Civil Engineering Reference
In-Depth Information
8.7
Variable Volume Package Rooftop Unit
This system (Fig.
8.3
) is constructed of one or two airside fans (supply and return/
exhaust), direct expansion cooling coil that absorbs the heat from the inside and
rejects that heat to the outside via condenser, and its fan assembly. This eliminates
the associate cost with separate chiller, chilled water pumps, cooling tower, and
condenser water pumps. Supply fan delivers a variable air volume to the terminal
units and return/exhaust fan modulate in track with the supply air to provide a proper
air balance in the building.
The main energy consumers in the system are supply fan power input, return fan
(if it is provided) power input, compressor power input, condenser fans power input,
and terminal units fan power input. Heat transfer through the ducts and duct air
leakage also contribute to energy consumption (waste) in this system. The small
energy consumed by low voltage power provided for control valves is another
source of energy consumption.
8.8
Self-Contained Water-Cooled Air Conditioner
This system (Fig.
8.4
) is constructed of one or two airside fans (supply and return/
exhaust), and direct expansion cooling coil that absorbs the heat from the inside and
rejects that heat to the condenser water loop. This heat then will be rejected to the
Fig. 8.3
Variable volume package rooftop unit
