While carrying out the initial research to get this building to meet PH targets, the design team came up against a significant hurdle: there were no PH-certified overhead doors that were available on the market. This gap prompted a customized approach to the design, modeling, and detailing of this assembly. Several design assumptions, as well as calculation methods, had to be employed and verified to ensure reliable data could be input for the garage into the PHPP model.
Interior Environment
The first decision, which heavily impacted the modeling outcome, revolved around establishing the realistic internal air temperature in the garage. Because of how the space is used—active snow ploughs and drivers in full winter gear coming into the space, completing their tasks, and leaving at irregular intervals—this type of facility does not typically require full heat in the winter, but rather is often heated to a minimum operating range of between 10°C and 18°C. With the overhead doors being open periodically (particularly when cross-ventilation occurs from the doors at each end of the garage being open simultaneously), heat loss and temperature drops are bound to occur consistently during the heating season. Because of this, reducing the minimum design air temperature in the model is an appropriate measure. However, because recently running vehicles are consistently entering the facility and giving off heat, some of this heat loss was assumed to be recovered, keeping the garage always above 10°C and, therefore, certifiable. The garage and office buildings were modeled separately in the PHPP to allow for these variations.
With this decision in mind, and an appropriate Passive House building envelope specified to surround the garage, the main component of interest was now the garage door. After much research, the design team found a workable option for this project, the Thermostop Sentinel Overhead Door.
Thermal Performance Criteria
The first challenge in finding suitable garage doors was identifying ones with sufficient insulation values. Several door manufacturers and door types (overhead and folding) were reviewed before landing on the Thermostop Sentinel doors, which provide an option that includes 100mm of polyurethane foam core insulation between steel panels. With this configuration the doors achieve a nominal thermal performance of approximately R-32.
The Thermostop doors also include an option for adding 600mm x 300mm (24-inch x 12-inch) double-glazed fixed windows with a thermally broken aluminum frame, providing a thermal resistance of R-5. As the doors would be taking up most of the wall area on the north and south elevations of this part of the project, the option of placing windows within the door assemblies was very beneficial.
To appropriately model these doors in the PHPP, the basic door assembly was created in the U-Values tab, and the glazing and window frame components were input into the Components tab in accordance with the performance values provided by the manufacturer.
To optimize solar heat gains and minimize heat losses, while providing adequate daylighting into the garage area, the design decision was made to include four windows on each door along the north elevation and twelve windows, consisting of three rows of four, on each door along the south elevation (see Figures 2, 3, and 4).