Reducing pumping costs

Michael Tobias, PE, LEED AP, CEM.
Michael Tobias, PE, LEED AP, CEM.

Reducing pumping costs in buildings with water conservation - Michael Tobias, PE, LEED AP, CEM. 

Water conservation measures offer three main types of savings for building owners. Consuming less water not only reduces the corresponding utility bill, but also the operating cost of water heaters and pumping systems. For this reason, water conservation can be considered an energy efficiency measure. In many cases, excessive water consumption can be attributed to old and leaky plumbing fixtures. For example, old toilets can consume four times more water per flush, compared with newer units - the federal baseline is 1.6 gpf, and an old toilet can use over 6 gpf.

Upgrading plumbing fixtures to reduce water consumption As a water conservation strategy, the US Environmental Protection Agency has created the WaterSense labeling program for plumbing fixtures. When a product has the label, it guarantees savings of 20% or more with respect to the federal baseline. So far, the WaterSense program covers eight categories of plumbing products, and several other categories are being reviewed for addition to the program. As of March 2019, the label applies for the following products: * Residential toilets * Showerheads * Bathroom faucets * Commercial toilets * Urinals * Pre-rinse spray valves * Irrigation controllers * Spray sprinkler bodies

When a building is upgraded with labeled plumbing fixtures, a significant reduction of pumping and heating costs is possible. An advantage of the WaterSense label is independence from specific manufacturers, since only a third-party laboratory can test and certify products according to US EPA requirements.

Once the water consumption of a building has been optimized, the pumping system itself can be upgraded with energy efficiency measures. High-efficiency motors and speed controls are often recommended by energy consultants to reduce pumping costs.

Improving pump performance with high-efficiency motors Once the workload on a pumping system has been reduced with water conservation, further savings are possible with energy efficiency measures. The operating cost of a pump can be minimized if it uses a high-efficiency motor with a speed control system. The highest motor efficiency rating in North America is NEMA Premium, while the IE4 Super Premium Efficiency rating applies for products manufactured under international standards. Due to the extended operating schedule of many pumping systems, even a minor efficiency gain can yield significant savings in the long run. To maximize the performance and service life of a pump motor, the impeller and shaft must be properly balanced and aligned. An adequate voltage supply is also very important: the efficiency and service life of a motor are negatively affected by undervoltage and phase unbalance.

How speed control improves pump efficiency Pumping systems operate at full output when water demand reaches it peak, but they are only partially loaded at other times of the day. While the flow from a pump can be controlled with a valve, doing so wastes energy:

* A control valve at the pump outlet reduces flow by restriction, causing a pressure drop. However, the hydraulic losses at the valve represent wasted pumping power, and the cumulative cost can be significant if the pump operates at part load frequently.

* An alternative control method is using a recirculation valve, which redirects the extra flow back to the pump intake. This control method tends to waste even more energy than a control valve at the pump outlet, while requiring extra piping. Adjusting the speed of a pump is a much more efficient way to control water flow, since there are no control valves causing hydraulic losses. A variable frequency drive (VFD) can reduce the speed of the pump motor until the flow provided matches demand. The potential savings with VFDs are increased when a pumping system is subject to a variable workload, which is precisely the case of plumbing installations. The applications of pump control with VFDs extend beyond potable water systems; significant savings are also possible by controlling the pumps of hydronic HVAC installations. When the building is not at full occupancy, and heating and cooling systems operate at reduced output, the pumps that provide chilled and hot water to fan coils can also be ramped down.

Michael Tobias, PE, LEED AP, CEM. 

Michael Tobias is the founder and principal of New York Engineers, an Inc 5000 Fastest Growing Company in America. He leads a team of 30+ mechanical, electrical, plumbing, and fire protection engineers from the company headquarters in New York City; and has led over 1,000 projects in New York, New Jersey, Pennsylvania, Connecticut, Florida, Maryland and California, as well as Singapore and Malaysia.