Tank plumbing for collectors

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I have a tank plumbing question. I am helping my brother-in-law with his solar water heating system. It is a simple flat plate collector system with tank and recirc. pump. The controller’s output relay to the pump fails to operate on occasion resulting in cold showers and lots of complaining so I am replacing it.

My question is about how the tank is plumbed and if performance is suffering as a result. Every drawing I have seen, including the piping diagram from our tank manufacturer shows the return to the collector going into the bottom of the tank with the piping back from the collector somewhere around the middle of the tank. Indeed, this tank has two large labels “To collector” and “From collector” plastered on the side of the tank. The return to the collector does go to the bottom of our tank. However, the hot water return “from collector” nipple in the middle of the tank is capped off. They have plumbed the hot water return from the collector into the bottom of the tank using the “to collector” nipple and used the drain valve fitting at the bottom to return water to the collector (which is less than a foot away from the inlet). At least they used a tee and kept the drain valve operational. This is not an indirect system tank so there is not a heat transfer coil inside.

This seems like a possible “short circuit” to me where heated water could be taken back to the collector too soon and possibly prevent the full possible tank temperature to be realized. Or, maybe it doesn’t really matter? It just seems weird and they also didn’t install a mixing valve. So, either they have a lot of practical experience in plumbing solar tanks (I have none) and have empirically found this to be a better method or they didn’t know what they were doing. They’re a well known company around here but maybe they had a new employee that day?

I would appreciate someone with experience to comment on the way this tank is plumbed as to possible performance issues.

Thank you,
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