AAON SA-070 - Manual (Page 30)

30
at 32°F. When water freezes in a heat
exchanger significant forces are exerted on
the components of the heat exchanger where
the water is confined.
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.
Unit is capable of operating with Entering
Water Temperatures (EWT) as low as 57°F,
during the 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 entering water
temperature to the unit 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 and also results 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
refrigerant-to-water heat exchanger and the
unit can operate without damaging unit
components.
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