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mikeb4444
Posts: 2
Registered: ‎01-17-2013

Heat generation hydronic application

154 Views, 3 Replies
02-28-2013 06:38 PM

I am having trouble using the Heat Generation boundary condition with the Temperature Dependent option enabled.  My application is a simple room with an insulated concrete floor heated with hot water.  I want to just apply a constant temperature to the floor and see what happens to the temperature distribution in the room.  Maybe just a constant temperature boundary condition on the floor surface would work, but it seems like a heat generation option is more applicable.  When I tried the simulation it converged well, but the temperatures were in the millions. 

 

A am really not understanding the input parameters for the Temperature Dependency options and I cannot find any guidance in the help areas.  The input dialog box has two columns - Value and Temp.   What goes in the "Value" column?  Is this just equivalent to the independent axis or x axis and the temp is the dependent axis?  Then why have the numbered rows on the left?   If I keep the Temp constant this should give me a horz line, right?, no matter what the "Value" is? 

 

Thanks

Mike

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Product Support
wildej
Posts: 953
Registered: ‎08-25-2011

Re: Heat generation hydronic application

03-01-2013 03:35 AM in reply to: mikeb4444

Hi Mike,

 

I think you are correct, best to use a volumetric heat load here. I would suggest initially running a steady state model with a minimal hea tload anf without the temp depedent load before switching to a table driven load and of course, a transient analysis. The steady state would be good just to ensure that the setup is sound before moving to a more complex setup and longer runtimes.

 

The table is heat load vs temp, so you can control the amount of energy inputted to the model based on the temp at a surface that you dictate.

 

Do you have suitable outlets or film coefficients on the external walls of the model to allow the heat to escape as it would in reality?

 

Hope that helps,

Jon



Jon Wilde
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New Member
mikeb4444
Posts: 2
Registered: ‎01-17-2013

Re: Heat generation hydronic application

03-04-2013 08:52 PM in reply to: wildej

Thanks for the clarification.  I was able to get the basic heat generation and the temp dependent heat generation model to work.  Also found out that letting it run as many iterations as it wants is important in the temp dependent mode.   Basically, this type of analysis tells me that the model design at the given heat generation rate is capable of keeping the room at the temp I want. 

 

However, I am really wanting to use the software to minimize the heat generation required to maintain a certain room temp based on different choices in materials and material thicknesses.  Questions like how much better is 3 inches of insulation versus 2 inches.  How much better is double pane windows versus single pane. 

 

I think I can do scenario trial and error to get the minimum heat generation (btus/ft3/s) that will just provide the temp in the room I want (using a basic, non temp dependent analysis).   Then I can change the material or material thickness and do another set of scenarios to determine the new heat generation requirement to just provide the same temp as before.  Calculating and comparing the total heat generation difference from before and after the material changes with the same temp allows me to determine if the material change is cost effective.  This method seems cumbersome.  It would be easier to have CFD tell me the heat generation required to maintain the same temp with the new material type or material thickness.   Another way of thinking about it is what is the total steady state heat loss from the room based on a set of materials and given boundary conditions for a desired room temp. 

 

Seems like a reasonable request, but it might be one extra step that's a lot of work for the software.

 

MIke

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Product Support
wildej
Posts: 953
Registered: ‎08-25-2011

Re: Heat generation hydronic application

03-05-2013 12:11 AM in reply to: mikeb4444

Hi Mike,

 

I can certainly appreciate how useful this would be. Right now it is not something that we can do automatically although CFD is set up to enable you to run multiple scenarios and then make direct comparisons with minimal setup.

 

Have you looked at cloning the designs/scenarios and also at summary parts/points/plots? You could also use the solver manager to batch run all of these. If you are using Sim 360, they would also be able to run in parallel.

 

Regards,

Jon



Jon Wilde
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