400 cfm) per tonne.
In critical application such as computer room which need higher rate of air flow, higher capacity fans with air flow up to 550 cfm are provided. This usually need to be factored in during the design of the system.
Two Refrigeration Systems
In some units, two independent refrigeration systems are included in the package. In this case, the cooling coils have a common tube sheets though the two systems are independent. The tubes of the coil are entwined.
Two separate water-cooled condensers or a condenser with an internal partition that forms two independent condensers are used. The water side is common to both the independent condenser portions.
It is a common practice to have one compressor running all the time with the other compressor control by a single-stage thermostat. In this case, the capacity can be controlled either to 50% or 100%. However, newer units have two-stage thermostat that can control the capacity from 0%, 50% or 100%.