Rising energy costs and international pressure has motivated governments and homeowners to reduce the energy consumption and greenhouse gas (GHG) emissions of new and existing dwellings. A popular technical approach to this problem is the adoption of net-zero energy targets, which can achieve substantial energy and GHG emissions reductions. Often focused on new builds, there is growing interest in retrofitting existing buildings to net-zero. Addressing existing stock is essential since they will continue to be a significant portion of the building stock for several decades.
Net-zero is not limited to single buildings, and potential benefits of community-scale retrofit projects include greater economic viability and economies of scale. However, challenges faced by such projects include few demonstrations in practice, and the need of detailed analytical models to analyze techno-economic feasibility. Another challenge is the lack of consensus on formal net-zero definitions.
This research was conducted to explore the feasibility and performance of retrofitting Canadian residential communities to net-zero, and the impact of net-zero definition on design. To meet this objective, a new modelling approach was developed which builds upon the detailed and validated Canadian Hybrid Residential End-Use Energy and GHG Emissions Model (CHREM). A new Canadian residential appliance and lighting bottom-up model was developed and integrated into CHREM which realistically captures the behaviour, variability and aggregate electrical demands of communities. Building envelope retrofit models, ground-source heat pump (GSHP) space heating, and heat pump hot water models were incorporated into CHREM. A new methodology was developed to estimate the impact of envelope retrofits on airtightness.
Retrofit community-scale energy systems considered included solar thermal and photovoltaic (PV) systems, district heating and thermal energy storage, and microturbine cogeneration. Detailed models of these systems were developed in the TRNSYS energy simulation tool. An optimization algorithm was used to determine the cost-optimal net-zero solutions for representative residential communities. Commonly used site and source net-zero energy definitions were considered. The results indicate that deep envelope upgrades and PV and GSHP system retrofits have potential to achieve net-zero and significant GHG reductions. The results also indicate that site net-zero likely realizes more GHG reductions compare to source net-zero.