Figure 1. This chart compares the original central plant to the new central plant, as well as projected savings per year.
The Field Museum is one of the jewels in Chicago's crown - a definite must-see for anyone visiting the Windy City. With its vast collection of cultural objects and biological specimens, not to mention Sue, the world's largest, most complete, and best preserved Tyrannosaurus rex ever found, there are enough exhibits in its 1 million sq ft of space to keep everyone busy.

A recent $23 million central plant renovation has been keeping museum personnel busy as well. The museum was constructed in the 1920s and still had its original high-pressure steam boilers in place. These boilers, along with the chillers that were installed in the early 1970s, were becoming more inefficient with every passing year. Not to mention that the reliability of the plant was becoming a bigger issue.

In September 2001, construction began to enlarge the existing central plant, followed by a total replacement of the major heating and cooling systems at the museum. In addition to the new boilers and chillers, a thermal ice storage system was installed to reduce the cost of electric consumption. The major work on the central plant was completed in late 2003.

Figure 2. This diagram of the new central plant sub-basement shows the layout of the new chillers, boilers, and storage tanks.

Structural Challenges

The renovation of the central plant was undertaken under the leadership of Jim Croft, vice president of finance and administration at the museum. Croft oversees the department of Facility Planning and Operations (FP&O) responsible for the maintenance and upkeep of the building and the management of its equipment.

Croft and FP&O had been struggling for years with the shortcomings of a plant that had reached old age. O&M of the plant had become more and more expensive and impractical. Indeed, the plant was so old that needed parts had to often be hand fabricated.

The success of the renovation was the result of a close collaboration between Croft and Frantz Cartright, president of CATH Associates, an Evanston, IL project management firm. Design consultants were subsequently selected. The architect, Urban Resource, Inc., the structural engineer Tylk Gustafson Reckers Wilson Andrews, LLC, the MEP engineer, McGuire Engineers, and other consultants put their heads together to undertake the challenging design task.

When the decision was first made to upgrade the central plant, Cartright, who is also director of FP&O at the Field Museum, said they thought about just replacing the chillers and boilers.

"After making many analyses, we discovered that would not have been possible, because there was not enough room for more equipment or bigger equipment. It became very obvious that we had to expand the footprint for the central plant. The old central plant was approximately 11,000 to 12,000 sq ft, and the new central plant is 30,000 sq ft," said Cartright.

The central plant is located below the southwest terrace and west parking lot, directly adjacent to the building's footprint. This means that the only way to make it bigger was to dig out more space. Enlarging the central plant took place in conjunction with the construction of the new Collections Resource Center (CRC), a 182,000-sq-ft space, which is presently being built below grade. The CRC will provide active storage space for many of the anthropology, zoology, and geology collections of the museum.

Anyone who has been to the museum knows that it is only a stone's throw away from Lake Michigan. Digging the hole took on special importance, because water needed to be kept out. This presented particular challenges for the excavation and construction of the reinforced concrete structure. Part of the central plant sits on a mat foundation and part sits on approximately 230 H-piles. The retention system used was the conventional sheet piling and lagging method.

The general contractor, a Walsh-Riteway joint venture, was able to keep the lowest level of the plant a little bit higher than the lake level and as a result, they were able to minimize the water concerns. Cost savings were realized with an efficient foundation system, and the general contractor proved to be instrumental in making possible some major cost savings, noted Cartright.

Figure 3. Forty-eight tanks store ice, which is made at night when energy is less expensive. The system's configuration provides the option of expanding tank capacity by another 25%, should the museum's needs grow in the future.

Boilers Go From High to Low

The original boiler plant consisted of three large high-pressure steam boilers that were designed for 125-lb steam. They were originally coal-fired and had been converted to gas firing at a later date. They were replaced by three new 400-hp low-pressure, natural gas-fired steam boilers from Superior. These boilers provide the building's hot water, as well as steam for space heating and humidification.

"In order to get the right moisture in the building, we have a reverse osmosis unit associated with the boilers, so we can treat the water before we feed it into the boiler. The result is that the boilers will last longer, and also that the steam we are using is clean steam with no chemical residuals in it," said Cartright.

When McGuire Engineers were first brought into the museum back in 1995, they originally wanted to get rid of the steam boilers altogether and replace them with hot water, which offers an easier, finer method of control.

"But as we got more and more familiar with the system, we found there were hundreds and hundreds of pieces, parts, and elements out within the building that were fed by steam. You can't shut down the building, get rid of the steam, and put in hot water. We reluctantly said, ‘Okay, steam needs to be what we utilize, because we have to keep the museum running,'" said Anthony McGuire, president of McGuire Engineers.

McGuire was happy about being able to move the museum from high-pressure boilers to low-pressure boilers. Having low-pressure boilers meant that it would no longer be necessary to have a licensed high-pressure boiler operator on duty 24 hours a day, 7 days a week. "That was a huge cost savings," noted McGuire.

Figure 4. The centrifugal electric chillers have a capacity of 750 tons each. The equipment has a chilled water volume of 1,300 gpm, entering at 55°F and exiting at 40°.

New Chillers

The chillers had to be replaced for a variety of reasons. First, they contained R-12, which the museum wanted to phase out. Second, they were old and inefficient. Third, the museum did not have the capability for 365-day cooling. And fourth, the chillers did not have the capacity to serve all the needs of the museum, as well as the new spaces being constructed or planned.

Because of this lack of capacity in the central chiller plant, many peripheral systems had been installed in the museum over the years. These included two remote 250-ton chillers, as well as numerous DX systems that were placed throughout the museum. The goal of the new chiller plant is to gradually incorporate these other systems. Cartright estimated that it will take another four years or so before these other systems will be removed.

"It's really a matter of financing," said Cartright. "The building has many needs, times are kind of tight these days, and there are competing demands for funds, such as new programs, new research projects, new exhibits, and new facilities, not to mention the ongoing maintenance of the building. So the museum's administration makes decisions on how fast to go and where to allocate the funds to get those things done."

Two new Trane centrifugal chillers were installed in the central plant. They both use R-123 and are rated at a nominal 750 tons each, which should help with the extra capacity needed. The new system utilizes a glycol mixture, rather than chilled water, and a two-pipe cooling system, so that mechanical cooling can be provided anywhere in the building at any time.

This is a huge benefit to the museum, because there are often warm winter days in Chicago. Previously, the museum had a two-pipe system: supply and return. In the winter, the pipes carried hot water and in the summer they carried chilled water. The problem with this type of system is that it does not allow for cooling in the winter.

"There were periods of time when everybody was uncomfortable," said Cartright. "What we've done is split the systems and now we have a two-pipe cooling system and a two-pipe heating system. Literally speaking, we are able to cool some areas of the building while we're heating other areas of the building. That's a phenomenal feature, because we're talking about a building that has about eight different requirements for climate control."

The distribution systems for both the boilers and chillers are gradually being updated as well. As McGuire noted, "Being a museum with exhibits and collections, we cannot readily go in and tear things up all over the place, so we have a distribution plan where we're upgrading pipe sizes around the facility as we're able to work in certain areas. That's an ongoing project."

The big worry about the original steam and condensate distribution piping is that it is now over 80 years old. There aren't any problems with significant leaks yet, but there is concern that the piping is at the end of its anticipated life expectancy.

The chilled water piping, which is only in the 30-yr range, is in pretty good shape, said McGuire, which is why in many areas it has been possible to keep the existing piping. Because larger capacities are being pumped through the piping, larger pipes are needed.

"In some of these cases, instead of just replacing the existing pipes, we're putting in parallel lines. For example, rather than replace a 12-in. line with a 16-in. line, we might be taking a 12-in. line and running a 10-in. line adjacent to it. That way we get the same capacity and it costs us less. The life of the existing 12-in. line should be good for another 50 years or so," said McGuire.

Figure 5. The new low-pressure steam boilers convert water to low-pressure steam, used for heating and humidification of the museum.

Thermal Storage Saves Energy

The thermal ice storage system, which includes two Trane 700-ton centrifugal ice-making chillers that have 1,250 tons in water chilling capacity, is a rather exciting new component to the central plant. The system uses 200,000 gallons of water, making ice at night when the cost of power is the lowest. The ice is stored in 48 tanks, then, during the day the ice is melted to generate chilled water, which is fed to the AHUs distributed throughout the building.

Choosing a system was a time-intensive endeavor. "We were confronted with about eight or ten different manufacturers of ice storage systems. And each one of them varied in the way the equipment worked. Their parameters for ice storage were all very different. Each one of them had their advantages and disadvantages, and each one of them presented challenges," noted Cartright.

The original design concept called for using an old underground coal bunker to house an ice slurry system. Then it was decided the bunker wasn't big enough, so the ice-making FAFCO system was used. The storage tanks have a capacity equivalent to 20,000 ton-hours of cooling. "We have an ability to add another 25% in tank capacity in the future should we desire," said McGuire.

System simplicity was another reason for the selection. "The museum is in the business of creating exhibits for educational purposes for the public, and it's a research institution for science. The museum is not an institution for creating central plants. I wanted a plant that would last a very long time, just like the old one, that probably will outlast all the technology and all the companies. I selected FAFCO for that reason," noted Cartright.

Other reasons why Cartright liked FAFCO were that it's easy to repair, and it fit just perfectly with the below-grade central plant. "Everything was right about this system: The temperature transfer to the walls, the thickness of the tubes, the length of the tubes, the velocity of the cooling fluid in there, absence of corrosion, simplicity of the piping and valving, and all that kind of thing," added Cartright.

Other Systems

As part of the expansion/renovation, the central plant received a new BAS from Automated Logic. The museum still uses an older BAS from another manufacturer, but McGuire noted that as of 1998, they've been making a concerted effort to change the museum over to the BACnet protocol.

"We have been incorporating BACnet into all the controls that we had put in. We still have the old BAS connected to things out in the museum, so right now we're running both systems and integrating the new with the old. It just wasn't possible to take the old system out and put a brand new one in. We still have lots of pneumatics all over the museum," said McGuire.

Automated Logic is one of three manufacturers that has installed BACnet systems within the museum. According to McGuire, there have been no big interoperability issues. "Everything has been integrating very well. I think that's because we haven't selected the systems based on price. Instead, we select the controls based on the service offered by the local representatives."

The new BAS will have its work cut out for it, because many areas of the museum require tight control of temperature and humidity. As Cartright noted, "In areas like the rare book room or where there are anthropological artifacts, we can't allow the humidity to go up, and the temperature needs to be exact. We also have special exhibit areas that house traveling exhibits. These exhibits often require the museum, by contract, to maintain precise temperature and humidity control in these areas."

The museum has also upgraded its electrical and water lines. On the electrical service side, the museum started experiencing power outages, due to the local utility's failing equipment. That became a huge problem for scientists in the museum, as some of them are working on tissue samples that need to be maintained at extremely low temperatures. Fortunately, no one lost any experiments due to power outages, but it did alarm museum personnel.

The original service consisted of one main coming from one substation, and that was changed so that the museum now obtains power from two mains coming from two different substations. In addition, transfer switches were installed on both the primary and secondary sides of the power system.

"On the primary, this will ensure that if one substation goes down, we will automatically switch to the other," said Cartright. "On the secondary side, if one transformer goes down, we will immediately switch to another transformer. That gives the museum the redundancy needed to provide continuous power to the building."

On the water service side, the museum originally had one 8-in. line coming into the building, which was no longer sufficient for two reasons. First, the size of the museum had increased and so had its water demands. Second, the museum is in the process of installing sprinkler systems in 100% of the building. Two new larger lines now meet the higher demands of the museum.

The existing fire pump was also not deemed large enough, so it was necessary to install a bigger one. In addition to the new electric fire pump, a second equal-sized diesel-powered fire pump was installed as a backup.

Even though it's been a lot of hard work, both McGuire and Cartright are very pleased with the final results. As Cartright noted, "I feel this is one plant that is going to deliver exactly what it was supposed to deliver." ES

‘Soft Management' Techniques Used One of the reasons why Frantz Cartright believes the new central plant project at the Field Museum was so successful is the fact that he used "soft management" techniques to run the project. What he means by that is he did not set up rigid parameters under which the consultants had to operate: Consultants were allowed to change their designs along the way.

"In construction, things have a way of not hitting target. The initial soft management resulted in efficient management of the design and construction and is probably the most economical way one could proceed without having cost overruns at the end or things that don't work. Many projects that are locked into the rigid design, bid, and construction sequence end up way over budget because the requirements change as you go," said Cartright.

He adds that consultants often struggle to make sure they keep the budget tight in order to deliver the design within the budget that is assigned to him. "By giving people some liberties, some flexibility, and some initiative, I think all the consultants were able to be very very innovative," said Cartright.

The end result is better systems, more innovative designs, and a project that came in right on budget.