What is a Zero Energy Home?

What is a Zero Energy Home?
Imagine a home that is not only energy efficient, but also produces its own power. Just like a typical home, a Zero Energy Home (ZEH) is connected to, and uses energy from, the local electric utility. But unlike typical homes, at times the ZEH makes enough power to send some back to the utility company. Annually, a ZEH produces enough energy to offset the amount purchased from the utility provider, resulting in net-zero annual energy bills.

A ZEH combines state-of-the-art, energy-efficient construction techniques and equipment with renewable energy systems to return as much energy as it takes on an annual basis. When renewable resources cannot provide the entire home's power (at night or on a cloudy winter day) the homeowner purchases energy from the utility provider. When renewable resources produce more than the house is using (during sunny days when no one is home) power is sent back into the utility grid. In some cases, the utility provider will operate the home's electric meter in reverse, essentially providing the homeowner with full retail value for their energy.

Why Build a Zero Energy Home?

One of the major issues we are faced with today is global warming, which is negatively affecting the environment and weather patterns worldwide. Global warming is a direct result of harmful gas which is being emitted into the earth's atmosphere. Zero Energy Homes do not consume energy, and therefore do not produce pollution or emissions which help to reduce global warming.

Is a Zero Energy Home Realistic?

Once just a concept, Zero Energy Homes are now a reality throughout Canada and the United States. The opportunities to construct ZEH’s are growing as solar and other renewable energy technologies become more affordable.  Never having to pay energy bills is a very attractive concept, however, only if achieving this high level of performance does not greatly increase building costs. 

Building a ZEH

By following the two simple steps below, a ZEH can be built without adding considerable costs.

1.       Design the house to minimize energy consumption.  By combining the several modern techniques highlighted below energy consumption can be reduced by approximately 70-80%.

Use a renewable source of energy to supply the remaining 20-30% of energy which regularly built home would consume. Either solar panels or wind mills can be used for that.

Techniques to Reduce Energy Consumption

A.       Design and Orientation. Carefully consider the design and orientation of the house. Points to consider for the design:

                            i.          Consider a bulky rectangular or square shape, with minimal wall surface area and very few corners.

                           ii.          Place several large windows facing south and very few facing north (for southern states do the opposite).

                          iii.          Minimize the number of external doors.

                          iv.          Ensure that at least half of the roof faces true south for solar collectors.

                           v.          Consider building a single-storey house.

                          vi.          Consider building a duplex with two or more apartments in one body.

2. Airtight Construction.  The house must be airtight. Ensure that all windows and doors meet the required air-leakage standards and the vapor barrier (where needed) overlaps by 500mm at the seams and is and sealed everywhere. (install ERV)
3. Concrete Thermal Mass.  Build exterior walls and floors with concrete. Concrete walls and floors accumulate and release large sources of heat when outside temperatures are low and remain cool when outside temperatures are high. 
4. High R-value Insulation. For a zero energy home, use insulation with a higher R-value than what is used for regular home construction.  Do not use fiberglass insulation for walls, it will settle over time and walls will have air gaps.
   Techniques B, C and D can easily be achieved by using Insulating Concrete Forms (ICFs) for the exterior construction. Attic fan. (wool insulation for sound)
5. Windows and Doors. Use triple glazed windows and well insulated or double external doors.  Use limited number of skylights (high quality double glazed only).  The passive gain of incoming solar heat through the windows will cover close to 40% of the heat losses if all guidelines are followed. Optimized south facing glazing with none or minimal window openings to the north is a requisite. Most windows should be fixed as these have a higher performance than the opening type. As with all components making up a ZEH, the total performance of the house must be considered. A large house with many doors will have much larger heart-losses and this must be compensated by significant improvement of all components. In many well designed houses of moderate size, the standard door is sufficient. Window shades or owning - trees. 
6. Avoid cold bridges.  Install insulation with efficient R value all around the house without any penetrations. Run ducting in heating/conditioning space only. 
7. Energy Efficient Appliances.  Use the most energy efficient models of appliances available and low energy lamps (for example modern high frequency fluorescents or LED). 
8. Radiant Floor Heating. Use Radiant floor heating which offers many advantages over traditional heating systems.  The most important advantage is the improved comfort level, especially when combined with a concrete floor. Radiant heating allows a room to be heated evenly by increasing the room's average surface temperature. Another key benefit of radiant heat is energy efficiency. You will save money on energy bills with radiant heating due to comfort at lower air temperatures, room by room zoning, and lower water temperatures. Other advantages include no visible components, noise reduction, and dependability.
9. Earth Temperature and Thermal mass. Install geothermal pump or/and ECO-AIR Thermo Ground – Air Exchanger or similar system.

                            i.          Tankless Water Heaters. Use instant electrical tankless water heaters.

                           ii.          Watersdaver. Install watersaver appliances, toilet tanks, aerators, etc.

                          iii.          Roof Garden.  Consider installing a roof garden, for additional insulation etc.