Using a Pump Curve w/No Design Data

[wuddog]

I need to justify the repair of a branch of an existing well water line in our plant. We are currently running city water to the areas this failed branch supplies and have meters to provide daily use requirements. I know what it's costing me to supply city water on a daily basis to these areas. Now I need to see what it's going to cost me to pump it from our well. The problem I have is that I have no design information from the original well installation. I have no pump discharge pressure or GPM data, so I am finding it hard to plot my operation point on the pump curve in order to obtain my pump efficiency in order to calculate my costs.
Long story short (too late) should I just assume the pump to be running at the BEP? If not, any suggestions on filling in the blanks? Although I know my daily well water consumption, I feel it would be incorrect to just calculate the average GPM for a 24 hr period as demand varies throughout the day.

Thanks for any help.

 

[BigInch]

If you feel the average daily "load profie" won't give you a useable answer, you go to the next step. Create a shift or even an hourly load profile and do a more detailed study based on those smaller time intervals.

Have your process flows changed since the well system was shut in? If the process volumes have not changed since then, probably the well system will support your needs today and you might be able to assume you will operate close to BEP. If not, consider the possibility of changing the pump. A quick sensitivity analysis of how the efficiencies affect the results will give you an idea of how much you could save by changing the pump to a model with a more exact efficiency match.

http://virtualpipeline.spaces.msn.com

 

[BRIS]

From your post I understand you know the average day consumption but not the head on the pump. Also from your post it would appear that the pump is pumping directly into your distribution system meaning that the pump is running up and down its curve depending on flow. If that is the case you are generating too much head at low flow which is wasting energy.

For the exercise you are doing of comparing cost it is far more important to consider the efficiency of your system, head and Q than the efficiency of your pump.

You need to describe the system in more detail.

 

[BigInch]

Bris, can I ask how, in the practical sense, should one, "Consider the efficiency of (a) system, head and Q (rather?) than the efficiency of your pump"? I get the concept... kinda'... in a qualitive sense, but I really don't know how you mean to consider system efficiency... in quantitive or practical terms. Do you mean to consider various possibilities of changing the system to be more efficient by changing the piping by reducing some head loss to flow ratio, adding tanks to smooth the flowrates, adding a VSD, or some other thing? What do you mean?

http://virtualpipeline.spaces.msn.com

 

[PumpSmart]

Wuddong,
Make a list of all your pumps, with Brand, Service and serial number, request Pump Performance to suitable pump manufacturer. They will provide performance curves, and all data to start a correct analysis.
To make Performance Curves in Field or Plot a operations points to verefy how much energy is lost, you will need to
measure capacity, presures (discharge amd suction) and amperage.
When you finally draw your duty points in Performance Curves, you realize if you are losing high Energy levels or not.

 

[BRIS]

BigInch -The point I was trying to make, but not very clearly was: from the original question I am guessing that the borehole is pumping directly into some sort of metered distribution system that has a diurnal variation in demand. If the pump is sized to meet the peak demand then it will be pumping too much head at lower demands. The system pressure will be higher than it needs to be. When working out the daily pumping costs the amount of power wasted in over pressurising the system during non -peak demand periods will likely have more impact on the costs than the reduction in pump efficiency when it is operating away from its BEP. The efficiency of a system can be improved by smoothing out demand variations on the pump (adding tanks) so that it is operating at its BEP. But there is not enough information in the original post to give any specific advice.

 

[BigInch]

Bris, OK. That's something I can get my teeth into.
Yes, absolutely. No point "running out on the curve" giving specific advice that depends on unknown details.

http://virtualpipeline.spaces.msn.com