Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

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LOW AMBIENT OPERATION
Condenser Head Pressure Control 1) Drain the cooler and water piping thoroughly for
Outdoor air-cooled units required by application to Drain fittings are provided on the cooler for this
start and run at ambients below normal summer purpose.
conditions require some means to keep the
condensing pressure high enough to insure adequate
expansion valve feed to the cooler to prevent low side
2) Add ethylene glycol to the chilled water system at
pressure trips, particularly during cold starts. Two a percent good for a freeze point at least 10
E
F
types of condenser fan control are available to allow below the minimum expected ambient.
the units to operate at the ambients and loads
indicated.
3) The field installed cooler heater disconnect switch
Standard Factory Installed Fan Cycling THIS SWITCH".
This commonly applied scheme cycles condenser 4) Make absolutely sure that responsible people know
fans "on" and "off" in response to head pressure to exactly how to react to general power failures.
maintain the head pressure within an acceptable
range for proper system operation. This methods will
permit starting and sustained running 20
E
F ambient.
The minimum ambient shown above reflect the
performance of the condenser surface exposed to the
operational fan(s) as well as that portion of the surface
rejecting heat by natural convection with related fans
"off". To further assist low ambient starts, all fans are
held "off" until the head pressure reaches 190 psig.
This alone cannot insure sustained operation if the
system load is not high enough to produce the
minimal pressures required.
Optional Variable Speed Fan Control
This scheme utilizes fan cycling but also adds speed
control to the lead fan or fans. This feature not only
serves to stabilize the head pressure between normal
fan staging but also allows for virtually "no fan"
operation down to 0
E
F ambient.
Cooler Freeze Protection - Low Ambient
Cooler freeze protection is a serious concern with
outdoor packaged chillers and the responsibility for
the proper implementation, monitoring and
maintenance of both factory and field installed
protective devices and procedures lies solely with the
customer. The ACDX coolers are heat tape wrapped
which utilize built-in 38
E
F thermostats and are
insulated for protection down to about -20
E
F.
However, this protection disappears if power fails,
power to the heater circuit is switched off or left off by
mistake, or the heater tapes burn out. In this regard,
it is advisable to read and log the heater circuit amp
draw at the first low ambient shut-down opportunity for
future service and monitoring reference. In light of all
the above, the following should be considered:
9
long term shut-down at ambients below 32
E
F.
must be permanently tagged "DO NOT OPEN