Setpoint Optimization Calculator

Energy savings from supply air temperature reset.

Fan/pump motor (HP)

Current speed (%)

Reduced speed (%)

Annual run hours

Electricity rate ($/kWh)

Current SAT setpoint (°F)

Reset SAT setpoint (°F)

Annual cooling cost ($)

Tab to move between fields

VFD power savings (kW)

9.78

Power reduction (%)

48.8

Annual VFD savings ($)

$7,043.00

≈ 7 smartphones

Current power (kW)20.05

Reduced power (kW)10.26

Annual kWh saved58,694

Estimated VFD cost ($)$5,625.00

VFD payback (years)0.8

Flow reduction (%)20

SAT reset savings ($/yr)$4,500.00

Total combined savings ($)$11,543.00

Pressure Reduction (%)36%

How to Use This Calculator

Enter Fan/pump motor (HP), Current speed (%), and Reduced speed (%).
Set Annual run hours, Electricity rate ($/kWh), and Current SAT setpoint (°F).
Adjust Reset SAT setpoint (°F), Annual cooling cost ($) as needed.
Review VFD power savings (kW), Power reduction (%), and Annual VFD savings ($) ($).
Use Current power (kW) and Reduced power (kW) to inform your decision.

How the result changes with Reduced speed (%)

Reduced speed (%)	VFD power savings (kW)	Power reduction (%)	Annual VFD savings ($)
19	19.91	99.3	$14,334.00
42	18.56	92.6	$13,364.00
69	13.46	67.1	$9,692.00
91	4.94	24.6	$3,557.00

Fan/pump motor (HP): Motor horsepower of the fan or pump to be controlled by VFD.
Current speed (%): Current operating speed as percentage of full speed.
Reduced speed (%): Target reduced speed. Affinity law: Power = (Speed)³. Even small reductions yield large savings.
Annual run hours: Hours per year the fan/pump operates. 24/7 = 8,760; typical office = 3,000-5,000.
Electricity rate ($/kWh): Blended electricity rate in dollars per kilowatt-hour.
Current SAT setpoint (°F): Current supply air temperature setpoint. Typical design: 55°F.
Reset SAT setpoint (°F): Optimized (higher) SAT during low cooling load. Each +1°F saves ~1.5-2.5% cooling energy.
Annual cooling cost ($): Annual cooling energy cost for SAT reset savings calculation.

VFD power savings (kW): Instantaneous power reduction from speed reduction per the affinity law (Power ~ Speed³).
Power reduction (%): Percentage power reduction. A 20% speed cut saves ~49% power.
Annual VFD savings ($): Annual dollar savings from VFD speed reduction.
Current power (kW): Motor power consumption at the current speed.
Reduced power (kW): Motor power consumption at the reduced speed.
Annual kWh saved: Total kilowatt-hours saved per year from VFD speed reduction.
Estimated VFD cost ($): Approximate VFD purchase and installation cost (~$225/HP).
VFD payback (years): Simple payback period for VFD installation.
Flow reduction (%): Percentage reduction in flow (linear with speed per affinity law).
SAT reset savings ($/yr): Annual cooling cost savings from raising the supply air temperature setpoint.
Total combined savings ($): VFD savings + SAT reset savings combined.

Identify Input Parameters
4 parameters
Fan/pump motor (HP) = 25, Current speed (%) = 100, Reduced speed (%) = 80, Annual run hours = 6000 = 8 input(s) provided
Calculate VFD power savings
VFD power savings = currentPowerKW - reducedPowerKW
9.78 = 9.78
Calculate Power reduction
48.8 = 48.8
Calculate Annual VFD savings
Annual VFD savings = annualKWhSaved * electricityRate
7043 = $7,043
Calculate Current power
Current power = fullLoadKW * pow(currentSpeedRatio, 3)
20.05 = 20.05
Calculate Reduced power
Reduced power = fullLoadKW * pow(reducedSpeedRatio, 3)
10.26 = 10.26