variable frequency drives (vfds) - maeep - vfd 12.12.13_0.pdf · variable frequency drives (vfds)...

12/6/2013

1

Variable Frequency Drives (VFDs)

Ryan R. Hoger, LEED APRyan R. Hoger, LEED AP

Commercial HVAC Energy Consumption

12/6/2013

2

Opportunities

• On average building fan systems in the US are oversized by 60%*

• Over 60% of industrial electricity demand is for driving electric motors

– A large proportion of this is for driving fans & pumps

*John Hopkins Univ. AICGS Policy Report

Motor Replacement Opportunities

• High efficiency motors not utilized or oversized– Do economic analysis and remove/replace with high

efficiency motors where economically– Upon burnout, upgrade to high efficiency– Do a motor load test and right-size the motor– Due to increasing manufacturing standards, all motors

sold will be NEMA-premium Efficiency

12/6/2013

3


• Retro-fit to fans and pumps • Varies the power input to motor• On average building fan systems in the US

are oversized by 60%*• If a motor running at 100% speed costs

$1,000/month, what about:– Running at 75% speed = – Running at 50% speed =

$420$125



• Soft start means less wear & tear on couplings, belts, and motors

• Many utilities provide additional incentives to install VFDs

• Paybacks less than 1 year for HVAC fans/pumps and 2 years for chiller compressors


12/6/2013

4

What Is A Variable Frequency Drive?

• A standard electric motor is essentially a fixed speed machine

• A Variable Frequency Drive provides the ability to fully control the speed of a motor from zero to maximum

• It also provides the ability to control the torque produced by a motor

Advantages

• Better Control– You drive the motor only as fast as you need to in

order to get the right air flow, water flow, space temperature and more

• Energy Savings– Just as you vary the amount of gas you put into your

car’s engine, the VFD varies the amount of power that it puts into the motor

– 50% flow for 13% power

• Maintenance Savings– Soft start/stop means less wear on couplings, belts

and motors– Controls tell staff when system needs attention

12/6/2013

5

If the speed of a device (pump or fan) is increased 10%:

•Volume flow (GPM or CFM) increases 10%

•Pressure (head or static) increases 21%

•Power increases 33 %

If we want to increase the volume flow GPM (or CFM) of an existing system 10%we have to increase the power supply 33%

Cubed Exponential Load – Affinity Laws:power is proportional to the change in speed cubed

Energy Savings3/4 motor speed = 42% power

58% power saved1/2 motor speed = 12.5% power

87.5% power saved

0 25 50 75 125 150

25

50

75

100

100

125

150

% Speed

Pow

er


Money SavedMotor without VFD

At 100% speed = $1,000 CostSame motor with new VFDAt 75% speed = $420 Cost

$580 SavingsAt 50% speed = $125 Cost

$875 Savings

12/6/2013

6

0 25 50 75 125 150

25

50

75

100

100

125

150

% Speed

For centrifugal pumps and fans - power requirements change sharply with small speed changes

Torque (mechanical force)Power (energy consumed)

50% speed = 12.5% power (0.503)(theoretical power reduction)

Pow

er75% speed = 42% power (0.753)


Reduced speed = HUGE $ Savings

Typical HVAC Load Requirements

% O

pera

ting

Tim

e

% Flow or Volume0

2

4

6

8

10

12

10050 75255

Data Supplied by the U/K Dept of Trade & Industry.

12/6/2013

7

Energy Conservation

By controlling the fan or pump speed to meet demand - sufficient flow - an enormous amount of power can be saved.

On continuously running plant -Over a 50% reduction has been achieved

Additional Benefits

• Improved control• Reduced noise & vibration• Simpler installation &

commissioning• Lower maintenance costs• Fewer complaints !

12/6/2013

8

Case Study – Merchandise Mart

• 29 VFDs installed on chilled water pumps and fans

– Incl. three 300 hp• Metered measured 1st

Case Study – Bally’s Atlantic City

• 102 VFDs installed• No adverse affects on

existing fan equipment• Goals:

– Improve temp conditions– Reduced “wind tunnel” &

building pressurization issues

• Annual savings of $175,000

– 2-year payback– Payback longer due to extra

1st cost of bypasses

12/6/2013

9

Case Study – John Muir Medical Center

• VFD retro-fit to compressors on Carrier and York chillers

• Goals:– Reduce operating

expenses– Correct electrical and

mechanical problems associated with chillers

– Match speed of compressors with cooling demand

– Show significant ROI

Case Study – Applied Materials Research Facility

• VFD retro-fit to chiller compressor plus condenser water supply temp optimization

• Goal was to optimize chiller energy performance which is best at 25-75% load

12/6/2013

10

• Converts AC power to DC power – Now we can do something with it.

• Converts DC back to AC – When it converts back, it switches power on and off to create the AC wave and to vary the frequency. Vary the frequency and you vary the speed.

How Does a VFD Work?

• NO…..unless it is a critical application…..life or death…..think hospital….

• It typically quadruples the price…..it would actually be cheaper to buy a spare VFD

• VFD technology has become extremely reliable…..don’t let a bad experience from 20 years ago make you think the drive will fail

• Bypass types– Electronic – Switch is “soft”, made with relays and

software– True Electrical – Hard, physical switch makes the

change

Do I need a bypass?

12/6/2013

11

Electrical Bypass Components

•Drive Output Contactor

•Overload Relay

•Control Transformer With Fusing

•Customer Terminal Strip

•Main Fused Disconnect

•“Bypass Run” LED Indicating Light

•Main Disconnect Handle

•Four Position Selector Switch; “Bypass/Off/Test/VFD”

•Drive Input Contactor

•Bypass Contactor

•“VFD Run” LED Indicating Light

• Built-in filters to prevent harmonic interference

• Built-in AC choke protection– Ensures harmonic currents never make it

back to power grid to create problems with other equipment and a low power factor that costs customers money

• Industrial-quality RFI filters, immunizing drive from the effects of interference

• Communication capabilities• BACnet®, LONWORKS®, N2, Modbus, etc.

What accessories do I need?

12/6/2013

12

• National Electrical Manufacturers Association– NEMA sets standards for VFD enclosures and the

protection they provide– It’s typical to see NEMA 1, 12, 3R and 4X.

• What do they mean?– NEMA 1: Protection against touching live parts and

falling dirt– NEMA 12: NEMA 1 protection plus against circulating

dust, lint, fibers, and flyings, and against dripping and light splashing of liquids

What is NEMA?

12/6/2013

13

Typical Pre-Engineered Apps

• Standard– Waiting for speed comand signal from

external source (i.e., BAS controller)– Accepts 4-20mA, 2-10vdc, etc.

• Local/Remote Control• Multi-step Speed Control• PID Control• Multi-purpose Control• Pump and Fan Control w/Auto

Changeover

Applications

Field Bus communications supported in all applications

12/6/2013

14

Fans

• Supply and exhaust fan• Cooling tower• Parking ramp ventilation• Boiler FD and ID fan

Machines• Refrigeration compressor• Air compressor

Pumps

• Chilled and hot water• Booster pump• Irrigation and fountain• Swimming pool circulation

HVAC Energy Savings

Opportunities

Cooling Tower Fan

Condenser Water Pump

Chiller Compressor

Chilled Water Pump

Supply Air Fan

12/6/2013

15

Variable Air Volume (VAV) Air Handler

Supply Air Fan

Space Static

Receiver

Controller

M

Supply Fan Volume Control

12/6/2013

16

Supply Air Fan

Return Air Fan

Receiver

Controller

M

Supply/Return Fan Capacity Control

Variable Air Volume Control Methods

Supply Fan• Static pressure control - 2/3 distance down main

duct in a straight in the main duct• Static high limit to prevent over pressurizing

system• Use DDC controller or PID controller application

in VFDReturn Fan• Common method is from a signal from the

supply fan VFD – doesn’t account for fan size difference or other exhaust systems

• Best way – measure supply cfm, return cfm and outside air cfm – expensive, most accurate, and best control to provide

12/6/2013

17

Primary Chilled Water

CC1

CC2

Evaporator 1

Evaporator 2

Cooling Tower Fans

12/6/2013

18

Cooling Tower VFD Benefits

• Drive the condenser water as low as possible for maximum chiller efficiency

• Reduced wear and tear on the electrical equipment

• Improved control (straight line) – stable chiller operation

• Energy savings

Variable Speed Pumping

• Add VFDs to pumps• Hot or chilled water systems• Control to differential pressure

at “farthest coil”• Requires 2-way valves at each

zone– Need bypass pipe/valve at end of

line or one far zone with 3-way valve

– Consider Pressure Independent Control Valves (PICV)

12/6/2013

19

Variable Speed Pumping

• For secondary loops, maintain pressure in system by having a min freq greater then zero -look at the pump curve

• For primary loops thru chillers and boilers

– Maintain minimum flow - use flow meter

– Pay attention to maximum rate of change rules

Energy Savings Estimation Tools

12/6/2013

20

Ryan R. Hoger, LEED [email protected]




Special Thanks to those who allowed me to use their graphics today…

Special Thanks to those who allowed me to use their graphics today…

variable frequency drives (vfds) - maeep - vfd 12.12.13_0.pdf · variable frequency drives (vfds)...

Documents