HONORABLE MENTION COMMERCIAL BUILDINGS, EXISTING … · 2019-12-31 · previous mechanical systems and the newly commis-sioned, high-efficiency systems shows a clear reduction in

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.


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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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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www.info.hotims.com/54430-6


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

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ands

(kW

h)

Janu

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2009201120122013

FIGURE 2 Historical natural gas energy consumption.

Natu

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as in

Tho

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ds (T

herm

s)

70

60

50

40

30

20

10

0

201120122013

Janu

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March

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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



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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