What is Energy? Session 1

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What is Energy?

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A word about multiplication factors

• Kilo (k) = 1,000

• Mega (M) = 1,000,000

• Giga (G) = 1,000,000,000

e.g. 1kW = 1,000W

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Converting J to kWh

= 3,600,000J

or 3.6 MJ

1 kilowatt-hour (kWh) = Energy consumed by 1 kW in 1 hour

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Common units for energy buying

• kWh is the main unit for energy utilities

• But we can convert

– Litres of oil

– Tonnes of coal

– Therms of gas

GrowSave Event B y W e ig h t B y V o lu m e S o lid f u e ls k W h / t o n n e C o k e 8 ,2 7 8 C o a l ( w e ig h te d a v e r a g e ) 7 ,4 4 4 L iq u id f u e ls k W h / t o n n e k W h / lit r e C r u d e O il ( w e ig h te d a v e r a g e ) 1 2 ,6 9 4 1 0 .7 H e a v y F u e l o il 1 1 ,9 9 9 1 1 .8 M e d iu m f u e l o il 1 2 ,2 5 2 1 1 .3 G a s /d ie s e l o il 1 2 ,6 6 6 1 0 .8 K e r o s e n e 1 2 ,8 3 3 1 0 .3 P e tr o l 1 3 ,0 8 3 9 .6 L P G 1 3 ,7 2 2 7 .4 E th a n e 1 4 ,0 8 3 5 .2 G a s e o u s f u e ls k W h / m 3 N a tu r a l g a s 1 1 .0 C a u t io n : L a n d f ill g a s 1 0 .7 S e w a g e g a s 1 0 .7 S o lid R e n e w a b le s k W h / t o n n e T y r e s 8 ,8 8 8 R e f u s e d e r iv e d w a s te 5 ,1 9 4 G e n e r a l in d u s tr ia l w a s te 4 ,4 4 4 S tr a w 4 ,1 6 6 H o s p ita l w a s te 3 ,8 8 9 In d u s tr ia l w o o d ( p a lle ts e .t.c ) 3 ,3 0 5 D o m e s tic w o o d ( lo g s ) 2 ,7 7 8 M u n ic ip a l s o ild w a s te 2 ,6 3 9 D e p e n d s o n c a lo r if ic v a lu e

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Conversions can vary

• The quality of fuel (calorific value) changes

slightly depending on the ‘batch’

• Gas calorific value is published for each Transco

region each month and appears on the bill

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Variation in calorific value by region

3 8 .6 3 8 .8 3 9 .0 3 9 .2 3 9 .4 3 9 .6 3 9 .8 4 0 .0 4 0 .2 4 0 .4 4 0 .6 Ea ster n Eas t M idland s No rth E ast Nor ther n No rth Th am es No rth W est Scot land Sout h E ast Sou ther n Sou th W est Wes t Mi dlands Wal es N orth Wa les S outh R e g io n C al o ri fi c val u e Up to 3.2% difference

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Measuring gas

• Gas meters don’t read kWh

– They measure volume

– m3_{, ft}3 _{or 100ft}3 _(HCF)

• Need to correct for

– Temperature changes

– Pressure changes

– ‘Correction factor’

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Large gas meters

• Have ‘correctors’ next to the ‘meter’

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Your gas bill…..

Shows consumption (or corrected consumption)

in ft3 _{or m}3

– May be a multiplier (e.g. x10, x100)

– Applies a standard correction factor

• if you have an uncorrected meter

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Multiplier (x10, x100)

Gas meter reading

Calorific value (MJ/m

₎

Correction factor

(for temp/ pressure - from bill)

Gas corrector reading

Multiplier (x10, x100)

Calorific value (MJ/m

)

div by 3.6 = kWh

div by 3.6 = kWh

100 ft

_{to m}

_{(x 2.83)}

100 ft

_{to m}

_{(x 2.83)}

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Example – calculate kWh from ft

• Meter readings show consumption of 12,565 ft3

• How many kWh is this?

– Conversion of 100 ft3 _{to m}3 _{= 2.83}

– Temperature and pressure conversion factor = 1.12

– Calorific value = 39.5 MJ/m3

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Answer

• Correction for temp and press

– 355.89 m3 _{x 1.12 = 398.26 ‘standard’ m}3

• Use calorific value

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About different oils

Buying different oils you must consider

• Price

• Energy value

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Comparing the cost of different fuels

Use conversion factors to calculate which fuel is cheapest

Units of purchase Cost per unit supply kWh per unit of purchase Cost per kWh Electricity kWh 8p (day) 4p (night)

Diesel / fuel oil Litre 35p

1

10.8

8p 4p 3.2p

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Application efficiency

You must also consider how efficiently the fuel is used to meet your needs

100% Boiler loss 25% ? Primary pipe Loss 10%? Distribution system Loss 10%? Application efficiency loss 10%? 55%?

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So which fuel is the cheapest?

I want to heat water - Should I use oil @ 35.6p / litre or electricity @ 4p / kWh?

• Electricity

– 100% efficiency for water heating

– 4 / 1 = 4p / kWh supplied

• Oil

– 35.6p / litre / 10.8 = 3.2p / kWh

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The efficiency rule

Real price

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Run a generator or buy electricity?

Diesel @ 36p / litre or electricity @ 8p / kWh?

• Generator efficiency = 30%

• Cost for generated electricity

– Convert litres to kWh = 36p / litre / 10.8 = 3.33p / kWh

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Remember

When choosing fuels ………..

………it is not just the cost of the fuel It is the cost of getting the result you want

– a tank of hot water?

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Calculating savings

• We buy energy

– kWh or units = kW x hours

• Energy = power x time

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Calculating savings

Saving = [current use – new use] x energy cost Example: a light bulb used for 2,000 hrs per year

– Now:100 W tungsten bulb

– Future?: 20 W compact fluorescent

Saving = [(100x2000) – (20x2000)] x (0.08/1000)

– £12.80 per year saved

– Lamp cost is £1

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Operating time is critical …

In our example ……

If the operating time was 1 hr / week

• Saving would reduce to £0.36 year

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Don’t always blame the biggest equipment

• 30 kW water transfer pump

– Used 1 hr / week

– 30 kW x 1 hour x 52 weeks x 8p /

kWh

= 1,560 kWh =124

• 500 W yard light

– Used 10 hr / day every day year

round

– 0.5 kW x 10 hours x 365 days x 8p

= 1,825 kWh = £146

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Worked example

Calculate the payback on a variable speed drive to be fitted on a water circulation pump

• Pump is rated at 5 kW

• Savings will be 25%

• Pump operates for 6,000 hours per year

• Average cost of electricity is 7p / kWh

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Answer

[(5kW x 6000hrs) – (5kW x 0.75 x 6000)] x £0.07 = £525.00

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Session 1 summary

• You buy energy to do a job

– It is the cost of doing the job that matters

• All fuels have different costs and …

– They can be compared on the same basis by converting

the cost in p / kWh

• When comparing fuels

– Consider both fuel cost and efficiency