Thermal Design of Buildings

Understanding Heating, Cooling and Decarbonisation

Phillip Jones

• Publisher: The Crowood Press
• Year: 2021
• ISBN:
  9781785008993
• Topic: Arquitectura
• Subtopic: Sostenibilidad en la arquitectura

The way we heat, cool and ventilate our buildings is central to many of today's concerns, includingproviding comfortable, healthy and productive environments, using energy and materials efficiently, and reducing greenhouse gas emissions. As we drive towards a zero-carbon society, design solutionsthat combine architecture, engineering and the needs of the individual are increasingly being sought.Thermal Design of Buildings aims to provide an understanding from which such solutions can bedeveloped, placing technological developments within the context of a wider world view of the builtenvironment and energy systems, and an historical perspective of how buildings have responded toclimate and sustainable development.

Chapter One

Introduction

THE BUILT ENVIRONMENT IS AT ONE LEVEL a necessity for providing shelter and security for people and their communities, while on another level it can promote a more positive feeling of delight. The challenge for thermal design is to produce technical solutions that lead to an overall improvement in the comfort, health and quality of life for all people, with the efficient use of energy and aiming towards zero carbon dioxide emissions.

Many aspects of heating and cooling are as dependent on architectural solutions, such as the form and fabric of a building, as they are on the engineering of mechanical systems. This is especially the case in relation to our need to reduce energy use and produce buildings that are affordable to operate, as well as comfortable and healthy to occupy. Close working between the architect and the engineer is essential for a successful solution. Heating and cooling systems should not be simply ‘bolted on’ once the architecture has been designed, but, rather, they should be fully integrated as part of a ‘whole building’ solution, whether we are dealing with a new building or retrofitting an existing one. As the building fabric becomes more efficient in reducing energy demand, the systems must be designed to respond to the reduced demand. Of course, throughout the thermal design process we must keep in mind the role of people, as end users, builders and regulators, and the need for them to be aware of what is possible.

The use of fossil fuel energy to construct and operate buildings is a major cause of climate change. Building integrated renewable energy generation is increasingly being used to supply a building’s energy needs, both for electrical power and heat. At the same time our energy supply grids are being decarbonized. Achieving an appropriate balance between building integrated renewable energy and grid-based renewable energy is therefore a major consideration in the drive towards energy-efficient zero carbon design. Sustainable design means that our buildings should be pleasing, and robust against a range of usage, rather than be dependent on control, constraint and enforced behavioural change.

Buildings do not exist independently of their surroundings. They will interact with neighbouring buildings and landscapes, creating local microclimates, which will affect energy use, and internal and external comfort. The supporting infrastructures for energy, water and sewage, waste, transport and information connectivity all have implications for energy use and sustainability.

Fig. 1.1 Thermal design.

Fig. 1.1 summarizes the main stages to thermal design, through an understanding of comfort needs; how the building interacts with climate; the heating, cooling and ventilation systems, renewable energy and energy storage; and finally within the context of the surrounding buildings and infrastructures.

Fig. 1.2 Environmental design concept model.

Fig. 1.2 summarizes the main elements of thermal design, beginning with climate and ending with environment and comfort. The passive design elements relate to the site location, the building’s form and mass, and its fabric and glazing. The active elements relate to the environmental services for heating, cooling, ventilation and lighting. Whereas passive solutions may use ‘free’ energy from the sun and the wind, active solutions rely on heating and cooling equipment that use ‘delivered’ energy.

There are various ways energy links to thermal design. The free energy is the energy gained from natural sources as part of the passive design process. The delivered energy is the energy used to power the components of active systems, such as heaters, chillers, fans and pumps. Delivered energy from fossil fuel sources will have associated carbon dioxide emissions. The eventual aim is to replace fossil fuels with renewable zero carbon energy. The activity energy is released within the building from activities and processes related to occupancy. It includes the heat from electric lighting and appliances, and the metabolic heat generated by people. These may result in a significant heat gain, which may be useful for space heating or, more often these days, may need to be exhausted by mechanical cooling to avoid overheating. The embodied energy is associated with the materials and products used during a building’s construction and fit-out, and subsequent renovations. As the delivered energy is increasingly reduced through energy-
efficient design, the embodied energy becomes a greater proportion of the overall energy balance.

There are a range of underlying topics and issues that are connected to thermal design. Globally, everything is changing, including climate, our energy systems, and people’s aspirations. The rate of construction is increasing, while our dependence on fossil fuel must cease. Recent pandemics have also challenged our vision of the future, and the role our built environment plays in the spread of infectious disease.

If we are to meet the challenge of creating a more sustainable zero carbon built environment, original thinking is needed with innovative solutions. This is often not the case in everyday building design, where there are cost and time constraints, all within a conservative construction industry that tends to resist change and an architectural profession that is often seduced by external aesthetics rather than internal functionality and in-use performance. Solutions need not be that complex, but they do need to be informed by a thorough understanding of building physics: the role of the building physicist needs to have a higher profile in the design process.

This book aims to provide an insight into current thinking in thermal design, with reference to its historical context, as well as signposting future developments. There will be no single solution for all building types and locations. The development of new technologies for reducing energy use and sourcing renewable energy means that today’s solutions may soon be overtaken by better ones in the near future. Therefore, the aim of this book is not to provide ready-made off-the-shelf recipes, but, rather, to provide an understanding of the subject of thermal design, and an awareness of what is possible, from which future innovative solutions can be developed.

Chapter Two

The Built Environment: Sustainability, Energy and Climate Change

What Is the Built Environment?

Let us begin by discussing what we mean by the built environment. The built environment spans from basic shelter to vast megacities, from rural to urban. It is the purpose-built physical space in which we live, work and play, as well as the ‘awkward’ intersections of developments and leftover space, for which people often find unforeseen solutions^2.1. The built environment comprises many building types and urban forms. And it is more than just buildings; it includes their supporting infrastructures of energy, water and sewage, waste, transport and communications. This total physical space facilitates the social and business interactions that make up our cities and communities. The buildings themselves are not the end products; they are part of the organizational processes that form the basis for society as a whole. We need to renovate and retrofit our existing buildings, as well as designing new ones. Much of the technology we develop for new buildings can be applied to retrofitting existing buildings, albeit with more challenges and generally higher costs. When new, buildings need to achieve specific performance standards for energy use and comfort, and they need to do this in a way that supports the range of activities that take place within them. A new building quickly becomes an existing building, constantly adjusting to meet the ever-changing needs of its occupants. A successful building will not only be zero energy, but will also bring multiple benefits of comfort, health, productivity, amenity and affordability, all of which depend on a successful thermal design.

New Build

New buildings allow us to pioneer our ideas and innovative technologies, especially in relation to energy-efficient design and the use of renewable energy generation.

Fig. 2.1 A ‘systems approach’ to low and zero energy design.

They provide the opportunity to respond to the immediate problems of climate change. A building’s energy use and greenhouse gas emissions are determined, firstly, by the embodied energy from sourcing materials and components, and during construction, renovation and eventual disposal; and, secondly, by the operational energy used by services for heating and cooling, ventilation, lighting and appliance loads, computers, and equipment associated with the building’s function. Within the current context of climate change, all new buildings should strive to be zero energy, and even energy positive in their design. This means high levels of energy efficiency combined with renewable energy generation and energy storage. We often use the term ‘systems approach’ (see Fig. 2.1), which integrates across all elements of construction and operation, balancing across reduced energy demand, efficient services, and renewable energy generation. The terms zero energy and zero carbon are often interchanged. A zero energy building will usually exchange energy with the supply grid, with energy imported from the grid, offset by energy exported to the grid from the building’s renewable energy generation; so it will be energy neutral over a year. It may have energy storage within the building, in order to maximize the use of renewable energy generated by the building. A true zero carbon building will have no carbon dioxide emissions associated with it, will operate ‘off-grid’, and will need a higher level of on-site generation and energy storage, or it may simply purchase green energy from the grid.

In spite of increasing government commitments to the zero carbon agenda, there has been a slow take-up by the construction industry, which is generally risk-averse to trying out new ideas, usually blaming high costs and lack of market demand. This is contrary to many products that are marketed on their use of the latest technology! So, opportunities to advance sustainable design are compromised. Sustainability is often regarded as an ‘inconvenient distraction’ from getting the job done. The person who will have to live with the building remains conveniently unaware! Nine times out of ten, the architect will do what they are told by the developer.

Fig. 2.2 Projected glo...