Variable Frequency Drives for HVAC...VFD Control for Multiple Fan Applications • One VFD controls several fans • Typical operating frequency 80HZ – 90HZ • Must have individual

Variable Frequency Drives for HVAC

Presented by Ron Heymann & Rich Harper

Why Use Adjustable Speed Drives?

$

Reduced Energy Consumption

Improved Process Control / Efficiency

Improved noise issues

Increased Product Quality

Expanded Automation / Integration

Broader Equipment Flexibility / Versatility

Increased Reliability / Availability

Reduced Maintenance

Reduced wear & tear on the motors

Provide precise control

© ABB Group

HVAC Variable Torque Applications

There are three basic types of mechanical loads that are encountered by any AC/DC drive system:

• Constant Torque (CT) e.g. conveyors

• Variable Torque (VT) e.g. centrifugal fans/pumps

• Constant Horsepower (CH) e.g. machine tools

In HVAC systems Variable Torque applications are dominant.

Proven energy savings resulting from varying the speed of the driven motors to optimize the system performance.

Definition of Variable Torque

© ABB Group

Variable Torque Applications

Return Fan

Supply Fan

Primary Condenser

Water Pump

Cooling Tower Fans Secondary Hot/Chilled

Water Pumps

Exhaust Fans

Primary Hot/Chilled

Water Pumps

(*Chiller VFDs)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60

Frequency (Hz)

% F

low

, %

To

rq

ue

, %

Po

we

r

Variable Torque

Torque requirement

varies

as the square of speed

Power requirement

varies as the cube of

speed

Affinity Laws (Energy Savings)

Flow varies

linearly

with speed

Typical VAV System Duty Cycle

Fan Power Consumption

0%

20%

40%

60%

80%

100%

120%

140%

0% 20% 40% 60% 80% 100%

% Rated CFM (rpm)

Po

we

r C

on

su

mp

tio

n

Pitch

Control

Variable Frequency Drive

Variable Inlet Vane

Outlet Damper

Constant Volume

© ABB Group

0

10

20

30

40

50

60

0 500 1,000 1,500 2,000

Pre

ssu

re (

ft o

f w

ate

r)

Flow (GPM)

0

10

20

30

40

50

60

0 500 1,000 1,500 2,000

Pre

ssu

re (

ft o

f w

ate

r)

Flow (GPM)

HVAC Variable Torque Applications for VFDs • How do VFDs save energy?

• Pump and Control Curves

Pump Curve

Control Curve

Operating Point

© ABB Group

0

10

20

30

40

50

60

0 500 1,000 1,500 2,000

Pre

ssu

re (

ft o

f w

ate

r)

Flow (GPM)


• Power

Flow

Pre

ssu

re

Power α Pressure x Flow

© ABB Group

0

10

20

30

40

50

60

0 500 1,000 1,500 2,000

Pre

ssu

re (

ft o

f w

ate

r)

Flow (GPM)


• Traditional Method: Adding a Flow Restriction

Wasted Energy

© ABB Group


• Efficient Method: Using a VFD to reduce flow and pump/fan pressure

P

© ABB Group

0

10

20

30

40

50

60

0 500 1,000 1,500 2,000

Pre

ssu

re (

ft o

f w

ate

r)

Flow (GPM)

HVAC Variable Torque Applications for VFDs Introduction • How do VFDs save energy?

• The system can follow the Control Curve

VFD Control for Unique Applications

• Optimal operation of water-filtration pumps • Exhaust Fan control based on building contaminants • One VFD controls several motors

VFD on Swimming Pool Filtration System

• VFDs are an efficient option to use on smaller systems such as swimming pools

• Nearly 40% of the total energy used by indoor swimming pools is consumed by the filtration and circulation pumps

Source: http://www.vfds.org/vfd-on-swimming-pool-filtration-system-110023.html

http://www.vfds.org/vfd-on-swimming-pool-filtration-system-110023.html














VFDs at South Windsor, CT Public Pools

A calculation of energy savings, utilizing drives to run the filter pumps serving three pools in South Windsor, CT.

Tag HP KWH Full Speed KWH W/VFD Savings (KWH) Savings ($)

Main Pump 30 66,825 44,726 22,099 2,431

Main Pump 30 66,825 44,726 22,099 2,431

Training Pool 20 38,519 25,829 12,690 1,396

Lap Pool 10 26,390 17,684 8,706 958

Total 198,559 132,965 65,594 $7,215

South Windsor, CT Pool Filter Pumps

7-Day Power Consumption

ABB VFDs Succeed Where Others Methods Fail South Windsor Public Pools Case Study

“Since the drives were installed, the pool recognized not only a dramatic reduction in energy costs, but also far less noise from the pumps. “Now we can actually stand in the pump house and hear each other talk, whereas before, we were never able to do that,” says Friend. The drives also enable the pool engineers to eliminate hard stops and starts. When the strainers need to be cleaned or other maintenance needs to be done, the engineers can ramp the motors down, shut them off, perform the necessary tasks and then ramp the speed back up - all without the high-demand and across-the-line surges from hard stops and starts. The ABB VFDs also serve to protect the pumps and the motors from over-current and the under-current, shutting down the system if problems occur, instead of allowing the motors to spin themselves into the ground.” ~Tim Friend, Town of South Windsor Department of Public Works

High Plume Fans – the Problem THE LAB EXHAUST AIR IS SELDOM

CONTAMINATED TO REQUIRE THIS LEVEL

OF DILUTION AND ENERGY USESAGE DILUTE

CONTAMINATED

LAB EXHAUST AT

HIGH EXIT

VELOCITIES OF

3,000 FPM OR

MORE

HIGH PLUME FANS

USE EXCESSIVE

AMOUNTS OF

ENERGY,

OPERATING AT

CONSTANT EXIT

VELOCITIES

CONTINUOSLY

1

2 3

4

Variable Frequency Drives– the Solution

How it Works

• Continuously sample each exhaust riser

• Use of calibrated photoionization detector (PID)

to sense contaminants.

• Fan velocity setback only when below

contaminant action threshold: High dilution rate 3000-4000+ ft/min typical Immediately reduce to 3,000 ft/min with

monitoring Optimize dilution rate: (e.g. 1500 ft/min or less)

through dispersion analysis & monitoring

• When contaminants are detected: Setback is disabled Sensor protection mechanism enabled All sampled locations must report clear before

enabling setback.

• Various override functions (e.g. Occ Sensor)

• Remote performance monitoring.

High Plume Fan Energy Savings • Lab exhaust air is often relatively clean, presenting an opportunity to safely

reduce fan dilution levels (bypass air reduction) to lower energy use

• Many compounds used in labs do not require the high dilution levels associated with typical fan settings (3000+ fpm)

• Current trend to use computational chemistry in labs substantially reduces actual fume hood and chemical use. Reducing demand for fan dilution.

• Internal system dilution from general exhaust can significantly dilute fume hood contaminant levels.

• Current trends in lab ECM’s to lower lab ACH increases the opportunity to lower exhaust fan total CFM.

Opportunity for Large Energy Savings Confidential and Proprietary Information

© ABB Group

Exhaust Sytems

• Exhaust Fans

• Dual, 50% fans with Isolation dampers

• TEFs, GEFs

• N+1 or Lead/Lag progression

• Fume Hood systems

• VAV control to maintain duct pressures or CV Exhaust Velocities.

• Garage Exhaust systems

• CO monitor and control

• Bi-directional Exhaust fans

• Reversing the Supply fans

• Tunnel smoke control

Other Exhaust Fan Applications

VFD Control for Multiple Fan Applications • One VFD controls several fans • Typical operating frequency 80HZ – 90HZ • Must have individual motor protection (overloads) • Across the line bypass will operate fans at reduced flow • Consider a redundant VFD for critical applications

© ABB Group

• Individual Motor Protection is required for a single VFD serving multiple motors.

• Size motor protection (MMPs) for the actual motor FLA.

• Replacement on failure service strategy assumes system can be “down” for 1-2 days.

• Total motor lead length is used for output filtering (dV/dt) if needed.

• Retrofitting opportunity Single fan to Fan Arrays

VAV Fan System: Fan Arrays

Caution with Over-speed applications.

Motor selection and VFD sizing needs to take into account the reduced Torque of the motor when operating fans at speeds

higher than the motor’s rated speed.

Single drive with multiple motors

© ABB Group

• Bypass operation assumes system can Safely operate with the outcome flow and/or pressures created by the motor’s rated RPM at 60 Hz.

• Bypass has a 15% - 25% add cost premium over the drive only configuration.

• Individual motor protection is required for a VFD serving multiple motors.


• Total motor lead length is used for output filtering (dV/dt)





Drive w/ Bypass & multiple motors

© ABB Group

• Bypass operation assumes system can Safely operate with the outcome flow and/or pressures created by the motor’s rated RPM at 60 Hz.

• Bypass has a 15% - 25% add cost premium over the drive only configuration.

• Individual motor protection is required for a VFD serving multiple motors.

• MMP panel provided by AHU manufacturer







Drive w/ Bypass & multiple motors

© ABB Group

• Individual Motor Protection is required for a single VFD serving multiple motors.


• Redundant drives vs. Bypass

• Up-time and Reliability

• Variable speed required e.g. 0-60 Hz, 72Hz vs. 60 Hz (Line)

• Cost premium over Bypass configuration.






Redundant drives & multiple motors

© ABB Group

• VFD provides protections to individual motors.

• Separation of Input and output power & control wires required.

• May require Input Line reactors to meet specified Impedance

• Harmonics- Individual reactor at each drive or one reactor sized for all drives and located at the Input power connection.

• Input Line reactors needed for Input Amps to equal Output Amps

• Individual isolation disconnect.





Drive per motor (N+1)

VFD Control Cooling Towers • Cooling Tower Fan • Condenser Water Pump • Integrated control for spray pumps, heaters, and level • Reverse operation for de-icing

© ABB Group

Condenser Water Systems

Cooling Tower Fan

T

• Generally controlled by the return water/ sump temperature

• Saves electrical energy

• Reduces mechanical stress

• Reduces the need for make-up water

• Reversing for de-icing the tower in Winter

• Pre-heat protects motor insulation

© ABB Group

Condenser Water Systems Condenser Water Pumps

• If a throttling valve was used to adjust the flow, the VFD can save additional energy.

• The pump speed can be controlled to maintain a constant flow as the strainer loads.

• The drive can also indicate when the strainer needs to be cleaned.

• Reducing the rate of condenser water flow can…

• Keep the spray nozzles from covering the fill (nozzles need min. pressures)

• Cause problems for the chiller

F

VFD Retrofit Applications

VFD Retrofits: Water/Wastewater Applications

Before Retrofit Complete Retrofit Transformation After Retrofit

VFD Retrofits: HVAC Applications

Before Retrofit

Rooftop Air-handling Unit

After Retrofit

© ABB Group

Questions?

Any Questions?

Rich Harper President & Sales Engineer

Flow Tech, Inc.

10 Bidwell Road, South Windsor, CT 06074 Phone: 860.221.0871 Cell: 860.559.9818

Email: [email protected]

Web: www.FlowTechInc.com Twitter: www.Twitter.com/FlowTechInc

LinkedIn: www.linkedin.com/company/flow-tech-inc

mailto:[email protected]

http://www.flowtechinc.com/

http://www.twitter.com/FlowTechInc

http://www.linkedin.com/company/flow-tech-inc





Documents

Variable Frequency Drives for HVAC...VFD Control for Multiple Fan Applications • One VFD controls several fans • Typical operating frequency 80HZ – 90HZ • Must have individual