QA5F24-P Modulating Damper Actuator

Product Overview

QA5F24-P is a compact modulating damper actuator for HVAC air handling units, ventilation ducts and fan coil systems. It positions an air damper proportionally rather than switching it, so the actuator holds the blade anywhere between fully closed and fully open in response to an analogue control signal, with a matching feedback signal reporting where the blade actually is.

The unit is small enough to fit against a damper shaft in a confined casing or a ceiling void, and it is designed around the shaft sizes that modulating dampers normally use: round shafts between 6 and 20 mm and square shafts from 5 × 5 to 16 × 16 mm. A mechanical position indicator on the housing shows the blade angle at a glance, and the manual override lets a commissioning engineer move the damper by hand before any control power is available. The enclosure is rated IP54, which covers the dusty and slightly damp conditions that dampers live in.

How a Modulating Damper Actuator Positions a Damper

In a modulating application the actuator is not simply told to open or close. It receives an analogue command — a voltage or a current that represents the required blade position — and drives the damper until the feedback it generates matches that command. The control loop in the controller can then treat the damper as a continuous device and adjust it in small steps, which is what allows a mixing box to hold a mixed-air temperature steadily rather than swinging between full outdoor air and full return air.

The value of the feedback signal is easy to underestimate. A command tells the controller what it asked for; feedback tells it what it got. On a mixing damper those can differ, particularly when the blade is stiff, when the shaft coupling has slipped, or when two actuators are being driven as a pair. A controller that can see the real position can compensate, and a commissioning engineer comparing commanded and actual positions can find a mechanical problem before it becomes a comfort complaint.

Key Features

• Modulating control with DC 0(2)…10V or 0(4)…20mA signal (optional)
• AC/DC 24V power supply with ±10% tolerance
• Low power consumption, with a minimal standby draw
• Fast two-second runtime over 95° for tight control
• Mechanical position indication
• Manual override via unlock knob
• IP54 enclosure protection
• Suitable for round shafts 6–20 mm and square shafts 5×5–16×16 mm

Available Configurations

The control interface is the main order-time choice. The actuator accepts a voltage command with a matching voltage feedback, or the equivalent current loop, and the input can be configured so that a small offset in the live-zero range is treated as fully closed — useful where a controller’s output does not quite reach its own zero. Current-loop control is the more robust option over a long cable run, while voltage control is simpler to interface to the analogue outputs that most terminal controllers provide; the two conventions are compared in HVAC control signals: 0–10 V and 4–20 mA.

The mechanical choices are the shaft coupling and the mounting orientation. The clamp accommodates the standard round and square shaft sizes, and the actuator can be mounted either side of the damper with the housing clear of the duct wall. The supply is AC or DC 24 V with a tolerance of ±10 %, which suits a controls panel supply and means the same actuator serves systems that differ only in whether the panel provides alternating or direct current.

Applications

The main duties are mixing and fresh-air dampers on air handling units, dampers in ventilation and smoke-exhaust systems, clean-room HVAC control and building automation generally — anywhere a damper has to be positioned rather than switched. In an air handling unit the modulating actuator is usually found on the outdoor-air, return-air and exhaust-air dampers, where the balance between them sets the mixed-air condition, and on the cooling or heating coil face-and-bypass dampers, where blade position directly controls the delivered air temperature.

Fast runtime matters in these applications. Positioning a damper across its full travel in about two seconds lets the controller make small corrections often rather than large corrections occasionally, which is what keeps a mixed-air temperature stable when outdoor conditions are changing. Slow actuators can still be stable in steady weather but tend to hunt or lag when the outdoor air temperature is moving quickly, which is exactly when the building notices.

How to Choose and Size a Damper Actuator

Start with the torque requirement, because an actuator that cannot hold the blade against the duct’s air pressure will be pushed open and the damper will leak when it is supposed to be closed. The torque a damper needs depends on its area, its blade arrangement and the pressure differential it has to hold, so the size of the damper is the first input; the damper actuator torque calculator works through that calculation for rectangular multi-blade dampers and indicates the torque to specify. Against that, this unit is intended for dampers up to roughly half a square metre, so a larger damper needs either a larger actuator or a pair of units driving the shaft together — a decision that belongs in the selection stage rather than at commissioning.

Next, confirm the shaft. The coupling covers round shafts from 6 to 20 mm and square shafts from 5 × 5 to 16 × 16 mm, and the shaft has to be long enough to accept the clamp. Then decide the control signal, the direction of rotation relative to the damper’s opening, and whether the feedback is actually used by the controller — a feedback loop that is wired but never read simply adds cable. The selection logic in more depth, including the relationship between torque, signal and feedback, is set out in damper actuator selection for HVAC and damper actuators 101: choosing the right torque, signal and feedback; the working principle is covered in damper actuator: working principle and applications, and the family is listed under the damper actuator range.

Installation and Wiring

Mount the actuator with the housing clear of the duct insulation and the shaft coupling accessible, and leave enough space to reach the unlock knob and the position indicator afterwards. Confirm the direction of rotation before the linkage is tightened, because an actuator driving the wrong way will hold the damper closed when the controller believes it is open — a fault that survives commissioning if the feedback is not being read.

Wire the supply and the command and feedback signals in separate runs where possible, use screened cable for the analogue pair, and earth the screen at the panel end only. After installation, stroke the damper manually with the unlock knob to confirm the blade travels freely and reaches both ends of its travel without binding; a damper that binds mechanically will defeat a correctly sized actuator. For systems commissioned over a network, commissioning a BACnet MS/TP damper actuator covers the network-side checks that follow the mechanical ones, and what is an HVAC control system places the actuator within the wider control scheme.

Frequently Asked Questions

How do I know whether this actuator is big enough for my damper?

The rated area of this unit is up to roughly half a square metre, so the first check is the damper’s size. The real requirement is torque: the actuator has to develop enough to move the blade and hold it against the pressure difference across the closed damper. For rectangular multi-blade dampers the damper actuator torque calculator derives that figure from the damper dimensions and the pressure it must hold, and the result is compared with the actuator’s rating with a margin for friction and for a blade that has aged.

Should I use the 0–10 V or the 4–20 mA interface?

Both are available. Voltage control is simpler where the controller provides a 0–10 V analogue output, which is the common case on terminal equipment. Current-loop control is preferred over long cable runs or in electrically noisy plant rooms, because a current signal is much less affected by cable resistance and induced noise than a voltage. The practical differences are set out in HVAC control signals: 0–10 V and 4–20 mA.

Why does the runtime matter on a modulating damper?

Because the quality of mixed-air control depends on how often the damper can be repositioned. An actuator that crosses its full travel in about two seconds lets the controller make small, frequent corrections, which holds the mixed-air temperature steady as outdoor conditions change. A slow actuator can appear perfectly stable in mild weather and then lag noticeably when the outdoor temperature is moving, which is when the building notices the deviation.

What is the feedback signal for?

It reports the damper’s actual position back to the controller. A command tells the controller what it asked for; feedback tells it what it received, which diverge when a blade is stiff, when the shaft coupling has slipped or when two actuators are driven together. Where feedback is wired, the controller can compensate and a commissioning engineer can compare commanded and actual positions to find a mechanical fault early. Where it is not wired, nothing is wrong — the capability is simply unused.

Can the damper be moved by hand during commissioning?

Yes. Pressing the unlock knob releases the drive so that the damper can be positioned manually, which is what allows the blade travel to be checked and the linkage set before control power is available. A mechanical position indicator on the housing shows the angle at any time, whether the actuator is powered or not.

OEM and Project Supply

DNARENS supplies the QA5F24-P for catalogue orders and as part of air-side packages that include the dampers, controllers and sensors used on the same air handling unit. Labelling, packaging and the control interface configuration can be adapted for OEM and project business, and actuators can be supplied as a schedule matched to the damper sizes and torque requirements on the drawing. Because the torque requirement and the shaft size decide whether an actuator will work, sending the damper schedule with the enquiry is the quickest route to an accurate selection. More on our OEM/ODM work is in your reliable OEM/ODM partner for smart HVAC controls.