This section provides information on the design features, incremental costs, and energy savings potential of zero energy homes, including project examples and brief descriptions of completed zero energy home projects
Energy Efficiency Features
There are many cost-effective opportunities to improve the energy efficiency of new homes through a combination of improvements to residential building design, construction practices, higher efficiency levels of installed equipment, and homeowner education about ways to save energy. Common energy efficiency design practices and measures that are used in high performance homes include:
- Proper site selection and building orientation, which can help reduce heating costs in the winter and cooling costs in the summer, and facilitate the use of on-site PV to generate electricity.
- Higher levels of ceiling and wall insulation (R-50 or higher) coupled with advanced framing techniques to minimize thermal bypasses.
- Radiant barrier installed on the inside of the roof to reduce solar heat gain and help keep the attic cool, particularly in hot-dry climates.
- Use of thermal mass for improved heating and cooling performance, including additional insulation in ceilings and walls, and use of 5/8" drywall.
- Properly designed and installed heating and cooling systems that help keep energy costs low and improve indoor air quality.
- High-performance windows with spectrally selective glass, which reduces solar heat gain in summer and reduces heating costs in the wintertime.
- Highly-efficient heating and cooling systems, including:
- Engineered HVAC (proper sizing and diagnostic testing of HVAC systems)
- Advanced evaporative cooling systems such as direct-indirect evaporative cooling systems
- Ducts placed inside conditioned space, with diagnostic testing
- Tankless or solar water heating.
- High-efficiency lighting (e.g., LED or fluorescent lamps and fixtures), or a combination of lighting products with lighting controls (e.g., dimmers and occupancy sensors).
- Energy-efficient appliances, including refrigerators, clothes washers, dryers, dishwashers and consumer electronics.
- Integration of controls to monitor home energy use, including switches and controls for turning off designated electrical outlets (to reduce losses from standby devices).
- Third-party verification (analysis of home design and onsite inspections and testing to verify and rate the energy performance of the home on the HERS or HES scale).
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Renewable Energy Systems and Features
Renewable energy systems and design features - such as incorporating passive solar thermal design strategies, solar PV electric systems and solar thermal hot water - can generate a portion of a home's electricity and water heating needs. Passive solar thermal design strategies can often be implemented at little or no incremental cost through proper building orientation, daylighting, and use of thermal mass. Typical residential solar PV systems are between 4 kW and 8 kW in size, and are capable of offsetting approximately 25-30% of total household electricity consumption. The initial cost of renewable energy systems has literally dropped to $0.00 because of the third party leasing model implemented by many solar companies including Solar City, SunRun and Namaste Solar. This model leases the solar system to the homeowner for up to 20 years, and in many cases for no cost to the homeowner. Solar PV systems can still be purchased and recently Solar City announced a new solar purchase program where the monthly payment fluctuates based upon the amount of power generated by the solar system. Although the initial cost of renewable energy systems remains high atapproximately $15-20,000 for a very small 2 kW solar PV system, the system costs are expected to continue to decline, and are made more affordable to the builder and homeowner by a combination of federal, state and utility tax credits or rebates now available in most Southwest states.1 Utilities can also utilize residential PV systems to satisfy state renewable portfolio standard requirements by offering renewable energy credits to homeowners that have installed grid-tied PV systems. Colorado, Nevada and New Mexico already offer homeowners a RECs purchase option for solar PV systems. For more information on renewable energy incentives, see the Utility Programs and Incentives for Zero Energy Homes web page.
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Energy Savings and Cost Effectiveness
Zero energy homes built today are capable of achieving 40-60% energy savings when compared to the 2006 IECC, by combining energy-efficient technologies and solar energy systems. These homes are cost-effective for homeowners, with net savings versus a code-built home when compared on the basis of the total cost of mortgage and utilities payments.1 Energy efficiency measures are more cost-effective to implement than renewable energy measures. Combinations of efficiency and renewables, however, are also cost-effective to the homeowner, and deliver valuable peak electricity savings for utilities.
The energy, economic and environmental benefits of improving the efficiency of new homes in the Southwest region are significant. SWEEP estimates that achieving a significant increase in the market penetration of high performance homes in the Southwest region would result in the following energy and cost savings between 2008 and 2020:
- Over 2.7 million GWh of grid electricity savings - enough electricity to meet the annual electricity consumption of approximately 250,000 typical households.
- Reduction in residential natural gas consumption of 228 million therms (up to 50% reduction in natural gas use per household).
- Summertime peak electricity demand would be reduced by nearly 200 MW annually by 2020; average hourly summertime peak loads per home would be reduced between 50 and 67%.
- Southwest households would reap $500 million in reduced electricity and natural gas bills, with savings of $30 million in the first three years alone.
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In 2007 SWEEP released a report on High Performance Homes in the Southwest and the savings potential we could achieve from these new measures. Since 2007 the energy code has advanced 30% in efficiency and in 2014/2015 the baseline code house is equivalent to what was envisioned as above code or high performance in 2007/2008.
Today builders look toward net zero energy, or zero net energy, however you refer to this level of efficiency. There are examples of small and large builders across the region who offer single family homes that reach the net zero energy annual goal.
For more information, see SWEEP's report on High Performance Homes in the Southwest: Savings Potential, Cost Effectiveness and Policy Options.
11 The homeowner cashflow analysis assumes a 30-year fixed rate mortgage with a 7% annual interest rate.