VFL

Functional description

The volume flow limiter 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 limited as a consequence.

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. As the differential pressure changes, the leaf spring adjusts the position of the damper blade such that the volume flow rate is limited.

Efficient commissioning

The volume flow limiter performs the previously tedious and expensive balancing of volume flow rates in ventilation and air conditioning systems.

Simple handling and perfect function help to save valuable working time on site. The required volume flow rate can be set at the point of installation, then the volume flow limiter is inserted into the duct. The set volume flow rate will then be limited and maintained within close tolerances.

Order example: VFL/100

Installation and commissioning

• Any installation orientation
• Set the required volume flow rate using a scale
• Insert the unit into the duct
• Mark the installation location

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.

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

B [mm]

Duct width

B₁ [mm]

Screw hole pitch of flange (horizontal)

B₂ [mm]

Outside dimension of flange (width)

B₃ [mm]

Width of device

H [mm]

Duct height

H₁ [mm]

Screw hole pitch of flange (vertical)

H₂ [mm]

Outside dimension of flange (height)

H₃ [mm]

Unit height

n [ ]

Number of flange screw holes

T [mm]

Flange thickness

m [kg]

Unit weight including the minimum required attachments for manual adjustment

Acoustic data

f_m [Hz]

Octave band centre frequency

L_PA [dB(A)]

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

L_PA1 [dB(A)]

A-weighted sound pressure level of air-regenerated noise of the VAV terminal unit 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

L_PA3 [dB(A)]

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

All sound pressure levels are based on 20 μPa.

Volume flow rates

V_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

V [m³/h] and [l/s]

Volume flow rate

ΔV [± %]

Volume flow rate tolerance from setpoint value

Differential pressure

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

Construction

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