Reducing Energy Use at Home A review of different ways of reducing domestic energy usage Updated 6 November, 2006
Introduction    Summary of   Free,  Low Cost   and  More Expensive Energy Saving Options Efficient Boilers    Lighting Summary    Lighting in Detail    Hot Water    Standby     Insulation     Draughts     The Modelled House Blewbury Energy Initiative   Contacts   Domestic Renewable Options   Facts and Figures   Legal Matters   Reducing Energy Use Background Information: Energy Links   Global Warming   Green Energy   Hydrogen as a Fuel   Saving Energy Main Blewbury Site

Introduction

This section discusses the options for saving energy in the home. The discussion is based on the energy needs of a modelled house. The model estimates the energy and fuel that would be used by the house in an average year, and prices it at the cost of gas and electricity after the series of price rises in the Autumn of 2005. Any calculation of expected energy savings is going to be approximate, and apply only to a specific house. However they provide a reasonable indication of the energy savings that can be achieved by the different measures.

This household energy bill over the typical year is expected to be £1,310. The energy bill of this house could be reduced by 40% through a series of free or fairly low cost changes. These, and some other options, are listed in the following tables and discussed in the rest of this section. The savings are similar or greater if oil, coal or wood is used in place of gas.

For a thorough discussion of how to save energy in a house see how the Yellow House reduced their energy requirements by two-thirds.

It may be helpful in seeking savings on electrical energy to fit an Electrisave. This device costing about £80 shows you exactly how much electricity the home is using at any time.

Free Savings

Low Cost Savings

More Expensive Options

Efficient Use of Boilers

Old boilers were fairly heavy, and this metal had to be heated each time the boiler fired. This reduced efficiency particularly if the boiler was used intermittently, for example to heat water during the summer. Modern boilers are lighter increasing their efficiency. A typical modern conventional gas boiler achieves an efficiency of about 78%. A condensing boiler reaches about 91%. This difference would save £80 a year on a £560 gas bill, though the condensing boiler costs perhaps £200 to £300 more. All new boilers are now condensing boilers due to regulations, so this is what (in 99% of cases) homeowners will have to install.

Condensing Boilers

Condensing boilers collect additional heat from the flue gases, in particular the latent heat in the steam generated. Thus a secondary heat exchanger pre-heats the water returning to the boiler. If the difference between the flow and return temperatures is too low, little benefit is gained from the preheat, so the difference is controlled automatically by adjusting the water flow and heat input. However the overall efficiency also depends on the design of the rest of the heating system.

Fitting enough Radiators

All boilers work most efficiently when generating the heat they were designed to produce,so it is desirable to ensure that the radiators can radiate the heat the boiler can generate, even if some are switched off.

Lower Temperature Heating

Condensing boilers gain most energy from condensing the steam in the flue gases if the water being drawn into the boiler starts cool. With higher input water temperature, more steam will escape as vapour and less energy will be captured through condensation. Efficiency begins to drop noticeably above about 40 degrees Celsius and efficiency falls of rapidly if the input water temperature exceeds 50 degrees. A generous area of radiators helps to cool the water before it returns to the boiler. A lower output water temperature also results in a lower input temperature, and this can still provide the heat needed if the radiator area is large enough.

Underfloor Heating

Underfloor heating allows condensing boilers to run at high efficiency, as it provides both the desirable features of a low temperature heat output and a large radiating area. It can be combined with conventional radiators and hot water heating as a separate control device can ensure that the water used in underfloor heating is at about 45 degrees Celsius rather than the 80 degrees needed by normal radiators.

Each method of heating has its relative benefits and disadvantages. Underfloor heating keeps walls free of radiators, but is not compatible with thick carpets.

Heating Water with Gas in Summer

Since electricity costs about four times as much as gas for the same energy, a gas boiler would need to be very inefficient for it to be more expensive for water heating than an electric immersion heater. In our modelled house the cost of water heating in the summer is £84 with gas and £203 with electricity.

Combi Boilers

Smaller properties can consider using a Combi boiler, which drives the central heating system and also supplies hot water directly, avoiding the need for a hot water tank and the associated heat losses. As the water is heated when it is required, the flow available is more limited than from a hot water tank.

Saving on Lighting

Using Low Energy Light Bulbs

Low energy light bulbs can be used in most places where conventional light bulbs are used, and they use only about a quarter of the energy for the same light output. Lighting the modelled house costs £117 a year, so a reduction to about 40% of this saves around £68 per year. They cost about ten times as much as conventional bulbs, but last about ten times longer, so over time the purchase cost is similar.

The ideal use of low energy light bulbs is in positions where the light is required for a reasonably long and continuous period, for example 4 hours a day. Low energy light bulbs are not suitable for all lighting purposes.

• Most cannot be used with dimmers designed for incandescent lights, though versions of the bulbs that replace incandescent bulbs are becoming available that can be dimmed in this way. Some low energy light bulbs can be dimmed using specific control systems.
• Manufacturers warn against using some kinds of low energy light bulb with electronic timers or photocells, the reason is not stated but is probably that the surge of current to start the light may damage the electronics.
• Low energy light bulbs are not ideal for situations where the light is switched on briefly many times a day, as the life of the bulb is likely to be reduced. A typical life is given as 50,000 cycles, so the bulb could be switched on 30 times a day and still last 6 years.

They also have some characteristics which differ from those of incandescent lights:

• Low energy light bulbs can take a second or two to switch on, which may concern occasional users who expect the instant response of an incandescent bulb.
• Some take a minute or more to reach full brightness.
• The light output is likely to drop somewhat over the life of the bulb.
• Fluorescent lights appear to provide a white light but in fact this is usually created by combining fluorescence in a small number of different wavelengths, so that colours may not look the same as under the continuous spectrum of daylight, or of an incandescent light.
• It may be necessary to change the lightshade to accommodate a low energy bulb.

There is a wide range of styles which can be viewed on web sites such as Bulbs Direct. Though many low energy light bulbs are made with the white light traditionally associated with flourescent bulbs, it is possible to obtain bulbs giving a warmer glow, and even coloured bulbs. Most bulbs sold for domestic use are currently designed as complete replacements for incandescent lights, and so include the "ballast" required to trigger the bulb. As the ballast lasts much longer than the bulb, it is also possible to get bulbs which are designed for fittings which contain the ballast. In principle these bulbs should be less expensive, but at present they do not seem to be so. Some such fittings are required by Building Regulations on all new houses, with the aim of encouraging the use of low energy bulbs.

The majority of light bulbs for both residential and commercial use are produced by three major light source manufacturers:
Philips, Siemens (Osram, Sylvana) and GE Lighting (Tungsram, Mazda)
each account for around 30% of residential light bulb sales in Europe.

Switching off Lights not in use

It is cost effective to switch off lights when a room is not being used.

Cheaper Hot Water

The modelled house uses a fairly large quantity of hot water. In our model house, heating the water used took 16 kWh a day, and 1.2 kWh a day was lost through the tank insulation. Both would be reduced by reducing the water temperature. The energy lost could be greatly reduced by more insulation of the hot water tank. The energy to heat the water used could be reduced by reducing the consumption, for example by taking 3 minute showers rather than baths, and by using a plug in the basin when washing hands or plates rather than using a running tap.

Minimise Equipment on Standby

Equipment such as televisions and computers typically give a standby option, which is easier to choose than switching off. Although the energy used may seem to be modest - for example 7 watts for a TV - this load itself would cost £4 a year. With some items of equipment such as screens, computer sound systems and particularly printers, it may not be obvious that the device is still using energy.

Add Insulation

The first improvement to look at is to Increase Roof Insulation. This is often possible and can have a significant effect at low cost. The modelled house already had 50 mm insulation in the loft. Even so 10% of the heat was lost this way, costing £47 a year. If this is increased to the recommended 200 mm the heat loss is reduced by two thirds saving £33 a year.

The largest heat loss in the modelled house was through its walls, even though these were cavity walls. The cavity was only 50 mm (2 inches) wide, but even so cavity insulation saved £109 a year. This has to be done professionally but is not very expensive at perhaps £450.

Some houses lose significant amounts of heat through the ground floor. It may be possible to insulate this economically particularly as part of a renovation. However it is important to retain ventilation to any underfloor space.

Secondary and Double Glazing is one of the most frequently applied energy saving measures, and one of the most expensive. In our modelled house the single glazed windows were responsible for 15% of the heating cost, and this could be halved by an additional layer of glass saving £39 a year. Secondary glazing is less expensive than double glazing, and is equally effective. Double glazing panes should be separated by an air gap of 20 mm or their insulation decreases significantly. A 10 mm gap is 30% less effective. The heat loss through double glazing can be reduced further by the use of special glass and by filling the gap with a gas such as Argon.

Grants for Insulation

Grants are available for the installation of insulation such as cavity wall insulation, loft insulation and hot water tank insulation. The work can be free for priority customers, but smaller grants are available for domestic owner-occupier premises. The Vale of White Horse can provide advice and may be able to add an additional Energy Incentive Grant of £50. Their Energy Saving team can be contacted on the freephone number 0800-592865 or by email to vet@whitehorsedc.gov.uk.

One source of grants may be Scottish and Southern Energy. Their Energy Efficiency Advice line is 0845-7776633 or email jan.hudson@scottish-southern.co.uk.

Limit Draughts

Excessive draughts not only make the house less comfortable, they also make it more expensive to heat, as the cold air needs to be warmed. On the other hand a house must not be completely sealed as we need fresh air to breathe, and some circulation is necessary to remove odours and avoid damp and mould. For this reason new houses, which should be built to exclude draughts, may need to provide air bricks to allow sufficient ventilation, and the air flow is often assisted by extraction fans in the bathroom and kitchen. It is also very important to provide a suitable direct supply of fresh air to boilers and open fires. The recommended ventilation for domestic houses is between 0.5 and 1 complete air changes each hour. Warming this air is likely to take up a significant proportion of the total heating requirement. In the modelled house, which had 1 air change an hour, it required 25% of the total heating requirement.

Nevertheless older houses can usually benefit by preventing most of the draughts, typically by providing draught exclusion round windows, doors and letter boxes, and sealing other gaps where draughts can be detected, for example under the skirting boards.

The Modelled House

The house modelled as an example is a 2 storey property. It is freestanding with a footprint of 8 by 8 metres. The room height is 2.4 metres. It has cavity walls with a 50 mm cavity, eight wood framed single glazed windows 1,480 mm by 1,230 mm, and two wooden outside doors. There is 50 mm of insulation below the loft. The ground floor has a concrete screed covered with parquet. Draughts round the external doors and windows replace the air in the house once an hour.

Heating is by gas, using a 10 year old boiler, with an efficiency averaging about 70%. The controls include a timer/programmer, thermostats in the main room and on the hot water tank, and some radiator thermostatic controls. When running the central heating system achieves a temperature of 21 Deg Celsius, However it is switched off overnight and during weekdays. The hot water tank holds 220 litres and has 50 mm of lagging. In the summer hot water is obtained by an electric immersion heater.

The kitchen includes an electric cooker, a microwave, and other electrical equipment used only for a short time. A utility room has a washing machine and separate dryer and a Fridge Freezer.

The electronic equipment includes a TV, a set top box, a video recorder, a computer and printer. All are left on standby when not in use. There are 14 lights with conventional 60 or 100 watt filament bulbs totalling 980 watts. They are on for 4 hours a day on average.

In a typical year this household uses 8370 kWh of electricity and 27,721 kWh of gas, at a likely cost in 2006 of £1,310. It is responsible for the emission of 8,866 kg of CO₂.

The Average Year

The The Energy Management Register web site maintained by Vilnis Vesma records a measure of the requirement for heating as degree days for different parts of the country. For the Thames Valley, the average degree days per year over the 20 years up to October 2005 was 1,977. That for the last year was only 1,683. If we apply last years temperatures to the model, the energy cost is reduced by £51. For a fuller explanation of the degree days measurement see Energy Management Leaflet 7 in the Energy Management Register.

Fuel Prices

The prices used in the model are the General Domestic prices specified by Southern Electric from 1st January, 2006. Other suppliers have similar rates. The prices used have not included any discounts for preferred paying options, such as direct debits.

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