Trane LO manual Pipewith Auxiliary Electric Heat Fan-coils, Terminal Unit Control TUC, Unit Type

Terminal Unit Control (TUC)

Entering Water

Temperature

Sampling Function

The entering water temperature sampling function allows water to circulate in an attempt to sense water cold enough to provide cooling. The function uses a timer to permit the controller and the valve to fully open while the water circulates for 3 minutes. The fan continues to run at the selected speed. If the changeover sensor does not sense the correct water temperature within this 3 minute cycle, the valve closes and the entering water temperature sampling function will cease until 57 minutes elapse. After this time lapse, the water circulates again through the unit to determine if the entering water temperature indi- cates a call for cooling or heating.

Note: The entering water temperature sampling function is for units with 2-way valves. This function is not necessary for units with 3-way valves since water flows continuously through this piping configura- tion.

Table 38. Unit Mode as Related to Water Temperature

Unit Type	EWT Sensor Required?	Coil Water Temperature
2-pipe changeover	Yes	· Can cool if:
		space temp - EWT ³ 5 deg F
		· Can heat if:
		EWT - space temp ³ 5 deg F
4-pipe changeover	Yes	· Can cool if:
		space temp - EWT ³ 5 deg F
		· Can heat if:
		EWT - space temp ³ 5 deg F
2-pipe heating only	No	Hot water assumed
2-pipe cooling only	No	Cold water assumed
4-pipe heat/cool	No	· Cold water assumed in main coil
		· Hot water assumed in aux. coil

2-Pipe with Auxiliary Electric Heat (Fan-coils)

The auxiliary electric heat option allows heating when the occupied space requires heating but the unit still has chilled system water flowing through it. The electric heat is also sufficient for use as the sole source of heat for the unit.

The TUC utilizes a heating only output to energize electric heat if hydronic heat is insufficient to meet the heating requirements. This output responds to a demand for heat as long as the entering water temperature is lower than 95° F. However, if the water temperature reaches 95° F or higher, the electric heat lockout switch (on the supply water pipe) disengages the electric heat. Electric heat be- comes available again when the entering water temperature falls to 65° F or lower (± 5° F).

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