Heater bypass

[dphanes]

My pool has a heater bypass. Should I always keep the bypass partially open so the bypass pipe doesn’t get stagnant water in it - and in the winter doesn’t freeze due to no water flow.
If I do a harsh treatment to the water I would temporarily bypas the heater all together but am curious about folks thoughts on partial bypass as normal operation.

thanks in advance

 

[ajw22]

If you know you water chemistry is good just let the water circulate through the heater normally. A heater bypass is for abnormal situations.

 

[sktn77a]

If you have a chlorine tab feeder, then its a good idea to have a check valve or bypass between it and the heater.

 

[mas985]

It is ok to have the heater bypass open as well as the heater path so water flows through both. However, if you use the heater, the pump RPM may need to be higher because of the reduced head loss in the heater.

 

[TexEdmond]

have the heater bypass open as well as the heater path so water flows through both.

I don't know if the numbers are trustworthy on my control panel, but I'm astounded that the GPM can stay the same at significantly lower pump RPM when I open the heater bypass. I'm actually considering seeing if it's possible to have an automated valve actuator that opens with the heater circuit. 99% of the time I could leave the heater (mostly) bypassed and it'll only close when the control panel turns on the heater. Or I guess I could just piggyback it on the spa valve wire because those actuators already exist... This is mainly to see how low of RPMs I can run the pump and still have enough flow over the SCG.

 

[ajw22]

Tex, a heater is the main restriction in the pool pad and causes more RPMs to be needed for the pump to deliver a GPM. A Heat Pump is even more restrictive then a gas heater. It has to do with the size and shape of the heat exchanger water needs to flow through.

 

[TexEdmond]

Understood. I also believe I saw something on the forum about how it's not just the actual tubing that's so restrictive, it's the heater's internal bypass and overheat safety mechanism that's the big bottleneck. At first I was worried because previous owners weren't so great on maintenance, so I was thinking there was enough scale buildup for me to have to consider acid flushing the heater somehow. When we got handed the keys the VSF settings were all over the place, bonkers high and the motor was quite noisy / rattling at times. Bypassing the heater I notice around 10psi drop on my filter gauge and as high as 13GPM increased flow thru the system, depending on which zone of the floor cleaners is active. I'm going to temporarily install that automatic valve and try that awhile.

 

[mas985]

Understood. I also believe I saw something on the forum about how it's not just the actual tubing that's so restrictive, it's the heater's internal bypass and overheat safety mechanism that's the big bottleneck.

There are several sections in a heater that cause head loss. The inlet manifold which the bypass is part of, the heat exchanger, the thermostat valve, and the outlet manifold.

The internal bypass actually reduces head loss in a heater not increases it. The valve opens with excess pressure at higher flow rates reducing the head loss. Without it, the head loss would be much higher. Many heat pumps do not have an internal bypass so the head loss can be quite high.

The heat exchanger is made up of several parallel tubes and relatively, it may contribute less head loss than some of the other components but it still adds head loss.

However, the thermostat valve at the outlet of heat exchanger that opens with increasing temperature is probably a major contributor to the head loss.