Re: [TRNSYS-users] TRNSYS-users Digest, Vol 87, Issue 13

[Nick LaHam <ndlaham@gmail.com>]

Laurent,

There is no flat plate HX module in TRNSYS yet, just HX simple models that either allow you to input "constant effectiveness" (Type91) or "overall heat transfer coefficient" (Type5). 

This makes things kind of difficult because those two inputs are determined by the fluid properties, flowrate, temperature, number of plates, material, area of plates, etc. SInce the flowrates and temperatures can be changing, so can the overall HTC. Also, you need to find a way to determine the overall HTC based on the geometry of the HX. This requires a lot of iterative calculations and is not that easy to accomplish.

Currently as a workaround, I am using GEA's software which is pretty good to size a flat plate heat exchanger for me, and then I give it the parameters that I would use it TRNSYS. It let's me select different size heat exchangers and then eventually, the software will spit out it's "Overall HTC" (in W/m^2-K) and a "nominal surface area" (in m^2). I simply multiply the values and use this as my input for "Overall heat transfer coefficient" in Type5b (I have found the counter flow version is the closest match for flat plates when using an overall HTC). You can login to the software as a web app here or download it too once you register a username. http://flatplateselect.com/site/pub/login.aspx?ReturnUrl=%2fsite%2fDefault.aspx

This isn't a perfect method obviously, because the overall HTC will change with varying temperatures and flowrates, but as long as you are in the ball park, it will be pretty close. If your flows and incoming temperatures don't change, then you will be even more accurate. If you only have one variable that changes frequently, you could develop a fit curve equation that determines the overall HTC and use that equation as an input for the "overall heat transfer coefficient". But this would require going through the GEA software and spitting out multiple outputs by changing your single input at several different points. Then you would have to put the data in excel or something similar to find an equation.

This is the best method I have come up with so far, but I am currently developing a set of equations using EES from Nellis & Klein's "Heat Transfer" book, that will mimic a flat plate by actually supplying dimensions, # of plates, thermal conductivty of plates, etc. It will also allow me to supply inputs that vary and should always give me an accurate heat transfer coefficient. I plan to tie the inputs to TRNSYS inputs (possibly using the Type66, or just perhaps writing new Fortran code) and execute the EES code in TRNSYS eventually. I'm working on it, but I"ll let you know how it turns out. The EES side is basically done, but I need to verify the equations.

Hope this helps.

Nick LaHam

2012/3/9 <trnsys-users-request@cae.wisc.edu>

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Today's Topics:

  1. type 56 (gabriela vlad)
  2. Natural ventilation (Chou Shen)
  3. Water to Water Plate Heat Exchanger (REYNIER Laurent)
  4. on cooled ceiling (Enyuan Hu)


---------- Forwarded message ----------
From: gabriela vlad <gabi_ev@yahoo.com>
To: "trnsys-users@cae.wisc.edu" <trnsys-users@cae.wisc.edu>
Cc: 
Date: Fri, 9 Mar 2012 03:34:57 -0800 (PST)
Subject: [TRNSYS-users] type 56

Dear users,

 

I want to model a building with type 56.  I divided the building into several thermal zones but two of them which are adjacent zones aren't separated by a wall (there is only air between them). Please, give me your opinion, How can the two zones be separated?

---------- Forwarded message ----------
From: Chou Shen <csz59@mst.edu>
To: trnsys-users@cae.wisc.edu
Cc: 
Date: Fri, 9 Mar 2012 08:24:34 -0600
Subject: [TRNSYS-users] Natural ventilation
Hello,

I am trying to use TRNSYS to simulate the situation when a building takes natural ventilation rather than air conditioning system in swing seasons. In that way, the air conditioning turns off when outdoor temperature is in the range of [tlow, thigh]. I want to see how much energy saving is achieved by implementing natural ventilation. Can I achieve my goal? How can I implement natural ventilation in TRNSYS? Thanks!

--
Chou Shen
Graduate Research Assistant
Department of Civil, Architectural & Environmental Engineering
Missouri University of Science and Technology





---------- Forwarded message ----------
From: REYNIER Laurent <Laurent.REYNIER@cstb.fr>
To: "trnsys-users@cae.wisc.edu" <trnsys-users@cae.wisc.edu>
Cc: 
Date: Fri, 9 Mar 2012 15:52:28 +0000
Subject: [TRNSYS-users] Water to Water Plate Heat Exchanger

Dear TRNSYS users,

I’m searching for a reliable model of a water-to-water plate heat exchanger.

Can you give me your opinion on the one you are using and which TRNSYS type you use for simulation.

 

Thank you in advance for your help.

Sincerely yours.

Laurent.

 

 

Laurent REYNIER

Département ESE/ Division Energie/ Ingénieur Etudes et Recherche

Centre Scientifique et Technique du Bâtiment

84 avenue Jean Jaurès - Champs-sur-Marne - 77447 Marne-la-Vallée Cedex 2

Tél : 01 61 44 80 55

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---------- Forwarded message ----------
From: Enyuan Hu <bearcharge@gmail.com>
To: trnsys-users <trnsys-users@cae.wisc.edu>
Cc: 
Date: Fri, 9 Mar 2012 11:36:37 -0500
Subject: [TRNSYS-users] on cooled ceiling
Dear TRNSYSers,

I was wondering if anyone can help me on the cooled ceiling mode. Specifically, I have several questions:

1. how should the cooled ceiling layer be defined? can we define it as part of the roof layer (category EXTERNAL and orientation Horizontal) or should we define it separately? separate definition is my feeling after reviewing some literature.

2. how should we set up the layer parameters? in the manual, it indicates that parameters like norm area can be obtained from the producer, does that mean that's the only way to reasonably set up parameters and otherwise there will be problem?

3. if would be best if some user can generously provide an example on this. This may be asking too much, but I really think it would help indeed.

Thanks.

Enyuan

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