Specifications

56 Catalog WSC/WDC-4
outlet of the pump. Vibration eliminator sections in the condenser inlet and outlet water lines are
not normally required. Where noise and vibration are critical and the unit is mounted on spring
isolators, flexible piping and conduit connections are necessary. If not factory installed, a flow
switch or pressure differential switch must be installed in the leaving chilled water line in
accordance with the flow switch manufacturer’s instructions.
Filtering and Treatment
Owners and operators must be aware that if the unit is operating with a cooling tower, cleaning
and flushing the cooling tower is required. Make sure tower blow-down or bleed-off is operating.
Atmospheric air contains many contaminants, which increases the need for water treatment. The
use of untreated water will result in corrosion, erosion, slime buildup, scaling, or algae formation.
A water treatment service should be used. McQuay International is not responsible for damage or
faulty operation from untreated or improperly treated water.
Machine Room Ventilation
In the market today, centrifugal chillers are available with either hermetic or open type motors.
Hermetic motors are cooled with refrigerant and dissipate their heat through the cooling tower.
On the other hand, open motors circulate equipment room air across themselves for cooling and
reject the heat to the equipment room. McQuay chillers have hermetic motors and DO NOT
require additional ventilation.
For chillers with open-drive type, air-cooled motors, good engineering practice dictates that the
motor heat be removed to prevent high equipment room temperatures. In many applications this
requires a large volume of ventilation air, or mechanical cooling to properly remove this motor
heat.
EXAMPLE: 1000 tons x 0.6 kW/Ton x 0.04 motor heat loss x 0.284 Tons/kW = 7 tons (24 kW) cooling
The energy and installation costs of ventilation or mechanical cooling equipment must be
considered when evaluating various chillers. For a fair comparison, the kW used for the
ventilation fans, or if mechanical cooling is required, the additional cooling and fan energy must
be added to the open motor compressor energy when comparing hermetic drives. Additionally,
significant costs occur for the purchase, installation, and maintenance of the ventilation or air
handling units.
Equipment room ventilation and safety requirements for various refrigerants is a complex subject
and is updated from time to time. The latest edition of ASHRAE 15 should be consulted.
Thermal Storage
McQuay chillers are designed for use in thermal storage systems. The chillers have two operating
conditions that must be considered. The first is normal air-conditioning duty where leaving
evaporator fluid temperatures range from 40°F to 45°F (4.4°C to 7.2°C). The second condition
occurs during the ice making process when leaving fluid temperatures are in the 22°F to 26°F
(-5.6°C to -3.3°C) range.
The MicroTech II control system will accommodate both operating points. The ice mode can be
started or stopped by an input signal to the microprocessor from a BAS or through a chilled water
reset signal. When a signal is received to change from the ice mode to the normal operating mode,
the chiller will shut down until the system fluid temperature rises to the higher setpoint. The
chiller will then restart and continue operation at the higher leaving fluid temperature. When
changing from normal cooling to the ice mode, the chiller will load to maximum capacity until the
lower setpoint is reached.
Computer selections must be made to check that the chiller will operate at both conditions. If the
“ice mode” is at night, the pressure differentials between the evaporator and condenser are usually
similar to normal cooling applications. The leaving fluid temperature is lower, but the condensing
temperature is also lower because the cooling tower water is colder. If the ice mode can also