getting the right amount of flow to a pool heater after downgrading the impeller

[haz]

I replaced the impeller on my Jandy Zodiac FloPro FHPM 2.0-2 with a 0.75 HP impeller to try to get better energy efficiency. I have 9 Heliocol HC50 solar panels on my roof, which is 25' high.

The solar was working fine with the 2.0-HP impeller in high-speed mode. When I changed to the 0.75 HP impeller, when it's in solar heating mode, with the pump in high speed, I can barely feel a current from the pool return in the spa. I see some spillover into the pool, but not a lot. At least today, I didn't see the pool temperate rise with the solar, and there was plenty of heat. When I would turn off solar (valve automatically shuts to the roof), even in low-speed, I could feel plenty of water return. Note that when solar heater is on, all of the water goes through to the roof with no bypass.

According to Jandy's specs:
http://www.jandy.com/~/media/zodiac/global/downloads/sa/sa6220.pdf
there should definitely be over 25' of dynamic head at the flow rates I would expect. Would it be reasonable to just try a 1.0 HP impeller to see if that works, and if not, then a 1.5 HP impeller?

 

[ps0303]

Not sure why you would swap out the impeller for better efficiency. You would have been better off getting a variable speed pump which is the correct way to do what you are looking to do. However, when you have to pump water up to solar panels, you need a good push. Go back to the old impeller or get a variable speed pump to do what you want to do correctly.

 

[haz]

Not sure why you would swap out the impeller for better efficiency. You would have been better off getting a variable speed pump which is the correct way to do what you are looking to do. However, when you have to pump water up to solar panels, you need a good push. Go back to the old impeller or get a variable speed pump to do what you want to do correctly.

From what I'd read on this site, putting say a 0.75 HP impeller on a 2 HP pump is basically equivalent energy-wise to running a 0.75 HP pump. So since I already have this pump and just need the maximum speed to pump water through the solar panels, I thought I should try to minimize the impeller to amount of HP I need to properly prime/supply the solar panel. Is this not correct? If I get a variable speed pump and need to use it at 2 HP to get the water through the solar panels, isn't that the same as staying with a 2 HP pump and 2 HP impeller?

 

[ps0303]

It does reduce flow rate so if you have anything that is flow rate dependent, that could be affected. If you went with a .75 on a 2HP pump, that is probably too much of a reduction especially with solar panels in play. You might need to look to see how much HP you need to pump up to the panels and to keep decent flow rate.

If you purchased a variable speed pump you would be able to adjust the RPM on the motor down as far as you could and still get water thru the panels. It's the RPM that you want to look at and not necessarily the HP.

 

[haz]

OK thanks, so even if say I got a 1.5 HP impeller and put that on my 2 HP pump, and that provided enough flow rate to the panels, that wouldn't be similar energy-wise to getting a variable speed pump and turning down the RPM to get a similar flow rate to my 2 HP pump with a 1.5 HP impeller? The variable-speed pump would be that much of a better option?

 

[ps0303]

I think the variable speed pump is the better way to go about this but it's not cheap. Plus when you aren't needing to pump water up to the panels, bypass the panels, you can set the speed lower and save more.

 

[mas985]

Sorry but I have to set a few things straight.

A 0.75 HP impeller should work just fine with your setup. I have a 1/2 HP impeller on my pump and it works just fine on a two story roof 25' high.

Also a 0.75 impeller will save quite a bit in energy costs so you did the right thing. It should save over 800 watts in energy on just high speed. A smaller impeller and lower RPM will both reduce flow rates and energy use.

But let's figure out why you are not getting much flow out of the pump. It might have to do with something other than the impeller.

What is your filter pressure with and without solar?

What was the old impeller filter pressure with and without solar?

 

[ps0303]

I know that people change out impellers for a smaller one but as a pool professional, I would never advocate doing this and it has nothing to do with trying to sell a product.

 

[mas985]

Performance wise, swapping out the impeller is no different then replacing the entire pump. The wet end parts are exactly the same as it would be with a new pump. However, swapping out an impeller is far less work and far less cost. There is absolutely nothing wrong with swapping out an impeller. The water distribution industry does it all the time as well as many on this forum. To insinuate there is something wrong is doing a disservice to this forum and to your customers.

 

[ps0303]

As pool professionals, we don't go out and swap out impellers and it's not a disservice at all. If Hayward and Pentair acknowledge this as a fix, then I would support this.

 

[mas985]

Of course manufactures don't recommend this because they want to sell pumps.

 

[Pool Clown]

I know that with Sta-Rite maxi series pumps if you go from a 2hp impeller to a 3/4hp you MUST also replace the diffuser, or it will not prime properly and it will "recycle". I didn't read the whole post, did i see something about a flow issue? That may be the problem.

 

[Pool Clown]

OK, just looked at my catalog. If your pump was originally a 2 hp FloPro series (2008 to present), your diffuser is a R0479701. If changing to a .75 hp, you will need a R0479702. No prevision/notes for a two speed motor. What you are looking to achieve is a good "close" fit of the inlet of the impeller to the center hole of the diffuser. Excessive clearance in that area is what causes the recycling, resulting in decreased flow to the outlet of the pump.

Hope this helps.

 

[mas985]

The FloPro has the same diffuser (R0479702) for all impellers 0.75-2HP: Zodiac Pool Systems

But looking at it again, I guess they do specify another one so it is worth a check.

What you are looking to achieve is a good "close" fit of the inlet of the impeller to the center hole of the diffuser. Excessive clearance in that area is what causes the recycling, resulting in decreased flow to the outlet of the pump.

But both diffusers should have exactly the same inlet fit. That should not change because it is determined but the pump housing inlet size. But if the impeller inlets are different sizes, then definitely you would have to change diffusers.

 

[haz]

Sorry but I have to set a few things straight.

A 0.75 HP impeller should work just fine with your setup. I have a 1/2 HP impeller on my pump and it works just fine on a two story roof 25' high.

Also a 0.75 impeller will save quite a bit in energy costs so you did the right thing. It should save over 800 watts in energy on just high speed. A smaller impeller and lower RPM will both reduce flow rates and energy use.

But let's figure out why you are not getting much flow out of the pump. It might have to do with something other than the impeller.

What is your filter pressure with and without solar?

What was the old impeller filter pressure with and without solar?

Hi, thanks for the replies. I could check the pressures tomorrow and get back with you, but unfortunately by the time I read this I'd put the original impeller back, so the 2 HP impeller is what's in the pump now, and that gives plenty of flow to the solar, and just looking at the spa spillover, there's plenty of flow.

Now in terms of the diffuser, I did change the diffuser too. Here's the diffuser I got, which is for 0.75 - 1 HP:
Zodiac R0479702 0.75 - 1-HP Diffuser, Backplate O-Ring and Screw Replacement for Zodiac Jandy FloPro FHPM Series Pump

There is a different inlet size of the 2 HP impeller that fits into the original diffuser, and the 0.75 HP impeller fits into the smaller inlet of this R0479702 diffuser

Anyway, with the 0.75 HP impeller and diffuser there was plenty of water flow to the pool (could feel at return) in low speed when the solar was turned off and the water was bypassing the solar panels on the roof. Just when I'd switch on solar, which opens the solar valve (and automatically switches the pump to high speed, which I know was happening because of the way it's programmed and because I can hear how the motor sounds when it is in high vs low-speed mode), would the return flow become so minimal. I could see spillover from the spa to the pool, but I really didn't feel much or anything from the return, and the pool temperature wasn't responding as it should in solar heating mode.

So I switched back to 2 HP impeller and the original diffuser, and the flow is good, and the water temperature increased as expected with solar (it had dropped several degrees with solar having been off for several days w/ the 0.75 HP impeller).

Would it make sense for me to try buying a 1 or 1.5 HP impeller and seeing if that works? If so, which would you think I should go with? I know I could have someone install a flow meter on the solar return, etc, to make sure I have the ideal water flow, but I can't do that myself, I won't need the flow meter always, and it could just add unnecessary resistance to my water flow, which is already an issue.

By the way, my pool and pump system are all relatively new. My pump in fact is just a month or 2 new, as some rodents got into my old pump and ruined it.

 

[haz]

Don't know if it's helpful for anyone, but I just check the pressures (with the 2 HP impeller & diffuser installed), and the pressure are:
in high-speed with solar on (to 25' roof): 26
in low-speed with solar off: 7

 

[mas985]

What is the filter pressure on high speed and solar off?

Do you remember what the filter pressure was with the 3/4 HP pump?

I could see spillover from the spa to the pool, but I really didn't feel much or anything from the return, and the pool temperature wasn't responding as it should in solar heating mode.

The flow rate of a 3/4 HP FloPro should be about 25% less flow rate than the 2 HP on the same plumbing so you will see some difference.

Do you have any spring loaded check valve that look like this:

 

[haz]

What is the filter pressure on high speed and solar off?

Do you remember what the filter pressure was with the 3/4 HP pump?
Do you have any spring loaded check valve that look like this:

The filter pressure on high speed and solar off is 22.

Unfortunately I didn't see your reply until I'd already swapped out the 0.75 for the original 2 HP impeller/diffuser, but I'm pretty sure the pressure on low speed, solar off didn't register anything on the pressure valve beyond the minimum 3 psi that it shows. I think you want to know the pressure w/ solar on in high speed though...

I do have a spring loaded check valve, which is on the outflow from the pump right before the solar valve:


by the way, I was told by a guy who once checked the gas heater to leave the bypass valve totally closed to maintain a good water supply to the gas heater (which feeds from the solar outflow pipe), so all of the water goes through this check valve and, if solar is on, to the solar panels.

If you think it would help, I could switch in the 0.75 HP impeller/diffuser again to see pressure in high speed w/ solar on, but if not necessary, much better!

 

[mas985]

When you had the the 0.75 HP impeller installed, you said you did get flow through the panels, correct?

Is the solar valve set so all the flow goes through the panels and none is bypassed around the panels? If not, you should have changed the solar valve setting for the lower HP impeller.

 

[haz]

When you had the the 0.75 HP impeller installed, you said you did get flow through the panels, correct?

Is the solar valve set so all the flow goes through the panels and none is bypassed around the panels? If not, you should have changed the solar valve setting for the lower HP impeller.

I did get some flow, as I saw spillover from the spa to the pool. But sticking my hand in front of the return, I didn't feel any pressure. I put my finger blocking the return hole, and I felt no buildup of pressure. And it didn't seem, from watching the temperatures, that the pool was heating up with the solar on.

Yes, all of the flow goes to the panels and, as per the rec from the gas heater guy, I shut the bypass off completely so all of the flow goes through the solar panels.