Plumbing diagram for Oil fired Pool Heater.

[Spedley]

Nearly done now! Most parts soldered together, just the compression fittings left for fine tuning. (Oops, the pump is the wrong way around)
If anyone notices a major problem let me know because I'm testing it tomorrow.
Hot water from top of boiler -> expansion pipe -> curved refill pipe - > pump -> pool or bypass valve (to keep minimum temp up) -> back to boiler at the bottom.

 

[RobTi]

Won’t the pump draw air down the expansion, I thought pump on the return

 

[Gasguru]

Won’t the pump draw air down the expansion, I thought pump on the return

It's 2018...pumps on returns were last recommended in the 70s when pumps were marginal operating at higher flow temps. Neutral point is the feed connection, the only negative part of the system is between the neutral point (point of no pressure change, whatever you want to call it) and the circulator inlet. The rest of the system is under positive pressure. Closely coupled feed and vent under virtually at the same pressure. A much better design to prevent air ingress.

Haven't read the rest of the thread but wasn't a sealed system an option?

 

[RobTi]

Sorry showing my age now with that pump position

 

[Spedley]

Plumbing is great, no sign of any problems except it fills rather slowly (and slight leak from top of the header feed - oops). Header tank gets slightly warm, wouldn't even call it lukewarm - I presume from cold water sinking and hot water rising (mostly prevented by the u-bend).

As to performance, I'm disheartened. The heat exchanger is very poor with very little difference between feed and return temps. When the boiler is set to 85'C it turns off every 3m35s and remains off for 2m05s, slashing it's effective output.
I suspect my 400W pool pump has exaggerated figures - it claims 170Lpm max which is what the heat exchanger is rated for, however my spare 500W pump claims 150Lpm max. This is presumably significantly lower once it has been through the sand filter and heat exchanger. It is strange though because with such a small change in temperature (about 3'C for pool water) I would expect a pump twice the size to just heat twice as much water but 1.5'C.

Not sure what to do next, may bypass the sand filter and see if there is any improvement.

 

[Spedley]

I've done a lot of research and I think the problem is flow rates, perhaps because the heat exchanger wants to be low resistance as part of a larger plumbing circuit.
I think there is a lot of laminar flow within the heat exchanger and this gives a lot of heat to a small volume of water in contact with it, the water then mixes back in the pool giving a small increase in temperature. Doubling the flow rate could double the volume of heated water without dropping it's temperature.