Triple Glazed Passive House Windows
A high performance triple glazed window is a critical component required to achieve up to 75% energy savings in a Passive House.
There are so many window products out there that even as a home and
building design studio we have to constantly question and re-evaluate windows. Not all windows are created equally so we hope that this article will serve as a guide for what qualities and components to look for when selecting windows for an energy efficient passive house.
Considering windows often account for upwards of 50% of all energy loss through a building envelope, it makes sense to invest in a high performance triple glazed window. By investing in high performance windows it allows a home or building designer to shrink the heating system, improve indoor air quality and take advantage of passive solar heating. All of these are good things because they all lead to the same result, saving you money!
Why are quality windows so important?
Number one, the thermal comfort of the occupants is directly impacted by the quality of the windows in the home or building. Everyone has seen a frosted single pane window in the winter and if you've ever spent any time sitting beside that old, frosted window you know that it is not a comfortable experience. So number one, at the very least, let's agree that a superior quality window will help to keep everyone warm and cozy in those winter months and cooler in the summer.
Number two, to minimize energy loss. Why? Because it saves you money! If you choose a quality window you are taking the right step to design and build a significantly better building envelope for your home or building which results in significant energy savings... $$$.
Why use a Triple Glazed Window vs. a Double Glazed Window?
The BC Building Code along with the other provincial and national building codes require windows to adhere to CAN/CSA-A440 which states that a window must have a thermal resistance lower than 1.8 W/(m².K). This rating is the equivalent of double glazed window with one Low-E coating. However, when compared to a high performance triple glazed window, that rating explains why most homes throughout Canada, and the world for that matter, require a large mechanical system to heat and cool the home due to the amount of energy lost through both the windows and the overall building envelope.
High performance triple glazed windows that meet Passive House certification standards are required to have a thermal resistance lower than 0.80 W/(m².K) for all of the components of the window including the frame, glass and even the spacers and gas in between the panes of glass. This is over double the thermal resistance and performance when compared to a minimum building code rated window. Further to that, direct and indirect solar gains are harvested through the glazing which results in more energy gained through the windows than what is actually lost, even throughout the winter. It is critical for the designer to correctly locate the windows as well as consider shading and summer/winter sun angles but this results in huge energy savings.
The energy savings can add up to 60% better when compared to a typical Low E/Argon Gas Filled/Double Pane window
A triple glazed window is warmer not only at its edges where condensation typically occurs in single and double pane windows, but warmer over its entire glazed surface
The added R-Value of triple glazing makes a HUGE difference in the overall heat/energy loss
Up to 80% less radiation heat transfer between the glazing and the room
The surface of a high performance triple glazed window will never drop below 17°C which eliminates any cold radiation into the room or a cold air pocket below the window at the floor level
Why is Window Frame Design so important in a Passive House window?
What most people don't realize is that the glazing unit which consists of three panes of glass, the spacers and gas in between the panes actually performs better than the frame itself. Therefore, the window frame has to be optimized as much as possible to meet the challenging Passive House thermal resistance requirement of lower than 0.80 W/(m².K). It is the combination of a well designed frame as well as an excellent glazing unit which defines a Passive House quality window.
The rapid escalation of Passive House design strategies in the last couple of years has now brought certified windows that are available in wood, vinyl, aluminum, fibreglass as well as many hybrid systems including aluminum clad wood window frames. They all have unique properties in terms of thermal conductivity, dimensional stability, insulated frames, durability and aesthetics but the critical requirement is that they meet the low thermal resistance requirements.
Thermal Bridge Free Design
Ψ PSI value of the Spacer - the spacer in between the panes of glass must have a low thermal conductivity to minimize any thermal bridging from pane to pane as well as to the window frame
Ψ PSI value of the Installation - equally as important, how the window is installed into the rough opening has a significant impact on the thermal bridging in between the frame and the rough opening so the key principles required in a quality window installation include placing the window as close to the centre of the insulation layer as possible, over-insulating the frame, avoiding extra framing and blocking at the rough opening and ideally if possible, use a non-metal sill pan flashing.
Passive House windows are triple gasketed to eliminate air leakage and windows frames are taped to the interior air/vapour retarding layer as well as the exterior weather resistance barrier
The expansion and contraction of the material which can have an effect on air tightness of the window assembly.
Insulated Frame and Over-Insulating the Frame
Considering the frame performs worse than the glazing unit, often manufacturers will include insulation on or within the core of the frame design to improve its performance
During construction, one strategy to improve the performance of the frame and minimize the Ψ PSI value of the Installation is to add "over-insulation" either on the exterior or interior of the window frames
A high performance Passive House window is designed to ensure that the internal surface temperature of the glass and frame is never below the point where condensation and mould can form on the interior surface of the glass or frame.
A colleague of ours explained it best, take a Ford pinto, place it beside a Stealth Fight Jet and that is the difference between a Passive House window and the rest. These are stunning windows to say the least!
What other elements are required in a high performance triple glazed passive house window?
Here are the other important components that must be considered when selecting a high quality window:
Low Conductivity Spacer System
Non-metallic spacers are critical in the design of a high quality window. They provide a separation in between the panes of glass but they also act as a thermal break in between the panes of glass and the frame. Traditionally, a hollow aluminum spacer is placed in between the panes but aluminum has a high thermal conductivity so they are a significant source of heat and energy loss.
Coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. The principal mechanism of heat transfer in multilayer glazing is thermal radiation from a warm pane of glass to a cooler pane. Coating a glass surface with a low-emittance material and facing that coating into the gap between the glass layers blocks a significant amount of this radiant heat transfer, thus lowering the total heat flow through the window. Low-E coatings are transparent to visible light. Different types of low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain.
Argon/Krypton Gas Filled
Rather than filling the area in between the windows panes with simply air, the space is filled with either argon or krypton gas because they have a lower thermal conductivity than air and it also reduces convection losses because it is heavier than air so the gas does not move as much in between the panes as air would.
Passive House Windows in Canada
In no particular order, if you are searching for the highest quality windows available in the world then look no further. This is by no means all of the manufacturers and products available as additional manufacturers can also be found using the Passive House Institute's Certified Component Library and the Passive House Institute US. Notice a real lack of Canadian manufacturers! That being said, we are aware of a number of Canadian manufacturers that are currently working on products that will be coming to market soon. In the meantime, any of the following suppliers will be happy to supply their products and we have worked with a number of these companies on previous projects.
Euroline - uPVC - Assembled in British Columbia, frames imported from REHAU Europe
Cascadia Windows - Fiberglass - Langley, BC
Alpen Windows - Fiberglass and uPVC Available - Colorado, USA
Optiwin - Wood and Aluminum/Wood - Austria
Klearwall - uPVC - Ireland - Munster Joinery
Glo - Wood/Aluminum - Montana, USA
Intus - uPVC - Virginia, USA
Zola - Wood - Colorado, USA
Casagrande Synergist - Wood - California, USA
Gaulhofer - uPVC, Wood, Aluminum/Wood - Austria
Smartwin - Wood, Aluminum/Wood, - Germany
Prossimo - uPVC - Poland
Internorm - uPVC, uPVC/Aluminum, Wood/Aluminum - Austria