7154 VFD7154 VFDPresentation #4Presentation #4

May 2002May 2002

Paul WeingartnerPaul Weingartner

Load typesLoad types

Standard motorsStandard motors

High instantaneous current High instantaneous current Lumber cutting exampleLumber cutting example

Fans, pumpsFans, pumps

Utility billingUtility billing

Energy costEnergy cost

Demand chargeDemand charge

Power factor (can be)Power factor (can be)

Energy cost (approx)Energy cost (approx)

Residential $0.07/kWhResidential $0.07/kWh

Commercial $0.06/kWhCommercial $0.06/kWh

Industrial $0.05/kWhIndustrial $0.05/kWh

Real-time pricing vs. DemandReal-time pricing vs. Demand

You can be billed either on a standard You can be billed either on a standard Demand type arrangement or,Demand type arrangement or,

Pay the real-time demand costPay the real-time demand cost

Real-time costReal-time cost

Supply and demand set the cost of power.Supply and demand set the cost of power.

The typical cost of $0.06/kWh can The typical cost of $0.06/kWh can skyrocket to $4-5/kWh for short periodsskyrocket to $4-5/kWh for short periods

$1/kWh for hours$1/kWh for hours

Energy rebate programsEnergy rebate programs

For larger customers that are willing to For larger customers that are willing to shed an agreed upon number of kWh shed an agreed upon number of kWh during peak times, if requested by Cinergy during peak times, if requested by Cinergy to do so, will get a credit for energy they to do so, will get a credit for energy they DON’T USE.DON’T USE.

DemandDemand

Demand chargesDemand charges

Demand charges 2Demand charges 2

Rachet – min billRachet – min bill

Summer periodSummer period

Look at what Look at what happened to happened to

California last yearCalifornia last year

Demand kWhDemand kWh

Power factorPower factor

Yearly billing infoYearly billing info

Pump application w/o VFDPump application w/o VFD

Without a VFD, a pump usually runs at Without a VFD, a pump usually runs at 100% speed100% speed

Flow is controlled with a control valveFlow is controlled with a control valve

A flow controller reads the flow rate from a A flow controller reads the flow rate from a flow meter and compares it against the flow meter and compares it against the setpointsetpoint

Runs at 100%Runs at 100%

The pump motor is running full speedThe pump motor is running full speed

Lots of wasted electricity $$$$Lots of wasted electricity $$$$

Assumptions – Assume __Assumptions – Assume __

That the motor in a non-VFD pumping That the motor in a non-VFD pumping application is using 75% of the nameplate application is using 75% of the nameplate powerpower

That Demand charges are not applicableThat Demand charges are not applicable

Power factor is not an issuePower factor is not an issue

All cost will be Energy aloneAll cost will be Energy alone

Motor efficiency =92%Motor efficiency =92%

Motor efficiencyMotor efficiency

5 HP example – non VFD5 HP example – non VFD

5 HP x 746 W/HP = 3730 W5 HP x 746 W/HP = 3730 W

3730W / 0.92 (eff) = 4054 W3730W / 0.92 (eff) = 4054 W

4054 W x 0.75 = 3040 W4054 W x 0.75 = 3040 W

3.040 kW * 8760 hrs = 26630 kWh3.040 kW * 8760 hrs = 26630 kWh

26630 kWh * $0.06/kWh = $159726630 kWh * $0.06/kWh = $1597

$1597$1597

Almost $1600/year in energy cost for 7 x Almost $1600/year in energy cost for 7 x 24 operation24 operation

What is we used a low eff motor?What is we used a low eff motor?

Let the eff = 83%, thenLet the eff = 83%, then

3730 W / 0.83 = 4493 W3730 W / 0.83 = 4493 W

4493 W x 0.75 = 3370 W4493 W x 0.75 = 3370 W

3.37 kW x 8760 hrs = 29,525 kWh3.37 kW x 8760 hrs = 29,525 kWh

29525 kWh x $0.06 = $1771/year29525 kWh x $0.06 = $1771/year

Diff in cost is $174/yearDiff in cost is $174/year

5 HP eff motor5 HP eff motor

Premium Efficiency Motor, 5 horsepower, Premium Efficiency Motor, 5 horsepower, 1755 RPM, 230/460 volts1755 RPM, 230/460 volts

  $448.25$448.25

5 HP std motor5 HP std motor

General Electric Definite Purpose Motor, General Electric Definite Purpose Motor, Rigid Base, Fan-Cooled, 3-Phase, Totally Rigid Base, Fan-Cooled, 3-Phase, Totally Enclosed, C-Face, 5 horsepowerEnclosed, C-Face, 5 horsepower

  $381.25$381.25

Difference in cost between Std & Hi Difference in cost between Std & Hi EffEff

$67$67

Pump Example with VFDPump Example with VFD

Don’t need a control valve = -$1000Don’t need a control valve = -$1000

Need a VFD = +$500Need a VFD = +$500

Need a high eff, inverter rated motor = +Need a high eff, inverter rated motor = +$150$150

Less maintenanceLess maintenance

Control valves require more maintanenceControl valves require more maintanence

Hard to tell without added hardware how Hard to tell without added hardware how many strokes the valve has mademany strokes the valve has made

Seals, etcSeals, etc

Less maintenance 2Less maintenance 2

VFDs provide diagnostics when problems VFDs provide diagnostics when problems occuroccur

Energy costEnergy cost

Assume that if total usage is averaged that Assume that if total usage is averaged that motor uses 33%motor uses 33%

Fan basicsFan basics

Affinity lawAffinity law When the impeller diameter of a centrifugal pump is When the impeller diameter of a centrifugal pump is

held constant the effect of changing the speed (RPM) held constant the effect of changing the speed (RPM) of the pump is in accordance with the following: of the pump is in accordance with the following:

Capacity: Q1/Q2 = N1/N2Capacity: Q1/Q2 = N1/N2 Head: H1/H2 = (N1/N2)2Head: H1/H2 = (N1/N2)2 BHP: BHP1/BHP2 = (N1/N2)3BHP: BHP1/BHP2 = (N1/N2)3 Q = Capacity, GPM Q = Capacity, GPM H = Head, Feet H = Head, Feet BHP = Brake Horsepower BHP = Brake Horsepower N = Pump Speed,RPM N = Pump Speed,RPM

UpshotUpshot

Torque increases as a square of speedTorque increases as a square of speed

HP increases as the cubeHP increases as the cube

Or look at it the other wayOr look at it the other way

If you reduce speed by 10% - new speed If you reduce speed by 10% - new speed = 0.9 of old speed= 0.9 of old speed

Torque = square (0.9) = ___Torque = square (0.9) = ___

HP = cube (0.9) = ___HP = cube (0.9) = ___

Centrifugal pumpsCentrifugal pumps

http://www.pricepump.com/pumpschool/pshttp://www.pricepump.com/pumpschool/psles.htmlles.html