Building Envelopes: An Integrated Approach

Energy: Minimizing and Maximizing

By Jenny Lovell

Foreword

By Bob Allies
Allies and Morrison, London

The last century saw a radical change in the nature of the building envelope. Rather than being considered as part of the structure – a single, homogeneous plane perforated by openings – it began to be conceived instead as a separate layer that, relieved of any structural responsibility, could fulfil the sole function of protecting the interior of the building from the vagaries of the outside world.
 

At first sight, this separation of a buildings structure from its envelope might be expected to be liberating, freeing the contemporary architect to invent new and radical solutions to the problems of creating building enclosure. But the reality, as this book makes clear, is at once more complex and more interesting. The design of the building envelope has to address a wide spectrum of issues, ranging from the technical performance of the individual materials and the nature of their assembly to the visual appearance and propriety of the resulting building form.
 

In setting down and explaining these various issues in this book, Jenny Lovell draws them fully into the design process, offering the prospect of generating architectural form and meaning directly from their resolution. For this to happen, an approach is required that fuses practical considerations of how a building works – how it maintains the physical comfort of its occupants – with aesthetic, or cultural, considerations of how a building looks – how it is assimilated into its context and what it represents. “Poetic sensibility integrated with pragmatic application,” as Lovell describes it.
 

When addressing these issues in the past, an architect would, conventionally, have interpreted his obligations as being on the one hand to the client – for whom the building was being provided – and, on the other, to his own professional reputation. Today, however, this is no longer enough. The threat of climate change, and the growing recognition of the need to combat it, has given architects a fundamental obligation to design buildings that consume a minimum amount of resources in their production as well as in their long-term operation and maintenance.
 

Inventiveness and ingenuity are therefore critical to the design of building envelopes in the future, and the complete integration of the skills and experience of all members of the design team will be fundamental to this process. The innovation needed is of a particular kind: it is not introduced in order to make one building look different from another, but is aimed at the development of new models and archetypes that have widespread relevance and application.
 

This requires a more thorough understanding of the issues that are to be addressed, more active research into the solutions that might be adopted, and more imaginative speculations as to how these problems might be solved. Because of the nature of the discipline, it also means architects must be capable of explain these issues to their client, thereby eliciting their support for the inevitable additional investment that will be required.
 

What this book also advocates, however, is that the architect should engage with the particularities of his or her specific project – the exact nature of the climate that it has to moderate, the precise type of activity it has to accommodate, and the context to which it has to contribute – to develop buildings of originality and imagination, building that go beyond the adoption of the run-of-the-mill solution.
A buildings envelope forms the critical interface between its interior life and the environment of the external world. Its design is therefore at the heart of the architectural process, a process that will be both informed and stimulated by the guidance that this book provides.
 

Energy: Minimizing and Maximizing
Reducing potable water demand by 10 percent could save approximately 300 billion kilowatt hours of energy each year in the US….Reduced water demand provided by rainwater harvesting systems translates directly to energy savings.
– Christopher Kloss
 

Energy: Problems
 
Our consumption of fossil fuels has accelerated global warming through carbon dioxide emissions. Nearly half (48 per cent) of all annual energy consumption and carbon emissions in the United States are associated with energy use in buildings, and 76 per cent of all power-plant-generated electricity is used just to operate buildings: heating, cooling, lighting, hot water, and the plug load (electrical use from equipment powered by plugging into an outlet). Most of these uses are directly affected by a perimeter enclosure condition in a building.
 

Data regarding energy use and carbon emissions is widely circulated, but it is often examined out of context and without consideration for the way people actually occupy and utilize space. A low rise office building will likely consume less energy per sqaure foot than an inner city high-rise but consume greater energy per capita. Architect and energy expert Michelle Addington explains this, writing “High-rise buildings generally have more than twice the number of occupants per square foot as low-rise buildings,” and “the typical high-rise buildings uses 50 to 70 per cent less energy per person than does the typical low-rise building.” Energy efficiency is expressed in kWh/m2/yr, which relates to physical space but not to inhabitation. Energy data statistics, energy use comparisons between building types, and the ways occupants think about the energy they are responsible for using are often difficult to correlate.
 

A widespread desire for glass commercial buildings with window areas far greater than the percentage required to achieve comfortable light levels – and with high conductivity – is directly at odds with the need to curb heating – and cooling – related energy use. Equally, buildings that do not take advantage of daylighting through appropriate building envelope design waste energy on artificial lighting.
 

Embodied energy and life-cycle metrics often consider only individual materials or components rather than whole assemblies and systems, such as a buildings envelope and its performance over time.
 

Energy: Principles
 

The performance of a buildings envelope is pivotal to the energy consumption of both commercial and residential projects, albeit in different ways. Housing typically has a greater envelope-to-volume ratio, meaning that energy consumption is greater for heating and cooling and less for lighting and plug loads. On the other hand, commercial buildings usually have a greater volume-to-envelope ratio, necessitating higher energy use for lighting than in housing. Additionally, plug loads for commercial buildings are dramatically higher than in residential buildings due to greater occupancy.
 

The energy related to a building must be considered from two different perspectives: the embodied energy of the materials from which it is constructed, including the recurring embodied energy of materials required for maintenance, repair and replacement during its life; and the energy required to run the building, along with the carbon emissions related to that energy use. The former relates to building fabric, the latter to building occupation.
 

In a typical office building, approximately 26 per cent of its total embodied energy (the acquisition, processing, manufacturing, transportation, and construction of raw materials) is associated with its envelope. The longer a building lasts, the greater its recurring embodied energy. However, the operating energy of a typical office represents 85 per cent of total-building energy at the end of a 50-year life span – as a building gets older, its operating needs go up, since the building fabric deteriorates to an extent over time.
 

The reduction of a building’s energy consumption should be addressed in the following order with regard to capital and operational costs: increasing systems efficiency and reducing loads; introducing passive systems such as massing, material specification, and solar utilization; and lastly, applying active systems such as photovoltaic panels. This order is based on a return of investment, the first reduction being the simplest and least expensive to implement if addressed early on in the design process.
 

Metering mechanisms are used to assess carbon dioxide emissions and energy efficiency, and energy consumption can also be compared to benchmarks. Through metering and post-occupation evaluation we can understand what, when, and how occupants use energy. For example, the largest single energy use in buildings is electricity. Electricity meter data generally registers as a lump-sum figure, with no way to differentiate between use for lighting versus cooling versus plug loads (such as computers, lamps, fans and heaters). Submeters can break down “building” loads, (the energy needed to run the building’s systems) from “process” loads (such as plug-in computers) and allow identification of increased peak loads and energy usage over time, throughout the day and year, so designers and building users can specifically assess how energy is used.
 

Best-practice reference standards such as LEED (Leadership in Energy and Environmental Design, in the United States) and BREEAM (Building Research Establishment Environmental Assessment Method, in the United Kingdom) are two examples of environmental measurements for the performance of a building. LEED gives points for the design of building envelopes and systems that maximize energy performance as a part of building rating. It calls for the use of a computer simulation model to assess performance and to identify the most cost-effective energy measures. Energy performance must be compared to that of a baseline building, as established by the American society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 90.1. A baseline building meets the building code and legislation as it stands and is relative to current ASHRAE standards.
 

Energy: Possibility
 

Since buildings are responsible for such a large proportion of energy consumption, they are potentially a huge part of the solution-any change in the building sector will have a global effect. Dramatic reductions in energy consumption and carbon emissions are possible with the application of fundamental, but not complicated, changes. Research into greenhouse gas (GHG) abatement by consultants McKinsey & Company show that there is potential to reduce GHG emissions in 2030 by 35 per cent compared with 1990 levels. This reduction could be even greater if inhabitant behaviour can be changed, i.e., if users start to take more responsibility for their interaction with the environment. Figure 1 shows the portion of the study related directly to the building sector.
 

Figure 1
This greenhouse-gas abatement cost-curve by McKinsey & Company provides a quantitative basis for discussions about what actions would be most effective in reducing emissions and how much they might cost. This extract shows abatement measures specifically related to the building sector-primary areas of address are directly related to the building envelope: insulation, airtightness, passive-solar utilization, and lighting. The y-axis measures abatement cost in Euros per metric tons of carbon dioxide emissions (the cost to make the reduction in emissions), and the x axis shows the abatement energy-savings potential (reductions in emissions potential), in million metric tons of carbon dioxide per year. The thicker bars indicate greater emissions abatement for less cost.
 

There are four major categories of abatement opportunities: energy efficiency, low-carbon energy supply, terrestrial carbon, and behavioural changes. In terms of building envelope performance, energy efficiency is directly related to airtightness and insulation performance. Effective design and maximum efficiency can be achieved without compromising design criteria.
 

To address energy efficiency in a building, its localized and regional site-including site shading, vegetation, orientation and prevailing winds-must be considered first and foremost. Passive cooling and natural ventilation, when combined with appropriate window ratios and sun-shading strategies, can reduce mechanical systems demand significantly in both residential and commercial buildings. Professor Joel Loveland, director of the University of Washington’s BetterBricks Integrated Design Lab and an expert in daylighting design, states that “Buildings that take advantage of diffuse, well-shaded daylight for illumination of critical task spaces often reduce their electrical use by more than 40 per cent through the reduction of electric lighting requirements and peak cooling demand.” It is easy to understand the huge potential of daylighting has for the reduction of carbon emissions and pollutants when considering that lighting accounts for about 20-25 per cent of the total energy consumption and even 30-40 per cent in the commercial sector. Business hours coincide with daylight hours, and naturally lit buildings reduce electricity loads and allow the building users to play a role in the control of lighting, contributing significantly to user satisfaction.
 

Behaviour changes related to building enclosure require a paradigm shift from steady-state expectations-where building performance is largely invisible to users-to a raised awareness of users, operators, and managers. Inhabitants must be “active, committed, and knowledgeable,” interacting directly with a building’s envelope and systems to have some degree of control over daily comfort. To quote Katherine Janda of the Environmental Change Institute at Oxford University, “Buildings don’t use energy: people do,” and in the face of climate change designers need to prepare inhabitants for an interactive role and seek way of integrating user involvement. A buildings envelope provides its most tangible opportunity of interaction and control, at a threshold between external and internal environments.
 

Figure-2
This diagram shows the conventional approach to providing comfort in building design practice, where emphasis is on mechanical and electrical systems and where consultants operate independently from each other.
 

Figure-3
This diagram explains an emerging expansion of the notion of comfort: a building and inhabitant system that aims for interactivity, with flexibility to adapt to the changing needs of the entire system over an extended time.
 

This extract has been taken from the book “Building Envelopes: An Integrated Approach” by Jenny Lovell from “Section II: Elements of a Holistic Approach”, “Energy: Minimizing and Maximizing”, published by Princeton Architectural Press, New York. I urge you to buy and read with care this excellent book. It is available on Amazon.