V. Principles of Operation
Kooltronic Air Conditioners are required when the equipment operating temperature must be kept near
or lower than the ambient room temperature, and/or the cabinet must be sealed from dust, fumes, oil,
corrosives and other contaminants. This Air Conditioner utilizes a "Closed-Loop Cooling System" to
ensure optimum performance of the installed components.
Closed-Loop cooling seals the electronic enclosure from hostile elements in the environment. Two
separate circulation systems are employed. The internal system cools and dehumidifies the air inside the
cabinet, totally isolating the sensitive electronics and other components from the environment. The
external system uses circulating ambient air or water to discharge the heat removed from the electronics.
The heat is dissipated from the enclosure by means of the vapor compression refrigeration cycle. This
takes place in a hermetically-sealed refrigeration system, utilizing either an air-cooled or water-cooled
condenser heat exchanger. The warm air inside the enclosure is drawn through the evaporator coil where
it is cooled, dehumidified and returned.
Enclosure moisture accumulated on the evaporator coil is collected and evaporated in the condensate
evaporator tray and released to the ambient air by the condenser blower. Excess condensate is released
to the ambient through the drain tube.
The heat removed through the evaporator coil is transferred by the compressed refrigerant to the
condenser coil. Ambient air or water is then passed through the condenser coil, where it absorbs the heat
and is then discharged to the environment.
The unit is equipped with a Bypass Thermostat to prevent the evaporator coil from freezing and eliminate
compressor cycling. The Bypass Thermostat controls a solenoid bypass valve which allows hot liquid
refrigerant to bypass the evaporator coil. The Bypass Thermostat must not be set below the factory
setting of 75°F (6°F differential). The air conditioner running in bypass mode has 20% of its maximum
cooling capacity. The NP47-1 is also equipped with a Low Temperature Thermostat. The set point of this
thermostat is 5°F lower than the set point of the Bypass Thermostat. If low ambient temperature and
internal enclosure load is less than 20% of the air conditioner’s capacity, the thermostat will shut off the
compressor. If necessary, the thermostat may be adjusted to increase the temperature within the cabinet.
Unlike the thermostats used in household air conditioners that control room temperature, the thermostats
used in the NP47-1 monitor the return air from the enclosure to prevent the evaporator from freezing. In
conditions of low ambient temperature and low enclosure load, the thermostat regulates the return air
temperature from 75°F to 85°F. If the unit is equipped with an optional non-adjustable high temperature
alarm, it will activate when the return air temperature reaches 130°F.
REFRIGERANT
FILTER DRYER
CONTROL
BYPASS VALVE
METERING
DEVICE
(Capillary Tube Shown)
COMPRESSOR
EVAPORATOR
HEAT EXCHANGER
CONDENSER
AIR INLET
(Ambient Air In)
CONDENSER
HEAT EXCHANGER
CONDENSER OUTLET
(Heated Ambient Air Out)
HEATED AIR
FROM ENCLOSURE
CONDENSER
AIR INLET
(Ambient Air In)
ACCUMULATOR
COOL AIR
TO ENCLOSURE
NP47
5
