2) This ratio is true (approximately) when the system curve does not change: bhp1/bhp2 = (cfm1/cfm2)3 Where: bhp = fan b

[answerhappygod]

2) This ratio is true (approximately) when the system curve does
not change:
bhp1/bhp2 = (cfm1/cfm2)3
Where: bhp = fan brake-horsepower (recall: 746 Watts = 1
horsepower)
cfm = fan airflow
If an office building requires 15,000-cfm of air under its highest
load, but will average 50% of this load
throughout the year, then how much money will a VAV system save
compared to a constant volume
system over one year if the cost of energy is $0.12/kW-hr and the
operating time is 5,000-hours per year?
Assume the motor uses 15-horsepower.
3) This ratio is a little closer to reality: bhp1/bhp2 =
(cfm1/cfm2)2
Calculate how the savings in question #3 above change when using
this “more realistic” ratio. The ratio in
question #3 comes from the Bernoulli equation and that is why it
isn’t quite true in reality.