Example A. These homes (see Figure 5.6) use 300mm of thermal insulation on the outside walls (see Figure 5.7) and feature a grass roof with solar water heating panels. The heat recovery ventilation unit is located in the loft space (see Figure 5.8).
Example B. The design principles for this private block of flats (see Figures 5.9 and 5.10) were the same as those applied to the social housing project. The details of the construction were:
• concrete core and floors;
• external walls rendered, timber support, 300mm sheep’s wool insulation, internal plasterboard and
skim; • windows – three layers of glass with low e-coatings;
frames coated aluminium and timber (on inside);
mechanical ventilation system giving three air changes per hour with heat recovery;
• heating supplied by preheating of ventilating air and low-level radiator in the bedroom;
• energy supply for the block by a wood-burning boiler – this also provides hot water as a backup to the solar water heating system;
• occupants say that in winter the inside temperature never drops below 22°C and in summer the flats never get warmer than 25°C (they do have external blinds).
Example C. Again this house (see Figures 5.11 and 5.12) uses the same constructional details to achieve the low heating demand.
Figure 5.6 Social passive housing
Figure 5.7 Section of the external wall showing the thickness of the thermal insulation
Figure 5.8 Heat-recovery ventilation unit in the loft space
Figure 5.9 South elevation of the block of flats
Figure 5.10 Internal view of one of the flats
Figure 5.11 Private house
Within the UK there has been a great deal of work carried out on the design strategies to be used to produce a house which uses 40 per cent less energy than current consumption. The main strategies to be adopted to produce such a dwelling by 2050 are:
• Electricity consumption for lights and appliances must be reduced by nearly one half to around 1600kWh per household.
• New-build homes will have close to zero heating demand.
Figure 5.12 Internal view of the house
Introduction
Facilitated by improved food supply through agriculture, the pattern of human development has been for people to concentrate into ever larger settlements – from villages to towns to cities or contiguous urban areas with tens of millions of people.
Rather than nomadic people travelling to where wild plant and animal food was available, resources of food and materials were grown and collected in the hinterland and transported to settlements. As transport improved, the resource catchment areas for settlements could be extended, enabling the collection of more energy as food and fuel and other resources, thereby sustaining larger higher-density settlements. Initially, both food and fuel for direct use by people were mostly from renewable biomass. Renewable energy was then used to supplement human energy in the form of animal power, and then, beginning approximately 2000 years ago, from the increasing utilization of solar heating and lighting, and water and wind mills. About 500 years ago, coal and then other fossil fuels were increasingly exploited and the higher energy densities of these fuels and other technology developments, such as railways and electricity generation and transmission, allowed the further growth of settlements using increasingly distant energy sources.
Currently, about half of the world’s people live in towns and cities, and this fraction is expected to grow towards the 80 per cent urbanization found in richer countries, although the trend may be altered by developments in energy and other resources, and by technologies. So, although this chapter is on renewable energy in cities, it should also be seen in the wider
context of national energy – providing energy services in cities is a national planning problem.
All cities currently import energy to meet service needs in buildings, for heating, cooling, lighting and electrical equipment, and for transport. They import because the density of settlement in cities and their location means that most cities have small or zero fossil fuel resources within their boundaries, and the resources of renewable energy are inadequate or not fully exploited because of economic or other reasons. Although cities have to import energy, they have the potential to be more efficient in terms of energy consumption per capita than low-density rural settlements. This is because electric and public transport systems are viable, and because large buildings and energy supply systems can be made more efficient than small ones. Set against this, people in cities are generally richer than those in rural areas, and rich people have higher demands for energy services and energy-consuming technologies.
In most countries, a large and often major fraction of the energy imported to cities originates from fossil and nuclear fuels – directly as coal, oil and gas or via electricity generated with fossil and nuclear fuels.
However, demand has grown and the reserves of finite fossil and nuclear fuels have depleted to the extent that over the next 50 years the availability of these fuels will decrease and the prices will rise. Figure 6.1 shows the remaining lives of finite fuels expressed as ratios of current reserves to production. These are indicative since reserves are partly determined by exploration, economic and technological parameters, and by the future levels of demand for the fuels, which will be influenced by many factors such as economic development, global warming and nuclear risks.