IM 439 / Page 7 of 24
1. All units are recommended to be connected to supply and
return piping in a two-pipe reverse return configuration. A
reverse return system is inherently self-balancing and re-
quires only trim balancing where multiple quantities of units
with different flow and pressure drop characteristics are
connected to the same loop. A simple way to check for
proper water balance is to take a differential temperature
reading across the water connections. To insure proper
water flow, the differential should be 10°F to 14°F (5°C to
8°C) in the cooling mode of operation.
A direct return system may also be made to work ac-
ceptably, but proper water flow balancing is more difficult
to achieve and maintain, and may require flow control
devices.
2. The piping can be steel, copper or PVC.
3. Supply and return runouts are usually connected to the
unit by short lengths of high pressure flexible hose which
are sound attenuators for both unit operating noise and
hydraulic pumping noise. One end of the hose should have
a swivel fitting to facilitate removal for service. Hard pip-
ing can also be brought directly to the unit although it is
not recommended since no vibration or noise attenuation
can be accomplished. The hard piping must have unions
to facilitate unit removal
(see Figure 10 for typical piping
setup)
.
Piping
Flexible
Connector
Transition
Duct
Main
Duct
Branch
Duct
Trunk Duct
Flexible Hose
with Brass
Pipe Fittings
Supply
Return
Balancing
Valve with
Close-off
Condensate
Figure 10.
Do not overtorque fittings. The maximum torque without
damage to fittings is 30 foot pounds. If a torque wrench is not
available, use as a rule of thumb, finger-tight plus one
quarter turn. Use two wrenches to tighten the union, one to
hold the line and one for simultaneous tightening of the nut.
4. Supply and return shutoff valves are required at each con-
ditioner. The return valve is used for balancing and should
have a “memory stop” so that it can always be closed off
but can only be reopened to the proper position for the flow
required.
5. No unit should be connected to the supply and return pip-
ing until the water system has been cleaned and flushed
completely. After the cleaning and flushing has taken place,
the initial connection should have all valves wide open in
preparation for water system balancing.
6. Condensate piping can be steel, copper or PVC. Each
unit is supplied with a FPT threaded fitting.
7. The condensate disposal piping must have a trap and the
piping must be pitched away from the unit not less than
1
⁄
4
" per foot (21 mm per meter). Generally, the condensate
trap is made of copper. A complete copper or PVC conden-
sate system can also be used. Union fittings in the copper
lines should be applied to facilitate removal.
8. No point in the drain system may be above the drain con-
nection of any unit.
9. Automatic flow controlled devices must not be installed
prior to system cleaning and flushing.
10. A high point of the piping system must be vented.
11. Check local code for the need of dielectric fittings.
Cleaning and Flushing
System
1. Prior to first operation of any conditioner, the water cir-
culating system must be cleaned and flushed of all con-
struction dirt and debris.
If the conditioners are equipped with water shutoff
valves, either electric or pressure operated, the supply and
return runouts must be connected together at each con-
ditioner location. This will prevent the introduction of dirt
into the unit. Additionally, pressure operated valves only
open when the compressor is operating
(see Figure 11)
.
Figure 11.
Return Runout
Supply Runout
Mains
Rubber Hose
Runouts Initially
Connected Together
CAUTION
!
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