What is Energy? Session 1 1
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 1kWh = 1,000Wh etc 3
Converting J to kwh 1 kilowatt-hour (kwh) = Energy consumed by 1 kw in 1 hour 1,000 J/s x 3,600 s = 3,600,000J or 3.6 MJ 4
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..to kwh using standard tables 5
By W eight By Volum e 6 Solid fuels kw h / tonne Coke 8,278 Coal (weighted average) 7,444 Liquid fuels kw h / tonne kw h / litre Crude Oil (weighted average) 12,694 10.7 Heavy Fuel oil 11,999 11.8 Medium fuel oil 12,252 11.3 Gas/diesel oil 12,666 10.8 Kerosene 12,833 10.3 Petrol 13,083 9.6 LPG 13,722 7.4 Ethane 14,083 5.2 Gaseous fuels kwh / m3 Natural gas 11.0 Caution: Landfill gas 10.7 Depends on Sewage gas 10.7 calorific value Solid Renew ables kw h / tonne Tyres 8,888 Refuse derived waste 5,194 General industrial waste 4,444 Straw 4,166 Hospital waste 3,889 Industrial wood (pallets e.t.c) 3,305 Domestic wood (logs) 2,778 Municipal soild waste 2,639 Poultry litter 2,444
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 Gas calorific value expressed in MJ/m 3 7
8 GrowSave Event Variation in calorific value by region 40.6 40.4 40.2 40.0 39.8 39.6 39.4 39.2 39.0 38.8 38.6 Calorific value Eastern East Midlands North East Northern North Thames North West Scotland South East Southern South West West Midlands Wales North Wales South Region Up to 3.2% difference
Measuring gas Gas meters don t read kwh They measure volume m 3, ft 3 or 100ft 3 (HCF) Need to correct for Temperature changes Pressure changes Correction factor Calorific value then applied 9
Large gas meters Have correctors next to the meter These adjust the volume for temperature and pressure 10
Your gas bill.. Shows consumption (or corrected consumption) in ft 3 or m 3 May be a multiplier (e.g. x10, x100) Applies a standard correction factor if you have an uncorrected meter Uses a calorific value to work out kwh 11
Gas meter reading 100 ft 3 to m 3 (x 2.83) Multiplier (x10, x100) Gas corrector reading 100 ft 3 to m 3 (x 2.83) Multiplier (x10, x100) Correction factor (for temp/ pressure - from bill) Calorific value (MJ/m 3 ) div by 3.6 = kwh Calorific value (MJ/m 3 ) div by 3.6 = kwh 12
Example gas bill what can you tell me? 13
Example calculate kwh from ft 3 Meter readings show consumption of 12,565 ft 3 How many kwh is this? Conversion of 100 ft 3 to m 3 = 2.83 Temperature and pressure conversion factor = 1.12 Calorific value = 39.5 MJ/m 3 1 kwh = 3.6 MJ 14
Answer Convert to HCF 12,565 ft 3 / 100 = 125.65 HCF Convert to m 3 125.65 HCF x 2.83 = 355.89 m 3 Correction for temp and press 355.89 m 3 x 1.12 = 398.26 standard m 3 Use calorific value 398.26 x 39.5 = 15,731.28 MJ Convert to kwh 15,731.28 MJ / 3.6 = 4,370 kwh 15
About different oils Buying different oils you must consider Price Energy value Suitability 16
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 LPG Litre 26p Mains gas Therms 75p 1 10.8 7.4 29.31 8p 4p 3.2p 3.5p 2.7p 17
Application efficiency You must also consider how efficiently the fuel is used to meet your needs 100% Boiler loss 25%? Primary pipe Loss 10%? 55%? Application efficiency loss 10%? Distribution system Loss 10%? 18
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 55% efficiency for water heating 3.2 / 0.55 = 5.8p / kwh supplied In this case electricity is cheaper 19
The efficiency rule Real price = Purchase price Efficiency of use (as a decimal) 20
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 Apply efficiency factor = 3.33p / 0.3 = 11.1p / kwh Excludes capital & maintenance costs Don t generate buy! 21
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? a greenhouse temperature of 20 o C? 22
Calculating savings We buy energy kwh or units = kw x hours Energy = power x time A 10 kw motor running for 5 hours = 50 kwh 23
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 Payback less than 1 month 24
Operating time is critical In our example If the operating time was 1 hr / week Saving would reduce to 0.36 year Payback would increase to 3 years 25
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 26 The larger piece of equipment used less
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 Drive cost is 1,500 27 Calculation is: (old technique use new technique use) x cost of energy = saving
Answer [(5kW x 6000hrs) (5kW x 0.75 x 6000)] x 0.07 = 525.00 Payback time = 1500/ 525 = 2.85 years 28
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 To calculate savings: (old technique use new technique use) x cost of energy 29