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ACH
Air changes per hour. The number of times the volume of air in a room needs to be changed in one hour depending on the activity in that space. Normally given as a range e.g. 15-20 ach; based on the level of usage.
Axial fans
Suitable for low pressure applications, where duct runs are short.
Branch
A section of a duct system serving only one or two inlets or outlets.
Centrifugal fans
Also known as radial fans, deliver the pressure needed to propel air through long duct runs.
dB(A)@3m
Decibel, unit of sound measurement based on pressure at 3m away from the source.
P17 of the Approved Document F of Building regulations recommends sound levels from whole house ventilation systems not exceed 30 dB(A) levels within bedrooms and living rooms.
Duct system resistance
The total resistance of the duct system can be calculated by simply adding up the resistance of each component at a specific air-flow rate. Each product within the Domus range has a measured resistance value for the main UK Building Regulation extract flow rates.
CIBSE Guide B, 2005
Recommends extract rates are calculated by multiplying the volume of the room (m3) by the following air changes per hour (ACH). This rate should always be greater than Building Regulations minimum requirements.
- Bathrooms 6 - 8
- Launderettes 10 - 15
- Bedrooms 2 - 4
- Laundries 10 - 15
- Billiard Rooms 6 - 8
- Lecture Theatres 6 - 10
- Cafés & Coffee Bars 10 - 15
- Libraries 3 - 4
- Canteens 8 - 12
- Living Rooms 4 - 6
- Cellars 3 - 10
- Offices 4 - 6
- Club Rooms 8 - 10
- Photo & X-ray Darkrooms 6 - 8
- Conference Rooms 6 - 10
- Public House Bars 6 - 8
- Entrance Halls, Corridors 3 - 5
- Restaurants 10 - 15
- Factories & Workshops 6 - 10
- Shops & Supermarkets 8 - 10
- Garages 6 - 10
- Shower / Bathrooms 15 - 20
- Gymnasiums 6
- Stores & Warehouses 3 - 6
- Hairdressing Salons 10 - 15
- Toilets (Public) 5+
- Hotel Bars 6 - 10
- Toilets (Domestic) 6 - 10
- Kitchens (Domestic) 10 - 15
- Utility Rooms 15 - 20
- Laboratories 4 - 15
Extract Rates are given in Table 5.1a and 5.1b of Approved Document F of Building Regulations 2010 which can be downloaded here or a printed copy requested from vent.info@polypipe.com or 08443 715523.
Electrical Safety Zones
Section 701 of British Standard 7671:2008 defines four bathrooms and shower room zones:
| Zone | Description | Permitted Voltage | Min IP |
|---|---|---|---|
| Zone 0 | Cuboid volume that contains the bathtub, shower or basic | None | None |
| Zone 1 | Area above Zone 0 up to a height of 2.25m above the floor | Separated extra low voltage (SELV) with transformer located outside Zone 2 | None |
| Zone 2 | Area above Zone 1 up to a height of 3m, as well as the area that is horizontally 0.6m from Zone 1 | Any | X4 protection against splashing water from all directions |
| Outside the Zones | Includes any space under the bath or shower that can only be accessed with a tool | Any | Any |
Fans with humidity controls and PIRs should not be located within splash Zone 1
Humidistat
A switched control that triggers the appliance once a set level of humidity is reached.
IEE wiring regulations
Publication of the Institute of Electrical Engineers. Also known as BS 7671.
IP Rating
Classification of degrees of protection for an electrical product developed by CENELEC. First digit describes degree of protection from solids, the second from liquids. Examples: IP44.
l/s
Litres per second - Measurement of volume flow.
l/s = m3/h ÷ 3.6
m3/h
Cubic metres per hour - Measurement of volume flow.
m3/h = l/s × 3.6
Mixed flow fans
Combine elements of axial and centrifugal and are therefore appropriate for medium length duct runs.
Pa
Pascal, unit of pressure for measuring system resistance or static pressure.
PIR
Passive infrared sensor, detects movement and is used to trigger appliances.
RH
Relative humidity. The ratio of the amount of water in the air at a given temperature.
- Outside humidity levels are usually between 60-70%RH
- The target for Indoor levels is normally between 40-60%
SELV
Separated Extra Low Voltage, used to describe fans operating at less than 25V.
Temperature
The metric measurement of which is Centigrade (or Celsius).
Thermal overload protection
A safety component designed to interrupt the current to a motor before the windings exceed their design operating temperature.
Trunk
The section of a duct system carrying the maximum flow of air to or from the appliance.
Watts
Measure of electrical power.
