Advanced District Heating and Cooling (DHC) Systems

Robin Wiltshire

• Publisher: Woodhead Publishing
• Year: 2015
• Print ISBN: 9781782423744
• eBook ISBN: 9781782423959
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Advanced District Heating and Cooling (DHC) Systems presents the latest information on the topic, providing valuable information on the distribution of centrally generated heat or cold energy to buildings, usually in the form of space heating, cooling, and hot water.As DHC systems are more efficient and less polluting than individual domestic or commercial heating and cooling systems, the book provides an introduction to DHC, including its potential contribution to reducing carbon dioxide emissions, then reviews thermal energy generation for DHC, including fossil fuel-based technologies, those based on renewables, and surplus heat valorization. Final sections address methods to improve the efficiency of DHC.- Gives a comprehensive overview of DHC systems and the technologies and energy resources utilized within these systems- Analyzes the various methods used for harnessing energy to apply to DHC systems- Ideal resource for those interested in district cooling, teleheating, heat networks, distributed heating, thermal energy, cogeneration, combined heat and power, and CHP- Reviews the application of DHC systems in the field, including both the business model side and the planning needed to implement these systems

Part One

Introduction

1

Historical development of district heating and characteristics of a modern district heating system

P. Woods*; J. Overgaard^{† *} Cofely Energy Services, London, UK
^† Ramboll, Copenhagen, Denmark

Abstract

In this chapter, the historical development of district heating is summarised, identifying the trends in both technology and heat sources with examples from many different countries. A more detailed description of the developments in the UK since 1950 is provided along with a description of the key features of a modern efficient district heating scheme, which deals with each of the four major elements: the building’s heating system, the building connections, the heat distribution network and the heat source. Finally, some non-technical organisational aspects are discussed, as these are critical in delivering successful schemes.

Keywords

District heating

History

Energy sources

Modern

Efficient.

1.1 Introduction

1.1.1 The historical development of district heating

For centuries, the heating of our buildings has been achieved by supplying fuel to the building and burning that fuel in various ways. The fuel has moved from wood through charcoal to coal, coke, oil and natural gas. Until the middle of the twentieth century, most fuel was burned in open fires and enclosed stoves and from 1900 onwards, it became increasingly common in most developed economies to burn the fuel to heat water or produce steam, which was then circulated around the building to supply radiators, which became known as central heating. This development started with larger buildings and continued through to domestic buildings. The process was accelerated in the UK with the widespread availability of natural gas, where the use of individual boilers in each dwelling became the norm. Larger apartment blocks were built with centralised boilers initially, often using coal or oil but many of these systems were later converted to individual boilers within each dwelling.

In industry, heat was also, at first, produced entirely by burning various fuels in hearths, ovens or in boilers for steam. The introduction of electricity in the industrial processes offered a new opportunity, and electricity was frequently generated on site using steam turbine based systems with the low-pressure steam, extracted from the turbine, used for process heating and space heating – the earliest form of cogeneration. However, as the national grid became established and larger-scale power stations offered economies of scale, local electricity generation declined and industrial heat was again supplied mainly by the combustion of fuel.

In some cases, direct electric heating has been used, mainly where gas was considered unsafe (in high-rise buildings), or in countries such as Norway and Sweden, where hydro-electricity was plentiful and cheap. More recently, heat pumps have been used to make better use of the electricity available there.

Although in the UK, there has been a clear path from open fires to individual boiler central heating, in other countries, especially Denmark, Sweden, Germany, many Eastern European countries and the USSR, heating provision moved to district heating (DH).

The hot water distribution construction in the fourteenth century, in Chaudes-Aigues in France, is often mentioned by historians as the earliest example of DH. Water from a number of geothermal sources was used in thermal baths and also for heating some 30 houses along the route of the hot water supply. Similar heating schemes may have existed elsewhere – it is known that the Romans transported heat around their buildings – but it is the steam distribution systems that were established in the United States from the late 1870s, which marked the beginning of modern DH. Interestingly, the purpose of the first steam systems was not to supply heat but to provide steam for the generation of electricity in the connected buildings – that would change after a decade, when electricity networks began to appear.

Steam distribution became the most common DH technology, not only in the United States but also in Europe. Steam could deliver the heat at high temperatures, which was very popular, and this had an influence on the design parameters used for building heating systems. In the United States, steam distribution would become the only recognised technology for more than a century, and although there are now a few hot water-based systems, notably the network in St Paul (Minnesota), American DH is still dominated by steam networks. The New York City steam distribution system, which commenced operations in 1882, is one of the largest DH systems in the world in terms of supply capacity.

European DH took a different direction. Steam systems were established in some of the major cities, but European engineers began to see an alternative in using hot water for heat distribution. Hot water systems were found to hold a number of advantages over steam systems, and they were to become the only option when considering new DH schemes. The early steam systems were kept in operation and in some cases, even saw expansion, but as the disadvantages of steam distribution became more obvious, in most cities they were gradually converted to, or replaced by, hot water systems.

It was recognised at an early stage that the energy wasted at power stations would provide a valuable heat source, and new waste incinerators, built to deal with the waste disposal problem in rapidly growing cities of Europe, became suppliers of heat. In the Copenhagen area of Frederiksberg, the first waste incinerator provided heat to the neighbouring hospital from 1903 and the earliest Danish DH scheme was a reality.

Another early example of DH is at Bloom St in Manchester (UK), where the power station, built in 1901, started supplying steam to heat nearby warehouses and factories, as from 1911. This steam supply continued to grow, supplying premises up to 1.5 km away. Customer pressure forced the continuation of steam supply long after the power station was closed.

The major growth of DH in Europe began during the 1970s, when the main alternative heating fuel, oil, rapidly increased in price as a result of the actions of the Organization of the Petroleum Exporting Countries (OPEC). For those countries with limited access to alternative fuels, a change from oil to coal in the power industry was an obvious choice. Some countries combined this with a dedicated development of DH to use the heat recovered from the power stations. Sweden had no access to natural gas at this time, and Denmark had also been slow to exploit its reserves in the North Sea. Both countries saw a number of DH schemes being developed with Denmark becoming the leading DH country in Europe due to a strong energy policy. The Netherlands had some years of DH development, mainly in the early 1980s, but the decrease in natural gas prices put the existing schemes into financial difficulties, and new projects were not viable. Each European country has its own background in terms of access to energy resources, availability of infrastructure, policy measures, energy taxation and building standards, which means that the progress of DH has taken very different directions across Europe.

Most countries developed DH in a response to the need to improve primary energy efficiency and hence minimise the importation of fuels. An example is Finland, another Nordic country that was heavily reliant on imported fuel (coal, oil and LNG), which found that DH schemes enabled fuel efficiency and so built up a comprehensive DH industry over a few decades.

Some countries were able to exploit indigenous energy resources through DH. For example, Iceland found that its plentiful geothermal energy could be used effectively for heating buildings by means of DH, an option identified by Winston Churchill during a visit to Reykjavik in 1942 and later mentioned by him in his book, The Second World War. Other countries found that DH was the best way of utilising the energy in municipal waste, and this option has been an important part of DH schemes in Germany, Switzerland and Austria. Waste-to-energy has also played a role in the cities with DH systems in northern Italy, a country which – like France – has a limited number of DH networks.

The USSR and Eastern Europe had limited access to alternative fuels. The built form in many of these countries was suitable for DH, as many high density areas had been constructed following war damage. Many major Eastern European cities developed city-wide DH, for example, Sofia, Budapest, Berlin, Belgrade and Bucharest. The growth in DH in the USSR was particularly significant. The development in the USSR and Eastern Europe did not see the same technological progress as in Western Europe. The Danish, Swedish, German and Finnish DH industries in particular spent time and money on research and development. The call for improved energy efficiency and in some countries, a dramatic change from oil to coal in the power sector, made combined heat and power generation (CHP) attractive, and DH temperatures became crucial to the overall efficiency of the cogeneration process. Research focused on optimising supply and return temperatures, and it also initiated the development of new and better piping technology for the DH networks. Pre-insulated piping systems had been invented in the 1960s, but they needed improvement to become the reliable, cost-efficient basis of new DH schemes.

With CHP providing an increasing amount of heat for DH purposes, it became more critical to find the right balance between supply and return temperatures, network design and capacity, investment in production and distribution facilities and operational costs. In most places, DH schemes supplied heat to exi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Woodhead Publishing Series in Energy
• Part One: Introduction
• Part Two: Energy sources and plant technologies
• Part Three: Component development, operational efficiency improvement and planning
• Part Four: Business models and urban planning for heat networks
• Index