Trying to get my head around this system in our cafe. It's the relationship between the circulating pump and the ?bypass (above the red knob on the right) that is not making sense to me.
It just seems like the circulating pump is dragging the cold water around and around through the loops. It's doesn't look like other manifolds I've googled...
The red knob is a thermostat. Hot water will flow in their, coming from the gas furnace most likely. The floor heating can't handle too hot water, so it's mixed with the circulating water coming from the top rail. The tube going from the thermostat to the top rail probably only has a thermometer in it, to measure the temperature of the returning water. If it's too cold, more hot water can be mixed in.
The pump you see is circulating water through the floor heating. The gas furnace will have another pump, distributing hot water through the building.