Trane VAV-SVX02B-EN manual Variable Air Volume Dual-Duct Calibration

Variable Air Volume Dual-Duct Calibration (3011)

Variable-Air-Volume Dual- Duct Calibration (3011)

Figure 16 is a typical piping diagram of aVAV dual-duct unit.The unit has a thermostat piped to both pneumatic volume regulators (PVR) which will operate the heating deck from a thermostat signal of 3–8 psi.The cooling deck will operate from a thermostat signal of 8–13 psi.With normal calibration of the PVR, the unit will have both the heating and cooling deck at minimum with a thermostat signal of 8 psi.

In order to have a unit minimum cfm and still have 0 cfm minimums on both the heating and cooling deck, special calibration is required.The PVR has a “reset start” adjustment knob, which allows the unit to be calibrated to a minimum cfm.This is achieved by crossing over the thermostat ranges. Figure 17 illustrates this concept.

Figure 17–Example

Figure 16–Typical VAV Dual-Duct Piping Diagram

Outlet
Heating		Cooling				H	L	T
a ve		a ve			Actuator	B
								Volume
Normally-		Normally-
								Regulator
pen		pen
LO		LO
HI		HI			S
								G
					20
					(137.9)
					Two-Pipe
	H	L	T	Restrictor	Remote-Mounted
					T-Stat
	B			Tee
Actuator					(Direct-Acting)
		Volume
		Regulator			S
					20
					(137.9)
		G
	20
	(137.9)

N.O. HeatingValve

Min 0 cfm

Max 1000 cfm

Max

Unit Min

Valve Min

Unit Minimum 400 cfm

N.O. CoolingValve

Min 0 cfm

Max 1000 cfm

4 7 8 9 12

Thermostat Range: 3–8 psi HeatingValve = 5 psi range

Thermostat Range: 8–13 psi CoolingValve = 5 psi range

Approximately 1000 cfm divided by 5 psi = 200 cfm/1b*

*Due to the relationship between velocity pressure and cfm; for both the cooling and heating PVR, a linear relationship between cfm and psi does not exist.

To obtain a unit minimum cfm of 400 cfm, the heating deck volume regulator must have its thermostat range changed from 3–8 psi to 4–9 psi.This is adjusted by changing the “reset start” point from 3 psi to approximately 4 psi.

The cooling deck volume regulator must have its thermostat range changed from 8–13 psi to 7–12 psi. This is adjusted by changing the “reset start” point from 8 psi to approximately 7 psi.

By overlapping the thermostat spring ranges, we were able to have 0 cfm minimum settings on both the heat and cool deck and still maintain the required unit minimum cfm of 400 cfm.

The calibration of the PVR is the same as the normal calibration procedures previously described in this manual.

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