The building is divided into four zones to stabilize pressure. At each zone, pressure reducing valves were downsized to maintain each of the zone's pressure requirements and the four bladder tanks were installed on the 6-in cold water express risers to sustain pressure when the system shuts off during low flow periods.
Using bladder tanks at the top of the express riser, pressure is stored so the system can shut off during low flow periods. As flow is consumed, the pump system will activate and supply water to the building at the desired pressure. Once the demand for water is reduced to a low flow period, the system will shut off once again. Significant energy savings are realized during low flow periods when using variable speed drives and bladder tanks in combination.
During installation of the pumps and controls, interruption of service did not occur to the building. "Since the existing booster system had two independent electrical feeds and the building could not be without water at any time, the electrical controls were built into two sections, which would be mated together during the second phase, DeGuiseppe said. DeGuiseppe spilt the new control panel into two sections. Blaze Electric installed the main control section first after disconnecting the first electrical feed, then installed the first two of four pumps using the new controls. Once the first two new pumps were online, Blaze Electric removed the old panel and installed the second half of the new control panel, which was designed to mate up to the first section. After that, the remaining two pumps were installed.
To commission the system and measure the savings, meters were installed to measure flow and energy consumption. Results appeared quickly with the installation of the first two pumps. Energy reductions in the first week were 34 percent. With completion of all the pumps, the bladder tanks came on-line, and the system was set for commissioning. Utilizing a system bypass and real-time flowmeter, various loads were created to allow for fine tuning of the drives and staging of pumps. With the removal of the top zone PRV, the system pressure was successfully lowered from 200-psi to 185-psi. Taking advantage of the bladder tanks, the nighttime mode was enabled, resulting in the cycling of pumps. Weekly evaluation has shown a reduction in energy by up to 50 percent with an anticipated annual energy reduction of over 125,000-kWh.
Within a decade, the system will pay for itself entirely on energy savings. The expected life of this system is more than 25 to 30 years, so eventually the system will not only pay the end user for the cost of the system but it will also pay the costs to replace itself in its lifetime.
According to Geiss, the completion of the retrofit work improved the overall performance of the system by lowering working pressure and reducing fluctuations throughout the system.
"For the first time we have experienced the most even flow and the best overall PSI performance at the top of the 10th, 18th and 25th floor zones," he said.
Reducing the size of the valves in the respective zones has tightened up the flow in conjunction with the smooth operation of the variable speed booster system and bladder tanks that feed and assist the entire system.
"Overall. . . all parties involved came through with the promise and commitment to a 2- to 4-psi swing, and an energy savings that will match the Merchandise Mart's committed effort to LEED providing for a greener tomorrow," said Geiss.