Passive House certification in cold climates

Passive House certification in cold climates

Completed in the summer of 2018, Alberta’s Valleyview Town Hall is the result of extensive collaboration between the municipality, the contractor, and a skilled team of designers including Scott Builders, Flechas Architecture, Marken Design + Consulting, Integral Group, Laviolette Engineering, Helix Engineering, and Kinnikinnick Studio. These parties worked together to target Passive House certification in a northern climate, aiming to create the first building in Alberta to achieve Passive House Classic certification and the first in the world to obtain Passive House Plus certification.

Located 350 km (217 ½ mi) north of Edmonton, the Town of Valleyview experiences a humid continental climate with long, cold winters and short, mild summers. Although temperatures can dip below zero from October through April, on average, local temperatures range from 22 C (72 F) in the summer to –20 C (–4 F) in the winter. Further, hours of sunlight in the region go from approximately 307.5 in the summer to 100.8 in the winter months. As a comparison, temperatures in Vancouver (the city with the highest number of Passive House buildings in Canada) rarely dip below zero and daylight hours range from 290 in the summer to 56.5 in the winter.

When the original town hall approached the end of its life, it became too expensive to run and maintain, as its heating systems could no longer keep habitable indoor temperatures in the colder months in an energy- and cost-efficient manner. The building also required significant interior renovations to update its functional layout, which would have required extensive system upgrades to meet the current building code.

Consequently, after considering the option of retrofitting and upgrading the existing building to extend its life for another 25 years, the town council decided on creating a new structure that would help lower operation and maintenance costs, as well as reduce greenhouse gas (GHG) emissions. This building would also be more fiscally responsible, as its sustainable design would help minimize the costs of long-term operation for the next 80 years.

Learning from the experience the town manager, Marty Paradine, had with the Passive House standard, the council realized the financial and environmental advantages of building the new town hall to meet the standard. In 2012, Paradine participated in the development of the City of Fort St. John’s Passive House, an award-winning demonstration project in northern British Columbia that showcased the energy-efficiency potential the standard offers for single-family homes at a lower cost.

 

Passive House certification is a German green building standard published by the Passive House Institute (PHI). It combines energy efficiency with optimal comfort, long-term affordability, and good indoor air quality (IAQ). Achieving certification meant producing a long-lasting, high-quality building that would guarantee year-round thermal comfort and a 90 percent reduction in heating and cooling costs. Further, meeting the Passive House standard would allow the building to become net zero with a minimum investment and ensure it could stand the test of time in terms of quality, efficiency, and future building code amendments in case of expansion.

In cold climates, the standard aims to “reduce peak heating loads to facilitate the provision of high comfort levels with simple and reliable mechanical systems. The thermal performance requirements of the standard allow a building to maintain a comfortable indoor temperature year-round while using less than 15 kWh annually to heat or cool 1 m2 (10 sf) of useable space, limiting primary energy use for the structure’s full operation.

This reduction of primary energy use facilitates the transition to net zero by decreasing the amount of energy produced onsite. Further, due to the ‘passive’ nature of the Passive House standard, components are adapted to local conditions, so buildings can maintain interior temperatures for days without power. When it comes to resilience and durability, Passive House-certified buildings provide a responsible use of capital dollars. Saving on operational costs across the total life expectancy of a building, the standard allows taxes to be directed to more relevant priorities, such as social programs.

In 2015, the process of evaluating the construction of Valleyview’s new town hall began. After completing a preliminary design, the town opened the bidding process for a design-build contract for a Passive House building at a competitive price, which controlled the possible cost overruns innovative technologies often require. In 2017, the design-build contract was awarded to Scott Builders and the team of designers and consultants it hired (mentioned earlier in this article).

Adhering to the standard’s requirements, Flechas Architecture designed the Valleyview Town Hall by following key principles of flexibility, functionality, accessibility, comfort, and sustainability. These values allowed the team to overcome various challenges faced during the design services, permit, and construction phases of the project.

In northern climates, site placement and design optimization are extremely important, and even more so when it comes to the Passive House standard, as controlled solar gains help compensate for the regular energy losses of the envelope. Due to the extreme cold temperatures experienced in Valleyview in the winter, having a large site with a long side facing south allowed the team to capitalize on sunlight exposure and the necessary heat gains. Here, the configuration of the 2773-m2 (29,848-sf) site was perfect to accommodate the owner’s statement of requirements as provided by the town and fulfill the requirements of the standard. Meeting the Passive House standard in such a cold climate and on a site with little sun exposure would have been difficult, if not impossible, otherwise.

The relationship between the building form and window configuration plays a seminal role in achieving Passive House certification. On this project, meeting the standard’s requirement for space heating of 15 kWh/m2 per year necessitated additional attention to the energy performance of the building envelope. For this reason, careful design considerations were made regarding sun exposure and fenestration needs.

With the main entrance located on the west side of the lot, the rectangular massing extends eastward and exposes the long side of the building to the south, where all high-traffic working areas are located, maximizing the benefits of natural light in the workplace and providing views of the green area south of the building. The building’s orientation and simple layout are designed to achieve the optimal levels of sun exposure required to heat the building in the winter, helping maintain comfort indoors even when it is freezing outside.

Sun exposure also posed a challenge in the longest and warmest days of the summer, as the project team then needed to reduce heat gains and ensure steady and comfortable indoor temperatures without compromising spatial flexibility. To ensure both energy efficiency and controlled natural light, as well as manage heat loss, Passive House-certified windows with a G-value of 0.57 were specified. This means the windows corresponded to a gain of 57 percent of the inwardly radiating energy. The size and spacing of the windows were carefully considered to accommodate future changes to the functional layout throughout the extended lifespan of the building. Ultimately, fixed exterior solar shades measuring 914 mm (36 in.) were specified above all south-facing windows to control sunlight and potential heat gains in the summer months.

Due to local unavailability of commercial Passive House-certified door systems compatible with common commercial hardware, it was necessary to specify light commercial doors. Regular commercial doors are compatible with many types of hardware, including automated closers, card readers, and panic bars. Most of these doors, however, perform badly when it comes to energy efficiency and air infiltration due to poor details at unit construction, latching, and accessible thresholds. This substitution was only possible due to the small occupancy of the structure (a Part 9 rather than Part 3 building under the Alberta Building Code [ABC]).

Despite the advantages provided by the site’s orientation and fenestration considerations, the extreme winter climate conditions remained a serious challenge, as maintaining a steady indoor temperature of 20 C (68 F) while it is –40 C (–40 F) outside demands more energy than permitted under the Passive House standard. In cold areas, insulation of the whole building envelope, high levels of airtightness, and efficient frost-protection strategies are crucial to keep the interior warm in the winter without an active heating element like a boiler or furnace.

Adhering to the Passive House standard allowed this building to compensate heat gains and losses throughout the envelope by using solar energy (42 percent), internal temperature gains (34 percent), and heating (23 percent). The high levels of energy efficiency allowed for the installation of 28 kW of solar panels to fulfill the structure’s total energy needs.

To ensure airtightness, the building envelope was designed to complement the super-insulated, thermal bridge-free timber structure with a rain-screen system in order to help prevent condensation and future issues related to moisture and frost. The structure is composed of full-perimeter insulation with a U-value of 0.097 on exterior walls 38 x 235 mm (2 x 10 in.) wide and a 38 x 140-mm (2 x 6-in.) insulated cavity space wall with an R-value of R-58, 3.4 times higher than the R-17 required by ABC.

This design combines the positive features of orientation, fenestration, building envelope systems, and airtightness to effectively maintain comfortable indoor temperatures year-round. However, several design and material trade-offs were made to acquiesce with the requirements of ABC and the Passive House standard.

To maintain steady temperatures across the three levels of the building, ventilation specifications included a mix of outdoor variable refrigerant flow (VRF) systems for cooling and heating and a high-efficiency energy recovery ventilator (ERV) with heat recovery. However, due to the climate conditions of Valleyview, the design team specified an ERV not certified by the Passive House Institute (PHI), resulting in a penalty on the performance values accepted by the Institute for Building Certification.

To improve the aesthetics and the contextual integration of the town hall, the main entrance is framed by a human-scaled canopy with a raised roofline, superimposed by a glass fiber-reinforced concrete (GFRC) wall on the second storey. This design results in an attractive, yet subtle presence at street level welcoming visitors to the facility. The main exterior finish of the building is phenolic panel siding on the visible south and east elevations and pre-finished metal siding on the north elevation.

Although the initial project budget did not consider government funding, designing to the Passive House standard provided access to provincial green building grants. For instance, energy-efficient buildings in Alberta are eligible for incentives helping bring down the initial investment for solar technology. A grant from Alberta’s Municipal Climate Change Action Centre (MCCAC) allowed for the installation of 25 kW of solar panels on the new building’s rooftop. With $18,000 of extra funding, the building is equipped to generate 26,945 kWh per year, maximizing operational savings and reducing GHG emissions by 17 tonnes (19 tons) per year.

Meeting the core principles of the Passive House standard, this state-of-the-art building ensures long-term financial and environmental sustainability for the Town of Valleyview. Moreover, the Valleyview Town Hall sets a precedent for the feasibility of Passive House-certified buildings in northern climates as a means to reduce carbon dioxide (CO2) emissions and fight climate change.


Oscar Flechas

Architect, AAA, AIBC, CPHD, MRAIC
Calgary

 

 

Originally published by ConstructionCanada.net

PHOTOS Oscar Flechas

 

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