Flexible urban energy

Schematic for an integrated district energy system

For a 1-hour overview of my research around the Stanford energy system, see this talk (April 29th, 2022).

As they become even more interdependent with the electric sector, urban energy systems will need to become more integrated and flexible. We will need to pay close attention to the way they operate. Decarbonization of electricity generation together with electrification of energy-and-carbon intensive services such as heating, cooling and transportation is needed to address ambitious climate goals. The Stanford campus district energy system (Stanford Energy Systems Innovations project; SESI) is roughly equivalent to a city of population 30,000 and provides a unique source of real data as well as an ideal test-bed for new ideas and control algorithms.

Stanford’s electrified heating and cooling system as an experimentation testbed

The bulk of Stanford’s heating and cooling needs are currently met by large electric heat pumps at the Central Energy Facility (CEF), which was built as a key component of the campus’ overall decarbonization strategy. The operations of the CEF can be scheduled to minimize the overall campus’s electricity bill and/or reduce the campus’ carbon footprint from electricity consumption; a key source of flexibility in doing so are large storage tanks for chilled and hot water1. In 2018, we participated in PG&E’s Capacity Bidding Program using prototype research software, in a megawatt-scale experiment where the campus was paid to respond to Demand Response events (announced one day ahead)2.

Live experiments in Stanford buildings show promising technical potential for flexibility

Our research team tested buildings on campus repeatedly in the summers of 2020, 2021 and 2022, in close partnership with the Stanford facilities teams. In total, over 1,200 days of experiment data were collected in eleven buildings. The tested buildings included offices, classrooms, laboratory buildings, a library, and a conference center. Distributed sensors and actuators were used to exclude 360 critical spaces from the experiments and control 1,300 others.

Our experiment data suggest that small adjustments to thermostat settings could significantly reduce daily building-level cooling loads without affecting critical spaces and indoor temperatures3. Extrapolating to the campus level, we find evidence of demand reductions that could provide significant value to campus operations during emergencies as well as to the California electricity grid4. Disaggregating to the zone level, we find that a small number of zones accounted for a large amount of energy use and energy flexibility5, unlocking the possibility for targeted demand flexibility strategies that balance zone-by-zone energy reduction with zone-by-zone costs to occupants.

The tests demonstrate real technical potential for targeted flexibility strategies. These strategies could unlock new energy demand flexibility options on the Stanford campus. Flexibility in chilled water demand provides further insurance policy to better prepare Stanford for the future, whether to guard against severe weather events or power grid failures. Flexibility can also be used to provide valuable services to support the California electricity grid.