Curtailment FAQs

Curtailment Stages and Impacts

Past heat waves have prompted questions about the university’s need to curtail cooling on the main campus. The following Q&A provides technical information about curtailment and the system that provides heating and cooling for campus. 

1. What is being done to improve the capacity of the system?

An extra 5,000 tons of cooling tower equipment has expanded the capacity of the system by 35 percent. A permanent expansion between the years 2020 and 2023 increased cooling capacity from 14,500 ton-hours to 28,500 ton-hours, with an additional 3,000 ton-hours of standby chilling providing N+1 capacity. The Board of Trustees gave concept approval for the project in February 2020 to support expected growth over the next decade nearly doubles plant capacity. Learn more about the resilience of the system.

2. Why do we need to curtail chilled water with this energy system?

The campus heating and cooling system relies on a district-level heat recovery process.  Heat recovery works by extracting excess heat from the chilled water system and repurposing it to the hot water system. At all times of the year, the university has a simultaneous need for both chilled and hot water service to most buildings. Chilled and hot water storage tanks add extra capacity to the system, functioning like large batteries that can be “charged” when campus demand is low and discharged when demand is high. This design meets our needed loads 99 percent of the time, given the current and expected temperature profile of the region. Of the approximately 1,600 days the Central Energy Facility (CEF) has been in service, curtailment has only occurred about 10 days, or less than one percent of the time. 

However, for extreme heat events, when the temperature or humidity spikes to record or near record temperatures, there is so much excess heat that the system cannot extract and expel it quickly enough to cool the chilled water to an optimal level.  When this happens, we curtail chilled water use though incremental stages (0-4) based on varied degrees of urgency to meet the load balance for a few days. With the expanded cooling equipment, this is not commonly expected. 

3. Will there be more curtailment in the future?

Added capacity to the system helps to limit the effects of these heat events on the campus community. Though there is always the chance that extreme weather events will cause future curtailment, the expansion of the system will help the CEF continue to provide adequate cooling to campus. 

4. What is the curtailment protocol?

During periods of curtailment, the situation is often very dynamic. The response may not always be systematic or progress sequentially through the specified stages, and some situations may require rapid escalation in curtailment stage levels with limited notice. To prevent and mitigate disruptions to research in the event of cooling curtailment, Land, Buildings & Real Estate has convened an advisory committee of faculty members and facilities directors to make recommendations to reduce the likelihood of rapid escalation to higher levels of cooling curtailment, including ways to further reduce loads in the early stages of a heat wave.

The campus community and critical users receive communication as Stanford goes through a curtailment process. During a curtailment event, the Central Energy Facility (CEF) as planned procedures for the event of curtailment and encourages community members to be prepared as well and to help in implementing mitigation measures in their areas. 

To reduce loads and minimize heat in buildings, it is always good practice to turn off lights in unused rooms, lower window shades, keep doors and windows closed, raise thermostat set points to 78F in office and common areas, shut off unused office equipment, close laboratory fume hood sashes when not in use, and, where possible, shut off lab equipment not currently being used. This will help to conserve energy and reduce chilled water loads. Learn more about how the campus proactively manages energy demand, and ways to get involved in office and lab sustainability programs.

For those in research areas, please be aware that elevated temperatures can affect any equipment that utilizes process cooling water, including vacuum pumps, cryostats, and microscopes. In extreme cases, it can also lead to the overheating of freezers, the need for equipment re-calibration (such as lasers), and fume hood shut downs. Finally, it could lead to differences in the performance of experiments including an increase in reaction rates, higher vapor pressure of volatile solvents, increased evaporation of solvents and/or increased condensation on equipment. There are a number of non-curtailable spaces that house life safety functions and will not be included in any curtailment stages.