Difference of heat transfer between Kiva in E+ and Kiva software

asked 2018-10-16 01:07:50 -0500

Alexis
545 ●1 ●9

updated 2018-10-18 08:50:17 -0500

I would like to simulate the ground temperature and the heat transfer floor/ground with Kiva. My slab is only concrete (conductivity = 2), 20cm, no insulation. The ground is sand.

image description

Additional informations : My project is in Indonesia (so hot ground temperature), and my inside temperature is set to 24 C for all the year.

I have used the kiva software, have set the good parameters (I think), the good weather file. I get what follow : image description
I dont know if these results are corrects but they are not inconsistent in my opinion.

Now, I have tried to use Kiva in E+, I followed the exemple ZoneCoupledKivaSlab, changed the outside boundaries conditions, deleted the sitegroundtemperature : buildingsurface, but when I simulate my model, it says that my cooling load is equal to 0W for all the rooms at the ground floor. So it means, my ground cools completely my rooms. No need AC. Practical but not very true I think.

My questions : In E+, what others parameters I need to set to have some consistent results ? What did I forget or what wrong parameters did I set ?
And In your opinion, my results with Kiva software seems consistent ? Can I use these temperatures in sitegroundtemperature : buildingsurface ?

Thank for your help

UPDATE : Below my settings for Kiva and E+ :
image description
What I dont really understand :
- in Kiva, is how to model my building, my project is a rectangle of 40 m x 14m, I didnt success to model it correctly so I have let the default number.
- in E+, what are these "surface segment exposed" ? I suppose that is the segment of my floor in contact with the ground.
In E+, there are not a lot of parameters so I dont know where I am wrong, it seems quite easy.

Link to my model and kiva file : https://drive.google.com/drive/folder...

Comments

I suggest you try the latest version of E+ (version 9.0), as there have been several bugfixes related to Kiva in subsequent releases.

shorowit ( 2018-10-18 09:33:49 -0500 )edit

I have downloaded the E+ 9.0, but the results dont make sense for me. According to the zone loads component summary, the heat transfer is -400 kW for a room of 300m2.

Alexis ( 2018-10-19 03:30:22 -0500 )edit

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answered 2018-10-16 12:54:13 -0500

Neal Kruis

4675 ●9 ●17 http://bigladdersoftware.com/

Here are some questions to look into:

What are the actual zone temperatures in EnergyPlus? Are they different than the constant 24C assumed in Kiva?
What are the boundary conditions settings in Kiva and EnergyPlus (Foundation:Kiva:Settings)? Are they identical? How deep is your deep-ground boundary and what type of boundary condition is it?
Are the material properties and dimensions identical in both tools?

(Perhaps you can edit your question to add the relevant Kiva YAML inputs and EnergyPlus IDF objects?)

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Comments

I have updated my answer with some screenshots, but I answered to your questions below.

In Energyplus, during my hours of operation schedule, my inside temperature is close to 24C (tolerance : ± 1 C). I checked the output zone mean air temperature, my setpoint is reach. However, the inside T is different during the night because no AC but I didnt take into account this in Kiva. I have set a constant T.
Yes same boundary conditions. My settings for deep ground boundary is "autoselect". I have followed the example.
Material properties are same. I have only concrete, even for wall.

Alexis ( 2018-10-16 20:27:26 -0500 )edit

Try changing your deep ground boundary condition to ZeroFlux. The Autoselect option will change the depth of the water table depending on the altitude of your site. The ground water can have a significant cooling impact on your building.

Neal Kruis ( 2018-10-17 09:37:56 -0500 )edit

I have changed this parameter but now the heat transfer is positive so the contrary of what kiva software give me. And I am surprised, according to zone loads component summary, for a room of 300 m2, I have +100 kW of heat gain only through the floor.
Is it make sense if I use the Kiva software temperatures in "sitegroundtemperature : buildingsurface" ? Please, If you have time, would it be possible for you to look at my file provide above

Alexis ( 2018-10-17 20:22:33 -0500 )edit

It looks like you have 12 zones with slabs. Each with different sizes. You need to compare each of these to a separate Kiva simulation with the same floor shape. I also noticed all of your SurfaceProperty:ExposedFoundationPerimeter objects are fully exposed. Unless your zones are not adjacent, this is likely not the case. Take a look at the documentation here.

Neal Kruis ( 2018-10-22 10:12:56 -0500 )edit

Hi, I have been following this discussion since the beginning, if I want to do the same thing, what variable do I need to check in Energy Plus result to compare with the result from separate kiva simulation to validate the model? Thank you