ASHRAE Journal - October 2024 - 49

2024 ASHRAE TECHNOLOGY AWARDS CASE STUDY
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 a
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 ongoing 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
this 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
ongoing commissioning and energy conservation
projects. Together with the design team, energy
conservation projects (primarily building automation
system [BAS] control strategies) have made 157 Berkeley
Street one of Boston's highest-performing commercial
office buildings, per the publicly disclosed Boston
Building Energy Reporting and Disclosure Ordinance
(BERDO) data.
As stated by one of the owner's staff, " energy
conservation is long, hard work. " Likewise, the owner
acknowledged that the design team's guidance can be
compared to " teaching patient fishing " by continuously
seeking energy reduction opportunities by repeating,
revisiting, comparing, contrasting and analyzing energy
management system (EMS) trends, data and utility bills.
This continuous review provides identifiers and triggers
to further implement EMS strategies and capital projects
to uphold their commitment to maintaining highperforming
buildings.
ENERGY EFFICIENCY
While the typical commercial office building in Boston
indicates a relatively constant energy use intensity
(EUI), the 157 Berkeley Liberty Mutual Tower has steadily
decreased its EUI. Energy reduction has been achieved
through consistent efforts as part of a master plan
with a focus on energy reduction and building system
optimization developed by the owner and working with
the design team on implementation. Note that from
initial occupancy until 2020, the 157 Berkeley building
was fully occupied and was trending below the median
EUI of all office buildings in Boston reported to BERDO
by 2018. During the COVID pandemic, occupancy
was minimal. In early 2021, the building was partially
occupied with a return-to-work policy beginning
September 2023.
Specific energy efficient control strategies
incorporated include:
z 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.
z 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.
z Implementing setback temperature in unoccupied
spaces such as freight elevator lobbies, storage
rooms during the day (i.e., adjusting setback to 68°F
[20°C] heating/75°F [24°C] cooling from 72°F [22°C]
heating/73°F [23°C] cooling). Implementing a higher
space temperature setpoint in computer/IDF closets
to 75°F (24°C ) from 72°F (22°C) with the design team
developing a controls strategy that included exhaust
ventilation staging.
z Starved box strategy has been integrated for
all air-handling units (AHUs), polling each floor's
terminal devices.
z Pairing conference terminal equipment (fan coils
and variable air volume [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.
z These VAV boxes have been paired to a common
control signal for VAV box airflow and hot water valve
eliminating fighting controls.
z Staged the enabling of the AHUs for one highrise
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.
A crucial factor in the continued achievement of
energy reduction is having a full-time BAS controls
O CTO B ER 2024 ashrae.org ASHRAE JOURNAL
49
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ASHRAE Journal - October 2024

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