About Systems Engineering Research

America's new homes can be cost effective to build as well as energy efficient to live in. In fact, the energy consumption of new houses can be reduced by as much as 50% with little or no impact on the cost of ownership through use of a systems engineering approach.

Building America teams work to produce houses that incorporate energy- and material-saving strategies from the very start of the building process—the design. Initial cost-effective strategies are analyzed and selected during the pre-design phase. The team then evaluates its design, business, and construction practices to identify cost savings. Cost savings can then be reinvested to improve energy performance and product quality. For example, the design might incorporate new techniques for tightening the building envelope that enable builders to install smaller, less expensive heating and cooling systems. These savings can then be reinvested in high-performance windows that further reduce energy use and costs.

After the design has been evaluated, the team builds a prototype or "test" house. When completed, the prototype's systems are tested for efficiency and the team makes any necessary changes to the design to increase efficiency and cost effectiveness. The design is then re-tested before it is used to build additional houses. The design must be tested and re-tested for ultimate performance before it is ready for use in production or community-scale housing.

Throughout the design and construction process, the systems engineering approach considers the interaction between the building site, envelope, and mechanical systems, as well as other factors. It recognizes that features of one component in the house can greatly affect others and it enables the teams to incorporate energy-saving strategies at no extra cost. System trade-offs, like the tightened shell that enables an engineer to recommend a smaller HVAC system, can improve the quality and performance of a home without affecting its costs—to the builders or to the consumers.

Advantages to Builder:

• Reduces callback and warranty problems
• Reduces construction costs
• Improves productivity
• Improves building performance
• Allows innovative financing due to predictable lower utility bills
• Gives builder a competitive advantage.

Advantages to Consumer:

• Increases quality without increasing cost of ownership
• Increases comfort and performance
• Does not detract from the home's aesthetic value
• Reduces utility bills
• Allows greater financing options.

Examples of systems engineering cost-saving trade-offs include:

• Advanced framing systems
• Tightly sealed house envelopes
• Shorter, less costly ductwork
• Disentangling the infrastructure
• Smaller, less expensive mechanical systems
• Modular construction.

Advanced Framing Systems

Building America teams use advanced framing and insulation methods to increase efficiency and comfort while decreasing costs. In Grayslake, Illinois, one Building America team used 2 x 6-inch studs instead of 2 x 4-inch studs, set 24 inches apart instead of 16 inches. This framing technique allows more room for thicker insulation, enhances the strength of the house, and reduces thermal bridging through the studs. It also reduces the overall amount of wood used during construction and because 30% fewer pieces have to be assembled, framing takes less time and labor costs are significantly lower. By using materials efficiently, the team reduced construction costs and was able to reinvest these savings in additional energy-saving features.

Tightly Sealed House Envelopes

To construct a tight thermal envelope on a home in Illinois, a Building America team uses a new double air-barrier system. OSB siding is replaced with R-7, 1-inch polyisocyanurate rigid foam sheathing on the house exterior. The insulation board is foil faced and its joints are taped so that it acts as an exterior air barrier as well as a drainage plane for rain control. This exterior sheathing eliminates the need for building paper or housewrap thus reducing construction costs.

Interior basement walls can be sealed and insulated with R-7.5 polyisocyanurate rigid board. Interior basement insulation helps prevent heat loss and reduces chance of condensation related mold problems. Tightly sealed thermal envelopes help reduce heating and cooling loads, enabling builders to install smaller heating, ventilation, and air-conditioning (HVAC) systems. This produces a significant cost savings that can be reinvested for increased performance elsewhere.

Shorter, Less Costly Ductwork

By moving the ducts into the conditioned space, Building America homes eliminate heat loss to the exterior and limit the temperature difference at the ducts. Combining this technique with the placement of the heating/cooling system in a central location enables builders to use shorter duct runs—a move that can cut material and installation costs by over 50% and can save energy. Some Building America homes also use new round ducts only 8 inches in diameter that are cheaper to install and easier to maintain.

Disentangling the Infrastructure

If the ductwork, plumbing and wiring are all placed inside the conditioned space, the house envelope will no longer need to be broken by entry and exit points. This saves labor and material costs and contributes to a tighter seal thus increasing the home's energy efficiency. The use of open floor web trusses allows for fast, easy installation of ducts, plumbing, and wiring in the conditioned space, thus saving construction time and costs. The open floor web trusses also allow for the installation of smaller more efficient, less expensive 8-inch ducts.

Smaller, Less Expensive Mechanical Systems

Once the house is tightly sealed, a smaller system is needed to condition it. Builders can realize substantial savings on heating and cooling system costs, as demonstrated by a test house built by a Building America team in Maryland. The house requires only a 1.5-ton system, while comparable homes require a 2.5-ton capacity.

Modular Construction

A Building America house in Cambridge, Massachusetts, is constructed of factory-made modules. The modules are stacked one on top of the other, which reduces construction time and costs. Instead of a simplified duct system, these houses are divided into zones. Each zone has its own thermostat so that it can be heated or cooled independently. Treating the modular construction process as a system, energy and environmental efficiency, health features, and high quality can be built in at the factory—resulting in lower costs to the home buyer.

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