Unexpected design-day heat flows vs U-values in simple building

DamonHD
21 ●3

Hi all,

I am trying to replicate a simplified form of the initial scenario from my paper:

https://www.mdpi.com/2071-1050/16/11/...

a single-zone square bungalow (though 4 equal-size rooms will appear inside in due course) , no floor losses, roof and walls same U-value, no windows or ventilation losses or occupants or other incidental gains. With these values and equilibrium conditions:

 IWL (Internal Wall Length) = 4m, thus whole external wall length 8m.
 IWH (Internal Wall Height) = 2.3m
 EWRU (Effective Wall and Roof U-value): 0.61 W/m2K
 Wall and roof surface: (4x18.4m2 + 64m2) 137.6m2
 Floor non-conducting
 Interior and exterior temperatures at design conditions: 21C / -3C

I calculate in the paper and by hand:

 Expected heat demand at design conditions: ~2000W

But the winter design day in the E+ model below shows ~1400W for several things in eplusout.eso, eg: ZONE ONE,Zone Predicted Sensible Load to Setpoint Heat Transfer Rate [W].

https://github.com/DamonHD/BuildingMo...

I am likely doing something very basic wrong for a 30% error!

You will see that I am a novice at E+, and that this is a work in progress, and that I may just be looking at the wrong things!

Any clues to point me in something like the right direction gratefully received!

Comments

Did you check that the floor has no heat transfer? That would be the first thing I checked.

rraustad ( Apr 9 )

I believe that the floor is transferring almost no heat, eg see the eplusout.eso file:

13,1,ZONE SURFACE FLOOR,Surface Average Face Conduction Heat Transfer Rate [W] !Hourly

13,-0.0018914190241975089

But also I am seeing the walls and roof transmit LESS heat than I expect, ie the building is losing LESS heat than expected given the conditions.

Thank you for your time!

DamonHD ( Apr 9 )

You can execute ReadVarsESO.exe or RunReadESO.bat (double click either file) in the same folder as your eso and you will get eplusout.csv where you can plot time-series data in excel. This may help identify sources of error.

rraustad ( Apr 9 )

Thanks: I did not know about that utility! I am having a little difficulty with the version on my Mac, but I'll get there. At the moment the .eso file is short enough to read by eye and each hour of the design day seems pretty much identical, and identically wrong/unexpected. Thanks again for pointing out the tool.

DamonHD ( Apr 10 )

When running your model with Birmingham climate data, getting ~1830W (vs 1600W) for heating. Switching the following: