Piping Help

[nj888]

Hopefully I've posted this in the correct category.

I am planning on adding a gas heater after my electric heat pump and have the return from the gas pump hook up right after the electric heat pump's outflow.

I've drawn out what I think the plumbing should look like. See attached picture of my current heat pump and piping.

Can I get your feedback of my piping schematic? Could there be a better way? Any corrections?

The pink highlighted are the valves I believe I will need and where I will install them. The 2 green highlighted are check valves I think will need as well and where it should be.

Thank you for your help.

 

[1poolman1]

You need a check valve in the output of the heat pump (right at the "right" arrow in the out line) so the gas heater does not try to push water backwards through it.
You don't want to have the output of the heat pump go into the gas heater and can eliminate that check valve. Not sure if you intend to run them simultaneously, but that would cause the gas heater to get false temperature readings and turn off early. If you were to run heated water through the gas heater while off, the heat exchanger could act as a radiator and cool it. Even though it would be slight, why waste the heat.

 

[Bill1974]

I think what you have will allow you to use just the heat pump, just the gas heater or the heat pump and gas heater in series. We don't know how you are controlling them and as 1poolman1 said the gas heater would get a false reading on what the pool temp is, but that may not make a difference depending on how you are controlling it.

As long as inlet 3 way valve on the HP is closing off flow to HP inlet and the outlet 3 way valve is closing off flow left or right it should fine. I don't think an added check valve is needed.

 

[nj888]

You need a check valve in the output of the heat pump (right at the "right" arrow in the out line) so the gas heater does not try to push water backwards through it.
You don't want to have the output of the heat pump go into the gas heater and can eliminate that check valve. Not sure if you intend to run them simultaneously, but that would cause the gas heater to get false temperature readings and turn off early. If you were to run heated water through the gas heater while off, the heat exchanger could act as a radiator and cool it. Even though it would be slight, why waste the heat.

Thanks 1poolman1. Do you mean a check valve where I highlighted the green arrow (right of outflow from heat pump)?
I did not know about the possibility of false readings and that the gas heater could actually cool the water (however slight).
I will have to make sure I run the pumps separately.

 

[nj888]

I think what you have will allow you to use just the heat pump, just the gas heater or the heat pump and gas heater in series. We don't know how you are controlling them and as 1poolman1 said the gas heater would get a false reading on what the pool temp is, but that may not make a difference depending on how you are controlling it.

As long as inlet 3 way valve on the HP is closing off flow to HP inlet and the outlet 3 way valve is closing off flow left or right it should fine. I don't think an added check valve is needed.

Thanks Bill1974 for reviewing.
My original thought was just as you described. I want the option to run each alone and in a series. Plus being able to bypass each if one goes down.

In your scenario when closing off the inlet to the Heat Pump I was afraid water will still be able to enter the Heat Pump via the outlet port. Thus I highlighted in green where I think I will need check valves (One on each side of the Outlet of the Heat Pump). Can you possibly clarify if I don't need it? I very much appreciate the advice!

 

[1poolman1]

Thanks 1poolman1. Do you mean a check valve where I highlighted the green arrow (right of outflow from heat pump)?
I did not know about the possibility of false readings and that the gas heater could actually cool the water (however slight).
I will have to make sure I run the pumps separately.

Yes.

 

[Bill1974]

If the inlet or outlet to either of the heat sources is blocked there is no flow through it. So the only other step you would need to take is blocking flow from bypassing the heater being used.

Running warmed water from the HP through the GH would loose some heat to the air and would also be more pumping resistance. How much I don't know.

If you want to get fancy you could add electrical actuators and automation to the valves so water only goes though the heaters when they are being used. This should also minimize the risk of running a heater with the valves in the wrong positions.

As for running the heaters in series, I don't know if the gas heater would shut off because the inlet water temp is at or above the desired pool water temp (because it's getting warmed water from the HP) or if would keep running as long as there was a call for heat. I am pretty sure it could be made to work and not bypass any of the safety features on either heater. By running them in series you may run in the saturation where the GH cut off because the output temperature is to high and if this does not happen you may be getting to temperatures that risk softening the outlet PVC piping.

If looking to just heat the water faster (not hotter), running them in parallel would be able to get the most out of them and minimize the possibility of the GH cutting out for an over temp or some other safety feature. This would also help flow and minimize the pretty drop from trying to push water through two heaters in series.

 

[1poolman1]

Gas heater would only call for heat if the inlet temp is below the set temp. The water from the heat pump may reach that point before the actual body needing the heat does and the gas heater turn off. Parallel may work to increase speed of heating.