Chicago’s Chase Tower celebrated its 40th birthday by realizing substantial efficiency gains (and utility savings) after a five-year, four-phase mechanical systems upgrade. Ductwork, VFDs, and chilled water upgrades all have the 60-story space feeling young on the inside.
Chicago’s Chase Tower was middle-aged and out of breath. Built in 1969, the 2.4 million-sq-ft., 60-story skyscraper was slowing down thanks to an inefficient mechanical infrastructure and soaring energy prices. An overhaul of the building’s mechanical systems was inevitable.
“It was actually a job of necessity from an operations perspective,” said Ken Bartman, Midwest asset manager and general manager of Chase Tower. “The building had obsolete systems; we were 40 years behind the technology. The utility bills were very high. Based on the new [mechanical systems] technology, we thought we’d be able to cut our utility bills in half.”
And they did. In 2004, Chase Tower Chicago began upgrading its mechanical infrastructure to include new fans, VFDs, cooling coils and dampers, pressure-independent control valves, rebuilt chillers, and more. Currently in its fourth and final phase, the project has already realized a 50% operational energy savings, earning it third place winner in ASHRAE’s Region VI 2009 Commercial Buildings-Existing Category. According to Bartman, electrical usage prior to 2004 measured anywhere between 15 and 24 MW, while today’s figures vary between 9 and 15 MW.
With 100% occupancy (JP Morgan Chase fills two-thirds of the building, while the other third is made up of high-profile, third-party tenants), keeping the building operational during construction was essential. Working nights and weekends in 2004, the team renovated the systems serving floors five through 22 which included the bank’s offices, followed by floors 25 through 57 in 2006. Currently, the team is concentrating on the fans serving the building’s basement area, where curbside restaurants and additional Chase offices are located.
The Fan SystemA total of 51 fan systems provide air conditioning and ventilation to the building. Most of these systems use two centrifugal supply fans and one vaneaxial return fan. Each floor is served by six fan systems: two for the south perimeter, two for the interior, and two for the north perimeter. Originally, they were dual-duct constant volume systems with constant volume mixing boxes, but they were renovated to variable volume cooling-only systems, using series flow fan power boxes.
The installation of VFDs for these fans brought home the lion’s share of operational savings for the renovation. Installed in new motor control centers, VFDs control fan speed based on cooling demand only, varying the amount of air as needed to maintain static pressure in the supply ducts. As air quantities are reduced, the savings in fan horsepower can be significant. For example, a fan operating at half speed uses only 1/8 of the horsepower. Additionally, for many operating hours at Chase Tower, the dual supply fan systems are able to operate in single fan mode, furthering the savings.
Comparing heating and cooling measurements before and after the infrastructure upgrade reveals a reduction of as much as 17,346,825 kWh annually. Based on the 2008 building electrical rate, Chase Towers’ cost savings for the same year was $1,602,847 (Table 1).
“By and large, the fans provided the biggest return on investment because they run all the time,” said Bartman.
Expanding the Duct WorkChase Tower was originally designed with high-static pressure fans and small ductwork which requires more horsepower and therefore more electrical usage to move air. Additionally, the original spray-on fireproofing under the decking on each floor contained asbestos. As office leases expired and the floors changed tenants, the ductwork was removed and the asbestos fireproofing abated. The original high-pressure hot and cold supply and return ducts were replaced with new medium-pressure supply ducts as well as a plenum return ceiling.
However, these updates also created a static pressure challenge for designers. The new fan power boxes require less than 0.1 in. of static pressure at the terminal unit inlet, while the mixing boxes require 1.5 in. of static pressure or more at the inlet. Each fan system serves a number of floors, and therefore during the renovation process, each fan system was potentially serving floors with both static pressure requirements.
The ultimate solution was to minimize the static pressure behind the new fan power boxes by employing motorized control dampers in the medium pressure ducts at the riser on the fan power box floors. These dampers are controlled by static pressure sensors located in the medium pressure ductwork on the floor. This required that each floor’s terminal units served by each fan system be converted from mixing to fan power simultaneously. Until all of the floors served by a fan system were converted, static pressure had to be set high enough to meet the requirements of the mixing boxes.
The Chilled Water SystemTwo of the four chillers that serve Chase Tower were renovated; the constant volume chilled water system was converted to a variable volume system, while new cooling coils were installed in each of the AHUs with new pressure-independent control valves. The chiller renovation included replacing the chiller compressor and motor as well as the installation of high-efficiency tubes to increase the chiller efficiency.
Additional electrical savings were realized by installing VFDs on the chilled water pumps and operating them off of chilled water demand. Cooling coil cleanliness was enhanced and mold growth reduced by installing UV lights downstream of the new cooling coils.
The BASIn order to monitor and control the upgraded mechanical system most effectively, the building control system was improved as well. A building infrastructure riser was installed to provide a high-speed pathway for control system communication throughout the building, while the BAS was upgraded to the latest version available. New DDC systems replaced 40-year-old pneumatic control systems on the fan systems, and the new fan power terminal units were installed along with DDC controls. All of these enhancements provided the building operations staff with the ability to closely monitor the building’s operations and potentially reduce energy consumption even further.
As Chase Tower looks to its next four decades with newly upgraded mechanical systems, maintenance, and systems optimization will prove central to realizing continued efficiency gains.
“We’re achieving what we intended to do, even with the obvious physical constraints of a 40-year-old building,” said Bartman. “We’ll continue to ring out the utilities as best we can, but I’m happy with what we’ve been able to achieve.” ES
Sidebar: Operational Efficiencies and TrainingWhile overhauling the mechanical systems was central to the annual energy savings achieved at Chase Tower in Chicago, optimizing operations continues to play a significant role in the process as well.
“It’s one thing to install the new technology, but the second part of the equation is to make it work,” said Ken Bartman, Midwest asset manager and general manager of Chase Tower. “You can have the systems in place, but if you’re not utilizing the controls to make them work, then you’re throwing money out the window.”
Meeting on a frequent basis, the building’s operations staff works to fine-tune a variety of procedures, including startup and shutdown times, fan loop controls, air handler efficiencies, and tying the BAS to new VFD technology to reduce as much utility expense as possible.
Additionally, the Chase Towers engineering staff is now required to participate in an educational program, featuring both controls and equipment manufacturer instructional sessions. With the ability to control the building’s BAS wirelessly, Bartman knows training is the key to achieving operational success.
“We’ve set aside money to send key people to training classes so they become masters at these operations,” said Bartman. “When something doesn’t make sense to them, they’ll know how to determine where the problem may be. This is going to be an ongoing process over the next few years. Currently, we’re about 40% there from a training perspective.”