[Greenbuilding] HDD and how they are calculated (daily avg. vs hourly avg)

RT Archilogic at yahoo.ca
Mon Nov 21 10:46:37 CST 2011


On Sun, 20 Nov 2011 22:09:39 -0500, Reuben Deumling <9watts at gmail.com>  
wrote:


> HDD calculated based on a simple average of the min and max temperature  
> in a day is not going to be the same number as the HDD calculated based  
> on,
> for instance, an average of 24 hourly readings.
>
> My question is whether any of you know of attempts to quantify the
> discrepancy between the two methods for calculating HDD?


Reuven;

My head is still a bit muddled but if I understand your question correctly:

Just now I opened up a spreadsheet and created a column with 24 hours  
listed and in a separate column, some hourly temperatures for a very COLD  
day (most likely very sunny too)/night.

It then occurred to me that I needed to convert those temps from Celsius  
to Fahrenheit, hence a third column.

Then below the columns of hours and corresponding temps, I put in the  
spreadsheet's MIN and MAX functions to find the values and then the  
spreadsheet AVERAGE function to get the average of the MIN and MAX.

Then below that, I put in the spreadsheet's AVERAGE function again, this  
time to find the average for the entire column of hourly temps.

======= Copied from the spreadsheet =======

Time	Deg C	Deg F
0:00	-38	-36.4
1:00	-39	-38.2
2:00	-40	-40
3:00	-41	-41.8
4:00	-41	-41.8
5:00	-41	-41.8
6:00	-42	-43.6
7:00	-41	-41.8
8:00	-40	-40
9:00	-38	-36.4
10:00	-37	-34.6
11:00	-34	-29.2
12:00	-30	-22
13:00	-27	-16.6
14:00	-28	-18.4
15:00	-29	-20.2
16:00	-29	-20.2
17:00	-29	-20.2
18:00	-30	-22
19:00	-30	-22
20:00	-33	-27.4
21:00	-35	-31
22:00	-37	-34.6
23:00	-37	-34.6
24:00:00	-38	-36.4

	Min	-43.6
	Max	-16.6
	Avg Min/Max	-30.1
	Avg 	-30.75454545

=========== End of copied material =====

As you can see in the above, the "discrepancy" between taking the average  
of the minimum and the maximum for the day vs the average of the 24 hourly  
temperatures for the day, is as one of my former profs (of East Indian  
descent) from WatJohn's faculty who used to (try) teach us Archies math  
used to say "negijiboo".


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  c a >
(manually winnow the chaff from my edress if you hit "reply")




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