Modern energy-efficient homes use very little energy. The houses are well insulated, preventing heat loss in winter and preventing heat gain in summer. There are no chimneys or wood stoves for winter heating. Fresh air is provided with a heat recovery ventilator (HRV also called an energy recovery ventilator, ERV, explained below).
These homes have comfortable temperature throughout the house, instead of fluctuating temperature gradients.
Sharply reducing the energy use saves money, increases comfort, and helps to protect the environment.
Energy-efficient houses are well-sealed. A key feature of effective sealing of the building envelope is that there is no venting other than through a heat recovery ventilation (HRV) system.
That means there are no fireplaces, no wood stoves, and no gas appliances. Sharply reduced heating load eliminates the need for fireplaces and wood stoves, which require houses to be leaky.
A house gets colder in winter if it has a fireplace or wood stove, because those devices expel air out of the house, requiring new cold air to enter the house through leaks in walls, doors and windows.
Likewise, gas appliances, including gas water heaters, and gas cooking stoves and ovens, produce combustion emissions that pollute the house air and require venting which causes the house to leak, making the house much colder in winter and much hotter in summer.
Highly efficient electric appliances replace all gas appliances, improving air quality indoors and outdoors.
A heat recovery ventilator (HRV also called an energy recovery ventilator or ERV) is a ventilation system that is built into your house and circulates fresh air from outside. It blows stale air from inside the house to outside, and brings in fresh outside air, while transferring the heat and humidity from the expelling air to the incoming air.
HRVs work like central air conditioners or heaters, in the sense that electricity is required to power fans. And HRVs also have filters that need to be changed or cleaned periodically, like central air conditioners and heaters.
However, an HRV has a very important difference compared to legacy AC or heating systems: it uses much less energy.
The incoming air may be preheated or precooled before entering the HRV, for example passing through underground ducting, to absorb heat from the ground in winter, and release heat to the ground in summer.
Energy-efficient heat pumps may also provide additional climatic conditioning for the house, such as radiant floor heating in the winter.
Heat pumps are already used for pre-existing homes that are less efficient (see Dandelion Energy link below); new efficient homes could use systems that are much smaller.
Even if conventional electric heating and cooling systems are used, they can be sharply reduced in size, substantially lowering both installation costs and operating expenses.
For a building to be energy efficient, it must be air-tight. In new construction, this is accomplished by carefully sealing all of the building envelope layers during construction, according to Passivhaus standards (also referred to as Passive House or Passive Home).
Certification by the Passivhaus Institute is optional. You can verify meeting Passivhaus standards by conducting a blower test of the home. If the house has less than a certain number of air exchanges for a given time interval, it is well-sealed.
Homes that do not pass a blower test can still be sealed by hiring an aerosol spray operation, conducted in an empty house (new home or remodel) which in combination, with a blower test that blows air into the house, migrates the special aerosol into outward air leaks whereupon the aerosol hardens to plug the leaks.
Another hallmark of energy-efficient construction, besides being well-sealed, is that the buildings are very well insulated. This combination, of high insulation and air-tightness, sharply reduces heating and cooling loads.
One way to achieve high insulation values is to use structural insulated panels (SIPs), consisting of thick foam insulation sandwiched between building boards. The geometry of each SIP assures high strength.
SIPs may be used as walls, roofs, floors, and foundations. For an example of using SIPs as a roof, see the JLC article listed below about a passive house built in California. In that case, SIPs were used for the roof, while spray-in cellulose insulation was used in extra thick walls (referred to as double walls).
Other possible ways of insulating walls include installing insulating foam blocks:
Foundations for energy efficient homes are usually constructed of insulated reinforced concrete, with barrier membranes to reduce insect and moisture infiltration.
ICF blocks can also be used to build entire walls, not just foundation and basement walls, but that is not recommended because other types of walls are more efficient above the foundation and basement.
Metal flashing to prevent termites is installed between the concrete foundation and stud walls.
Foam panels may be used instead of ICF blocks to make foundation walls thicker, provide more insulation, and use fewer seals (for less thermal bypassing).
Energy-efficient homes use windows that have three or four panes of glass, with inert gas (instead of air) filling the space between the panes of glass, and thermal breaks to reduce thermal bypassing through the window frame.
Inert gas between glass panes may be argon as shown here, or argon mixed with other gases to allow somewhat closer spacing of panes without the full additional cost of only using other gas.
A hinged window (shown above) has better sealing than sliding windows when closed, and allows more of the window area to provide air flow when open (reducing the need for extra window area).
Transparent films or coatings may be used between panes to reduce infra-red heat transfer. For more information, see: Energy Efficient Windows
Energy efficient windows have been common in Europe, and are now starting to be manufactured in the United States.
Windows have less insulating value than walls, providing incentive for windows to be medium sized instead of very large.
Before the advent of LED lighting, when lighting was more expensive with less options, there was incentive to make windows larger. That is no longer necessary, because lighting now uses much less energy and is higher quality.
The use of larger windows for providing interior lighting was called daylighting.
Daylighting can still play a role in design, for example as accent lighting and for emergency lighting (power outages), but will play a much smaller role than before, because some LED features provide superior health benefits than daylighting, for example ability to control glare and color, and provide more uniform illumination. New luminaires and architectural designs to incorporate them will be developed to better harness the potential of LEDs an important new area of opportunites.
Another reason to avoid extra-large windows, besides substantial energy waste costs, is to prevent breakage from climate change.
Climate change is driving up wind speeds in storms in all climate zones. Increasing occurrence of wild fires means more debris from fire-generated winds will strike houses. The larger a window is, the more susceptible it is to breakage that allows the storm or fire into the house.
While windows should not be too big, they also should not be too small, because thermal bypassing of the edges comes out to a larger fraction of the glazing area if the windows are small.
For example, it is usually better to have a medium size window instead of three small windows that add up to the same glazing area as the medium size window, because the smaller windows will have more thermal bypass edges than the medium size window for the same glazing area.
Energy-efficient homes need to implement shading of windows to prevent solar heat gain in summer. This may be accomplished with shading devices or shade trees.
Examples of shading devices include awnings and window overhangs.
When planting shade trees where there are cold winters, consider deciduous trees that lose their leaves in winter to allow winter solar gain. Examples of small to medium size deciduous shade trees include Emerald Sunshine Elm and Redpointe Maple.
Avoid planting trees that have high resin content, like pine trees, since they are much more flammable. And avoid planting shrubs that are woody or sappy, like manzanitas and star jasmine. Plant Ceanothus (California Lilac) instead. No plants are fire-proof, but if you are going to plant trees or shrubs, grow plants that are fire-resistant.
In fire-prone areas, besides growing plants that are fire resistant, exterior walls should be fire resistant, for example coated with stucco.
Aerosol Sealing of Building Envelopes (WCEC)
Double Wall Framing (Steven Winter Assoc.)
Passive House in Wildfire Country (JLC)
Panelization / Passive Building (Builder)
Prefab Passive Houses (Architect magazine)
Phoenix Haus (Colorado Prefab)
I-joist Cellulose Insulation Framing (JLC)
Dandelion Energy (Heat Pumps in New England)
Window Types and Technologies (Energy.gov)
Windows: Heat loss & Heat gain (UK)
Fire Adapted Communities (Nevada)
Construction in Wildfire Zones (FEMA)
Fire-Resistant Landscaping (CalFire)
France Promotes Heat Pumps (Reuters)
Retrofit Building Facades (PBS)
Payette Glazing Config (Boston)
Portland Sustainable Building (Oregon)