ASHRAE Journal - August 2024 - 39

TECHNICAL FEATURE
speed chillers and waterside economizing chillers.
Moreover, CalEPA had already implemented several
energy savings measures, resulting in the building
being LEED Platinum certifi ed and achieving an Energy
Star performance rating of 100 (on a scale of 1 to 100)
even before the project. However, CalEPA remained
committed to pursuing innovative solutions to further
enhance the building's energy effi ciency and to increase
the resilience of their mission-critical data center. Thus,
CalEPA embarked on an energy savings performance
contract (ESPC) project in collaboration with an energy
service company (ESCO) to achieve a remarkable 34%
reduction in total building energy consumption at this
highly effi cient headquarters building.
The project involved a comprehensive approach
that encompassed IT equipment consolidation,
virtualization and modernization, as well as a complete
re-architecture of the data center cooling infrastructure.
This re-architecture included replacing the watercooled
CRAHs (that were dependent on the chilled water
plant) with air-cooled computer room air conditioning
(CRAC) units and redesigning the rack confi guration
to enable increased economization, higher operating
setpoints and independent operations. Furthermore,
the project also achieved a 40% reduction in the data
center's footprint (freeing up valuable real estate)
and a signifi cant improvement in resiliency through
the addition of 2N redundancy and backup power
infrastructure.
Existing Conditions
The pre-project chilled water system of the building
relied on cooling towers positioned on the roof and three
chillers located in the basement (a 300 ton [1,055 kW],
an 800 ton [2,813 kW] and a 1,200 ton [4,220 kW] unit).
The chillers had three condenser water pumps (30 hp
[22 kW], 75 hp [56 kW] and 100 hp [75 kW], respectively);
three secondary chilled water pumps (all 50 hp [37 kW]);
and three primary chilled water pumps (50 hp [37 kW],
40 hp [30 kW] and 20 hp [15 kW]). This arrangement
necessitated pumping condenser water from the roof
to the basement and then back up to the cooling tower
during cooling mode, resulting in signifi cant energy
consumption from the pumps and cooling tower fans.
The data center hosted 114 kW of UPS load. While
the data center occupied only a small portion of
the building's total fl oor area (approximately 1%),
it exhibited certain ineffi ciencies. These included
an oversized uninterruptible power supply (UPS)
operating at 50% effi ciency, the absence of hot/cold
aisle containment, a relatively cool space setpoint of
68°F (20°C) and constant-speed water-cooled CRAHs
on the eighth fl oor that required a continuous supply
of chilled water from the central plant due to the data
center's constant cooling demand. Consequently, the
cooling towers, condenser water loop and chilled water
loop had to operate almost continuously despite a data
center cooling load of only 35 tons (123 kW), even during
unoccupied periods (e.g., nights and weekends) or when
cooling was unnecessary elsewhere in the building (e.g.,
during winter and shoulder seasons).
Nevertheless, the overall CalEPA headquarters building
remained highly effi cient due to prior implementation
of various energy saving measures, including LED
light fi xtures, delamping, high-effi ciency chillers,
condensing boilers, waterside economization with heat
exchangers for the central plant, airside economization
for air-handling units (AHU), variable-speed pumps and
fans and controls retro-commissioning. The building
occupants were also already accustomed to a wide dead
band between heating and cooling setpoints (68°F - 76°F
[20°C - 24°C]). Further, due to Sacramento's coolingdominant
climate, the building seldom required
signifi cant heating.
Solution
Recognizing the importance of improving energy
effi ciency and resilience, CalEPA and the project team
devised a three-step approach to address the challenges
effectively. The solution was grounded in data gathering
and analysis of the following:
* UPS effi ciency. The UPS was identifi ed as
oversized, nearing end of life and highly ineffi cient,
consuming signifi cantly more input power than it
delivered output power.
* Removal of unused equipment. The chief
information offi cer (CIO) had fl agged numerous pieces
of outdated equipment that were no longer in use or that
could be virtualized. This project prompted the removal
of some of the redundant equipment.
* Pumping and cooling tower energy consumption.
Signifi cant energy consumption was observed in
pumping and cooling tower operations, particularly
due to continuous circulation of chilled water to serve
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