This paper discusses the question of the absence of long-term goals and standards in the Passive and Low Energy Architecture movement. It also presents the larger context – the Sustainable City - in which a clear goal and operational definition will establish a valid basis for performance goals. Sustainability as a larger context will sometimes even present counterintuitive indications of how building scale goals may manifest.

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In a paper titled, "What you say, What it is, What they get," (1) the British researcher Simos Yannis posed many provocative questions. Among these questions were:

-How low should "low energy" be?

-How green or ecological should buildings become?

-…have you doubted whether a building presented as having such attributes (i.e. low-energy, energy conscious, bio-climatic, green, ecological, appropriate, sustainable…etc.) truly had them, and exactly what that meant?

The paper consisted of these and several dozen similar questions. It was not the purpose of the paper to try to provide answers, but in order for work in Passive and Low Energy Architecture to continue to be taken seriously in the future, these sorts of questions must be given answers. Perhaps one of the reasons no answers were offered was that these questions in fact, cannot have any direct or simple answers. These questions can only have meaningful answers within a larger context. The nature of that larger context is the subject of this paper.

Any immediate answers we might pose to these questions or any standards we would try to impose would be rather arbitrary and in any case would be only temporary, always to be made more stringent in the future. The Wuppertal Institute in its best selling book, “Factor Four”, proposes that in order for Germany to become sustainable, that country’s resource and energy efficiency would need to improve by a factor of four, or perhaps even a factor of ten. Such proposals on the one hand seem to be impossible to achieve as performance goals and on the other, interpreted as policy proposals, they have begun to provoke cries of eco-fascism

More general questions would be: Why are we trying to save energy in the first place? Is it to save money, or to slow the depletion of non renewable resources, or to improve the national balance of payments, or to slow the buildup of greenhouse gasses…? The global answer to all these questions is that we see all these ecologically oriented efforts as steps in an as yet unstated and undefined process of achieving ecological sustainability.

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A critical problem in confronting the challenge of ecological sustainability is that it has been subdivided into many separate problems and issues and is being addressed by many separate, often isolated disciplines and organizations. While it is in the nature of scientific analysis to work through specialization and subdivision, it becomes very difficult to reassemble the problem of sustainability from its artificially disaggregated parts or even to understand the overall nature of the problem or the appropriate scale(s) at which to address it. It often occurs that solving problems at one scale creates new problems at larger, more important, more intractable scales. Is the production of more fuel efficient motorcars, as an example, really the solution to anything, if the larger effect is to attract more people to drive more cars for greater distances? More and bigger highways have the same effect while weakening public transport, weakening the quality of public space and ending up creating more congestion than they sought to alleviate in the first place. There is increasing evidence that much of our outstanding work in solar energy applications has used this same sort of local optimum solution approach, i.e. increasing local performance without creating outward linkages which could help to offset imbalances at the larger scale. Solving a problem locally is at the same time removing that problem from the equation thereby also eliminating its potential as a catalyst for solving the larger equation. Such an action diminishes the load on the larger system and thereby also diminishes the pressure for change, thus some of the potential for transforming it into a sustainable, balance-seeking system is also diminished.

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In contrast this approach to what we have called the "fifth operating principle for sustainable cities (now part of the Aalborg Charter, which states that "all imbalances are to be negotiated outward," (2). This is the principle which locates passive solar approaches within buildings, buildings within public space, public space within neighborhoods, neighborhoods within cities and cities within their Sustainable Area Budget or SAB (i.e. their "partnerland" or city-region). This means that there is a dedicated relationship between the smaller scale and larger scale entities where imbalances, byproducts, or problems which exceed one scale, are accounted for at the larger scale.

This principle suggests that all our excellent work and experience in low energy architecture should be leading toward an approach which doesn't just concentrate on finding ways to continually lower the energy consumption of individual buildings to some unspecifiable goal (How low is low enough?.) Rather a building in question, which may well use innovative means to lower its needs for imported energy, must be located within a larger context where its need for additional energy is also supplied from local renewable resources. In such a regime, maximizing the performance of the individual building would be a good deal less important than developing a city-region where all energy needs come from local, regenerative sources. As the processes which power our modern economies consume enormous quantities of energy, whose by-product is that same energy as waste heat, in the sustainable city of the near future this waste energy, cascaded down through various cogeneration processes will certainly find the heating of residences as its final end use. This means for example, that it will be of less interest to use the inconsistent availability of the winter sun for solar heating and of greater interest to use it for its own sake in daylighting. This doesn't mean that we won't be concerned with producing energy efficient buildings. Any energy saved will always be of value somewhere else in the city-system budget. But it does mean that as we begin to apply the marvelous range of tools, details, materials and systems which we have developed for energy conservation at the building scale, to the scale of the sustainable city, we can expect altogether new and sometimes counterintuitive opportunities to emerge. This has been the experience at the Westbahnhof.

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The fifth operating principle for sustainable cities is also useful in supporting what we have proposed as the operational definition of the sustainable city. It is our contention that only through an accurate and widely accepted operating definition can Professor Yannas' questions find their case specific answers and only through such a definition can our work at smaller scales be validated. Here is that definition for your consideration:

Sustainability is a local, informed, participatory, balance-seeking process, operating within a Sustainable Area Budget (SAB), exporting no imbalances beyond its territory or into the future, expanding the spaces for possibilities to flourish.

A full explication of this definition may be found elsewhere (3), but a brief discussion here will be useful. To paraphrase Tip O'Neal, "All sustainability is local," that is to say, all imbalances and offenses to the environment are caused locally. This means that, following the fifth principle, imbalances are either to be resolved locally or their accountability must be negotiated from some agency beyond the local scale. Local here means city-region as it is the metabolism of the city and the city's demands which generate any problems we need address. "Informed" describes an enlarged and engaged societal role for science. Informed means that before decisions are made and implemented, the effects of those decisions are modeled as their influence reverberates through the city- system. In this way the imbalances created through alternative courses of action can be understood and accounted for before any actions are actually taken. Alternative systems models of the emerging city are created and stakeholders through a participatory process can experiment with and negotiate the future form and structure of their city. The process itself is a balance-seeking process, that is, in order for any proposal to persist and eventually prevail it will have to become part of a city scenario where the system has the capacity to regulate itself toward balance. But the resources available to effect these balances are not unlimited. There is a Sustainable Area Budget, which needs to be established for each city-region. In concept this land budget is rather simple. It is the same fraction of the country's land area as the city-regions population is a fraction of the country's population. Such a local process will follow the fifth operating principle of sustainable cities and export no imbalances beyond its territory or into the future. Such a process is not a mechanistic operation. Because each city-region has a different location with different resources, different people with different histories, traditions, skills and ideas, each sustainable city will evolve its unique form and structure as the process so described will expand the spaces for possibilities to flourish. .

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The city of Vienna, Austria is interested in considering building a Sustainable City Implantation as a solution to a long standing urban problem: the necessity for the overbuilding of a major train yard at the Westbahnhof. Developed conceptually through numerous architectural design studio projects, the Sustainable City Implantation (SCI) is inspired by the historic medieval European hilltown. This City-as-a-Hill prototype, rendered through a sophisticated and flexible computer systems dynamics model called the Sustainability Engine© presents a new holistic, people centered, urban vision. In the SCI, sustainability is non-negotiable. This means that all major material flow processes are regenerative and the implantation is completely powered by solar renewable resources.

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Having established a coherent, consistent and complete theory of the sustainable city/region, the question remains as to how to proceed from theory to practice. In fact the evolution of the theory has been paralleled by the co-evolution of a new urban form. In seeking an appropriate form and structure for the sustainable city of the future, it is not so much a question of identifying means to solve the many problems of existing cities. Rather the more productive approach has been to synthesize a new model where the problems of the modern city never even appear and the above process definition of sustainability can be strongly supported. In the iterative, trial and error process known to all designers, numerous different concepts are proposed and studied. Unproductive directions are eliminated and promising models are saved. By circling around the problem over and over again, a locus of mutually supportive relationships slowly emerges. It is not just a question of seeking a perfect form or the right form. It is rather determining and developing a family of forms related to one another, with the flexibility and responsiveness to accommodate a variety of possible local preferences.

Thus structures are chosen at a variety of scales which have mutually supportive tendencies, that can be associated with the needs and possibilities of sustainable cities. From the definition of the sustainable city/region a number of strong tendencies can be inferred. The definition suggests a dense, compact city with a dynamic balance between community and privacy. It suggests a community rich in form, public space and individual and collective opportunity. It suggests a city with a strong sense of itself as a place, a clear and defined form and a common destiny. It suggests a human scaled environment, without such overscaled structures which in the modern city, are sized to accommodate vehicles, industries and faceless institutions. Yet it also suggests a city able to find appropriate space and place for the various larger scaled industries and infrastructure necessary to accommodate the metabolic and economic processes of a modern city.

Some of the characteristics which have been integrated in the Westbahnhof Sustainable City Implantation and the design studies which preceded it include:

-Right Size: An urban form small enough to be easily walkable and small enough to eliminate even the desire for the private automobile, yet large enough to provide the variety of opportunities and services that would constitute a rich urban life.
-Three Dimensionality, Accessibility, Imageability, Density, Compactness: continuity of walking surface, many different handicap accessible pedestrian routes through the city without over reliance on elevators and escalators. Of such structure and organization that virtually all needs and services for the great majority of inhabitants may be provided within the sustainable city implantation. Maximizing the use of all horizontal surfaces to create a great variety of useful spaces at many scales. Having a clear form and boundary, and a clear yet complex three dimensional structure.
-People oriented spaces: Of such structure that no large monofunctional buildings or buildings with large spaces front on public paths where they would create dead or dangerous zones within the city.
-People oriented Scale: Enhancing the public spatial realms while providing for many scales of private realm.
-A green city implantation: which absorbs material and energy flow problems which overflow the surrounding unsustainable city and export ecological, equity and economic benefits to that city.
-Complex and Flexible Urban Concept/System: developed to support participatory design processes and sustainability balancing, governing and managing processes.

In seeking to discover an urban structure with the above characteristics, our proposal for a new type of city district combines some of the most compelling aspects of the medieval European hilltown with the best of modern processes and technology. Instead of the medieval city on a hill, this proposal is for a City-as-a-Hill whose outer surface in scale and texture resembles the pedestrian scaled medieval towns built to human measure. Using advanced computer modeling software, which allows for the possibility of generating many varieties or models of such SCI's in an interactive and participatory manner, this new urban configuration creates many opportunities not possible in the modern unsustainable city (1&2). In our City-as-a-Hill model the outer (upper) surface of the city contains all of the dwellings and neighborhoods, the smaller scaled commercial and institutional activities and the network of public buildings and public spaces that is, the streets, walkways, stairs and squares which give historic medieval towns their life affirming, pedestrian character. Inside the City-as-a-Hill, daylit by courtyards and light wells, is a series of concourses and gallerias along which are located the large scale commercial, institutional, and industrial spaces as well as the infrastructure and other activities necessary to support a modern sustainable economy.

Over the years in which these models have been developed, the structure and complexity of our studies have increased at many scales. A new concrete structural system, the Coupled Pan Space Frame, with unusual flexibility and efficiency, which generates a complex family of building geometries is being used as the framework for both spanning the train tracks below and for creating the inner hill and the urban fabric above (6,7). This permits the negotiation of both level and sloping streets on the constructed hill, giving it the sort of three dimensional, organic character rarely seen in modern architecture and modern cities. More recently, the use of computers to assist in converting theory into practice has made it possible to increase both the flexibility and the complexity of the urban models.

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Behind the Westbahnhof, one of Vienna's main rail terminals, lies a train yard 1.5km long by 200m wide. For many years this yard has been a wound within the city, dividing a neighborhood and creating near slum conditions on either side of the yard. There have been many proposals to overbuild the yard but none has been either a suitable economic proposition or a sufficient urban contribution to be acceptable the city. The present proposal (4,5) builds a glazed, vaulted train shed behind the terminal building at the east end of the site. It is in part in the tradition of the early glass train sheds still to be found in many major European cities, except that at the Westbahnhof the hectares of glazing contain integrated photovoltaic collectors that deliver a substantial percentage of the Implantation's energy requirements, while modulating the climate and quality of light entering the terminal. A pedestrian street starts from the terminal and runs the length of the site to the west, parallel to the tracks, rising up the constructed City-as-a-Hill at a gentle six percent slope. As it rises it crosses other horizontal floor levels and at every third level (levels 4,7,and 10) it passes through a public square or piazza. A streetcar runs along this otherwise pedestrian street and after passing through the main piazza (Hauptplatz) at level 10 it descends through piazzas at levels 7, 4, and 1 to join an existing trolley track at ground level. At the center of the Hauptplatz is an "Energy Fountain." On the surface of the constructed hill - its new ground - is a human-scaled town with networks of streets, and stairs-piazzas and paths, weaving between three to five story neighborhoods of dwellings and a full variety of shops and services. Also on the hill's surface is a winter garden growing food year round, and a network of south-facing greenhouses. At the west end of the village is an east-west exchange center which is roofed by a large terraced ecological park, connected to the existing technological museum. At this end of the site from an existing park begins another sloping street which is more like a linear park culminating at the level 10 Hauptplatz. On the surface of the constructed hill - its new ground - is a human-scaled town with networks of streets, and stairs-piazzas and paths, weaving between three to five story neighborhoods of dwellings and a full variety of shops and services. Also on the hill's surface is a winter garden growing food year round, and a network of south-facing greenhouses. At the west end of the village is an east-west exchange center, which is roofed by a large terraced ecological park, connected to the existing technological museum. At this end of the site from an existing park begins another sloping street which is more like a linear park culminating at the level 10 Hauptplatz. By this main square is a fountain which is also an energy gnomon--that is, the height of the fountain is an indication of the amount of renewably generated energy the Implantation is exporting to the surrounding neighborhoods. Overflow from the fountain trickles down through the linear park, feeding various ponds and other green areas along its course. The roofs of the outer city are either glazed greenhouses or flat roofs which are all utilized either as private or semi private terraces, gardens, courtyards or public parks, playgrounds or piazzas.

Running almost the length of the site a three-story high galleria runs within the hill at level 4 and another shorter one runs at level 7 connecting the piazzas at those levels. #Levels 4 and 7 as the major horizontal circulation levels, connect courtyards in the outer city to each other and to the piazzas, as well as connecting to the inner gallerias. Along the gallerias, daylit through courtyards and light wells from above, are all the large major institutional, commercial, and industrial activities as well as infrastructure, service, parking, tracks and transportation; activities whose large scale and people unfriendly aspects often disrupt the integrity of a traditional urban fabric, but which are necessary to sustain a modern urban economy. In the City-as-a-Hill they fit in very well, providing maximum accessibility without compromising its small-scale, village character.

The Sustainable City Implantation is a totally urban construction, which multiplies value, in part because it multiplies real estate. Railroad services occupy almost the entire site at the original ground level, but there are additional levels of developable real estate in the framework above with their own appropriate functions and activities. Because it is completely urban, and has no open ground of its own, the Implantation is to be linked with a rural partnerland, which is dedicated to its sustainability rebalancing process. On this land most of the agriculture and energy from solar/regenerative sources would be negotiated with its urban counterpart. The urban implantation together with its rural partnerland would constitute a contained ecological footprint (appropriated environmental space)--that is, the combined land area that would provide all the major energy and resource needs of this equitable territorial partnership while resolving any ecological imbalances on site.

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In subsequent stages of the work, the city models and their parts will become the framework for the integration of other systems including: mechanical, electrical, material and infrastructural systems, facilities management, information, energy and material flow models, economic activity, imports and exports (input/output) to the city, and the modeling of the ecological balances within the city and between the city and its rural partnerland. This will be done on a systems dynamics program we call the Sustainability Engine©. Our operational definition describes the Sustainable City Implantation as one that exports no problems to its larger environment or to the future and absorbs some of the larger city's problems while exporting to the city a positive sustainability quotient. Thus we set sustainability as the one non-negotiable characteristic and begin our other negotiations from there.

The Sustainability Engine© is the autonomic nervous system of the Sustainable City Implantation (6). Both during the design process and in the governance and management of the city the Sustainability Engine© houses the energy, material flow and process models that are studied and experimented with in the development of the city. As the city, its processes and industries are studied, the Sustainability Engine© provides frequent feedback on the ongoing state of the system and indicates the sectors where it is out of balance. It is also intended to provide many utilities to facilitate the balance-seeking, and negotiation, within the design process.

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By adopting this theoretical framework as the basis of regional planning and management, a city/region will be able to operate within the realm of sustainability. Once the viability of such a sustainability process is demonstrated, the success of that example will be a catalyst to the proliferation of sustainability to the countless other city/regions of the planet. This definition has profound implications for the future of the design professions. The major challenge of our times is to forge an equitable way of living on this planet, within the limits of nature. This challenge is seen as a design problem, a major part of which is an urban design, urban management and an architectural design problem. More importantly, the methods to be used in this process will derive from and are much more akin to traditional architectural design methods than they are to science and its analytical methods. Sustainability is seen as a process for transforming society from an exploitative, consumerist enterprise to an equitable society where the balances between human enterprises and between humankind and nature are negotiated locally. Although such a process derives from traditional design processes, a new expanded architectural design process is envisaged. Instead of relying solely upon the hoped for genius of individual architects, the sustainable design process will also benefit from the collective genius of all the individual stakeholders in the equitable ecological city/region (7). In spite of the fact that the sustainability design process will require working in a highly interactive way with other professionals and stakeholders, the architect will be located in a much more critical position than conventional practice affords. Thus for the architect, both challenges and opportunities will greatly increase in the design and management of the sustainable city of the future.

The issue of urban sustainability promises to create the next major transformation both in architecture and in our cities. In many ways the Sustainable City will represent the rebirth of Modern Architecture. The Athens Charter became a disaster for our cities. Because of the mechanistic ways in which it separated functions and activities, it reinforced the economic tendencies toward unsustainability. In contrast, the sustainable city will demand a dense, diverse, highly integrated urban fabric. It will demand a whole new range of architectural and urban form and structure. It will put architects and architecture at the center of a participatory process demanding the skills and creativity of all it participants. It will complete the agenda of Modern Architecture by making it whole.

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1. S. Yannas, ‘What you Say, What It Is, What They Get’ 1993 ISES Conference, Budapest

2. E.J.Yanarella,., and R. S. Levine. ‘'Does Sustainable Development Lead to Sustainability?’ in ‘Futures’ # 24, (October 1992): 759-774.

3. H. Dumreicher, R.S. Levine, E.J. Yanarella, T. Radmard, 'Generating Models of Urban Sustainabilty: Vienna's Westbahnhof Sustainable Hilltown,' Jenks, Burton, Williams eds. in, 'Achieving Sustainable Urban Form,' (Routledge, London 2000)

4. H. Dumreicher, and R.S. Levine, ‘Stadthugel Westbahnhof: Ein Kostprobe,’ (Vienna, Oikodrom 1995)

5. H. Dumreicher,, and R. S. Levine, 'Stadhugel Wien Westbahnhof: Zweiter Teil Die Dreidimensionale Stadt - Strassen, Platze, Menschen,' (Vienna, Austria: Oikodrom. 1996)

6. R.S. Levine, ‘The Coupled Pan Space Frame: A Structural Framework for Solar Conserving Buildings,’ ‘Progress in Passive Solar Energy Systems,’ (American Solar Energy Society, National Passive Solar Conference, Knoxville, Tennessee, 1982)

7. R.S. Levine, ‘The Future Medieval City,’ ‘Spazio e Societa, Space and Society 10’, (Milan, 1987)

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