Issue with SurfaceControl:MovableInsulation for roof applications

asked 2020-11-12 16:14:16 -0600

Ammar De's avatar

updated 2021-04-02 12:09:19 -0600

I have been working on dynamic insulation systems and I was able to use the surface construction actuator within EMS. Now, I would like to explore the SurfaceControl:MovableInsulation object within energyplus but I am struggling to understand some of the discrepancies that I am getting! I checked the documentation and the two example files that use interior and exterior movable insulation to check how it is modeled. The table below shows a summary of the tests I have been running using the "Material:NoMass" class and CondFD algorithm with a 3 min timestep. I expected that all the matching colors would have similar energy use since I am using the same construction materials but surprisingly they are not the same! some of them are not even close!

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1- I notice a big difference between the results when I add the insulation material as part of the construction compared to when I have it in the movable insulation object which is similar to the issue described in SurfaceControl: Movable Insulation vs Construction Properties @ EnergyPlus. This difference appears to be significant when I consider inside movable insulation (Rows highlighted in yellow) and less significant when I consider outside movable insulation (Rows highlighted in green) as shown in the table. I tried adding the material using both "Material" and "Material:NoMass" classes but the issue still persists.

2- If I consider inside movable insulation, then the results are completely off. It seems there is an issue with the heat balance for the movable insulation. I am reporting the node temperatures in addition to the inside and outside surface temperatures of the roof. When I check these results, I get some temperature values for inside and outside surface temps but for all the roof nodes (including node 1 and last node) the temperatures are always 23 C which I think is the initial temperature. Do you think this issue is related to the materials I am using as part of the roof construction that could influence the heat balance? could it be related to the heat balance algorithm (i.e. CTF vs CondFD) as I can see that everything is related to CTF in the C++ code in Surface Heat Balances With Moveable Insulation. Also could it be related to the surface convection algorithm (inside/outside)? I am using TARP for inside and Adaptive for outside.

3- You can notice that when I use inside movable insulation (#7) with a schedule of 0 (OFF), this results in exactly the same energy use as when the construction has no insulation (#1), however, this is different when using outside movable insulation with a schedule of 0 (#4).

Theses cases were simulated using the CondFD algorithm as I eventually want to include PCM as part of the construction. However, I tried the tests without including a PCM layer and considering CondFD as well as CTF but both showed similar patterns except that CTF results in a large heating energy use (39,267 kWh) compared to the ... (more)

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