Daikin McQuay AWS210BDS, Руководство по установке, Страница: 11 / 216

IM 1167 11
Installation and Startup
Optional Inlet Strainer
An inlet water strainer kit is available as a shipped-loose
option, sized per
Table 2 and with the pressure drop shown in
Figure 12 . The kit is field installed and consists of:
• Y-type 40% open area strainer with 304 stainless steel
perforated basket, Victaulic pipe connections and
strainer cap
• Extension pipe with two Schrader fittings that can be
used for a pressure gauge and thermal dispersion flow
switch. The pipe provides sufficient clearance from the
evaporator for strainer basket removal.
• ½-inch blowdown valve
• Two Victaulic clamps
Table 2: Strainer Sizing Data
Figure 12: Strainer Pressure Drop
Installing Optional Inlet Strainer
The extension pipe is located adjacent to the evaporator with
the strainer then mounted to it. The strainer must be mounted
per manufacturer's instruction with the arrows in the direction
of flow; inlet and outlet are noted along with the arrows.
Use one Victaulic clamp to mount the extension pipe to the
evaporator and the second to mount the strainer to the pipe.
The clamps to mount the field piping to the strainer are field
supplied. The piping and strainer must be supported to prevent
any stress on the evaporator nozzle.
The extension pipe has two Schrader fittings that can be used
as desired, frequently for mounting the optional Daikin
McQuay thermal dispersion flow switch and a water pressure
gauge. The ball valve can be installed in the strainer basket
cover as a blow-down valve.
System Water Volume
All chilled water systems need adequate time to recognize a
load change, respond to that load change and stabilize, without
undesirable short cycling of the compressors or loss of control.
In air conditioning systems, the potential for short cycling
usually exists when the building load falls below the minimum
chiller plant capacity or on close-coupled systems with very
small water volumes.
Some of the things the designer should consider when looking
at water volume are the minimum cooling load, the minimum
chiller plant capacity during the low load period and the
desired cycle time for the compressors.
Assuming that there are no sudden load changes and that the
chiller plant has reasonable turndown, a rule of thumb of
"gallons of water volume equal to two to three times the
chilled water gpm flow rate" is often used.
A properly designed storage tank should be added if the
system components do not provide sufficient water volume.
Variable Speed Pumping
Variable water flow involves reducing the water flow through
the evaporator as the load decreases. Daikin McQuay chillers
are designed for this duty, provided that the rate of change in
water flow is slow, and the minimum and maximum flow rates
for the evaporator are not exceeded.
The recommended maximum change in water flow is 10
percent of the change per minute. For example, if the
maximum (design) flow is 200 gpm and the flow is reduced to
a minimum of 140 gpm, the change in flow is 60 gpm, so the
maximum change per minute would be 10% of 60, or 6 gpm
per minute. It would take ten minutes to change the flow
through the entire range.
The water flow through the evaporator must remain between
the minimum and maximum values listed on
page 108 . If flow
drops below the minimum allowable, large reductions in heat
transfer can occur. If the flow exceeds the maximum rate,
excessive pressure drop and tube erosion can occur.
Evaporator Freeze Protection
Pathfinder chillers are equipped with thermostatically
controlled evaporator heaters that help protect against freeze-
up down to -20°F (-28°C). The immersion heater itself may
not be able to properly protect the evaporator from freezing
without circulation of water, and it is important that the chilled
water pumps are wired to, and controlled by, the chiller’s
controller. Additionally, use at least one of the following
procedures during periods of sub-freezing temperatures:
1
Add a concentration of a glycol anti-freeze with a freeze
point 10°F below the lowest expected temperature. This
AWS Model
Strainer
Size (in.)
Strainer Plus
Pipe Length
(in.)
Strainer
Weight
(lbs)
175ADS-250ADS
210ADH-250ADH
6 30.5 72
280ADS-350ADS
280ADH-405ADH
8 36.0 125
375ADS-530ADS
445ADH-530ADH
10 43.0 205