The words "sustainable design" have crossed Architects’ and Engineers' desks many times, with potential clients frequently requesting it for their projects. Most would probably respond to such a query by saying, "Of course, that's what good design is!"

The reality, however, is a bit grayer.

Sustainability should involve more than the individual engineer, engineering department or consultant. In fact, effective sustainable design requires participation from the entire building team, including the owner and government agencies.

Public interest in sustainability has expanded from its base as a small offshoot of the 1970s solar movement to building-team professional organizations. The private sector has also begun to show interest as companies have started using sustainability as a criterion in selecting their building team.

Defining sustainable design in building construction is the use of techniques that, if carried to their ultimate, will result in a building that, over its lifetime, will be a "net producer" of energy, food, clean water and air, and promote healthy humans and communities. While this is not necessarily achievable with a typical client, many facility owners would be interested in buildings that consumed less energy, offered a healthier environment and increased worker satisfaction without costing more to build.

This is the promise of sustainable design--a building that requires fewer resources over its lifetime.

There are two good reasons to practice sustainable design: the environment and the bottom line. The impact of sustainability on operating and personnel costs is many times the construction cost. For example, a mechanical engineer may specify € 2 million of conventional heating, ventilation and air-conditioning (HVAC) equipment in a typical year, which requires a megawatt of energy. However, by applying sustainable technology, a 20-percent to 50-percent reduction can be made in peak demand. Over a building's lifetime, an engineer's designs could save € 40 million, enough to cover the annual salaries of 1,600 office workers.

Some examples of things that can assessed during a design:

• Research on individual temperature controls, day lighting and indoor-air quality has also shown measurable increases in worker productivity. While such research favors sustainable design, two entrenched facets of conventional design--building-team compartmentalization and short-term economic goals--are impediments.


• Compartmentalization reduces the ability of team members to work together to optimize the project because each team member's decisions impact the others. The building itself is a whole system and the design should take this into account. For example, fenestration and glazing impact the visual aspects of the building, applicability of light-level controls, heat gain/loss, landscaping, routing of plumbing and furniture/room layout. These items then affect the next level of design elements. Discussion and communication between team members allow each of the systems to work together. Trade-offs between building systems can increase overall building performance and reduce cost.


• As for economics, sustainable design elements can be integrated within a conventional design budget, but a much greater impact on sustainability can be achieved through a long-term view of owning and operating costs, as well as budgeting by looking at the project as a whole rather than system by system.


• Not only do the budgets of conventional projects emphasize the costs of individual systems, but the design also follows that pattern. Conversely, sustainable design looks at the building as a whole. For instance, if air intakes are analyzed according to their relationship with other building systems, they can be positioned to minimize site-generated heat gain and maximize the quality of outside air.


• A more difficult issue with the conventional design process is the lack of incentive to innovate and "right-size." It is far too easy to oversize and underdesign because there are few economic incentives, seemingly shorter and shorter project timelines and no liability for inefficiency. In fact, those projects that base fees on project cost often reward overdesign.


• Understandably, owners and occupants do not want insufficiency, but having a clear understanding of the design intent can provide a measurement of sufficiency that can be agreed to by all. Design priorities of the systems' design provide the most efficient way to achieve project goals is the bread and butter of building-team engineering. But how is efficiency defined? Is it kilowatt/ton? Capital cost? Operating cost? Life-cycle cost? Design cost? Completion time? Environmental impact?


• The creation of a design-intent document categorizes and prioritizes goals of the design. There is no right answer as each project has different goals, but sustainable designs concentrate on long-term values over short-term gains. Better design is more sustainable because better design optimizes resources.


• There are a number of guidelines and tools that can be used to create sustainable building designs. Because an integrated design process is important in creating sustainable buildings, the guidelines and tools involve the whole building team. Only portions of these tools are directly applicable to engineering, but it is important to consider the project-scale issues in order to view the building as a system.


• For example, the BREEAM and LEED (and others) guidelines help engineers to prioritize and identify possible sustainable strategies. These assessment documents tools identify goals, categories, possible strategies and measurement tools. Points are awarded based on these goals, but achieving the design is more important than the raw score. Categories that involve the M/E consultant to a high degree include interior environment, energy performance and water strategies. Sustainable HVAC Sustainable HVAC design falls under both interior environment and energy-performance categories. The interior environment factors are closely linked to CIBSE and ASHRAE, with additional emphasis on individual controls and HVAC-system monitoring. Many building codes also base the design of mechanically-ventilated occupancies on CIBSE/ASHRAE documents, so those buildings with compliant design receive basic credit.


• It is important to note that some codes allow operable windows instead of a mechanical ventilation system in certain occupancies, which, in extreme climates, reduces indoor-air quality to an unacceptable level. Other sustainability goals promote the use of operable windows and the possible elimination of major mechanical systems. However, assuring acceptable air quality requires more engineering. It is in the energy-performance category that the most dramatic gains in efficiency, and thus sustainability, can be realized.


• Basic system selection and equipment sizing affect energy consumption to a great degree. According to a recent study, oversized HVAC equipment and a lack of lighting controls are among the top three missed opportunities to save energy in commercial buildings.


• Good design does not mean over-design. The majority of mechanical/electrical devices and systems perform at their best when selected near their maximum capacity. If future capacity is desired, it is wise to plan for this, especially to take advantage of improvements in technology and performance to the greatest extent possible. Computerized design tools, in place of the conventional steady-state hand-calculation methods, can assist in selecting properly sized equipment by allowing a more accurate dynamic thermal model of the building to be created. When selecting equipment such as chillers, it is better to look at the integrated part-load value efficiency, which models the performance of a chiller based on load profiles for a given location instead of the standard part-load efficiency.