PUMP EFFICIENCY vs PUMPING EFFICIENTLY Victor Elefante, VICTOR ELEFANTE TECHNICAL SERVICES, INC. After ten years serving municipal and commercial water supply idustries,here on Long Island, conducting tests of both new and old pumping equipment, our experience is that while many are operating at or near their best efficiency point, most are not putting water into the system as efficiently as they should. Whether or not pumps operate efficiently can be effected significantly and for many reasons a pump can be operating at its Best Efficiency Point and yet may be consuming more energy than necessary (not Pumping Efficiently). This can be the result of various factors; but most often, especially in new installations, it is due to Total Dynamic Head being too high and so pump has to be throttled to maintain Design Capacity. Very often when a well pump has been replaced; it was not discovered, until after, that well condition had deteriorated requiring flow to be restricted. Increased draw down or lower static water level may necessitate restricting flow from pump, in order to maintain safe pumping levels. Other times, System Requirements have changed, because Distribution piping has been improved, by adding mains or increasing diameter, reducing friction losses. Since original pump design pressure was higher than is now required, yield will be increased, unless changes in operation are implemented or modifications made. In some situations Flow must be regulated to meet varying system conditions, such as when a Well Pump is putting water into a treatment system and a booster pump is required to meet distribution system changing conditions and still maintain a specific clear well level. It is nearly impossible to match well pump & booster pump flows and even if it were possible, changing system pressures will cause booster pump flow to vary while well pump yield will not. There are also special conditions and times, such as when elevated tanks are out of service, when a specific system pressure must be maintained. Depending on design of pump, it may be necessary to increase discharge pressure 15% to achieve a 20% decrease in flow; but input horsepower changes only 5%. In each case, a relatively small change in discharge pressure can result in a significant Increase in energy to pump. Here are a few possible solutions, which can be employed, to remedy this condition, with pay back times sometimes as short as 2 years. Replace throttling valve on discharge of booster pump with Variable Speed Drive on its motor, which will allow exact matching of booster flow to well pump output, resulting in both pumps operating at peak efficiency. Another option is to replace or modify existing pump to suit or come closer to actual operating conditions. Sometimes changes, such as adding various sized pumps, if storage of treated water is adequate to allow pumps to operate individually or in combination to meet various system conditions. Extra care when selecting or specifying a pump, which can provide a wide range of operating conditions where the pump will operate very close to peak efficiency. It is usually best to pick a design point on the steepest part of the head curve; so that a small change in pressure will not result in a dramatic change in flow, with a corresponding loss in efficiency. Also be very careful when adding in "safety factors" Whenever possible, operate with valves opening fully, allowing pumps to operate unrestricted, which may result in lower pump efficiency, but still reduce energy cost to pump (Kwh/1000 gallons). In multiple pump installations run highest head pump only when other pumps are already operating causing higher system pressures. If multiple pumps, running at the same site have different design points or head curves, try to match pump flow to actual system conditions. Do not try to match Booster Pump flow to We11 Pump flow by throttling either. Allow pumps to cycle instead, if possible. I know that very often booster stations utilize multiple pumps with different capacity ratings. When storage tanks are filled using well pumps, fill rate is almost always different than distribution system demands (withdrawal rate). If storage capacity is adequate to allow tank levels to rise and fall it is more efficient to use the fewest number of pumps to meet system demands. The following is a comparison of test results from an actual Case Study, where a booster pump is being used to pump well water from a clear–well, after treatment, to the distribution system and shows how replacing a modulating valve, with a variable speed drive, reduced power costs: Greenlawn Water District We11 #12 Booster Pump (Design: 1200GPM vs 250’ TDH) Operating condition Original Corrected Change Modulating VaIve Throttled Fully open 52% Flow Rate (GPM) 1065 1065 0% Pump Speed (RPM) 1780 1636 on VFD Pump Pressure 109psi 88psi 19% System Pressure 85psi 82psi 3.5% Demand (KW) 86.29 63 27% PUMP Efficiency (%) 63 69.94 11 Energy (KWH/1000 gallons) 1.35 .98 27% Cost to Pump 1 million Gallons: Operating Condition Original Corrected Savings 1996 Estimate ($.12/kwh) $162.58 $118.14 $44.44 1998 Actual ($.16/kwh) $216.00 $156.80 $56.20 1999 Actual ($.19/kwh)l $256.50 $186.20 $70.30 The graph shown below represents LIPA 1998/1999 Billing Comparison.(1998 in Red Bar and 1999 in Blue Line. Installation cost of V.F.D., labor, equipment, etc. $21,395 (LIPA Rebate) - 11,250 "Out of pocket cost" $10,145 Annualized savings on modified pump power usage ($ 7,935) Return on investment could be less than 2 years @ present savings rate. Conclusion Efforts made to operate pumps so that they are pumping efficiently can result in not only reduced energy consumption, but also actually improved overall system operation, which will reduce all aspects of cost to pump. Obviously, reducing energy consumption will lower power costs, but in addition, since most electric utilities charge for demand generated during their and usually our peak periods, annual cost for electric service can also be reduced dramatically. As can be seen from the Greenlawn Water District example, both energy (Kwh/1000 gallons) and demand (KW) dropped by 27%. But since the District used this booster less in 1999, than it did in 1998 and Plant12 is on a Demand Ratchet Rate, their actual annual cost for power rose from $.16/Kwh to almost $.19/Kwh because Demand charges became a larger percentage of their total cost for Power. So again, this points out the need to perform a thorough study of the operation pumps, for the entire system, to determine how to best operate equipment. In order to make sure your pumping equipment is Pumping Efficiently, it not only needs to be designed and constructed to operate as close to its Best Efficiency Point, but also allowed to run, at that point, without unnecessary restriction. Doing this will not only lower power cost, but could also very possibly reduce maintenance costs, as a result of running pumps less, because they are pumping at higher rates for shorter periods.