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E.2.7.2.5 Ensure that there will be no pressure differential between the area of the fan outside the enclosure, and along the return air paths around the boundary of the enclosure under test. This may be done visually or by pressure measurement.

E.2.7.3 Measurement of bias Pressure during fan testing (P_bt)

E.2.7.3.1 Р_ы is used to correct the measured inside-outside enclosure pressure differential in order to calculate the enclosure leakage characteristics.

E.2.7.3.2 Seal the fan unit and, without the fan(s) operating, allow the enclosure differential pressure reading to stabilise if possible (which may take up to 30 s) and record the pressure differential (P_bt) and its direction. Take P_bt as positive if the inside pressure is above the outside pressure, and negative if the inside pressure is below the outside pressure. If the magnitude of Р_ы is greater than 3 Pa (i.e. |P_bt| > 3 Pa) it shall be reduced before proceeding with the integrity test.

E.2.7.3.3 Make every effort to reduce the static pressure P_bi by shutting down air handling equipment even

though it can operate during the hold time.

If a subfloor pressurisation air-handler cannot be shut down for the test and leaks exist in the subfloor, these leaks cannot be accurately measured. During the test as many floor tiles as necessary should be lifted to eliminate the effect of subfloor pressurisation, or every effort should be made to reduce subfloor leaks to insignificance.

WARNING — The removal of raised floor tiles creates a serious safety hazard. Appropriate precautions should be taken.

E.2.7.3.4 If P_bt fluctuates (e.g. due to wind effects), it may not be possible to achieve the necessary correlation accuracy in the fan test results. The fluctuations may need to be reduced, before accurate fan tests can be carried out, by sealing leakage paths between the enclosure and the source of fluctuating pressure.

E.2.7.4 Measurement of leakage rate

E.2.7.4.1 Measure the air temperature inside the enclosure T_e, and measure the air temperature outside the enclosure P_o, at several points. If the location of leaks is not known, use the average value; otherwise, use the average value weighted according to the known location of the leaks. Verify the temperatures at the end of the test.

E.2.7.4.2 Unseal the fan inlet or outlet and connect the fan flow pressure measuring device.

E.2.7.4.3 Use the fan unit to depressurize the enclosure to the maximum extent, but preferably by not more than 60 Pa, as at higher differential pressures the flow characteristics of the leak paths may change. Allow the enclosure differential pressure reading to stabilize (which may take up to 30 s) and record the pressure differential i.e. (P_f + P_bt) which will be negative. Repeat at not less than four more fan unit flow rates to give five readings more or less evenly spaced over the range down to 10 Pa or 10 |P_bt| whichever is the higher. At each pressure difference, measure the air flow and pressure difference across the enclosure/fan boundary. After the fan and instrumentation have stabilised, the average over an interval equal to, or greater than, 10 s should be used if fluctuations are observed. If stable readings cannot be obtained at the minimum pressure difference (10 Pa or 10 |P_bt|) then only go down to the lowest pressure at which stable readings can be obtained.

E.2.7.4.4 Use the fan unit to pressurize the enclosure and repeat the procedure of E.2.7.4.3. Again record values of (P_f + P_bt), which will be positive.

E.2.7.4.5 Repeat the zero flow pressure difference (bias pressure P_bt) measurement. If the reading differs from the initial zero flow pressure difference reading by more than 1 Pa, repeat the test.

E.2.7.5 Field calibration check

E.2.7.5.1 Calculate the enclosure's equivalent leakage area (average of pressurization and

depressurization), at a reference pressure differential of 10 Pa, using equations (E.30) and (E.31). See E.3.2.

E.2.7.5.2 In a sheet of rigid material, less than 3 mm thick and free of any penetrations cut a sharp-edged circular calibration check orifice. The area of the orifice shall be large enough to cause an easily measurable increase in the enclosure's leakage rate, but not so large that a different range of the fan unit shall be used to measure the increased flow. A geometrical area about 50 % of the enclosure’s equivalent leakage area is likely to be suitable. Install the sheet in an unused fan unit port if possible. Otherwise, install the sheet in some other convenient enclosure opening but consider that this will modify the enclosure's leakage characteristic and reduce the accuracy of the field calibration check.

E.2.7.5.3 Seal the fan unit and orifice, repeat the measurement of bias pressure during fan testing (see E.2.7.3) and record the value of P_bt.

Open the calibration check orifice and repeat the measurement of leakage rate (see E.2.7.4).

E.2.7.5.4 Calculate the equivalent leakage area (average of pressurization and depressurization) of the enclosure with the orifice at reference pressure differential (10 Pa).

E.2.7.5.5 The measured equivalent leakage area of the calibration orifice is the equivalent leakage area of the enclosure with the orifice minus the equivalent leakage area of the enclosure alone.

E.2.7.5.6 The field calibration check is acceptable if the measured equivalent leakage area of the orifice is within ± 15 % of its geometrical area. If the difference is greater than 15 %, the fan unit should be recalibrated.

E.2.7.6 Measurement of bias pressure under hold time conditions (P_bh)

E.2.7.6.1 P_bh is the bias pressure under hold time conditions that is used in the calculation of the hold time.

E.2.7.6.2 Set the enclosure, its surroundings, and services, to the conditions that would apply during the hold time, using the information from E.2.5.

E.2.7.6.3 Seal the fan unit and, without the fan(s) operating, connect a manometer so as to measure the pressure differential (Р_Ьп) and its direction. Measure between a single fixed reference point inside of the enclosure, and a) a point immediately outside the upper leakage and b) a point immediately outside the lower leakage. Allow the enclosure differential pressure reading to stabilise if possible (which may take up to 30 s) and record the pressure differential (P_bh) and its direction for both positions. Take P_bh as positive if the inside pressure is above the outside pressure, and negative if the inside pressure is below the outside pressure.

If the enclosure is large, repeat the pairs of measurements at several points so as to determine the average value of P_bh, but note that if P_bh varies significantly from place to place then it may cause non uniform flow through leakage areas, invalidating the hold time equations.

The value of P_bb for hold time calculations is given by:

• for extinguishants heavier than air (p_a < p_e), P_bh = A>h(iower) - /’bh(upper);

• for extinguishants lighter than air (p_a > p_e), P_bh = P_bh(u_PPer) - Pbh(iower)-

The tubing used to connect the manometer to the points outside the upper and lower leakages should be filled with air at ambient temperature, so that the measured value of P_bb will not be affected by gravity acting on the air between the upper and lower leakage.

E.2.7.6.4 If P_bh fluctuates (e.g. due to wind effects) the predicted hold time will be uncertain. In this case, use the most negative value of P_bh when checking whether flow reversal will occur (see E.2.8.4) and the most positive value when calculating the predicted hold time (see E.2.8.7, E.2.8.8 and E.2.8.9).

E.2.7.6.5 If the bias pressure P_bh has a numerical value greater than 25 % of the initial extinguishant/air Column Pressure [see Equation (E.6) in E.2.8.4], i.e. |P_bh| > 0,25 P_mi then the hold time is likely to be low and the enclosure may not hold the specified extinguishant concentration. The source of the excessive Bias Pressure should be identified (and traced using inert smoke) and if possible permanently reduced. If it cannot be permanently reduced it shall be recognised that the hold time may be adversely affected.

E.2.8 Calculation

E.2.8.1 Selection of appropriate hold time equation

For enclosures without continuous mixing, the standard enclosure hold time equation is easier to solve than the non-standard enclosure equation. In certain circumstances, it may be acceptable to use the standard enclosure equation to calculate the hold time for a non-standard enclosure, although the non-standard enclosure equation will be more accurate.

For enclosures where the horizontal cross sectional area decreases from the top of the enclosure to the bottom (e.g. a ship’s hull or a flat topped and vertical walled room with a cable trench), the standard enclosure equation will underestimate the hold time (in the upper part of the enclosure) for extinguishants heavier than air, and overestimate it (in the lower part) for extinguishants lighter than air.

For enclosures where the horizontal cross sectional area increases from the top of the enclosure to the bottom (e.g. enclosures with pitched roofs), the standard enclosure equation will overestimate the hold time (in the upper part) for extinguishants heavier than air, and underestimate it (in the lower part) for extinguishants lighter than air

.

It is important to use the non-standard enclosure equation when the standard enclosure equation will overestimate the hold time, because the standard enclosure equation may predict a pass for an enclosure that would actually fail.

It is less important to use the non-standard enclosure equation when the standard enclosure equation will underestimate the hold time, although the standard enclosure equation may predict a fail for an enclosure that would actually pass.

Expert advice should be sought in case of doubt.

E.2.8.2 Symbols

The symbols of the quantities, and their units, used in the calculation are given in Table E.1.

Table E.1 — Symbols, quantities and units

Table E.1 — Symbols, quantities and units (continued)

E.2.8.3 Depressurisation and pressurisation leakage characteristics

From the measured values of (P_f + P_bt) and P_bt calculate the values of P_f and, using the fan calibration data (see E.2.3.1), the corresponding airflow rates Q_f through the fan.

For each set of results (pressurisation and depressurisation) express the fan test results in the form:

|

(E.1)

Q_f| = ^o|P_f|ⁿ

Determine k₀, n, and the correlation coefficient (r or r²) using ordinary least squares regression to fit:

ln|g_f| = InAo + n ln|P_f| to the data. Check that the correlation coefficient of each set is not less than r = 0,99 or r²- 0,98. The two sets will almost always have different values of A_o and n.

If the correlation coefficient is too low:

— repeat the test;

• check for fluctuating bias pressure;

• check for damper/vent movement during the test.

Calculate the corrected values of k₀ using Equations (E.2) and (E.3), as appropriate, and call them for depressurization

pc¥ +273)V^/2 l¥₀ +273¥ P_t(20 + 273) *) ¹ ~ °I^P_t(r_c +273)J 1^7;+ 273J[l,013(T_o + 273)j

(E.2)

for pressurization

__k ґ Р_С(Г_О +273)Y^/2 Ґ T_e +273 ¥ P, (20 + 273)
^{1- <}P_;(T_C +273)J [t_o +273j|j,013(7; +273)J

(E.3)

NOTE Equations (E.2) and (E.3) correct the flow rates for the effects of temperature and pressure differences on air density, assuming that:

• the flowmeter is of the usual type which gives a pressure signal proportional to the air density and the square of the volume flow rate;

• for a given inside-outside pressure difference, the volume flow rate through the enclosure leakage is inversely proportional to the air density to the power n.

The correction is approximate as the second assumption is an approximation, and the effects of humidity and viscosity are ignored.

E.2.8.4 Column pressures

Calculate the density of the extinguishant/air mixture at 20 °С at the initial concentration using the equation:

(E.4)

For enclosures with continuous mixing, calculate the density of the extinguishant/air mixture at 20 °С at the concentration c_min using the equation:

_ ^Cmin ₊ 100 ^cmin

^Pm' ^Pe 100 ^Pa 100

(E.5)

Calculate the initial extinguishant/ air mixture column pressure /'_m) using the following equation:

Pmi 9n ¥ ІРті " Pal

(E.6)

For enclosures without continuous mixing, if c_min is less than 0,5 c, then take the equivalent sharp interface height H_e as equal to H. Otherwise, calculate H_e as follows:

For extinguishants heavier than air (p_a < p_e)

Н_е=Н_о-(Н_о-Н)-^-

^2cmin

(E.7)

and for extinguishants lighter than air (p_a > p_e)

P. =H— 2c ^vmm

(E.8)

For extinguishants heavier than air and c_min > 0,5 q, the value of H_e shall be in the range 0,5 H_oH_e< H_o; for extinguishants lighter than air and c_min > 0,5 q, the value of H_e shall be in the range Q< H_s< 0,5 Я_о. If this is not the case the equations for H_e and hold time are not valid (as there will be no extinguishant/air mixture at the initial concentration remaining in the enclosure).

For all enclosures, calculate the final extinguishant/air mixture column pressure P_mf.

For extinguishants heavier than air (p_a < p_e) in enclosures without continuous mixing:

Pmf Pe |Pmi Pal

(E.9)

For extinguishants lighter than air (p_a > p_e) in enclosures without continuous mixing:

Pmf 9n (7/q “ Pe ) ІРті Pal

(Е.Ю)

For all extinguishants in enclosures with continuous mixing:

Pmf Pn Pq |Pmf Pal

(E.U)

For all enclosures, if P_bh is negative check that P_mf is greater than the absolute value of P_bh. If this is not the case the hold time equations are not valid (as bias pressure will cause flow reversal).

E.2.8.5 Average leakage characteristics

Determine the average values of the leakage characteristics and n, as follows.

Calculate the average values (i.e. of the pressurisation and depressurisation data) of Qi = ШГ for values of P_f equal to P_mi, and for P_f equal to 0,5 P_mi. These are (2i_m and 0i_m/2 respectively: