Appendix A
Calculation Of Flue System Equivalent Resistance
The pressure resistance of the flue system (Pr) = 1.5 * [(PFF*H/D+SRF)Qm/Wm2] (pa)
Where H = Effective flue height in m
D = Internal Diameter of flue in m
PRF (Pipe Friction Factor) = 0.118*(0.21147/D0.4)
Where D = Internal Diameter of flue in m
SRF (Sum of individual resistance factors)
Typical resistance factors for individual components are as follows
Segmented 90° bend 0.5
45° Elbow 0.4
Cowl 1.0
Qm (Mean Density of the column of exhaust gas in kg/m3) = 97000/(300*Tm)
Where the mean temperature of the column of exhaust gas (Tm) = 288+((Te-TL)/0.2)*(0.18)
Where Te is the exhaust gas temperature in °C
TL is the external air temperature in °C
Wm (Mean exhaust gas velocity in m/s = M/(A*Qm)
Where A is the cross sectional area of the flue in m2
M is the exhaust gas mass flow in kg/s which for this heater is
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Every effort is made to ensure accuracy at time of going to press. However as part of our policy of continual product improvement, we reserve the right to alter specifications without prior notice.
HEATING DIVISION
Hort Bridge
Ilminster, Somerset TA19 9PS
Tel: 01460 53535 Fax: 01460 52341
BSI Registered Firm
FM 414
Ind. & Comm. Air Heaters;
Air Moving Equipment;
Natural, Smoke & Heat
Ventilators;
Powered Supply & Extract
Fans & Systems.
ISO 9001
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