Mystery lines into furnace plenum

Can anybody shed any light on the possible meaning of these pipes? At first I wondered about a ‘poor mans geo’ which shows up around here now and then…where somebody just runs well water through a coil for some cooling effect and it exits through a sprinkler or something. But wait…then I spotted the TPR valve and thought of no reason why that might be needed for well water cooling. I wondered about a home made weird heat exchanger…might set up aid in keeping the water in the hot water supply warm? there is what appears to be a small rainman pump on one pipe. There happened to be a plumber there at the same time and he had no idea. Perhaps somebody has run into a similar setup.
mike in MN

Was there a circulation pump at the water heater?

no pump at the heater…however the little pump right next ot the plenum. and whats up with the crossover pipe at the top with shutoff valve. evidently whats ever in there can be isolated.

granpa mike in mn

Yeah I see the cross over but it is blocked from view and also does it transition to PVC?
Looks like it.

Where do pipes go (connected to) after leaving the unit?

From one grandpa to another ya need to follow the lines back to where they started ya will very likely find a water heater or at least something that will give ya a clue

thanks for all the replies…this a older home and everything was built into something else so difficult to follow the pipes to their termination. im just happy enough that its something thats hard to recognize for other top o’ the line inspectors too…and therefore not some obvious thing i was just currently too dumb to figure out. i think its a homeowner custom invention to unknown end. thanks for looking
grandpa mike in mn

hydronic heating?

I would go crazy not knowing.
Here sir,please keep tapping till I say stop.

Could be hydronic cooling but lines are not insulated well and no sign of sweating. My vote is hot water heating with a hot water boiler outside or in an equipment room.