**1. Introduction**

experiments where the "cigar" firing technology is investigated for combustion of biomass

Chapter 4 deals with the analysis of photovoltaic Maximum Power Point Trackers. This is vital since the output voltage and current from PV modules depend on environmental condition such as solar radiation and temperature. Here, a converter and a tracking

The remaining two chapters focus on industry and residence building with the aim to achieve increased sustainability. In chapter 5 a methodology for industrial energy audit with measurement examples are presented, while the last chapter describes case studies where Building Performance Evaluation is used (here the focus is indoor climate verse energy use). The search for energy supply security, economic growth and an energy system with minimum impact on the environment underscores the importance of sustainable energy as

The purpose of this book is not to provide answers to how to achieve a sustainable energy system, but rather an effort that leads in that direction by presenting a series of research. The book presents a series of research results ranging from theoretical studies to advanced

> **Alemayehu Gebremedhin** Sustainable energy group

Gjøvik University College

Norway

Department of Technology, Economy and Management

technological solutions to improve the use of some of the renewable energy sources.

algorithm which enables an optimal operation of photovoltaic systems is proposed.

bales.

VIII Preface

never before.

Economic development in transition countries, such as China and India, increase global en‐ ergy use. Therefore, the demand for energy carriers grows, which should increase energy prices. Global energy supply is dominated by fossil fuels, such as coal, oil and natural gas, and this situation is likely to remain for many years even if the use of renewable energy sources (e.g., biomass, solar energy and wind energy) is expanding. Higher energy prices make certain changes of the energy system more profitable: use of *free* energy sources, such as sun and wind, efficiency improvements of energy supply, as well as energy conservation measures, which reduce energy use.

Several policies on various levels now promote increased utilisation of renewable energy sources and reduced energy end-use, for example in buildings. But there are also compre‐ hensive systems that link energy resources with demand for energy. *District heating* is such a concept, which is common in many countries where space heating of buildings is required, for example Iceland, Latvia and Denmark. In a district heating system, heat is distributed through a network of hot-water pipes from heat-supplying plants to heat consumers in a single block or a whole city. The heat is mostly used for space heating and domestic hot wa‐ ter. District-heating systems range from a single development to city-wide networks. *District cooling* works in the corresponding way. *District energy* includes district heating and district cooling. District heating is sometimes called community heating, especially in the UK.

More than one-fourth of the primary energy supply in Europe becomes losses by energy conversion, mainly as heat that is wasted by electricity generation in condensing power plants. These losses are of the same magnitude as the European heat demand [1]. District heating is a means to utilise such losses, which otherwise are wasted, to cover demand for

© 2012 Henning and Gebremedhin; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Henning and Gebremedhin; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

various kinds of heat and even cooling. District heating helps us utilising large amounts of heat that now are wasted in Europe.

are also used. Some oil is used in heat-only boilers when it is very cold. The units used at high demand have higher heat production costs and are generally more polluting than the plants used at lower demand. Therefore, the marginal cost for district heating production

District Heating and Cooling Enable Efficient Energy Resource Utilisation

http://dx.doi.org/10.5772/51837

3

The fossil-fuel-fired CHP plant and the heat pumps in the system in Fig. 1 were once built as plants covering the base load but later the wood-fired CHP plant was built, which could produce heat at lower cost and the annual utilisation times for the older plants were de‐ creased. The introduction of industrial surplus heat reduced the use of all other plants to their present levels. District heating demand and production are often shown with a dura‐ tion curve, which represents heat demand in descending order from the coldest winter days

District heating is used extensively in Sweden. Sweden has nine million inhabitants. Fifty annual TWh of district heating cover one-half of the heat market. There is a district heating system in every municipality with more than 10 000 inhabitants and in total there are more than 400 systems. One-half of Swedish district heating is supplied to multi-family houses, the rest mainly to premises, such as schools and offices, and small but growing fractions to industry and single-family houses [3]. House owners chose whether to connect to a district-

Figure 2 shows the energy sources used for district-heating supply in Sweden since 1970 [4]. The total supply varies between cold and warm years. The last year (2009) was a very cold year. The fuel use for district-heating production in Sweden has switched from almost only using oil in the 1970s to a present mixture with many heat sources. Now, two-thirds of Swedish district heating is produced from wood and waste fuel. Sweden utilises much in‐ dustrial surplus heat compared to most countries and heat pumps take heat from sewage

varies in a similar way as the heat demand during the year.

**Figure 1.** District heating production in a Swedish system (GWh)

to the warmest summer nights (see e.g., [2]).

**1.2. District heating in Sweden**

heating grid or not.

Thus, district heating is not only a technology for energy distribution but it increases the amount of available energy resources. District heating can utilise energy sources that are dif‐ ficult to use for individual buildings, such as unrefined biomass fuels, heat from waste in‐ cineration, heat from electricity generation in combined heat and power (CHP) plants and industrial surplus heat, for example heat from pulp and paper mills or production of auto‐ motive biofuel. Little of this energy could be utilised without district heating. Therefore, dis‐ trict-heating expansion may be beneficial for economy and environment.

District heating is used for heat supply to various kinds of buildings in villages and cities, primarily multi-family buildings and service premises, where the heat is used for prepara‐ tion of domestic hot (tap) water and for space heating, normally, through a central water‐ borne heating system for the whole building.

District heating systems connect energy sources and energy users. District heating can pro‐ vide affordable energy to consumers by using low-cost energy sources, such as surplus heat and waste. Many of these heat sources can be of local origin and promote local business and industry. What is the most suitable solution depends on the local conditions. By using vari‐ ous energy sources, district heating becomes a central component for waste management systems, forestry, power production and efficient energy use in industry.
