Author Topic: "Heating Degree Days"  (Read 3217 times)

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Offline xykotik

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"Heating Degree Days"
« on: June 04, 2011, 09:54:18 AM »
I'm still trying to get my head around this, because I think it could be useful in calculating my energy costs.

My propane supplier occasionally lets me run out, and blames their "heating degree day calculator" for the mistake. 

I noticed that WeatherLink has some "heating degree days" and "cooling degree days" bells and whistles.  Can someone give me a lesson on this subject and how I might use such a tool to track my energy use and/or needs?


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Springtime in Seattle...  March comes in like a lion and out like a wet lion.

Offline Farmtalk

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Re: "Heating Degree Days"
« Reply #1 on: June 04, 2011, 09:56:13 AM »
This is all that I know about it:

Heating degree days are defined relative to a base temperature - the outside temperature above which a building needs no heating.


So I'm joining the wagon on this thread :grin:
"Make it simple but significant"

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Online SteveFitz1

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Re: "Heating Degree Days"
« Reply #2 on: June 04, 2011, 10:16:33 AM »
Not to sound trite, but you'll find more than you care to know simply by Googling 'heating degree days'. One suggestion I'd make is to ask your propane supplier what baseline temperature they use for their calculations (it's probably around 65 F). You want to make sure you're using the same value in Weatherlink.

Steve

Offline mfd38

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Re: "Heating Degree Days"
« Reply #3 on: June 04, 2011, 10:24:34 AM »
Farmtalk is on the right track with this. The hdd/cdd values are determined based on the temperature above or below a base temp. In the USA the base temperature is typically 65 degree F. So temperatures below 65 would indicate heating degree days and temps above 65 would indicate cooling degree days. Utilities and Energy companies rely on the degree day data to forecast energy demand for a specified period of time, typically 24 hrs. This way they can plan on how much natural gas or propane needs to be purchased or how much electricity needs to be generated, etc. for a given day.

Here is a link to a site with some more info and a calculator - http://www.degreedays.net/#

Hope this helps,
Paul

Offline d_l

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Re: "Heating Degree Days"
« Reply #4 on: June 04, 2011, 10:37:10 AM »
farmtalk is correct.  There is a base temperature used for each of the two measurements which is supposed to be your inside house temperature.  The cumulative difference of the actual average air temperature from that base temperature is either the heating or cooling degree days.  Those two measurements are then directly proportional to the amount of energy used for heating or cooling.

If your propane supplier is using an incorrect base temperature for your residence, e.g. too low, then they would underestimate your heating degree days, your energy usage, and allow your propane to run out. Also if your propane supplier is using daily temperatures that are warmer than those you are reading at your place, they would also underestimate your propane consumption.

You have to figure out your average house temperature which can be tough to do if you use a set back thermostat and then apply that as the base temperature in Weatherlink.  Then you have to relate the heating degree days that you measure to your propane consumption rate.  Once you have that relationship, you can "project" how soon your tank of propane will run out if you forecast the heating degree days that might occur in the future.

I believe the Fuel Demand calculator in weatherlink does most of this (it doesn't do fuel consumption projections), but I've never used it properly.  I tried setting it up for natural gas which I think should also work, but gave up.  The problem was estimating the "K factor" for natural gas.  Your fuel supplier should be using a program like the Fuel Demand calculator.
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Offline xykotik

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Re: "Heating Degree Days"
« Reply #5 on: June 04, 2011, 09:14:57 PM »
Quote
you'll find more than you care to know simply by Googling 'heating degree days'
But GOOGLE isn't much of a conversationlist.  I found THIS place by googling a problem I was having with weatherlink, and since then, most of my wx-googles lead me back here anyway.  Just trying to save a step and be efficient (like with my propane consumption).  ;)

Some good starting info from Dave.  Once I have a stable year of average data in WL from the indoor temp readings on my console (I use multiple setbacks and daily schedules) could that possibly help nail it down?  It sounds like my propane supplier probably is using a regional average number.  Their office is about 70 miles north of here in the PSCZ (Puget Sound Convergence Zone) which is a microclimate of infinite unpredictability.  I'll be chatting with by buddy in Lake Stevens about our downpouring rain while he is mowing his lawn.

I periodically have them fax me the dates and quanities of each fill.  I keep them hoping to somehow, someday correlate it to this HDD formula.  I'll keep digging.  Keep the opinions coming.


Facit solem suum oriri super bonos et malos et pluit super iustos et iniustos.

Springtime in Seattle...  March comes in like a lion and out like a wet lion.

Offline Jim18655

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Re: "Heating Degree Days"
« Reply #6 on: June 05, 2011, 12:10:43 AM »
I always got stumped by the 'K' factor. How is it used in the calculation and how would you estimate it?

Offline d_l

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Re: "Heating Degree Days"
« Reply #7 on: June 05, 2011, 09:39:21 AM »
xykotik, if you have a heating season's worth of daily indoor temps, you should be able to average those to get an HDD base temperature.  If the daily setback temps are not changed the next winter, then you should have a very accurate base temp.

Jim18655, as I understand it, the K-factor is a propane consumption rate per degree day and weatherlink can calculate it for you from the propane gallons used during a time period using your unique base temp and the cumulative degree days that have transpired during that time period.
--Dave--

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People always talk about the weather, but they never do anything about it.  Not me.  I'm gonna measure it.  www.tceweather.com

Offline xykotik

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Re: "Heating Degree Days"
« Reply #8 on: June 05, 2011, 10:21:08 PM »
Quote
...and weatherlink can calculate it for you from the propane gallons used...

NOW, we're gettin' there.  I'm glad I have those propane bills.  (Well, not the bills per se, but the gallons and dates).


Facit solem suum oriri super bonos et malos et pluit super iustos et iniustos.

Springtime in Seattle...  March comes in like a lion and out like a wet lion.

Offline Jim18655

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Re: "Heating Degree Days"
« Reply #9 on: June 06, 2011, 07:29:18 PM »
Makes sense now. I keep fairly detailed records of my fuel use so the 'k' factor was easy once I knew what it was. August 5, 2010 I had a fuel delivery to bring the total to 705 gallons of oil. I also have  an hour meter on the furnace burner so I can track fuel usage over the year. Since I have an in-ground tank it's easier to read a meter to estimate remaining fuel than it is to measure the fuel depth. One hour of run time equals 1 gallon of fuel. Plugging the numbers into the k-factor calculator (didn't know it was there) gave a k-factor of 17.03 and 335 gallons remaining which is within 10 gallons of  the hour meter calculation.