honorable mention commercial buildings, existing … · 2019-12-31 · previous mechanical systems...
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A S H R A E J O U R N A L a s h r a e . o r g J U LY 2 0 1 52 4
BUILDING AT A GLANCE
Don McLauchlan, P.E., is a founder and principal of Elara Energy Services, Hillside, Ill.
An ASHRAE Level II audit iden-
tified 10 energy conservation
measures for this existing build-
ing including a steam-to-water
conversion, a chilled water plant
overhaul, redesign of the perim-
eter HVAC system to incorporate
active chilled beams, a new inte-
rior VAV system and replacement
and refurbishment of AHUs.
HONORABLE MENTIONCOMMERCIAL BUILDINGS, EXISTING
ChicagoVintage Restored
2015 ASHRAE TECHNOLOGY AWARD CASE STUDIES
29 North WackerSun Life Assurance Company
Location: Chicago
Owner: Sun Life Assurance Company
Principal Use: Office & Retail
Includes: Private office, open office, restau-rant, storage
Employees/Occupants: 24
Gross Square Footage: 137,544
Conditioned Space Square Footage: 140,000
Substantial Completion/Occupancy: April 2013
Occupancy: 80%
BY DON MCLAUCHLAN, P.E., BEAP, MEMBER ASHRAE
29 North Wacker, owned by the Sun Life Assurance Company, is a 10-story, 1962 vintage office building (140,000 gross ft2 [13 006 m2]) located in the heart of Chicago’s downtown business district. This project’s comprehensive retrofit of the building’s major mechani-cal systems was implemented while the building was occupied.
The retrofit provided better comfort, controllability, reduction of noise and improvements in the aesthet-ics and space of each office. Specific improvements included upgrading the heating plant via a steam-to-water conversion design, redesigning the perimeter induction system to incorporate chilled beams and installing a building automation system with Web-based direct digital controls (DDC).
© NAI Hiffman
This article was published in ASHRAE Journal, July 2015. Copyright 2015 ASHRAE. Posted at www.ashrae.org. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org.
J U LY 2 0 1 5 a s h r a e . o r g A S H R A E J O U R N A L 2 5
ABOVE New insulated knee wall after removal of original induction unit.
LEFT The building’s lobby features efficient lighting.
2015 ASHRAE TECHNOLOGY AWARD CASE STUDIES
An energy use intensity (EUI) comparison between the
previous mechanical systems and the newly commis-
sioned, high-efficiency systems shows a clear reduction
in energy use throughout the building. Over the course
of 42 consecutive months, the new design reduced the
building’s EUI from 113 kBtu/ft² (1283 MJ/m2) (40% occu-
pied) in 2009 to 81 kBtu/ft² (111 kWh·m2) (95% occupied)
in 2013—a reduction of 28% despite the occupancy of
the building more than doubling in the same amount
of time. The resulting Energy Star score for the building
is 88 (improved from 66) and translates into an electri-
cal energy reduction of almost 417,000 kWh annually,
along with a natural gas energy reduction of 31,000
therms per year. The energy use over the course of a
full year was also monitored and revealed that the new
system performs at $1.03/ft² ($11.09/m2) versus $2.33/ft²
($25.08/m2) on the old system (which was approxi-
mately 44% higher than current minimum require-
ments of local building code)—a reduction of greater
than 50%. The building was awarded a LEED Existing
Buildings: Operations & Maintenance certification of
Gold in 2014.
ConceptThe concept for the mechanical upgrade project was
created in 2010, when a detailed mechanical assessment
report for the building was performed. The assessment
report was necessitated by increasing utility costs and
the recent emphasis on green technology. The ASHRAE
Level II commercial building energy audit identified
opportunities for improvement in energy efficiency,
comfort, maintenance and reliability of the existing
major mechanical systems.
Shortly after delivery of the report, the design team
was enlisted to implement an infrastructure upgrade
for the building based on 10 of the energy conservation
measures (ECMs) identified in the energy audit. These
ECMs included a steam-to-water conversion featuring
the installation of high-efficiency condensing boilers, a
chilled water plant overhaul, redesign of the perimeter
HVAC induction system to incorporate active chilled
beams, a new interior variable air volume (VAV) system,
refurbishment of other existing air-handling units, con-
version to variable pumping and a demand controlled
ventilation system, a new garage CO controlled exhaust
system, a domestic water system upgrade, a lighting
system upgrade, the addition of insulation to the perim-
eter spandrels and perimeter ceiling headers and a
new building automation system (BAS) with Web-based
direct digital control (DDC).
Heating PlantThe building’s original heating plant was comprised of
two scotch-marine steam boilers located in the second
floor mechanical room. Each boiler had a maximum
capacity of 8,400 MBtu/h (2.5 MW) and was equipped
with natural gas burners with 3:1 turndown ratios. These
boilers produced low-pressure steam used to heat the
building via several steam-to-water heat exchangers,
steam heating coils and unit heaters. The boilers were
original to the building, were over 40 years old at the time
of the energy audit and had been converted from fuel oil
to natural gas.
In addition to the inherent inefficiencies associated
with steam heating (i.e., radiant losses, distribution
losses, etc.), the 3:1 turndown ratio and the sizing of
the boilers compared to the load profile of the building
resulted in frequent cycling and loss of efficiency. At the
time of the energy audit, most of the building used hot
water for heat; however, for a hot water boiler plant to
be feasible, the remaining steam users (air-handling
unit preheat coils and steam unit heaters) needed to
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A S H R A E J O U R N A L a s h r a e . o r g J U LY 2 0 1 52 6
be converted to hot water. With a goal of maximizing
energy savings, high-efficiency condensing technology
was preferred. However, for the savings to be realized,
low water temperatures would be required (typically
less than 130°F [54°C]). The existing hot water users
(perimeter induction system, reheat coils and heating)
are all candidates for low water temperatures, but the
existing perimeter induction system and reheat coils at
the building were designed for 180°F (82°C).
These systems were subsequently identified for
replacement with systems capable of using low tem-
perature water. The resulting steam-to-water conver-
sion design replaced the two original oversized steam
boilers with four, 2,000 MBtu/h (586 kW) each gas-fired,
high-efficiency condensing hot water boilers that were
installed within the footprint of a single demolished
steam boiler. Two hot water pumps equipped with vari-
able frequency drives (VFDs) were added to supply
heating hot water to the air-handling units, new active
chilled beams, radiant systems and unit heaters (which
were converted to hot water). High-efficiency condens-
ing boiler technology can increase the seasonal effi-
ciency of a boiler plant by as much as 30% to 40%. The
boilers specified are also capable of 20:1 turndown ratio
that allows for increased control and savings at low-load
conditions.
Chilled Water PlantThe existing chilled water plant was comprised of
two 250 ton (879 kW) centrifugal chillers that provided
chilled water to the air-handler cooling coils and the
building’s perimeter induction system.
The original design was a single absorption chiller
with no redundancy. Although the existing chillers were
not original to the building, they were over 25 years old,
which is greater than the ASHRAE mean service life for
this type of equipment. The condensing water side of the
chilled water plant was comprised of two constant speed
pumps and a dual cell two-speed cooling tower equipped
with 25 hp (19 kW) fans. The condensing water pumps
were dissimilarly sized and were sequenced in connection
with the chillers.
After inspection and analysis of the chilled water plant,
the design team identified that the existing chillers were
oversized and often required to work below their stable
operating point (shutting down on surge alarms as a
result), that the cooling tower was also oversized and
not equipped with a VFD (resulting in tower fans cycling
frequently and numerous fan motor failures) and that
both existing chillers were located in the same room as
air-handling units, which is against current building
code due to the high potential for spreading a refriger-
ant leak.
As a result, the design team recommended an upgrade
to the existing chilled water plant. The design called for
a single 400 ton (1407 kW) variable speed screw-type
chiller to replace one of the existing chillers, while the
second chiller was left in place for redundancy. The new
chiller was located in the boiler room in the place of one
of the demolished steam boilers. Additionally, a water-
side economizer was added.
These improvements allow the staff to extend the
operating window of the chiller to provide comfort cool-
ing during shoulder months and reduce the amount of
energy use. To support this design, the existing cooling
tower was refurbished including new fan motors, VFDs
and a basin coating. To accommodate the waterside
economizer, one cell of the cooling tower was retrofit
with low-flow nozzles and isolation valves to isolate flow
during waterside economizer use.
Heating and Cooling DistributionThere were four main hydronic distribution loops
associated with heating and cooling for the existing
building. A dual temperature loop provided the perim-
eter induction units on Floors 3 through 10 with either
hot or chilled water, depending upon the seasonal
mode; the induction units were wall mounted and
Exterior view of 29 North Wacker building at dusk.
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A S H R A E J O U R N A L a s h r a e . o r g J U LY 2 0 1 52 8
installed below the windows. The three other loops were
hot water-only systems with two providing heating and
the third serving a reheat loop. The pumps supporting
these systems were designed to run at full load simulta-
neously and operate at constant flow. This presented an
opportunity for energy savings as the facility was over-
consuming electricity to satisfy a pump load even during
low demand.
The new design called for reuse of the existing induc-
tion dual temperature piping system to support a new
active chilled beam system for conditioning the perim-
eter zones. Two-way valves were installed on each chilled
beam, which converted the constant flow system to a
variable flow system. All reheat coils were eliminated
for the interior system, which was converted to VAV. The
dual temperature loop was already piped correctly for
cooling mode integration with higher chilled water tem-
peratures used by the chilled beams.
HVACThe existing HVAC systems were comprised of six air-
handling units (AHUs) located on the second floor, four
of which were paired with return/exhaust fans. These
fan units provided space heating, cooling and ventila-
tion to the various floors of the building. The vast major-
ity of the building was served by three AHUs (S-1, S-2
and S-3). AHU S-1 provided ventilation and conditioned
air to the perimeter induction system and was equipped
with a cooling coil and steam-heating coil. Induction
units were fed conditioned ventilation air from S-1
located on the second floor. The perimeter induction
system required a high volume of high pressure air
(approximately 11 in. w.c. [2740 Pa]) to operate correctly.
Although the induction units adequately conditioned
the spaces, they were costly to operate, very noisy and
original to the building. Therefore, the design team
recommended replacement of the perimeter induction
system with active chilled beams mounted in the drop
ceiling to reduce the static pressure requirements and
improve heating and cooling effectiveness. A new insu-
lated knee wall filled the space under the windows left
by the induction system, while additional insulation was
added along the perimeter above the drop ceilings.
As an additional architectural modification, a blind
air gap was created along the perimeter using the drop
ceiling, which acts as a return air path for the chilled
beams. Since the chilled beams required significantly
different airflow and pressure than the induction sys-
tem, S-1 was replaced with a custom AHU re-engineered
for the active chilled beam system with reduced airflow
and designed for enhanced dehumidification using
internal glycol runaround coils to deliver very dry air to
the chilled beams. S-1’s return/exhaust fan was retrofit-
ted with a VFD. Since the new chilled beams use zone
control valves, the dual temperature pump that served
this system was replaced with a new pump with a VFD
designed for the new variable water flow requirements.
AHU S-2 originally served interior zones and was a
constant-volume reheat system equipped with a cool-
ing coil and reheat coils located on each floor. The new
design converted the S-2 constant-volume reheat system
to pressure-dependent VAV and removed the reheat
FIGURE 1 Historical electrical energy consumption.
350
300
250
200
150
100
50
0
Elec
tricit
y Use
in T
hous
ands
(kW
h)
Janu
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mber
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mber
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mber
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ary
2009201120122013
FIGURE 2 Historical natural gas energy consumption.
Natu
ral G
as in
Tho
usan
ds (T
herm
s)
70
60
50
40
30
20
10
0
201120122013
Janu
ary June July
Augu
st
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J U LY 2 0 1 5 a s h r a e . o r g A S H R A E J O U R N A L 2 9
coils on each floor. Two pressure-dependent control
dampers were installed and created a north and south
zone on each floor. S-2 was then replaced with a custom
AHU engineered for the pressure-dependent VAV sys-
tem and equipped with a cooling and heating coil. S-2’s
return/exhaust fan was also retrofitted with a VFD.
AHU S-3 served retail spaces on the first floor and was
a constant-volume reheat system. As S-3 served retail
spaces with dramatically different requirements, it was
not an ideal candidate for VAV and only a few simple
modifications were made. VFDs were installed on the
supply and return/exhaust fans, the outside air damp-
ers were replaced and a new heating coil was added to
facilitate the use of high-efficiency condensing boilers.
Domestic Hot Water SystemThe original building domestic hot water system used
three 85-gallon (322 L) natural gas-fired hot water heat-
ers. These water heaters provided hot water to the toilet
room lavatories and janitor sinks throughout the build-
ing. The domestic water system used a duplex 25 hp (19
kW) pump to pressurize water throughout the building
for a variety of uses. At the time of the energy audit, the
duplex system was operating on one pump with zero
redundancy. Additionally, the functional pump had
recently been submerged underwater when the nearby
river overflowed its banks and flooded the area. Given
these conditions, the continued reliable operation of the
existing pump was questionable. As a result, the existing
pumping system was replaced with a new duplex pump-
ing system equipped with VFDs.
As there are no showers at this building, the domestic
hot water demand is minimal. The centralized domestic
hot water system was replaced in favor of a point-of-use
system taking into account the renovated bathrooms,
which incorporated low-flow fixtures throughout.
LightingThe existing building’s lighting system was equipped
with various fluorescent lighting fixtures throughout the
floors and spaces (mostly T-12). The design team recom-
mended the installation of replacement T-8 fluorescent
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fixtures and new fixtures for previously unoccupied
floors to reduce utility use. In addition to efficient fix-
ture selection, lighting controls were included in any
tenant build-out or completion of unfinished space
including common areas and toilet rooms.
Building AutomationAlong with the implementation of the several energy
conservation and mechanical upgrades described
above, a new BAS was designed and installed. The
existing building automation system (BAS) was an
expandable controls system built on BACnet proto-
col. However, its installation was fairly limited, and
it did not encompass the entire building’s operation.
Further, almost all of the existing damper actuators
and control valves were pneumatic. Although pneu-
matic control can be acceptable, it is hard to maintain
and wastes energy when compared to modern elec-
tronic controls. The new design upgraded the BAS
system to a fully operational direct digital control
(DDC) system with a Web-based graphical front end to
provide increased monitoring capability, remote access
and control. In addition, all pneumatic controls were
replaced in favor of electronic controls. Occupancy
sensors were also installed to control both lighting and
ventilation.
IAQ and NoiseIn addition to energy savings, indoor air quality was
improved by increasing the ventilation effectiveness
provided by the new variable equipment which allows
for improved control on the air delivery side. The
pressure-dependent ventilation systems actively control
proportions of makeup air to maintain the building’s
pressure and decrease infiltration, thereby protect-
ing the building façade and reducing dynamic thermal
conditions. MERV 13 filtration was incorporated into the
chilled beams and new AHUs. Further, the noise level of
the HVAC system was dramatically reduced by a total of
6 dBA.
Phased Construction and ImplementationBecause 29 N. Wacker is a combination of retail and
commercial spaces, the entire mechanical upgrade
project needed to be completed with the building occu-
pied throughout construction. So, it was necessary to
phase the construction and implementation of the new
systems and equipment. Installation of the new chiller
and boiler plant took place during the shoulder months
and improvements to occupied areas took place dur-
ing off and overnight hours to minimize the disruption
to existing tenants. Further, chilled beam units were
initially installed with a pressure reduction device on
the supply duct so they could receive high static pres-
sure from the existing AHU S-1. Once the AHU had been
replaced with the new low static pressure AHU, the
pressure reduction devices were removed for normal
operation.
Cost EffectivenessConversion of the induction air delivery systems from
conventional induction units to active chilled beam
units allowed for reduced retrofit costs. Because the new
system reused the dual temperature piping layout, con-
struction costs associated with new piping were elimi-
nated. Removing the wall-mounted induction units also
allowed the perimeter to be exposed and retrofitted with
insulation for enhanced building thermal resistance at
little first cost.
High-efficiency fixtures and increased lighting control
also reduced associated maintenance costs of replac-
ing bulbs and fixtures. The selection of high-efficiency
condensing boilers with low NOx burners reduced the
amount of harmful emissions ejected to the environment.
Gas and electricity savings are also a result of the upgrade
project, thereby reducing overall carbon emissions.
ResultsThe most dramatic result of this project is reflected in
its energy savings as discussed above and demonstrated
in over $150,000 procured through utility rebates and
incentives as a result of the energy savings demonstrated
by the renovated systems. However, the replacement
of the perimeter floor-mounted induction units with
ceiling-mounted chilled beam units also increased the
usable square footage of the office and dramatically
improved the aesthetics and lowered the sound level in
each office.
By improving comfort, controllability, reduction of
noise and improvements in the overall aesthetics and
space of each office, the leasing activity of the build-
ing was significantly improved as demonstrated by the
increase in occupancy since the implementation of this
project.
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