VSD SAVINGS CALCULATOR FOR PUMPS

References and Equations

References:

For the energy savings analysis, this tool used power curves developed from data obtained by measuring the operating characteristics of various fans and from information provided in "Flow Control", a Westinghouse publication, Bulliten B-851, F/86/Rev-CMS 8121. The curves are representative, not precise. Final economic analysis should be based on actual power (kW) measurements of the pumping system.

Constants:

Conversion Constant (kW/hp) = 0.746
Polynomial Coefficients A1, A2, A3 and A4:
Type of Flow Contorl A1 A2 A3 A4
1 55.21240 0.63700 -0.00190 0.00000
2 16.39683 -0.05647 0.01237 -0.00003
3 13.51137 0.34467 0.01269 -0.00007
4 102.00000 0.00000 0.00000 0.00000
VSD 27.44751 -1.00853 0.01762 0.00000

Equations:

Power at Design CFM = Nameplate Horsepower × Conversion Constant (kW/hp) × Motor Load at Design GPM / Nameplate Efficiency
Computed for each capacity level:
Percent of Design kW = A1 + (A2 × Capacity) + (A3 × (Capacity2)) + (A4 × (Capacity3))
Percent of Design kW for VSD = A1 + (A2 × Capacity) + (A3 × (Capacity2)) + (A4 × (Capacity3))
Current Power (kW) = Percent of Design kW × (Power at Design CFM / 100)
VSD Power (kW) = Percent of Design kW for VSD × (Power at Design CFM / 100)
Current Energy (kWh) = Current Power (kW) × (Percent of time at this Capacity / 100) × Operating Hours 
VSD Energy (kWh) = VSD Power (kW) × (Percent of time at this Capacity / 100) × Operating Hours
Current Annual Energy Use = sum of all Current Energy (kWh)  
VSD Annual Energy Use = sum of all VSD Energy (kWh) 
Annual Energy Savings = Current Annual Energy Use – VSD Annual Energy Use 
Annual Cost Savings = Annual Energy Savings × Cost of Electricity
VSD Savings Calculator For Pumps
Nameplate Horsepower hp Annual Operating Hours hp
Nameplate Efficiency % Type of Flow Control
Motor Load at Pump Design GPM % Cost of Electricity RM/kWh
Duty Cycle
Percent of
(cfm)
Percent of Time
at this Capacity
% %
% %
% %
% %
% %
% %
% %
% %
% %
% %
Energy and Cost savings
Current Annual Energy use kWh/yr
VSD Annual Energy Use kWh/yr
Annual Energy Savings kWh/yr
Annual Cost Savings RM/yr
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