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VAV-PRC011M-EN 145

Application Considerations

Currently, VariTrane offers two models of pneumatic volume regulators in its controls offering—

the 3011 regulator (used in most applications) and the 3501 model (used in dual-duct constant-

volume applications). The primary difference is the 3501 PVR’s ability to change the velocity

pressure linearly with a change in thermostat pressure, which results in improved stability at low

flows. In contrast, the 3011 PVR resets the velocity pressure with a change in thermostat pressure.

Reset Control of Minimum and Maximum Flow—The 3011 PVR and 3501 use fixed reset control of

minimum and maximum flow settings. The primary benefit of fixed reset in a pneumatic volume

regulator is stable flow control without excessive damper movement.

Fixed Reset—A fixed reset controller operates over a thermostat signal change of 5 psi between

minimum and maximum flow, regardless of the differential pressure flow sensor signal. The

thermostat is usually set for a gain of 2.5; i.e. it produces a 2.5 psi output change per degree of space

temperature change. This control strategy provides stable flow control with the primary air valve

throttling between minimum and maximum flow over a 2°F space temperature change.

Example 1: Air valve with a 6" inlet, Pneumatic thermostat gain = 2.5 psi/degree:

Minimum Flow=0 cfm, 0.0 in. wg flow signal

Maximum Flow=680 cfm, 2.0 in. wg flow signal

2.0 in. wg signal range

The damper will modulate from zero to maximum position over a 2°F temperature change.

Bleed Port to Atmosphere—Bleeding air to the atmosphere is a normal operation for a volume

regulator. The 3011 volume regulator addresses this function with a dedicated bleed port. When air

is bled through the flow sensor, the differential pressure signal from the sensor is affected. As a

result, the flow sensor signal can be radically altered if the volume regulator is bleeding air, and

may cause excessive damper movement.

Calibration—The minimum and maximum settings are independent of each other and need to be

set only once during calibration.

Signal Configuration Flexibility—Both can be configured to work with both normally-open and

normally-closed pneumatic air valves, and both direct-acting and reverse-acting thermostats.

Pneumatic Volume Regulators

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Trane Round In/Round Out Seznam dílů Strana 145