AAON M2-036 - Manual (Page 46)

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need for head pressure control. If the EWT
is expected to be lower than 50°F or more
stable operation is desired, a field provided
water regulating valve may be used.
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 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.
Condenser water connections range in size
from 1-18”-4” OD copper or black pipe.
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.
Condenser water pump must be field sized
and installed between the cooling tower and
self contained unit. System should be sized
in accordance with the ASHRAE Handbook.
Use engineering guidelines to maintain
equal distances for supply and return piping
and limit bend radiuses to maintain balance
in the system. Balancing valves, permanent
thermometers and gauges may be required.
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