HONEYWELL CP980F (01) PDF DOCUMENT

The four models available for the HONEYWELL CP980F Velocitrol Velocity Controller are:

1. A reverse acting controller for normally closed dampers.

2. A direct acting controller for normally open dampers.

3. A Type B controller providing high and low air volume limits, used in conjunction with a one-pipe bleed thermostat.

4. A Type C controller used for two-pipe thermostat applications and for sequencing with reheat.

The HONEYWELL CP980F combines air velocity sensing with a pneumatic controller to detect and control airflow in air terminal units, independent of system static pressure. It does not depend on differential air pressure for sensing.

Functional Operation (Type B controller example):

Air from the main line pressure supply (Port 1) passes through a primary jet restriction to a secondary jet restriction, as well as to the minimum and maximum flow limits. The minimum flow limit provides supply air for a bleed-type thermostat. The pressure from the thermostat determines the pressure to the secondary restriction, which is kept within the selected minimum and maximum flow limits. This, in turn, determines the flow through the emitter tube and the jet velocity.

The jet collector pressure is directly proportional to the jet velocity and inversely related to any jet deflection from airflow through the sampling tube. A two-stage bleed-type amplifier then amplifies this jet collector pressure to provide the branchline pressure.

For reverse acting models: Branchline pressure is inversely proportional to the air velocity in the sampling tube.

For direct acting models: Branchline pressure is directly proportional to the air velocity in the sampling tube.

With a Type B controller, the air velocity is reset between adjustable minimum and maximum settings by a bleed thermostat. When the pressure at the thermostat increases, the velocity control point also increases. The selected orifice and the controller settings determine the velocity range. The maximum and minimum limits set the range as a percentage of the rated velocity established by the orifice.

Once the thermostat sets a velocity control point, an increase in velocity causes a decrease in branchline pressure to the damper actuator (for reverse acting models), which closes the damper to reduce the velocity back to the control point. A change in space temperature modulates the thermostat pressure, providing a new pressure to the secondary jet restriction (within the limits) and resetting the velocity control point.

The Type C controller application is similar to Type B, but the thermostat must have its own air supply. It maintains the minimum selected velocity until the thermostat signal increases to 9 psi (62 kPa). To reset the velocity above the minimum, the required thermostat signal will be proportionately higher for higher minimum dial settings.

For sequencing control, a pressure signal from the thermostat operates the pilot of a ratio relay, which acts as a bleed valve controlling pressure to the secondary jet restriction. The ratio relay is biased to a 9 psi (62 kPa) start point at zero velocity. This allows any thermostat signal below 9 psi to sequence other control devices. If the minimum adjustment is set above zero, the start point for thermostat reset will be proportionately higher than 9 psi.

The HONEYWELL CP980F Velocitrol is compatible with bleed-type thermostats (TP973, TP975) and also operates with capacity-type thermostats (TP970, TP971, TP972). The Type C controller, with its isolated pilot chamber, is suitable for all thermostats, regardless of whether they require sequencing. For these, the reset action occurs over half the thermostat’s throttling range (9 to 15 psi [62 to 104 kPa]).

When using a two-pipe thermostat (with its own main supply) with a B controller, an RP470B relay must be used as a repeater.

NOTE: Bleed thermostats or equivalent bleed devices other than Honeywell, when connected directly to Port 3 of a Type B controller, must be capable of bleeding down to 1.25 psi (9 kPa) at a compressed airflow rate equivalent to that of a 0.007-inch restriction with a mainline pressure of 20 psi (138 kPa).

1. Check the main pressure to ensure it is at a minimum of 18 psi (124 kPa).

2. For a Type B controller, cap the thermostat Port 3. For a Type C controller, connect main air to Port 3.

3. Install flow measuring test equipment.

4. Measure the actual flow in ft³/min (m³/s).

5. Adjust or calibrate the MAX dial to the desired flow level using the flow measuring equipment. Write the new dial setting and airflow on a tag or on the unit for future reference.

1. Vent Port 3.

2. Turn the MAX dial above 10.

3. Install flow measuring test equipment.

4. Measure the actual flow in ft³/min (m³/s).

5. Adjust or calibrate the MIN dial to the desired flow level using the flow measuring equipment. For future reference, write the new dial setting and airflow on a tag or on the unit.

1. Divide the required minimum and maximum flow values by the duct area to determine the required velocity.

2. Refer to Table 1 to calculate the percent of velocity rating.

3. Select an orifice that is as close to 70 percent of the velocity rating for maximum as possible. This provides optimum adjustment of the maximum scale.

4. Check the dial settings. For a minimum set at shut off, select a setting of 0.

The HONEYWELL CP980F sensor consists of two small tubes (an emitter jet and a collector tube) separated by a fixed gap. It does not depend on the velocity pressure of the flowing airstream. Instead, a strong signal from a compressed air jet moves from the emitter tube to the collector tube across the gap, perpendicular to the airflow in the duct.

The jet collector pressure is a direct function of the supply air pressure and is inversely proportional to the velocity of the duct air. As duct airflow increases, it deflects the jet, so less supply air bridges the gap to the collector tube. As duct airflow decreases, more supply air bridges the gap.

By varying the supply air pressure, the sensor’s velocity range is controlled. With increased pressure, the air jet requires a greater duct air velocity to deflect it. This allows the sensor to provide usable pneumatic output signals at duct air velocities as low as 100 ft/min (0.50 m/s).

The HONEYWELL CP980F controller is ultrasensitive over a wide range of duct air velocities. To increase the control range to higher velocities, an orifice is used. The orifice proportionally reduces the velocity of the air entering the flow tube, which allows the more sensitive velocity jet to maintain control even at higher overall duct velocities.

For example, a red orifice (B) can reduce a duct air velocity of 1250 ft/min (6.33 m/s) to a flow rate of 500 ft/min (2.5 m/s) inside the sensor tube.

Different orifices allow the velocity sensor to accurately control duct velocities from as low as 100 ft/min (0.5 m/s) to as high as 3500 ft/min (17.7 m/s).

The high and low limit regulators on the HONEYWELL CP980F set the maximum and minimum flow control points by limiting the supply pressure to the emitter tube.

High Limit: If the high limit adjustment is set at a certain thermostat pressure (e.g., 10 psi), it establishes a maximum flow control point (e.g., 300 ft/min). Any further increase in space temperature (and thus thermostat pressure) will have no effect on the emitter pressure and consequently no effect on the airflow.

Low Limit: If the low limit adjustment is set at a certain thermostat pressure (e.g., 3 psi), it establishes a minimum flow control point (e.g., 80 ft/min). The system will not operate below this velocity, even if the thermostat calls for less.

When both high and low limits are in use, the system operates at duct air velocities between the ranges dictated by these settings, regardless of thermostat demand outside this range.

If the low limit adjustment is set at a pressure greater than the high limit adjustment, the high limit control point takes precedence and acts as both the high and low limit, establishing a fixed control point.