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Modeling heat recovery chiller with air-cooled condenser

asked 2023-08-29 11:54:44 -0500

updated 2023-08-29 20:47:55 -0500

What is the guidance for modeling a heat recovery chiller with air-cooled condenser in energyplus. This type of equipment is becoming very common. It is also one of the most feasible ways to reduce fossil fuel usage on site. The industry desparately needs a way to model this.

Currently, all the chillers in energyplus only support heat recovery if the condenser is water-cooled. Is there a feasible work-around?

Is this on the roadmap for the energyplus development team? This is omething I need to get off my chest. I would love to see this prioritized. If energyplus can't handle this then my shop will be foreced to use something else. In general, I think energyplus needs to take a look in the mirror. What is the real goal of energyplus? It seems that it is so focused on exotic corner cases for PhDs instead of helping the industry being able to model real-world systems. Energyplus is still not very practical for practitioners after years of funding and development

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Where would you like the chiller compressor heat to be used in E+? The EMS language should be able to help with this although I am not sure where you expect that heat to go (OA preheat?).

rraustad's avatar rraustad  ( 2023-08-29 12:11:40 -0500 )edit

Are you referring to equipment such as:

willyJohan's avatar willyJohan  ( 2023-08-29 18:18:21 -0500 )edit

yes, and the heat wuld be transferred into a HW plantloop so it can be used for preheat and reheat.

Lincoln's avatar Lincoln  ( 2023-08-30 15:46:38 -0500 )edit

Not specifically an answer to your question, but here is where you can submit E+ development requests for next fiscal year.

mdahlhausen's avatar mdahlhausen  ( 2023-08-30 15:47:44 -0500 )edit

@Lincoln, so you are looking for a desuperheater for use in a heating plant loop. I see the Coil:Heating:Desuperheater that can move compressor heat to the air loops. You are looking for this type of model to use in the plant.

rraustad's avatar rraustad  ( 2023-08-30 15:56:08 -0500 )edit

3 Answers

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answered 2023-08-30 16:43:17 -0500

The I/O documentation is out-of-date.

It seems air-cooled heat recovery chillers have been available in EnergyPlus since at least the 2014 release.

I'm able to make a model with an air-cooled chiller with heat recovery (OpenStudio 3.6.1, E+ version 23.1.0).

I made an issue on the E+ repo to clarify the documentation and provide and example .idf file of a model with an air-cooled heat recovery chiller.

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Email me if you'd like a copy of a draft of an OpenStudio measure to apply a heat recovery chiller to a model. It's not on BCL yet b/c we are still working on the curves and testing, but it is at least a starting point to see how to wire it up in the model.

mdahlhausen's avatar mdahlhausen  ( 2023-08-30 16:50:04 -0500 )edit

Hi, I would be very interested in having this measure, as I have to model a system with an air-cooled chiller with heat recovery to DHW tank. Would it be possible for you to share it with me as well? Thanks!

jordibrunet's avatar jordibrunet  ( 2023-08-31 03:24:52 -0500 )edit

After wrestling with the measure you sent I was able to create almost what I was looking for. Everything looked good except openstudio mixed up the heat recovery and condenser loop assignments. I was able to manualy fix this in the .osm file. Howver, energyplus threw a sever error because there was no condenser water loop.

* Severe * GetElectricEIRChillerInput: Chiller:Electric:EIR="CH-1" * ~~~ * Heat Recovery requires a Water Cooled Condenser.

So I'm afraid the E+ documentation is actually correct. Thank you sending the measure, it was very helpful.

Lincoln's avatar Lincoln  ( 2023-09-20 22:53:55 -0500 )edit


As an update, the issue that @mdahlhausen posted to EnergyPlus GitHub was addressed and is now part of EnergyPlus v23.2 released last week. You should now be able to connect hydronic heat recovery nodes to an air-cooled chiller using the Chiller:Electric:EIR object class, and documentation has been updated accordingly. This previously worked for the Chiller:Electric object class only, which is what Keigo tested with in his response below.

Aaron Boranian's avatar Aaron Boranian  ( 2023-10-04 17:32:08 -0500 )edit

thumbs up. thanks

Lincoln's avatar Lincoln  ( 2023-10-05 10:09:29 -0500 )edit

answered 2023-08-29 21:33:45 -0500

Keigo's avatar

What is your specific problem with modelling air-cooled chiller with heat recovery?

I have designed an HVAC system with it as an MEP engineer in a building where cooling and heating demands can occur simultaneously. I have not modelled an energy model with it in my actual projects, but I saw your question and modelled it as a test based on the ExampleFile HeatRecoveryElectricChiller.idf i.e., I changed the condenser type of Chiller:Electric from WaterCooled to AirCooled and deleted the condenser water loop. The revised model HeatRecoveryElectricChiller_Rev_AirCooled.idf (V23-1-0) appeears to work at first glance.

Energyplus is still not very practical for practitioners after years of funding and development

Agree. We, the practitioners, need to keep reporting bugs and requesting new features.

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The documentation clearly states:

* Field: Design Heat Recovery Water Flow Rate*

Note that heat recovery is only available with Condenser Type = WaterCooled.

So is the documentation outdated or incorrect. How did you tell it was working correctly at first glance?

Lincoln's avatar Lincoln  ( 2023-08-30 15:44:24 -0500 )edit

I took a look at Output:Variables. There is Chiller Heat Recovery Mass Flow Rate while the chiller is operating. However, this is not my model originally, so I haven't checked the detailed input of internal loads, various schedules and temperature setpoints, etc. You know, we need to be careful when modelling chillers with heat recovery so that the cooling demand and heating demand occur simultaneously.

Keigo's avatar Keigo  ( 2023-08-30 19:21:17 -0500 )edit

answered 2023-09-21 10:48:38 -0500

updated 2023-09-21 11:01:26 -0500

There are 3 sets of nodes in the chillers. Apparently you can use the heat recovery nodes with an air-cooled chiller to add heat to a HW plant.

A5 , \field Chilled Water Inlet Node Name
   \type node
A6 , \field Chilled Water Outlet Node Name
   \type node
A7 , \field Condenser Inlet Node Name
   \type node
   \note Not required if air-cooled or evaporatively-cooled
A8 , \field Condenser Outlet Node Name

A11, \field Heat Recovery Inlet Node Name
A12, \field Heat Recovery Outlet Node Name

The fatal error that happens with this configuration was probably a mistake and may be corrected. This fatal error seems to occur only with Chiller:Electric:EIR and Chiller:Electric:ReformulatedEIR. Heat recovery should work, without a fatal error, for Chiller:Electric. Condenser flow rate must be specified so that heat recovery calculations can be performed.

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How would it be corrected, can you please ellaborate? It looks like the chiller:electric isn't supported natively in OpenStudio. Can this error be corrected without having to switch to chiller objects that aren't natively supported by OpenStudio?

Also, the E+ documentation explicitly state the chiller:electric heat recovery can only be used if water-cooled. So why does it magically works if I switch chiller typs when the documentation is saying the same limitations apply?

Lincoln's avatar Lincoln  ( 2023-09-21 13:13:07 -0500 )edit

I'm fixing it now.

rraustad's avatar rraustad  ( 2023-09-21 16:59:21 -0500 )edit

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Asked: 2023-08-29 11:54:44 -0500

Seen: 264 times

Last updated: Sep 21 '23