IM 1044-2
Centrifugal Chillers
11
Notes from previous page:
1.
A segmented 3-inch paddle (1, 2, and 3 inches) is furnished mounted, plus a 6-inch paddle loose.
2.
Flow rates for a 2-inch paddle trimmed to fit the pipe.
3.
Flow rates for a 3-inch paddle trimmed to fit the pipe.
4.
Flow rates for a 3-inch paddle.
5.
Flow rates for a 6-inch paddle
6.
There is no data for pipe sizes above 8-inch. A switch minimum setting should provide protection against no
flow and close well before design flow is reached.
Alternatively, for a higher margin of protection, normally open auxiliary contacts in the pump starters can be
wired in series with the flow switches as shown in Figure 19, Field Control Wiring Diagram on page 32.
CAUTION
Freeze Notice: Neither the evaporator nor the condenser is self-draining;
Both must be blown out to help avoid damage from freezing.
The piping should also include thermometers at the inlet and outlet connections and air vents at the high points.
The water heads can be interchanged (end for end) so that the water connections can be made at either end of the
unit. If this is done, new head gaskets must be used and control sensors relocated.
In cases where the water pump noise can be objectionable, vibration isolation sections are recommended at both
the inlet and outlet of the pump. In most cases, it will not be necessary to provide vibration eliminator sections in
the condenser inlet and outlet water lines. But they can be required where noise and vibration are critical.
Cooling Towers
The condenser water flow rate must be checked to be sure that it conforms to the system design. Some form of
temperature control is also required if an uncontrolled tower can supply water below about 65
°
F (18
°
C). If tower
fan control is not adequate, a tower bypass valve is recommended. Unless the system and chiller unit are
specifically for condenser bypass or variable condenser flow is not recommended since low condenser flow rates
can cause unstable operation and excessive tube fouling.
The condenser water pumps must cycle on and off with the compressor. See Figure 19, Field Control Wiring
Diagram on page 32 for wiring details.
Tower water treatment is essential for continued efficient and reliable unit operation. If not available in-house,
competent water treatment specialists can be contracted.
Heat Recovery Chillers
HSC heat recovery chillers control the chilled water leaving temperature. The cooling load determines
compressor loading and unloading, the same as in a conventional chiller. A heat recovery chiller’s control
algorithms are identical to a conventional cooling-only chiller.
The temperature of the hot water being supplied from the recovery condenser to the heating load is established by
manipulating the cooling tower water temperature. The 3-way cooling tower bypass valve is controlled by the
heating water inlet temperature to the recovery bundle of the condenser. Based on the signal the 3-way valve gets
from the heating hot water sensor, it will bypass sufficient water around the tower to force the tower condenser
water loop high enough for the recovery bundle to produce the desired hot water temperature.
The chilled water and its control system do not sense that the condensing pressure and condenser water
temperatures are being regulated in this manner.
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