Start-Up

Table 23. Local fan switch enabled

Communicated

Fan switch (local)

Fan operation fan speed input

 

 

 

Off

Ignored

Off

 

 

 

Low

Ignored

Low

 

 

 

High

Ignored

High

 

 

 

Auto

Off

Off

 

Low

Low

 

High

High

 

Auto

Auto (configured default, determined by heat/cool mode)

 

 

 

Table 24. Fan operation in heating and cooling modes

 

Heating

Cooling

 

 

 

 

 

Fan mode

Occupied

Unoccupied

Occupied

Unoccupied

 

 

 

 

 

Off

Off

Off

Off

Off

Low

Low

Off/high

Low

Off/high

High

High

Off/high

High

Off/high

Auto (continuous)

Default fan speed

Off/high

Default fan speed

Off/high

 

 

 

 

 

Two- and Four-Pipe Changeover Operation

Tracer™ ZN controllers offer accurate and reliable unit changeover using 2-way valves and the controller’s entering water temperature sampling function. Only units using the main hydronic coil for both heating and cooling (2-pipe and 4-pipe changeover units) use the entering water temperature sampling function.

Two-pipe and 4-pipe changeover applications require an entering water temperature sensor to allow the main coil to be used for heating and cooling. This sensor is factory-provided and should be field-installed on the entering water pipe.

The entering water temperature sampling function periodically opens the two-way valve to allow temporary water flow, producing reliable entering water temperature measurement. To ensure accurate unit changeover without sacrificing the benefits of 2-way, 2-position valves, Tracer™ ZN controllers periodically test the entering water temperature on all hydronic main coil changeover units. Hydronic heating/cooling changeover operation requires central plant operation, and the unit controller must use an entering water temperature sensor to verify delivery of the correct water temperature from the central plant.

Entering Water Temperature Sampling Function

The entering water temperature (EWT) must be five degrees above the space temperature for hydronic heating and five degrees below the space temperature for hydronic cooling. When water

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Trane BCHC Two- and Four-Pipe Changeover Operation, Entering Water Temperature Sampling Function, Local fan switch enabled