Specifications
54 Catalog WSC/WDC-4
Oil Coolers
McQuay centrifugal chillers, sizes 063 through 126, have a factory-mounted, water-cooled oil
cooler with a temperature controlled water regulating valve and solenoid valve for each
compressor. Cooling water connections are located at the rear of the unit, near the compressor
and are shown on the specific unit certified drawings. Models WDC 063 through 087 have the
cooling water connections in the lower portion of one tube sheet. Models WSC and WDC 050
chillers have refrigerant-cooled oil coolers and do not require a cooling water connection.
WDC 063, 079, 087, 100 and 126 dual compressor chillers are equipped as above, but the water
piping for the two oil coolers is factory piped to a common inlet and outlet connection.
Field water piping to the inlet and outlet connections must be installed according to good piping
practices and must include stop valves to isolate the cooler for servicing. A 1" minimum cleanable
filter (40 mesh maximum) and drain valve or plug must also be field installed. The water supply
for the oil cooler must be from the chilled water circuit, or from an independent clean source such
as city water. When using chilled water, it is important that the water pressure drop across the
evaporator is greater than the pressure drop across the oil cooler or insufficient oil cooler flow
will result. If the pressure drop across the evaporator is less than the oil cooler, the oil cooler
must be piped across the chilled water pump, provided that its pressure drop is sufficient. The
water flow through the oil cooler will be adjusted by the unit's regulating valve so that the
temperature of oil supplied to the compressor bearings (leaving the oil cooler) is between 90°F
and 110°F (32°C and 43°C).
Compressors using chilled water for oil cooling will often start with warm "chilled water" in the
system until the chilled water loop temperature is pulled down. With cooling water in the 40°F to
55°F (4°C to 13°C) range, considerably less water will be used and the pressure drop will be
greatly reduced. The following table contains oil cooler data at various inlet water temperatures.
Table 7, Oil Cooler Performance
Hot Side
POE Lub
Cold Side
Water
Cold Side
Water
Cold Side
Water
Cold Side
Water
WSC 063 - 087
Flow, gpm 9.9 11.9 2.9 2.0 1.54
Inlet Temperature, °F
118.0 80.0 65.0 55.0 45.0
Outlet Temperature, °F
100.0 87.3 94.5 98.3 101.4
Pressure Drop, psi - 4.3 0.3 0.14 0.09
WSC 100 - 126
Flow, gpm 15.8 21.9 5.11 3.5 2.7
Inlet Temperature, °F
120.0 80.0 65.0 55.0 45.0
Outlet Temperature, °F
100.0 87.0 95.0 99.0 102.3
Pressure Drop, psi - 3.78 0.23 0.11 0.07
NOTES:
1. Data is for a single compressor (oil cooler). Double the flow rates shown for WDC dual compressor chillers.
2. Pressure drop includes the oil cooler and control valve.
When supplied with city water, the oil piping must discharge through a trap into an open drain to
prevent draining the cooler by siphoning. The city water can also be used for cooling tower
makeup by discharging it into the tower sump from a point above the highest possible water level.
NOTE: Particular attention must be paid to chillers with variable chilled water flow through the
evaporator. The pressure drop available at low flow rates can very well be insufficient to supply
the oil cooler with enough water. In this case an auxiliary booster pump can be used or city water
employed.