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Use of Drives to enhance energy efficiency in Green Buildings

Introduction

• Variable Frequency AC Drives (VFD’s) constitute a major chunk of energy efficient devices in use on various electrical equipments.

• They are efficient (>98% eff.), use high speed power switching devices (IGBT’s) and are very compact.

• Usage of the simple expedient of speed variation of motors driving variable torque loads leads to significant energy savings.

• By virtue of being equipped with serial communication capability, VFD’s can be easily integrated into building Management Systems (BMS).

• The net result is lower initial costs and reduced operation expenses.

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Typical Energy Usage in a Commercial Building in Tropical climates

Other Equipment

15%

AHU/FCU24%

DHW12%

Lighting10%

Central Plant39%

VFD’s can help reduce energy costs and improve comfort levels for occupants.

Dedicated VFD’s for HVAC applications can be

integrated into the BMS and help to reduce intital cost in many cases.

In all these applications some form of flow setting or control device is used.

T

AHU

CHILLEDWATER

SECONDARY CHILLED

WATER PUMPS

COOLINGTOWERS

AHU

CONDENSER WATER 35ºC

RETURN CONDENSER WATER 30ºC

15ºC

15ºC

15ºC

MA

IN R

ISE

RR

ET

UR

N 9

- 1

2 ºC

MA

IN R

ISE

R F

EE

D 6

ºC

T

T

T

T

T

T

F

FCU

F

F

F

F

F

F

F

CONDENSERWATER PUMPS

F

Condenser water makeup

AHU

15ºC

T

T

F

FFF

CO

ND

EN

SE

R

EV

AP

OR

AT

OR

PRIMARY CHILLEDWATER PUMPS

CH

ILLE

R 3

CH

ILLE

R 2

CH

ILLE

R 1

RETURNAIR FAN

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Why control flow?

• HVAC Systems are designed for “worst case” conditions.

• This implies that in most cases, excess capacity is available.

• Flow control matches capacity with the actual demand.

• This means increased comfort level for occupants & reduction in energy consumed.

Methods of Flow Control

• Air flow

– Outlet dampers

– Inlet guide vanes

– Variable pitch fan

– Eddy current coupling

– Variable Frequency Drive (VFD)

• Fluid flow Centrifugal Pumps

– Bypass valve (three way)

– Throttling valve (two way)

– Variable Frequency Drive (VFD)

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Air flow control with VFDs

• The graph of power consumed with various control methods is shown alongside.

• At 80% flow rate (typical for many installations for much of the time):

– Damper control – absorbs 93% motor power

– IGV control – absorbs 70% of motor power

– Eddy current coupling control –absorbs 67% of motor power

– VSD control – absorbs 51% of motor power

Liquid flow control with VFDs

• The graphs alongside show that VFDs are a more efficient means of controlling flow, compared to valves

Control with 2-way valves Control with VFD

Control with 3-way valves results in same power at all flows – flow is just diverted

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Use of VFDs- a superior method of flow control ….

• VFD’s provide an optimum method of controlling the air conditioned space and save energy costs for the end user

• The slides to follow show how dedicated VFD’s can be applied to HVAC systems.

• With specific HVAC functions, these VFD’s reduce other system components resulting in a lower initial cost for the system

Salient features of dedicated Drives for HVAC Application

• IP20 and IP54 versions.

• IP20 version for mounting in IP42/IP54 switchboards/panels.

• IP54 version for mounting directly in plant rooms or on/in AHU’s.

– Reduced installation cost due to proximity with AHU/Pump.

– IP54 enclosure ensures long term reliability

�

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Integral filters

• HVAC Drives have Integral RFI and harmonic filters.

• They reduce the risk of interference with other equipments and do not require installation time.

• Inbuilt DC Reactor ensures low harmonic content and high PF.

• PFC capacitors are therefore unnecessary.

�Programmable “skip”frequencies avoids vibrations

� Automatic Switching Frequency Modulation (ASFM) ensures quiet motor operation

� Reliable flying start under all conditions

� Automatic Energy Optimisation simplifies commissioning and gives additional power saving.

Other dedicated features

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By incorporating these functions, without a BMS, the VFD can fulfil many control system requirements without the need for other components

� Fan belt breakage monitoring

� No need for differential pressure switch and I/O point

� Gives output to BMS

Reduced system component costs

� Integrated 2-zone (2 setpoint/2 feedback) PI(D) controller (e.g. VAV static duct pressure and high pressure limit protection)

� Stand alone controller

� Sensor connected directly to and powered from VFD

� Set point and feedback in engineering units (e.g. Pa, °C, Bar)

� User friendly Keypad and display with

� Hand-Off-Auto feature.

� Onboard display of parameters- Motor Current, kW, KWH, Pressure …..

Easy integration with BMS

• VFD’s can be integrated into a BMS, using a single serial communications cable.

• Various HVAC protocols including Lonworks, Metasys N2, FLN, Modbus, BACnet enable a vast array of devices to be controlled/monitored.

• Minimises hardwired I/O points and associated engineering and commissioning costs.

• Provides increased diagnostic info.

• All drive Inputs/Outputs and performance parameters can be monitored.

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Integrated SolutionsApplication Examples

Delivering a system with the lowest initial costs and providing the greatest operational savings

Minimize Initial Costs

• No external starter

• No external overloads

• No Power factor correction

• Only 3 motor cables

• Size cables & fuses to meet FLC

• External metering of motor performance parameters not required.

• Reduced I/O & field hardware to BMS.

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Value Added Engineering – Built in as standardHVAC Application specific features.

• Built-in fan belt breakage monitor– eliminates DP switch, DI point & cable

• Built-in filter dirty monitor –eliminates DP switch, DI point & cable on CAV or connect to VFD on VAV, save DI on BMS

• Built-in 2 zone PID control – e.g.:Static pressure control on VAV or DP control of SCHW pumps, reduces I/O on BMS

• H/O/A selection – eliminates rotary switch on panel & save 2 x DI on BMS

VAV boxes

Cooling Coil

Heating Coil

Flow

Flow

P

Filter

Supply Fan

Return Fan

D1

D2

D3

Typical Large HVAC System

Return Fan

Supply Fan

Secondary Hot/Chilled

Water Pumps

Primary Hot/Chilled

Water Pumps

Cooling Tower Fans

Condenser

Water Pump

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System cost comparisonSystem cost comparison

Conventional System:

• System not using VFD for flow control:

• Wardrobe type panel with 3-phase fused supply, motor starter with overload, run, stop & trip lamps, Hand-Off-Auto switch, Ammeter

New System:

• System using dedicated HVAC VFD for flow control:

• IP54 version complete with integral RFI and harmonic filters, 3-phase fused supply

• BMS Integtration For Both The Systems:

• I/O point is fully wired and commissioned.

Application Examples

Cleanroom Supply Fans

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CAV Supply Fan – Filter Control

• CAV filter systems move a constant volume of air through a filter and into the controlled space.

• The VFD monitors the static pressure in the ductwork after the filter.

• The filter’s resistance increases as it clogs.

• The VFD automatically increases the supply fan’s speed to maintain a fixed pressure to ensure precise air flow.

• Clean room applications

• Hospitals

• Laboratories

• Semiconductor/Electronics Industry

• Pharmaceutical Industry

• Sensor Placement

– Pressure sensor downstream of pre-filters and micro filters

– Fan speed automatically changes to maintain design duct pressure

– Automatically compensates for filter resistance maintaining clean room air flow rate as filters become dirty

CAV Supply Fan – Filter Control

Open Space

Filter

P

Pre-filter

HEPA Filters

Micro Filter

Clean Room

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CAV Supply Fan – Filter Control

• Advantages:

– Large energy savings – the fan operates at full speed (= full power) when the filter is clogged.

– Elimination of dampers

– Reduced noise

– Increases filter life (reduced flow when not necessary)

– Reduced I/Os for BMS integration thru’ serial communication.

Clean room System – Integrated Solution

•Operate from mains supply

•Operate from mains supply

•Maintains unity power factor

•Zero inrush current/motor rated

•4 Line Alpha numeric LCP

•HVAC control functionality with

8 x DI,3 x AI, 2 x AO, 2 x DO

•KWH & hours run monitor

•H/O/A keypad selection

•Variable flow/pressure control

FEATURE VALUE

•No external starter/overloads

•Only 3 motor cables not 6

•No PFC equipment needed

•Lower cable & fuse ratings

•No instrumentation needed

•Reduced I/O and control wiring & less pre-commissioning

•No CT & transducer required

•Eliminate rotary switch

•Eliminate over capacity & easier balancing

Clean Room Standard BMS Control - Fixed Speed

No. I/O Desciption AI/AO DI/DO BMS / DDC VFD1 Damper Control 3 x AO 3 x AO2 Filter Dirty DP 1 x DI3 Chilled Water Valve 1 x AO 1 x AO4 Pressure control N/A N/A AI13

5 Fan Start/Stop 1 x DO BO5

6 Fan Airflow DP 1 x DI ADF48

7 Space Temp 1 x AI 1 x AI8 H/O/A Status 1 x DI BI96

9 Run/Trip status 2 x DI BI5 / BI10

10 Motor Current / kWHr 1 x AI AI21Sub Total 6 6 5Total 12 5

Integrated Solution

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Hi Efficiency & Supply Friendly HVAC Drive systems

High Efficiency HVAC Drive System

• The use of a HVAC VFD with PM Motor and Fan has resulted in a more efficient drive system.

• HVAC VFD controller has a specially developed algorithm for use with a PM Motor from a preferred supplier.

• The resultant efficiency is higher than other combinations using a high efficiency (IE2 Class) Motor and drive.

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System efficiency matters, not component efficiency!

Example System Efficiencies ø450 Centrifugal Fans*

IE2 Motor + VSD + direct driven fan

ηηηηDrive = 83%

ηηηηFan = 75%

ηηηηSystem = 63%

EC motor + electronics + fan

ηηηηDrive = 89%

ηηηηFan = 68%

ηηηηSystem = 60%

PM motor + VSD + direct driven fan

ηηηηDrive = 89%

ηηηηFan = 75%

ηηηηSystem = 66%

*data based on fan catalogue data and measured drive (motor + control electronic) efficiencies at comparable loads

� High component efficiency does not ensure high system efficiency

� On centrifugal fans, the size of the hub is important for the fan efficiency. Big hubs create

turbulence and reduce flow efficiency.

The Low Harmonic Drive (LHD)

• An active mitigation solution

• The first of its kind

• A new trendsetter

• A tuned solution

• An excellent alternative to AFE

The Low Harmonic Drive is

a solution to:

• Meeting IEEE519 requirements

• Meeting all EN61000-3-x product standards

• Generator powered (or backup) installation

• Installation of HP-drive in grids with limited excessive power capacity

(small transformer)

• HP-drives mostly running at partial load

The Low harmonic Drive is:

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IEEE519 compliance

The VLT® Low Harmonic Drive meets

toughest harmonic standards and

recommendations. Although no product

standard exist for products <75 A,

the VLT® Low Harmonic Drive is designed

to meet:

• IEEE519 for Isc/Il >20

• EN61000-3-4

• EN61000-3-12

Thus:

• THiD guarantee of <5% at max. 2% unbalance

• Major reduction of harmonics <25th

• Meeting individual levels of IEEE

• Lowering THiD will reduce the THvD significantly

IEEE519 compliance

0

2,5

5

7,5

10

12,5

15

17,5

20

22,5

2 6 10 14 18 22 26 30 34 38 42 46

FC302P200T4E21L2

FC302P200T4E21H2

IEEE519 Isc/IL 20<50

IEEE519 Isc/IL <20

Thank You!