topic Re: Autodesk CFD flow and temperature distribution help in CFD Forum

Autodesk CFD flow and temperature distribution help

Anonymous — Wed, 15 Jul 2020 00:02:24 GMT

Hello,

I'm Juan and I'm quite new to CFD(CFD 2019) and in the HVAC topic in general. I'm currently doing my engineering capstone project. And I'm in the middle of it all so far. My goal is to create my home model that's realistic and accurate at first in terms of flow and temperature distributions and to create improvements on it to be shown on a second simulation. There's 7 supply vents and 1 big return vent in the residential home model. I used Autodesk Revit 2019 to design this model. The screenshot below show my progress so far. The left plane is the velocity plane, which seems to be in working order. The plane on the right is the temperature plane. I assigned a 72 degree inlet temperature in the supply vents. However, it seems to be that the temperature going out of the supply is the same throughout the room(the whole room is colored blue). This doesn't seem accurate and I've been trying to find a way of fixing it. Could anyone give advice on how to work around this? Thank you in advance!

Re: Autodesk CFD flow and temperature distribution help

marwan_azzam — Wed, 15 Jul 2020 12:00:59 GMT

Hello Juan,

Any chance you can provide the support share file of your model (*.cfz) in zipped format?

Marwan

Re: Autodesk CFD flow and temperature distribution help

Anonymous — Thu, 16 Jul 2020 01:05:36 GMT

Here's my latest support file.

Re: Autodesk CFD flow and temperature distribution help

marwan_azzam — Thu, 16 Jul 2020 21:31:47 GMT

Hello,

Thank you for sharing the model.

The only thing I found, so far, are some extra P=0 boundary conditions.

You state the following:

"There's 7 supply vents and 1 big return vent in the residential home model."
The 1 big vent, I assume, is surface # 2104. You also have three other surfaces, internal to the model at that, with a P=0 boundary condition as shown in image below.

I deleted the extra 3 BCs and am rerunning the model now.

Marwan

Re: Autodesk CFD flow and temperature distribution help

Anonymous — Thu, 16 Jul 2020 21:43:59 GMT

Those three other sources with P=0 serves as a transfer grille where air could circulate out of each room back into the one big return. I really didn't know what type of condition I need to make them act as transfer grilles. Did I do it wrong by setting P=0 on them?

Re: Autodesk CFD flow and temperature distribution help

marwan_azzam — Thu, 16 Jul 2020 21:50:28 GMT

I see.

Yes, it is wrong to set them as P=0. It will mess up the flow field.

Any BC at an internal surface is not recommended.

These surfaces are at the interface between two Air volumes. Just let them be (no boundary condition) and air will pass through them from one room to another.

Marwan

Re: Autodesk CFD flow and temperature distribution help

Anonymous — Thu, 16 Jul 2020 22:06:59 GMT

I see. Would assigning a higher temperature(boundary condition) to each volume than the supply temperature before hitting solve work in terms of creating some temperature distribution? It looks weird(on the png above) that even the bathroom(the room without supply) is registering 72 degrees as well. Like, shouldn't the air coming out of the supply be cooler than let's say when it's close to the return?

Re: Autodesk CFD flow and temperature distribution help

marwan_azzam — Thu, 16 Jul 2020 22:11:02 GMT

You have air coming in at 72degrees and the humans generating heat. This will create a certain temperature distribution.

The minimum temperature in the model will be 72 degrees.

Marwan

Re: Autodesk CFD flow and temperature distribution help

Anonymous — Thu, 16 Jul 2020 22:24:13 GMT

Well, the bathroom(room without supply) doesn't get any air supply. It shouldn't be at 72 degrees(which it is after solve) when it's a closed space like that. If anything, it should maybe get hotter over time in there.

Re: Autodesk CFD flow and temperature distribution help

Anonymous — Thu, 16 Jul 2020 22:24:58 GMT

Also, is 60W total heat generation enough for each human?

Re: Autodesk CFD flow and temperature distribution help

marwan_azzam — Thu, 16 Jul 2020 22:27:32 GMT

I suppose the 60W value depends on how how hot these people are.

60W is the common value used for an average person.

Marwan

Re: Autodesk CFD flow and temperature distribution help

Anonymous — Thu, 16 Jul 2020 23:20:27 GMT

Other than humans, what else would generate heat constantly that could add more into the temperature distribution?

Re: Autodesk CFD flow and temperature distribution help

marwan_azzam — Thu, 16 Jul 2020 23:52:39 GMT

You can have appliances like a fridge adding heat and lights and television and computers.

Marwan