Heating efficiencies and greenhouse emissions

Heating energy sources discussed include: electricity, coal, gas, firewood, and oil. Methods of electrical generation discussed include: biogas, biomass, coal, nuclear, oil, gas, wind, solar heat, solar photovoltaic, and hot dry rock. Electrical heating methods discussed include reverse cycle air conditioning (heat pump) and heat bank as well as the more obvious ones. Always remember that warming a room requires much less energy than warming a whole house and warming a person within a room requires much less energy than warming the whole room. I want to make this site as useful, informative, and correct as possible. If you believe I've missed an important home heating method here, or if you think I'm wrong on some point, I'd be very pleased to have your comments.

Contents Major sections on this page are... Heating: characteristics Table 1 Coal | Electricity | Firewood | Gas | Oil Electricity generation: methods Table 2 Biogas | Biomass | Coal | Hot dry rock | Hydro | Nuclear | Oil | Solar photovoltaic | Solar thermal | Wind Electrical heating: methods Table 3 Simple radiator | Oil filled convection heater | Fan heater | Heat bank | Reverse cycle air conditioner General notes Table 4 Glossary Misconceptions Link Acknowledgements Index

Some related pages... Passive temperature control in buildings Pros and cons of various methods of generating electricity Fuels compared Climate change More related pages are below...   Search these pages

This page uses several technical units. Energy units, definitions and conversions are available on an additional page. Table 1 Various forms of home heating: greenhouse emissions, other pollution, efficiency, and sustainability compared Also see energy cost calculator to help calculate the cost of your heating energy.

Fuel	Greenhouse emissions	Other pollution	Efficiency	Sustainability
Coal	High; large production of CO2. Coal is mainly carbon. Burning one tonne of carbon produces about 3.7 tonnes of carbon dioxide.	Smoke can be a problem, especially in cities. In an efficient stove, burning high quality coal and run correctly, there should be little smoke. Some coal contains sulphur and mercury, which produce toxic gasses when burned. The ash contains toxic substances that can leach into streams and groundwater.	An open, old-style, fireplace is probably no more than 15% efficient, a well designed stove is 50% to 70%; possibly 80% when new.	Not sustainable. Coal is a fossil fuel.
Fuel	Greenhouse emissions	Other pollution	Efficiency	Sustainability
Electricity	Depends entirely on how the electricity is generated, see Table 2.	No pollution where the electricity is consumed, but possibly major pollution where the electricity is generated.	100% or better in the home, but the inefficiency is in the electricity generation process. Methods of electrical heating are discussed in Table 3.	Depends entirely on how the electricity is generated.
Fuel	Greenhouse emissions	Other pollution	Efficiency	Sustainability
Firewood	Carbon dioxide is released, but so long as trees are planted at the same rate as they are burned there is no net increase in greenhouse carbon dioxide.	Smoke can be a problem, especially in cities. In an efficient stove, burning dry wood and run correctly, there should be little smoke. Ash must be disposed of.	Similarly to coal fired heating, an open, old-style, fireplace is probably no more than 15% efficient, a well designed stove is 50% to 70%; possibly 80% when new. Wood pellet burning heaters can also be highly efficient.	Fully sustainable, so long as trees are planted at the same rate as they are burned. See also notes on gathering firewood.
Fuel	Greenhouse emissions	Other pollution	Efficiency	Sustainability
Gas	Carbon dioxide in released. Moderate amounts if natural gas, large amounts if 'town gas'.	Little pollution of consequence outside the house, but if burned in an un-flued stove they can release the highly toxic carbon monoxide and oxides of nitrogen inside the house.	Non-flued types are 100% efficient in that all the heat is retained inside the house; flued types should be 50% to 70% efficient.	Not sustainable. Gas is a fossil fuel, whether the gas is 'town gas' or natural gas.
Fuel	Greenhouse emissions	Other pollution	Efficiency	Sustainability
Oil	Poor (better than coal, marginally worse than natural gas)	Little air pollution, may be some SO2 depending on the oil.	Around 50% to 70% if working well.	Not sustainable, oil is a fossil fuel.

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Table 2

Methods of generating electricity: greenhouse emissions, other pollution, efficiency, and sustainability compared.

Table 3

Methods of home heating using electricity

Thanks to Australian Consumer's Association (Choice) for this illustration. It represents a room in cross section. "This heat map of a test room clearly shows the stratification effect created by a convection heater when there's little air movement in the room: the yellow bar at the ceiling represents about 22°C, the purple bit (where your cold feet would be) about 14°C." It is important to consider where the heat from a heater will go; warm air rises, cold air falls.

Item	Comments
Biogas	Organic matter confined in an environment with little oxygen (as in a landfill rubbish dump) will rot and produce methane gas. The methane can be collected and burned to generate electricity. Methane, generated by methods such as this, is called biogas.
Coal	There are different types of coal ranging from lignite to anthracite. Lignite contains 60 to 75% carbon, anthracite 90 to 98%. Coals may also contain high percentages of water, which makes them less valuable as a fuel, especially if the water is saline. The water must be removed before the coal can burn. If heat from burning the coal is used to 'boil off' the water, there is a corresponding decrease in the efficiency of the power station. Sodium contained in salt can cause clogging in the combustion chamber. Coal may also contain sulphur which becomes sulphur dioxide when burned. In turn, sulphur dioxide becomes sulphuric acid after reacting with water in the atmosphere; this is one of the chief causes of acid rain. Coal can also contain significant amounts of the toxic heavy metal mercury, which can be released into the atmosphere when the coal is burned.
Cogeneration	Waste heat from industrial processes, or from thermal power stations, can be used for other purposes. In some cases more electricity may be generated, the heat could be used for community heating, or it might be used for desalination. Cogeneration can increase the effective efficiency of electrical generation from the typical 33% of fossil fuel power stations to 50 or even as high as 84%. (The 84%, or 314 kgCO2/MWh, has been achieved in Australia; from AGO).
Combined cycle	An electrical power generation system where a flammable gas is burned to power a gas turbine and then the heat from the burned gas is used to produce steam which drives a steam turbine to generates more electricity. The flammable gas may be produced by the gasification of coal, or it may be natural gas, biogas, etc.
Efficiency	The efficiency of a method of producing electricity is important when fossil fuels are being burned for energy because of the link between energy output and carbon dioxide output. The more efficient the method, the more energy per kilogram of carbon dioxide produced. However, efficiency of greenhouse friendly methods of producing electricity, eg. wind power, generally has no such connection to any form of pollution.   Home Top Contents Index The efficiency of fossil fuel electrical generation methods can be expressed in two main ways: Efficiency of conversion of the heat of combustion into electricity; Electricity output per unit of carbon dioxide produced. The latter method is used when greenhouse is the main concern.
Gathering firewood	How the firewood is obtained is of great environmental importance. Cutting forest or scrub removes habitat, can increase the likelihood of flooding, and can cause loss of biodiversity. Even collecting dead wood removes habitat because many macro and micro organisms live in rotting wood. Cutting down old trees containing hollow limbs removes nesting sites for birds and 'homes' for other animals. You could also see my notes on firewood in its relationship to greenhouse, overpopulation, exercise, and environment.
Geosequestration	As applied to the energy industry geosequestration is the deep burial of carbon dioxide. It is most talked about today as a potential means of stopping the carbon dioxide produced by fossil fuel fired power stations from entering the atmosphere. (Carbon dioxide is the major man-made greenhouse gas.) Geosequestration of carbon dioxide is entirely unproven on a commercial scale. Cost estimates vary around US$40 to US$60 per tonne (or US$50 to $100 per megawatt hour of electricity produced). Note that geosequestration does not destroy the carbon dioxide, it only removes it from the environment; hopefully, for a very long time. Also see Sequestration and Geosequestration on my Greenhouse page.
Geothermal electricity	This is generated by tapping naturally occurring steam from volcanic areas. In regard to greenhouse and other environmental concerns, it is very similar to hot dry rock.
Green electricity	Many electricity retailing authorities offer 'green' electricity for sale. Consumer who buy green electricity pay a premium on the price for non-green electricity. For every kilowatt hour of green electricity that an electricity retailer sells, it is committed to buy a kilowatt from a an electrical generator that produces power by a greenhouse friendly method; that is, by a method that does not produce greenhouse gasses. It is also usual that these producers must not use any method that causes significant environmental damage of other types.
Heat bank home heaters	These could theoretically be adapted to 'green' energy systems where the electricity is generated, and the heat bank heated, when the wind blows or when the sun shines. The heat could then be released into the home at some later time, when required. However, the sun often does not shine much at the time of year when home heating is required, and the wind may not blow for several days at a time. I suspect, therefore, that larger heat banks would be required than those found within the types of heaters contained within the living parts of homes. A suitable large capacity heat bank could be a water tank beneath the floor of the house.
Shale oil	Shale oil is oil that can be extracted from shale by mining a shale that is saturated with oil and roasting it at about 500 degrees Celsius to extract the oil. The roasting process generally involves burning oil that has previously been extracted from the shale, so shale oil results in a very large net level of carbon dioxide release to the atmosphere. It is one of the most greenhouse polluting and least desirable forms of fossil fuel from an environmental point of view.
Smoke	Smoke from coal and wood fires contains policyclic aromatic hydrocarbons (PAHs). These are carcinogens, and are very slow to be broken down by micro-organisms. While in the atmosphere they may be gradually broken down by ultraviolet light. You could also see my notes on firewood in its relationship to greenhouse, overpopulation, exercise, and environment.
Uranium as a fuel	Current nuclear power stations can consume only the U235 isotope of uranium. This makes up only 0.7% of naturally occurring uranium; most of which is U238. It is possible to convert U238 into plutonium (Pu239) in what is called a fast breader reactor. This Pu can then be used to produce power in much the same way as U235. However, Pu can, if stolen, be used by terrorist to make nuclear bombs; so having many tonnes of Pu in many places around the world would be a hazard. Proposed ' fast ' reactors, combined with a fuel reprocessing method that does not separate plutonium 239 from other transuranic elements and isotopes, can use most of natural uranium.

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Term	Description
AGO	Australian Greenhouse Office AGO
Bagasse	Plant residue after the primary product has been extracted. For example, the grape mark remaining after the juice has been extracted for wine making, or the sugar cane pulp residue after crushing.
Biomass	As used here, any matter of recent biological or organic origin. For example, forestry waste, bagasse, much of domestic refuse, garden waste.
Greenhouse intensity	In the electricity generating industry this is the amount of carbon dioxide released into the atmosphere for each unit of electrical energy generated. For example, in combined cycle gas fired power stations the greenhouse intensity is typically around 0.4 Mt CO2/TWh (equivalent to 0.4 tonnes of CO2/MWh). Coal fired power stations do much worse at around 1 Mt CO2/TWh
H	Hydrogen
CO2	Carbon dioxide is one of the main greenhouse gasses in the Earth's atmosphere. It is also the major cause for greenhouse warming. See also methane. Carbon dioxide has a much longer residence time in the atmosphere than does methane. Burning 1 tonne of carbon produces about 3.7 tonnes of carbon dioxide.
CO	Carbon monoxide is an odourless gas that is highly toxic. It can be produced by partial combustion of carbonaceous material in an environment having insufficient oxygen for full combustion.
Fossil fuel	A fuel that formed from the remains of plant and/or animal matter millions of years ago and has been mined from the earth. The rate of replenishment is virtually zero.
Isotope	A form of a chemical element having a different atomic mass to other isotopes of that same element, but almost indentical chemical properties.
Magnesite	A mineral composed of magnesium carbonate. As thermal capacity is generally greater in elements with lower atomic numbers, and magnesium, carbon, and oxygen have fairly low atomic numbers, one would expect the thermal capacity of magnesite to be quite high. It also can be heated to high temperature without damage.
Methane	CH4. A highly flammable organic gas. Per kilogram methane is a much more effective greenhouse gas than is carbon dioxide. Methane has a shorter residence time in the atmosphere than does CO2.
Natural gas	Piped or compressed natural gas (CNG) is a mixture mainly of methane and ethane. Liquified natural gas (LNG) is mainly propane, butane and probably pentane. All of these are fossil fuels which are drawn from wells.
N	Nitrogen
NOx	Nitrogen oxides. A toxic gas, and one that is involved in acid rain.
Passive solar heating	The heating of a home by maximizing the use of sunshine. Generally it is combined with appropriate insulation, some sort of passive heat storage medium and control of sunshine in summer.
Photovoltaic	The direct conversion of light into electricity, using a 'solar panel'.
SA EPA	South Australian Environmental Protection Authority
SO2	Sulphur dioxide. This gas is corrosive. If released into the atmosphere it eventually changes to sulphuric acid, the main cause of acid rain. This has lead to the wide-spread acidification of lakes and loss of forest.
Thermal capacity	The amount of heat required to raise a unit mass of a substance by a unit of temperature. Put simply, the amount of heat that can be stored in something when it is heated.
Thermodynamics, first law	The conservation of energy, which states that energy cannot be created or destroyed, but only converted from one form to another.
Thermodynamics, second law	When energy is transformed from one form to another, it tends to flow from a higher grade or more ordered form - such as mechanical, electrical energy, chemical or high-temperature heat - to a lower-grade or more disordered form, ultimately low-temperature heat. So energy becomes degraded and less useful to humans. It is possible to reverse this natural flow, pushing low-grade energy 'uphill', but only by expending more high-grade energy at the input than is received at the output.
Town gas	Also known as producer gas. A mixture mainly of CO and H, but also the nonflammable CO2 and N, produced in a process that involves the partial combustion of carbonaceous substances, usually coal, in an atmosphere of air and steam. It has a lower heating value than natural gas.

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