What Does Net Zero Energy Mean?

Part 1 of a series on Net Zero Energy Houses for builders and homeowners.

The premise of  “Net Zero Energy” in the building industry is that a building should produce as much (renewable) energy in a year as it consumes.

This usually takes on the form of a building fitted with a more-or-less conventional space conditioning and water heating system and a site-based energy system like a photovoltaic (PV) array (solar electric). The building is connected to the electrical grid, and essentially trades energy with the utility. When the building needs energy from the grid, it gets it. When the building doesn’t need energy from the grid, and the sun is shining, energy goes back into the grid.

The building does not have to get all of its energy from the grid: conventional gas or oil space and water heating systems can be used. However, the site-based energy generating system must be sized to compensate for all of the energy the building uses in the course of a year.

  • Net Zero Energy

  • Zero Net Energy

  • Zero Energy

There are some variations on the name, but the fundamental idea is the same: produce as much energy in a year as you consume. In the US, the Department of Energy has settled on a program named Zero Energy Ready Homes. In Canada, Natural Resources Canada and the Canadian Home Builders’ Assocation are sticking with the name Net Zero Energy Housing.

There are also targets out there, like DoE’s Zero Energy Ready, that range out on either side of the ‘Net Zero’ point. These other targets are out there, in part, because, OCCUPANTS.

No builder or program authority or building code amendment is going to be able to control or accurately predict the behavior of the people who live and/or work in a building. They will be using lights, appliances, electronics, and opening windows and turning comfort systems on and off as they like, with no regard to any directives from on high.

In addition, all bets are off in a year with a winter or summer that spikes past the 10- or 20- year seasonal norms that design temperatures are based on. So, while a best guess is useful for determining how a house could be a net zero consumer of energy, there’s really no guarantee.

Also, the biggest expense for getting to Net Zero or Zero Energy is the site-based renewable energy system. Making a building ‘Ready’ means that significant pre-planning and design time has been spent on making sure the building can easily and cost effectively be fitted with, or connected to, a renewable energy system.

Currently, nearly every building standard or program is focussed on new construction. It makes sense, because Net Zero Energy (or Deep Energy) Retrofits are harder to achieve, catalogue and promote. This is due, in no small part, to the fact that you can do all the planning in the world, but until you open up that wall in an existing building, you really don’t know what you’re working with. Integrating cutting edge technology and innovative materials is always going to be easier on a new build, and showcase homes can be built to demonstrate the benefits of technology to a wide range of prospective buyers and/or tenants.

Net Zero Energy and Sustainability


Under the bare bones definition or concept, Net Zero Energy does not take into account things like carbon loads and greenhouse gas emissions for the energy that the building consumes, nor does it require water conservation, sustainable materials choices or any environmental responsible practices.

It’s simply a target for balancing out the equation:

Energy in = Energy out

There are several national and regional building standards and programs that combine all the layers and nuances of sustainability, are but most of them do not go as far as Net Zero Energy in the requirements under ‘energy efficiency’.

It’s a complicated place, this part of the building industry: so many valid options to choose from, but very few of them cover all aspects of sustainability and require a net zero energy target as well. The commonly used terms and names are starting to shake themselves out as different sectors agree (or agree to disagree) on concepts, definitions, and terms.

However, the problem is: you can have a house that meets the NZE target that does not address anything other than energy efficiency, missing the boat on long-term sustainability. You can also have a certified sustainable building that incorporates green material choices, water conservation, site planning, occupant health and broader planning issues, but addresses actual energy efficiency in the most minimal way, also missing the boat on long-term sustainability.

You can have an energy efficient building that is not sustainable

You can’t have a sustainable building that is not energy efficient.


Next up: What makes sustainability sustainable?

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