Pumps & Systems, March 2008
Outdated water systems are pumping beyond their original specifications, resulting in inefficient operation, higher maintenance and operation costs and the potential for a system shutdown. This article takes a look at updating the controls and pumps for a water system.
Many domestic water supply systems in Chicago's luxury condominiums are as old as the buildings themselves. Most of these systems were state-of-the-art during their installations decades ago, but the buildings have evolved as water demands increase due to luxury bathrooms, personal laundry facilities, dishwashers and in-house businesses. Unfortunately, these outdated systems are pumping beyond their original specifications, which results in inefficient operation, higher maintenance and operating costs and the potential for a system shutdown.
When the original domestic water supply system in Chicago's Harbor Point Condominiums began to show its age, the Condominium Association had to decide whether to refurbish the original system or replace the entire system with up-to-date technology.
Built in 1972, the upscale residential/commercial Harbor Point Condominiums offers views of both Grant and Millennium Parks and sits on Monroe Harbor, known for its beautiful yachts and sailboats. Residents of the 742 units have access to various amenities and the 22 commercial businesses located in-house.
Older System Versus New System
The original domestic water supply system was a triplex constant speed system in need of replacement. It operated constantly 24 hours a day, seven days a week, even during low flows. Individual pressure regulating valves on the discharge pipe of each pump controlled pressure output from the pumps-a common design during the period of time in which the facility was constructed.
An inherent flaw in this design stems from the operation of the pumps during the evening and other low-flow periods. During these periods, the pumps operate at full-speed with relatively no flow, causing pressures within the pumps to climb to their peak.
Of the three pumps, one pump would always run, one pump sat deadlined and the third pump (the largest) would run infrequently, causing surges in the water main and bursts of water through the residential showerheads. After further investigation, I determined that the pumps needed replacement and could not be refurbished.
Before the Condominium Association would grant McGuire Engineers approval for the new installation, they wanted to examine prices and options of a new domestic water system. In order to complete this request, I provided a new calculation of the entire building's water demand. Since 1972, the building's water demand grew dramatically due to luxury bathrooms, dishwashers and personal laundry facilities that were added in each unit over the years. The recalculation was critical in determining the exact pumping solution needed while staying accurate on price.
After the completion of the calculations, the Condominium Association learned they had two options: a variable speed triplex system or a variable speed quadraplex system. After contemplating the pros and cons of both systems, I recommended a quadraplex pumping system because of the longer life expectancy of the system from four pumps versus three, and the fourth pump would serve as standby in case of emergency.
Just as the Condominium Association was poised to give the approval, the one constant-running pump on the original pump system failed, forcing the largest and last remaining operational pump of the original three to run constantly. The amount of wasted water and energy generated by the huge pump was significant.
Metropolitan Industries, Inc. (Romeoville, IL) was chosen to design and build a quadraplex variable speed pump and control system. They recommended replacing the outdated design of the original pumps with their System 2100 submersible-turbine pumps and energy-saving variable speed controls. A typical system-which I have used in many downtown Chicago projects including the American Dental Association Building, John Hancock Building, Inland Steel Building and the world-renowned Field Museum-utilizes horizontally or vertically mounted submersible-turbine pumps. A submersible pump is unique because both the pump and motor are submerged in water, which promotes self-cooling and lubrication and reduces noise considerably. For this project, Metropolitan installed the pumps vertically, allowing placement of multiple pumps side-by-side, saving critical space.
"Submersible turbine pumps are able to provide high pressure water with minimal noise. The motors and pumps are sound-insulated by the water," said Metropolitan Chief Mechanical Engineer Paul Larson.
Great Lakes Plumbing of Chicago was chosen to perform the installation. According to Great Lakes Plumbing Project Manager Bobby DeGuiseppe, there would not be an interruption to water service during installation and start-up of the new pump and control system. "The key here was a smooth transition from the old system to the new system," DeGuiseppe said.
DeGuiseppe's plan called for installation to take place in the middle of the night when water demand would be at its lowest. Of the three original pumps, the two non-operational pumps were pulled and the larger pump remained to continue water service while installation of the four new pumps occurred. After only a couple of hours, installation of both the new pumps and variable speed control panel was complete. Start-up of the new system went according to specifications and what was left of the original system was quickly eliminated.
Harbor Point Condominium's new domestic water system pumps 725-gpm at 292-psi. The control technology included a programmable logic controller, operator interface panel and variable frequency motor drives for all the new pumps. This method of operation allows for greater hydraulic control of the flow and pressure by allowing the chief building engineer to configure the system's operation and set-points when required.
The Condominium Association's decision to choose a variable speed control versus a constant speed panel provides greater electrical efficiency and reduces maintenance costs of the pump components. The system will pay for itself in a few years due to the electrical efficiency and energy and water savings of variable speed control systems.