| Home | Insulation | Conserving Energy Heating | Books | Links |
|
INTRODUCTION: By general consensus, global warming is one of the most dangerous instabilities that we are introducing into our ecosystem. So what is the relationship between global warming and the way we use energy in our homes? GLOBAL WARMING There are four main “greenhouse gases” that contribute to global warming: carbon dioxide (GO methane (CH the chlorofluorocarbons (CFCs), and nitrous oxide (N Carbon dioxide’s warming contribution is about 50%, whereas the contributions of methane, the CFCs, and nitrous oxide are approximately 18%, 14%, and 6% respectively. The surprisingly large contribution of these latter gases is due to the fact that methane is 25 times more effective than CO as a greenhouse gas, CFCs up to 10,000 times, and nitrous oxide 150 times. Nevertheless, carbon dioxide is the most important greenhouse gas, all the more so because it is integrally bound up with the carbon cycle and our use of fossil fuel in energy, transportation, and industrial applications. The amount of the sun’s energy falling on the earth has increased about 25% since the beginning of life; carbon dioxide has played an important role in moderating this increase, through its gradual absorption by plant forms, mainly in the earth’s oceans. We are now in danger of destroying this delicate natural balance by exhausting ever-increasing quantities into the atmosphere. The results could be catastrophic. During the energy crisis in the 1970s, the concern was with our diminishing reserves of gas, oil, and coal; the concern now is to reduce the quantity of CO that reaches the atmosphere: ironically, we may never be able to use our reserves of fossil fuels to the full! What can we do to halt this trend? Our daily patterns of consumption in Western “civilization” provide much of the answer. The decisions we make to boil a kettle for a cup of tea, take a bath, turn up the central heating, or drive to the supermarket all contribute incrementally to fossil fuel consumption and , hence, to global warming. We spend the major part of our time in our homes, and much of the rest we spend in our cars and trans port systems or working in factories and offices, often in order to acquire and consume even more energy goods. Estimated CO2 Emissions by End Use for US (2010)
Source: US Dept. of Energy, Energy Information Administration (Sept. 2009) The above table shows that almost one-fifth of all CO2 emissions produced in the US is caused (either directly or indirectly) by the use and misuse of energy in our homes. It is clear that the way we use energy is extremely inefficient. If all of the measures outlined in this section were carried out, the amount of CO produced by all households could be reduced by 75%. If we were also to change our lifestyle and use renewable sources of energy, we could reduce this figure still further, perhaps to as little as 5% of our original CO emissions. THE HOUSE AS AN ENERGY SYSTEM It is useful to think of the house as a total system when it comes to the way energy behaves. First we can look at the overall amount and form of the energy that is entering the house. Then we can see the ways in which this energy is being used. Lastly we can see how the resultant heat is lost to the outside:
This diagram helps us to understand what is happening in our homes, and to work out the ways in which we can reduce our carbon dioxide emissions to a minimum. The important point to notice is that a saving can be made in CO emissions at every stage in the system. This can be done by: • Choosing the sources of energy emitting the least amount of CO • Finding the most efficient ways of using the energy in our heating systems, lighting, and appliances. • Conserving the heat in our homes through draft-proofing, ventilation control, and , most important of all, insulation. These different aspects are all examined in this section, including the storage of heat energy, either in the building fabric or in hot water. (Both of these are seen as increasingly important once we are using insulation to full effect.) A further aspect of the energy equation is that used in the manufacture of building materials. This is addressed in the sections on MATERIALS. Improving the overall energy efficiency of our houses is no longer controversial. It is only a question of the resources that can be directed to the task and how far to go with each measure. This is a case where investing pays off for everyone! Sources of Energy Which sources of energy are least harmful to the ecology of the planet? It is the purpose of this section to establish an order of priority when choosing a form of energy for a particular function or appliance. The most important of the criteria to be applied will be the relative amounts of carbon dioxide (CO2 produced by different energy sources. Other environmental factors mainly involve other forms of air pollution such as sulfur dioxide (SO2 one of the causes of acid rain. This section starts with an analysis of fossil fuels, continues with a separate look at electricity, and then draws comparisons between these different energy sources. It ends with a look at renewable energy. THE FOSSIL FUELS There are three basic forms of fossil fuel: • Solid: coal and its products • Liquid: oil and its products • Gas: natural gas and liquefied petroleum gas (LPG) All fossil fuels are organic in origin, that is, they all contain carbon to a greater or lesser degree. This means that there is no way to avoid emitting CO2 when we burn fossil fuels. However, there are considerable differences in the proportion of carbon in each of these different fuels and thus in the amount of CO2 emitted. When we compare the burning of coal with the burning of oil or gas we arrive at a very interesting and relevant comparison. (It is assumed that coal is pure carbon, oil is represented by approximately one carbon atom to two hydrogen, and methane is CH4 a carbon-hydrogen ratio of 1 to 4): • Coal/coke (carbon): C • O2 = CO • Heating oil: C • 3O2 = 2CO +2H • Gas (methane): CH • 2O2 = CO • 2H If we compare the above chemical reactions we can see that the main product of combustion of coal is CO whereas with both oil and gas, water (which is ecologically neutral) is produced as well, indicating a less polluting burn. In fact, as a rule of thumb, the higher the proportion of hydrogen (a high-energy burner) in a fuel, the less harmful it is. The ultimate ecological fuel is hydrogen (in which the only product of combustion is water); there is a growing lobby for its development linked to solar power. We thus have a range of fuels with carbon (coal) at one end and hydrogen at the other. Solid Fuels (Coal and Coke): The use of coal presents us with another problem. Besides burning with the highest proportion of CO2 coal can be polluting in other ways. The constituents of coal vary enormously from anthracite, which is around 94% pure carbon, to brown coal or lignite, which contains many other compounds, including sulfur. Most of the coal in the US and UK lies somewhere between these two extremes. When burnt, not only CO2 but also sulfur dioxide (SO2 is produced; this combines with water to form sulfurous acid (H2SO3) -- main cause of both smog and acid rain. In Britain, the clean air acts of the 1950s and 1960s, which introduced smokeless fuel zones, reduced the sulfur pollution in the big cities; yet this pollution was merely transferred to the upper levels of the troposphere (the lowest layer of the atmosphere, up to 11 miles high) via the tall chimneys of coal-fired power stations and coking plants. In other words, the burning of coal went from being a local problem of smog in large cities to being the regional/global problem of acid rain. Fewer and fewer people are now burning solid fuel in their houses, for reasons of dirt, smell, pollution, inefficiency, time, and cost. This trend is likely to continue, and from an ecological point of view should not be discouraged. Burning coal in an open hearth, where 90% of the heat goes up the chimney, belongs to a bygone age. If, however, you are heating your house with one of the latest high-efficiency solid fuel boilers, you are doing less damage to the environment than if you used electricity for the same purpose. Liquid Fuel (Oil and its Derivatives): In Britain, oil had its heyday as fuel for heating during the 1950s and 1960s; a combination of the discovery of North Sea gas and then the 1973 energy crisis put an end to its popularity. If we look at the chemical reaction in the last section, we can see that, when oil is burnt, approximately one molecule of water is produced for every carbon dioxide molecule. This points to oil being a better fuel to burn than coal in terms of CO2 emissions. On average the sulfur content of oil is also considerably less than that of coal. This makes oil a more benign fuel than coal to burn in terms of acid rain and other pollutants; however, we need also to take into account the other environmental costs of extraction and transportation. The main environ mental cost of oil is that of marine pollution, which is a growing concern. Liquefied Petroleum Gas (Propane and Butane) LPG is a product of oil; it exists in two forms, propane (C: and butane (C These are both members of the paraffin series, of which methane is the first member and heating oil is about the sixteenth. Both have a carbon content closer to oil than to natural gas. Energy costs for its distribution are higher than for natural gas, and similar comments can be made about its polluting effects on the sea as with heating oil. The most interesting recent development in the use of LPGs is as a substitute for the chlorofluorocarbons (CFCs) in refrigerators. Natural Gas (Methane) Methane is the cleanest of all the fossil fuels to burn, as there are two molecules of water produced for every one of carbon dioxide. It has very few impurities and its cost in terms of extraction and distribution is only 7%, which makes it the most efficiently distributed of all the fossil fuels. This is because of the huge network of gas mains that crosses Britain. The efficiency of appliances that use natural gas can be of a very high order (as will be explained in the heating section; condensing gas boilers can extract up to 95% of the available fuel heat in peak conditions). However, there are also gas appliances with very low efficiencies, such as the coal fires with open fireplaces, where most of the heat goes straight up the chimney. Natural gas is therefore the most ecological choice among the fossil fuels, but we should use it very sparingly as we may have little more than 30 years accessible reserves. However, methane could become a renewable fuel source for the future: in China methane gas is commonly manufactured from agricultural biomass. Other nations could do the same. The other side of the coin is the fact that methane has become an increasingly serious greenhouse gas: approximately one billion tons is released into the atmosphere every year from garbage dumps and agriculture, contributing nearly 20% of global warming. If a higher proportion of this gas could only be collected and used before escaping into the atmosphere, we would be solving two serious problems at once. ELECTRICITY Electricity in cables is a very convenient way of transporting energy. It is also fundamental to the quality of modern life: it can be produced in many ways, and has many uses for which there is no substitute. It can be produced by burning fossil fuels in generators, by using rainwater and the force of gravity (hydroelectric power),by wind turbines, and directly from the sun in photo voltaic cells. It travels almost instantaneously down power lines either above or below ground. Once the electricity arrives at the place it is required, it can either be transformed into another type of energy, such as light or motive power, or used directly in computers or telecommunications. Heat is nearly always the end product of using electricity, but there is increasing (and misguided) encouragement for householders to use electricity for central heating and water heating. The charts below show just how short-sighted and unsustainable a practice this is. The percentages of electricity produced from different fuel sources in the United States (2009) are approximately as follows:
Source: US Dept. of Energy, Energy Information Administration It is possible to make a comparison between the different sources of fuel and the amount of CO produced:
From these two charts it is possible to see just how polluting electricity really is. The second chart shows that electricity produces three times the CO2 pollution that natural gas does for the same amount of heat; more than twice as much as oil and coal. If we were to compare electricity generation purely from coal we would find an even worse picture: it is only because there is considerable electricity generation from oil, gas, and nuclear power that the picture looks better. Besides the pollution from coal-fired power stations, much of the energy produced is thrown away in cooling towers. In addition there are energy losses in the national grid. It is for these reasons that the efficiency of electricity in terms of the carbon dioxide produced per kilowatt of power is so very low. ‘What then would be a positive ecological strategy for the electricity industry? The following measures would help: • Drastically reduce the use of electricity for heating except where there is absolutely no ecological alternative. • Introduce the latest energy-efficient technology in all areas of high electrical usage. The savings in energy that would result from these measures would be more than enough to enable the phasing out of inefficient existing coal-powered generating stations, and to bring the remaining power plants up to a high standard of energy efficiency and pollution control. Also, waste heat should be used for district heating where possible. • There should be massive investment in wind energy generation with a plan to replace electricity generation from carbon- dioxide—producing stations. All the above measures are technically feasible today: it requires only the political will to see them enacted. Carrying out these measures would mean that electricity users could then use electricity with a clear conscience. Paying the real price for electricity would also encourage conservation in its use and the development of more energy-efficient appliances. Electricity, as it is presently generated, is a nonrenewable energy source and the most polluting form of power in terms of the production of carbon dioxide and acid rain. It is only now beginning to be realized that the cost of conserving energy is far less than the real cost of producing it, let alone the cost of building new power stations. RENEWABLE SOURCES OF ENERGY What are the renewable sources of energy that are available to the home owner? The most obvious is that from the sun: solar energy. This is such an important energy source that it has been given a section of its own. The next most favored form of renewable energy is that of organic material in one form or another, collectively known as biomass. The burning of wood is the most common example of the use of biomass. All forms of renewable energy, except geothermal energy, are indirect forms of solar energy. Biomass stores the energy from the sun through photosynthesis. There are other ways of using biomass energy besides burning; these are mentioned below. Lastly, wind or water power from small-scale wind turbines or water turbines is available to the few people who have a suit able location and enough money for investment in the technology. Biomass Biomass is a shorthand term for organic material which can be used to create energy. Traditionally it has been the main method of heating and lighting, through the use of wood and inflammable organic matter. Now it is seen as an increasingly important way of gaining energy from organic waste without necessarily burning it. There are a number of methods for converting biomass into energy: • Direct combustion of dry organic matter. • Pyrolysis: heating organic compounds, either in the absence of air or in the presence of oxygen, water vapor, or hydrogen, to produce different gases such as methane, carbon monoxide, or hydrogen. • Anaerobic digestion: bio gas (methane) is given off when wet sewage sludge, animal manure, or green plants are allowed to decompose in a sealed tank under anaerobic (oxygen-free) conditions. • Fermentation: alcohol is produced by the fermentation of sugar solutions (sugars can be obtained from many different processes and products, even from cellulose). After fermentation the solution is distilled to extract the alcohol. A combination of these conversion methods could provide a considerable proportion of our energy requirements in the future, and could lead to the substitution of renewable biogas for natural gas. It is doubtful whether any of these methods, except the wood-burning stove, will be applicable at a domestic level, but on many farms there is a significant potential for using agricultural waste in methane digesters to meet most, if not all, of the farm’s energy needs. Wood-Burning Wood, if used in a sustainable manner, should not contribute to global warming. However, if we look closely at our use of timber on a global scale, we see that we are cutting down many times the quantity of trees that we are planting. In Britain, we are net importers of large quantities of timber. In these circumstances it is sometimes difficult to see wood as a truly renew able energy source. However, there is so much waste wood at present available that burning it efficiently can be a useful service. After all, the carbon from decaying or rotting wood eventually returns to the atmosphere as part of a natural global cycle. Burning wood just speeds up that process of return; yet we should always be careful to burn as cleanly and efficiently as possible. So, if you are using a wood stove, endeavor to feed it with scrap wood or with wood harvested selectively from a sustainable, well-managed woodlot. Wood smoke can be very polluting: the worldwide use of wood for burning contributes millions of tons of pollutants. These pollutants can be considerably reduced by careful control of your wood stove to ensure as clean a burn as possible. A few years ago, the US government’s Environmental Protection Agency (EPA) issued stringent emissions standards for all new wood stoves sold in the country. These “Phase II” standards are aimed at drastically reducing the atmospheric pollution caused by burning wood, which is particularly serious in places like Denver, Colorado. The new Phase II stoves are mainly divided into two classes, catalytic (“cat”) and non-catalytic (“non-cat”), depending on whether or not the stove design includes a catalytic converter — the same emission-control device that is required on cars. The pellet stove is an altogether different kind of wood-burning appliance that may be attractive to homeowners who don’t enjoy the mess or the labor of dealing with cordwood. Pellet stoves burn fuel pellets that are made of highly compressed sawdust and other wood by-products. These pellets burn very efficiently, cleanly, and at a steady rate, due to a screw-type mechanism that transfers the pellets from a hopper to the firebox. The main disadvantage to pellet stoves is that they are electrically driven and thus use energy (probably derived from fossil or nuclear fuel) in their operation. Another potential drawback is the fact that pellets are not yet widely avail able throughout the US and buying bags can prove expensive unless you live in a region like the Pacific Northwest, where most pellets are produced. Wind and Water The possibility of generating power from wind and water on your own land is available to very few households. However, there is often great interest in these sources, so they have been included mainly for information. It may be that in the future a suitable windmill will be designed for use on houses, but that moment is not yet here. Historically, wind and water have been important sources of energy. In the US, over 8 million mechanical windmills have been installed since the 1860s: in the 1920s and 1930s, before subsidized rural electric power lines, many of these were wind generators, each delivering 200 to 300 watts, and providing all the electrical needs of outlying farms at the time. In the 17th, 18th, and early 19th centuries in Britain there were thousands of windmills and water mills, which formed the main source of motive power. Wind energy is almost certainly the most effective way of generating renewable energy in Britain, particularly in midwinter, just when our energy requirements are at their greatest, and the amount of energy that can be harvested from the sun is reduced to almost zero. On a domestic scale, the main requirement for a successful wind turbine is having a good location to site the mast. Unfortunately, attaching one to the top of your house, unless you have a specially designed chimney stack, is not recommended because of the buffeting it will receive and the vibrations it will generate (quite apart from your neighbors’ likely concerns). At present, wind turbines are only suitable for housing with enough land and a suitable location: they need to be positioned as high as possible and away from any obstacles such as buildings and trees that would interfere with their efficiency. It is clear that not many sites in built-up areas would be suitable. Proper advice about installing a wind generator is beyond the scope of this guide. However, the following points may be helpful: • A wind turbine should almost certainly not be attached to your house, as the vibrations and noise would pose a problem unless the structure has been specially designed for it. • Nothing should interfere with maximum winds. Any tower should extend so that the turbine reaches 20 feet above any obstruction for at least 500 feet all around. This is a severely limiting condition and will preclude the use of wind power for the majority of locations. • Any wind plant should ideally be located within 100 feet of the house to reduce transmission losses. • Towers must be strongly built. • The wind should be tested for at least three months beforehand to check feasibility. It is also necessary to do a considerable amount of homework (in the absence of professional advice) if you wish to set up your own wind turbine. Opportunities for using a water turbine are even more remote for the average homeowner, since a hillside with a decent head of water, either a small amount over a long fall (for a turbine) or a large amount over a short fall (for a water-wheel), is required (see the REFERENCES and BIBLIOGRAPHY section in this guide for other sources of information). PRIORITIES FOR ACTION • When deciding on a choice of fossil fuel, choose one that produces the least amount of CO per unit of energy delivered. For most of us this will be natural gas or bottled gas. • Reduce your reliance on electricity to the minimum. On average, electricity releases up to four times the amount of CO per unit of energy delivered, as compared with natural gas. Use it only where it is the most energy-efficient choice, and in particular avoid using it for heating if at all possible. • If you use wood for heating, try as much as possible to use waste wood that would otherwise be thrown away. Alternatively, use a source from a properly managed woodlot. Also, be prepared to adjust the stove to achieve as clean a burn as possible. • Remember that the cheapest source of energy is conservation, so before investing in any more expensive form of energy collection or generation, such as photovoltaic modules or even a wind turbine, properly draft-proof and insulate your house to the maximum degree possible. Next: Draft-Proofing and Ventilating Prev: SPACE: Extensions |