Unexpected design-day heat flows vs U-values in simple building
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!
UPDATE:
I fudged things to get to 2025W heat demand:
https://github.com/DamonHD/BuildingMo...
I'm not entirely happy with it (I don't understand enough) and there are some coordinate errors later fixed, but it's progress. Thanks for all suggestions.
Did you check that the floor has no heat transfer? That would be the first thing I checked.
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!
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.
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.
When running your model with Birmingham climate data, getting ~1830W (vs 1600W) for heating. Switching the following:
... gives ~2121W (+16%). Not stating you should apply these - but maybe dig a bit deeper into environmental parameters. Cheers.