HONEYWELL CP980D (01) PDF DOCUMENT

Four models of the HONEYWELL CP980 Velocitrol Velocity Controller are available:

A reverse acting controller (such as the HONEYWELL CP980D): For normally closed dampers.

A direct acting controller: For normally open dampers.

A Type B controller: Provides high and low air volume limits and is used in conjunction with a one-pipe bleed thermostat.

A Type C controller: Used for two-pipe thermostat applications and for sequencing with reheat.

The HONEYWELL CP980D operates based on air velocity sensing that does not depend on differential air pressure. Air from the main line supply passes through restrictions. The pressure from the thermostat determines the pressure to a secondary restriction, which in turn sets the flow through an emitter tube and thus the velocity of a jet of air.

The sensor consists of two small tubes, an emitter jet and a collector tube, separated by a fixed gap. A compressed air jet moves from the emitter to the collector tube, perpendicular to the airflow in the duct. The pressure at the jet collector is directly proportional to the jet velocity and is an inverse function of any jet deflection caused by the duct airflow. As duct airflow increases, it deflects the jet, and less supply air bridges the gap to the collector. A two-stage bleed type amplifier then amplifies the jet collector pressure to provide the branchline pressure.

For reverse acting models like the HONEYWELL CP980D, the branchline pressure is inversely proportional to the velocity of the air flowing through the sampling tube. An increase in velocity results in a decrease in branchline pressure to the damper actuator, which closes the damper to reduce velocity back to the control point.

The HONEYWELL CP980D Velocitrol design is compatible with bleed type thermostats (TP973, TP975) and also operates with capacity type thermostats (TP970, TP971, TP972).

When using a stat with its own main supply (two-pipe) with a B controller like the HONEYWELL CP980D, you must always use an RP470B relay 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 main pressure to assure 18 psi (124 kPa) minimum.

2. For a Type B controller like the HONEYWELL CP980D, cap thermostat Port 3. For a Type C controller, connect main air to Port 3.

3. Install flow measuring test equipment.

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

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

1. Divide the required flow values for minimum and maximum 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 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.

High and low limit regulators on the HONEYWELL CP980D dictate the maximum and minimum flow control points. These adjustments operate by limiting the supply pressure to the emitter tube. For example, if the high limit is set at a thermostat pressure of 10 psi, it establishes a maximum flow control point. Any further increase in space temperature sensed by the thermostat will have no effect on the emitter pressure and consequently no effect on airflow. Similarly, the low limit adjustment establishes a minimum control point. The system will then operate at duct air velocities between the minimum and maximum points, even if the thermostat senses temperatures that would ordinarily require velocities outside this range.

The HONEYWELL CP980D is ultrasensitive over a wide range of duct air velocities. The control range can be increased to higher velocities by using an orifice. An orifice proportionally reduces the velocity of the air entering the flow tube, allowing the more sensitive velocity jet to maintain control at higher overall duct velocities. Different orifices allow the velocity sensor to accurately control duct velocities as low as 100 ft/min (0.5 m/s) or as high as 3500 ft/min (17.7 m/s).

The following table outlines the ordering system for the HONEYWELL CP980 series controllers.