Figure 3: Pump, "Pump -as-Turbine", and Systems Head-Capacity constant speed performance, when PAT selected to operate at same flow rate as pump |
With equal flow rates for pump and PAT: Figure 3 shows the head-capacity curves for both pump and PAT performance and the respective system curves at the same flow rates for the pump and PAT. As can be seen, the pump will operate to the left of, but very close to its best efficiency flow rate (95% - 2,850 gpm), while this flow rate will put PAT operation at 80% of its bep flow rate.At a slightly lower pump flow rate then figure 3, but with negligible System Friction Head: Figure 4 shows the head-capacity curves for both pump and PAT performance and the respective system curve(s), at a slightly lower flow rate then in figure 3, but with negligible system friction head. As can be seen for this case, while the pump will operate a slightly lower flow rate (90% of bep - 2,700 gpm), during PAT operation, the turbine will operate even closer to its bep, (93% flow rate - 3,330 gpm). So in addition to the energy savings benefit from the reduction in pipe friction for larger piping, this reduced pipe friction can also improve the pumpxPAT net operating efficiencies, by allowing the PAT to operate closer to its bep, with very little reduction in the pump percent bep flow.