As part of a project at Town Hall to replace our chillers, which provide water for our central air conditioning plant, the Facilities Maintenance Department (FMD) changed the two pumps that circulate hot and chilled water (depending on the season), throughout the building. These pumps are set up to take turns, but one of them will be running at any given time to circulate water for either heating or cooling.
The older, conventional pumps that we replaced ran at only one speed. The first graph shows that the amperage draw, which is a measurement of the amount of energy required to run the pump, was approximately 10 amps per phase.
Replacing the Pump
We replaced these two pumps with variable speed pumps controlled by a built-in microprocessor, that also have other features such as differential pressure sensors and “soft start” capability. The variable speed function and differential pressure sensors allow the pumps to optimize pressure and to run at a lower speeds to respond to the building needs as thermostats send signals to close valves when room temperatures meet their set points.
The “soft start” feature of these pumps allows the pumps to ramp up slowly to operating speed rather than requiring a big surge of electrical power to initiate operation.
The second graph shows that we are using significantly less energy, approximately an average of 4.5 amps per phase, to operate the new Grundfoss variable speed drive pumps.
Measurement of the Draw
It should be understood that the measurement of the amp draw cited above is the actual amp draw of one phase only, on a three phase motor. So the actual energy use reduction (savings) is three times greater: conventional pump amp draw is 3 X 10 (30 amps +/-), while the Grunfoss variable speed drive pump amp draw is 3 X 4.5 (13.5 amps +/-). This significant electrical savings doesn’t even factor in the benefit of a soft start on the life of the equipment.
The FMD will continue to keep you posted on our sustainability efforts and goal of reducing energy across all 20 buildings.