Functional description

The volume flow controller is a mechanical self-powered unit and works without external power supply. A damper blade with low-friction bearings is adjusted by aerodynamic forces such that the set volume flow rate is maintained within the differential pressure range.

The aerodynamic forces of the airflow create a closing torque on the damper blade. The bellows extends and increases this force while at the same time acting as an oscillation damper. The closing force is countered by a leaf spring that unrolls over a cam plate. The shape of the cam plate is such that a change in the differential pressure leads to an adjustment of the damper blade in a way that the volume flow rate is maintained almost exactly.

Efficient commissioning

The volume flow rate setpoint value can be set quickly and easily using the pointer on the external scale; no measurements are required.

The advantage over flow adjustment dampers is that there is no need for repeat measurements or adjustments by an air conditioning engineer. Should the system pressure change, e.g. by opening or closing of duct sections, the flow rates in the entire system will also change if flow adjustment dampers are used; however, this is not the case with mechanical self-powered volume flow controllers A mechanical self-powered controller reacts immediately and adjusts the damper blade such that the set constant volume flow rate is maintained.

Notes on the order code

RN-S

• RN-S-A2/80: no lip seal (D2)

RN

• RN/80: no flange (FL), no matching flange (G2)
• RN-A2/80: no lip seal (D2)

Order example: RN/160/D2

Order example: RN-D-FL/250/G2/B50

RN-S

• Compact-height volume flow controller for constant volume flow rate control
• Spigot to make connections to the ducting

RN

• Volume flow controller for constant air volume flow control
• Spigot to make connections to the ducting

RN-D

• Volume flow controller with acoustic cladding for constant air volume flow control
• Spigot to make connections to the ducting
• For rooms where the case-radiated noise of the unit is not sufficiently reduced by a false ceiling
• The circular ducts for the room under consideration must have adequate acoustic insulation (provided by others) on the fan and room ends
• Acoustic cladding cannot be retrofitted

RN-FL

• Volume flow controller for constant air volume flow control
• With flanges to make detachable connections to the ductwork

RN-D-FL

• Volume flow controller with acoustic cladding for constant air volume flow control
• With flanges to make detachable connections to the ductwork
• For rooms where the case-radiated noise of the unit is not sufficiently reduced by a false ceiling
• The circular ducts for the room under consideration must have adequate acoustic insulation (provided by others) on the fan and room ends
• Acoustic cladding cannot be retrofitted
• Powder-coated surface (P1) or stainless steel construction (A2) not possible

Materials

Surfaces

Installation and commissioning

• Any installation orientation
• Volume flow rate can be set using an external scale; no tools required
• No repeat measurements or adjustments by an air conditioning engineer are necessary
• RN-D: For constructions with acoustic cladding, ducts on the room side should have cladding up to the acoustic cladding of the controller

Upstream conditions

The volume flow rate accuracy ΔV applies to a straight upstream section of the duct. Bends, junctions or a narrowing or widening of the duct cause turbulence that may affect measurement. Duct connections, e.g. branches off the main duct, must comply with EN 1505. Some installation situations require straight duct sections upstream.

Free air intake only with a straight duct section of 1D upstream.

Space required for commissioning and maintenance

Sufficient space must be kept clear near any attachments to allow for commissioning and maintenance. It may be necessary to provide sufficiently sized inspection access openings.

Space required

Prinipal dimensions

ØD [mm]

Outside diameter of the spigot

ØD₁ [mm]

Pitch circle diameter of flanges

ØD₂ [mm]

Outside diameter of flanges

ØD₄ [mm]

Inside diameter of the screw holes of flanges

L [mm]

Length of unit including connecting spigot

L₁ [mm]

Length of casing or acoustic cladding

H₁ [mm]

Screw hole pitch of flange (vertical)

n [ ]

Number of flange screw holes

T [mm]

Flange thickness

m [kg]

Unit weight including the minimum required attachments for manual adjustment

f_m [Hz]

Octave band centre frequency

L_PA [dB(A)]

A-weighted sound pressure level of air-regenerated noise of the CAV controller, system attenuation taken into account

L_PA1 [dB(A)]

A-weighted sound pressure level of air-regenerated noise of the CAV controller with secondary silencer, system attenuation taken into account

L_PA2 [dB(A)]

A-weighted sound pressure level of case-regenerated noise of the VAV terminal unit, system attenuation taken into account

qv_nom [m³/h] and [l/s]

Nominal volume flow rate (100 %)

• The value depends on product type and nominal size
• Values are published on the internet and in technical leaflets, and stored in the Easy Product Finder design software.
• Upper limit of the setting range and maximum volume flow rate setpoint value for the CAV controller

qv [m³/h] and [l/s]

Volume flow rate

ΔV [± %]

Volume flow rate accuracy in relation to the setpoint (tolerance)

Δp_st [Pa]

Static differential pressure

Δp_st min [Pa]

Static differential pressure, minimum

• The static minimum differential pressure is equal to the pressure loss of the CAV controller when the damper blade is open, caused by flow resistance (bellows, crossbar)
• If the pressure on the CAV controller is too low, the setpoint volume flow rate may not be achieved, not even when the damper blade is open
• Important factor in designing the ductwork and in rating the fan including speed control
• Sufficient duct pressure must be ensured for all operating conditions and for all controllers, and the measurement point or points for speed control must have been selected accordingly to achieve this

Galvanised sheet steel

• Casing made of galvanised sheet steel
• Parts in contact with the airflow as described for the product type
• External parts, e.g. mounting brackets or covers, are usually made of galvanised sheet steel

Powder-coated surface (P1)

• Casing made of galvanised sheet steel, powder-coated RAL 7001, silver grey
• Parts in contact with the airflow are powder-coated or made of plastic
• Due to production, some parts that come into contact with the airflow may be stainless steel or aluminium, powder-coated
• External parts, e.g. mounting brackets or covers, are usually made of galvanised sheet steel

Stainless steel (A2)

• Casing made of stainless steel 1.4201
• Parts in contact with the airflow are powder-coated or made of stainless steel
• External parts, e.g. mounting brackets or covers, are usually made of galvanised sheet steel