Case Study: Consulting Engineering

Liberty Mutual Boston

Liberty Mutual BostonBoston, Massachusetts

One of the Best-Performing Office Buildings in Boston

Located in Boston’s Back Bay neighborhood, the 157 Berkeley Street Liberty Mutual Tower is one of two major building complexes that comprise the Liberty Mutual Home Office campus. The 22-story, 757,000 SF tower was completed in 2013 and is structurally connected to the adjacent 330 Stuart Building, integrating the 130,000 SF historic building with the new construction. From initial occupancy to the present, CMTA has helped this LEED Gold certified building consistently decrease its energy use and operating costs through continuous commissioning, making Liberty Mutual Tower one of Boston’s highest-performing commercial office buildings.

The Challenges

  • Improve building energy efficiency by optimizing existing systems
  • Reduce operational carbon emissions through a reduction in energy consumption
  • Efficiently develop, test, commission, and verify various control strategies to maximize energy reduction and identify continuous improvement opportunities
  • Prioritize occupant comfort, health, and wellness
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We are excited to celebrate our growth and investment in the economic future of the city we have been proud to call home for more than 100 years. Created with Sketch.

David Long

Liberty Mutual CEO

The Solutions

The 157 Berkeley Street / 330 Stuart Liberty Mutual expansion project was LEED Gold certified when constructed. As part of the LEED certification, a LEED occupant survey was conducted, with the results reviewed by the owner. Feedback from the survey included thermal comfort complaints, indicating the need to adjust, optimize, and fine-tune the building controls strategy for improved occupant comfort, system operation, and efficiency.

This initial occupant survey alerted the owner to the concept of continuous commissioning, laying the foundation for 157 Berkeley Street to become one of the best-performing office buildings in Boston. The owner is committed to continuously improving the building’s HVAC systems’ operation to ensure occupant comfort, health and wellness, energy efficiency, and optimum operation. From initial occupancy to the present, energy use and operating costs have continuously decreased through continuous commissioning and energy conservation projects.

While the typical commercial office building in Boston indicates a relatively constant energy use intensity (EUI) over time, the 157 Berkeley Liberty Mutual Tower has steadily decreased its EUI. From 2014 to 2022, the owner reduced the total annual energy consumption by an impressive 60.7%, bringing the EUI down from 89 to 35 and saving the owner $4.5 million in utility costs since 2014. This impressive achievement is a result of the owner’s ongoing efforts and strategic approach to energy reduction and building system optimization, as outlined in their Master Plan. CMTA has helped Liberty Mutual Boston implement the following energy efficient control strategies:

  • Optimizing hot water condensing boiler operation with pumping speed control strategy using delta T with modifying boiler pumping from primary / secondary to primary pumping. Reset hot water temperature based on occupancy and day versus night setpoints.
  • Optimizing hot water pump activation based on polling interior zone temperature instead of outdoor air temperature. Implementing summer lockout for heating while not impacting occupant comfort level.
  • Implementing setback temperature in unoccupied spaces such as freight elevator lobbies, and storage rooms during the day, i.e., adjusting setback to 68°F heating / 75°F cooling from 72°F heating / 73°F cooling. Implementing a higher space temperature setpoint in computer/IDF closets to 75°F from 72°F with the design team developing a controls strategy that included exhaust ventilation staging.
  • Starved box strategy has been integrated for all AHUs, polling each floor’s terminal devices.
  • Pairing conference terminal equipment (fan coils and VAV boxes). The majority of this building’s conference rooms have foldable partitions enabling a variety of configurations, with the typical large conference room served by two or three VAV boxes in adjoining spaces. These VAV boxes have been paired to for a common control signal for VAV box airflow and hot water valve eliminating fighting controls.
  • Staged the enabling of the AHUs for one high rise and one low rise floor. They work in pairs to incrementally turn on, allowing the building chillers to be slowly staged on. This minimizes the building peak electric demand to provide peak electric load savings.

Designed for 2,900 occupants, the owner prioritized occupant comfort, health and wellness throughout the building’s continuous improvement project. To ensure proper ventilation, motion sensors and additional CO2 sensors were installed to maximize the effectiveness of demand control ventilation strategies in large collaboration spaces. The installation of VAV control for chilled beams ensures that the required ventilation air is provided based on occupancy, while also maintaining CO2 levels below the alarm setpoint. This commitment to indoor air quality is reflected in the building’s maintained Energy Star certification, which requires an annual site visit and IAQ testing. In 2022, the average CO2 concentration of five randomly tested spaces in Liberty Mutual Tower was found to be 512 ppm, well below the ASHRAE steady-state CO2 concentration ventilation requirements. These results are a testament to the owner’s dedication to optimizing indoor air quality.

Operational Carbon Reduction

After construction, a commercial building’s most significant environmental impact is its operational carbon footprint. On average, Liberty Mutual Tower’s energy consumption has been 58% natural gas and 42% electricity. While many new buildings aim to minimize this impact by going all-electric and using solar panels for clean energy, the original design of 157 Berkeley Tower did not follow an all-electric approach. In cases where the equipment is reaching its end of life, it makes sense to retrofit to all-electric. However, since Liberty Mutual Tower’s equipment is only ten years old, it has not yet reached that point.

Instead, Liberty Mutual has focused on reducing overall energy consumption to reduce operational carbon emissions. Since 2014, the building has lowered its operational carbon from 4,456 Metric Tons of CO2e to 1,697 Metric Tons of CO2e in 2022. This reduction is equivalent to the amount of carbon sequestered by 3,290 acres of trees!

The Results

Liberty Mutual Tower highlights the energy and cost saving opportunities afforded by pursuing continuous improvement and system optimization. Through energy conservation projects primarily targeting BAS control strategies, the owner has demonstrated their commitment to energy efficiency, occupant health and wellness, and carbon reduction.

CMTA’s continuous commissioning efforts have helped 157 Berkeley Street become one of Boston’s highest-performing commercial office buildings, per the publicly disclosed Boston Building Energy Reporting and Disclosure Ordinance (BERDO) data.

Liberty Mutual Carbon Footprint Reduction

[{"x":"2014","Median EUI of All BERDO Reported Buildings":"71.2","Liberty Mutual Site EUI":"89.3"},{"x":"2015","Median EUI of All BERDO Reported Buildings":"71.5","Liberty Mutual Site EUI":"91.0"},{"x":"2016","Median EUI of All BERDO Reported Buildings":"70.1","Liberty Mutual Site EUI":"77.8"},{"x":"2017","Median EUI of All BERDO Reported Buildings":"70.7","Liberty Mutual Site EUI":"76.1"},{"x":"2018","Median EUI of All BERDO Reported Buildings":"78.0","Liberty Mutual Site EUI":"68.9"},{"x":"2019","Median EUI of All BERDO Reported Buildings":"78.5","Liberty Mutual Site EUI":"61.8"},{"x":"2020","Median EUI of All BERDO Reported Buildings":"58.0","Liberty Mutual Site EUI":"39.5"},{"x":"2021","Median EUI of All BERDO Reported Buildings":"57.0","Liberty Mutual Site EUI":"26.5"}]