Energy Efficiency and Budget for Building New
Impact of Materials Selection and Enclosure Design on Buildings
Oct 27, 2009
Design for energy efficient structures is always tempered within the budget allocated for building. Tradeoffs have to be made between the expense of more energy efficient material and equipment choices versus the developer’s timeframe for return on investment.
Most buildings are designed for a 50 to 100 year lifespan. Economizing on material choices can result in a building shell that fails to perform to its design life. Money invested in a superior enclosure quickly repays itself in reduced operating costs.
The wild card in many pro forma is factoring in the cost of energy. Most industry observers agree the price will rise. Designers must work with clients to weigh the immediate cost of installing low energy systems like solar compared to exclusive use of fossil fuels for the building’s mechanical plant.
Design Principles for New Buildings
The easiest way to bring down operational costs in architecture is to design a smaller footprint. Another alternative is to renovate a building, reusing the embodied energy that exists in the building’s shell.
Operational requirements and associated costs can be reduced through design of high performance enclosures. The initial expense of a high performance building may be higher, but payback times for energy efficient buildings are rapid.
The features of a high performance enclosure include:
- Air tightness: Careful detailing of the design’s component parts, and equally assiduous attention to their construction result in enclosures that do not leak air.
- High R values: Increasing insulation in walls, roofs, basements or at-grade concrete slabs contributes to thermal mass and reduces heating and cooling requirements.
- Control solar or heat effects: Reducing the heat burden on a building, through exterior and interior wall and window shading, and ensuring there are no heat islands around the building all improve energy efficiency.
- High efficiency mechanical equipment and appliances: These are two other ways to improve energy performance in a building.
Economizing in the Design of a High Performance Building
Some low energy choices are more expensive than others, with longer payback times. Building science specialist John Straube distinguishes between these choices on the basis of ease or difficulty of upgrading some years after the erection of the building.
Upgrading insulation in an attic, from R40 to R75, is inexpensive and easily accomplished. Energy inefficient lighting can be replaced without extensive renovations. Windows have to be replaced every 20 years; more air tight and energy efficient glazing units can be selected for an upgrade. Ditto for mechanical equipment.
Some upgrades are more difficult to conduct and have high price tags. Examples would be replacing an exterior wall assembly or trying to improve the R value of a slab at grade. Glazed walls in high solar gain situations will pose an energy burden even if individual window units are upgraded.
Incorporating alternative or clean renewable energy systems can, in some cases, be delayed until later in a building’s life if measures are taken during the design phase. A good example would be the design of a roof with a sloping pitch on the unshaded south side of the edifice. Solar panels could be erected later on to reduce reliance on fossil fuels.
The ultimate goal is a building that weathers well for its climatic context, reduces energy demands and is thermally comfortable for occupants. Reducing a building’s footprint is the first and most important route for improving the building pro forma.
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