Setting our WeatherCat Heating/Cooling Degree Days ???

[elagache]

Dear WeatherCat "power users,"

So you think you know absolutely - everything - about WeatherCat - don't ya'!

So what have you set your Heating/Cooling Degree Days to?

You Heating/Cooling Degree what'sas? 

I do not jest.  Go to Misc2 of the preferences and in the right column about 2/3s of the way down are those settings.  Don't believe me?  Go to page 169 in the current WeatherCat manual.  Quoting from the WeatherCat manual:

Individual base temperatures can be set for both heating degree days and cooling degree days in the preferences (these temperatures also affect HDD's and CDD"s on NOAA reports). Tick the ?Show On Year Over Year Statistics to display these values on the year over year statistics.

Since this does appear on our NOAA reports, we should be concerned about these values.

That just leaves one tiny problem.  What in da' blankety, blank are Heating/Cooling Degree Days?

Well it took some web searching but I found this short piece explaining the concept:

http://www.degreedays.net/introduction

In a nutshell, it is an attempt to correct for the effect of the actual weather when attempting to assess if your structure is more or less energy efficient.

Here is another more complicated article:

http://www.energylens.com/articles/degree-days

I'm kind of busy right now with fuel injection issues, but if somebody could look over this stuff and tell the WeatherCat community how we should be setting this thing - I for sure would be appreciative!

Cheers, Edouard 

[Blicj11]

Very interesting reads. Thanks for posting. I think I understand the theory. Now we some genius to tell us his or her thinking on how to set the HDD and CDD.

[Bull Winkus]

I'm just guessing, but? I suspect the individual base temperatures for HDD's and CDD's are anticipated baseline temperatures for a structure's interior, to be compared to external temperatures for relative energy consumption analysis, or something. Seems like it would be more useful and accurate, if it simply grabbed the internal temperature.

I have seen it, but I didn't delve into it. I haven't even looked at the NOAA reports yet.

 

[Blicj11]

I have made it this far:

I reason that where I live, the CDD and the HDD should not be set at the same temperature, because that implies that above that temperature, you have the AC on and below that temperature you have the heat on. This is not the case for living at high altitude. We do not ever reach a temperature that requires air conditioning. We just open the windows. So the CDD can be set fairly high. For me, somewhere between 68 and 70F seems reasonable.

On the other hand, HDD should be set at the (external) temperature below which, you need to turn on your heat. Where I live, there a gap between HDD and CDD because there is a temperature range that is comfortable enough that you require neither cooled nor heated air. It is a little more complicated because we have seasons here. During the winter the HDD is probably around 60 to 65F, whilst in the summer the HDD is likely lower by at least 10 degrees.

I conclude I will use the winter setting for HDD year around, because we have far more winter months than summer months at this elevation. We have about 8 colder months and 4 warmer months.

I have been playing with these settings today and looking at how they impact the calculated numbers displayed by WC. It's interesting to try to make sense of all this.

Herb, these particular statistics not only display on the NOAA Style Reports, which you are apparently saving for a special occasion to review, but they also show up in your Year Over Year Statistics if you check the box for that option in Preferences.

[elagache]

Dear Blick, Herb, and WeatherCat power users,

Thanks for looking into this for me.  One of these days, I'll also try to make sense of it, but for the moment my "to do" queue simply gets longer and longer . . . . 

Cheers, Edouard

[Bull Winkus]

It seems that the information derived from this dataset is more for statistical observation. I'm not sure if we can benefit from the calculation for a single residence, or location. It might mean more to me if, instead of using an "average of the daily maximum and minimum temperatures," for the baseline, the actual inside temperature were used. I'm sure that the "mean daily temperature" is used to establish the baseline only because of the application as demographic data, and actual baseline is impossible to obtain.

Here's the



Explanation of the weekly and monthly degree day data summaries.

1. Station data

Degree day is a quantitative index demonstrated to reflect demand for energy to heat or cool houses and businesses. This index is derived from daily temperature observations at nearly 200 major weather stations in the contiguous United States. The "heating year" during which heating degree days are accumulated extends from July 1st to June 30th and the "cooling year" during which cooling degree data are accumulated extends from January 1st to December 31st. A mean daily temperature (average of the daily maximum and minimum temperatures) of 65?F is the base for both heating and cooling degree day computations. Heating degree days are summations of negative differences between the mean daily temperature and the 65?F base; cooling degree days are summations of positive differences from the same base. For example, cooling degree days for a station with daily mean temperatures during a seven-day period of 67,65,70,74,78,65 and 68, are 2,0,5,9,13,0,and 3, for a total for the week of 32 cooling degree days.


-=-=-=-=-

Being able to export HDD and CDD tables for creating graphs in Numbers might prove to be very interesting, but only if it were based on actual measured internal temperatures.

 

[mcrossley]

Basing HDD and CDD on the internal temperature would make no sense at all. If you have heating in your house then it may never fall below the HDD threshold (likewise if you have air-conditioning for the CDD). They give you a measure of the amount of heating or cooling you may need to apply in a period. I use separate thresholds for each value as there is a temperate zone between the two where neither hearing not cooling is required.

I have a pretty good correlation between the monthly HDD  total and my central heating gas consumption.

[Bull Winkus]

I see where you're coming from, and quite disagree.

With no heating or cooling energy applied, the structure's internal temperature would still vary from the outside temperature due to convection and radiation loss at night, and solar heat gain during the day. With heating and cooling through energy consumption, the inside temperature is maintained within a comfort range. It is the difference between that comfort temperature and the outside temperature that provides the indirect measure of energy consumption needs, when used as a modulating baseline. Even then, natural daytime solar heat gain and rate of nighttime heat loss introduces a slight error to the correlation between ∆T and ongoing energy consumption. But, this is negligible compared to the error from simply selecting an arbitrary number for the baseline.

The original formula uses mean daily temperature, but is an aggregated measure. Substituting guessed at baselines helps in applying a statistical formula to an individual household. However? In building a table that's insightful of energy consumption for 1 structure, ∆T for the baseline makes more sense. Unless, I'm missing something. I did say that I've never looked at the NOAA reports. Is there something there that makes my observations all wet?

[mcrossley]

Hi Herb, you are right for an individual structure its internal temperature would give a better measure, for that structure, but...

 - Most people heat/cool their properties, therefore that 'natural' unregulated internal temperature is not available to them. Once you apply any heating/cooling then the internal temperature is useless.
 - By deriving the HDD/CDD for a particular property it tells you something interesting about that structure, but the NOAA report is a general report allowing you to compare different locations and/or times. To do that you need a generalised figure, the outside temperature is the standard used to derive those figures.

I don't know how WC does it (I don't use it), but Cumulus calculates HDD/CDD on a running basis based on the current temperature. If you ask it to calculate the values historically it uses the daily average temperature, but that again is aggregated average, not the mean of max/min - though in practice the difference between the two is usually minimal, at least for my location.

[Bull Winkus]

I see. So, Cumulus compares outside temperature to a baseline on a running basis, but compares to the aggregated average calculated over all the samples taken that day?

I'm thinking of it simply in terms of what would be useful to me as an individual property owner. So, all of my speculation, not having looked at the report, was based on building a temperature table where each row in the table contains the outside, inside and temperature differential segregated into negative and positive numbers for HDD and CDD respectively. But, now that I've looked at the report, I see that I was being a little too granular for the NOAA Style Report. It appears that WeatherCat's NOAA Style Report does a daily high and low temperature, averages the two, then subtracts the average from the baseline to get either HDD (if positive) or CDD (if negative).

I'm not completely unconfused just yet. But hopefully, I'm getting there.

I don't suppose Cumulus reports anything to NOAA, or has the option to, does it? I don't think WeatherCat does.

 

[Blicj11]

The clearest source I can find for understanding these calculations is the first link Edouard posted earlier in this thread. Also, in that article is a link to a website where they calculate your heating degree days and cooling degree days based on external temperature data they pull from your WU uploads. Comparing their calculation to WC's calculation produced very similar data. The reason the data is not exactly the same is that WC has more data points than WU, and I believe WC is more accurate.

[WCDev]

WeatherCat uses the hourly data to calculate HDD's and CDD's (not the daily average).

Here's what wikipedia has to say on the subject: https://en.wikipedia.org/wiki/Heating_degree_day

[elagache]

Howdy Stu and WeatherCat building energy efficiency managers,

Here's what wikipedia has to say on the subject: https://en.wikipedia.org/wiki/Heating_degree_day

Thanks for the link.  Indeed it is a very interesting concept and Wikipedia does a good job of giving an overview.  I definitely need to change at least the CDD, however, I need to think back it a bit to decide what is a reasonable value for it.

WeatherCat is truly amazing!    Stu you really rock! 

Cheers, Edouard 

[Blicj11]

Thanks to everyone who has contributed here. After further reflection, I decided to lower my Base HDD to 62? F and raise my base CDD to 75? F. Our altitude is fairly high and the higher CDD is justified by the fact that we do not ever use significant energy to cool down; we just open the windows and turn on ceiling fans. My reasoning for lowering the HDD is that for the months of warmer weather the HDD should probably be set to 58? F. For the months of colder weather, it should be set to 65? F. I compromised at 62? F.

[elagache]

Thanks Blick for sharing with us your thinking on this setting.

That's exactly the sort of considerations I need to ponder to come up with a decent setting for my station.

Cheers, Edouard