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Variable Volume Controls

Extracting less air means less replacement air is needed.  It is the heating, cooling and conditioning of this replacement air that uses the majority of  energy associated with running a fume cupboard.

As a fume cupboard sash is lowered, the opening area is reduced and  less volume of air is required to provide the same velocity of air across the opening. A fume cupboard VAV control monitors the height of the sash or the face velocity and adjusts the extract volume accordingly, using a fast-acting motorised damper or similar.


VAV Control Valve

Fumair can supply and install fume cupboard VAV control systems as part of a new laboratory installation. Equally, we can install VAV controls retrospectively to existing fume cupboards as part of an energy-saving exercise.

As well as the controls themselves we offer a number of ancillary items designed to maximise the energy savings VAV control bring, items such as:

  • Auto sash closure devices and reminders

  • Supply air and room pressure controls

  • VAV bleed branches and dampers

  • Extract manifold systems

VAV is not always a cost-effective method of controlling a fume cupboard. Certain conditions must be met in order to truly benefit from the energy savings they offer. Please contact us for further advice.

How a VAV system works

A VAV system works by controlling the volume of air extracted from the fume cupboard, usually via a fast-response motor-driven damper. The damper continuously modulates and, as such, long-term reliability can be a concern. The extract fan serving the cupboards runs at a constant speed, irrespective of the requirements at each fume cupboard and, to maintain the minimum efflux velocity when the majority of the fume cupboard sashes are closed, additional air is introduced into the inlet of the fan via a further modulating “bleed” damper. The additional air is drawn from the atmosphere rather than the laboratory so that no conditioning is required.  The cost of the bleed damper is not included in the above indicative price as it will vary depending on the installation.

Note: When calculating fume cupboard energy savings that VAV systems offer, the cost of a large continuously running extract fan is often overlooked. For example, an installation comprising 5 no. 1500mm wide fume cupboards on a common extract would typically require a 2.2kW fan motor. To run this fan via an inverter for 10hrs a day would cost approx. £580 per annum. The equivalent cost of running 5 no. individual extract fans with the FlowMaster/inverter control systems would be less than £100 total per annum.

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