Comparing Net Zero Energy homes to Passive House solar gain designed homes: a head-to-head analysis

The Net Zero Energy home.

The concept of the Zero Energy home is appealing in its simplicity: a residence that generates as much renewable energy for heating and electricity as it consumes. Its annual energy balance is neutral, and its greenhouse gas emissions are 100% offset. The design model home in Canada known as the Equilibrium House is endorsed by the Canada Mortgage and Housing Corporation (CMHC) with 1,696 homes completed.

The passive solar house - alternatively termed 'bioclimatic', "Passive House" or 'Passivhaus'

The passive solar house is designed to capture as much of the sun's rays as possible, thanks to its large south-facing windows (over 60%), its thermal mass and its very high level of insulation and airtightness. This design approach significantly reduces heating costs without relying on additional grid-fed power or on-site renewable energy generation.

A word of warning: many ecological houses claim to be 'passively-designed' without actually complying with the demanding German Passivhaus certification. Keep this in mind whether you are buying a home or hiring an architect / designer. You can find Passive House accredited designers here in the Ecohome Professionals Directory. 

Passivehaus is represented in Canada by the Canadian Passive House Institute (CanPHI), and in the United States by the The Passive House Network who are the official iPHA Affiliate organisation as of March 2018 - although there is also the Passive House Institute US (PHIUS). Read this guide to understand the difference between the Passive House Institute or PassivHaus in the US and Passive House or PHIUS certification.

Key principles of the Net-Zero house and passive solar design

These two types of home share the following characteristics: modest size with large, south-facing ENERGY STAR certified windows with triple glazing and argon gas, record insulation, excellent airtightness, and thermal mass to store and release heat for added efficiency.

Also crucial for performance are high-efficiency ventilation using a heat recovery ventilator (HRV), ENERGY STAR certified household appliances, and so on.

For the real energy-efficiency keeners, another surprisingly high consumer of power that you can address are 'phantom loads'. Household items such as computers, stereos and TVs can consume up to 1,200 kWh a year in the average home, so having them on a kill switch (or unplug them when not in use) can reduce your power consumption.  

Key principles of the Net Zero Energy home

The Zero-Energy principle (i.e. producing as much, or more, than is consumed) allows for all kinds of renewable energies: thermal and photovoltaic solar panels, geothermal energy, wood pellet heating, wind turbines, solar water heaters, etc.

For example, 90% of the hot water needs of the Abondance le Soleil triplex are met by its solar thermal water heating system. The building's effective insulation means that geothermal energy is used only occasionally. As for the electricity produced by the photovoltaic solar panels, it is fed directly into the hydroelectric grid, which supplies the triplex with the equivalent.

The Zero-Energy principle is particularly appropriate on a neighbourhood scale, since pooling energy production systems means that they pay for themselves more quickly and surplus energy can be easily stored.

Main principles of the Passive House

The Passivhaus standard is defined by energy consumption thresholds: heating consumption must not exceed 15 kWh/m2 per year and total energy consumption 120 kWh/m2. Is this possible in all latitudes? It can be, but the amount of insulation required to do so (and its embodied energy) can actually have a higher carbon footprint over the life of the house than adding a bit of heat. In any case, we need to maximise south-facing windows, insulation, airtightness and thermal mass.

The Lost Lake Passive House, the first in Canada to obtain Passivhaus certification, features R-65 double-framed walls insulated with rock wool, an R-65 floor, an R-82 roof, triple glazing and a third-generation heat recovery ventilator.

The chalet's airtightness is four times better than the Novoclimat standard. A small electric boiler is planned to power the under floor radiant heating system, but this installation should be of little use given the low heating requirements.

Passive solar and Net Zero - how much does it cost?

This is obviously the trickiest part... while these homes are profitable in the long term because of the energy savings, the initial investment is a significant factor for future owners, and subsidies and incentive programmes are not plentiful. With that said, let's compare the two types.

Note : See here to learn why better insulated homes are worth the money in the long run. 

Costs of a Net-Zero Energy home

While the costs of materials and labor shortages significantly influence the expenses of any construction project, net-zero homes typically can be constructed at a range of $175 to $180 per square foot. One of the most popular sayings in the industry is “if you can afford a new home, you can afford a zero energy home”

The only way to build a true net zero is to incorporate a lot of passive principles before adding renewable energy sources," explains Malcolm Isaacs, director of CanPHI. One goes hand in hand with the other. In terms of budget, a Zero Energy house costs almost double the price of a traditional single-family home.

Passive solar house costs

A passive solar house costs around 10% more than a conventional house. To this estimate must be added the cost of specialist support, which varies from one consultant to another.

However, according to hard-line supporters of German certification, strict application of Passivhaus criteria requires importing German materials. This requirement is expensive, but also comes with increased embodied energy due to oversea shipping. An argument against going for Passive House certification, is 'buying local' since it is easy to find suitable and efficient materials to meet Passive House standards with 100% North American manufactured products.

In either case, compromises are possible. In Canada, the designers of a Zero Energy home have an interest in borrowing some of the principles of the passive solar house to offset the costs of installing solar panels or wind turbines. Conversely, architects who favour passive solar houses can incorporate a few solar panels to save on insulation costs.

Passive solar houses and Net Zero houses: are they really green?

Both types of home are environmentally friendly, since they radically limit energy consumption and greenhouse gas emissions. What's more, because Zero Energy homes are connected to the hydroelectric grid, there's no need to store energy production in batteries that are harmful to the environment, unlike completely self-sufficient off grid homes.

On the other hand, the use of environmentally-friendly materials is not a requirement in either case, because energy efficiency is the sinews of war. The lifestyle choices of the future occupants in terms of transport or water consumption are not included in the criteria either.

Finally, the fact that the energy that can be consumed in a Passive House is calculated per square metre (120 kWh/m2 in all) may encourage the construction of large areas, which is not environmentally friendly in itself.

Conclusion 

In Canada, the prudent approach involves constructing a highly efficient Passive House connected to the hydroelectric grid, striking a balance between energy efficiency, cost considerations, and environmental impact.