First published in the December 2019 issue of Energy Matters
Unnecessarily running your domestic water booster pumps can waste energy, water, and money. Many apartment buildings have oversized pumps to provide constant pressure during peak periods. However, oversized pumps tend to cycle on and off more frequently in order to maintain required pressure, and this frequent cycling can wear the equipment and use more electricity than other pump configurations. Alternatives such as pumps with variable frequency drives (VFDs) or a series of smaller contact speed pumps can help you reduce your electricity and water use and reduce wear and tear.
Domestic water booster pumps are typically installed in mid- or high-rise apartment buildings to supplement municipal water pressure and ensure constant, adequate pressure right up to the top floor. These pumps are often oversized to support periods of peak demand, such as in the morning when most tenants are starting their day. Since they achieve the set point pressure faster due to their larger size, these pumps will surge on and off more frequently. During low use periods, pressure must still stay constant for toilets and taps to operate properly, and the oversized pumps will run at a minimum constant pressure that is not very efficient compared to more appropriately sized systems or systems with VFDs.
How to Spot an Oversized Pump
In many cases, an oversized pump system will provide more pressure than needed. In certain buildings, particularly mid-rises, a water booster pump may not be required at all, a situation that can be determined by consulting an engineer. The building operator often discovers this accidentally when they have to shut the pump down for other purposes yet the water pressure remains adequate at the top floor.
It is common to see water pressure that exceeds 100 psi on the top floor of apartment buildings with oversized pumps when the pumps are on. This pressure is far above the normal range of 50 to 70 psi and is a good indicator that the pump is too big.
How to Achieve Pump Savings
To optimize the domestic water booster pump system in your buildings, you can:
- Add variable frequency drives (VFDs) on pump motors to enable the booster pump to operate at lower volumes in response to water demand, while maintaining the correct range of pressure. The best candidates for VFDs are pumps that are designed for peak loads but that normally run at much lower volumes.
- Use a series of smaller constant speed pumps that are sized and sequenced to provide pressure appropriate to the load. One pump can provide for the base load and then a series of pumps can turn on as demand increases in the building. The pump providing the base load will operate close capacity, where it is using electricity most efficiently.
Installing pumps with VFDs or smaller constant speed pumps in series can provide energy and water savings and reduce wear and tear on pipes. Additionally, electricity utilities may provide incentives to add VFDs to pumps that can cut your payback time.
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