Heatcraft Refrigeration Products CC-CUBZTB manual Head Pressure Control

HEAD PRESSURE CONTROL

Refrigeration condensing units must efficiently	Operation
perform at varying ambient conditions. A properly
sized unit will adequately perform at even the	As the ambient temperature falls, the system
highest summer ambient temperatures. However,	condensing pressure is also reduced. This pressure
in situations where the system must operate the	is maintained by a regulator (ORI-6-65/225) at the
majority of the time at less than design temperature,	condenser drain. At approximately 75°F saturated
a means of providing adequate head pressure	condensing pressure the regulator restricts the flow
for refrigerant flow is desirable. The CDV & CDD	of liquid refrigerant from the condenser causing the
units have an adjustable method of head pressure	condenser to flood. This condenser flooding allows
control.	the liquid refrigerant in the condenser to become
	subcooled by the ambient air flowing through the
This system provides year round control of refrigerant	condenser. As the regulator continues to flood the
	condenser, a pressure differential will be established
head pressure without the use of special refrigerant
	between the receiver and the compressor discharge.
expansion valves. As the ambient temperature falls,
	At a predescribed differential, a second valve (ORD-
the reciever pressure is allowed to fall to a minimum
	4) will open and allow discharge gas from the
of 75°F saturated condensing pressure. The reduced
	compressor to bypass the condenser and flow into
discharge pressure at the compressor increases the
	the top of the receiver. This gas is used to pressurize
compressor capacity and lowers the input watts
	the receiver. These valves are adjustable and the
from the compressor motor. The system also uses
	minimum receiver pressure may be reset higher or
the reduced ambient temperature to subcool the
	lower depending upon application situations of a
liquid refrigerant in the condenser. This subcooled
	particular job.
liquid also increases system capacity. As a general
rule, every one degree of subcooling results in 0.50%	Subcooled liquid is further enhanced by the routing
increase in system capacity. Together these result
in greater efficiency, greater capacity, and reduced of liquid from the receiver liquid line outlet to the
run time.	condenser before leaving the condensing unit.
Benefits:
• Automatic year-round control of refrigerant head
pressure without the use of special expansion
valves.
• Energy savings in mild ambient conditions due
to reduced compressor discharge pressure and
refrigerant subcooling
• Provides easy restart during low ambient
conditions.

5