Degree days

Tom Blackwell_2

I have been crunching numbers and would like to see what others are seeing....

Woodstock Ga. house 3,000 square feet with 2,000 square foot heated basement.

Last month used 298 therms of gas for 33 days. Published degree day data for this period showed 869 degree days. 1429 btu/degree hour and 68,500 btuh input at 17 degree design, based on these consumption numbers.  How does this compare with other areas? Our yearly average is about 3,500 degree days. The 68,500 number yields 13.7 btu/sq ft not accounting for boiler efficiency.

Gordy

A bit dated. 1997 numbers

You can compare the result to the table below to determine how your home is doing relative to other single family homes in cool and cold portions of the U.S. (the states of the Northeast, Midwest, and West). The table has been developed from a U.S. Department of Energy survey that was taken in 1997. It shows that slightly less than one-eighth of all single family homes using propane or natural gas in the Northeast, Midwest, and West used less than 5 BTUs per SqFt per HDD; and about 10 percent used more than 25 BTUs per SqFt per HDD. If your house uses 7.30 BTUs per SqFt per HDD, you are not among the best or the worst. Almost certainly there are things you could do to improve the way your house uses fuel and to save money.Table: Distribution of Single Family Homes in the Northeast, Midwest, and West Census Regions using Propane or Natural Gas as the Primary Space Heating Fuel in 1997

 Range of Energy Use

Realtive Frequency Under 5.0 BTUs/HDD/Sq.Ft.

12.2 percent Between 5.0 and 10.0 BTUs/HDD/Sq.Ft.

39.4 percent Between 10.0 and 15.0 BTUs/HDD/Sq.Ft.

23.9 percent Between 15.0 and 25.0 BTUs/HDD/Sq.Ft.

14.7 percent Over 25.0 BTUs/HDD/Sq.Ft.

9.8 percent



Improved, But More Complex

The method described above is only one approach to benchmarking. A better, but more complex, method separates out the fuel used for space heating from that used for baseload purposes, like water heating. Andy Padian wrote a fine article that describes a such a method in the November/December 1999 issue of Home Energy magazine. (He looked using fuel oil for space heating, a fuel popular in the Northeast.) If your home is using more than 15 BTUs per SqFt per HDD, you should certainly investigate whether your house is wasting energy through baseload or space heating.

An Internet-based tool for analyzing your home is available from the U.S.

 

Gordy

HDD

 If you have a thermostat that has a timer to keep track of how long the system calls for heat in a 24 hour period its nice.



 I just hit the button to see how many hours the boiler ran. Look up the HDD on the weatherunderground.com website. Calc it out from there using the net boiler output.



 It all depends what you are looking for. Using the gross input to see how many therms your burning will not work with my method because the boiler is not always firing during the heat call.



I like to know what the envelope is doing myself. If you want to keep track of gas usage accuratley then you really need to rig up a hour meter to the gas valve.



 I'm running 6-7 btus a sf/hdd. But I only use the main floor sf. The basement is radiant heat also should probably count it, but I think it skews things a bit if I did I drop to around 5-6 btus sf/hdd.



 I use to use the gas bills, but they read one month, and estimate the next.

So each month is not truly accurate for your usage. If they blow the estimated ( and they usually do) they make it up on the actual so I quit doing it that way. That can make you shake your head, and wonder.



I live in the midwest our hdd last year were 6254



Gordy

Brad White

May I add?

When doing a base energy analysis using gas bills, I typically subtract the lowest three months of gas usage (summer usage) and average them. Say J-J-A has 28, 30 and 32 therms, average 30. This is a rough baseline for domestic HW and cooking usage (even if one does less cooking in the summer or one factors in THE GRILLE



Anyway, you subtract this average number from all months to arrive at a net heating therm use.



Oil is easier if DHW is separate, but that is another story, when it was delivered vs. burned. I need three years of delivery records to even start with some accuracy.



But as stated, you can back-calculate and even approximate a heat loss with estimated factors for efficiency and miscellaneous offset gains.



I tried to add a USAF weather packet in PDF form for Atlanta GA which should be close to your area and for what it is worth. I find these very handy but it would not "stick". If you e-mail me off line I will be happy to send it to you.

Gordy

And one other variable.

 Good points Brad as usual.  Wanted to add the absent minded chef forgetting to turn the grill off for a day or two (Yeah ME). Plus the daughter who turns the pool heater up with out you knowing it making it it into a Jacuzzi (removed that knob).  You know your pool is to hot when its 85* air temp, and you walk by it 5' away, and feel this intense radiant enrgy source hitting you (What the ??).



 Gordy

Jean-David Beyer

When doing a base energy analysis

When I did that, I got about 4.5 therms per month in 2010. But I am not a big hot water user, and cook with electrictiy. I do not know if this is because of my modest hot water use, or because an indirect hot water heater is so efficient. I cannot compare with previous use as I had an electric hot water heater then, and could not separate the hot water cost from the total electricity usage.

Brad White

Old Confucius Say...

"Man with low summer gas bill either not bathe much, has large solar panel array or has family membership at the Y"



(sound of gong)

Jean-David Beyer

No solar array

No family membership at the Y, but since I am a family of one, I do have an individual membership there. I seem to bathe enough to retain my friends.