Trane VAV-SVX02B-EN manual Thermostat Selection and Location, Thermostat Piping

Thermostat

Thermostat Selection and Location

In general, both one- and two-pipe thermostats have a gain of 2.5 psi per degree Fahrenheit, unless special thermostats are used that provide a different gain. The major difference between them is that a one-pipe thermostat is considered a low- capacity thermostat and a two-pipe thermostat is considered a high- capacity thermostat.

When selecting between one-pipe and two-pipe thermostats consider the following:

Use one-pipe thermostat when:

￿tubing runs are less than 50 feet from thermostat to controller.

￿a single thermostat will control no more than three controllers.

￿slower response is desired from the thermostat.

Use two-pipe thermostat when:

￿tubing runs exceed 50 feet from thermostat to controller.

￿a single thermostat will control four or more controllers.

￿high capacity air is required due to restrictions in the air line.

Thermostat Piping

The two-pipe thermostat (Figure 1) includes a restrictor (internally). Attach supply air line and output pressure (branch) line to the thermostat.

The one-pipe thermostat (Figure 2) requires an external restrictor tee. Connect main air supply to restricted leg of restrictor tee. Connect branch line from restrictor tee to the thermostat.

Figure 1–Two-Pipe Remote Thermostat (Reverse-Acting)

Tee

Two-Pipe

Remote-Mounted

T-Stat

(Reverse-Acting)

S

520

1

	)	.9)
	.4
3
0		(137
(1

Figure 2–Typical One-PipeThermostat (Reverse-Acting)

		Restrictor	One-Pipe
	Tee	Tee
			Remote-Mounted
			T-Stat
			(Reverse-Acting)
		S	Restricted Leg
		20
	Fan	(137.9)
	P.E.
Switch±1
	(N.O.)

9PSI

(62.06 kPa)

2 VAV-SVX02B-EN