Rev.01 03-27-17
Page 13 of 67
Compu-Aire
Cooling-Direct Expansion
Direct Expansion Cooling is designed to operate when the water flow switch senses that there is
no water flow. A digital signal is sent to the system from the controller to modulate the three (3)
way valve to cut water flow to the chilled water coil and the backup system direct expansion
cooling should start. The controller signals the compressor to start cooling. The outdoor
condenser gets energized as needed.
3.5
Air Side Economizer
Summary of Equipment
The Economizer Mixing Box is factory provided; however, it might be installed in the field by
others. Typically, the Air Side Economizer Mixing Box is provided for our Maxi-Kool unit with
System 2200 series controller.
Sequence of Operation
The evaporator fan and a set of dampers for the economizers are energized depending on heating
or cooling demands. The CONTROLLER controller commands the economizer box to bring either
the minimum amount of outside air or only outside air based on outside air temperature and
humidity. The controller determines whether the outdoor air temperature and humidity is
suitable for “economizer
-
cooling”. If the outdoor air is suitable, mechanical cooling shall be
locked out by the outdoor enthalpy control. The set of economizer damper actuators shall be
energized, operating the outdoor air and the return air dampers. The economizer damper
actuators shall be regulated to maintain proper discharge air temperature. When outdoor air is
not suitable for “ec
onomizer-
cooling”, the Economizer shall be locked out and the outdoor air
damper shall maintain minimum position while the indoor fan is operating. Upon unit shutting
down or power loss, the spring return motor actuator shall close the outdoor air damper. The
Economizer shall be automatically locked out during the heat mode (if applicable).
The Air Side Economizer box shall include: prewired modulating spring return damper actuators,
economizer control logic with compressor assist option, minimum outside air damper position
control, economizer control sensors including outdoor air temperature and humidity (enthalpy)
sensor, supply air and/or mixed air sensors. The supply air temperature sensor is used to maintain
the desire supply air temperature using DX and Economizer cooling together. The exhaust of
room air during economizer cooling mode shall be done by others in the field.
3.6
Water Side Economizer Energy miser (EM) Unit Using 2-Way Valves
Summary of Equipment
Energy miser units are provided with Dual Cooling options. DX cooling using Compressor based
system and Economizer cooling using Water Side Economizer Coil.
The primary system shall be Direct Expansion Cooling. The free cooling Energy miser coil is
provided together with the DX cooling coil. If the Water temperature drops below the Energy
