Water Connections; General; Condenser Piping - McQuay SWT C Series Installation And Maintenance Manual

Water Connections

General

Due to the variety of piping practices, follow the recommen-
dations of local authorities. They can supply the installer
with the proper building and safety codes required for code-
compliant proper installation.
Basically, the piping should be installed with a minimum
number of bends and elevation changes for best perfor-
mance. Piping should contain:
1. Vibration eliminators to reduce vibration and noise
transmission to the building.
2. Shutoff valves to isolate the unit from the piping system
during unit servicing.
3. Manual or automatic air vent valves at the high points of
the system.
4. Some means of maintaining adequate system water
pressure (e.g., expansion tank or regulating valve).
5. Temperature and pressure indicators located at the unit
to aid in servicing.
6. A strainer or some means of removing foreign matter
from the water before it enters the pump. It should be
placed far enough upstream to prevent cavitation at the
pump inlet (consult pump manufacturer for recommen-
dations). The use of a strainer will help prolong pump
life and help maintain system performance.
7. Size piping to minimize system pressure drop.

Condenser Piping

1. Units may be specified with water and condensate con-
nections on either end of the unit.
2. All units have an individual condenser per refrigerant
circuit. All condensers are factory piped for a common
condenser supply and a common condenser return con-
nection.
3. Field piping connections are made to factory provided
piping located as indicated on the unit submittal draw-
ings. Units with factory provided water side economizer
coil have the piping connections run to the outside of
the unit cabinet. Connections are located behind a fac-
tory mounted shipping cover. Connections are located
behind a factory mounted cover plate. All connections
are copper, sweat connections as indicated on unit
dimensional drawings.
4. Supply and return water connections must be made at
the proper locations as indicated by the dimensional
drawings. Supply (water in) connection is always the
lower connection.
5. Units with factory mounted water side economizer
should not require head pressure control. The econo-
mizer will typically elevate the water temperature by 5
8
to 10°F before entering the condenser, allowing suitable
condenser water temperatures whenever the tower sup-
ply temperature is 50°F or higher. Without head pres-
sure control, mechanical cooling is locked out below
55°F EWT.
6. Head pressure control must be provided if no econo-
mizer is used and if entering condenser water tempera-
tures will go below 55°F. Fan cycling and/or modulating
discharge dampers on the cooling tower are often used,
or a 3-way bypass around the tower. Cooling tower con-
trol to maintain the temperature at >55°F is generally
more cost effective if multiple units are in the loop. If
valves are installed on the individual SWP units, a sin-
gle water regulating valve controlled by circuit #1 head
pressure should be used. The Lead/Lag option must
equal "NO". When Lead/Lag equals "NO" circuit #1 is
always first on and last off. The refrigerant pressure line
from the valve should be connected to a gauge port on
any liquid line service valve located in compressor #1
refrigerant circuit. Compressor #1 is located at the far
left of the cabinet.
Figure 4. Condenser Regulating Valve (refrigerant
pressure controlled
)
If the water regulating valve is placed in series with the unit
condensers, it should be installed in the water line leaving
the condenser and should shutdown to prevent water from
siphoning out of the condensers. For systems where a con-
stant pumping head is required, the water regulating valve
may be installed in a bypass line around the condensers. It
must then open on falling discharge pressure.
These typical systems, depending on the specific application,
must maintain a constant condensing pressure regardless of
temperature conditions and must assure adequate head pres-
sure for proper thermostatic expansion valve operation. A
minimum head pressure of 160 psig (86°F condensing tem-
perature) is recommended.
7. Condenser tube velocities must not exceed 10 feet per
second. Flow and velocity will be satisfactory if water
volumes do not exceed those shown in Table No. 4.
IM709