What does heating my water do to my RODI unit performance? | BRStv Investigates

[randyBRS]

Hey guys,

Today we are investigating RODI even further by testing the effects of heated water on RODI unit performance. I think you may surprised with the results, even though most manufacturers test their membranes at 77 degrees!

Let us know what you think about heating your water prior to filtering it!

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[jsker]

Very interesting, thank you for another informative video.

 

[lariat8099]

Following

 

[slim_santa_chris]

I don't know much on this topic. but I would want to run at a temp where I get the most gallons per membrane that factors is way more important to me then the flow rate a day. With this info it sounds like running cold water is better due to the TDS reading going in is less then the warm or hot water. If anyone else has an info on what I've said I would love to hear them.

 

[karo25]

Yep, TDS is much more important to me than 150 gallons a day.

 

[Randy Holmes-Farley]

Just to be clear, the total ions (TDS) hitting the front of the RO membrane is independent of temperature. It is the rejection rate and flow that changes with temperature.

 

[Randy Holmes-Farley]

FYI, I presume BRS didn't temperature compensate, or didn't compensate correctly, for the temperature impact on TDS measurement for the input water TDS. I'd be very surprised if they actually dissolved that much metal from the pipes, which is where the "increased' TDS would have to come from.

 

[Randy Holmes-Farley]

The simple reason that TDS appears to rise as water warms is that the same total number of ions conduct electricity better when warmed. For that reason, conductivity and TDS measurements must always be corrected for temperature. Unfortunately, unless you know exactly what is in the water, you can only use a generic correction equation, which may not be perfectly accurate with whatever ions are in your water.

An interesting experiment for those with conductivity meters that purport to correct for temperature changes is to take some warm or cold tap or tank water warm, measure the conductivity, and then let it cool or warm to room temp and see if the conductivity changes. It shouldn't, but it likely will.

 

[Ryanbrs]

FYI, I presume BRS didn't temperature compensate, or didn't compensate correctly, for the temperature impact on TDS measurement for the input water TDS. I'd be very surprised if they actually dissolved that much metal from the pipes, which is where the "increased' TDS would have to come from.

Fair point and I absolutely appreciate your help sharpening the information we share. I know we are going to make some missteps along the way and you certainly set the standard of responsible knowledge in the reefing community Our water heater for the utility sink is pretty small and doesn't get used a lot so it's hard to say if there is something unique about that set up.

For the hot verse cold tap water I let the water rest to room temp but it's still warmer than cold tap. For the membrane performance the results matched the anticipated performance data from Dow so the assumption was the testing results were accurate. We are using a Hach HDQ meter which I am pretty sure compensates for temperature. We are setting up for reefapalooza so it's difficult to get the details on the meter at the moment.

 

[Ryanbrs]

An interesting experiment for those with conductivity meters that purport to correct for temperature changes is to take some warm or cold tap or tank water warm, measure the conductivity, and then let it cool or warm to room temp and see if the conductivity changes. It shouldn't, but it likely will.

When we get back I will absolutely do this and share the results!

 

[Jstn]

77f or 25c is standard iupac testing conditions

 

[Randy Holmes-Farley]

Fair point and I absolutely appreciate your help sharpening the information we share. I know we are going to make some missteps along the way and you certainly set the standard of responsible knowledge in the reefing community Our water heater for the utility sink is pretty small and doesn't get used a lot so it's hard to say if there is something unique about that set up.

For the hot verse cold tap water I let the water rest to room temp but it's still warmer than cold tap. For the membrane performance the results matched the anticipated performance data from Dow so the assumption was the testing results were accurate. We are using a Hach HDQ meter which I am pretty sure compensates for temperature. We are setting up for reefapalooza so it's difficult to get the details on the meter at the moment.

Thanks.

FYI, I do not doubt the conclusions of the experiment.

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

Various factors, such as temperature and pressure, impact not only the flow rate through the membrane but also the purity of the resulting water. Lower temperatures make the water more viscous and less likely to flow through the small pores, reducing the production of purified water. The effect of temperature on purity is much smaller, with purity decreasing slightly at higher temperatures. Higher line pressure across the RO membrane results in higher rates of production and quality, although a pressure that is too high can damage the membrane. Any backpressure on the effluent will degrade performance. Very high TDS (total dissolved solids) in the source water also leads to higher osmotic backpressure, reducing the membrane's effectiveness. As a rough guide, every 100 ppm of TDS produces 1 psi of osmotic backpressure.

 

[ss30]

Very interesting, make as much water as you can when it's colder then

 

[Kaybee]

Did you notice if the temperature made a difference to the water efficiency? i.e. what was the waste water volume? This is important for a lot of people.