Energy Intensity (gal/kwh) at a ground surface water (water loss-leaks

[gakgx61]

Hello Everyone,

I am working as an energy auditor at a water treatment plant. One of the project I am working on is calculating the energy wasted to treat water that is lost due to leaks.
A water balance based on production and amount of water metered showed 30% unaccounted water. Since I can't determine the accurate amount of water lost due to leaks, I am considering 3 scernarios to give a ballpark estimates.

The 3 scenarios:
1. 80% of unaccounted water is due to leaks.
2. 60% of unaccounted water is due to leaks.
3. 30% of unaccounted water is due to leaks.

To determine the energy wasted,I calculate the energy intensity (gal/kwh) at each of the three wells the of the water system over a period of one year. The calculations is done by energy intensity=
(water pumped per month)/(Electricity usage per month).
Then using energy intensity the energy wasted is calculated according to amount of water lost due to leaks.

The problem with that calculations is that I get large variations in energy intensity between the different months at the same well. I am assuming it because the relationship between energy use and gallon pumped is not linear.

However, I can't exaplain why it's not linear. I would love to hear your input about the subject.

Also, if i wasn't clear about anything I would be happy to explain it.

Thanks,
Gil

 

[bimr]

The height of the water in the storage tower (or distribution system pressure) is not constant. You probably have an daily operating minimum/maximum of 15-18 psig.

You may also have a fluctuating water level in the well.

The changes in water elevation will give you variations in the energy usage.

For your purposes, it is suggested that an average energy use over time can be calculated. The average energy use will serve your needs.

 

[gakgx61]

Correct, there is a variation in the water level at the reservoir according to water demand.

Can you elaborate about the average energy use calculations?

 

[hydrae]

The power required to pull water out of the well will vary
as a first factor, is specific capacity SC(gpm/ft of draw down). On initial start up the well will have it best SC. As it pumps longer both in short term and long term the SC will drop, but will regain most of it during times of non operation, again both short and long term effects.
As the SC decreases more power will be required to move the same amount of water. if you have a large water loss creating a large demand, the pump will run longer with shorter down times increasing the power needed per gallon.
how steep that curve is will depend upon the formation and its recharge characteristics.

Second factor, pump selection may have placed the best efficiency at the start up SC, thus when the SC had decreased, the pump is not as efficient, again increasing the power needed.

I would suggest comparing the kwh/gal to total production during each month to get a characteristic of the curve of how the last gallon produced is more expensive that the first.

Hydrae

 

[bimr]

For the purpose of your study, it would seem that an average water production cost would suffice. It is not clear why you would need to have a high level of precision in the water production cost, especially since the accuracy of your unaccounted for water is so high.

To calculate the average water production cost, use the average well(s) water level and average storage tank level.