Nature has given us illimitable sources of prepared low-grade heat. Will human organisations
cooperate to provide the machine to use nature's gift?
John A. Sumner (1976)
Many of you will be familiar with the term geothermal energy. It probably conjures
mental images of volcanoes or of power stations replete with clouds of steam, deep
boreholes, whistling turbines and hot saline water. This book is not primarily about
such geothermal energy, which is typically high temperature (or high enthalpy, in
technospeak) energy and is accessible only at either specific geological locations or at
very great depths. This book concerns the relatively new science of thermogeology.
Thermogeology involves the study of so-called ground source heat: the mundane form
of heat that is stored in the ground at normal temperatures. Ground source heat is
much less glamorous than high-temperature geothermal energy, and its use in space
heating is often invisible to those who are not 'in the know'. It is hugely important,
however, as it exists and is accessible everywhere. It genuinely offers an attractive
and powerful means of delivering CO2-efficient space heating and cooling.
Let me offer the following definition of thermogeology:
Thermogeology is the study of the occurrence, movement and exploitation of low enthalpy
heat in the relatively shallow geosphere.
By 'relatively shallow', we are typically talking of depths of down to 300m or so.
By 'low enthalpy', we are usually considering temperatures of less than 40°C.
1.1 Who should read this book?
This book is designed as an introductory text for the following audience:
graduate and postgraduate level students;
civil and geotechnical engineers;
buildings services and heating, ventilation and air conditioning (HVAC) engineers
who are new to ground source heat;
applied geologists, especially hydrogeologists;
planners and regulators;
1.2 What will this book do and not do?
This book is not a comprehensive manual for designing ground source heating and
cooling systems for buildings: it is rather intended to introduce the reader to the
concept of thermogeology. It is also meant to ensure that architects and engineers are
aware that there is an important geological dimension to ground heat exchange
schemes. The book aims to cultivate awareness of the possibilities that the geosphere
offers for space heating and cooling and also of the limitations that constrain the
applications of ground heat exchange. It aims to equip the reader with a conceptual
model of how the ground functions as a heat reservoir and to make him or her aware
of the important parameters that will influence the design of systems utilising this
While this book will introduce you to design of ground source heat systems and
even enable you to contribute to the design process, it is important to realise that a
sustainable and successful design needs the integrated skills of a number of sectors:
The architect, who must ensure that the building is designed to be heated using
the relatively low-temperature heating fluids (and cooled by relatively high-temperature
chilled media) that are produced efficiently by most ground source heat
pump/heat exchange schemes.
The buildings services/HVAC engineer, who must implement the design and must
design hydraulically efficient collector and distribution networks, thus ensuring
that the potential energetic benefits of ground heat exchange systems are not frittered
away in pumping costs.
The electromechanical and electronic engineer, who will be needed to install the
heat pump and associated control systems
The pipe welder and the driller, who will be responsible for installing thermally
efficient, environmentally sound and non-leaky ground heat exchangers.
The owner, who needs to appreciate that an efficient ground heat exchange system
must be operated in a wholly different way to a conventional gas boiler (e.g. ground
source heat pumps often run at much lower output temperatures than a gas boiler
and will therefore be less thermally responsive).
If you are a geologist, you must realise that you are not equipped to design the infrastructure
that delivers heat or cooling to a building. If you are an HVAC engineer,
you should acknowledge that a geologist can shed light on the 'black hole' that is
your ground source heat borehole or trench. In other words, you need to talk to each
other and work together! For those who wish to delve into the hugely important 'grey
area' where geology interfaces in detail with buildings engineering, to the extent of
consideration of pipe materials and diameters, manifolds and heat exchangers, I recommend
that you consult one of several excellent manuals or software packages
available. In particular, I would name the following:
the manual of Kavanaugh and Rafferty (1997) despite its insistence on using such
unfamiliar units as Btuft-1 °F-1, so beloved of our American cousins;
the set of manuals issued by the International Ground Source Heating Association
(IGSHPA) – IGSHPA (1988), Bose (1989), Eckhart (1991), Jones (1995), Hiller (2000),
and IGSHPA (2007);
the recent book by Ochsner (2008a);
the newly developed Geotrainet (2011) manual, which has a specifically European
perspective and has been written by some of the continent's foremost thermophysicists,
thermogeologists and HVAC engineers;
the German Engineers' Association standards (VDI, 2000, 2001a,b, 2004, 2008);
numerous excellent booklets aimed at different national user communities, such
as that of the Energy Saving Trust (2007).
1.3 Why should you read this book?
You should read this book because thermogeology is important for the survival of
planet Earth! Although specialists may argue about the magnitude of climate change
ascribable to greenhouse gases, there is a broad consensus (IPCC, 2007) that the continued
emission of fossil carbon (in the form of CO2) to our atmosphere has the
potential to detrimentally alter our planet's climate and ecology. Protocols negotiated
via international conferences, such as those at Rio de Janeiro (the so-called Earth
Summit) in 1992 and at Kyoto in 1997, have attempted to commit nations to dramatically
reducing their emissions of greenhouse gases [carbon dioxide, methane, nitrous
oxide, sulphur hexafluoride, hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs)]
during the next decades.
Even if you do not believe in the concept of anthropogenic climate change, recent
geopolitical events should have convinced us that it is unwise to be wholly dependent
on fossil fuel resources located in unstable parts of the world or within nations whose
interests may not coincide with ours. Demand for fossil fuels is increasingly outstripping
supply: the result of this is the rise in oil prices over the last decade. This price
hike is truly shocking, not least because most people seem so unconcerned by it. A
mere 10 years ago, in 1999, developers of a new international oil pipeline were worrying
that the investment would become uneconomic if the crude oil price fell below
$15 USD per barrel. At the time of writing, Brent crude is some $105 per barrel, and
peaked in 2008 at over $140 (Figure 1.1). The increasingly efficient use of the fuel