Pentair Variable Speed Pump with Pool Heat Pump

[ajw22]

I don’t think greater water flow through the heater will heat the water faster. Heaters put out a fixed amount of BTUs. 1 BTU raises 1 lb of water 1 degree.

Let’s say we have a 100 BTU heater.

We run 100 lbs of water per minute through it then it should raise the water temperature by 1 degree.

We run 200 lbs of water per minute through it then it should raise the water temperature by 1/2 degree.

That water then needs to mix with the larger water body in your pool to raise the pool temperature.

Once you have sufficient flow to operate the heater pressure switch then the water flow rate does not change the efficiency of the heater. The same BTUs from the heater transfer to the water and into the pool regardless of water flow rate.

 

[Hootz]

I don’t think greater water flow through the heater will heat the water faster. Heaters put out a fixed amount of BTUs. 1 BTU raises 1 lb of water 1 degree.

I agree with this statement, although I don't have any scientific proof to back it up.
My speed sweet spot is 2025 rpm ( about 25% power). Any lower speed and my skimmer performance suffers. I have an electric heat pump as well. I can take the water temp from 82 to 90 degrees in about 5 hours with ambient air around 85.

 

[poolrookie22]

I agree with this statement, although I don't have any scientific proof to back it up.
My speed sweet spot is 2025 rpm ( about 25% power). Any lower speed and my skimmer performance suffers. I have an electric heat pump as well. I can take the water temp from 82 to 90 degrees in about 5 hours with ambient air around 85.

Interesting your pool must be much larger. I can go from 82 to 90 in around an hour or two with 85 degree ambient air. That's with a 121k btu heater and about a 7500 gallon pool

 

[ajw22]

Interesting your pool must be much larger. I can go from 82 to 90 in around an hour or two with 85 degree ambient air. That's with a 121k btu heater and about a 7500 gallon pool

@Hootz has a pool 3X your size. The math makes sense. Science, which TFP is based on, never fails. ?

 

[poolrookie22]

@Hootz has a pool 3X your size. The math makes sense. Science, which TFP is based on, never fails. ?

I would love 3x the size good for him! Yes that would make sense then. Everything seems to be working well now thanks to you guys. Only issue is top of water not skimming nearly as well any more even at 2500rpm.

 

[Jimrahbe]

P,

Water skimming is one of those things that can be visually deceptive.. If you had single speed pump running at full speed, you might be used to seeing a lot of action in the skimmer.. When you switch to a VS pump running at a low RPM, it appears that all this action has stopped, so everyone wants to increase the pump speed.

I have found that just having a little patience works best.. I run my pump most of the time at 1200 RPM.. at that speed, when I look down into my skimmers, it almost appears like the water is not moving. But the skimming action still works just fine. It is true that if I have a couple of leafs in my pool that the skimmers do not reach out into the middle of the pool and drag them in. But, if I just don't watch them, and come back in a hour or two, they will be in the skimmers.

Far more important to skimming well is the Weir door.. The weir makes it appear that the water in the skimmer is lower than the pool, and water being water, likes to flow down hill. When it does, it drags anything on the surface with it.

I understand that all pools are different, but I would not give up on skimming at a low speed, just because you don't see a whirlpool in your skimmer..

Thanks,

Jim R.

 

[mas985]

I don’t think greater water flow through the heater will heat the water faster. Heaters put out a fixed amount of BTUs. 1 BTU raises 1 lb of water 1 degree.

For heat gain out of the heater, this is true. However, for heat loss in the plumbing, it is a different story. Heat loss is dependent on the temperature difference of the water vs the environment. The larger the difference, the faster the heat loss but only through the plumbing. The heat loss in the pool itself will be the same either way. But when you slow down the water, it gets hotter coming out of the heater so the heat loss in the plumbing will increase and the efficiency of the system will decrease. How much is dependent upon a lot of factors but if you double the temperature difference (water vs environment), the heat loss is twice as fast through the plumbing. But again, that is only a fraction of the total heat loss because the pool will lose quite a bit more than just the plumbing.

 

[ajw22]

But again, that is only a fraction of the total heat loss because the pool will lose quite a bit more than just the plumbing.

So praticalky a higher flow rate will not make a pool heat visibly faster. Which was the question the OP asked.

 

[JamesW]

If you put eyeballs in the returns, you might be able to drop the rpm down a little bit while still getting the heater to work.