Trane LO Entering Water Temperature Sampling Function, Tracer ZN.520, Fan Start on High Speed

Tracer® ZN.520

Fan Start on High Speed

Entering Water

Temperature

Sampling Function

Heating or Cooling Required

On a transition from off to any other fan speed, the Tracer® ZN.520 controller automatically starts the fan on high speed and runs the fan at high speed for 0.5 seconds. This provides the ample torque required to start all fan motors from the off position.

Tracer® ZN.520 can sample the entering water temperature for 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 desired water temperature from the central plant.

When three-way valves are ordered with a Tracer® ZN.520 control, the controller is factory-configured to disable the entering water tempera- ture sampling function, and the entering water sensor is mounted in the proper location. Disabling entering water temperature sampling eliminates unnecessary water flow through the main coil when three- way valves are used.

The Tracer® ZN.520 controller offers a control solution for two-way valve applications that does not require special unit considerations, such as those required by bleed lines. The controller includes an entering water temperature sampling function that periodically opens the two-way valve to allow temporary water flow, producing reliable entering water temperature measurement.

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Only units using the main hydronic coil for both heating and cooling (2-pipe changeover and 4-pipe changeover units) use the entering water temperature sampling function. Two-pipe changeover and 4-pipe changeover applications allow the main coil to be used for heating and for cooling; therefore, these applications require an entering water temperature sensor.

The entering water temperature value is useful to the unit controller only when heating or cooling is required. The entering water tempera- ture must be five degrees above the space temperature for hydronic heating and five degrees below the space temperature for hydronic cooling. When water flows normally and frequently through the coil, the controller does not invoke the sampling function because the water temperature is satisfactory for the desired heating or cooling. The controller invokes entering water temperature sampling only when the measured entering water temperature is too cool to heat or too warm to cool. Entering water is cold enough to cool when it is five degrees below the measured space temperature. Entering water is

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