33
Without ambient control, the system would
shut down on low discharge pressure. The
flooded condenser method of low ambient
control fills the condenser coil with liquid
refrigerant, decreasing the heat transfer
capacity of the coil, which allows the coil to
operate at an acceptable discharge pressure.
The condenser coil will not be flooded during
summer ambient temperatures, so a receiver
is included to store the additional liquid
refrigerant required to flood the condenser
coil in low ambient. The receiver is factory-
sized to contain all of the flooded volume.
Without a receiver there would be high head
pressures during higher ambient conditions.
The low ambient system maintains normal
head pressure during periods of low ambient
by restricting liquid flow from the condenser
to the receiver, and at the same time
bypassing hot gas around the condenser to the
inlet of the receiver. This reduces liquid
refrigerant flow from the condenser, reducing
its effective surface area, which in turn
increases the condensing pressure. At the
same time the bypassed hot gas raises liquid
pressure in the receiver, allowing the system
to operate properly. CF Series condensers
and condensing units use an LAC valve for
low ambient operation.
LAC Valve
The Low Ambient Control (LAC) valve is a
non-adjustable three way valve that
modulates to maintain receiver pressure. As
the receiver pressure drops below the valve
setting (2034 kPa [295 psig] for R-410A), the
valve modulates to bypass discharge gas
around the condenser. The discharge gas
warms the liquid in the receiver and raises the
pressure to the valve setting. The following
schematic shows an example system using
the LAC valve.
Figure 8 - LAC Piping Example
Refrigerant Piping
(See back of the manual for refrigerant piping
diagrams.)
General
Piping from the condensing unit to the air
handler is the responsibility of the installing
contractor.
REFRIGERANT PIPING
Line sizes must be selected to meet
actual installation conditions, not
simply based on the connection sizes
at the condensing unit or air handling
REFRIGERANT PIPING
This section is for information only and
is not intended to provide all details
required by the designer or installer of
the refrigerant piping between the
condenser or condensing unit and the
air handling unit. AAON, Inc. is not
responsible for interconnecting
refrigerant piping. Consult ASHRAE
Handbook – Refrigeration and ASME
Standards.
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