Daikin WMC Specifications download pdf (Page 42)

42 Catalog 602-2

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. 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. To obtain the lowest possible

energy cost, the interaction between compressor

power, fan power, and pumping power should all

be studied.

Even with tower fan control, some form of water

flow control such as tower bypass or variable

speed condenser water flow may be required to

maintain minimum acceptable entering condenser

water temperatures. must be used. The MicroTech

II control is capable of controlling tower fans and

bypass valve directly or indirectly through an

output signal to the building automation system

ensure stable and efficient chiller operation.

Figure 15 and Figure 16 illustrate two temperature

actuated tower by

pass arrangements. The “Cold

Weather” scheme, Figure 16, provides better

startup under cold am

bient 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 15, Tower Bypass, Mild Weather

Operation

Figure 16, Tower Bypass, Cold Weather

Operation (Bypass Indoors)

Pumps

To avoid the possibility of objectionable

harmonics in the system piping, 4-pole,

1800/1500 rpm system pumps should be used.

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.

Include thermometers and pressure gauges at

the chiller inlet and outlet connections and

install air vents at the high points of piping.

Where noise and vibration are critical and the

unit is mounted on spring isolators, flexible

piping and conduit connections are necessary.

Install a flow switch or pressure differential

switch in the leaving chilled water line, if one is

not factory installed.

Variable Speed Chilled

Water Pumping

Variable speed pumping involves changing

system water flow relative to cooling load

changes. Daikin McQuay centrifugal chillers

are designed for this duty with two limitations.

First, the rate of change in the water flow needs

to be slow, not greater than 10% of the change

per minute. The chiller needs time to sense a

load change and respond.

Second, the water velocity in the vessels must

be 3 to 10 fps (0.91 and 3.0 m/sec). Below 3 fps

(0.91 m/sec), laminar flow occurs which

reduces heat transfer and causes erratic

operation. Above 10 fps (3.0 m/sec),

excessively high pressure drops and tube

erosion occur. These flow limits can be

!

CAUTION

Freeze Notice: The evaporator and

condenser are not

self-draining. Both must

be blown out to completely remove water

to help prevent freeze up.

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