High head loss from heater

[mzuniga]

Hi guys. After finishing my pool I had the heater bypass valve closed for the 30 recommended days (quartz pool). Rpm and gpm numbers were in the expected range at that point. Now that I opened the bypass valve in the heater (and everything else being equal than before) I'm noticing a very sharp drop in gpm throughout the curve. So much so that in order to get the minimum 24 gpm my Intellichlor requires I need to ramp up my pump to 2000 rpm (before I would achieve that gpm with 1500 rpm). I've attached a graph with my curves. Light blue line is gpm before opening the heater and the dark blue line is after. Are these numbers ok? I seem weird to me to have this massive head loss only from going through the heater coil.

Any help and/or bumps will be appreciated.

Thanks!

MZ

 

[JamesW]

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/manuals/training/Sta-Rite%20Basic%20Training%20Manual.pdf

 

[mzuniga]

Thanks for the prompt response @JamesW. So how 7ft of head loss would correlate with gpm reduction? I'm a big ignorant in all things engineering related and just learning the ropes. Thanks!

 

[JamesW]

This is from the Jandy JXI, but it has a similar design, so the head loss should be similar.

It has a double pass heat exchanger.

 

[JamesW]

https://aquamagazine.com/service/how-to-read-pump-system-curves.html

 

[mzuniga]

If i'm reading this correctly i should not have such massive fall in gpm then

 

[JamesW]

Check the GPM, RPM, Watts and system pressure from the keypad display for several speeds around your target flow rate and also report the filter pressure.

 

[mzuniga]

Check the GPM, RPM, Watts and system pressure from the keypad display for several speeds around your target flow rate and also report the filter pressure.

Well, that is the first chart I posted above. Filter preassure remains unchanged at sam rpm in both scenarios.

 

[JamesW]

I don't really understand the chart you posted.

Check the GPM, RPM, Watts and system pressure (PSI) from the keypad display for several speeds around your target flow rate and also report the filter pressure when the water is going through the heater and when the water is not going through the heater.

 

[mzuniga]

Sure. So, at my desired flow of 25 GPM I get the following numbers:

Heater bypassed: 1300 RPM, 125 Watts, filter at 9 psi
Heater open: 1800 RPM, 274 Watts, filter at 10 psi

Filter and salt cell are recently cleaned

 

[JamesW]

OK, that helps, thanks.

Let's also get the following information at 1,500 rpm and 2,350 rpm.

Heater Bypassed.
RPM.........GPM.......Watts.......System pressure.....Filter Pressure.
1,500
2,350

Heater Open.
RPM.........GPM.......Watts.......System pressure.....Filter Pressure.
1,500
2,350

 

[mzuniga]

Thank you @JamesW. I'll find out later today. I don't have access to the main screen of the pump since the Intellicenter has control (it says Display Off or something to that effect). I cannot find the system PSI number anywhere in the Intellicenter interface.

 

[JamesW]

Put the system in "Service" mode so that the pump display becomes active.

 

[mzuniga]

So here:

 

[JamesW]

So, the system pressure was the same in bypass or in heater mode?

7 feet of head is about 3 psi.

The filter pressure went up by 2 psi, which is less than the expected 3 psi.

The system pressure should have gone up by about 2 or 3 psi as well.

Heaters are poorly designed as far as flow goes, so the extra RPM needed to achieve the same flow is about what you should see.

 

[mzuniga]

Yes. No additional pressure spike. Ok. So I should not worry about it then. I'm just concerned by the additional energy cost. Thanks a bunch James!

 

[JamesW]

Heaters are horrible for hydraulics.

That's why Jandy came up with the VersaFlo Bypass, which only activates when the heater is active.

It's a good idea, but it is expensive and unnecessarily complicated.

A better idea would be to remove the thermal regulator and install a Jandy valve and a valve actuator that is activated when the heater is activated.

If the bypass valve is closed when there is no call for heat, the thermal regulator is not needed.

In my opinion, all heaters should have a 3-way valve to bypass the heater when no call for heat or to go to the heater on call for heat.

Put a check valve at the heater output.

Put a flow switch in the heater instead of a pressure switch.

Make the heat exchanger a single pass rather than 2 or more passes.

The three way valve can be actuated by a standard 24 VAC valve actuator powered from the heater or from automation.

Below, you can see the VersaFlo head loss vs. the heater head loss.

https://www.jandy.com/-/media/zodiac/global/downloads/sl/sl6971.pdf

 

[mzuniga]

Agree. Will consider doing something like that. Thanks!!

 

[JamesW]

Note that my suggestions were for general improvements and not specific recommendations for any system.

Do not make any changes unless you are 100% sure that you know what you are doing.

You can install an external bypass, but make sure that the heater is off when bypassed because the pressure switch can still be activated even if you close valves going to and from the heater.