Natalie Leonard is an engineer, Passive Buildings Canada member, and founding partner at Passive Design Solutions. Leonard is dedicated creating cost-effective, beautiful, super-efficient homes for the future. She is also the first certified Passive House Consultant and Certified Passive House Builder in Canada. This is Leonard’s take on the simplicity of Passive House and the road to Net-Zero.
By Penny Beaudry
Passive House Approach
The Passive House Approach is the world’s leading energy efficiency standard. A Passive House is a high performance building standard that strives for low-carbon, energy efficient buildings. Approximately 50% of energy efficiencies are achieved by smart design, while the other 50% are achieved with what is put into the building. While the building orientation, shape and layout are important, it’s key principles are as follows:
Eliminate thermal bridging
High performance windows and doors
High efficiency mechanical and electrical systems
Passive House originated as PHI (Germany), where the standard is based on one set of targets regardless of location. The challenge with using this approach is the huge range of climate zones in North America. For example, Nova Scotia has longer winters; more Heating Degree Days; and more solar radiation compared to Germany. The The German Annual Heat Demand target does not ensure comfort in Nova Scotia where more heat is needed for the longer, colder winter and only a tiny cooling demand is required. The standard has since been adapted in the PHIUS (USA) Passive Building Climate Adjusted standard to suit North America’s various climates.
The Passive House (PH) energy requirement is so low that it doesn’t require a conventional heating system. Typically, point source heaters are installed to meet the peak heat load requirement which is a very user friendly solution. The cost savings from eliminating the central heating system helps cover additional PH construction costs. To build to the PH Standard typically adds 5-10% to the budget, however it is more cost effective to save energy than to generate it with active systems. Energy Efficiency is the cheapest fuel!
The Climate Adjusted Standard allows for higher plug loads which results in more internal gains, but also higher baseline total energy. The numbers are normalized by the number of people occupying the home instead of size of the house. The occupancy is based on the number of bedrooms plus one. This should encourage smaller houses with more density which is better for the planet.
Principles of Design - Size
As the years increase, so does the square footage of houses. The best thing to do to be environmentally responsible is to design the smallest possible space that meets the program needs while increasing density.
Principles of Design - Shape
Design with compact building shapes in mind. Be aware of the surface area of the building envelope to volume ratio of the building. This is typically easier to achieve in bigger buildings.
Passive Design - Site Considerations
Orientation to south is an important way to gain free heat from the sun. Shading from other buildings, from building reveals, and from trees can affect a buildings performance. Exposure to prevailing winds will change from summer to winter and must also be designed site specifically.
Burlington Passive House
Solar orientation plays a huge role on net-energy gain, natural lighting, overheating, or net-energy loss. Some basic guidelines include:
East glazing - Morning light, small net-energy gain, doesn’t contribute to overheating.
South glazing - Daylight all day, good net-energy gain, subject to overheating from August to October.
West glazing - Evening light, small net energy gain, major overheating, and difficult to shade.
North glazing - Filtered light, large net-energy loss, minimal overheating
Project glazing design strategies may include: limiting north glazing while maximizing south glazing; using windows with triple glazed, low-e, argon filled glass; and design shading to reduce overheating.
Continuous, High R-value Insulation Assemblies
Building science plays an important role on passive design and must always be considered. For energy efficiency use thick insulation layers; eliminate thermal bridging in assemblies; and consider other environmental impacts of materials. Energy modelling tools can also be used to optimize insulation levels.
Benefits of Airtight Construction
In a Passive House fresh air is supplied by the mechanical ventilation system or by opening windows. An airtight building can reduce heat loss by up to 50%. Also good to know, air transports moisture. This means that if there is air leakage, there is also moisture in the assemblies that can cause mold and rot issues. Living in an “airtight” home is more comfortable anyway! There are fewer drafts; easier to maintain temperature; much quieter; and has better indoor air quality. In a Passive House fresh air is constantly being brought in and stale air taken out.
Principles of Design - Mechanical
Once the building envelope is optimized, mechanical systems are designed to meet the tiny heating and cooling loads of a Passive House. A high efficiency mechanical ventilation unit provides a balance of fresh air supply and exhaust to the home.
Lighting & Plug Loads
Lighting and plug loads are responsible for only 20% of typical residential energy consumption. In a low-energy house, lighting and plug loads are responsible for up to 50%-70% of energy consumption. This means the homeowner’s behaviour can positively impact the total energy use in the home by turning off lights, electronics, etc.
From Passive House to Net-Zero
A Net-Zero building produces as much energy onsite as the building uses annually. This is achieved by good design as described above and by a renewable energy source. Typically, solar panels and net-metering are used with the power grid where the grid acts as a 100% efficient battery. Roof space is a limiting factor when considering net-zero because it determines the amount of solar panels that could fit, thus how much energy could be produced. To put it in perspective, a code built 2000SF home may need 55 solar panels, whereas a Passive House only needs 25 panels to generate the required energy for Net Zero.
Passive Houses are carefully designed, affordable, and energy-efficient. They contribute to lowering collective carbon footprint for today and future generations to come. The projects shown in this article demonstrate that this is possible! Stay tuned for more information, photos, and methods in the upcoming articles.
“Good design is sustainable. Great design is responsible. ” - Passive Design Solutions