Glossary

Volt.

Volt-Ampere.

(1) A disc type wheel within a cylinder, a set of air guide vanes located either before or after the wheel and including driving mechanism supports for either belt drive or direct connection.

(2) A fan in which the airflow is driven by an airscrew mounted on an axis pointed along the desired direction of flow.

Vane mounted at the fan inlet, can be adjusted in order to change the fan performance by controlling the swirl of the fan inlet.

The change from liquid or solid phase to the vapour phase.

(1) Gas which is released from a solid substance or liquid.

(2) Gas emanation coming from the transformation of a liquid under the action of heat or from the sublimation of a solid.

A moisture impervious layer applied to the surfaces enclosing a space, or to the external surface of thermal insulation to limit moisture migration

(1) The pressure exerted by a vapour. If a vapour is kept in confinement over its liquid so that the vapour can accumulate above the liquid, the temperature being held constant, the vapour pressure approaches a fixed limit called the maximum, or saturated, vapour pressure, dependent only on the temperature and the liquid.

(2) Vapour pressure denotes the lowest absolute pressure that a given liquid at a given temperature will remain liquid before evaporating into its gaseous form or state.

(3) Pressure for which the gas phase of a substance is in balance with its liquid or solid phase. It depends on the temperature.

The change from liquid or solid phase to the vapour phase.

A supply air system that holds the supply air temperature constant but varies supply air flow to compensate for the thermal loads in the space.

The variable aperture flowmeter is a instrument measuring the flow of the liquids and gas in pipe works. It consists of a graduated tube in which the fluid to be measured runs out from the bottom to the top of the tube and in which there is a mobile float. This float goes up as the flow increases, in such a way that the hydraulic forces are always balanced by the opposite force coming from the weight of the float which remains constant whatever the flow is. The level of the float represents the measurement of the flow. The value of the flow is read by using the graduated scale in % or in physical units.

Costs that change depending on the level of sales or production. These could include commissions for salespeople, sales discounts, etc.

The blade angle of the impeller can be varied whilst the impeller is rotating, all blades being simultaneously varied by one operation.

Speed can be varied either continuously or in steps by variable speed motor, slipping coupling, gearbox or other means.

Variable air volume.

Visual display unit; video display unit.

The pressure produced by the movement of air, such as the wind, or the air coming from a fan.

An opening in a vessel or other enclosed space for the removal of gas or vapour.

A device permitting fluid flow in order to maintain the balance of pressure between the atmosphere and the system.

A vent through which bad air or flue gases is discharged to the atmosphere.

A vertical stack or duct used to provide efficient ventilation of the drainage system to prevent the accumulation of foul air.

(1) The process of supplying and removing air by natural or mechanical means to and from any space.

(2) Ability of a mechanical (or natural) ventilation system to remove pollution originating in a room, either of a steady state or transient nature.

That portion of supply air which is outdoor air plus any recirculated air that has been treated for the purpose of maintaining acceptable indoor air quality.

A pipe to allow the release of air from the system.

Any means of ventilating a room or of removing the dust, the gas or the smoke from the ambient air.

The resistance of a fluid to flow.

Spoiled, impure or polluted air.

Organic compounds (usually with boiling points less than 100-120°C) that are vaporized during incineration.

The cubic space of a room bounded by walls, floors, and ceilings determined by the mathematical equation Volume=Length x Width x Height of space.

Quantity of air flow.

Electromotive force or potential difference that, when applied to conductors, will produce current in the conductors.