Specifications

Cat 604-3 31
Application Considerations
Condenser Water Temperature
When the ambient wet bulb temperature is lower than design,
the entering condenser water temperature of Magnitude WME
chillers can be lowered to improve chiller performance.
Chillers can start with entering condenser water temperatures
as low as 40°F (4.4°C). For short periods of time during
startup, the entering condenser water temperature can even be
lower than the leaving chilled water temperature.
Magnitude WME chillers are equipped with electronic
expansion valves (EXV) and will run with entering condenser
water temperatures as low as shown in Figure 24 or as
calculated from the following equation on which the curves are
based:
Min. ECWT = 5.25+(LWT)-0.75*DT
FL
*(PLD/100)+14 *(PLD/100)
2
Where:
ECWT = Entering condenser water temperature
LWT = Leaving chilled water temperature
DTFL = Chilled Water Delta-T at full load
PLD = The percent chiller load point to be checked
Figure 24: WME Minimum Entering Condenser Water
Temperature (EXV) (10°F Range at Full Load)
For example; at 44°F LWT, 10°F Delta-T at full load, and 50%
full load operation, the entering condenser water temperature
could be as low as 49°F. This provides excellent operation
with water-side economizer systems.
Depending on local climatic conditions, using the lowest
possible entering condenser water temperature may be more
costly in total system power consumed than the expected
savings in chiller power would suggest, due to the excessive
fan power required.
In this scenario, cooling tower fans would continue to operate
at 100% capacity at low wet bulb temperatures. The trade-off
between better chiller efficiency and fan power should be
analyzed for best overall system efficiency. The Energy
Analyzer program (available from your Daikin McQuay Sales
Representative) can optimize the chiller/tower operation for
specific buildings in specific locales.
Even with tower fan control, some form of water flow control,
such as tower bypass, is recommended.
Figure 25 and Figure 26 illustrate two temperature-actuated
tower bypass arrangements. The “Cold Weather” scheme,
Figure 26, provides better startup under cold ambient air
temperature conditions. The bypass valve and piping are
indoors and thus warmer, allowing for warmer water to be
immediately available to the condenser. The check valve may
be required to prevent air at the pump inlet.
Figure 25: Tower Bypass: Mild Weather Operation
Figure 26: Tower Bypass: Cold Weather Operation (Bypass
Indoors)
Condenser water temperature control
The standard MicroTech controller is capable of three stages of
tower fan control plus an analog control of either a three-way
tower-bypass valve or variable speed tower-fan motor. Stages
are controlled from condenser-water temperature. The three-
way valve can be controlled to a different water temperature or
track the current tower stage. This allows optimum chilled
water plant performance based upon specific job requirements.
Pumps
The condenser water pump(s) must be cycled off when the last
chiller of the system cycles off. This will keep cold condenser
water from migrating refrigerant to the condenser. Cold liquid
refrigerant in the condenser can make start up difficult. In
addition, turning off the condenser water pump(s) when the
chillers are not operating will conserve energy.
30
35
40
45
50
55
60
65
0 102030405060708090100
Per cent Load
ECWT (°F)
46°F LChWT
44°F LChWT
42°F LChWT
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