# Differences between annual results for UDI and calculated from ILL

Hello everybody,

Call me picky, but, I have been comparing the results from the UDI from annual read results I and annual read results II (I input the ILL “space_0” so both results would include the blinds). As they were slightly different (with differences in some points of up to 7-10% depending on the simulation) I opened the ILL “space_0” and calculated it myself in excel. My results show an average difference between my calculated percentages and the annual read results II is 1%, the problem is that 1% is not consistent throughout the points.

My guess is that the annual read results I interpolate the results to get the luxes for the hours like 9.0 instead the 9.5 of the ILL, however, the annual read results II, as they are closer to my calculations do not appear to do that.

So, I wanted to ask, why are they different? is there a mistake? is the calculation different from mine? why is this happening?

I have uploaded my excel so you can see the differences. Basically it is the ILL but on top you have the calcs and results I obtained from both annual read resultsEdimburg_Office_south_C3_0_space_0 FOR FORUM.rar (8.0 MB)

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Well, I prefer to call you a great building simulation practitioner who takes the time to validate the results of the study.

There are two main differences between Read Annual Result I which uses Daysim’s difference is Daysim’s binaries to calculate the UDI and Read Annual Result II which does a calculation similar to what you have done manually.

1. Daysim counts for daylight saving, the other component doesn’t.
2. Daysim tries to model the behavior of the person inside the space and makes several assumptions on how they would behave in different conditions. That is where the difference is coming form. You can read more about this on Daysim’s website: See this and this as the starting point.
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Thanks for that @mostapha,

I also checked the points with higher differences and they are those with UDI values below the 70’s, so, it makes sense.

Regarding the results on the read results II… Checking the code, I have done the same in my manual calculations than the component (correct me if I am wrong), so, there shouldn’t be that inconsistent 1% difference. Hence, there is something that I am missing. So, what is causing that?

For that one I need to check your file and that will take some time for me to get a chance to do it! I hope someone else can check the files before then.