The Shape of Things

Feb 1, 2008 12:00 PM, By Joe Aliotta and Gerald Pde

A high-performance school relies first on form and materials, and then on systems.

Ventilation strategies

An effective ventilation strategy also is critical in a high-performance school because it improves indoor air quality and thermal comfort, and reduces reliance on conventional mechanical systems. Today's displacement ventilation strategies go well beyond the use of conventional mixed ventilation. Ventilation strategies also can be analyzed early in the design process to assess their energy efficiency and life-cycle costs. These strategies can include simple systems, such as side-wall displacement terminals, and more complex underfloor systems.

In addition to widely available raised-floor systems, non-conventional underfloor air systems can deliver air and improve the thermal comfort in a space. They reduce the need for ductwork and drop ceilings, and provide radiant and forced-air heating through a network of steel forms embedded in the concrete slab. Another alternative distributes ventilation air via a duct integrated with the partition walls between two classrooms. The supply vents can be on the wall or integrated with classroom furniture.

Meeting demands

Displacement ventilation and envelope strategies can reduce cooling and heating loads in the building. Mechanical energy is required to meet the remainder of the building load and provide a comfortable environment. After the building envelope is optimized, the school and design team may choose to evaluate supplementary mechanical systems, such as chiller-boiler mechanical systems or advanced geothermal systems. The team, ideally, also will consider further strategies to optimize the chosen system, including careful selection of variable frequency drives, fan motors, heat-rejection equipment and building automation controls.

A geothermal heating and cooling system can be a good choice for a school that has relatively uniform heating and cooling loads, and that is on a site that offers adequate installation area, such as athletic fields, to serve as a geothermal well. In this system, a geothermal heat pump takes advantage of the relatively stable earth temperature (45°F to 58°F) deep in the ground. Water or another liquid is circulated through pipes buried in a continuous loop in the geothermal well. Depending on the temperature in a building, the water is used to transfer heat into or out of the building.

In addition to these key issues and systems, a high-performance school design also requires analyses of water-management issues — in particular, stormwater management, landscape design and maintenance, and indoor plumbing fixtures. For example, rainwater-harvesting strategies that employ the roof structure may be investigated during the building envelope study.

Aliotta is principal of Swanke Hayden Connell Architects, New York City. Pde is an associate, practice leader-building simulation and systems analysis, with Atelier Ten Consulting Environmental Designers, New York City. The firms collaborated on the Hamilton Avenue School (see sidebar above).

45 to 58

The Earth's relatively stable temperature in degrees Fahrenheit. A geothermal heat-pump system takes advantage of this temperature.

Achieving the gold standard

The new Hamilton Avenue School, a pre-K to 5 facility under construction in Greenwich, Conn., was designed as a high-performance school.

The project includes 60,000 square feet of new construction, along with the partial restoration and reuse of a historic 1938 building, accounting for an additional 16,000 square feet of space. The contemporary design of the new portions of the building complements the historic fabric of Hamilton Avenue in Greenwich through the preservation of the civic front of the existing school, a brick and stone building with a slate roof and signature cupola. Classrooms are organized in clusters by age group. The new gymnasium and cafeteria will be designed to accommodate multiple functions and community use.

Designed to the equivalent of LEED gold certification, the school features a geothermal system, extensive daylighting and top-lighting of the classrooms, displacement ventilation and a super-insulated building envelope. The school chose not to pursue formal LEED certification because it would have incurred additional cost for registration and submittal, and certification is not a Connecticut state mandate.

The design incorporated energy and daylighting analysis; modeling studies and life-cycle cost analyses of certain aspects of the building envelope; natural ventilation strategies; and assessment of the costs and benefits of using a geothermal system over a chiller-boiler system.

For example, factoring in the results of the building envelope, ventilation and daylighting studies, the geothermal energy modeling study compared a ground-source heat-pump system to a four-pipe chiller boiler system. The results found that the geothermal system would achieve a simple payback in just 8.1 years, returning a net-present-value savings of more than a quarter million dollars over 25 years.

Overall, a life-cycle energy cost analysis projected a five- to seven-year payback for the upfront costs of high-performance design strategies compared with a conventionally designed school.