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Table 1
 Initial capital cost (£)Saving (%)Operating cost (£)Saving (%)Whole life cost (£)Whole life saving (%)
    (over 30 years)   
Pre-insulated       
ductwork37,00021.567,67220.4104,67220.8
Insulated       
galvanised       
sheet metal47,154 85,058 132,212 
Table 2
Velocity (m/s)Cross-sectional Flow rate (l/s)Flow rate plus galvFlow rate plus rigidReduction in Reduction in
 area (m²) sheet steel ductworkphenolic pre-insulatedflow rate (%) fan power (%)
   leakage (l/s)ductwork leakage (l/s)  
50.3618002168.051811.0416.541.7
7.50.3627003068.052711.0411.631.0
100.3636003968.053611.049.024.6