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

asked 2018-09-14 16:58:44 -0600

Hi !

I am supposed to simulate a building with only one CHP unit (15kw), but it seems like I need to implement 2 different CHP because I have 2 plantloops as shown below:

image description

when I tried to use just one CHP in e+, the simulation failed saying that there is one component that has different nodes. So instead of using one CHP with a power of 15kW, I am using two units of 7.5kW each, but the results won't be accurate, as it should be.

Does anyone you have any suggestion that could help me with this ?

NB: I used openstudio at the beginning but it turned out that I can not realize this kind of design (MicroCHP or MicroTurbine unit) with OS, even if it is in the loop in the images above, but it is not taken into account during the simulation and does not appear in the results, so I had to export the file into IDF file and I then I added the MicroTurbine.

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answered 2018-09-14 19:04:28 -0600

mldichter
2565 ●2 ●11

This a somewhat boneheaded way to do what you want, which may also be the only solution.

You can't put the CHP on two plant loops. Energyplus won't allow it. If you wanted a CHP to provide hot water to two water plant loops, what you can do is make a plantloop containing the CHP on the supply side, and two water heaters on the demand side. Then you can insert those two water heaters into other plant loops since WaterHeater:Mixed objects have a pair of Use Side nodes and a pair of Source Side nodes. This lets you place one water heater on two plant loops.

Hopefully both your supply objects have something similar to the Use Side and Source Side nodes of the WaterHeater:Mixed. Otherwise, you'll probably need to add in at least one more WaterHeater:Mixed object into your model that is solely for transferring heat from the CHP to a plant loop.

image description

I've had to do something similar in the past, and this is the best I came up with.

PLEASE let me know if you come up with a more elegant solution.

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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 ( 2018-09-15 19:23:58 -0600 )edit

@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?

mldichter ( 2018-09-15 23:50:29 -0600 )edit

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 ..

Raghda Derbel ( 2018-09-16 07:13:04 -0600 )edit

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

Raghda Derbel ( 2018-09-16 07:13:46 -0600 )edit

@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.

mldichter ( 2018-09-16 08:11:21 -0600 )edit

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