Above is a scatter plot of Heating Degree Days (HDD) taken from Weather Underground data from the weather station in Springfield VT. Not exactly Newport, NH but close enough for this graph. It’s important to note that the beginning of October was quite nice which resulted in a fair number of days of timed burns, starting the boiler at 4 pm and running it until 9 pm for example. It quickly became obvious with Novembers below average weather that this would not result in satisfactory comfort and the boiler has been running continuously for most of the month. The trend-line looks like you would expect to see it, but the scatter data is quite varied. It will be interesting to see if this data correlates better as the winter continues.
The total pounds of fuel burned Heating season to date: 92 bags @40 pounds/bag= 3680 pounds vs. a total HDD to Date of 1444. Last year’s data for December indicates a HDD total for the month of 1069. This should result in 68 bags burned for the month for a total of 2720 pounds. Using $215 per ton this should be a monthly cost of $292.40 This is both heat and hot water. Be interesting to see at the end of the month how close the prediction comes.
You may remember I added a function to collect HDD data at one point, however it never seemed to work as well as it should have so I stopped using it, I am now considering reviving a variation of that function using an array for the max and min hourly numbers to get a more accurate HDD local number. I’ll post the code when I finish.
I went out on a customer issue the other day, I had to meet a locksmith at a customer’s house. After the job was done the locksmith who I have done business with for years and is a friend came back to the shop for a check and a beer. Naturally I showed him my home built boiler. He rent’s so he wasn’t particularly interested but mentioned he buys a 5 gallon can of off road diesel to bring home to heat his house every day. The price is about $3.77 per gallon which is about what the local oil company would charge to deliver. So if it’s the same price why not have it delivered? Because he doesn’t want to, or can’t tie up the $471.25 the fuel company would want for a minimum sale. That amount of fuel would last him about 25 days at his 5 gallon a day rate, maybe less time if the 10 gallon nights are accounted in as well. Since it was quite cold he was planning on buying two cans that night. He said the normal 5 gallons cost him $19/day. Rounding this to $20 for ease of math and multiplying by 30 days per month this is approx. $600 per month for fuel oil. We bought our third ton of of pellets for the heating season for $209 at Tractor supply last week. So our total fuel costs for the year are approx. $800 from November to mid February. What a difference! Not to mention I can’t imagine going to the gas station every day for fuel. What a pain. Having diesel trucks and fueling up at the same pumps I see many different people filling five gallon cans every time I fuel my trucks. I’m not the best at budgeting in the world, but I realize my blessings when I witness first hand how the paycheck to paycheck underemployed crowd deals with winter.
I’ve started calculating the Heating degree days with the Arduino program. It’s a pretty accurate look at the day’s heating requirements. I want to correlate those temperatures to fuel usage. I also have updated the CNC plasma cutter to the 5 start lead screw. Before I made the upgrades I needed to limit the cutter to a linear travel rate of 13 inches per minute to avoid vibration issues. After reassembly I tested the machine to 40 inches per minute with no problems. It may be even better than that I just got so giddy I quit testing. I am hoping this will significantly reduce the slag produced by the plasma cut. Not much motivation to take anything apart at this point. It’s just too damn cold out. It was -5°F this morning here, the HDD days yesterday was 65.5. Stay warm out there. I could back the tractor out of the shop and do some woodworking, maybe build the chip dryer…..
I restarted the boiler with a friend on Friday afternoon on the 13th of January. At present it is Sunday morning at 6:45. Thirty nine hours since starting, in that time the temperature has dropped to a low of -5°F which is the current temperature and the fuel usage has been a total of 5 bags. The house is still comfortable and has not shown any dip or problems in maintaining temperature. The only noticeable differences are two things. The lack of the oil fired boiler running which I can hear upstairs and always makes me a little twitchy. The second difference is the temperature of my office. My office is off the utility room which holds the furnace and so is normally quite warm after a cold night. Today it is the temperature the thermostat is set to maintain.
A few numbers, I paid $215/ton for the pellets, so the cost per 40 lb bag is $4.30. The hours per bag is approx. 7.8. This will need a longer time average to confirm but is probably a reasonably good number so in rough terms this is 3 bags per day for a cost of $12.90/day. I looked back to see if I had a furnace run time data which I did have a limited amount. On October 17, 2007 the furnace ran a total of 4.1 hours on a day that had a high of 51 and a low of 33 for a total Heating Degree Day of 22.7. (Heating Degree Days are calculated as (in °F) 65-(day’s max temp-day’s min temp)/2 or to restate 65-average temp) . Taking the furnace run time as 4.1 hours x nozzle rate of 1 gal per hour this translates to 4.1 gals usage for a total cost at $3.85 per gallon of $15.78 for one day relatively mild day. Yesterday’s HDD calculation using a high of 29 and a low of 11 yeilds and average of 20. So 65-20=41. Using a simple ratio of HDD/Furnace Run time would calculate to a furnace run time of 7.4 hours per day for a cost of $28.50 per day. Contrasting this with the pellet costs yields a savings of $15.60 for that one day.
So is that accurate? That was a lot of math using some not very exact calculations. The math was done correctly but Heating Degree Day calculations are notoriously rough. Many oil companies have moved onto more sophisticated methods and of course this is just a snap shot of one day. But as an reality check at this point I am confident 5 tons of pellets would easily get this building through the winter for a total cost of $1075. If I used 800 gals of oil throughout the heating season this would cost me $3080 at a cost of $3.85 per gallon. So yeah I think the numbers are reasonably accurate if not conservative. Wait until I try chips at a cost of $40/ton……too fun.