Passive / Active / Net Zero...?
DESIGNING for ENERGY EFFICIENCY - with MZE Architects
Facing the reality of ever-increasing energy costs, as Canadian homeowners, we are beginning to look more seriously toward methods of reducing our energy consumption - a practice that has been more readily exercised in Europe for well over a decade. Each of the three approaches described below share a few fundamental principles in design, yet provide varying benefits & results, depending on the goals established by the homeowner. Ideally, these principles are most cost-effective when implemented into the design for new construction, however many of these elements can be applied as retrofits to existing construction, to improve energy efficiencies.
Whether you are planning to build, or want to improve the energy performance of your existing home, let the MZE Team help you to determine which approach best suits your goals, and create an effective design solution to meet your needs.
PASSIVE HOUSE or PASSIVHAUS
A dwelling that provides year-round comfort in cool climate zones, with minimal heating/cooling energy usage, achieving 80 – 90% in energy performance savings, compared to conventional construction. Widely practiced in Europe, PASSIVE HOUSE design is beginning to take hold in North America, as a reasonably affordable construction alternative. The Canadian Passive House Institute recommends thoughtful consideration of the following categories, for designing an effective & efficient PASSIVE HOUSE:
- PRE-PLANNING - In order to meet PASSIVE HOUSE performance standards, it is important to clearly define these goals at the start of the project, to ensure that they are integral to all aspects of the design development.
- SOLAR EXPOSURE - Passive solar energy gains generally serve as the main component of the heating requirements of a dwelling. Proper site orientation of the dwelling to maximize on solar exposure & gain is essential, and generous south-facing glazing, with minimal north-facing glazing should be considered when designing for cool climates such as Canada.
- EFFICIENT BUILDING SHAPE - Heat loss from a building’s envelope is directly proportional to its surface area. The ‘Shape Factor’ of a building is determined by the ratio of the building’s surface area divided by its volume. For example, sprawling designs, and exposed floors can contribute to higher Shape Factors, often resulting in higher levels of heat loss.
- SUPER-INSULATION & THERMAL BRIDGE-FREE CONSTRUCTION - To achieve proper PASSIVE HOUSE performance standards, complete insulation coverage for all parts of the building envelope including the roof, exterior walls & floor slabs is essential, to eliminate heat loss due to thermal bridging. In fact, Canadian dwellings actually need 3 – 7 times better insulation performance than what is currently required by the national & provincial Building Codes.
- ADVANCED WINDOWS - Generally, windows represent the thermally weakest component of the building envelope, contributing to 50% of all heat loss for a dwelling. Installing quality windows will ensure that interior glazing & frame surfaces remain warm on cold nights, to minimize interior cold spots & downdrafts. Triple glazing is best suited for the Canadian climate, using double low-e coatings & Argon (of Krypton) gas fill, as well as insulated spacers & window frames. Unfortunately, it is challenging to find windows offering all of these features in the current Canadian market.
- AIR-TIGHTNESS - High levels of air-tightness must be achieved in order to minimize heat loss from air infiltration, as well as to protect the dwelling’s structure against moisture damage.
- VENTILATION with HEAT RECOVERY (HRV) - It is essential to install a quality ventilation system that consistently supplies fresh air, to provide excellent indoor air quality, while also allowing heat contained in the exhaust air to be recovery & re-used.
- VENTILATION AIR PRE-HEATING - Simple & relatively inexpensive geothermal heat exchangers can be incorporated into the Heat Recovery Ventilation System (HRV), allowing the cold incoming airstream to be pre-heated, which keeps the HRV unit frost-free. This system can also provide active cooling & dehumidification during the warmer summer months.
Building on the fundamentals of super-insulation, air-tightness & optimal solar exposure integral to PASSIVE HOUSE design, an ACTIVE HOUSE dwelling expands its focus beyond energy efficiency, to an overall improved quality of life for occupants. Promoting increased natural light & ventilation through the use of windows & skylights, by default an ACTIVE HOUSE is less insulated than its predecessor, relying on renewable energy systems such as solar water heaters & geothermal heat pumps to compensate for potential heat loss. Cutting edge technologies are implemented into the design to provide automated opening/closing of windows & skylights, as well as the operation of blinds & awnings for shade control. Unfortunately, due to the currently cost-prohibitive nature of many of these new technologies for the average homeowner, ACTIVE HOUSES are far less prevalent than PASSIVE HOUSES. According to activehouse.info, ACTIVE HOUSE design is centered on the following three categories:
- COMFORT - A generous supply of fresh air, natural light, and materials that have a neutral impact on comfort and indoor climate all contribute to the creation of a healthier and more comfortable life for the homeowner.
- ENERGY - All energy requirements are supplied by renewable energy sources that are integrated into the dwelling’s design, or from the nearby collective energy system & electricity grid, in order to achieve a positive energy balance for the dwelling.
- ENVIRONMENT - An ACTIVE HOUSE interacts positively with the environment through an optimized relationship with the local context, focused use of resources, and its overall environmental impact throughout its life cycle.
NET ZERO ENERGY HOUSE
NET ZERO ENERGY (NZE) HOUSES could be considered a hybrid between the PASSIVE & ACTIVE HOUSE, since their design & construction focuses on energy efficiency and renewable energy generation, while also including technologies and practices that enhance indoor air quality and comfort, reduce environmental impact, conserve natural resources, and improve affordability. NZE HOUSES are designed and built to minimize household energy needs, and generally include on-site renewable energy systems, so that the house may produce as much energy as it consumes on a yearly basis. Not to be confused with an ‘off-grid’ house, NZE HOUSES are typically connected to the local electricity grid, so that it can supply electricity to the grid when it is producing more than it needs, and draw from the grid when household demands exceed the amount of electricity produced on site, thus achieving net-zero annual energy consumption. Accordingly to the Canada Mortgage & Housing Corporation, there are three basic elements to consider, when designing a NZE HOUSE:
ENERGY REQUIREMENTS - Similar
to both PASSIVE & ACTIVE HOUSE design, a well-insulated building envelope
(roof, walls & beneath the floor slab), the elimination of thermal bridging,
and a robust air barrier are essential to reduce heat loss & prevent air
infiltration. Recommended R-Values are as follows:
- ATTIC - RSI 11, R 60 +
- ABOVE GRADE WALLS - RSI 7, R 40 +
- BELOW GRADE WALLS - RSI 3.5, R 20 +
- BASEMENT SLAB - RSI 2, R 10 +
- Proper site orientation & placement of windows with shade controls are important to take advantage of solar energy gains, while preventing over-heating during warmer months.
- Installing an energy efficient mechanical ventilation system with heat recovery is essential for maintaining a healthy indoor living environment. Grey water (drain water) heat recovery systems can also assist in harnessing and re-using otherwise wasted heat.
ENERGY SYSTEMS TO MEET REQUIREMENTS
- Reliable, low maintenance rooftop photovoltaic (PV) systems are the most common option to meet the energy needs of an NZE HOUSE, and enable the homeowner to sell surplus energy back to the local utility provider. PV systems that are connected to the local electricity grid are generally easier to install & maintain, than systems that require a form of energy storage, such as battery packs. Although storage-based systems require dedicated space within the dwelling, they can provide uninterrupted power during black outs, unlike their grid-connected counterpart.
- Wind or water turbines are also viable alternatives for producing energy depending on site conditions, and rooftop solar thermal panels can often incorporated, for their ability to produce hot water.
- Due to the significant initial costs associated with installing many of the above mentioned systems, homeowners may opt to plan ahead by installing ‘solar ready’ wiring & piping conduits, as well as roof reinforcement during new construction, to accept these systems at a later date.
OPERATION OF HOUSE
- It is essential for homeowners to be mindful of how energy is used within the dwelling, by selecting Energy Star rated appliances, installing LED light fixtures, and regulating temperature settings. Installing a ‘Dashboard’ is a visually-effective way to provide useful real-time information about the energy production / consumption of the house to the homeowner.
MZE's project, the Centre for Conservation at Ball's Falls Conservation Area, has been identified by a leading Sustainable Design authority as one of their top 10 projects most eligible for Net Zero designation.
Click this link to see some more of MZE's Sustainably Designed Projects...