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# Modeling Heat Recovery Chiller in EnergyPlus using Heat Exchanger

That would be greatly appreciated if anyone could help me with modeling Heat Recovery Chiller in EnergyPlus using HeatExcganger:FluidToFluid object. While there is an example file on modeling it using a WaterHeater:Mixed, I'm still struggling with the HeatExchanger:FluidtoFluid modeling approach. There are few questions posted in this topic (including this link and this link). However, all is recommended was following the water heater approach.

In specific, I'm getting consisitently a severe error message that crashes my simulation run and says:"The "Loop Demand Side" connections are not on the Demand Side of a plant loop", while i just replaced the water heater by a heat xchanger and changed the branchs and loops accordingly.

Any help would be greatly appreciated.

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@jmcneill would you please let me know why you recommnded using WaterHeater:Mixed in your answer here: https://unmethours.com/question/19434...

( 2022-03-03 17:20:09 -0500 )edit

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I explain based on the Example File: HeatRecoveryElectricChiller.idf. Please find the revised idf file Here. It's EnergyPlus V9-6-0.

What I revised are as follows:

1. WaterHeater:Mixed has been replaced by HeatExchanger:FluidToFluid.
2. In PlantLoop, Plant Side and Demand Side of Heat Recovery Water Loop have been swapped.
3. Sizing:Plant objects have been added.

Only the first revision is not sufficient. You have the severe error. Drawing a water-side schematic helps to identify the cause.

HeatExchanger:FluidToFluid needs to be connected to two Loops, and one should be Supply Side and the other should be Demand Side. However, both sides of WaterHeater:Mixed in HeatRecoveryElectricChiller.idf are Supply Side. For the second revision, you can swap Node, Branch List and Connector List Names of Plant Side (Supply Side) and Demand Side as follows.

Third revision is required if some parameters of HeatExchanger:FluidToFluid are "autosize". In my revised idf file, I have set Heat Exchanger U-factor Times Area Value to "autosize".

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Thank you so much @Keigo for your wonderful detailed answer and all your valuable comment and effort. By following your answer, I could fix the sever/fatal error that I was struggling with. Meantime, and just as a reference to anyone who might follow this post in the future: not only in the PlantLoop, demand and supply fileds of the Heat Recovery should be swapped, but also it applies for HeatExchanger:FluidToFluid object.

Update: @Keigo I was wondering if you have experienced any similar issue with the Heat Exchanger issue, as describd in the following. The issue is that even I could simulate my model using the HX object, I'm still not getting reaonable results. In specific,I added the following 3 sets of Output Variables to my model idf file:

1. Chiller Heat Recovery Inlet Temperature, Chiller Heat Recovery Outlet Temperature, and Chiller Heat Recovery Mass Flow Rate.
2. Fluid Heat Exchanger Loop Supply Side Inlet Temperature, Fluid Heat Exchanger Loop Supply Side Outlet Temperature, and Fluid Heat Exchanger Loop Supply Side Mass Flow Rate.
3. Fluid Heat Exchanger Loop Demand Side Inlet Temperature, Fluid Heat Exchanger Loop Demand Side Outlet Temperature, and Fluid Heat Exchanger Loop Demand Side Mass Flow Rate.

However, I'm getting exact same inlet and out let temperature for Chiller Heat Recovery and Fluid Heat Exchanger Loop Demand Side (number 1 and 3 from the above list. Also, for those two categories (HR Chiller and HX Demand Loop), I'm getting absolute zero mass flow rate. Meanwhile, I have some non-zero mass flow rate for the supply loop and non-identical temperature between inlet & outlet.

Those indicate some problems about the HR Chiller modeling, especifically about the demand side. Any ideas/thoughts would be greatly appreciated.

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but also it applies for HeatExchanger:FluidToFluid.

I'm sorry that I haven't mentioned how to replace WaterHeater:Mixed to HeatExchanger:FluidToFluid in detail. When you copy&paste Node Names of WaterHeater:Mixed to HeatExchanger:FluidToFluid, Use Side Node Names of WaterHeater:Mixed correspond to Loop Supply Side Node Names of HeatExchanger:FluidToFluid, and Source Side Node Names of WaterHeater:Mixed correspond to Loop Demand Side Node Names of HeatExchanger:FluidToFluid.

( 2022-03-16 04:10:04 -0500 )edit

About your Update, I don't know the detail of your model, but various reasons are possible. What is Heat Exchange Model Type and Control Type of HX? Please try the default settings Ideal and UncontrolledOn first. If you want to use other types, Heat Exchanger U-Factor Times Area Value affects. IMO, it should not be autosized. Other parameters such as design flow rates of HX and Pump are also worth checking.

( 2022-04-25 17:29:49 -0500 )edit

Thanks for the update. However, I added the above listed output variables for the same revised model that you had provided (HeatRecoveryElectricChiller_Rev.idf). It came actually with the same explained issues above, meaning the temerature and mass flow rate issues that exist with the HR Chiller modeling and the demand side. Any ideas would be appreciated.

( 2022-04-26 10:03:28 -0500 )edit

Which month's result are you looking at? This system works only when there are both cooling load and heating load.

If there is no heating load in summer, HX does not operate.

If there is no cooling load in winter, compressors in the chiller does not operate. Therefore, no heat is generated by the chiller.

If you run the revised Example File with Chicago's weather file, you will see some temperature difference and flow rate in Jan to May and in Nov to Dec.

( 2022-04-26 11:50:03 -0500 )edit