HONEYWELL CP980E (01) PDF DOCUMENT

The HONEYWELL CP980E combines ultrasensitive air velocity sensing with a pneumatic controller to detect and control air flow in air terminal units, regardless of the system’s static pressure. It provides a modulating pressure output to a pneumatic damper actuator to maintain a constant air velocity.

The HONEYWELL CP980E’s sensing does not depend on differential air pressure. Instead, a strong signal from a compressed air jet moves from an emitter tube to a collector tube across a fixed gap. This jet is perpendicular to the air flowing through 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, and less supply air bridges the gap to the collector. This method allows it to accurately sense velocities lower than 100 ft/min (0.5 m/s).

For reverse acting models, the branchline pressure is inversely proportional to the velocity of the air flowing perpendicular to the jet in the sampling tube. For direct acting models, the branch line pressure is directly proportional to the velocity of the air flowing perpendicular to the jet in the sampling tube.

Each HONEYWELL CP980E package consists of a sensor and a controller. An orifice, if required, is provided separately. The sensor contains the controller mechanism, and the controller unit contains two pressure regulators, a filter, and restrictions only.

With a Type B controller, velocity is reset between adjustable minimum and maximum settings by a bleed thermostat. A pressure increase at the thermostat increases the velocity control point. The 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.

When using a Type C controller for sequencing, a pressure signal from the thermostat operates the pilot of a ratio relay, which controls the 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 (62 kPa) to sequence other control devices. If the minimum adjustment is set above zero, the start point for thermostat reset will be proportionately above 9 psi (62 kPa).

Fast response is a key characteristic of the HONEYWELL CP980E controller. The system reacts quickly to changes in velocity caused by sudden changes in static pressure, usually fast enough that there is no noticeable change in discharge airflow or noise.

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).

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

HONEYWELL CP980E controllers ordered as a matched set come factory calibrated. This calibration is very accurate. If both the controller and sensor units are replaced, the minimum and maximum flow calibrations are maintained. However, if only the controller or the sensor is replaced, the original flow calibration is lost.

Follow these steps to calibrate the maximum flow:

1. Check main pressure to assure it is at least 18 psi (124 kPa).

2. For a Type B controller, cap 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.

Follow these steps to calibrate the minimum flow:

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.

Follow these steps for orifice selection and scale setting:

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 ordering system is as follows:

The high and low limit regulators dictate the maximum and minimum flow control points by limiting the supply pressure to the emitter tube. For example, if the high limit is set at a thermostat pressure of 10 psi (69 kPa), it establishes a maximum flow control point. Any further increase in space temperature has no effect on the emitter pressure and airflow. Similarly, setting the low limit establishes a minimum control point. The system will then operate between these two dictated air velocity points, even if the thermostat calls for velocities outside this range.

The HONEYWELL CP980E 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. This reduction allows the more sensitive velocity jet to maintain control, even at higher overall duct velocities. Different orifices allow the 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 ranges of the low and high limit adjustments overlap. If the low limit adjustment is set at a pressure greater than the pressure of the high limit adjustment, the high limit control point takes precedence and acts as both the high and low limit. This effectively establishes a fixed control point.

If a sequencing relay is added to the system, the thermostat pressure must be higher than 9 psi (62 kPa) before the volume controls begin to operate. Below 9 psi (62 kPa), the thermostat signal can control another device, such as a reheat coil, while the minimum limit adjustment controls the duct air velocity.