how to measure energy use?

[science]

so im doing a science fair project on the energy costs of reverse osmosis...

is there any way i can measure how much energy my system is using? thanks!

[Andy CWS]

As compared to what?

[pawaterguy]

Things I would think would need to be taken into account: municipal water vs well water (the cost to treat municipal water plays into things vs a private well system). efficiency of the particular unit you're working with. some RO units will use 6 to 8 gallons of water to make one "good" gallon while others use much less (less than half that). Trying to track energy use would be difficult without going deeper than you probably wanted to go when you thought of using the RO in the project.

[science]

well, i was planning on comparing the energy uses using different sized solutes, like the small molecules of NaCl vs large molecules of sugar. i'm not looking for so much of an answer on the forums, but just a way to measure how much energy the system would use to purify each solution. sorry if i wasn't clear in the OP

[pawaterguy]

What are your operating specs and what type of unit? A typical residential unit requires no power to operate so I'm not sure I know how to answer your question. Incoming line pressure is what the unit operates on with the rejection rates being determined by temperature and pressure. There are charts to show you what it will reject at what temp/pressure/etc.

[science]

well yesterday i just got a GE reverse osmosis system. my plan is to attach a pump to it rather than connect it under the sink so that i can both measure its energy use and change the types of water that i feed the system. do you know what type of pump would be effective and maybe how i can measure the energy it uses (ie: with a tool, amount of time it takes, etc)

[pawaterguy]

Well, I'm confused. Either I don't understand what you're doing or you aren't quite familiar enough with how reverse osmosis works. I'm not sure what "energy" you're trying to calculate here and will now bow out of the discussion so as not to interfere with anyone who may have a better grasp of what is trying to be done here. Good luck with the project.

[science]

well ill see if i can explain it more clearly.

rather than attaching my RO system to my plumbing underneath the sink, the way it is normally done, i am going to attach it to an external pump as the driving force for osmosis. this way, i can change the water i'm using rather than the city water and i can measure the energy used. my only issue is i dont know what kind of pump to use :P

basically, im using a pump to bypass my plumbing system and have more control over what goes through the RO system.

if im still not clear please tell me i can try to explain better

[Andy CWS]

Are you using a static water source? Cistern? Holding tank?

[pawaterguy]

OK. But, in order to attain any sort of quantifiable results you need to state some sort of objective. What are you looking to do with the TDS of the water? Just see what they will be? Bring them down to zero? Again, the results of your TDS reduction depend on the temp and pressure of the water coming to the unit...and also the status of the membrane which will be new in your case. But, if you did the same test with this same unit 5 years from now your results would be different. These are the things that confuse me on how you are going to answer your question.

[science]

i believe i am going to be having a holding tank of some sort where the water is not moving (which is why i need a pump to pressurize it).
ill probably end up letting the solutes leave the solution as it is expelled by the filter with all that waste water
my most important concern however, is what kind of pump to use. do reverse osmosis pumps exist that i can obtain? or another pump repurposed to pressurize my water? thanks for trying to help me