ch2 - energy fundamentals

8/12/2019 CH2 - Energy Fundamentals

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CHAPTER 2

Energy

Fundamentalsfor Energy Auditors


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What is Energy?


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Energy Lets Us Do Work Energy is the ability to do work.

As such, energy is important to all living things in

order to maintain life functions from the smallestpart of a cell to the organism as a whole.Humans also use energy to modify their

environment and perform work. Energy is measured by the amount of work it is

able to do. The units for measuring energy are

Joules (J). One Joule is a very small amount of energy,

but 1000 Joules is roughly the heat energy

produced by burning a blue tip kitchen match.


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Sources of Our Energy The energy sources that we use every day are

divided into two groups: Renewable an energy source that we can

use over and over again, and can be replaced

naturally in a short period of time. Non-renewable an energy source that we

are using up and cannot recreate in a short

period of time.


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Sources of Our Energy

The renewable energy sourcesinclude solar energy, which comesfrom the sun and can be turned

into electricity and heat. Wind,geothermal energy from inside the

earth, biomass from plants, andhydropower from water are also

renewable energy sources.


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What Is Power? Work can be done at different rates,

sometimes slow, sometimes fast. Sincework involves the transformation ofenergy, the faster the work is done, thequicker energy must be transformed.

Poweris the term used for the measure of

how fast work can be done. Or in otherterms, power is defined as the rate atwhich work is done.


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What Is Power? In mathematical terms power equals work done

divided by time required, so the units of powerwould be Joules per unit time, most commonlyJoules per second, or watts:

Power is an important concept because it ties

the dimension of time into the energy picture.

RequiredTimeDoneWorkPower


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Almost all mechanical and electricalequipment have nameplate ratings in

terms of the maximum power that theycan supply, not the energy they cansupply.

As we will see later, almost allmechanical devices like motors are ratedin terms of their maximum poweroutput,

while almost all purely electrical devicesare rated in terms of their maximumpower input.


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Energy and power are often confusedwith each other.

A useful analogy can be found in ourcar where we have both thespeedometer that tells us how fast we

are going in kmph, and we also havean odometer which tells us how farweve gone in km.

KMPH


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The odometer is like an energy

meter that tells us the totalamount of energy in Joulesthat weve used.

The speedometer is like a powermeter that tells us the rate at whichwe have used that amount of energy in

Joules per second, or watts.

With our car, the quantities of interest

are km and kmph. With our electricaland mechanical equipment, thequantities of interest are Joules and

Joules per second, or watts.

KMPH


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Electrical Power When dealing with electricity, power isdefined in the same way.

Electrical devices provide resistance whichdescribes the amount of work that needs tobe done for a specific task.

A certain amount of work must be done tomove electrons through the resistance.

More resistance means more work mustbe done to move electrons through theresistance and allow the device tooperate.


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Electrical Power The rate which that work is accomplished isrelated to the power applied. More electrical

power means energy is being converted at afaster rate.

This electrical energy is supplied by the source

of the electrical current like a battery or electricalgenerator.

Electrical power is measured in units calledwatts, which are related to the number of Joules

of energy expended per second.

1 watt = 1 Joule/second


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This means the energy can be expended atdifferent rates depending on how fast thework needs to be done.

Some devices use more power toaccomplish a task that others do with muchless power.

For example light bulbs come in differentsizes meaning different wattages. Somelight bulbs are rated 60 watts while others

are rated 100 watts. The 100 watt bulb willgive off more light than the 60 watt bulb butif you only need the amount of light from the60 watt light bulb, you are using more powerthan necessary.


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Units of Electrical Energy The watt (W) is a physical unit which is

named for James Watt, the inventor of

the steam engine. Since the unit refers to a personsname, we abbreviate it with a capital W.

The basic unit of electrical energy is the watt-hour, orWh.

1 Wh = 3600 Joules1 kWh = 1000 Wh = 3600000 Joules = 3.6 MJ1 MWh = 1000 kWh

1 GWh = 1000 MWh

1 kW = 1000 W

1 MW = 1000 kW


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One barrel of oil produces

about 550 kWh in a thermalpower plant


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One kg of coal produces about

2 kWh


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Energy Units And

Energy Conversions

minutes

degreesCelsius


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Energy Units And Energy

Conversions The basic unit of energy is the Joule (J)

One thousand Joules is about equal to theheat produced by burning an ordinaryblue-tip, kitchen match.

One Joule is not a very large amount ofenergy, so you will often see one of twocommon multipliers of Joules; the kJ, or one

thousand Joules; or the MJ, which is 1000kJ, or one million Joules. For even largeramounts of energy, the GJ = 1000 MJ.


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Word and Numerical

Equivalents

One J = 1 J.

One thousand J = 1000 J = 103 J = 1 kJ

One million J= 1,000,000 J = 106 J = 1 MJ One billion J = 1,000,000,000 = 109J = 1 GJ


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Energy Conversion Unit Table

1 kWh .. 3.6 MJ

1 m3 LPG..25.56 GJ

1 kg #2 fuel oil . 43.3 MJ

1 m3 natural gas.. 37 MJ

1 m3 #2 fuel oil 39.85 GJ

1 litre LPG gas ... 7.1 kWh

1 kg LPG gas12.68 kWh

1 litre #2 fuel oil11.07 kWh1 kg #2 fuel oil..12.03 kWh


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Energy Unit Conversions and

the Railroad Track Method Since we have several different basic energy units

and many different energy unit multipliers, energymanagers must often convert from one set of energyunits to another. There is a very systematicapproach that can be applied to basic conversions,

and also to more complex conversions andcalculations.

The principle of this unit conversion method is simply

to carry out algebraically correct multiplications anddivisions using correct units at each step, startingwith the given piece of information and transformingit into the desired units using one or more conversion

factors.


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For example, if we want to find the number(X) of Joules in 1000 cubic metres of naturalgas, we can use this method as follows:

= 1000 37,000 kJ

= 37,000,000 kJ

= 37 109 J

= 37 GJ

From Table C-20

kJ000,37

m

m1000=

mkJ000,37m1000=gasofGJX

3

3

33


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In the above calculation, cubic metresin the numerator and cubic metres inthe denominator cancel out, and the

remaining unit on the right side of theequation is J.

Our goal was to end up with J as ourdesired unit on the right, and we madeour unit conversions on the right side

until we had the same unit as on theleft side.


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If we ever perform one of these basicunit conversion calculations, and findthat we have different units on the left

and the right we do not have thecorrect answer in terms of the desiredunits.

This method is given the colloquialname Railroad Track Method, because

the vertical separation lines remind usof railroad tracks.


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Find the number (X) of kWh in 1000 cubicmetres of natural gas.

= 1000 37,000 kWh/3600

= 10,278 kWh

Example Problem

3600

kWh1

kJ

kJ000,37

m

m1000=

kJ3600

kWh1

m

kJ000,37m1000=gasofkWhX

3

3

3

3

From Table C-20


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Example Problem

Solution

X J = 10 kWh 3.6 MJkWh

= 36 MJ

In this example, the two kWh unitscancel out, leaving the remaining unit

on the right side as J.

How many J are in 10 kWh?


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Example Problem

How many kWh are in 2500 mJ?Solution:

In this example, the two MJ unitscancel out, leaving the remaining uniton the right side as kWh.

kWh44.694=MJ

kWh6.3MJ2500=kWhX


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Example Problem A tank is filled with 100 litres of Number 2 fuel

oil. How many GJ of energy is contained in thetank of oil?

Solution

From Table C-20, there are 39 MJ per litre of oil.

= 3.9 GJ

In this example, the two litre units cancel out, and thetwo MJ units cancel out, leaving the remaining unit onthe right side as GJ, our desired unit.

MJ1000

GJ1

L1

MJ39L100=GJX


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Benchmarking

A benchmark is a value youcompare something against.


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Energy Benchmarking for

Buildings Building energy benchmarking is the

comparison of whole-building energy userelative to a set of similar buildings.

It provides a useful starting point for individualenergy audits and for targeting buildings forenergy-saving measures in multiple-site audits.

Benchmarking is of interest and practical use toa number of groups.

Energy service companies and performancecontractors communicate energy savingspotential with typical and best-practice

benchmarks.


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Control companies and utilities can providedirect tracking of energy use and combinedata from multiple buildings forbenchmarking.

Benchmarking is also useful in the designstage of a new building or retrofit todetermine if a design is relatively efficient.

Energy managers and building owners havean ongoing interest in comparing energyperformance to others.

Large corporations, schools, andgovernment agencies with numerousfacilities also use benchmarking methods tocompare their buildings to each other.


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Benchmarking Audit Benchmarking Audits are associated with

the idea that after the energy bill data iscollected and processed, some facilityinformation will be collected on a walk-through, and the data will be run through

some benchmark to determine if there is apotential for significant improvement inenergy efficiency and reduction in energy

operating cost.


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Benchmarking Criteria

Energy Use Index - MJ/m2/year, kWh/m2/year Total, Electric, Gas, Oil

Energy Cost Index - $/m2/year Total, Electric, Gas, Oil

Productivity Index

kJ/kg, kJ/person, kJ/student, kJ/tonne, kJ/item kWh/kg, kWh/person/ kWh/tonne, kWh/item L H2O/kg, or /student, or /item (also sewer)

System performances kWe/kW cooling, LPS/kW air, kWh/L pumping


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Basic Energy Accounting

Basic energy accounting deals with thefollowing ideas:

Recognizing different energy and fuel types Electricity, gas, light oil, steam, chilled water

Understanding energy related units

kWh, kJ, MJ, kW, kJ/h, L or kg of oil, m3 ofgas

Performing conversions to different energyrelated units

For example, 1 kWh = 3600 kJ = 3.6 MJ


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The Facility Energy Use Index The facility Energy Use Index (EUI) is a

statement of the number of MJs (or kWh) of

energy used annually per square metre ofconditioned space (heated or cooled, or both).It is a basic measure of the facilitys energyperformance the lower, the better.

To compute a facilitys EUI Identify all the energy used in the facility

Add up all the MJs (or kWh) of energy

Find the total square metres of conditioned space

Divide the total MJ (or kWh) used per year by thesquare metres of space.


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ExampleA facility with 1,000 square metres of

conditioned space uses 100 GJ ofgas and 150,000 kWh of electrical

energy in one year. What is thefacilitys EUI?


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Solution (in MJ/m2

yr)

yrm/MJ640=yrm000,1

MJ)000,540+000,100(=EUI 22

yr/MJ000,100=GJ

MJ1000

yr

GJ100

=MJgas

yr/MJ000,540=kWh

MJ6.3

yr

kWh000,150=MJelect


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Solution (in kWh/m2

yr)

yrm/kWh8.177=

MJ6.3kWh1

yrmMJ640=EUI

2

2


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1999 CBECS EUI Data - USA

kWh/m2/yrAll Bldgs 236

Education 208 Vacant 44.5Food Sales 561 Food Service 669

Health Care 490 Lodging 278

Retail Stores 200 Office 251

Assembly 228 Safety 242

Churches 88.9 Service 346

Warehouse 122 Other 400

E U I d f C i l B ildi


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Energy Use Index for Commercial Buildings

kWh/sq metre/yr

0

100

200

300

400

500

600

700

AllBldgs

Education

FoodSales

FoodServ

Health

Lodging

Retail

Office

Assembly

Safety

Churches

Service

Warehouse

Other

Vacant

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