How “Digital Twins” Are Enabling City-Wide Electrification
Digital building modeling tools are helping the City of Ithaca find the most effective ways to electrify its building stock. Here are three key takeaways for other cities.
The City of Ithaca is planning to do something more ambitious than perhaps any other US city to date: electrify its entire building stock to significantly reduce carbon dioxide emissions from the building sector and reach city-wide carbon neutrality by 2030. Such large-scale electrification projects are often difficult to plan, especially with limited resources. Ithaca is eager to understand where and what to invest in first, and early insights offer lessons for other cities looking to do the same.
To help the city understand what it would take to reach this ambitious goal, researchers from Cornell University’s Environmental System Lab (ESL) and RMI collaborated to create a socioeconomic urban building energy model to analyze the cost and climate impact of retrofit measures for 5,468 buildings within the city’s geographic boundaries. Specifically, this analysis seeks to answer the following two questions:
- Which retrofit measures, alone or in combination, would provide the greatest opportunity for cost-effective decarbonization?
- Which properties should the community prioritize for building decarbonization efforts to most effectively reduce emissions and support socially vulnerable communities?
The City of Ithaca continues to aggressively seek pathways toward accelerated decarbonization of our building stock. Through digital twin, cost estimation, and energy modeling technology, we can strategically identify properties for electrification, facilitating thoughtful outreach and allocation of limited municipal funds and resources.
What does it look like to model over 5,000 buildings?
Cornell and RMI were able to produce detailed energy models for 5,468 buildings by integrating two analytical software tools: the ESL’s automated Urban Building Energy Model (UBEM) and RMI’s Green Upgrade Calculator (GUC).
ESL’s UBEM analyzes the cumulative effects of building electrification and forecasts energy consumption across different scenarios. Starting from creating a digital replica of the energy performance of all buildings in Ithaca, the model tests the most common building retrofit measures to identify the optimal combinations for each building individually. In particular, this analysis considered energy efficiency upgrades, electrification of space heating and water heating systems, and on-site solar installations.
RMI’s GUC enables energy professionals and policy analysts to swiftly evaluate the cost and environmental benefits of common residential decarbonization solutions for prototype homes in the United States. To understand the impacts of electrifying both residential and commercial buildings at the city level, ESL scaled up the GUC and combined it with its automated (UBEM) workflow.
Three key takeaways from the initial analysis
The Ithaca buildings analysis offers three crucial lessons for other cities looking to conduct large-scale electrification projects:
1. Improve the building envelope before electrifying
One important insight was the critical role that energy efficiency measures can play in supporting the City’s dual priorities of reducing emissions and energy costs. Given the cold winters in Ithaca, electrifying heating loads with air-source heat pumps (ASHP) represents a critical element of the City’s decarbonization plans; however, adding ASHP is not necessarily economical due to Ithaca’s cold climate and high electricity prices. On average, modeled monthly energy costs increase by $43 across commercial and residential buildings in the city.
However, installing envelope improvements alongside ASHP flips this outcome while providing important community benefits. Incorporating envelope improvements (e.g., adding insulation and upgrading windows) in addition to ASHP helps maintain safe and comfortable indoor temperatures and reduces the monthly operating expenses by an average of $330 for commercial and residential buildings. Tighter envelopes also enable owners to reduce the size of their heating equipment on average from 3.5 tons to 2 tons, thereby reducing upfront equipment costs.
Moreover, the reduced loads mean that the community-wide electricity demand in an all-electric scenario only increases about 13% compared to the status quo, while the increase can be more than 33% without any insulation improvements. These reductions in overall demand can lower the need for investment in costly new generation, transmission and distribution.
2. Pair solar installation with electrification
While energy efficiency and ASHPs offer a means to reduce operating costs, in some cases the overall costs for the property owner may still remain high due to the larger upfront investment required. Fortunately, rooftop solar can offset a heat pump’s electrical usage and further enhance cost effectiveness due to New York’s favorable net-metering policy and fairly high electricity rates.
For example, for an average pre-1980 townhome heated by natural gas in Ithaca, adding an ASHP and insulation and sealing air leakages will generate about $45 in annual energy cost savings. Not appealing enough? Adding solar panels, along with ASHP and envelope improvements, will create about $1,742 in annual energy cost savings and more than $12,400 savings in over 15 years, compared to continue using a gas furnace and a central air-conditioner without any upgrades.
3. Identify the optimal pathways that align with the community priorities
This modeling approach is particularly powerful in providing communities with insights to help them prioritize and optimize their efforts against community goals. For example, a local government that wants to reduce community-wide carbon emissions as much as possible might start electrification efforts with buildings that have the highest cost-benefit ratios, measured by carbon reduction per dollar spent. The chart below shows the cost-benefit ratio distribution across thousands of buildings in Ithaca, with group A representing the highest cost-benefit ratio group, and therefore the highest priorities for electrification, and group F representing the lowest.
These same groups are also represented in the bar chart below, which shows cost-benefit ratios across all 5,468 properties. The A-F grouping has been identified by Cornell and RMI staff to reflect a handful of logical archetypes or properties across the community.
In Ithaca, the following two building types stand out.
- Residential homes in low-income communities (Group A): Residential homes in low- to moderate-income (LMI) communities offer a compelling means for Ithaca to cost-effectively electrify buildings while supporting communities most in need. The initial bars at the far left-hand side of the chart (Group A) represent a small percentage of single-family and multi-family homes in low-income communities that can benefit from a range of complementary funding programs (and therefore can be electrified at little-to-no cost to homeowners). These programs include the High-Efficiency Electric Home Rebate, Affordable Multifamily Energy Efficiency Program (AMEEP), and more. Meanwhile, most buildings in Group A are older, low-income homes where envelope improvement is often highly beneficial, which contributes to a high cost-benefit ratio. Importantly, prioritizing the electrification efforts in these communities not only helps lower the carbon emissions but also provides health benefits that are particularly important for vulnerable residents.
- Commercial buildings in the downtown area (Group B): Some commercial buildings offer another compelling decarbonization opportunity. In contrast to the energy efficient commercial properties built in recent years (e.g., those reflected in Groups E & F), the commercial properties in Group B offer high emissions reductions opportunities. Moreover, while there are relatively few of these properties, commercial properties often consume significantly more energy compared to residential homes due to their relatively large floor areas, higher occupancy densities, and specialized commercial equipment.
To electrify 6,000 buildings, we need to leverage both proverbial sticks and carrots. In this case, the model is helping us to better understand how to balance financial incentives, the carrots, to best shape building performance standards, or the sticks. By understanding where the return on investment is highest, we can create a tiered, or phased, policy that limits financial impact to building owners and gives time and flexibility in building decarbonization planning.
Bringing this analysis beyond Ithaca
Across the United States, more than 125 cities and counties have adopted policies that require or encourage the move from fossil fuels to all-electric homes and buildings. This analysis shows how the latest modeling technologies can enable communities to evaluate the status quo at a granular level and design evidence-based electrification programs aligned with their priorities. By taking into account these lessons from Ithaca’s ambitious project, other local governments can reduce building emissions while helping residents and businesses maximize cost savings.
If you’re interested in learning more from Ithaca’s approach or using the GUC to evaluate the impact of green upgrades for your own community, reach out to Jingyi Tang jtang@rmi.org, Hung Ming Tseng ht495@cornell.edu, and Timur Dogan tkdogan@cornell.edu.
Acknowledgements:
The authors are grateful for thoughtful insight and feedback on this work from Rebecca Evans from the City of Ithaca, and generous support from the Cornell Atkinson Center.
