An Introduction to Thermogeology

Ground Source Heating and Cooling

David Banks

• Publisher: Wiley
• Year: 2012
• ISBN:
  9781118447505
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This authoritative guide provides a basis for understanding the emerging technology of ground source heating and cooling. It equips engineers, geologists, architects, planners and regulators with the fundamental skills needed to manipulate the ground's huge capacity to store, supply and receive heat, and to implement technologies (such as heat pumps) to exploit that capacity for space heating and cooling.

The author has geared the book towards understanding ground source heating and cooling from the ground side (the geological aspects), rather than solely the building aspects. He explains the science behind thermogeology and offers practical guidance on different design options.

An Introduction to Thermogeology: ground source heating and cooling is aimed primarily at professionals whose skill areas impinge on the emerging technology of ground source heating and cooling. They will be aware of the importance of the technology and wish to rapidly acquire fundamental theoretical understanding and design skills.

This second edition has been thoroughly updated and expanded to cover new technical developments and now includes end-of-chapter study questions to testthe reader'sunderstanding.

1

An Introduction

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 300 m or so. By ‘low enthalpy’, we are usually considering temperatures of less than 40°C.¹

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;
• architects;
• planners and regulators;
• energy consultants.

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 reservoir.

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 thermogeologist
• 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 Btu ft⁻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 ...

Table of contents

• Cover
• Dedication
• Title page
• Copyright page
• About the Author
• Preface to the First Edition
• Preface to the Second Edition
• Acknowledgements
• 1 An Introduction
• 2 Geothermal Energy
• 3 The Subsurface as a Heat Storage Reservoir
• 4 What Is a Heat Pump?
• 5 Heat Pumps and Thermogeology: A Brief History and International Perspective
• 6 Ground Source Cooling
• 7 Options and Applications for Ground Source Heat Pumps
• 8 The Design of Groundwater-Based Open-Loop Systems
• 9 Pipes, Pumps and the Hydraulics of Closed-Loop Systems
• 10 Subsurface Heat Conduction and the Design of Borehole-Based Closed-Loop Systems
• 11 Horizontal Closed-Loop Systems
• 12 Pond- and Lake-Based Ground Source Heat Systems
• 13 Standing Column Wells
• 14 Thinking Big: Large-Scale Heat Storage and Transfer
• 15 Thermal Response Testing
• 16 Environmental Impact, Regulation and Geohazards
• References
• Study Question Answers
• Symbols
• Glossary
• Units
• Index