2 Reducing space heating demand
Heat energy is used in houses and offices to provide the energy service of ‘comfort’. This means providing space heating in winter with some kind of heating system and possibly cooling in summer. The heating system will usually also provide hot water, discussed in Section 3.
A little history
Life indoors in the UK was very cold in winter in the past. Houses in the nineteenth and early twentieth centuries had a central fire (usually fuelled by coal), often also used for cooking and water heating, and were lit with either oil or gas lamps. They had to be well ventilated both to supply the combustion air for the fire and to get rid of the fumes from the lamps. The basic principle of keeping warm was to wear lots of clothes, sit as close as possible to the fire during the day and retreat under a thick pile of blankets in bed at night. In the nineteenth century, offices did introduce the relative luxury of central heating, fed from large coal-fired boilers.
Most pre-1918 buildings in the UK have solid brick walls, usually two bricks thick, though they may be three or more bricks thick in taller buildings. Buildings of this age still make up about 20% of the housing stock.
UK building standards improved slowly throughout the twentieth century. In the 1920s cavity walls (with an air gap between two separate skins of brick) were introduced, largely as a method of preventing damp penetration. The coal fire remained the normal mode of heating in UK homes well into the 1960s. These homes weren’t very warm – a survey in 1949–50 showed average whole-house temperatures ranging from 12.4°C to 14.2°C (Danter, 1951).
With the introduction of North Sea gas in the 1970s there also came gas-fired central heating. The proportion of the housing stock with central heating rose from 31% in 1970 to over 97% in 2014 (BEIS, 2018c). It also became expected that houses should be fully heated to an acceptable comfort temperature.
Concerns about death rates, particularly of the very young and the elderly, have given rise to the concept of fuel poverty. A household is currently (2019) considered to be fuel poor if in order to achieve a satisfactory heating regime (21°C for the main living area, and 18°C for other occupied rooms):
- they have required fuel costs that are above average level and
- were they to spend that amount, they would be left with a residual income below the official poverty line.
In 2015, it was estimated that in England alone there were 2.5 million households in fuel poverty (BEIS, 2018b). Not surprisingly, fuel poverty is most common in the homes with the worst energy efficiency standards.
Loft insulation was only introduced into the building regulations for new UK houses in 1974 and then only to a thickness of 25 mm. Since then standards for new buildings have steadily improved and government campaigns have encouraged householders to install insulation. However, there is still a considerable proportion of the existing housing stock that is relatively poorly insulated.
The picture for the services sector is not much better. The 1960s saw a fashion for ‘curtain wall’ office construction where a steel or concrete frame was used to provide the structure and the walls were largely made of thin concrete panels and large sheets of single-glazing. These offices were hard to heat in winter and often overheated in summer. Fortunately office buildings tend to be regularly refurbished as new occupants come and go, but even so, making major improvements to the thermal performance can be difficult.
The insulation standards of new and refurbished buildings are covered by Building Regulations. The responsibility for these in the UK is devolved to the regions, i.e. Scotland has slightly different regulations from those of England and Wales and Northern Ireland. The regulations for the Republic of Ireland tend to follow a similar pattern to those in the UK. Where references are made to ‘the Building Regulations’ in this course they refer to those for England and Wales.
Since 2006, the regulations covering the thermal performance of buildings have been mainly worded in terms of ‘target CO2 emissions’ rather than specific insulation levels. There may, however, be specified minimum standards for windows and suggested insulation levels for other parts of the building fabric and guidance for heating and ventilating systems.