How to Model AHU with DOAS in DesignBuilder?

3

asked Apr 25

Anurag_G
51 ●3

updated Apr 25

Aaron Boranian

14375 ●90 ●25 http://bigladdersoftware.com/

Hello everyone,

I am currently working on a project where I need to model an Air Handling Unit (AHU) with a Dedicated Outdoor Air System (DOAS) in DesignBuilder. I am looking for guidance on the best practices and steps to accurately set up this system within the software.

Specifically, I would like to know:

How to configure the DOAS to supply conditioned outdoor air to the AHU.
The process of integrating the DOAS with the AHU in the DesignBuilder interface.
Any tips on setting the parameters for both the DOAS and AHU to ensure accurate simulation results.

Any detailed instructions, screenshots, or references to relevant tutorials would be greatly appreciated.

Thank you in advance for your help!

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7

answered Apr 26

Andy Tindale
191 ●4 ●2

DesignBuilder v2025.1 provides access to EnergyPlus DOAS air loops, and the first beta with this included will be released in the next week or so. If you would like to access a beta now, I suggest contacting the DesignBuilder Support Desk.

link

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1

answered Apr 28

mdedoes
101 ●3 ●4

Hi Anurag, even though you may not be able to model your system exactly in DesignBuilder, there is almost always a way to model airside systems using DesignBuilder's available objects in a way that gives you an accurate estimation of energy use (without having to use the custom EMS or Python scripting). Without knowing your exact system, here are a few ideas that I thought of: - combine the DOAS and AHU into one unit in the model (using a standard AHU in an Air Loop). You - if your AHU serves a single zone, you could model your DOAS as the AHU in the Air Loop, and your AHU as a FCU in the zone

If those don't clear it up, are you able to provide a bit more detail on how your system is set up, maybe a little diagram or something? I may be able to give you a better suggestion.

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Hi Mr. mdedoes,

It is far more complicated than the thing you have mentioned. An AHU is serving multiple zones and a single DOAS is connected to multiple AHUs. Unfortunately I don't have a diagram to show the same.

Can you make the most closest representation of this scenario?

Anurag_G ( Apr 28 )

1

OK, that helps. To make it easiest on yourself, I would model the system as if each AHU had its own DOAS unit and include all components for both the DOAS and the AHU in the AHU object in DesignBuilder. Based on your comments to other users, you can put both a DX coil and a chilled water coil in the same AHU and control them using different setpoint managers. You'll just have to make sure that the setpoint manager for the DOAS coil is immediately downstream of the coil in the model.

Hope this helps!

mdedoes ( Apr 28 )

Did you mean immediately downstream of DOAS coil and immediately upstream of the chilled water cooling coil? Also, do you recommend adding an additional fan too? I am not sure whether DB allows that

Anurag_G ( Apr 28 )

You may have to mess with the locations for the setpoint managers (I always have to do it a bit by trial and error), but I'm pretty sure you need one immediately downstream of the DOAS coil. The location for the setpoint manager for the second coil may be flexible.

And no, I don't think DB will let you put 2 supply fans in, so just enter the pressure in DB as the sum of the pressure of both of your fans.

mdedoes ( Apr 28 )

As you have mentioned trial and error here to replicate the closest model, I also wanted to know whether you have tried the heat recovery option in AHU? The final I/O summary report provides the same energy consumption whether you add a heat recovery wheel or not. Any thoughts on why this happens?

Anurag_G ( Apr 28 )

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0

answered Apr 26

Keigo
4474 ●1 ●52 ●25 https://www.linkedin.c...

As long as I know, DOAS and AHU in series can't be modelled in DesignBuilder.

AirLoopHVAC:DedicatedOutdoorAirSystem was implemented for the first time in EnergyPlus V9-2-0.

The latest DesignBuilder, v7, uses EnergyPlus V9-4-0 as a calculation engine, but the user interface of DesignBuilder does not support to model AirLoopHVAC:DedicatedOutdoorAirSystem. My sense is that DesignBuilder supports only 20 to 30% of the whole EnergyPlus features.

The user interfance of OpenStudio also does not support to model AirLoopHVAC:DedicatedOutdoorAirSystem.

I suggest using EnergyPlus directly or IES-VE. Please note that the latest version of EnergyPlus should be used because there are many bugs in the old versions. You can search AirLoopHVAC:DedicatedOutdoorAirSystem on UnmetHours and find bug reports.

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Comments

Designbuilder does have a default template as DOAS,DX precool with Heat Recovery but that does not meet my requirements for AHU with DOAS. As the DOAS is serving to precool the air before it enters the AHU and gets distributed to the spaces, do you recommend using 2 cooling coils ( 1 DX coil and another Chilled Water Coil) to closely resemble the scenario?

Anurag_G ( Apr 26 )

2 cooling coils ( 1 DX coil and another Chilled Water Coil)

That's quite different from DOAS + AHUs, you know.

Answers are shown on this page. You can model with EnergyPlus, IES-VE, or DesignBuilder v2025 as Andy mentioned. I haven't tested DB v2025.

Before AirLoopHVAC:DedicatedOutdoorAirSystem was added to EnergyPlus, I used to model DOAS + AHUs with DOAS + Variable-speed FCUs in EnergyPlus. However, DesignBuilder v7 can't even model variable-speed FCUs. I'm not sure the reason you stick to DB. I recommend using EnergyPlus directly for your better understanding of energy simulation.

Keigo ( Apr 28 )

Our organization is using DB for almost a decade now I guess. Thats the reason we have still stick to DB and finding ways to mimick the closest representation to this. I am not sure how much will DOAS as AHU and AHU as an FCU inside the zone will closely replicate the situation as wrote by Mr. Mdedoes

Anurag_G ( Apr 28 )

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