Apex users, you can monitor your return pump flow with, temperature probes

[Bent]

I figured this out the other day and thought I would share.

You can monitor the effective flow of your return pump pretty accurately with just one temp probe, and very accurately with two. Here’s how.

Single probe method you can place the temp probe in the first chamber of the sump where the display drains. Then place your heaters in the return pump section. When you start to notice your temp drifting colder, that indicates the return pump flow is slowing down.

Double temp probe method is similar to the single probe method, except you plsce the second probe in the return chamber with the heaters. The larger the difference between temp 1 and temp 2, the slower the return pump is flowing.

I don’t know if it’s possible to set the apex to alert or not if the drift between the two temp probes gets greater than a certain number, but I’m sure you could.

[Salty Waffles]

Thanks! You just gave me something else to experiment with this afternoon!

[Bent]

No problem!

I think the further away from the display the sump is, the better this works. My sump is in the basement so I think the temp diff between the display and the sump is slightly more pronounced than what it would be in a standard under tank setup.

[Bent]

I slightly cranked down the valve on my return pump to experiment and you can plainly see the dip in the baseline and the subsequent return after I turned it back up.

[jamie1981]

Where the heaters on/off or on and off when you did this? I would think that is going to make your temp vary more than reducing the flow a bit.

I don't see how you would determine flow rate based on temp though.

[BrettDS]

It’s an interesting thought, but I suspect ambient air temp will play into this as well. Your tank water will likely lose more heat in the winter than in the summer, assuming that the air temp in your house is different.

Also, keep in mind that the water may normally lose a degree or two as it travels up to your tank and back down to the sump. If you are measuring the colder water where it drains into the sump, but heating the water in the return section your tank temp may be a degree or two warmer than you think it is.

[Bent]

Originally Posted by jamie1981

Where the heaters on/off or on and off when you did this? I would think that is going to make your temp vary more than reducing the flow a bit.

I don't see how you would determine flow rate based on temp though.

It’s pretty simple actually if you think about it.

The display gets the best from the heaters in the sump. As the return pump flow decreases, less heated water gets into the display tank. As a result, the display tank temperature will drop slightly. So you will have a difference between the temperature of the display and the temperature in the return section of the sump with two probes. With a single probe in the input chamber of the sump or in the display itself, you will see a gradual decline in temperature as the flow drops. Because naturally if the flow stopped completely, the display tank would continue to drop until it equalized with the room temp while the temperature in the return section of the sump would stay the same.

Obviously the amount of drift is going to vary from system to system based on many factors, but it will be present if you are measuring the display tank temperature and heating the return section of the sump.

[Bent]

Originally Posted by BrettDS

It’s an interesting thought, but I suspect ambient air temp will play into this as well. Your tank water will likely lose more heat in the winter than in the summer, assuming that the air temp in your house is different.

Also, keep in mind that the water may normally lose a degree or two as it travels up to your tank and back down to the sump. If you are measuring the colder water where it drains into the sump, but heating the water in the return section your tank temp may be a degree or two warmer than you think it is.

Agreed, this is more about trend monitoring than individual readings and knowing what your peak, troughs and means are.

[jrhupp]

I believe the scheme as proposed is fraught with artifacts and is probably in workable. But Bent's general concept is not too far off. Look into methods used to measure stem flow and wind speed. googling "heat pulse sap flow" and "hot wire anemometer" should turn up some relevant material. You will find that indeed, fluid flow can be derived from temperature measurements.

[Bent]

Originally Posted by jrhupp

I believe the scheme as proposed is fraught with artifacts and is probably in workable. But Bent's general concept is not too far off. Look into methods used to measure stem flow and wind speed. googling "heat pulse sap flow" and "hot wire anemometer" should turn up some relevant material. You will find that indeed, fluid flow can be derived from temperature measurements.

I’m not saying you can accurately calculate GPH with this. What I am saying is that if your return pump partially clogs and starts operating at half or 1/4 it’s necessary output, this is a good way to figure it out if your not home at the time.

[Salty Waffles]

Well, in my case I approached this less from a pump efficiency standpoint vs. a Apex temp probe reading a more true display temp standpoint.

Partially out of convenience, I located my temp probe in the fuge which feeds directly off the manifold after the return pump. My heaters are in the return chamber. Ive always figured the short loop going to the fuge then to the return chamber was giving the system a false elevated temp reading. The temp probe I have in the display has always read a degree or so lower than the Apex, presumably due to the short loop of freshly heated water going to the fuge then back the the return chamber.

Moving the temp probe to the skimmer/drain chamber has brought the two temp readings to nearly equal readings.

I know, not exactly what the OT is about, but the subject shook loose some rocks in my head and helped me dial in things a little better. Thanks!!

[ca1ore]

It's a good 'check' though. Been doing this for a while, even though I also monitor flow directly with apex flow sensors. FWIW, heat loss from return piping is negligible, thus not worth considering. It's important also to make sure that the temperature sensors are 'synchronized'. The issue with inferring flow problems this way is that it can take some time for the two water bodies to diverge, particularly in larger systems. Problems resulting from flow loss may manifest before the temp differential alerts you.

[windlasher]

Unrelated: Tell me how to get my salinity probe calibrated properly and I'll sing your praises forever. lol

[BrettDS]

Originally Posted by windlasher

Unrelated: Tell me how to get my salinity probe calibrated properly and I'll sing your praises forever. lol

The salinity probe is a tricky animal. It can be very sensitive to interference from other electronics, so if you see a drift when your lights are on, for example, then it might be getting interference from that. Try not to let the salinity probe cord travel next to any other cords as this can affect the readings.

It also can be very affected by bubbles. If it’s in an area that has any bubbles or micro bubbles then that can definitely affect the reading. Try to keep it free of any bubbles.

Finally, it takes a good two weeks of being in the water before it settles. My personal theory here is that it is getting a coat of algae or bacteria. But if you calibrate it and put it in the water you will notice that it drifts for a good two weeks, then finally becomes stable, but likely at a point that is different from where it was calibrated.

The best thing to do is to put it in the tank without calibrating it and give it about 2 weeks. Keep an eye on it and when it seems reasonably stable and stops drifting, then you can go ahead and calibrate it. But when you calibrate it, don’t clean it or you’ll start the two week drift all over again. What I do is rinse it in some RODI water, then use compressed air (or just my breath) to blow into the bottom of the probe to try to get most of the water out for the ‘dry’ part of the calibration. Once it’s calibrated stick it back into the tank and it should remain reasonably stable.

[Bent]

Originally Posted by BrettDS

The salinity probe is a tricky animal. It can be very sensitive to interference from other electronics, so if you see a drift when your lights are on, for example, then it might be getting interference from that. Try not to let the salinity probe cord travel next to any other cords as this can affect the readings.

It also can be very affected by bubbles. If it’s in an area that has any bubbles or micro bubbles then that can definitely affect the reading. Try to keep it free of any bubbles.

Finally, it takes a good two weeks of being in the water before it settles. My personal theory here is that it is getting a coat of algae or bacteria. But if you calibrate it and put it in the water you will notice that it drifts for a good two weeks, then finally becomes stable, but likely at a point that is different from where it was calibrated.

The best thing to do is to put it in the tank without calibrating it and give it about 2 weeks. Keep an eye on it and when it seems reasonably stable and stops drifting, then you can go ahead and calibrate it. But when you calibrate it, don’t clean it or you’ll start the two week drift all over again. What I do is rinse it in some RODI water, then use compressed air (or just my breath) to blow into the bottom of the probe to try to get most of the water out for the ‘dry’ part of the calibration. Once it’s calibrated stick it back into the tank and it should remain reasonably stable.

This and make sure you float the calibration fluid in the tank so the calibration fluid is the same temp as the tank it will be sitting in.

The SG of the calibration fluid at room temp will be different than the SG of the fluid at tank temp. If you calibrate the probe in the room temp fluid and then stick it in the tank it will be off.