1.3.- La tradición oral y los juegos tradicionales

This section illustrates some aspects of renewable energy planning for a fictitious UK city of 5 million people with some 1.9 million households in 1990 growing to 2.8 million in 2050. Other demands (non-domestic buildings, transport) are excluded (the illustration is based on a simple dwelling stock model of the author and is just that, an illustration). Energy efficiency and renewable energy can be introduced into dwellings at rates that depend upon how fast new houses are built, and how fast existing dwellings are refurbished and have conventional energy systems replaced or supplemented with renewable energy systems.

Figure 6.6 shows the number of dwellings built before 1990 (labelled ‘pre-1990 orig’) and then refurbished after 2010 (labelled ‘pre-1990 refurbished’), allowing for loss of these due to demolition. It then shows in subsequent layers the number of new houses built in each five-period from 1990 to 1994, 1995 to 1999 and so on.

First, energy efficiency is applied to reduce space heat demand, both through refurbishing pre-1990 dwellings and by efficiency regulations applied to the construction of new dwellings. This is depicted in Figure 6.7. The lowest band represents dwellings existing in 1990, and then later refurbished, and the upper bands those dwellings built in the periods of

1990 to 1995, 1995 to 2000 and so on. It should be noted that the slow turnover of the stock means that existing dwellings still predominate in 2050, emphasizing the importance of energy efficient refurbishment and the retrofitting of renewable energy technologies, such as solar water heaters. This also emphasizes that there are two approaches to

increasing the fraction of renewable energy supply:

first, reduce demand and, second, increase renewable supply.

Growth in population and number of households results in water heat increasing to about half of heat demand, as shown in the Figure 6.8. Solar water heating is one of the more practical options in the Figure 6.6 City-dwelling stock population

Figure 6.7 City dwellings: Space heat demand

UK – typically, a dwelling system will provide about half of hot water demand – and so it can meet an increasing fraction of total heat demand.

The changes in space heat efficiency and water demand will change the monthly and hourly patterns of heat demand, as shown in Figures 6.9 and 6.10. Figure 6.9 depicts monthly variation in space heat demand that arises because of a lack of solar energy; this underlines the

difficulty of meeting this demand with solar heating – the peak demand is in winter when there is least sun.

However, energy efficiency means that space heat demand does decline. Also, lower temperatures in the winter make heat pumps less efficient.

Heat demand for dwellings, without any heat storage varies throughout the winter, as depicted in Figure 6.10.

For active solar and heat pump systems, this diurnal Figure 6.8 City dwellings: Space and water heat demand

Figure 6.9 City dwellings: Space and water heat demand in 2050 (monthly variation)

variation can be accommodated with heat storage, such as hot water tanks. For passive solar heating, it is more difficult to store heat from day to night.

Heat demands may then be added to other demands, such as cooking and appliances, to arrive at the total energy demands of the city’s dwellings. These demands are

then met with solid, liquid, gas fuels, solar and CHP heat, and electricity, as illustrated in Figure 6.11. An increasing fraction of the CHP heat and electricity would come from renewable sources. This shows how the demand for fossil fuels might gradually be reduced through energy efficiency and renewable energy supply outside and inside the city.

Figure 6.10 City dwellings: Space and water heat demand in 2050 (hourly variation)

Figure 6.11 City dwellings: Energy supply

In this particular illustrative example for dwellings, there is some renewable supply in the city; but the major portion would be imported as renewable electricity from wind turbines and so on. A similar picture would result if the city energy scenario were extended to cover non-residential sectors – commercial and services buildings, transport and industry.

Implementation

Having used technological and economic analysis to devise what may be close to an optimal least-cost plan for energy efficiency and renewable energy in a city (as illustrated above), the problem, then, is to implement the plan. Renewable energy may be implemented using a range of instruments: planning, regulation, market, public investment and information. These instruments need to be tailored to account for the technologies involved for different contexts of buildings, ownership and so forth. It is particularly important to ascertain whether renewable energy planning is to be used for new urban areas or buildings, or for retrofitting existing built environments. Some instruments can be applied by local government; others are controlled by national government or international bodies such as the European Union. Table 6.3 provides some examples of instruments. The reader is encouraged to consult other examples of how cities are developing plans for sustainable energy futures with low environmental impacts (e.g. Greater London Authority, 2007).

Conclusions

People are congregating in cities of ever-increasing size and growing wealth, and the adoption of Western lifestyles is leading to the concentration of energy service demands into small geographical areas. At the

same time, fossil fuel use – particularly oil and gas – will decline because of reserve depletion and efforts to combat global warming. This poses the problem of meeting energy service needs in cities with renewable energy resources that are diffuse, and geographically and temporally variable. There is no problem with the absolute availability of renewable energy as resources are more than adequate for all people to enjoy the lifestyles of the rich today. The challenge, however, is to find renewable energy supply solutions that are socially equitable and environmentally acceptable, and that meet needs at reasonable cost. There is no global best renewable energy solution for cities; systems have to be designed to suit the city, regional, national and international context.

The great advantage of renewable energy systems is that they are generally safe and stable economically, whereas the availability of finite fossil and nuclear fuels will diminish and their prices will escalate unpredictably. Renewable energy development must go hand in hand with cost-effective demand management and energy efficiency. Exercising these options will ensure a secure and sustainable future with a high quality of life for people living in cities.

References

Barrett, M. (2007) ‘A renewable electricity system for the UK’, in Boyle, G. (ed) Renewable Energy and the Grid: The Challenge of Variability, Earthscan, London

Boyle, G. (ed) (2004), Renewable Energy, second edition, Oxford University Press, Oxford

BRE (2008) A Review of Microgeneration and Renewable Energy Technologies, NF 7, IHS BRE Press on behalf of NHBC Foundation,

Greater London Authority (2007) London CO₂: Action Today to Protect Tomorrow – The Mayor’s Climate Change Action Plan, Greater London Authority, February, www.london.gov.uk Table 6.3 Examples of instruments to implement renewable energy

Regulation/planning Market Public investment

Local/city Renewable energy requirement Taxation related to energy Renewable energy on public

on new developments buildings

National New building regulations Subsidy/tax relief/feed-in Renewable energy on Sectoral targets for renewable energy tariffs for renewables public buildings International Technology performance standards Renewable certificate trading

(buildings, appliances, vehicles) National targets for renewable energy

Introduction

A heat pump is any device that extracts heat from a source at low temperature and gives off this heat at a higher temperature. The basic objective of heat pumping is exactly the same as the objective of refrigeration: the heat is removed at a low temperature and rejected at a higher temperature. The difference between these two systems is that a refrigeration system generally transfers heat from a low-temperature object to the ambient, whereas a heat pump transfers heat from the ambient to a higher-temperature object – for example, from a low-temperature heat source (e.g. air, water or ground) to a higher temperature heat sink (e.g. air or water).

The idea of using a reverse heat engine as a heat pump was proposed by James Thomson and his brother William Thomson (later to become Lord Kelvin) in the middle of the 19th century; but it was only during the 20th century that these practical devices came into common use.

Growing environmental awareness has focused human attention on the utilization of renewable energies. Fossil fuels, such as gas and oil, are finite. We have become increasingly aware of this fact – and it is this awareness that spurs us on to utilize renewable forms of energy to provide us with heat. There is now also a stronger political drive to use fossil fuels with greater consideration of their impact on the environment. Apart from the finite nature of fuel reserves, climate protection plays an important role. The reduction of CO₂emissions and those of other climate-affecting gases cannot wait if the threat of climate change is to be averted. All of these arguments support the use of renewable energies. Heat pumps provide

a particularly energy efficient and environmentally friendly solution to the demand for central heating.

Heat pumps utilize renewable energies from the environment. Solar energy stored underground, in groundwater and in the air, is converted into convenient heating energy using electricity. Heat pumps are efficient enough to be usable as a sole heating source – all year round.

As a consequence, heat pumps have experienced a renaissance. They have the advantage of being combustion free, and thus there is no possibility of generating indoor pollutants such as carbon monoxide.

Initial technical shortcomings, which brought a rapid end to their first boom in the 1980s, have now been remedied. Today, heat pumps provide a reliable, cost-effective heating system, which operates with particular environmental responsibility.

They are suitable for providing heat in any type of building, such as detached houses and apartment blocks, hotels, hospitals, schools, office buildings and industrial structures, in newly built and modernization projects alike. Trying to meet all of the requirements specified for energy efficient houses almost inevitably induces the need for a heat pump.

There is a saying that a heat pump is ‘a unique device which enables man to outwit nature in order to get more then invested’. Basically, as is well known, it is a well-conceived organization of energy flows and processes: a smaller amount of exergy (available energy) is added to a greater amount of anergy (unavailable energy), which together increases the exergy of the working fluid (process medium) (see Figure 7.1).

According to the definition of efficiency (the use of which, in this case, represents an incorrect approach to