I Single Package Heat Pumps
7. EconomizerAccessory
Installation Instructions
NOTE: For installation and wiring of economizer
see"Low Voltage Wiring of Economizer Option"
(pg.10).
The purpose of an economizer is to:
• Provide cool outdoor air to the conditioned space
during the cooling cycle to minimize the use of com-
pressors.
• Bring outdoor air into the conditioned space to meet
minimum ventilation air requirements whenever the
circulation blower is running.
logic module also controls the compressor staging based
on the thermostat input.
The minimum opening position of the outdoor air dampers
is field adjustable. It is set on the logic module of modulat-
ing economizers or on the actuator motor of three-position
economizers.
The outdoor air enthalpy sensor is factory installed on the
outdoor air dampers. The enthalpy change-over point is
adjustable on the logic module.
Theory of Operation
The economizer has two sets of dampers that are mechan-
ically linked together. The outdoor air dampers regulate the
intake of outdoor air and the return air dampers regulate
the flow of return air (see FIGURE 12). When the outdoor
air dampers modulate open, the linkage causes the return
air dampers to modulate closed. A barometric relief damp-
er is installed in the return air side of the system. It relieves
any positive pressure in the unit created by the economiz-
er.
The economizer is controlled by a logic module which field
connects to the unit controls through a harness plug. The
A mixed air sensor is field installed in the blower inlet. The
mixed air sensor keeps the mixed air above 56°F (13.3°C).
See the economizer installation instructions for the location
of the mixed air sensor.
A positive pressure is created in the building when the out-
door air dampers open and the return dampers close. This
pressure must be vented or the air will not circulate proper-
ly. This is the function of the barometric relief dampers. A
positive pressure forces the passive exhaust dampers to
swing open.
The outdoor air dampers open to the mininum position for
outside air whenever the circulation blower is ON in the
cooling or heating mode.
FIGURE 12 J Typical Downflow Economizer
Outdoor Air Dampers
Mixed Air Sensor
Actuator Motor and
Logic Module
80-50-28b
Return Air
Dampers
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