NOAA Heat Degree Day

mcrossley · **Posted:** Fri Dec 23, 2011 2:46 pm

Is this working correctly or is my understanding wrong.

I changed the "Heating threshold" on the NOAA setup dialog from 18.3 C to the UK standard 15.5 C.

But looking at the reports in the viewer and 'updating' the heat degree days does not change? Though the report does reflect the new threshold value at the bottom.

steve · **Posted:** Fri Dec 23, 2011 2:52 pm

Degree days are calculated on a minute-by-minute basis and the totals for each day are stored in dayfile.txt. Changes to the threshold values cannot therefore apply retrospectively. But: if the dayfile.txt entry doesn't have the degree days in it, then it uses the day's average temperature to produce a 'simplified' heating or cooling degree days figure (but obviously never both at the same time) and in that case it does use the current threshold settings.

mcrossley · **Posted:** Fri Dec 23, 2011 3:26 pm

Got it. Thanks Steve. As the bulk of the data will have calculated retrospectively I may look at changing the baseline. I think this is worth a wiki entry as changing the baseline WILL change the baseline figure on updated reports, but the data will still reflect the original baseline.

entered from my phone so excuse errors

steve · **Posted:** Fri Dec 23, 2011 3:37 pm

mcrossley wrote:

changing the baseline WILL change the baseline figure on updated reports, but the data will still reflect the original baseline.

Yes - I'd assumed that people would set their required thresholds once (if they weren't using the defaults) and then leave them. It's not practical to allow accurate calculation of the degree days and allow 'what if' experimentation with the thresholds.

mcrossley · **Posted:** Fri Dec 23, 2011 3:59 pm

v. true, I just discovered that the UK standard was different from the default

steve · **Posted:** Fri Dec 23, 2011 3:59 pm

I've amended the help...

steve · **Posted:** Fri Dec 23, 2011 4:01 pm

mcrossley wrote:

v. true, I just discovered that the UK standard was different from the default

I didn't even know that there was a UK standard! Interesting to note that being tougher than our trans-Atlantic cousins, our heating threshold is lower than theirs :lol:

mcrossley · **Posted:** Fri Dec 23, 2011 4:06 pm

Wusses

Some American friends said that was one of things that they took some getting used to over here; we don't have the heating on 24x7

Metanges · **Posted:** Fri Jul 13, 2012 6:27 pm

steve wrote:

Degree days are calculated on a minute-by-minute basis and the totals for each day are stored in dayfile.txt. Changes to the threshold values cannot therefore apply retrospectively. But: if the dayfile.txt entry doesn't have the degree days in it, then it uses the day's average temperature to produce a 'simplified' heating or cooling degree days figure (but obviously never both at the same time) and in that case it does use the current threshold settings.

Hello,

I'm a little bit surprised because on my dayfile.txt, I can see I have Heating Degree Days and Cooling degree days not null together. Every days except one, when the cooling degree days is not null, the heating degree day is also not null.

I don't understand how it is possible because Cumulus is calculating the both with the same temperature average and the same trigger.

Can someone help me ?

Thanks

Claude0

steve · **Posted:** Fri Jul 13, 2012 6:50 pm

Metanges wrote:

I'm a little bit surprised because on my dayfile.txt, I can see I have Heating Degree Days and Cooling degree days not null together. Every days except one, when the cooling degree days is not null, the heating degree day is also not null.

I don't understand how it is possible because Cumulus is calculating the both with the same temperature average and the same trigger.

The figures in dayfile.txt aren't calculated using the average temperature, they are calculated on a minute-by-minute basis throughout the day. It's perfectly possible, during the course of a day, for the temperature to be below the heating threshold at some time, and above the cooling threshold at another time.

Unless you have reason to believe that it's not calculating correctly?

Metanges · **Posted:** Sat Jul 14, 2012 9:29 pm

OK thank you very much for your answer

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NOAA Heat Degree Day

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