Glossary:
Net zero emissions means achieving a balance between the greenhouse gases (GHG) put into the atmosphere and those taken out.
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, which is commercially utilized for electricity generation.
Solar PV has a specific advantage as an energy source: once installed, its operation generates no pollution or GHG emissions and it can be scaled to power needs.
A heat pump is an air conditioner running in reverse. Working at temperatures as low as minus 5 degrees Fahrenheit, the pump takes cold air from outside and produces warm air inside. It runs on electricity but is three times more efficient than the space heater under your desk. Greater efficiency translates to lower costs but the real savings come from using solar PV, which is cheaper than grid electricity.
The concept of a building envelope relates to design and construction of the exterior of the house. The building envelope of a house consists of its roof, subfloor (foundation beneath finish flooring materials), exterior doors, windows and the exterior walls. An energy-efficient building envelope is airtight, reducing energy demand for heating and cooling. For example, materials such as fiberboard or uncoated concrete blocks should not be used in home construction because air passes through them easily. Of course all buildings must have sufficient ventilation for comfort.
Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage.
Summer Reading Selections (excerpts and paraphrased)
Berrill, Wilson, et al. (2022). Decarbonization pathways for the residential sector in the United States:
The lowest emission scenarios rely on very rapid decarbonization of electricity supply alongside extensive renovations to existing homes—focused on improving thermal envelopes and heat pump electrification of heating. Reducing the size, increasing the multifamily share, and increasing the electrification of new homes provide further emission cuts, and combining all strategies enables emissions reductions of 91% between 2020 and 2050.
The first pillar of reducing residential emissions is rapid decarbonization of electricity supply through increased reliance on solar and wind technologies.
The second major pillar of decarbonizing the residential sector is extensive renovation of existing homes, involving major improvements to building envelopes through increased insulation and reduced infiltration [air leakage], and replacement of space and water heating equipment with high efficiency heat pumps and electric water heaters.
As construction becomes increasingly important in the lowest emission scenarios these more extensive measures targeting reduced floor area could make zero emissions targets more attainable. [The author suggests reducing] floor area consumption to 40 m2/cap [that’s 431 square feet per resident].
IPCC, 2022: Summary for Policymakers. In: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
Reducing consumption-based urban emissions to net-zero GHG can only be achieved by addressing emissions beyond cities’ administrative boundaries, including smaller towns and cities, suburbs, and rural areas.
In 2019, global direct and indirect emissions from residential buildings increased by about 50% compared to 1990. This increase was mainly driven by the increase of the floor area per capita, population growth and the increased use of emission-intensive electricity and heat.
Interventions to reduce building-related emissions include use of low-emission construction materials at the construction phase, highly efficient building envelope and the integration of renewable energy solutions to heating and cooling requirements, such as solar PV, small wind turbines, solar thermal collectors, and biomass boilers.
Professor Shoshanna Saxe/University of Toronto, quoted in Large carbon footprint of new house construction mostly due to concrete basements (2021):
“The vast majority of the conversation about sustainable houses right now is about gadgets and technology. People want to put solar panels on the roof, or point out how they are using better insulation. Those are great, but it’s also really important to think about how much of a difference you can make by building something that is reasonably sized, using a reasonable amount of material.
...you’ll see that mostly what we’re building these days is single-family homes. That form is inherently challenging when it comes to carbon emissions, and it’s made more so by the fact that we’re building much bigger houses than we used to…Simply put, you should build as small as you can for what you need, and if possible, you should avoid having a [concrete] basement.
…concrete is carbon-intensive – a lot of emissions get created during its manufacture. This is in contrast to other materials such as wood, which is theoretically carbon neutral.”
Yang, Hu, et al. (2022) Key strategies for decarbonizing the residential building stock: Results from a spatiotemporal model for Leiden, the Netherlands:
Decarbonizing the building stock plays an important role in realizing climate change mitigation targets. Compared to our reference scenario of modest energy efficiency improvements of residential building stock, we found that annual GHG emissions can be reduced by about 90% under an ambitious scenario where all suggested decarbonization strategies are simultaneously implemented. These included:
Wood construction
Heat transition away from natural gas
Renewable electricity
Rooftop PV
Reduced floor area (15% below 2015 average floor area by 2050)*
Reduced home heating during winter (target: max out at 65°F by 2050).
* Per Statistica: “In 2020, the average size of a single-family home built for sale in the United States amounted to 2,491 square feet.” Reduce by 15% = 2,117 square feet = 530 sq ft per person. Still plenty big for a family of 4 including two working adults, each with a home-office nook, which could have other uses.
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References and Suggested Reading:
IPCC, 2022: Summary for Policymakers. In: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926.001
Large carbon footprint of new house construction mostly due to concrete basements. By Tyler Irving/University of Toronto Engineering News September 29, 2021
P.E. Berrill, J. H. Wilson, et al. (2022). Decarbonization pathways for the residential sector in the United States, Research Square. https://doi.org/10.21203/rs.3.rs-1199406/v1
Solar-powered Heat Pumps Warm Upper Peninsula Homes for Less. University Marketing and Communications/Michigan Tech News December 2, 2021
Yang, X., Hu, M., et al. (2022) Key strategies for decarbonizing the residential building stock: Results from a spatiotemporal model for Leiden, the Netherlands. Resources, Conservation and Recycling 184: 106388. https://doi.org/10.1016/j.resconrec.2022.106388