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Facts and Figures for Energy Assessments

Facts and Figures for use in energy calculations

Updated 12 July, 2007
  
CO2 Emissions    Heat Units    Typical U Values
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CO2 Energy and Emissions from Common Fuels

The energy output and emissions of fuels such as coal, wood and gas vary. The figures in the following table are therefore only within about 10% in most cases. Part of the energy from burning such fuels appears in the form of steam. This part of the energy generated used to be lost in domestic applications. Now Condensing Boilers can recover some of this energy.

Fuel Unit of Supply Energy
kWh/unit		CO2
kg/kWh 		Notes
Butane LPG kg
litre		 13.7
7.8		0.23 Butane weighs 0.57 kg/litre
Propane LPG kg
litre		 13.9
7.1		0.23 Propane weighs 0.51 kg/litre
Coal kg 9 0.32  
Wood kg 4 N/A A renewable resource, if from a
sustainably managed wood source
Oil - kerosenelitre 10 0.27  
Mains Gas 100 cu.ft 31.59 0.19 The kWh/unit is for the Blewbury area
Hydrogen kg 33 DependsThe CO2 depends on the hydrogen production method
1 gram of gaseous Hydrogen at atmospheric pressure occupies 11.2 litres
Electricity kWh 1 0.43 CO2 varies with contribution of Nuclear Power
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Heat, Energy and Work Units

Force
Newton
The force required to accelerate 1 kg at a rate of 1 metre/sec/sec. The force of gravity at the earth's surface is 9.8 Newtons per kilogram.
Energy
Watt
A rate of work of 1 Joule per second.
kilowatt
A rate of work of 1000 watts.
Household
The energy of wind farms or other energy sources is often given in households. In these presentations the electrical energy used by a typical household may be assumed to be about 4700 kilowatt-hours per year - which if spread evenly over the year would be a continuous load of 0.54 kilowatts. Thus a wind farm with a peak rating of 3 megawatts, which is expected to provide an average output of 30% of peak, or 900 kilowatts, may be said to be able to supply 900/0.54 or 1666 households. This only supplies the typical electrical load of a household. A typical total energy consumption of a household, including heating by fuel such as gas, is closer to 20,000 kilowatt-hours per year.
Work
Joule
The energy expended when a force of 1 Newton moves through 1 metre.
kilowatt-hour
The energy expended when a kilowatt of energy is expended for 1 hour. It is equal to 3,600,000 Joules or 3413 BTU.
Heat

Metric units are used in the UK. The USA still uses imperial units, which can cause confusion. For example the value of U - the measure of Heat Conductance of a material - is 5.6 times greater American web sites, as they are using the Imperial unit of 1 BTU per sq foot per degree Fahrenheit, while most other sites are using the Metric unit of 1 watt per sq metre per degree Celsius. Thus a Heat Conductance of 0.56 U in a UK site will be the same as a Heat Conductance of 0.1 U in an American site.

calorie
The energy required to heat a gram of water through 1 degree Celsius at 15 degrees Celsius and standard atmospheric pressure. A calorie is equal to 4.18 Joules. The energy in food is measured in Calories, where a Calorie is 1000 calories.
U
Heat conductance of a material, the watts transferred through 1 sq metre of material, with a temperature difference of 1 degree Celsius across it. This is equivalent to 3600 Joules or 860 calories per sq metre per hour with a temperature difference of 1 degree Celsius.
Unit of Gas
The Unit of gas supply is 100 cu.ft. In the UK because of the slight pressurisation of the supply this is assumed to be 102.264 cu. ft at standard temperature and pressure. The energy in mains gas varies through small differences in composition, in the Blewbury area it is billed at 39.3 million Joules per cubic metre, as a result one Unit is assumed to supply 31.59 kWh.
British Thermal Unit (BTU) - Not now used in Britain
The energy required to heat a pound of water through 1 degree Fahrenheit, equivalent to 252 calories or 1055 Joules
Therm - Not now used in Britain
100,000 British thermal units (BTU), 105,500 Joules or 29.3 kWh. 1 unit of gas generates approximately 1 Therm of heat.
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Typical U Values

Because of the range of materials and construction used, the actual U values for each kind of material vary significantly. The following are only indicative.
Material U Value
watts/sq.metre/Deg C
Slab on Ground Floor 0.65
Suspended Timber Floor 0.21
Suspended Concrete Beam Floor 0.25
4.5 inch Thickness Brick Plastered Wall 3
9 inch Thickness Brick Plastered Wall 2.1
11 inch Brick Cavity Wall 1.35
13 inch Plaster Brick and 100 mm Insulated Cavity Wall 0.33
Can be reduced by better insulation materials
Uninsulated Ceiling Depends on construction
Plasterboard with 25 mm insulation above 1.1
50 mm insulation 0.65
100 mm insulation 0.36
200 mm insulation 0.19
Single Glazed Window - Wood frame 4.4
Double Glazed Window - Wood frame 1.9
Single Glazed Window - Aluminium frame 5.1
Solid Wooden External Door 2.1

The UK's Standard Assessment Procedure defines the following U values to be applied for new dwellings when the actual materials are not known.

Material Assumed U Value   Max Average U Value allowed
  in 2006 Building Regulations
Walls 0.35 0.35
Floors 0.25 0.25
Roofs 0.16 0.25
Opaque door 2.0
Windows and glazed doors 2.0 2.2
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