Using solar heater inline with gas heater

[discipulus]

Hello,

I have a solar heater and gas heater here in the Pacific NW where I need to use my gas heater often just to keep my pool comfortable enough to swim. Right now my Jandy controller will only allow solar heat OR gas heat but not both at the same time. I'm tempted to put an external Solar controller like the Hayward GL-235 on that 3 way valve to turn on the solar panel when it has enough heat to preheat the water going into my gas heater.

I figure I might as well get the heat out of my solar and then into the gas heater. Is there a reason the Jandy won't allow this? Am I missing something? Thank you.

 

[ps0303]

I routinely see where the solar panels feed the gas heater all the time. So water into the panels and then the heater and then the pool.

Can you post a picture your set up?

 

[Pool Clown]

Yes, there is a reason for this. While not likely, there is a possibility that you could get scalded from having both running at the same time.

Say it is in the middle of the day and you want to use the spa. Once the spa reaches the temp you like, ~104 degrees, you get in. After a while, the temp drops to the point where the automation turns on the heater(s). Typically, your heater whether it is the gas heat or solar heat will have a temp differential of about 4 degrees between the inlet and the outlet. So, the gas heater is first and it raises the water temp by 4 degrees. Now your water is ~106-107 on its way to the roof to collect MORE heat. If that isn't hot enough, the initial heat of the water exiting the (once empty) solar panels can be as much as 10 degrees hotter than the water entering the panels before it settles down to its 4 degree differential. So now the initial "blast" of water coming from the roof en-route to your skin (because you like to sit in front of the water return) is going to be say, 115 (conservatively) before it settles down to say, 110, again conservatively. Now granted, this scenario is a perfect storm, BUT possible.

So, the automation manufacturer would rather not leave themselves exposed to THAT lawsuit.

Also, that would be too much of a heat rise for the automation to control. IOW, once the heated water made it back to the temp sensor (at the equipment) to turn off the heater(s) the temp in the spa would be in excess of the set point. So initial heat up would also be in excess of the set point as well, causing tech support to get a call which they would not be able to address.

"Well, you could just install bypasses on the heaters to keep this from happening"

Yes, but that would:
1) Defeat the whole reason for benefiting from two heaters in the first place.
2) The manufacturer could never be able to guarantee that the installer would install said by-pass(s) needed to keep them out of court. (a good lawyer can defeat printed instructions requiring said plumbing).

 

[discipulus]

Looks like I need to make a quick board with a pic32 micro controller to manage a 3rd temp sensor after the solar and before the gas heater that compares a preset max temp of the solar output that interrupts the signal to my heater in case the temp gets above 108 F so it will lock it out. Also, I can use the JVA signal that switches the spa vs pool to only use solar for pool. That should simplify it and mitigate any issues.

I might as well include a heater bypass JVA controller to bypass the heater when it's not in use but still run a heater cool down timer for the valve. And if I'm doing all of this, adding in the solar temp and control should be cake lol. Looks like it's time to draw something up.


Sent from my iPhone using Tapatalk

 

[ps0303]

Yes, there is a reason for this. While not likely, there is a possibility that you could get scalded from having both running at the same time.

I have never seen or heard of this happening. I routinely see solar and gas together with solar being first and then the water goes thru the heater. just like having a heat pump and feeding the water thru the gas heater last. Yes many of them have a controller for the panels but I still have never seen any issues.

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Also, that would be too much of a heat rise for the automation to control. IOW, once the heated water made it back to the temp sensor (at the equipment) to turn off the heater(s) the temp in the spa would be in excess of the set point. So initial heat up would also be in excess of the set point as well, causing tech support to get a call which they would not be able to address.

Have you seen this happen?

 

[airbrush]

My solar heater feeds directly through my heat pump. There is no worry about overheating. The heat pump works off the discharge water temp of the solar collector. If I want 104 degree water in the Jacuzzi and the solar discharge temp is less than 104, then the heat pump kicks in. Pool Clown is incorrect in his assertion. If you leave the solar in series with the gas heater, no need for a bypass - simply turn off the gas (or alternatively leave the temp setting less than the solar discharge temp).

 

[mas985]

My panels are plumbed before the heater in series and the controller I have has a mode where I can set solar as a priority. The way it works is that solar first heats the water as much as it can and only after solar shuts off, does the gas heater turn on. That way you use the free energy first and then only if necessary, use the energy that costs $$. But most of the time, we never use it this way because when is really hot outside, we would rather have the spa a little cooler.

 

[gwegan]

California requires that all gas heater installations have ,I believe, 36 inches of pipe before the heater, to permit later solar installation.

 

[Pool Clown]

Yes, i have seen this before. Especially with a small body of water. Once in a while you come across a home brew system.

As stated previously, the danger of scalding in that scenario is not there in every instance, all the factors would need to be in place for it to happen.

You, as the home owner, can obviously do as you like. I am here to only offer advice and suggestion, and to make you aware of possible dangers.

I won't entertain discussion about whether or not i'm wrong.

I know what i see in the field, and when it's dangerous.

I apologize if my post implied that you can't have more than one heater available to heat, because, of course, you can. My suggestion is that you be careful if you choose to run more than one at the same time for reasons i have brought to light.

You will find that automation manufacturers will not give you the option to run two heaters at the same time. There is a reason for this, and it is not an oversight.