Unit installation

803 C – 01/05 A – pag. 4/17
recommended. McQuay International is not responsible for damage or faulty operation from untreated or
improperly treated water.
Head pressure control, tower system
The minimum entering water temperature to the condenser must not be lower than 18 °C at full tower water flow. If
lower temperature water is used, the flow must be reduced proportionally. Use a three-way bypass valve around
the tower to modulate the condenser water flow. Figure 2 shows a three-way pressure actuator water regulating
valve used for cooling applications. This regulating valve will assure an adequate condensing pressure if the inlet
condenser water temperature falls below 18 °C.
Head Pressure Control, Well Water System
When using city or well water for condensing refrigerant, install a normally closed direct acting water regulating
valve in the outlet piping of the condenser. This regulating valve will assure an adequate condensing pressure if
the inlet condenser water temperature falls below 18 °C. The condenser service valve provides a pressure tap for
the regulating valve. The valve can modulate in response to head pressure. On shutdown, the valve closes,
preventing water from siphoning out of the condenser. Siphoning causes condenser waterside drying and
accelerates fouling. If a valve is not used, Figure 3 illustrates the recommendation of a loop at the outlet. Size the
loop height (H) to offset the negative pressure caused by the siphoning effect. A vacuum breaker may be required.
Figure 2, Bypass valve Figure 3, Well Water System
Temperature and Water Flow Limitations
PFS units are designed to operate in conditions from -8 °C to +15 °C leaving water temperature on the evaporator
side and +18 °C to +50 °C entering water temperature on the condenser side. Glycol in the evaporator is required
on all applications below +4 °C leaving evaporator fluid temperature. The maximum allowable water temperature
to the cooler in a non-operating cycle is 40 °C. Flow rates below the minimum values shown in the evaporator and
condenser pressure drop curves may cause freeze-up problems, scaling and poor control. Flow rates above the
maximum values shown in the evaporator and condenser pressure drop curves will result in unacceptable
pressure drops, excessive nozzle and tube erosion and possibly cause tube failure.
Evaporator Freeze Protection
When freeze protection is a concern, do the following:
• If the unit will not be operated during the winter, drain and flush the evaporator and chilled water piping with
glycol. Drain and vent connections are provided on the evaporator.