Pumps & Systems, October 2008
The Merchandise Mart in Chicago, Ill. is the world's largest commercial building, largest wholesale design center and a premier international business location. Encompassing 4.2 million gross square feet, the Mart spans two city blocks and stands 25 stories high. It welcomes more than three million visitors each year to its retail shops; boutiques; 11 floors of permanent showrooms for gift, residential, casual and contract furnishings; 10 floors of office space; dozens of trade shows and a myriad of special educational, community and consumer events.
When the Merchandise Mart began the task of obtaining LEED-EB certification, it was just the fifth building in Chicago to go "Green." Adhering to standards set forth by the LEED Green Building Rating System, a voluntary, consensus-based national standard for developing high-performance, sustainable buildings, the Merchandise Mart focused on five key areas of green building strategy: sustainable sites, water efficiency, energy efficiency, materials/resources and indoor environmental quality. Such ongoing improvements involved reevaluation of capital programs for replacement of windows, roofs, controls, plumbing fixtures, utility meters and lighting.
To better target energy efficiency, one of the many strategies directed by Merchandise Mart's Vice President of Engineering, Mark J Bettin, P.E., was replacing an outdated domestic water supply system that was a large consumer of energy and an inefficient supplier of water.
The original system consisted of five pumps ranging in size from 40-hp to 75-hp. The pumps ran at a constant speed intended for the highest demands even during low-flow periods such as the middle of the night. The system was designed to deliver over 1,250-gpm, churned at 290-psig. Pressure reducing valves on the discharge of each pump maintained a system pressure at 200-psig. At any flow less than peak flow, the pressure reducing valves would throttle flow and waste energy.
"With recent restroom renovations complete, the water consumption and demand reduced annually by more than 35 percent, resulting in an oversized, inefficient pumping system. It required large amounts of energy to run, and replacing it would help in the buildings' ongoing energy reduction efforts and contribute in maintaining the standards of LEED certification," Bettin said.
According to Merchandise Mart's Plumbing Foreman, John Geiss, prior to the retrofit and during heavy usage, the domestic water system would see momentary swings in the system as much as 40-psi at the top end of the system, resulting in noticeable fluctuations at the fixtures and excessive pipe movement.
During peak flows, which typically occur during a large tradeshow event or the workweek, demand can reach 750-gpm when up to 20,000 people populate the building during major exhibitions. However, during low flows, such as the early morning hours, demand can slow to a few gallons a minute. With such a wide range of flows and demanding show schedule where water consumption constantly changes, the new domestic water system would need to match not only extremely high flow demands, but also the low flow demands using the least amount of energy necessary.
During the bidding process, quality, service and experience were the criteria important to Bettin when choosing the companies to complete the work."We pre-qualified the companies such as engineer KGWW, Metropolitan Industries, Inc., Great Lakes Plumbing and Blaze Electric based on their experience and reputation," he said.
Chicago-based Great Lakes Plumbing was awarded the design/build contract based on the proposal they submitted. Great Lakes' Bob DeGuiseppe, project manager, served as the general plumbing contractor; pump and control system manufacturer Metropolitan Industries, Inc. (Romeoville, Ill.) designed the new system and pressure reducing zone stations; Blaze Electric (Broadview, Ill.) served as the installing electrical contractor and KJWW (Chicago, Ill.) served as engineer during the project.
The New "Green" System
The pump system and pressure reducing zone station design was based on two specific goals: reducing energy costs on day one of start-up and ensuring enough redundancy to prevent any future loss of service due to power or mechanical issues.
Working closely with DeGuiseppe, Metropolitan Chicago Sales Manager Mike Ponx suggested installing a variable-speed system. Since the system can precisely match demand using only the minimal amount of energy necessary, it would reduce energy costs by half.
The system supplied was a variable speed, quadraplex booster system using vertical, multistage pumps, total system rated at 1000-gpm at 200 psi. Since peak flows are 750-gpm, the system will still be able to handle the load without shut down if a single pump fails. To add to the redundancy, two separate power feeds are divided between the system. Feed A runs three pumps and Feed B runs two pumps. If either Feed A or Feed B is lost, the building will still have one electrical feed to supply water to the building without interruption or system shutdown. The electrical control system and plumbing design was also configured to one existing pump to operate as a manual standby pump.