Variable Frequency Drives (VFDs)

Size: px

Start display at page:

Download "Variable Frequency Drives (VFDs)"

Claude Lane
7 years ago
Views:

1 Variable Frequency Drives (VFDs) Ryan R. Hoger, LEED AP Commercial HVAC Energy Consumption 1

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 &

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 2

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 = $420 Running at 50% speed = $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 3

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 4

5 Cubed Exponential Load Affinity Laws: power is proportional to the change in speed cubed 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 Power % Speed Energy Savings 3/4 motor speed = 42% power 58% power saved 1/2 motor speed = 12.5% power 87.5% power saved Money Saved Motor without VFD At 100% speed = $1,000 Cost Same motor with new VFD At 75% speed = $420 Cost $580 Savings At 50% speed = $125 Cost $875 Savings 5

6 Cubed Exponential Load Affinity Laws: power is proportional to the change in speed cubed For centrifugal pumps and fans - power requirements change sharply with small speed changes Torque (mechanical force) Power (energy consumed) Power % speed = 42% power ( ) 50% speed = 12.5% power ( ) (theoretical power reduction) Reduced speed = HUGE $ Savings % Speed Typical HVAC Load Requirements % Operating Time % Flow or Volume Data Supplied by the U/K Dept of Trade & Industry

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! 7

Case Study Merchandise Mart 29 VFDs installed on chilled water

three 300 hp Metered measured 1st Case Study Bally s Atlantic

equipment Goals: Improve temp conditions Reduced wind tunnel &

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 1 st cost of bypasses 8

Case Study John Muir Medical Center VFD retro-fit to

operating expenses Correct electrical and mechanical

compressors with cooling demand Show significant ROI Case

chiller compressor plus condenser water supply temp

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 9

10 How Does a VFD Work? 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. Do I need a bypass? 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 10

Electrical Bypass Components VFD Run LED Indicating Light Bypass Run LED Indicating Light Four Position Selector Switch; Bypass/Off/Test/VFD Drive Input Contactor Bypass Contactor Drive Output

11 Electrical Bypass Components VFD Run LED Indicating Light Bypass Run LED Indicating Light Four Position Selector Switch; Bypass/Off/Test/VFD Drive Input Contactor Bypass Contactor Drive Output Contactor Overload Relay Control Transformer With Fusing Customer Terminal Strip Main Fused Disconnect Main Disconnect Handle What accessories do I need? 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. 11

12 What is NEMA? 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 12

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 13

HVAC Energy Savings Fans Pumps Supply and exhaust fan

Chilled and hot water Booster pump Irrigation and fountain

Air compressor Opportunities Cooling Tower Fan Condenser

14 HVAC Energy Savings Fans Pumps Supply and exhaust fan Cooling tower Parking ramp ventilation Boiler FD and ID fan Chilled and hot water Booster pump Irrigation and fountain Swimming pool circulation Machines Refrigeration compressor Air compressor Opportunities Cooling Tower Fan Condenser Water Pump Chiller Compressor Chilled Water Pump Supply Air Fan 14

15 Variable Air Volume (VAV) Air Handler Supply Fan Volume Control Supply Air Fan Space Static M Receiver Controller 15

16 Supply/Return Fan Capacity Control Return Air Fan Supply Air Fan M Receiver Controller 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 VFD Return 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 16

17 Primary Chilled Water Evaporator 1 CC1 CC2 Evaporator 2 Cooling Tower Fans 17

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

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) 18

Variable Speed Pumping For secondary loops,

minimum flow - use flow meter Pay attention to

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 19

Ryan R. Hoger, LEED AP 708.670.6383 ryan.

com Special Thanks to those who allowed me to

20 Ryan R. Hoger, LEED AP Special Thanks to those who allowed me to use their graphics today Ryan R. Hoger, LEED AP

HVAC Applications. VFD considerations for HVAC systems...

HVAC Applications. VFD considerations for HVAC systems... HVAC Applications VFD considerations for HVAC systems... 1 COMMON TERMINOLOGY VFD (VARIABLE FREQUENCY DRIVES) AFC (ADJUSTABLE FREQ. CONTOLLER) ASD (ADJUSTABLE SPEED DRIVES) VSD (VARIABLE SPEED DRIVES)