Net Zero Energy Homes Defined
A typical home has an energy “footprint.” We require some form of energy to run electrical appliances, lights, generate hot water, cook food and keep our homes warm (or cool). Electricity usage is measured and billed in kilowatt-hours (kWh), and natural gas consumption is charged by the gigajoule, which is the amount of energy contained within a given volume of gas. However, some homes may also use propane, firewood, wood pellets or other sources of fuel to power certain operations. By compiling all of this consumption from the various sources, one is left with a yearly energy total, representing all of the energy demands that a home and its occupants incur in that period. This is the energy footprint of that house.
The goal of a net zero home is to actively produce, on-site, all of the energy that a building and its occupants will use. While it is possible to produce bio-diesel and other types of fuel energy, by far the most common approach is to use equipment to create electricity. There are two methods of using electricity producing equipment to achieve the net-zero goal.
One method is to have some means of storing all the produced energy on site. The most common way of doing so is a bank of rechargeable batteries. This type of net-zero building may be connected to the electrical grid, in order to use its batteries for power outages or to avoid using grid electricity during peak cost times. However, a battery backup system does not need to be connected to be grid inter-tied. A building on a remote island would be a great example of this kind of off-grid scenario.
The other method is to have a building connected to the conventional electrical grid. The home would draw energy from the electrical utility whenever needed, and in as much quantity as needed. It would also produce its own energy on-site, which would feed backwards into the electrical grid when the home was producing more than it required at any given moment, supplying electricity to other homes and businesses in the area. Over the course of a calendar year, the total amount of energy produced and sent out to the grid would be equal to the total amount drawn from the grid.
In both of these methods, the yearly energy needs of the home are ultimately produced on-site. In the “off-grid” case it is stored on site to be used whenever production can’t meet demand, and in the grid-tied case, it is really an energy accounting situation, where power out to the grid must equal power in from the grid over the course of the year.
What creates the energy on-site? Two active technologies achieve this far more frequently than any other. Small-scale wind turbines are used to turn the kinetic energy of wind into electricity, and are quite common on larger properties, such as farms and medium-sized businesses, where zoning, physical land space and lower population densities will make them more acceptable. (It is also widely used in large scale energy production, but that is another story entirely.) The lion’s share of on-site electricity production, however, comes from photovoltaic modules. These are panels that are roughly 2’ x 4’ in size, and about 1.5” thick and are mounted in arrays where many modules are aligned in rows and connected to one another. When sunlight strikes a photovoltaic (PV) module, the energy of that sunlight is converted into electrical current, which can run through wiring to provide power to any electrical device in the home, or to the electrical grid outside of the home, servicing other energy demands in the area. PV arrays require almost zero maintenance, and typically last over 30 years with little drop in energy production. While their upfront cost is high, they will more than pay for themselves in energy savings over their life span. While other technologies for producing energy on site are available, wind and solar serve the vast majority of net-zero homes in existence.
The energy footprint of a house can change drastically from year-to-year, which can make predicting the size of energy production equipment difficult to determine. For example, more or less efficient appliances might be purchased, the number of residents may increase or decrease, the average annual temperature will change from year to year, the addition of an electric vehicle charger could be added, and a nearly infinite number of other variables can all have varying degrees of effect on the energy demands of a home. Perhaps the most influential effect on the consumption of a home, however, is the behavior of the occupants themselves. There is a saying that “There is no such thing as a net-zero home, only a net-zero family.” One family could be extremely conscious of the energy that they use, keeping showers as short as possible, never leaving lights on in rooms that they aren’t using, keeping the thermostat set to 20 degrees during the day and 17 degrees at night, etc.
Another family, in an identical home with identical appliances and equipment in the same neighborhood may enjoy frequent baths and/or long showers, constantly have a television on, have the thermostat set to 22 degrees all day and night, and frequently entertain large groups of people for dinners, placing more demand on kitchen appliances. While nothing is different between the two actual buildings, the behavior of the occupants of the spaces will greatly affect the energy footprint of the home over the course of a year. To size the energy-producing equipment required to offset the annual energy consumption, using realistic baselines for occupant energy consumption and accurately modeling the heat losses and gains of the building envelope is imperative.
Pheasant Hill Homes does have the ability to provide energy modeling services, which will estimate the energy consumption of a specific home, with an identified number of occupants. This modeling takes into account all predicted energy uses including hot water consumption, heating and cooling equipment, ventilation requirements and lighting/appliance/fixture loads. It is often very close to the actual energy usage of the building when it is complete.
Over the years that net zero homes have been constructed, it has been determined that it is usually more economically and environmentally sensible to focus on energy consumption significantly by constructing a better building envelope. This is partly because the cost of installing equipment to generate electricity is quite expensive, meaning that if one can reduce the amount of energy required, a smaller amount of expensive equipment will be required.
Conservation is also favourable because the measures that reduce energy consumption, such as increasing insulation in walls, using better quality windows and doors and making a home more airtight are all things that both improve comfort in the home, and require zero servicing or maintenance over the life of a home. There is a cross-over point where the cost of reducing energy consumption becomes more expensive than the cost to offset energy waste by generating more energy on site. A knowledgeable contractor will be able to perform energy modeling of the building and construction estimates to determine where that cross-over point is to keep the cost of building to a net-zero standard as reasonable as possible.
There is also the option of building a home that is “net zero ready.” This is a home which has instituted all of the energy conserving measures which make economic sense, and has made mechanical provisions to easily add active energy -producing equipment at some point in the future.
Typically this means designing a building that is sited properly for solar exposure and minimal heat loss, has an envelope with very high R-values on all six sides, has windows and doors with greatly improved thermal properties, reduces energy-wasting air leakage out of the envelope, incorporates a highly efficient ventilation system, and has included structural provisions and conduit runs so that solar PV equipment can be easily mounted on-site down the road. These houses are becoming much more common, and Pheasant Hill Homes has the education, training and experience building them to meet the growing demand.
As we draw nearer to the day that all homes will be required to be built to the Net Zero standard, more and more people are seeing the merit in building to this standard now. While not our current bread-and-butter work, this is what we are most passionate about, and always strive to present as many energy conserving options to clients as possible towards building a future with the lightest energy footprint possible. To see a recently completely project that is completely net-zero ready, with battery backup power already in place, visit our Oceanfront Net Zero Ready House blog. To discuss how Pheasant Hill Homes can help you design and/or build a remarkably energy efficient house that will take you into the future, contact us here.