Advocate Illinois Masonic Medical Center (AIMMC) is a 1,143,379-sq-ft hospital with a century-long record of service to Chicago’s north side. The facility is part of the Advocate Health Care network, which includes 13 hospitals and more than three dozen outpatient sites. The network has a strong commitment to environmental responsibility, recognized by the Illinois Sustainable Technology Center’s Governor’s Sustainability Award and by multiple System for Change Awards from Practice Greenhealth. AIMMC was Chicago’s first hospital to earn the EPA’s Energy Star designation in 2008.

Advocate recently targeted AIMMC for a major chiller plant overhaul, with the goals of providing a more reliable cooling system, improving energy efficiency, reducing staff labor related to chiller plant maintenance, and shifting to Montreal Protocol-compliant refrigerants. During planning, water conservation emerged as an additional benefit.

The project replaced the hospital’s three main chillers and associated pumps and cooling towers. A key surgery chiller was also replaced. Budget remained at the end of planning, so Advocate was able to afford three additional new chillers to serve specific procedure areas. The installation significantly improved energy efficiency, provided N+1 redundancy on refrigeration machines, and eliminated ozone-depleting refrigerants for all major chillers.

The $4.2 million AIMMC project involved numerous challenges, both for devising the most appropriate plan and for staging the deliveries and installation. It provides a good snapshot of how health care facilities with aging infrastructure can approach such a major upgrade while leveraging utility incentives to reduce capital expenditures.


Planning and Energy Modeling

Implementation began with Advocate’s management and facilities team, in consultation with MEP engineering firm Grumman/Butkus Associates (G/BA), developing a master plan for AIMMC’s cooling systems. The team created an infrastructure report card to set priorities for replacing major HVAC equipment. Existing equipment was given a rating of A to F, based on its age, expected service life, capacity, redundancy, energy efficiency, refrigerant type, potential code violations, and overall condition.

The report card helped the team determine that the aging main chillers (with capacities of 650, 650, and 800 tons, respectively) were top priorities for replacement. Two of the three had exceeded the ASHRAE 23-year median service life for a centrifugal chiller, and the third unit was fast approaching this threshold. The north surgery chiller (120-ton capacity) had exceeded its expected service life of 20 years and was also identified as a priority replacement project.

To further guide planning, energy modeling was performed, including chiller, pump, and cooling tower energy use based on an 8,760-hour simulation in a spreadsheet.

Thirteen chiller packages were received from manufacturer’s representatives. All included three 700-ton centrifugal chillers, with various combinations of key parameters:


  • Compressor bearing type
  • Quantity of VFD-equipped chillers
  • Condenser water temperature difference (from 9˚F to 15˚F)
  • Factory performance test witnessed by the owner (yes/no)
  • Warranty/maintenance costs

For each of the 13 submitted packages, a “map” of performance was entered to a curve-fit spreadsheet to model the power use of each chiller, based on leaving chilled water temperature, entering condenser water temperature, and part-load capacity. Power consumption during each hour was calculated using the DOE2 chiller equations, based on a modeled facility cooling load determined from chiller logs. G/BA also considered feedback from the AIMMC facilities staff in estimating the cooling load.

Energy and maintenance costs were entered into a life-cycle cost spreadsheet. Advocate eventually selected the chiller package that minimized energy consumption, though the first cost was higher than that of other options.

The final equipment list, including the three procedure-area chillers that were added to the scope when it became clear budget would be available, comprised the following.

  • Main medical center chillers (CH-1, -2, and -3). Three 700-ton magnetic bearing water-cooled centrifugal chillers utilizing R-134a. (NPLV 0.339 kW/ton).
  • Surgery chiller (CH-4) dedicated to surgery AHUs. One 250-ton inverter-driven screw compressor air-cooled chiller utilizing R-134a (EER 9.9, IPLV EER 19.3).
  • Procedure-area chillers (CH-5, -6, and -7). Two 170-ton air-cooled chillers with inverter-driven screw compressors (CH-5 and -6, EER 9.4, IPLV EER 17.3) using R-134a and serving three procedure-area AHUs. One 90-ton air-cooled chiller with a scroll compressor (CH-7, EER 9.7, IPLV EER 15.4) using R-410a and serving the GI Department AHU.

The selected equipment includes premium-efficiency motors for maximum energy savings.

The project proceeded through design, using an equipment pre-purchase arrangement to reduce total costs, shorten the timeline by about 10 weeks, and optimize energy efficiency according to the owner’s prioritization. This required close cooperation between the owner, the engineer, and the general contractor, Power Construction of Schaumburg, IL.


Installation Logistics

The hospital had to remain fully operational throughout installation. Surgery chillers were staged first, allowing this critical load to be served while the main chiller plant was off-line.

The chiller plant is located in the center of a complex that spans an entire city block in a densely populated neighborhood. This made the installation particularly challenging. The general contractor used 3-D modeling for MEP coordination as well as laser mapping of the existing space prior to coordination, helping to facilitate reuse of the main chiller room without an expansion. Use of 3-D modeling included developing the route for equipment through the hospital corridors and into the sub-basement machine room.

Trucks were unable to use the hospital’s main loading dock on Wellington Street due to concerns about interfering with key operations; instead, deliveries had to be made to a less busy zone behind the hospital on Nelson Street. The air-cooled chillers and the cooling towers were crane-lifted to the roof, requiring numerous neighborhood notifications and a system of barricades, traffic control, extra security, and nighttime staging. Ambulance and delivery access to the hospital was preserved at all times.


Multiple Benefits from Innovative Design

The design included many features that led to optimal results. For instance, the cooling system was converted from a primary-secondary arrangement to a variable-primary flow configuration. This reduced the project cost and saved space by eliminating half the existing CHW pumps. In-line pumps were installed since new base-mounted pumps would not fit, and the design intent was to accomplish the project within the room’s existing footprint. The new chillers were larger than those they replaced, so creative configuration of the space was necessary.

The use of three identical chillers, an efficient layout, fresh paint, and new LED lighting resulted in an aesthetically attractive chiller room (Figures 1 and 2). The simplified layout is a significant benefit for the operations staff, compared with the prior configuration. Control upgrades installed with the chillers also allow more efficient use of staff resources, in addition to improving reliability and reducing service tickets.

The project produced a major gain in redundancy. The three main chilled water pumps were installed on a header, allowing any one pump to be out of service at any time. One pump is always available as a standby pump. Condenser water pumps are also on a common header so that any one pump may be out of service. The addition of condenser water pump VFDs minimizes pressure losses related to balancing of the system.

The dedicated, 250-ton air-cooled chiller that serves surgery AHUs is cross-tied to the main chilled water system as a backup. This chiller has multiple compressor circuits, allowing for part-load operation if one compressor is out of service.

Installing air-cooled chillers with capacities of 170 tons (two) and 90 tons to serve other high-load areas of the hospital eliminated any need for the main chiller plant to operate year-round. These chillers also have multiple circuits that allow a level of redundancy that was not available in the existing equipment.

New cooling towers (Figure 3) include VFDs. The full-load design temperature difference was increased from 10°F to 12°F to further reduce flow and pumping energy usage.

Cooling-coil condensate from four AHUs in the fan room next to the cooling towers is used for cooling tower make-up water. These AHUs represent nearly 160,000 cfm, using about 85,000 cfm of outside air. The condensate recovery feature is saving AIMMC about 315,000 gallons of water during the cooling season (based on actual performance data). The condensate is colder than city water make-up and has fewer contaminants, allowing AIMMC to reduce the amount of chemicals needed for water treatment.

Significant environmental benefits were also achieved by eliminating the use of ozone-depleting refrigerants (previously, R-123 for the main chillers and R-22 for the smaller units). In addition, use of magnetic bearing compressors eliminates the need for oil in the refrigerant systems of the three large chillers, reducing time spent for maintenance by the facility operating staff and reducing the need for oil storage or risk of spills and leaks.

Nearly $270,000 was recouped through incentives from the electric utility ComEd, which helped offset the costs of the high-efficiency chillers selected for the project.


Energy Efficiency Verification

G/BA worked with Advocate to verify energy-use reductions. The building permit was applied for in 2011 based on the Illinois Energy Conservation Code, which at that time referred to ASHRAE 90.1-2007. AIMMC installed chillers that exceeded ASHRAE 90.1-2007 requirements by 32% to 46% based on NPLV, as shown in Table 1 (below).

Actual metered data compiled during June and July 2014 showed the total plant (including chillers, pumps, cooling towers) running between 0.400 kW/ton on mild days, and up to 0.670 kW/ton during warmer weather, in line with the design intent (Figure 4). Measured data for 2015 (through mid-September, data not shown) indicates average annual efficiency of 0.48 kW/ton for the whole plant, with a high daily average of just under 0.70 kW/ton when daily average temperatures are in the 80s. As outside air temperatures approach 60°F, the plant has been operating below 0.40 kW/ton.

Figure 5 shows pre- and post-retrofit electricity demand at utility meter #83058020, serving the chiller plant. (The air-cooled chillers are not on this meter.) The chart encompasses 2012 through the billing period ending in July 2014. Winter months with no demand were removed. The figure demonstrates that electricity use has been lower for all weather conditions post-retrofit, except for one outlier.

Energy use is further reduced due to the new, higher-efficiency air cooled machines and primary-only pumping configuration. Figure 6 is a representation of electricity usage per day for the AIMMC campus, showing electricity-use reductions attributable to the retrofit project. A calculation of EUIs appears in Table 2 (below).

Despite these improvements in electricity use, hospital site EUI increased in the 12-month period spanning July 2013 through June 2014. This is due to the “polar vortex” weather pattern that afflicted Chicago in winter 2013-14, which resulted in significantly higher heating degree days during the heating season (44% more than the average for the prior two years).

Figure 7 shows the impact of weather on recent natural gas consumption. Although a boiler burner retrofit, implemented as a separate project, improved the facility’s response to heating degree days by 10%, the net effect of the anomalous polar vortex was an increase in overall site energy use.

Overall, the project resulted in estimated energy savings of over $100,000 per year. Water savings related to the condensate recovery system have been impressive. Just over 950,000 gallons have been saved thus far over the project’s lifetime (three cooling seasons).

The achievement of this effective design was recognized with the ASHRAE Illinois Chapter’s Excellence in Engineering Award and a First Place ASHRAE Region VI Technology Award. ES


Craig and David were leaders in the Advocate Illinois Masonic Medical Center chiller upgrade project, along with G/BA staff members Dennis LeBlanc, P.E. (mechanical engineer), Tim Jendrycki, P.E. (project manager), and other staff, and Advocate’s Darryl Dylla (AIMMC’s HVAC and Power Plant Manager).