Building Services Design for Energy Efficient Buildings

Paul Tymkow, Savvas Tassou, Maria Kolokotroni, Hussam Jouhara

• Publisher: Routledge
• Year: 2013
• Print ISBN:
  9780415596374
  9780415596367
• Edition: 1
• eBook ISBN:
  9781136893650
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

The role and influence of building services engineers is undergoing rapid change and is pivotal to achieving low-carbon buildings. However, textbooks in the field have largely focused on the detailed technicalities of HVAC systems, often with little wider context. This book addresses that need by embracing a contemporary understanding of energy efficiency imperatives, together with a strategic approach to the key design issues impacting upon carbon performance, in a concise manner.

The key conceptual design issues for planning the principal systems that influence energy efficiency are examined in detail. In addition, the following issues are addressed in turn:

Background issues for sustainability and the design process

Developing a strategic approach to energy-efficient design

How to undertake load assessments

System comparison and selection

Space planning for services

Post-occupancy evaluation of completed building services

In order to deliver sustainable buildings, a new perspective is needed amongst building and services engineering designers, from the outset of the conceptual design stage and throughout the whole design process. In this book, students and practitioners alike will find the ideal introduction to this new approach.

Chapter 1

The imperatives for an energy efficient built environment

1.1 Introduction

This chapter provides a brief introduction to the key background issues related to sustainability in the built environment, primarily those arising from carbon emissions due to the use of fossil fuels. It starts by looking at the principal threats to the global environment and the need to undertake development in a sustainable way. The background issues of global warming and climate change are summarised, together with an outline of the predicted impacts which indicate the scale and urgency of the challenge. The UK targets for limiting carbon emissions are described, together with an indication of recent performance against the targets. In order to show the relevance of these issues for building services design, the carbon impact of the built environment is outlined. An important factor is the processes through which energy is delivered to buildings, including the key issue of energy wastage through conversion and distribution, and other impacts of using fossil fuels.

A separate impact of fossil fuel usage is examined through looking at the reduction in reserves available, together with the adequacy of infrastructures to meet the anticipated supply side and demand side of energy requirements in the near future. A further aspect of energy strategy relates to materials used in building construction and operation, and to identifying ways in which their impact can be reduced.

The final part of the chapter looks at general principles that apply to the design of sustainable products and services. These are put into context for buildings, with an emphasis on the need for a whole-life approach and to challenge prevailing solutions, with a primary focus on demand reduction.

It should be noted that this chapter focuses primarily on the carbon and energy aspects of sustainability, rather than the wider factors.

1.2 Principal threats to the global environment

To understand the imperative for sustainable development in the context of the built environment, it is necessary to start from a perspective of the wider nature and range of environmental factors that threaten man’s continued habitation on Earth; and then identify those causes that specifically arise from the built environment. By identifying the priorities for attention, it is possible to focus on the key aspects related to design for the built environment, while accepting that a wider range of environmental factors will require attention to contribute to the broader objective of sustainability in practice.

A major study was undertaken by a group of scientists in 2009 to identify the principal environmental processes that could cause significant disruption to human life on Earth. The study, which was under the auspices of the United Nations, also sought to calculate boundaries for these processes which, if exceeded, could limit the planet’s ability to sustain human life. Summaries of this study were reported by Foley (2010) and Pearce (2010), and identified nine key environmental processes:

• climate change

• ocean acidification

• stratospheric ozone depletion

• nitrogen and phosphorous cycles

• fresh water use

• biodiversity loss

• land use

• aerosol loading

• chemical pollution.

The study identified target values for all the processes (except for the last two, because it was felt that there was insufficient understanding to do this). Of the seven processes where targets were set, it was found that three processes have already passed their safe limit: climate change, biodiversity loss and nitrogen pollution. It was also found that the others were moving closer to their safe boundary level. For two of the processes – climate change and the increasing acidification of the oceans – the principal cause is increased levels of CO₂ in the atmosphere arising from mankind’s use of fossil fuels (Foley 2010; Pearce 2010). As the movement of any of these key processes towards their threshold levels could result in significant environmental damage, the imperative for society is to ensure that each process should be maintained as safely within the boundary figure as is practically possible. While the processes and limits were presented separately, it was acknowledged that they were interconnected in many ways. For example, the increased acidification of the oceans could have a severe impact on their ecosystems, with implications for biodiversity; and as a consequence, threaten the food chain. A further consequence is that the ocean’s ability to absorb CO₂ would reduce with acidification, with implications for the rate of climate change as a positive feedback relationship (Foley 2010; Pearce 2010). Climate change is likely to have implications for fresh water, biodiversity and land use.

The key message that emerges is that mankind now has a clearer indication of the limitations of the Earth’s resources and their rate of usage. There is also better understanding about the ability of the Earth to absorb the waste and emissions arising from their use. It is incumbent upon society, therefore, to ensure that its activities are maintained within the limiting operational boundaries of the Earth’s environmental systems.

The issues outlined above relate to the key environmental processes that need to be addressed on an urgent basis. It is, however, recognised that development in all senses needs to adopt principles that will allow continued and sustainable habitation on Earth. Sustainable development has been defined in the 1987 Brundtland Report as ‘Development that meets the needs of the present without compromising the ability of future generations to meet their own needs’ (UN 1987). This introduced the concept of sustainable development being a satisfactory balance between environmental protection, social equity and economic development, sometimes known as the ‘triple bottom line’, as shown in Figure 1.1. While there is a wide range of challenges involved in achieving such a balance (Drexhage and Murphy 2010), there is a prevailing scientific view that the most significant threat to a sustainable future is climate change arising from ‘anthropogenic’ (i.e. caused by mankind’s activities) global warming. This is mainly due to the presence of greenhouse gases (GHGs) in the troposphere, as described in the following section.

1.3 The greenhouse effect, global warming and climate change

There are a variety of natural factors that have altered the climate of the Earth in the past, and there is a natural ‘greenhouse effect’ that has warmed the Earth’s surface for millions of years (DECC 2012a). These natural factors cannot, however, account for the extent of warming that has been observed since 1990 (DECC 2012a). The evidence from the spatial pattern of warming, and the results of modelling, indicate this warming has largely been due to increased emission and accumulation of greenhouse gases (GHG) caused by mankind’s activities. This has created an ‘enhanced greenhouse effect’, alongside which are feedback processes that cause amplification of the warming (DECC 2012a, 2012c).

The physics and mechanisms associated with the interaction between the Earth’s atmosphere and fossil fuel consumption are, obviously, extremely complicated and well beyond the scope of this book. For the purpose of understanding the basic concepts and terminology related to climate change, a highly simplified approach is sufficient, as shown in Figure 1.2.

Figure 1.1 Sustainable development: the ‘triple bottom line’

Source: UN 1987

Figure 1.2 The greenhouse effect

Source: derived from Christopherson 1997: figure 4.1

The sun’s rays are the sole energy input and the radiation is mostly in the visible part of the spectrum (Coley 2008). This short-wave, high-frequency radiation reaches the Earth’s atmosphere where it is absorbed, reflected or scattered. A proportion (about 31%) is reflected back into space by the atmosphere, clouds and the lighter coloured areas of the Earth’s surface. This fraction is termed the ‘albedo’ (Coley 2008). Therefore, the whiteness of cloud cover, and the relative lightness of the different parts of the Earth’s surface play a significant factor in the proportions reflected or absorbed. The residual radiation heats the atmosphere and the Earth’s surface. The relatively low temperature of the Earth’s surface gives rise to long-wave, low-frequency (infrared) radiation back to space.

The radiation from the Earth is, thus, a mix of visible range that is directly reflected and infrared that is re-radiated. Over time, the Earth re-radiates an average 69% of incoming energy to space. The presence of certain greenhouse gases in the troposphere traps the heat and delays it in the atmosphere. Some of the energy is re-radiated back towards the Earth. This is known as ‘back radiation’, and warms the surface and the lower atmosphere. This warming phenomenon is known as the greenhouse effect (DECC 2012a, 2012c), as the GHGs create an effect similar to that created by the glass in a greenhouse, letting heat in but preventing it from escaping. These climate mechanisms are described in detail in various texts (Boyle 2004; Christopherson 1997; Coley 2008; Goudie 2000). To provide a perspective in terms of heat alone, it has been estimated that the total heat arising from all human activities is only about 0.01% of the solar energy absorbed at the surface (Goudie 2000).

The overall increase in heat that results is called ‘global warming’. It is estimated that the Earth is warmer than it has been at any time during the past two thousand years (Coley 2008). The atmosphere close to the surface of the Earth has risen in temperature by about 0.75°C since about 1900, and much of this temperature rise, about 0.5°C, is estimated to have occurred since the 1970s (DECC 2012a). There has been other evidence of global warming in recent times, including rises in sea level and reduced levels of sea ice in the Arctic (DECC 2012c).

Global warming will affect the world’s climate in numerous complicated ways, giving rise to climate change. ‘Climate change’ is a more useful term than ‘global warming’, because it conveys the understanding that the effect could bring about colder as well as warmer climate impacts in different locations, plus other climate disturbances. It is also necessary to distinguish between weather and climate. Weather relates to the short-term variability in a particular location, whereas climate relates to the long-term pattern of statistics for conditions in a particular region (Coley 2008). The term ‘climate change’, as used in this context, refers to a change in the climate that is identifiable and continues for decades or longer and often refers to changes arising from man’s activities since the Industrial Revolution (DECC 2012a).

The principal international body on this subject is the United Nations Intergovernmental Panel on Climate Change (IPCC). This panel is made up of respected scientists from around the world, and has been publishing comprehensive reports every few years on the scientific viewpoint. The IPCC’s 4th Report (also known as Assessment Report 4, or AR4) of 2007 was regarded as pivotal because it provided a consensus of certainty on the influence of human activities on climate change. The Report concluded that most of the global warming that has been seen since the mid-20th century is very likely to be due to the increase which has been observed in the concentration of GHGs caused by human activity creating an ‘enhanced greenhouse effect’ (IPCC 2007). It considers the probability to be more than 90% (DECC 2012a).

The most important greenhouse gases are carbon dioxide, methane, chlorofluorocarbons, nitrous oxide and ozone. The relative contribution of each gas to the enhanced greenhouse effect depends on its global warming potential and the level of concentration in the atmosphere. The relative contributions have been noted by Coley (2008):

CO2	65%
Methane	20%
CFCs, HCFCs	10%
N2O	5%

Because so much impact arises from CO₂ emissions, a key question is: what is the upper threshold of CO₂ that can be tolerated in the long term, and that can, therefore, be a target? Scientists have indicated that a level of 350ppm by volume would be a relatively conservative target. It is considered that this target would maintain the relevant processes on the safe side of the tipping points for the climate (DECC 2012a). It should be noted that the generally assumed figure for pre-industrial CO₂ is about 280ppm. It is estimated that CO₂ levels have risen by about 40% since the onset of the Industrial Revolution, and are now at about 390ppm by volume. The level is now higher than it has been for 800,000 years (DECC 2012a) and has been increasing at a rate of about 2ppm per year during the past decade. Scientists reckon that a reduction of 80% in carbon dioxide emissions below 1990 levels by 2050 will be necessary to halt the rise to an assumed acceptable level, typically related to a 2°C temperature rise (although there is continuing debate on the most appropriate target). Anything less than this reduction is likely to only slow the rate of accumulation. It is clear that, to prevent the most damaging climate change impacts, the level of CO₂ and other GHG emissions has to be stabilised and then reduced to well below the present levels.

The emission of CO₂ into the atmosphere is not the only environmental impact of using fossil fuels. Burning fossil fuels also emits sulphur dioxide and nitrous oxides and particulates, with considerable impact, including ‘acid rain’ and air quality (Coley 2008). These emissions reduced considerably in the period from 1990 to 2007 (DEFRA 2009a), and have been overshadowed by the far more pressing emission of CO₂; but they have not disappeared.

There are many other direct consequences arising from energy use, such as resource depletion, despoliation of the landscape, heat, radiation, noise, etc.; together with indirect consequences (Coley 2008). Other environmental issues related to energy consumption are the manufacture, use...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• List of figures
• List of tables
• List of abbreviations
• Acknowledgements
• Introduction
• 1 The imperatives for an energy efficient built environment
• 2 The design process
• 3 Generic design strategies for low-carbon buildings
• 4 Post occupancy evaluation for optimal energy and environmental performance
• 5 Energy efficient ventilation
• 6 Air-conditioning systems
• 7 Cooling, heating and thermal energy distribution systems in buildings
• 8 Low energy approaches for the thermal control of buildings
• 9 Energy efficient electrical systems, controls and metering
• 10 Building thermal load calculations
• 11 Building electric power load assessment
• 12 Space planning for services
• References
• Index