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Energy Survey Workshop . The first step in energy management Andrew Ibbotson Joe Flanagan. What is an energy survey? . For a site, dept, or process Establishes the energy cost and consumption Is a technical investigation of the energy flows

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the first step in energy management andrew ibbotson joe flanagan

Energy Survey Workshop

The first step in energy management

Andrew Ibbotson

Joe Flanagan

what is an energy survey
What is an energy survey?

For a site, dept, or process

  • Establishes the energy cost and consumption
  • Is a technical investigation of the energy flows
  • Aims to identify cost effective energy savings
  • Examines both the technical and ‘soft’ management issues.
why carry out a survey

Why carry out a survey?

  • Identify savings
  • Establish the viability of an energy management programme
  • Establish a ‘baseline’
the energy management process

Identify where Energy is Used and Develop an Action Plan


Senior Management Commitment

Measure Energy Consumption and Production

Review Performance and Action Plan

Develop Targets

Implement Energy Saving Measures

Produce Reports to Monitor Energy Use Against Output

The Energy Management Process
diy or consultant

DIY or Consultant?


  • Expertise
  • Fresh pair of eyes
  • Should not be afraid to poke into any corner
  • Opinions may carry more weight
  • Job will be completed


  • No cost
  • No learning curve
  • Projects should be viable
choosing a consultant

Choosing a Consultant

  • Salesman or consultant?
  • Ensure he/she is experienced in your process
  • Don’t be afraid to take up references
  • Cost - day rate of fixed price
the survey process
The Survey Process
  • Define the scope
  • Establish energy balances
  • Identify priority areas
  • Identify energy saving projects
    • Low cost (control, housekeeping, awareness)
    • Medium cost (revenue expenditure <1 year payback)
    • High cost (capital expenditure <2-3 year payback)
  • Reporting
how much effort is required
How much effort is required?

Depends upon

  • complexity of the site and scope
  • Level of detail available (esp. sub-meters)
  • Size and energy intensity
  • Rule of thumb
    • Up to €200,000 – 6 mandays
    • Up to €1,000,000 – 10-15 mandays
  • Electricity, gas, oil, solid fuel etc
  • ?Water, effluent, industrial gases
  • In general further detailed study will be required for medium and high cost opportunities
energy balances and data analysis
Energy Balances and Data Analysis
  • Last 12 months bills
  • Sub-meter readings
  • Principal energy users
  • Production and climatic data
  • 1st Law of Thermodynamics – energy can neither be created or destroyed
electricity bills
Electricity Bills
  • Maximum Demand charges (kVA, kW)
  • Capacity charges (kVA, kW)
  • Day and night rates
  • Power factor
power factor





Power Factor

PF = kWh/kVAh

= cos φ

From the electricity bill

kWh = 17,400

kVArh = 8,700

What is the power factor?

power factor13
Power factor

tan φ = 8,700/17,400

= 0.5

φ = 26.5º

cos 26.5 = 0.89

PF improved by adding capacitors

Worthy of further investigation below 0.85-0.90

gas bills
Gas Bills
  • More frequently estimated (in the UK)
  • Errors more prevalent
  • Very rarely obtain ½ hourly demand
  • Can obtain some useful energy management information
electrical balance
Electrical Balance
  • Sub-meters help – but rarely provide all the required information
  • Need to list major electrical consumers (pumps, fans, compressors, chillers, lighting, process heating etc)
  • Need rating and running hours
estimating electricity22

Design kW = rating on equipment

e.g. plate rating of a motor; wattage of a bulb

Estimating Electricity
estimating electricity23

Actual kW = best estimate of actual power

e.g. based on ammeter reading or design data

Estimating Electricity

kW = √3*V * I * PF

estimating electricity25

Total should = metered total

either for whole site or for a sub-meter

Estimating Electricity
estimating electricity26
Estimating Electricity
  • High accuracy is time consuming
  • ±10% is very good
  • Portable data logger useful for large users
  • Don’t underestimate the large number of small users e.g. conveyors, fans, pumps
fuel balances
Fuel Balances
  • Process vs. space heating from a year of monthly or weekly data
  • Difficult to estimate the distribution among process users if there is no metering
  • Most gas process plant will operate well below MCR – manufacturers specification
  • No portable gas metering
could chp be feasible
Could CHP be feasible?
  • Power demand >500 kW
  • Coincident heat (steam or hot water) demand?
  • Heat to power 3:1
  • High operating hours > 2 shift 5d/week
  • Comparison to a published benchmark often seen as method for estimating savings
  • Treat with caution
    • ‘best practice’ often refers to ‘state of the art’
    • Utilisation has a large influence
  • Generally confirms what you already know
  • Greatest validity for ‘basic’ industry – metals, ceramics, glass etc..
  • Lots of information at
basic combustion process
Basic Combustion Process

Natural gas

8N2 + CH4 + 2O2 CO2 + 2H2O + 8N2

Plus the release of ~10 kWh/m3 of CH4

10 volumes of air required for 1 volume of methane

heat recovery process
Heat Recovery Process

Gas Passes -



Furnace Tube - radiation

boiler losses


(~20% on gas, ~16% on oil)

Convection &


(1% to 1.5% @

max continuous

rating (mcr))

Air & Fuel



Boiler Losses

Convection proportional to T

Radiation proportional to T4

combustion losses
Combustion Losses
  • heat loss in flue gases
  • Latent heat of water vapour in flue gases
  • incomplete carbon combustion
  • ‘Excess’ air must be kept to a minimum
  • Generally at least 10% excess is required to ensure good combustion
  • Combustion losses depend upon volume and temperature of flue gases
excess air
Excess Air
  • measured by inference from O2 in exhaust or level of CO2 in exhaust
  • Portable instrument (measures O2, temp and CO
  • Permanent zirconia probe in stack linked to air/gas valves (oxygen trim)
best boiler efficiency
Best Boiler Efficiency
  • optimised fuel / air ratio well insulated (shiny surface)
  • clean burner nozzles
  • clean boiler surfaces
  • minimum steam pressure / temperature
  • reasonable load (~80%)
  • optimised TDS controlling blowdown
  • 1% efficiency increase, 79% to 80% savers 1- 0.8 = 1.25% fuel
    • reduction of 02 by ~2%
    • reduction of exhaust temperature by ~20ºC
  • oxygen trim control; 1% to 1.5% on well adjusted boiler
  • Air preheat (duct from air compressors or boilerhouse) saving 0.5% to 1%
  • maintaining recommended TDS levels ensures clean heat transfer surfaces
  • operating low TDS waste energy, water, chemicals and increases effluent costs
  • heat recovery (for large boilers payback 2-3 years)
  • check optimum load on boilers
  • rank multiple boilers to operate the group with minimum loss
  • Shutdown Loss Minimisation
    • gas side isolation with dampers
    • water/steam side isolation with crown valve
heat recovery
Heat Recovery
  • economiser (to feedwater)
  • recuperator (to wash water)
  • check existing quality
  • insulate all hot pipework, flanges (1m pipe), valve bodies (5m pipe)
  • hotwell cover and insulation
key points for the boiler house
Key Points for the Boiler House


  • Boiler efficiency
  • Blowdown procedure
  • Condensate return
  • insulation
the nature of steam
The Nature of Steam

Item Heat Content

KJ/kg %

Latent at 7 bar g 2050 74

Flash at Atmospheric from 7 bar g 300 11

Condensate at Atmospheric 420 15

Total 2770 100

Breakdown of heat content of 7 bar g saturated steam

system standing losses
System Standing Losses

Fixed loss from:

  • Pipework
  • Valves
  • Fittings etc.

Losses range from 2% to 5%

system variable losses
System Variable Losses

Flash and % losses with steam at

condensate ? bar g & cond. at 0 bar g

return 7 5 3 0

Total loss 26 24 22 15

50% cond. return 19 17 15 7

management control
Management Control
  • Automatic isolation systems
  • Pressure reduction
  • Energy management:
    • Metering
    • Data analysis
    • Action
fixed losses
Fixed Losses
  • Insulation
  • air ingress
  • steam leaks
  • Size:
    • cost trade-off
  • Installation:
    • air removal
    • condensate drainage
    • weather sealing
    • group users
pressure reduction
Pressure Reduction
  • More efficient
  • Saves fuel
  • Cost incurred for:
    • pressure reduction sets
    • larger heat exchangers
    • larger traps
  • Consider life cycle costs
steam leaks
Steam Leaks



12.5 mm



10 mm

7.5 mm



5 mm




3 mm




Steam Leak = 7.5mm diameter

Steam Pressure (barg) ( or pressure difference between steam and condensate) = 6 bar

Steam Loss = 100 kg/h












steam trapping air venting
Steam Trapping & Air Venting
  • Steam trapping
    • function
    • testing
    • group trapping
    • sizing traps
  • Air venting
  • Scale and dirt removal
condensate recovery
Condensate Recovery

Saves costs for:

  • Water
  • Treatment chemicals
  • Fuel
  • Effluent

Produces rapid payback

flash steam recovery
Flash Steam Recovery


  • Indirect method
  • Direct method

Potential sinks:

  • BFW
  • Wash water
  • Process fluid
  • Space heating
key points for steam systems
Key Points for Steam Systems
  • Pipe insulation
  • Leaks
  • Isolation of redundant plant/off line plant
  • Steam traps
  • Condensate return
  • Overview of main industrial lighting types
  • Their efficiency
  • Common savings
  • Typically 10-50% of electricity use
  • Good lighting is critical to all manufacturing operations
  • Survey is relatively easy to carry out
estimate of load
Estimate of Load
  • Rating of lamp
  • Number
  • Operating hours
  • Add 10% for control gear
common industrial lighting types
Common Industrial Lighting Types
  • Fluorescent
    • Offices, general manufacturing
    • Good colour rendering
    • Instant instantaneous on and off
  • Metal Halide (HPI, MBI)
    • Good colour rendering
  • High Pressure Sodium (SON)
    • Poor colour rendering
  • Low Pressure Sodium (SOX)
    • Very poor colour (orange yellow)
    • Very efficient
savings with fluorescents
Savings with Fluorescents
  • Change T12 for T8
  • Control (PIR, zoning, daylight)
  • New systems
    • High frequency ballasts
    • High efficiency reflectors/diffusers
    • Payback 2-4 years
savings with metal halides
Savings with Metal Halides
  • Convert to SON (beware of colour issues)
  • Payback ~1 year if replace 400W MBF to 250W SON (8760h/y). Cost of SON €100
  • Convert to fluorescent if switching off is possible
top tips for lighting
Top Tips for Lighting
  • Lux measurement is worthwhile
  • Switch off
  • Need high lighting hours (2 shift) to justify replacement
  • Plenty of suppliers will carry out free surveys
compressed air69
Compressed Air
  • Background to Compressed Air
  • Reducing loads and pressure
  • Improving distribution
  • Improving generation
compressed air70
Compressed Air
  • very expensive form of energy
    • typically costs 1€/kWh
  • often used unnecessarily or inappropriately
    • Cooling, cleaning etc
  • similar philosophy to steam / refrigeration
    • minimise loads and pressures
    • minimise distribution system losses
    • maximise generation efficiency
potential savings
Potential Savings
  • Compressed air can account for up to 20% electricity use.
  • Enviros study identified minimum potential savings of 27%
    • generation (7%)
    • distribution (11%)
    • end usage (3%)
    • new technology (6%)
what to look out for use
What to look out for - use
  • Leaks
  • Main uses of air such as tools, painting, instrumentation or process
  • Misuses such as open ended lances, full pressure blow guns, product ejection and vacuum venturis
  • End of line pressure
  • Ring or spur mains?
check each load
Check Each Load
  • why is air being used
    • a key requirement or ‘habit’?
  • can a load be eliminated or reduced
    • replace pneumatic valves with electric
    • ‘amplifier’ nozzles
  • pressure and air quality requirements
    • is it as low as possible
    • how does it compare with other loads
  • Three main issues:
  • pressure drops
  • water
  • leaks
the distribution system
The Distribution System
  • examine the pressure drop across the system (velocity 6-9 m/s)
  • pipework is rarely upgraded when system extended
  • small bore pipe, elbows and short bends increase pressure drop
  • internal corrosion increases friction losses
  • A 1 bar pressure drop increases energy cost by 10%
distribution lines the effect of water
Distribution Lines – The Effect of Water
  • Problems with water
    • Causes corrosion
    • Product quality
    • Increases pressure drops
  • Is drying adequate? Additional automatic drain points
leakage losses
Leakage Losses
  • typically 25 - 50% of full load usage!
  • regular maintenance required to identify and repair leaks especially where flexible connections are used
  • identify and tag leaks at the weekend when production areas are quiet
some ways of reducing losses
Some Ways of Reducing Losses
  • Isolate air supplies outside working hours
    • to the machines
    • Interlock air supply with machinery
    • to areas of the factory with different working hours
  • Use the lowest possible operating pressure
    • reduce pressure locally if possible
  • If some consumers use low pressure air install a separate system
life cycle costs of compressor


Energy Cost





Life Cycle Costs of Compressor
what to look out for in the compressor room
What to look out for in the Compressor Room
  • Type, make, capacity, hours run and control of each compressor
  • Type make and configuration of treatment package
  • Room ventilation, inlets in or outside?
  • Is waste heat recovered?
  • What is the generation pressure?
  • Is there a group controller?
  • What is the estimated demand?
  • Are the feeding mains OK are there any other bottlenecks?
  • Do they have electronic zero loss condensate traps?
  • Filters cause pressure drops.
    • To save energy meet the minimum requirement
    • Undersizing raises pressure drop
    • Every 25mbar pressure drop increases compressor power consumption by 2%
  • Ambient air at 15oC contains about 12.5g water per cubic metre
  • Most condenses in the aftercooler
    • An after cooler might remove 68% of the water in the air if cooled to 35oC
  • Further drying is usually necessary
    • Deliquescent - energy efficient, cheap
    • Refrigerated - popular, 3-5% energy cost (dew point 3ºC)
    • Desiccant – air regenerated can consume 15-20% of air produced (dew point -60ºC)
guidelines for drying
Guidelines for Drying
  • Generally design to dry air to 6ºC below ambient temperature
  • Don’t run pipework outside if possible
  • Only dry as much air as is necessary (i.e. have a separate wet and dry system)
compressor efficiencies



Capacity Nm


Specific Power






Good with step unloading and low

Lubricated Piston



off load power





Good with step unloading and low

Oil Free Piston



off load power





High power on part load

Lubricated Screw/Vane







Two step with good part load power

Oil Free Screw







Good over modulation range




Above 2,000


Compressor Efficiencies
reciprocating compressors
Reciprocating Compressors
  • Single or multi stage
  • Idling losses normally around 25% of full load current
  • Relatively efficient on part load
  • Valve deterioration reduces efficiency
  • Noisy
  • High maintenance
rotary screw compressors
Rotary Screw Compressors
  • Normally provide cleaner air
  • Most popular unit
  • Packaged units available with integral heat recovery
  • Very efficient if run with variable speed control
  • Unloaded power greater than reciprocating machines
centrifugal compressors
Centrifugal Compressors
  • High capacity base load machines
  • Large machines have very good efficiency on full load
  • Part load operation achieved by inlet throttling modulation
  • Modulation should only be used around full load conditions, very poor efficiency at low loads
rotary sliding vane
Rotary Sliding Vane
  • Normally used for less demanding duties
  • Generally low capital cost machines
  • Used for single shift operations
  • No integral heat recovery
  • Part load operation very inefficient
control general rules
Control - General Rules
  • On/off control (where possible) is better than variable speed, which is better than modulating control
  • Modern control systems can select the optimum combination of compressors
  • For multiple compressors check hours run and loaded meters
modulating and variable speed control
Modulating and Variable Speed Control




Variable Speed




heat recovery94



Building Services

Space Heating

Water Heating

Compressed Air Treatment


Boiler Pre-heating

Feed Water

Combustion Air

Heat Recovery

Into air or water for:

heat recovery example
Heat Recovery Example
  • A 20kW compressor would satisfy the combustion air requirements of a 1 MW boiler
  • For each 20oC rise in combustion air temperature there is an approximate 1% rise in boiler efficiency.
  • If this air is at 60oC, an efficiency increase of 3% may result.
intake air temperature
Intake Air Temperature

For every 4C that the intake air temperature falls:

The energy required for compression falls by 1%

intake air temperature example
Intake Air Temperature - Example
  • A compressor draws air from a plant room that is typically at 25oC, and consumes 75kW
  • The average UK/Ireland outside air temperature is 10oC
  • Taking the air from outside means that the average temperature is 15oC lower
  • Saving 3.75%, 2.8kW, £1000/yr
  • compressed air is very expensive
    • often equivalent to >50p/kWh
  • only use when really necessary
  • minimise system pressure
  • minimise leaks
    • simplify distribution
    • isolate unused sections
  • optimise generation efficiency
top tips
Top Tips
  • Check compressor instrumentation (hrs run, on-load etc.)
  • Simple ‘rotameters’ for (temporary) flow measurement are very cheap
  • Install automatic drain traps
  • Look carefully what happens at meal breaks, shift changes and weekends





High Balanced

Score 3 or more on all columns

Excellent performance; the challenge is to maintain this high standard


Low Balanced

Balanced score of less than 3 on all columns

Is this balance a symptom or orderly progress or stagnation



The two outside columns are significantly higher

Expectations have been raised







The two outside columns are significantly lower

Achievement in the centre is likely to be wasted



A single column is significantly lower than the rest

Underachievement in this column may well hold back success elsewhere



A single column is significant higher than the rest

Effort in this area could be wasted by lack of progress elsewhere



Two or more columns are 2 points above or below average

The more imbalance the harder it is to perform well

general comments
General comments
  • Refrigeration systems are often complex
  • Maintenance often sub-contracted
  • Poor energy efficiency not obvious
  • Savings potential is good ~20%
the refrigeration process 1


Ambient Cooling Stream

Substance Being Cooled


The Refrigeration Process (1)

High pressure liquid

High pressure vapour

Expansion valve


High P

Low P

Low pressure vapour

Low pressure liquid/vapour

refrigerants a few examples
Refrigerants - A Few Examples
  • Ammonia R717
  • CFCs R11, R12, R502
  • HCFC R22
  • Pure HFCs R134a, R32
  • HCFC blends R403B, R408A
  • HFC blends R404A, R507
  • Hydrocarbons R290
system efficiency
System Efficiency

Coefficient of Performance (COP) = useful cooling/system power

Theoretical efficiency (Carnot efficiency)= Te/(Tc – Te) (T is degK)

Useful approximation COP=0.6Te/(Tc – Te)

Chillers often specified in tons (US) 1 ton = 200 BTU/min (3.52kW)

measurement of t c t e
Measurement of Tc & Te
  • Often chillers only equipped with pressure gauges
  • Pressure can be converted temp. if refrigerant is known
typical compressor cops
Typical Compressor COPs


Air Conditioning 15°C 5

Chilling 3°C 4

Freezing -30°C 2

calculation of cop
Calculation of COP
  • Need to know
  • Compressor power
  • Flow/return temps of primary/secondary refrigerant
  • Flow rate of primary/secondary refrigerant
  • Thermodynamic properties/specific heat of primary/secondary refrigerant
  • Only possible on large systems
improving cop
Improving COP
  • From Carnot = Te/(Tc – Te) theoretical efficiency increases as:
  • Tc – Te approach 0
  • Te increases for the same temperature lift (Tc – Te)
increasing t e
Increasing Te
  • Efficient heat transfer in evaporator
    • Clean heat exchange surfaces (e.g. ice on evaporator)
  • Avoid overcooling of product
    • e.g. product stored at -20ºC, but freezer cools to -30ºC
  • Temperature set point unnecessarily; low ΔT between refrigerant and process liquid <5ºC
    • Two stage cooling
  • Increase Te 1ºC increases efficiency by ~3%
  • Water cooled shell and tube (with CT)
    • Water approach temp 5ºC
    • Water temp rise ~ 5ºC
    • Condensing temp 15 ºC greater than wet bulb
  • Air cooled
    • Condensing temp 15 ºC greater than air
  • Evaporative condensers
    • Similar to shell and tube
  • Decrease Tc 1ºC increases efficiency by ~3%
compressor performance
Compressor Performance

% of full load COP



and screw





% of full duty

case study a poor part load control of 3 modular water chillers
Case Study (a) poor part load control of 3 modular water chillers

Load % Power kW

Compressor 1 33 90

2 33 90

3 33 90

Chilled water pumps 1 100 25

2 100 25

3 100 25

Condenser pumps 1 100 20

2 100 20

3 100 20

Total Power Absorbed - 405

case study b good control
Case Study (b) good control

Load % Power kW

Compressor 1 100 150

2 0 0

3 0 0

Chilled water pumps 1 100 25

2 0 0

3 0 0

Condenser pumps 1 100 20

2 0 0

3 0 0

Total Power Absorbed - 195

what can be easily assessed
What can be easily assessed?
  • If possible calculate COP
  • Minimise cooling loads
    • Free cooling in HVAC systems
    • Two stage
    • Cold store housekeeping
  • Check ΔTs
    • Condition of heat exchangers
  • Background to Motors and Drives
  • Using High Efficiency Motors
  • Using soft starts for better control
  • Using voltage controllers for partly loaded motors
  • Using variable speed drives
motor and drives
Motor and Drives
  • constitute over half of industrial electrical demand
  • overall saving potential - 10% across Industrial & Commercial sectors
  • A motor will consume its capital cost in just a month of continuous operation. SoThe capital investment is insignificant compared to running costs.
motor operation costs
Motor Operation Costs

132kW motor, cost £3600, efficiency 93%

22kW motor, cost £660, efficiency 90%

Electricity cost 4p/kWh, both motors fully loaded

nominal motor efficiency v rating
Nominal Motor Efficiency v. Rating

Motor Efficiency %

Motor Rating (kW)












Total Loss

I2R (copper) loss

stray loss

iron loss

friction and windage

0 40 80 120

Load (%)

high efficiency motors
High Efficiency Motors
  • reduced Iron (Steel) Losses
  • reduced copper Losses
  • stray losses minimised
  • more efficient motor generates less heat
high efficiency versus standard motors payback period
High Efficiency Versus Standard Motors Payback Period

New Motor - 7.5 kW

Hours of Electricity Additional Payback

Usage p.a. Cost Savings Costs Years

£ p.a. £

2000 36 83 2.3

4000 72 83 1.2

6000 108 83 0.8

At 4p/kWh for electricity, the

incremental cost payback occurs after about

5000 hours.

high efficiency motors conclusions
High Efficiency Motors - Conclusions
  • most suitable for highly loaded motors
  • justified on new or replacement motors
    • rewinds introduce extra losses – buy HEM instead of rewinding
  • on 4,000 hrs or more operation, marginal payback just over a year
switch it off
Switch it off!
  • don’t leave motors running needlessly
  • fit automatic controls to avoid motors being left on
    • e.g. timers or load sensors on conveyors
  • look for fixed loads
    • e.g. tank mixers – why not switch motor off for 1 minute every 5 with a saving of 20%
soft start equipment
Soft start equipment
  • can enable switch off strategies to work
  • gives a more controlled motor start
    • by ramping up motor voltage
    • replaces DOL or star-delta starters
  • reduces power surge
  • reduces mechanical wear on motor, drive and connected equipment
  • makes it possible to stop and start motors more frequently
motor voltage controllers
Motor Voltage Controllers
  • improve efficiency at loads below 50%
    • regulate the voltage at the motor terminals
    • iron losses are reduced
    • efficiency and power factor are improved
  • suitable for variable load motors that operate under 50% load for long periods
  • do not use on highly loaded motors
    • reduce efficiency at high load!
variable speed drives
Variable Speed Drives
  • excellent “new” technology to help reduce electricity consumption
  • for pumps / fans savings can be dramatic
    • cubic relationship between power and flow
    • reduce flow to 80%, reduce power to 50%
  • not applicable to all motors
    • e.g. difficult for refrigeration compressors
advantages of vsd
Advantages of VSD
  • many loads run at fixed speed, but user requirement is varying
    • e.g. pumps and fans
  • system often designed for worst case
    • then designer adds a safety margin
  • under average conditions flow too high
  • at fixed speed control is inefficient
    • e.g. dampers, flow bypass etc.
  • VSD can provide excellent savings
    • e.g. 80% flow at 50% power
ways to vary the speed
Electro-mechanical variable speed systems

Electronic Variable Speed Drives (Inverters or VSDs)

Variable Speed Motors

Some savings, but losses in transmission systems

Good savings, efficiency maintained reasonably well

Better than an inverter, but a special motor

Ways to vary the speed
electro mechanical drives
Electro-Mechanical Drives
  • Mechanical (V-belts & gears)
  • Hydraulic Couplings (Slippage between discs)
  • Eddy Current Couplings
variable speed motors
Variable Speed Motors
  • Two speed AC Motors
  • AC 3-phase Commutator Motors
  • AC Switched Reluctance Motors
  • DC Motor & Drive Systems
inverter vsds
Inverter VSDs
  • can be applied to most existing 3 phase motors
  • AC current is rectified into DC and then “inverted” back to AC at any desired frequency
  • motor speed proportional to frequency
    • speed can go from ~10% to ~120%
    • speed range depends on motor design and load requirements
getting the savings wrong
Getting the savings wrong
  • Some consultants, salesmen and suppliers assume that the cube law always applies
  • IT DOESN’T apply, if
    • the variable speed is set to maintain a constant pressure at the pump or fan discharge
    • if a liquid is being pumped up to a tank at higher level (called “static head”)
estimating vsd savings properly
Estimating VSD savings properly
  • See Good Practice Guide 249, Appendix 3
  • You will need
    • An understanding of the static head of your system
    • A good picture of the flow requirements of your system
    • The fan/pump curves from the manufacturer
    • The motor and VSD efficiency curves from the manufacturer
achieving the maximum saving

Control point A

Control point B

Achieving the maximum saving

Fan feeding large ductwork system

achieving the maximum saving147

Control point A

Control point B

Achieving the maximum saving

At control point A, the pressure cannot change, so the new power will be in simple proportion to the flow:

Reduced power = old power x (new flow/old flow)

achieving the maximum saving148

Control point A

Control point B

Achieving the maximum saving

At control point B, the pressure through most of the system can change as friction reduces, so the new power will follow the cube law:

Reduced power = old power x (new flow/old flow)3

case study variable speed drive townsend hook paper
Case Study - Variable Speed DriveTownsend Hook - Paper
  • Fan Drives
  • 3x45kW fan motors
    • damper controlled and drawing 30kW
  • £15,750 to install inverters on 3 motors
  • Savings 20kW/motor or £13,500/annum
  • Simple payback 14 months
case study variable speed drive townsend hook paper153
Case Study - Variable Speed DriveTownsend Hook - Paper
  • Pump Drives
  • Two pump motors, 1x75kW and 1x37.5kW
  • £12,500 to install inverters on both motors
  • Savings 74kW or £16,650/annum
  • Simple payback 9 months
  • most electricity consumed via electric motors
  • HEMs should always be selected
  • motor rewinds can introduce losses
  • motor switch off strategies should be adopted where possible
  • VSDs can improve control significantly
top tips155
Top Tips
  • Look for large motors with long running hours
  • Big motors >20 kW
  • Variable flow (fans and pumps)
  • Inventory listing
  • HEM policy
where to insulate
Where to Insulate
  • Generally any hot surface above 60 ºC and any cold surface less than 5 ºC
  • Types of insulation
    • Mineral fibres (bonded or loose)
    • Polyurethane
    • polystyrene
estimating heat losses q r
Estimating Heat Losses (Qr)

Radiation Qr = CE(T4s –T4a) W/m2

C= 5.67x10-8

E = emissivity (0.1 – 0.9)

T = K (ºC +273)

estimating heat losses q c
Estimating Heat Losses (Qc)

Radiation Qc = C(T1 –T2)1.25 W/m2

C= 2.56 upward horizontal hot or down horizontal cold

= 1.97 flat vertical surfaces at least 0.5 m high

= 1.32 downward facing hot

= 2.3 horizontal cylinders greater than 150mm diam

Use a factor of V0.8 to allow for forced convection

heat loss from open tanks
Heat loss from open tanks
  • Can be very large at high temperatures
  • Typical areas – metal treatment vats, hot wells
  • Losses can be reduced by ~80% with lids and insulation balls
process integration162
Process Integration
  • Commonly used technique in the chemical industry to optimise heat recovery between hot and cold streams
  • Complex process but worthwhile quantifying fluid heating and cooling streams

Identify where Energy is Used and Develop an Action Plan


Senior Management Commitment

Measure Energy Consumption and Production

Review Performance and Action Plan

Develop Targets

Implement Energy Saving Measures

Produce Reports to Monitor Energy Use Against Output

headline numbers update
Headline Numbers Update

Total Energy Cost Year to May 2003 $5.2 million

utility management
Utility Management
  • In 2001, utility consumption data was very poor
  • Metering is now excellent
  • The only significant gap is the RTO
  • Environmental drivers are more powerful
  • Montage, Powerlogic and ORCI all provide excellent data
priority areas
Priority Areas
  • Compressed air
  • Chillers
  • RTO
  • Colour Line
air compressors
Air compressors
  • Well metered
  • Annual energy consumption is 5.3 million kWh/year ($480,000)
  • Centacs now meet all demand
  • One machine is shutdown at weekends
  • Manual control






Air Compressors Hourly Electricity Use

scope for savings
Scope for Savings
  • Run a Centac and the Broomwade - estimated saving $150,000/year
  • Just run the Broomwade at night and weekends estimated saving $30,000
  • When Prime Line restarts investigate a heat regenerated drier
  • Chillers, pumps and CTs consume 6 million kWh/year ($550,000)
  • 1 chiller in the winter and 2 in the summer
  • System is oversized and inflexible
  • In the winter cooling load from ASH is 74kW (+90kW from old compressors) actual cooling is 750kW and compressor power is 350kW i.e. effective COP of 0.4

3 Pumps

4 Pumps

2 Pumps

5 Pumps

6 Pumps

chillers potential savings
Chillers Potential Savings
  • In the summer one chiller is switched off at weekend
  • Corresponding pumps are not always switched off – potential saving 60,000 kWh/year ($5,400)
  • Can a chiller be switched off at night in the summer 3hrs@50 days – potential savings 60,000 kWh/year ($5,400)
  • VFD for glycol pumps
  • Small chiller for winter
  • Meter has not yet been configured
  • Estimated gas use $1.4 million/year
  • Electricity use of RTO fan 1.6 million kWh/year ($140,000)
  • Control of flow and LEL to the RTO is essentially manual
rto savings potential
RTO Savings Potential
  • Weekend setting for night non productive time estimated saving 280,000 m³/year ($90,000) for gas and 50,000 kWh/year ($4,500) for electricity
  • Optimization of LEL set points (and air flows) Saving ?$100,000/year
colour line
Colour Line
  • Is comprehensively metered
  • Total gas cost is $400,000/year
  • Total electricity is $600,000/year
  • Is well controlled

Thurs Fri Sat Sun Mon Tues Weds Thurs Fri Sat Sun Mon

Colour Line Hourly Electricity Use


colour line gas savings potential
Colour Line Gas Savings Potential
  • Appears well controlled
  • Improving shut down and start up procedure would save $3-4000/year for gas and $6,000 for electricity
potential savings190
Potential Savings

Other significant areas are lighting and space heating

  • Level of data is very impressive
  • Major gaps are:
    • RTO
    • Main site gas meter
    • Correlate chiller performance to ambient conditions and/or COP
  • Next step is to analyse and act upon the data