Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
1

How to calculate thermal (cooling and heating) loads in EnergyPlus without designing HVAC system?

asked Aug 25

updated Aug 29

Hi,

I want to determine the overall cooling and heating load in my EnergyPlus model, without designing the actual HVAC system - this will serve as my baseline model, the results of which I can compare with "advanced" (modified) EnergyPlus model.

The only way I came across to do this is via defining an object in EnergyPlus called ZoneHVAC:IdealLoadsAirSystem.

Further, the Output:Variables which can help to estimate this are:

  1. Zone Ideal Loads Zone Total Heating Rate
  2. Zone Ideal Loads Zone Total Cooling Rate
  3. Zone Air System Sensible Heating Rate
  4. Zone Air System Sensible Cooling Rate

Can anyone from the community help me in understanding if I am on the right track pertaining to the above mentioned, if not, how can I achieve this effectively? - any sort of guidance will be welcomed and appreciated.

Apologies, if the question is not clear enough.

Thank you!

Edit-1:

image description

Preview: (hide)

Comments

@Denis Bourgeois thank you again, for clarifying my doubt on this. Regarding the files, I indeed referred to the "/5Zone_IdealLoadsAirSystems_ReturnPlenum.idf" - the same which you have referred to in your comment. It certainly was of help.

Another question, shouldn't both the sensible and latent thermal (cooling/heating) rates be taken into account for assessing the loads?

MHW's avatar MHW  ( Aug 27 )
1

"[...] shouldn't both the sensible and latent thermal (cooling/heating) rates be taken into account"? From the IO Reference: "All of the ZoneHVAC:IdealLoadsAirSystem loads and energy use are reported for Sensible Heating, Latent Heating, Total Heating, Sensible Cooling, Latent Cooling, and Total Cooling". I may be misunderstanding your question.

Denis Bourgeois's avatar Denis Bourgeois  ( Aug 27 )

@Denis Bourgeois actually what made me to ask this question is I was looking at the results generated by the EnergyPlus model for a weather environment classified as 1A. This is highly hot climate. When I compared the sensible and latent cooling loads, sensible loads turned out to be much higher - I was expecting latent cooling loads to be higher, but I understand this is mainly driven by the outdoor humidity than the People occupying the buildings? - I hope my question is clearer?

MHW's avatar MHW  ( Aug 28 )
1

@MHW, I would indeed expect outdoor humidity driving latent cooling loads (more so than internal loads) in CZ1A (hot & humid). Although this would ultimately depend on what's going on in that facility (e.g. greenhouse? industrial laundry/cleaning?), and on selected "Dehumidification Control" options. Fortunately, the ZoneHVAC:IdealLoadsAirSystem object allows you to output/compare "Outdoor Air" vs "Supply Air" vs "Zone" Latent Cooling Energy. You can do the same for Sensible or Total, allowing you to pinpoint when/where sensible vs latent loads are being picked up.

Denis Bourgeois's avatar Denis Bourgeois  ( Aug 28 )

@Denis Bourgeois perfect that clarified my doubts to a greater level. I think the "Humidification/Dehumidification Control" might be a factor too which influences the latent heating and cooling loads, as the aim is to maintain humidity close to 50%.

I have attached the image of the "IdealLoadsAirSystem" under Edit-1 of the original question. This is from my current (baseline) model. Since, the "Humidification Control" is chosen to be "None" - it might be leading to low latent thermal loads, correct me if I am wrong.

MHW's avatar MHW  ( Aug 28 )

2 Answers

Sort by » oldest newest most voted
1

answered Sep 2

updated Sep 2

MHW, I concatenated my initial August 26 comments as an answer to your original question. Cheers.


@MHW, you're correct on the use of ZoneHVAC:IdealLoadsAirSystem to address your needs. Note: I updated your Engineering Reference link to 24.1 (updated since from 8.0). I suggest you check out as well the 24.1 IO Reference:

  • how required energy is metered/reported
  • required fields
  • actual outputs
  • better documented in general

You may also find it insightful to consult related issues, past or current. And consulting any example file(s) that come with EnergyPlus is always useful.

(see above for follow-up Q/A)

Preview: (hide)
link

Comments

2

Thanks for providing us like this good info

Freddie Townsend's avatar Freddie Townsend  ( Jan 22 )
1

answered Jan 24

You're on the right track using the ZoneHVAC:IdealLoadsAirSystem in EnergyPlus; it is one of the great ways to make an estimation of heating and cooling loads without designing a full HVAC system. Focus on output variables you mentioned, especially the total heating and cooling rates, to get accurate baseline data. The use of HVAC estimating services allows checking your model's assumptions against real-world applications and enables better comparisons for your advanced model.

Preview: (hide)
link

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops

Careers

Question Tools

1 follower

Stats

Asked: Aug 25

Seen: 567 times

Last updated: Jan 22