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Using more than one splitter-mixer pair in one Plant Loop

asked 2019-04-05 09:07:30 -0500

acme's avatar

updated 2019-04-05 11:25:13 -0500

Hello World Again!

I am newby in EnergyPlus and also in UnmetHours. I have 2 questions about my case,

1- Now I have a problem about how to use more than one splitter-mixer pair in one plant loop. As you can see in the line diagram that I have uploaded, I have an Acummulator Tank which is used for Thermal Energy Storage, and I have 2 scenario to operate the system,

For Winter Season, Acummulator Tank serves to meet the Heating Demand. For Summer Season, Acummulator Tank serves to meet the Cooling Demand through Absorption Chiller.

It is written in Plant Application Guide on page-9, article-7, "The PlantLoop accepts only one splitter-mixer pair per half loop." link text

How can I get over this issue?

2- Heating seasons' pipe is connected directly to the Heating Collector which is also supplied by Boiler in real case. (But I am not going to add the boiler loop in my model.) Actually I would rather add it as "Heating Load" instead of "Heating Coil". Does Energy Plus run my simulation if I add it as "Heating Load"??

Thanks in advance,


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answered 2019-04-05 13:15:49 -0500

1 - To get around the limit of one splitter / mixer pair per plant loop, you will need a total of three plant loops and two ideal fluid-to-fluid heat exchangers (FFHX). To achieve this, set the Heat Exchange model Type input field to Ideal.

  • one plant loop to connect accumulation tank on supply side to both FFHXs on demand side
  • one plant loop to connect winter FFHX on supply side to heating coil on demand side
  • one plant loop to connect summer FFHX on supply side to absorption chiller on demand side

Below is a diagram of these connections (not as nice as yours :) )

image description

You'll need to play around with the other FFHX inputs like Availability Schedule Name and Control Type for operational controls.

2 - Yes, you could add a plant loop component on the demand side as a heating load using the LoadProfile:Plant object instead of a heating coil. This requires you to provide a schedule of heating load values. If you don't have that information, then you may need to define the heating coil-to-boiler plant loop as well.

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Dear @Aaron Boranian,

The first 2 questions are about adding more than one splitter-mixer pair, and 3rd question is about Heating Load.

1- First of all, it is needed to use Tee on the FFHX Winter Heat Exchanger (according to your diagram). How can I add a Tee on EnergyPlus. 2- While setting the Heat Exchanger type as IDEAL are we going to prevent the Heat Exhcanger losses? Because being a mechanical system, it should have an efficiency.

3- Actually, I am looking for the Solar System's efficiency, so I need to calculate the solar contribution. Boil will be more suitable I guess?


acme's avatar acme  ( 2019-04-08 13:24:45 -0500 )edit


1 - a Tee in the diagram is a splitter or mixer (one splitter-mixer pair for each side of the three plant loops). Any dashed arrows in my plant diagrams are bypass pipes.

2 - Yes, an Ideal FFHX will have no losses. Due to EnergyPlus limitation of one splitter-mixer pair, we can't have water flow through these according to your diagram, so passing the "full heat transfer" from the accumulation tank to either the heating coil in winter or the absorption chiller in summer via FFHX is the necessary workaround.

3 - I'm confused if the collector is connected to the tank or heating coil.

Aaron Boranian's avatar Aaron Boranian  ( 2019-04-10 11:42:19 -0500 )edit


If you want to easily model something in an EnergyPlus plant loop to provide heating, I would recommend the DistrictHeating object. This can apply heating on the supply side at your specified capacity.

Aaron Boranian's avatar Aaron Boranian  ( 2019-04-10 11:44:21 -0500 )edit

Dear @Aaron Boranian, I have a query regarding to the FFHX issue. As I know that energyplus loop needs at least one pump, but if the total loop only have one set of pump, then how to model it? Is there a pump which have no energy consumption and heat gain?

szsz's avatar szsz  ( 2020-06-09 09:09:42 -0500 )edit

@jsz is this related to your question in this post? If so, I'll respond there.

Aaron Boranian's avatar Aaron Boranian  ( 2020-06-09 10:46:19 -0500 )edit

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Asked: 2019-04-05 09:07:30 -0500

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Last updated: Apr 05 '19