variable frequency drives (vfds) - maeep - vfd 12.12.13_0.pdf · variable frequency drives (vfds)...
TRANSCRIPT
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
Variable Frequency Drives (VFDs)
• 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
*John Hopkins Univ. AICGS Policy Report
Variable Frequency Drives (VFDs)
• 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
*John Hopkins Univ. AICGS Policy Report
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
Cubed Exponential Load – Affinity Laws:power is proportional to the change in speed cubed
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)
Cubed Exponential Load – Affinity Laws:power is proportional to the change in speed cubed
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]
Ryan R. Hoger, LEED [email protected]
Ryan R. Hoger, LEED [email protected]
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…