System Modeling Efficiencies: Energy Saving Investigation Process

What do the icons below mean?

One of the first steps necessary to the proper development a comprehensive energy audit of a system is to perform an extended period computer model to evaluate the source, distribution, and pumping system’s functions and performance. While the modeling can be somewhat complex, system personnel and others can assist with the data gathering and mitigation or repairs necessitated thereby. Modeling—particularly “Extended Period” modeling—is also a dynamic process which needs to be regularly reviewed and “fine-tuned” as needs arise, new data becomes available, and system conditions change. As a part of this evaluation, the following energy demanding scenarios (among others, such as water quality conditions) should be studied. We begin with the “4-Ls,” or the primary efficiency modeling “red-flags”:

Looping

Yellow TriangleBlue IconThe process of unwarranted or repeated boosting of the same water. Ask this question: Could a pump or system of pumps be boosting water, or any portion thereof, in one or more continuous loops? Such loops can be found, among other possibilities, in the following places:

  • Green In the distribution system piping through inter-zonal connections, where a booster station pumps water from a lower zone to a higher zone, and water can be routed back down (around the booster and back to the suction side) through one or more locations or devices, such as:
    • PRV stations, where one or more stations are designed to be normally closed (open only in very high flow or fire flow situations), but failures occur through:
      • Improperly maintained PRVs, failed solenoid controls, or relief valves and related PRV pilot control systems.
      • Leaks in a PRV valve diaphragm or across the valve seat.
      • Leaks in a standby or larger backup fire-flow PRV.
      • Leaks in a by-pass gate or butterfly valve.
    • Leaking through normally closed zone isolation valves. Often these are also accidentally opened when their purpose is not understood. A normally closed valve should be marked as such in a valve box with an inserted pole, 2×4 board, flag, etc.
    • An improperly designed or applied PRV station (due to future distribution modifications), which should be kept closed or could be simply eliminated.
  • Green In pumping stations where failures may occur through:
    • Leaking pump check valves, when one or more pumps are off.
    • Leaking surge anticipator or pressure relief valves, which discharge to the pump suction zone.
    • Leaking pump by-pass PRV or solenoid valve systems used to deliver fire return flows from the higher pressure pumped zone to the pump suction zone.
    • Water cooled chiller or air-handling systems used to cool a pumping plant, where a solenoid or control valve feeding the coils leaks from the higher pumped zone back to the suction side.
  • GreenSource and treatment facilities through:
    • Chemical (i.e., chlorine gas) feed systems or ejection systems, i.e., leaking pump check valves, solenoid valves, etc.
    • Leaks from corroded or damaged source well pump lines or well columns, where the water flows or circulates back into well casing annular space. This can also involve screen and corrosion issues.

Leaping

Yellow TriangleBlue IconThe process of unnecessarily pumping a source, such as a well around (or “leaping” over) a higher PRV separated pressure zone (often through a separate pumping line) to a tank, when the pump would be using significantly less energy by simply pumping the necessary demand pressures (or a portion thereof) directly into the pressure zone in which it is located. The remediation can usually be fully utilized if there are other sources or pumps that can supply the actual higher tank zone. The PRVs are now only used for high flows, emergency backup, or when the well or pumps cannot meet the necessary supply. Leaping can be mitigated by:

  • Well or booster pump stations pumped exclusively into a hosted pressure zone, with flow controlled by zone pressure, i.e., VFDs or multiple pumps.
  • Well or booster pump stations pumped into upper tank zone pipeline only when needed by an automatic diverting valve, but used in lower zone as much as possible.
  • A combination of the first two points above, achieved by adding separate or smaller pumps (or dividing up pumps) to keep the hosted zone in water, with the others used to supply the upper zones.
  • Performance can be monitored by metering the pumps and the inter-zone PRVs.

Losing Head

Yellow TriangleBlue IconThe process of unnecessarily dropping or breaking a usable water supply pressure, which could have been utilized in a local or adjoining zone without the drop. These conditions may be found in the following situations:

  • Breaking a spring HGL pressure pre-maturely or re-pumping a spring unnecessarily.
  • Underutilization of a flowing well, even if it is seasonal in nature.
  • Breaking a high-pressure zone in a pumped system, just to be pumped up again to that zone or another higher pressure zone.
  • Remediation of this problem often involves re-provisioning or installing new pipelines to bring the pumping systems into a more efficient condition.

Loading

Yellow TriangleBlue IconThe processes involved in the efficient timing and efficient capacity loads and control of pumping systems. If done properly significant savings can be realized, but if pump operations are random or uncontrolled or not optimized the costs can be excessive. This problem is remediated as described in other sections of the Handbook but is mentioned here because it is often discovered in the computer modeling processes. It is seen in a pumping and energy model by the following:

  • Well and booster pumps which pump a very high flow of water to a tank or user demand zone for short periods of time, i.e., less than 20 percent of the day.
  • Pumping systems engineered for some distant build-out capacity, but the current operational needs are only a fraction of the limit.
  • Pumping cycles which create an excessive head loss on the system.
  • Pumping systems which do not perform in their most efficient pump curve zones, or have an inadequate or poor suction head.
  • Well drawdowns which have changed significantly since the initial pump
    sizing.
  • Tanks and reservoirs which are sized too small to allow for a custom timed pumping cycle.
  • Pumping systems which model well if run in “off-peak” scenarios, but are not run as such.
  • Pumping systems utilizing an ineffective or efficient electrical rate tariff.
  • Pumping systems which are artificially restricted to control flows, such as valving, etc.
  • Pumps not prioritized and operated by efficiency constraints.
  • Worn or improperly maintained pumps.