Net Zero is a term that’s been tossed around for a few years. As with all green building concepts in this economy, it is being shelved until the industry picks back up. I think it’s worth studying and implementing once that happens.
The US Department of Energy defines Net Zero as a house that is 60-70% more energy efficient than a model home, and the remaining 30-40% of energy is created with renewables, such as solar, wind, and geothermal, to bring the energy use to zero.
A net zero home can be on-grid (net metered) or off-grid. Earthships are net zero homes. They create all their own power as well as harvest their own water and deal with their own waste products. This is truly net zero, but probably not suitable for the average homeowner.
How to build a Net Zero home
The road to net zero is to first design a house that conserves energy. A small home is and efficient home. It uses less materials in construction, there is less waste, and it takes less energy to run and maintain. I would say that is the very first step to having an efficient home – build what is essential, and forget the luxurious extra rooms.
Start with a super-insulated envelope to keep temperatures even. Earth-bermed homes are ideal for this. The temperature 6’ below the surface of the ground is a constant 55 degrees. It is easier to heat and cool from that base temperature than working against 0 in winter or 100 in summer. Earth is a wonderful insulator! Strawbale and SIPs are also excellent insulating materials.
Energy efficient windows and doors are part of the envelope. Windows and skylights are placed to bring in natural light to cut down on the need for lights during the day. Window and door openings take advantage of natural breezes for cooling. The house is oriented for passive solar heating, and thermal mass is an integral part of the main structure.
Inside the house, the HVAC system is properly sized for the estimated energy use and savings that the envelope will provide. Plumbing fixtures save water, and rainwater is caught and filtered for domestic use. CFL and LED lights are used instead of incandescent light bulbs.
Efficiency considerations for a Net Zero Home
The home needs to be as efficient as possible before installing renewables. The size of the solar, wind or geothermal generating systems will be based on the projected energy use of the building. Harvesting energy at the home site cuts energy loss when it does not have to travel through a maze of transmission lines. It’s much more efficient than power you get from your utility!
Ultimately, the house will generate all the power it needs, eliminating the need for fossil fuels. The only embodied energy in the home will be in the materials and their transport, so recycled, local and sustainable materials will reduced that load and the home’s carbon footprint.
Net Zero homes rely on green lifestyle choices too
The occupants then must continue to conserve energy by closing lights in rooms that are not being used, saving water, using solar hot water during peak heating times, putting small appliances on power strips to eliminate phantom loads, lowering the thermostat, keeping the fridge and freezer full, and other basic ways to conserve energy.
The cost of a net zero home will be slightly more than building a conventional home, but those costs will be recovered in savings. Theoretically, there are no utility bills, but if the residents are using more energy than the house is capable of producing, there will be bills. Or if you are using natural gas appliances instead of electric, you will have a gas bill. The energy you generate on site, though, will offset that cost. Utility bills should be minimal, though, and your ROI high and fast.
By supplementing an efficient envelope with renewable energy, you will have a net zero home and minimal or no energy bills. What a great way to protect yourself from unstable prices and supplies! Net zero should be the only way we build when the industry gets busy again.