1 The importance of energy use in buildings

Appreciating the importance of energy use in buildings requires a look at UK national energy statistics. These use two categories of energy:

• Primary energy − this is essentially energy in its ‘raw’ form. Examples include crude oil before it is refined and the fuels used to generate electricity: coal, natural gas and nuclear heat.
• Delivered (or final) energy − this is the energy that the consumer actually receives (and pays for): refined petrol and diesel, mains electricity, piped natural gas.

The statistics also split energy use into different sectors: the domestic sector − people’s homes; the services sector – shops, offices, schools, etc.; transport and, finally, industry.

Figure 1 shows the breakdown of UK primary and delivered energy for 2015 in different ways. The top bar shows the actually primary fuels used. The three bars below show the delivered energy use expressed in three ways: by fuel, by energy sector and by end use.

Figure 1 UK primary and delivered (or final) energy use for 2015 (Sources: BEIS, 2021a; BEIS, 2021b; BEIS, 2021c)

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The chart shows the primary and delivered energy consumption of the UK for 2015, with delivered energy split fuel, by sector and by end use. It has four horizontal bars. The x-axis is marked in petajoules and runs from 0 to 9000. The top bar shows primary energy. It starts with about 1100 petajoules of coal use, shown in black, plus a further 2800 petajoules of oil use, shown in brown, plus a further 2800 petajoules of gas use, shown in blue green, plus a further 800 petajoules of nuclear heat, shown in purple, plus a further 700 petajoules of renewables, shown in green, giving a total primary energy demand of about 8200 petajoules. The second bar shows delivered energy broken down by fuel. It starts with 100 petajoules of solid fuel, shown in black, plus a further 2600 petajoules of liquid fuel, shown in brown, plus a further 1700 petajoules of gas, shown in light blue, plus a further 1100 petajoules of electricity, shown in dark blue, plus a further 200 petajoules of renewables and heat, shown in green, giving a delivered energy total of about 5700 petajoules. The difference between this 5700 petajoules and the 8200 petajoules in the top bar is 2500 petajoules marked as ‘lost in conversion and delivery’, shown in grey. The third bar shows delivered energy broken down by sector. The domestic sector, shown in blue, consumes about 1700 petajoules, the services sector, shown in light blue, consumes a further 800 petajoules, the transport sector, shown in orange, a further 2300 petajoules, and industry, shown in pink, a further 1000 petajoules, giving a total of about 5700 petajoules, i.e. the same as in the second bar. The fourth bar shows delivered energy by end use. Space and water heating, shown in yellow, uses about 2200 petajoules, heat above 100 degrees Celsius, shown in dark red, uses about a further 300 petajoules, cooking, shown in light purple, uses about a further 100 petajoules, transport, shown in orange, uses about a further 2300 petajoules, lights and appliances, shown in light yellow, use about a further 600 petajoules and machinery, shown in light brown, uses a further 200 petajoules, giving a total of about 5700 petajoules, i.e. the same as in the second and third bars.

Figure 1 UK primary and delivered (or final) energy use for 2015 (Sources: BEIS, 2021a; BEIS, 2021b; BEIS, 2021c)

Note that although UK primary energy consumption in 2015 was about 8200 PJ, the delivered energy use was less than 6000 PJ. As shown in the second bar of Figure 1, there were losses of about 2500 PJ ‘in conversion and delivery’. Most of this is waste heat rejected from power stations in cooling towers or into the sea. Typically generating 1 kWh of electricity in a conventional thermal power station requires between 2 and 3 kWh of primary energy input.

It can be seen in the third bar that the delivered energy use in the domestic and services sector is about 2500 PJ. This is almost entirely consumed within buildings. Adding the fraction of industrial energy use that is also used in buildings means that ‘energy in buildings’ makes up almost half of the UK’s delivered energy use. The domestic and services sectors also account for over 60% of the UK’s electricity use. When this and its attendant generation energy losses are taken into account, buildings are responsible for nearly half of UK primary energy use and about 30% of national greenhouse gas emissions (CCC, 2017).

Energy use is, of course, only the means to provide various energy services. The real task is to provide these at a lower energy and environmental cost. The energy services in buildings include:

• the provision of comfortable homes and working environments
• hot water for washing
• cooking food
• safe chilled food storage
• adequate lighting for homes and offices
• the ability to use electronic equipment for communication and entertainment (and producing and studying material such as this course).

The fourth bar of Figure 1 shows that over 2000 PJ of delivered energy were used for space heating (i.e. warming the internal spaces of buildings) and water heating. These applications only require low temperature heat (i.e. less than 70°C). Space heating is a prime target for energy efficiency programmes.

There is a considerable potential for using some of the low temperature waste heat from power stations for heating buildings using combined heat and power generation (CHP), as is widely done in countries such as Denmark.

Of the energy use in buildings about two-thirds was used in the domestic sector and about a further 20% in the services sector.

Within the domestic sector there is a familiar range of energy uses (see Figure 2).

Figure 2 UK domestic sector energy consumption by end use, 2016 – total 1730 PJ (Source: BEIS, 2021c)

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This is a pie chart showing the estimated percentages of energy consumption for different applications. Starting at the top and moving clockwise the proportions are: space heating, shown in light brown, 70.3%; water heating, shown in light blue, 12.5%; cooking, shown in orange, 2.1%; lighting, shown in yellow, 2.8%; cold appliances, shown in purple, 2.4%; other appliances, shown in dark blue, 9.9%.

Figure 2 UK domestic sector energy consumption by end use, 2016 – total 1730 PJ (Source: BEIS, 2021c)

In 2016 about 70% of the delivered energy was used for space heating and 13% for hot water. While these particular figures have only changed slowly over the past 40 years, the amount of electricity for ‘other appliances’ (e.g. radios, TVs, computers and other electronic devices) has increased by a factor of more than five. Given that the domestic sector accounts for 30% of UK electricity demand this is a matter of concern and is discussed in Section 4.1.

The services sector contains a wide range of different buildings such as offices, schools, shops and hospitals. Although just over half of the delivered energy was used for space heating, this sector uses large amounts of electricity, about 30% of UK demand. A large amount of this is for lighting (see Figure 3) – in retail premises (i.e. shops) about 20% of the energy use in 2016 was for lighting.

Figure 3 UK services sector energy consumption by end use, 2016 – total 810 PJ (Source: BEIS, 2021c)

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This is a pie chart showing the percentages of energy consumption for different applications. Starting at the top and moving clockwise the proportions are: space heating, shown in light brown, 45.2%; water heating, shown in light blue, 6.3%; catering, shown in orange, 9.8%; lighting, shown in yellow, 10%; cooling and ventilation, shown in purple, 6%; computing, shown in dark blue, 4.6%; other, shown in red, 18.2%.

Figure 3 UK services sector energy consumption by end use, 2016 – total 810 PJ (Source: BEIS, 2021c)