Alpha Technologies Radium MiniBay - Manual (Page 23)

2 044-001-C0-00, Rev. C
2.0 DC Air Conditioner
2.1 Overview and Theory of Operation
The MiniBay DC Air Conditioner comes in 24V and 48V models and uses a brushless
compressor and variable speed controller. A temperature control board varies capacity by
varying compressor speed depending on the enclosure internal setpoint temperature. The
compressor runs between 50% and 100% of full speed depending on the load and enclosure
set point temperature. When the temperature drops more than 4°C below the set point, the
compressor and condenser fans shut off. The evaporator fans run continuously regardless of
the set point to maintain an even temperature inside the enclosure.
Theory of Operation:
1. Low pressure gas is drawn into the compressor.
2. The high pressure gas is sent through a condenser where air is blown over it, cooling the
gas into a liquid.
. The high pressure liquid passes through an expansion valve, where the liquid is allowed
to expand and boil off into a gas. As the gas expands, it cools.
4. The cool saturated low pressure gas is sent through the evaporator. Warm interior air is
blown over the evaporator and back into the interior, several degrees cooler.
5. The low pressure gas is then drawn into the compressor, where the cycle starts over.
Fig. 2-1, DC Air Conditioner Basic Block Diagram
Evaporator Fans
(always on)
Suction Line
Variable Speed
Compressor
Discharge Line
Liquid Line
Condenser Fans
(thermostatically controlled)
Sight Glass
Temp
Control
Board
20A
Speed Control
Board
Minor Alarm Connect
Major Alarm Connect
-48VDC Bus
Ground
Return Bar
Condenser
Hot gas is cooled by outside
ambient air and condensed
into a high pressure liquid.
Thermostatic
Expansion Valve
Evaporator
Liquid is allowed to expand at
low pressure back into gas,
cooling interior air.