Navien NFC-175 Installation & Operation Manual page 31

Air Handler Interface
The Navien NFC boiler can control the operation of an air handler
when a thermostat is used in combination with the air handling
unit. The Air Handler Interface is designed to stop air handler
operation when the boiler's space heating function is not
operating due to DHW supply demands, boiler errors, or low water
conditions.
The air handler contacts (A/H) turn off when the following
conditions arise:
The PCB DIP SW2 #7 is set to ON.
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Thermostat is turned off.
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The boiler is supplying DHW, or it is in stand-by mode for DHW
●
demand.
Level 2 or higher errors occur.
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The boiler is turned off.
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Thermostat Configuration for the Air Handler Interface
Set the PCB DIP SW2 #7 to down position (OFF) to use a thermostat
with the Air Handler.
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Refer to the "3.1.1 Guidelines for a Space Heating Installation" on
page 45 for wiring connections.
WARNING
The boiler, when used in conjunction with an air conditioning
●
system, must be installed so that the chilled medium is
piped in parallel with the heating boiler. Appropriate valves
must be used to prevent the chilled medium from entering
the boiler.
If the boiler is connected to heating coils located in air
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handling units where they can be exposed to refrigerated
air, use flow control valves or other automatic means to
prevent gravity circulation of the boiler water during the
cooling cycle.
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3.6.1 Temperature Control Device Applications
NFC series boilers come with water adjustment valves and mixing
valves included as to ensure a stable supply of hot water without
requirements for additional direct water pressure control valves
(flow restrictors) or mechanical mixing valves.
When setting up the system, do not install water pressure
●
control valves or flow restrictors on the direct water supply lines.
When setting up the system, do not install additional
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mechanical mixing valves on the DHW supply line.
Water Adjustment Valve
The adjustment valve works in conjunction with the flow sensor to
detect and control the direct water flow within the system, and is
installed on the water piping module. Refer to "1.4 Components"
on page 11 for details.
Mixing Valve
The mixing valve controls the amount of cold water that is mixed
with the hot water in order to provide a stable supply of DHW. It is
installed on the water pipe module. Refer to "1.4 Components" on
page 11 for details.
3.6.2 Examples of System Applications
Refer to the following examples to properly implement a system
for space heating, DHW supply, or both. These examples are
provided to suggest basic guidelines when you install the boiler
system. However, the actual installation may vary depending on
the circumstances, local building codes, or state regulations. Check
the local building codes and state regulations thoroughly before
installation, and comply with them fully.
Installing the System Piping 31