Table of Contents
Advertisement
It is necessary to prevent the recirculating water from approaching freezing conditions when the system is
operating under load. The most « critical » situation occurs, if operation at subfreezing conditions coincides with
light load conditions. The key to protecting the recirculating water is capacity control by adjustment of air flow to
maintain the temperature of the recirculating water minimal above freezing point. As a rule of thumb this minimum
temperature is 5°C, but there are applications, where even lower temperatures can be accepted. (Contact your
local BAC Balticare representative for advice.)
The desired method to match the cooling capacity to load and weather conditions is to adjust the air flow by the
use of modulating controls (variable speed drives).
Alternatively, multi speed fan motors or fan cycling can be applied, but fans operating on a common heat exchange
section should always be operated simultaneously.
It is not recommended to cycle the spray pump as a means of controlling the unit capacity.
Whenever two speed motors are used for capacity control, a time delay of at least 15 seconds is required when
switching form high to low speed. Sudden switch over might damage the drive system or the motor.
When the equipment is operated with a variable fan speed control device, steps must be taken to avoid both
operating at or near to the fan's «critical speed» and below a minimum of 15 Hz for a belt driven unit (or direct
driven fans) or 20 Hz for a unit with gear box. For more information consult your local BAC Balticare
representative.
When operating with VFD drives above nominal frequency be aware of the potential risk for motor overload
or mechanical damages.
It is recommended to provide sinus filters on the VFD to prevent bearing damage on fan motors.
Refer to fan motor nameplate data when programming a VFD.
The purpose of a low level cut out switch for pump protection is to protect the pump from running dry in case of
make-up failure or extreme water loss. The status of the alarm can be checked prior to pump start-up, but should
not be considered during the first minute after start-up, since activation of the pump can cause a water level drop,
that might trigger the alarm. Normal make-up will stabilize the water level after a short period of time.
In case the low level alarm signals, that there is no longer enough water in the cold water sump to guarantee a
proper operation, the pump should be stopped (after a time delay of 60 seconds) and only manually restarted after it
has been verified that the water in the sump is at or near the overflow level.
In case the low level pump alarm is used to stop the pump, appropriate control logic should be incorporated
to prevent hunting of the pump motor. Once the spray pump is stopped, the water in suspension will drain
back to the tank and raise the water-level above the alarm level, which will reset the alarm immediately. A manual
reset of the alarm after solving the root cause of the low level alarm is recommended. Frequent start/stop or
hunting will damage the motor.
FRP propeller
At temperatures below -20°C, FRP fans should be started at reduced speed to assure their structural integrity.
16
W W W . B A L T I M O R E A I R C O I L . E U
CAUTION
Advertisement
Table of Contents
