Seite - 49 - in Water, Energy, and Environment - A Primer

in this discussion. Other ZEB definitions take into account any source energy losses in generation and transmission, emissions (zero carbon buildings), total cost (cost of purchased energy is offset by income from sales of electricity generated on-site to the grid), and off-site ZEBs where the offsetting renewable energy is delivered to the building from off-site generating facilities. Details on these definitions can be found in the National Renewable Energy Laboratory (NREL) report CP-550-39833 entitled ‘ZeroEnergyBuildings:ACritical Look at theDefinition’ (27). The keys to achieving net zero energy buildings are straight forward in principle: first focus on reducing the building’s energy demand through energy efficiency, and then focus on meeting this reduced energy demand, on an annual basis, with onsite renewable energy – for example, use of localized solar power generation. This allows for a wide range of approaches due to the many options now available for improved energy efficiency in buildings, and the rapidly growing use of increasingly less expensive solar photovoltaics (PV) onbuilding roofs, covered parking areas, and nearby open areas. Most ZEBs use the electrical grid for energy storage/backup, but some are grid-independent and use on-site battery or other formsof energy storage (e.g., heated or cooledmaterials). A prime example of what can be done to achieve ZEB status is NREL’s operational Research Support Facility (RSF) at its campus in Golden, Colorado. It incorporates demand reduction features that are widely applicable to other large new buildings, and some that alsomake sense for smaller residential buildings and retrofits (cost issues are discussed below). These include: • optimalbuildingorientationandoffice layout, tomaximize heat capture from the sun in winter, solar PV generation throughout the year, and use of natural daylight when available Energyoptions 49