Installation manual

IM 1029-2 Magnitude™ Frictionless Centrifugal Chillers – Model WMC 7
Flow Switch
Note: Chiller units must have flow switches for the evaporator and
condenser. Daikin furnishes factory-installed and wired, thermal-
type flow switches as standard equipment on Magnitude chillers.
Field-installed and wired Delta-P switches can be used instead.
T
hey prevent the unit from starting without sufficient water flow
through the vessels. They also serve to shut down the unit in the
event that water flow is interrupted to guard against evaporator
freeze-up or excessive discharge pressure.
Additionally, 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 the Field Wiring Diagram on page 41.
Cooling Towers
The condenser water flow rate must be checked to be sure that it conforms to the system design. A tower
bypass valve, controlled by the unit controller, is required to control the minimum condenser entering
temperature. Unless the system and chiller unit are specifically designed for them, condenser bypass or
variable condenser flow is not recommended, since low condenser flow rates can cause unstable operation and
excessive tube fouling.
Cooling towers used with Daikin centrifugal chillers are normally selected for condenser water inlet water
temperatures between 75°F and 90°F (24°C and 32°C). Lower entering water temperatures are desirable
from the standpoint of energy reduction, but a minimum does exist.
Condenser Water Temperature
When the ambient wet bulb temperature is lower than design, the entering condenser water temperature can be
allowed to fall, improving chiller performance.
Daikin chillers will start with entering condenser water temperature as low as 55°F (12.8°C)
providing the chilled water temperature is below the condenser water temperature.
Depending on local climatic conditions, using the lowest possible entering condenser water temperature can
be more costly in total system power consumed than the expected savings in chiller power would suggest due
to the excessive fan power required.
To obtain lower than 55°F (12.8°C) entering condenser water temperature with a tower selected to produce
85°F (29.4°C) water temperature at design ambient air temperatures, cooling tower fans must continue to
operate at 100% capacity at low wet bulb temperatures. As chillers are selected for lower kW per ton, the
cooling tower fan motor power becomes a higher percentage of the peak load chiller power. The offsets of
compressor power and fan power must be examined. On the other hand, the low condenser water
temperatures can be easy and economical to achieve in mild climates with low wet bulb temperatures.
Even with tower fan control, some form of water flow control such as tower bypass must be used and
controlled by the chiller MicroTech II controller.
Figure 3 and Figure 4 illustrate two temperature-actuated tower bypass arrangements. The “Cold Weather”
scheme, Figure 4, provides better startup under cold ambient air temperature conditions since most of the
piping is indoors and not subjected to cold ambient air. The check valve may be required to prevent air at the
pump inlet.
Figure 2, Unit-Mounted Flow Switch