Whole Building Life Carbon Assessment of an Existing, Retrofit, and New Construction for a Toronto Detached Home Case Study

This major research project was developed to better understand the whole building life cycle carbon analysis as a comparison between an existing baseline, a retrofit, and new construction of a detached case study home in Toronto. It investigates whether a deep energy retrofit, or new construction leads to lowest lifetime carbon emissions, accounting for both operational, simulated in DesignBuilder and Helioscope, and embodied carbon, calculated in OneClick LCA, over a lifetime of 60 years. A variety of energy saving strategies were applied consistent with leading practice such as air source heat pumps (ASHP), ASHP water heaters, low carbon high thermal resistance constructions, and photovoltaic renewable generation. Two scenarios for converting electricity to carbon emissions were used including marginal, resulting in high emissions, and baseload or average, resulting in low emissions. In all scenarios, both the retrofit and new build significantly reduced the emissions compared to the existing building. Depending on assumptions of carbon intensity of electricity, emissions factors (EFs), and details of specification, the carbon savings for the retrofit ranged from 76% to 98% and ranged from 88% to 97% for the new build. Thus, the retrofit’s carbon emissions are slightly less compared to the newbuild, supporting the time value of carbon ideology. Including renewable energy generation, none of the options resulted in a net-zero carbon status due to the case study urban site limitations. However, through other means of carbon offsetting such as purchasing carbon offsets and purchasing electricity from renewable energy source providers. Using different emission factors creates a large variation in the results and EFs with greater accuracy are required from the industry since the actual EF would be a combination of both baseload and marginal.