how to calculate efficiency of VFD HVAC system vrs. other control

Here's a simple formula for calculating efficiency of a VFD based HVAC system as compared to other forms of HVAC volume control, or no control (cv).

1. convert motor HP toKw:
__HP x 7.46=__Kw1

2. multiply vfd(variable frequency drive) power ratio from below times Kw1 above
__ratio x__Kw1=__Kw2(vfd)

3. multiply ratio of control now being used (from info below) times Kw1 from above:
__ratio x __Kw2=__Kw3(current mehod)

4. Minus step 2 from step 3, Kw3-Kw2:
__Kw3 minus __Kw2=__Kw4(savings versus vfd)

5. multiply step 4 savings times total hours of operation in fiscal year per Kwhr of electricty.
__Kw4 x __Hrs x $__/KwHr=$__

this gives you your annual savings using vfd

list of ratios

ratio for fan control
.32 VFD
.69 inlet guide vane
.94 outlet dampers
1.00 bypass dampers

ratio for pump control
.41 VFD
.83 discharge valve
1.00 bypass dampers
1.00 bypass valve
1.00 no control


Example:

a 60 hp fan running 8760 hrs a year & utility charges of $0.12 per KwHr:

60hp x .746=44.76Kw1

.32x44.76=14.32Kw2

.94 x 44.76=42.07Kw3

42.07-14.32=27.75Kw4

27.75x8760x0.12=29,170 in savings