AAON SB-018 - Manual (Page 21)

21
Unit is capable of operating with Entering
Water Temperatures (EWT) as low as 57°F
during cooling mode without the need for
head pressure control. If the EWT is
expected to be lower than 57°F or more
stable operation is desired, a factory
provided head pressure control water valve
option is available.
Glycol solution should be used if ambient
temperatures are expected to fall below
freezing or if the loop water temperature is
below 50°F while operating in the heating
mode (heat pump units only). Adding glycol
to condenser water causes an increase in
pressure drop resulting in a decrease in unit
performance. A minimum concentration of
20% glycol solution is recommended.
Table 2 - Glycol Freezing Points
% Glycol Ethylene
Glycol
Propylene
Glycol
20 18°F 19°F
30 7°F 9°F
40 -7°F -6°F
50 -28°F -27°F
Water loop piping runs through unheated
areas or outside the building should be
insulated.
Water Piping
Installing contractor must ensure a
differential pressure switch or water flow
switch is installed between the condenser
water supply and return connections. This
sensor provides a signal to the unit
controller that water flow is present in the
heat exchanger and the unit can operate
without damaging unit components.
Only use approved water pipe material.
Avoid using galvanized material for water
lines/fittings as the material is corrosive and
may cause fouling of the water system.
WATER PRESSURE
Prior to connection of condensing
water supply, verify water pressure is
less than maximum pressure shown
on unit nameplate. To prevent injury
or death due to instantaneous
release of high pressure water, relief
valves should be field supplied on
water piping. Supply water
connection may require a backflow
preventer to prevent supply makeup
water from backing up into the public
water system.
WARNING
WATER FREEZING
Failure of the condenser due to
freezing will allow water to enter the
refrigerant circuit and will cause
extensive damage to the refrigerant
circuit components. Any damage to
the equipment as a result of water
freezing in the condenser is excluded
from coverage under AAON
warranties and the heat exchanger
manufacturer warranties.
WARNING
PVC (Polyvinyl Chloride) and CPVC
(Chlorinated Polyvinyl Chloride) are
vulnerable to attack by certain
chemicals. Polyolester (POE) oils
used with R-410A and other
refrigerants, even in trace amounts,
in a PVC or CPVC piping system will
result in stress cracking of the piping
and fittings and complete piping
system failure.
CAUTION