The Noise Insulation (Railways and Other Guided Transport Systems) Regulations 1996

Specifications for inlet ventilator systems

8.  The inlet fan ventilator system shall consist of a sound-attenuating inlet fan ventilator unit (in this paragraph referred to as a “ventilator unit”) and an air supply duct and cowl or grille; such air supply duct and cowl or grille may be of separate construction from the ventilator unit or integral with it, but the following conditions shall be complied with—

(a) the air supply duct and cowl or grille shall be designed so as to allow the passage of air between the ventilator unit and the external air at all times and shall be so constructed that when installed in a cavity wall exposed to the weather—

(i) the weather resistance of the cavity is retained; and

(ii) the external cowl or grille provides protection against the passage of snow, rain and vermin;

(b) the ventilator unit shall consist of a controlled variable-speed inlet fan with sound attenuating duct and cover, shall be fitted with an easily removable and washable air filter on the inlet side of the sound attenuating duct to afford adequate protection for the acoustic lining, and shall be capable of supplying fresh air to the room directly from outside by means of the supply duct and cowl or grille;

(c) the ventilator unit shall be securely fixed to the wall in such a position that the air filter can be easily removed, and the junction between the ventilator unit and the face of the wall shall be fully sealed by means of compressible strip or other equally effective means;

(d) the air supply duct and cowl or grille shall be securely fixed to the wall and the junction between the air supply duct and the internal leaf shall be fully sealed by suitable means;

(e) the ventilator unit shall be electrically safe in operation and maintenance and shall not present a fire hazard;

(f) the ventilator unit with air filter in position, by itself or with an integral air supply duct and cowl or grille, shall be capable under continuous control of giving variable ventilation rates ranging from—

(i) an upper rate of not less than 37 litres per second against a back pressure of 10 pascals and not less than 31 litres per second against a back pressure of 30 pascals, to

(ii) a lower rate of between 10 and 17 litres per second against zero back pressure; and if there is no continuous control of the ventilation rate, the following intermediate settings shall be provided—

(A) a ventilation rate of greater than 31 and less than 33 litres per second against a back pressure of 10 pascals; and

(B) a ventilation rate of greater than 21 and less than 26 litres per second against a back pressure of 10 pascals;

(g) the effective area of the air path through the inlet fan ventilator system with the fan switched off and the air filter in position shall be not less than 3,250 square millimetres and such area shall be ascertained by measuring the static pressure difference across the system for various air flow rates through the system and calculating the effective area from

• (where Q is the measured air flow rate through the system in litres per second and Δp the measured static pressure difference across the system in pascals): effective areas shall be calculated for air flow through the system in both directions and the lower calculated value shall be taken for the effective area;

(h) the ventilator unit by itself or integral with the air supply duct and cowl or grille shall be so constructed that—

(i) when it is in operation in any room the sound level in the room due to the operation of the unit at a ventilation rate of 31 litres per second against a back pressure of 10 pascals, measured at any point not nearer than one metre to the unit or any of the room surfaces and normalised by the subtraction of

(where A is the equivalent sound absorption in the room in square metres measured at each one-third frequency interval from 100 to 3,150 Hertz), does not exceed 35 of B(A) and at the maximum ventilation rate of the unit does not exceed 40dB(A) against a back pressure of 30 pascals; and

(i)

the element-normalised sound pressure level difference, measured in accordance with British Standard number BS EN 20140—10: 1992, is not less than the figure shown in Table 3 below except for total adverse deviations (at all one-third octave frequencies) not exceeding 32 decibels and an adverse deviation at any one one-third octave frequency not exceeding 8 decibels.

TABLE 3

One-third octave frequency band centre (Hertz)	Normalised sound pressure level difference (decibels)
100	30
125	33
160	36
200	39
250	42
315	45
400	48
500	49
630	50
800	51
1,000	52
1,250	53
1,600	53
2,000	53
2,500	53
3,150	53