This short article on Passive Design is next in the series, What you can do RIGHT Now. This article is specifically for a practitioner who is looking for pragmatic guidance on immediate steps to embrace contemporary passive design strategies.
What is Passive Building Design?
Contemporary passive design relies on understanding climate and taking advantage of siting, form, detailing, and construction assemblies to create buildings that achieve design excellence while reducing the need for energy consuming equipment to provide comfort and health. Reducing the need for energy makes it possible to downsize HVAC equipment, shorten operating times and seasons, shorten duct runs and, in some cases, eliminate equipment entirely. Passive design can mean shifting first cost from equipment to improvements to the building enclosure. Passive design requires focusing on the architecture first, before supplementing with active systems.
Passive design was an essential aspect of all building design until well into the 20th century as there were few alternatives to provide a more comfortable environment. With limited energy sources and technologies, architects and builders needed to understand the local climate and the thermal properties of regionally available building materials.
Climate & Daylight
Passive design starts with climate. Climate will influence orientation, shading, air movement, siting, and materials, among other things. Providing controlled daylight and enabling users some control over natural ventilation, when conditions and building type permit, are almost always preferred design strategies because they create pleasing spaces that connect building occupants to nature. Access to daylight is recognized as an essential element of human health and regulation of circadian rhythms.[i] While LEDs have reduced energy loads from electric lights, controlled daylight is always desirable and electric lights that are dimmed or switched off in response to daylight still save energy.
The 1970s saw the growth of passive solar design in response to resource shortages and other environmental concerns. Passive solar emphasized direct solar gain through expansive, seasonally-shaded, south-facing glass with internal thermal mass used for heating and cooling. Improvements in technology, insulation levels, quality of construction, and better understanding of the importance of air infiltration and air sealing have resulted in significant rethinking of passive solar design strategies. A building enclosure designed, detailed and built to deeply minimize thermal bridging and infiltration, with moderate amounts of glazed wall area, can achieve excellent energy performance even with a suboptimal site or orientation. Major improvements to the enclosure permit greater variation from the bioclimatic ideal. It is important to understand that well-insulated, air-sealed buildings do require mechanical ventilation! This is confusing to those who assume every aspect of performance is to be passive, including the ventilation. Buildings can and should open to the exterior, operating in different modes in response to outdoor conditions.[ii] Well-insulated, air-sealed buildings can open to the exterior during moderate weather, but can achieve deep operational energy reductions while supplying filtered ventilation air when outdoor conditions are inhospitable.
Contemporary passive design strives to mechanically heat or cool the building with the smallest possible energy use when you can’t achieve comfort with operable windows, thermal mass, or stack ventilation. With the impact of climate change, which has led to higher temperatures and poor air quality from wildfires, this is more relevant and appropriate than ever. Passive design means designing buildings that are very ‘tight’, minimizing interior sources of poor air quality such as combustion appliances and off-gassing materials, and providing filtered ventilation with outside air. Improved building enclosures permit greater aesthetic freedom, while still achieving excellent energy performance.
Today, the Passive House movement represents the leading edge of Passive Building Design. Passive House Institute[iii] was founded in Germany by Wolfgang Feist, inspired by super-insulated homes built in North America in the late 1970s.[iv] In North America, the Passive House movement split into two groups in 2014 with modest variations in approach and requirements. The North American Passive House Network (NAPHN)[v] remains affiliated with the German Passive House Institute. Passive House Institute US (PHIUS)[vi] instituted climate-specific requirements developed in cooperation with the US Department of Energy and Building Science Corporation. The two Passive House standards in North America both call for a super tight enclosure and mechanical ventilation, among other requirements. The Passive House standards apply to both residential and nonresidential buildings and are best thought of as Passive Building Standards. Both standards require a series of blower door tests throughout the construction process to document that the targeted level of air sealing is actually achieved.
The principles of climate based design still apply. Elongating a building axis in an east/west direction makes it easier to control sunlight and daylight and supports occupant well-being. South facing roofs can shade windows and maximize effectiveness of installed solar electric systems, especially with inclusion of battery storage. Modest amounts of thermal mass in nonresidential buildings, on the interior side of insulation and protected from direct sun, can increase comfort by absorbing heat over the course of a day.
Things You Can Do Right Now to Use Passive Design in Architectural Practice
Tools and Resources:
BC Housing (British Columbia, Canada) offers numerous residential design and construction guides. See https://www.bchousing.org/research-centre/library/residential-design-construction (accessed 09/16/2020).
Heat Recovery Ventilation Guide for Houses, RDH Building Science, https://www.rdh.com/wp-content/uploads/2017/07/HRV_Guide_for_Houses.pdf (accessed 09/16/2020).
Cladding Attachment Solutions for Exterior-Insulated Commercial Walls, RDH Building Science, https://www.rdh.com/resource/cladding-attachment-solutions-for-exterior-insulated-commercial-walls-guide/ (accessed 09/16/2020).
Building Envelope Thermal Bridging Guide, BC Hydro, https://www.bchydro.com/powersmart/business/programs/new-construction.html#thermal (accessed 09/16/2020).
How to Implement Passive Solar Design in Your Architecture Projects, Arch Daily, https://www.archdaily.com/900418/how-to-implement-passive-solar-design-in-your-architecture-projects (accessed 09/16/2020).Daylight Harvesting for Commercial Buildings Guide, UC Davis, https://cltc.ucdavis.edu/publication/daylight-harvesting-commercial-buildings-guide, (accessed 09/16/2020).
Details Green Book Passive House Design, Arch Daily, https://www.archdaily.com/771475/detail-green-books-passive-house-design (accessed 09/22/2020).
Climate Consultant Software, Energy Design Tools, https://energy-design-tools.sbse.org/.
Blower Door Tests: https://www.energy.gov/energysaver/blower-door-tests
[iv] Allison Bailes, The Evolution of Passive House in North America, https://www.energyvanguard.com/blog/the-evolution-of-passive-house-in-north-america#blog-comments (accessed 09/04/2020).
[vii] Kevin Van Den Wymelenberg, Alen Mahić, Annual Daylighting Performance Metrics, Explained, Architect Magazine, April 12, 2016. https://www.architectmagazine.com/technology/lighting/annual-daylighting-performance-metrics-explained_o (accessed 9/22/2020)
[viii] Joseph Lstiburek, Building Science Insight 091: Flow Through Assemblies. https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-091-flow-through-assemblies (accessed 09/4/2020).
[ix] Joseph Lstiburek, Building Science Insight 0939: Five Things. https://www.buildingscience.com/documents/insights/bsi-039-five-things (accessed 09/4/2020).
[x] Jonathan Smegal, John Straube, Research Report -1014: High-R Walls for the Pacific Northwest–A Hygrothermal Analysis of Various Exterior Wall Systems. https://www.buildingscience.com/documents/reports/rr-1014-high-r-walls-pacific-northwest-hygrothermal-analysis/view (accessed 09/4/2020).
[xi] BUILDING AMERICA BEST PRACTICES SERIES Retrofit Techniques & Technologies: Air Sealing, 2010 https://www.energystar.gov/sites/default/files/asset/document/DOE_Air%20Sealing%20Guide%20for%20Contractos.pdf
[xii] BC Housing, Illustrated Guide to Achieving Airtight Buildings, 2017. https://www.bchousing.org/research-centre/library/residential-design-construction/achieving-airtight-buildings, (accessed 9/23/2020).
[xiii] John Straube, Building Science Digest-022: The Perfect HVAC. https://www.buildingscience.com/documents/insights/bsi-022-the-perfect-hvac (accessed 9/22/2020)
[xiv] Architect’s Guide to Building Simulation, American Institute of Architects, 2019. https://www.aia.org/resources/6157114-architects-guide-to-building-performance:41 (accessed 9/23/2020).
Authors: Bill Burke & Elena Nansen