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Renewable Energy - The Green Alternative Way to Heat your Home


Renewable energy is usable energy from resources such as sun, wind and water. These, and others, are resources which are naturally replenished.


Wood-Burning Stoves and Fireplaces

For centuries people have burned wood to heat their homes. Wood is traditionally an abundant resource, simple to use and it produces plenty of heat as it burns. The wood-burning stoves and fireplaces many of us still use in our homes are based on technology that has remained unchanged for many decades. But, in these days when most of us are conscious of the effect of our carbon footprint, is this the most efficient way to heat our homes?


Older wood-burning stoves and fireplaces

The concern with many of the older models of stove and fireplace is that they are particularly energy-inefficient and invariably a source of pollution. This leads to higher energy bills, inefficient use of our precious fuel resources and higher levels of atmospheric pollution. Smoke pollution also affects our homes and can be a cause of health problems. According to the United States Environmental Protection Agency (EPA) wood smoke pollution ‘has been linked to cancer, asthma and other serious health conditions.’

Open fireplaces are particularly energy-inefficient, as most of the heat produced is lost up the chimney. We all love to see a roaring log fire, but as a means of heating your home an open hearth is inefficient, fuel-hungry, expensive and produces high levels of emissions. You should also pay attention to the quality of fuel that you burn: dry, seasoned wood burns far more efficiently than newer wood with a higher moisture content, and it produces less pollution too.


Newer wood-burning appliances

These are much more energy-efficient than previous models which means they reduce fuel costs and produce far less smoke and dust pollution. The newer high-tech wood-burning stoves are up to fifty percent more energy efficient than older versions and can produce the same heat as a comparable older model while using one third less fuel. In addition they result in far less creosote build-up in the flue, which lessens the risk of chimney fires and reduces cleaning costs.

Replacing your old wood-burner or fireplace with a newer model of stove will result in a number of environmental benefits too. Newer stoves combust their fuel more efficiently, which means it burns at a higher temperature thus reducing levels of CO2, black carbon and methane emissions. Less smoke pollution reduces the risk of smoke-related illnesses among the general population which in turn reduces the nation’s health-care bill.


Gas Boilers

The cost of providing heat for our homes, particularly during the cold UK winter, makes up some sixty percent of the average household’s fuel bill. It is, therefore, important that we use efficient forms of heating. Gas boilers are the most popular source of domestic heating and hot water in Britain and the efficiency of the system we use is very much related to the age and type of boiler we have installed.

A modern condensing boiler is the most efficient way of heating your home with gas. In fact, the Energy Saving Trust estimates that if every UK household using gas or oil for heating were to install a modern condensing boiler with heating controls, the national saving in fuel-efficiency would be enough to heat just short of 1.9 million additional homes. In terms of carbon footprint, this would save some 6.7 million tonnes of CO2 emissions.


Types of Gas Boiler

In simple terms, a gas boiler burns the gas as a fuel to heat cold water via a heat exchanger. The hot water is then pumped to circulate within the home to heat the system’s radiators and to provide domestic hot water.


Condensing boilers

By far the majority of boilers installed these days are condensing boilers. A condensing boiler operates on the principle of reusing heat that would have otherwise been wasted in previous systems. This makes it a particularly energy-efficient way to heat your home and provide hot water. In simple terms a condensing boiler has a second heat-exchange unit which extracts further heat from the hot gases within the boiler. This can make a condensing boiler up to ninety percent efficient in terms of using the heat it generates. There are three major types of condensing boilers: the combi boiler, heat-only (or ‘conventional’) boiler and the system boiler.


Combi boiler

Combi boilers are currently the best-selling variety of gas boiler in the United Kingdom. They operate by providing hot water on demand. Water is drawn directly form the mains and quickly heated once a tap is turned on, which means the household can enjoy limitless instant hot water. Installation is straightforward as all the parts of the boiler come as a single unit. Also there is no need for a cold water tank or cylinder. Combi boilers can produce nine to eighteen litres of hot water per minute and are a good, economical choice for a smaller home.

There are one or two disadvantages with the combi boiler and these become particularly relevant if one is considering installing one in a larger home. A combi boiler can only deliver maximum water pressure to one tap at a time. In a home with more than one bathroom this could be a problem if two or more baths or showers are used at the same time. The nature of the way a combi boiler heats up water means that there is a delay before the hot water starts to flow from the tap. This can mean that it takes a long time to fill a bath and that a power shower cannot be operated. One final disadvantage is that a combi boiler cannot be combined with an immersion-heater, which means the household has no back-up system should the gas boiler fail.


Conventional boilers

These are also known as ‘heat-only’ boilers and until the last ten years or so were the most common form of gas boiler installed in British homes. A conventional boiler provides direct heat to your home’s radiators and water for domestic use is heated and stored in a hot-water cylinder. This means you can run several hot water taps at once which makes this type of boiler especially suitable for a larger home.
The disadvantage of a heat-only boiler is that the amount of hot water available is limited by the size of the hot-water storage cylinder. Also, unless it is exceptionally-well insulated, it loses heat from the cylinder, which is wasteful, and the whole system takes up more space than a combi boiler.


System boiler

A system boiler is particularly suited to a larger home with a high-demand for hot water. Like a conventional boiler, it works on the principle of stored hot water. However, with a system boiler many of the heating and hot-water system components are built in to the set-up, which saves space and makes installation easier.

The chief advantages are having a storage tank of hot water which means several taps can be run at once, a pump is incorporated into the boiler which gives a quicker response and lower running costs and it removes the need for a loft-based feed and expansion tank. On the negative side a system boiler takes up more space than a combi and the amount of hot water immediately available is limited by the size of the cylinder. Also, unless the hot-water cylinder is well-insulated, it is liable to lose heat.


Oil Boilers

Some 1.5 million homes in the United Kingdom use oil for their central heating. This figure has the potential to rise as it is still the case that upwards of four million, mainly rural, households are not connected to the mains gas network.

Most oil-fired boilers installed today are of the condensing type. Depending on the type selected, they can be sited internally, in a kitchen or utility, or externally in a ‘cabin’. Whatever boiler you choose, you have to provide somewhere suitable to site the system’s oil tank.

Oil boilers are very efficient, with modern condensing boilers achieving efficiencies of ninety percent or more. Traditionally oil has been a relatively expensive fuel, with price spikes caused by political uncertainties and increases in demand in severe weather. In 2014 prices reached their lowest level for many years, but there is no guarantee this will continue.

One of the major disadvantages of an oil boiler is the requirement to have the fuel delivered by road. This means that, unless one carefully monitors fuel levels, there is always the danger one could be left without oil while awaiting a delivery. Most systems also require an annual service of the tank and boiler.


Electric Boilers

Traditionally domestic heating fuelled by electricity operated in very different ways from systems based on other fuels, such as oil and gas. Electricity was used for storage-radiator and warm air systems. The advantage of such systems is that running costs are relatively competitive as they make use of reduced-rate, off-peak electricity tariffs.

Warm air systems, however, are not very effective during particularly cold periods and the disadvantage of storage heaters is that they are not very responsive. In other words one has to have them on all the time or not at all.

More recently, however, new electric-powered boilers have begun to come onto the market. In terms of function they are directly comparable with gas and oil boilers, but they take up very little space and make use of cheap-rate electricity. One unique feature is that they are relatively silent when operating. Electric boilers are potentially a good choice for homes with no mains gas supply.

But there are disadvantages to this form of fuel. Firstly there is cost: running costs at the present time are slightly higher than other forms of fuel. Secondly, if one lives in a part of the country where power cuts are not uncommon, and this can be the case in some rural areas which also have no mains gas, one’s heating system can be vulnerable to outages. In terms of the environment, electricity is a very clean fuel at the end-user level with no harmful CO2 emissions. However, most UK electricity is still generated from carbon-producing fossil fuels so the net effect is no better than gas or oil.


What are the Alternatives?

In the last two decades worldwide economic changes and technological improvements have made a number of alternatives to traditional fossil fuels a much more viable option.


Renewable Energy

The gas and oil many of us use to heat our homes are fossil fuels and, indeed, much of the electricity we currently use in the UK comes from burning this type of fuel too. There are two problems with fossil fuels. One is that they are a finite resource. To put it bluntly: when they’re gone they’re gone forever. Secondly, burning fossil fuels produces CO2 which is then discharged into the atmosphere. The vast majority of climate scientists now assert that it is human activity, and in particular producing greenhouse gases from fossil fuels, that is the cause of global climate change and all its negative effects.

Renewable energy, on the other hand, is a resource which constantly replenishes itself and, in most cases, does not produce any pollutants. Examples of renewable energy sources include solar, wind, wave, tidal, hydro-electric and geothermal power. These are all clean energy sources too. Biomass and wood are also renewable sources of power if there is controlled replanting of the crops and trees used. These two fuels, however, have issues with pollutants and greenhouse gases when they are burned for power.


Air Source Heat Pumps

Air source heat pumps (ASHPs) are a clean, renewable source of hot water and household heating that can be installed and operated in your home. Essentially the device extracts heat from the surrounding air and uses it to provide domestic hot water and to power radiators or other home heating systems. An ASHP needs electrical power to operate, but typically it produces 1.5 to three times more heat energy than electrical power consumed.


How does an air source heat pump work?

The device extracts heat from the air and absorbs it into a fluid. This is then passed through a compressor which causes the temperature of the fluid to be increased to a level where it can heat water or air for household use. Air-to-water systems operate with a ‘wet’ central heating system and provide heat to your radiators or underfloor heating together with domestic hot water. Air-to-air systems provide the heat for warm-air heating systems, but generally not hot water.


What are the practicalities?

Your ASHP needs to be sited outdoors, usually on the rear or one of the side walls of your home and the pump needs an electrical supply to operate. Whilst they can operate to maximum efficiency when the ambient temperature is higher, ASHPs still work even in sub-zero temperatures. For heating your home with an air source heat pump, you are best to select either underfloor-heating or radiators that are much larger than average. This is because the water is not heated to as high a temperature as that achieved by a conventional boiler, a greater surface area is needed in order to achieve a comfortable room temperature.

For maximum efficiency an ASHP will work best in a new build property because of the higher insulation standards present when compared with older properties and because it gives the opportunity to include underfloor heating in the initial building specification. The current advice from the Consumers’ Association is that you will achieve greater savings from installing an ASHP to replace an oil, electric, LPG or solid fuel system than you would by replacing gas. Renewable Heat Incentive (RHI) payments are currently available for people converting to ASHP.


Tell me about the pros and cons

Air source heat pumps use a renewable energy source and produce no greenhouse gas emissions. They are relatively straightforward to install and require very little maintenance. On the negative side you will need enough space to install a unit on the side of your house and the condenser can be quite noisy when running. Obviously they are not completely carbon-neutral, as the pump requires mains electricity to operate.


What are the costings?

The Energy Saving Trust (EST) estimate that the cost of installing an ASHP system comes in at between £7,000 and £11,000. The period time to recoup this initial investment and to start makings net savings will vary according to the running efficiency of your new system and the costs of your old heating source. However, the EST have estimated some typical annual savings for a four-bedroom detached home with a new ASHP system:
  • If replacing a non-condensing oil boiler savings of between £360 and £555 a year;
  • If replacing a non-condensing LPG boiler savings of between £1,200 and £1,805 a year; and
  • If replacing an electric storage heater system savings of between £715 and £1,295 a year.
In addition to these savings, you might also receive between £905 and £1,365 a year from Renewable Heat Incentive payments.


Ground Source Heat Pumps

Ground source heat pumps (GSHPs) draw in heat from underground and use it to provide heating and hot water for your home.


How does a ground source heat pump work?

A network of pipes are buried in the garden of your property. A mix of antifreeze and water is pumped around this loop and this absorbs the naturally-occurring heat from the ground. Below the surface the ground remains at a fairly constant temperature so the GSHP can be used throughout the year. The heat from the ground-loop fluid is transferred to your domestic heating and hot-water system via a heat exchange unit and a pump is used to circulate it through your home.


What types of pump are available?

A number of factors affect the choice of ground source heat pump for your property. These include soil type, climate and access. There are two major system types: closed-loop and open-loop. A closed-loop system circulates its own fluid through a network of piping absorbing ground- heat as it does so. An open-loop system draws in well or surface water and circulates it through the GSHP. The water is then returned to its source. The choice of available systems includes:

Horizontal – This is a closed-loop system. It is the most effective type in a domestic setting, particularly for new-build properties. However, as the loop is laid-out horizontally in four-foot trenches, the property needs to sit in a sufficiently large plot to make this possible.

Vertical – Another closed-loop system, this is most commonly used in commercial buildings or homes sitting on small plots. The loop is stretched out into a vertical bore-hall, sometimes as far down as the bedrock. It is a more expensive system to install, but causes less upheaval to the surrounding landscape.

Pond/Lake – Again, this is a closed-loop system. Where a building has a sufficiently large lake or pond nearby, the loop of piping can be laid along its base at a depth of a least 2.5 metres. This is a cheaper option than excavating the land adjacent to the building.

Open loop systems – This system replaces the normal heat-exchange fluid with well or ground water from the surrounding land. The system relies on there being sufficient clean water available and compliance with strict environmental regulations.

Hybrid Systems – Some of the most promising research in the GSHP field is now looking at hybrid systems. These combine ground source heat pumps with conventional central heating systems and hold out the possibility of cheaper, more efficient domestic heating and hot water.


What are the practicalities?

You will need a garden of sufficient size to take your ground-loop and access to the garden area for the digging machinery. The extent of the ground-loop depends on the size of your property and your heating and hot water requirements. In some cases, where the garden is small, a vertical bore can be constructed.

Your GSHP will heat the water in your domestic system to between 1.5 and four-times that of the ground temperature. The resultant heat then circulates around your home by means of either radiators or underfloor heating. Since the central heating water in a GSHP is generally heated to a lower temperature than is the case with gas or oil, your radiators will not feel as hot to the touch. For maximum effectiveness, you will need to keep your central heating on all the time in winter and you may wish to have some form of back-up heating available.


Tell me about the pros and cons

The chief advantage of a ground source heat pump is that it uses a renewable source of energy and produces far less greenhouse gases than a conventional heating system. While the system uses mains electricity for the pump, the amount of electrical energy consumed is far less than that of the heat energy produced. A GSHP will help you achieve substantial savings on your annual fuel bill and you may also be entitled to grants under the Renewable Heat Incentive (RHI) scheme.

The most significant disadvantage, however, is the cost of installing a GSHP system, which can be upwards of £11,000. Furthermore, the process of installing a system can be quite disruptive and may require planning permission. For this reason, a GSHP is often a better choice for a new-build property rather than an existing one.

In terms of heating your home, a GSHP system operates best with underfloor heating. People who convert from a gas boiler to GSHP often find that, because the radiators operate at a lower temperature, they need to run some form of supplementary heating in winter. Finally, although a GSHP will substantially reduce your home’s carbon-footprint, it cannot be classed as a truly renewable source of energy as it needs the input of mains electricity.


What are the costings?

Depending on the size of the system you require, it typically costs between £11,000 and £15,000 to install GSHP. If you wish to operate an underfloor heating system this will be an additional installation cost. According to the Energy Saving Trust, installing a GSHP will bring you savings of between £410 and £2,000 a year, depending on the system you previously used. Grants from the RHI scheme can bring in an additional £2,610 to £3,940 per year for a typical four-bedroom detached home.


Debunking the myths

Some myths have grown up around geothermal heating options, usually repeated and passed on without really looking more closely at the facts that are available. Some people will argue that GSHPs should not be regarded as renewable energy technology as they use electricity, that they are noisy and that they pose a danger to ground-water quality. In reality GSHPs use only one unit of electricity to create five units of heat, they produce no more noise than a conventional central heating system and there is absolutely minimal risk of any leakage of heat-exchange fluid into the ground-water.


Solar Water Heating

A solar water heating system is a form of renewable energy technology which uses energy from the sun to provide domestic hot water. The system should not be confused with photovoltaic panels (PV). PV produces electricity, whereas solar heating panels produce hot water. Homes with a sufficiently large roof can have both systems in place if they wish.


How does solar water heating work?

The system uses solar panels fitted to the roof of your house which harvest solar energy to heat up water. The hot water is then stored in a tank or cylinder to be drawn on for domestic use. In temperate countries, such as Britain, you may wish to choose to add a conventional boiler or immersion heater to the system to make the warm water hotter or to use on days when very little solar energy is available.


Active solar water heating systems

There are two types of active solar water heating systems. Direct circulation systems will pump domestic water through the panels and back into your home. These are best-suited to warmer climates. Indirect circulation systems, on the other hand, use a heat-transfer fluid and heat-exchange unit. The latter are best suited to cooler climates where there is a risk of freezing.


Passive solar water heating systems

Passive systems are cheaper than active ones, but are generally not as efficient. However, they tend to be less prone to problems and often last longer. There are two types of passive systems: integral collector-storage and thermosyphon systems.


Storage tanks and solar collectors

Your solar water heating system will require a storage tank with a high-level of insulation to ensure it operates efficiently. Some systems have an additional pre-heating tank. Whichever model you choose, you need to ensure that you have sufficient loft space for the cylinder.

Three types of solar water heating collectors are commonly used: evacuated tubes, flat-plate collectors and integral storage-collectors. Flat-plate collectors can be integrated into the structure of your roof or fitted to the tiles. Evacuated tube systems utilise a series of glass tubes and, generally speaking, operate more efficiently than flat-plates. Integral storage-collectors are more suitable for warmer climates as freezing will prevent them from operating.


Selecting a solar water heater

There are a number of factors to consider when choosing a solar water heating system. Firstly you need to look at your household and estimate your hot-water requirements. This will determine the capacity of the system you need. Secondly, you should look at your location and calculate how much solar energy is potentially available. This will include not just climate but which way your roof orientates. You should also look at whether there are any local planning issues or restrictive covenants.

With this information to hand, you can determine whether or not solar water heating is the right option for your home and, if it is, which system suits you best.


Installing and maintaining the system

Solar heating panels should always be fitted by a specialist company. All systems will need regular maintenance, though passive systems need attention less frequently than active ones.


What are the benefits of solar water heating?

Sunlight is the ultimate source of all of our energy. Solar water heating is, therefore, a primary renewable energy option. With a back-up system in place, solar water heating will provide your home with hot water throughout the year, even in the more northerly parts of the United Kingdom. You will also make substantial annual savings on the cost of your hot water usage.


What are the costs and savings?

A typical system will cost between £3,000 and £5,000 to install. Savings on the cost of your hot water requirements will vary from season to season, with lower savings in the winter months when less solar energy is available. Overall, the Energy Savings Trust (EST) estimates that the average household will save between £60 and £70 per year depending on the type of system they are replacing. You may also qualify for payments under the government’s Renewable Heat Incentive scheme. The EST estimates that payments would be in the range of £195 to £470 a year depending on the size of your household.


Thermal Stores

Thermal stores are becoming increasingly popular for use with a number of different domestic renewable energy systems as a means of storing excess heat generated by the system. They can also be used with conventional boilers or immersion heaters.


How does a thermal store work?

The thermal store is a way of storing heat until it is required. The technology makes use of a well-insulated tank to hold the hot water and a heat-exchange unit to access the stored heat. The thermal store may also include an immersion heater in case the water temperature falls below a usable level.

The technology can be incorporated with a range of renewable heat sources as well as conventional ones and, depending on the system, outputs can take the form of heat for central heating or hot water.


What are the advantages of a thermal store?

A thermal store allows you to access heat when it is available and store it until you require it. It also allows you to combine heat sources. For example, a heat store can enable you to heat water from solar collectors and, at times when less solar energy is available, combine the heat stored with further hot water from an immersion heater or conventional boiler.

A thermal store is a good way of maximising the potential of your renewable energy source. For instance, a wood-burning heater operates best at maximum output. A thermal store allows you to do this, but only use the heat when you need it. It can also give you ‘on demand’ hot water from a renewable source.


Types of thermal store

Thermal store tanks can be linked to a number of renewable technologies:
  • Biomass and wood heating systems – a thermal store increases the efficiency of biomass systems, and particularly that of log-burning heaters, by allowing it to operate at full capacity and enabling hot water and space heating energy to be stored and accessed when it is required;
  • Solar water heating systems – even in the UK a sunny day can enable your solar collectors to harvest more heat than is needed by your domestic hot water requirements. With a thermal store and heat-exchange unit you can store excess heat for space heating as well as hot water;
  • Air and ground source heat pumps – by storing hot water from your air or ground source heat pump you can avoid the need to have the pump running constantly, which will save on wear and tear and potentially lengthen its operating life; and
  • Combined technologies – Crucially, a thermal store provides you with the means to combine two or more types of renewable systems and allows you to link it with conventional technologies too. This offers both maximum efficiency and maximum convenience.
Renewable energy, then, lessens your household’s dependence on fossil fuels and reduces your carbon footprint. Converting your home to renewable energy sources, even with conventional sources as a back-up, reduces your contribution to global warming and stimulates the further growth of the renewable sector. But, as a bottom line effect, it can also help you to reduce your heating bills while still enjoying a warm, comfortable home.


Resources:


» Energy Efficiency | Burn Wise | US EPA - United States Environmental Protection Agency

» Boiler energy efficiency - Boiler reviews - Heating, water & electricity - Which? Home & garden

» Oil central heating - Home heating systems - Creating an energy saving home - Which? Energy


» Air source heat pumps | Energy Saving Trust


» Air source heat pumps explained - Creating an energy saving home - Which? Energy


» Air-Source Heat Pumps | Department of Energy


» Ten Myths About Geothermal Heating and Cooling & The Great Energy Challenge Blog


» Ground source heat pumps | Energy Saving Trust


» Ground source heat pumps explained - Creating an energy saving home - Which? Energy


» Solar water heating | Energy Saving Trust


» How does solar water heating work? - How to buy solar panels - Creating an energy saving home - Which? Energy


» Solar Water Heaters | Department of Energy


» Renewable heat - Wikipedia, the free encyclopedia


» Domestic Renewable Heat Incentive | Ofgem


» Renewable heat technologies | Good Energy

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