How to implement one component (CHP unit) for two plant loops ?

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@mldichter, I tried to do as you said but from the beginning in OS, it doesn't let me drag the boiler nor the Water heater to the demand side and gives this msg , So I tried using E+ instead, but it still doesn't work because the water heater and boiler have respectively different inlet/outlet nodes assigned (nodes in the 3rd loop and nodes in the original loop) and when I tried to assign to them in the 3rd loop the same nodes as the ones in the original loops I had the error of duplicate occurrence,Non-unique node name

@Raghda Derbel Are the Use Side and Source side node names all unique? Was there anything else to that error? Does it say what node is non-unique?

Now I tried to use the same use side node name for the water heater as the node name assigned in the demand branch of the water heater in the 3rd plant loop, and the same source side node name for the water heater as the node name assigned in the supply branch of the water heater in the 2nd loop. But I couldn't do that with the boiler because there is only water inlet and outlet node name (no source side and use side) so for the boiler I have assigned the same nodes in the demand branch of the 3rd loop and supply branch of the 2nd loop who are already defined as ..

who are already defined as water inlet / outlet node in the Boiler object.

@Raghda Derbel So in the plant loop with the boiler, you will have to insert an additional water heater on the demand side of the loop on a branch at the outlet node of the demand side of the plant loop. The water heater should have a setpoint of 1C or similar so it never actually turns on, and the water heater should probably have a very low volume to heat easily. It is really only for transferring heat between the plant loops.

You will continue to find that energyplus isn't as flexible as we'd like, so you'll have to do weird stuff like this every once in a while to model a building.