I finished the assembly of the two carriages on the x axes of the CNC machine. The y axis is mounted and this next week the goal is to assemble the carriage to Acme nut connections and build the linear carriage for the y axis. So if all goes as planned next weekend or sooner could be the first prototype test of the machine, the z axis will not be workable but I am sure I can find a way to attach a pencil the axis to see movement. That is a great goal for the week.
My SparkFun package of an FTDI Adapter board and and second board will allow me to reload the firmware on the OpenLog board I ordered in January. I am dreading this a bit, electronics and computer area things are my weakness so I am a bit nervous but will tackle this job and test in a example sketch this week. I’ll bet that will take any free time I may have up but will get me that much closer to my goals.
Minor changes in the software that force the boiler to maintain a tighter range from the set point has cut the fuel consumption from 3 (40 pound) bags of pellets to 2 daily. These software improvements and a extension to the pellet hopper mean the boiler will now run 24 hours without needing additional fuel. The hopper extension adds at least another 40 lb bag of pellets capacity bringing the total capacity to approx. 2 1/2-3 bags. I haven’t measured only estimated.
The boiler set point is currently set at 135°F which seems to work just fine for the temperatures we have been having and the software is consistently running within4 degrees of set point. This range may seem excessive but seems to run just fine. The program is becoming more modular in that there is only one number to change, the set point. The set point currently is a variable declared in the setup section of the program but eventually the set point will be self adjusted by the program based on the outside temperature. Economy and efficiency by software optimization is the goal for this next week.
We have had a very mild winter in my opinion. The Heating Degree Day total for the month of Dec 2011 was 1091 as measured by the local weather station. The normal is 1209 HDD a difference of 118 HDD, not as much as I would have thought. The total for the month of January 2012 so far is 1140 with four days to go, with a normal of 1419. We’ll see how the month ends but if it continues as the average day it will be short approx the same number of HDD as last month,December. My interest in HDD is to see if there is a correlation to HDD and fuel consumption. There should be and if there is than the fuel economy is starting to improve. As I told a friend of mine, at this point the boiler is like a truck I used to own, 10 mpg going uphill loaded, 10 mpg empty going downhill….so seeing fuel consumption changing to track the weather will be the first step to seeing some optimization.
Software work on fuel economy and the extrapolation of costs for the upcoming remainder of the season is of great interest. The next step in fuel economy may be better insulation of the boiler and piping and will not be as simple as software improvements. But if I can get a correlation between the outside temperature and fuel consumption that is measurable then the software will be nearly optimized and further improvements will have to come from physical changes. This week sees a 40 pound bag and $4.00 improvement per day, $28/week, $112 per month. Next week’s goal: another $60/month. I am hoping for a total seasonal heating cost of $500 or less using $200/ton pellets. I will consider that a huge victory for heating a 2300 sq ft house with 3 garage doors.
The sprockets have been replaced and improved with key ways cut into the jack shaft and auger. This allows positive feeding without slippage. The jack shaft placement was constrained so adjustment of the chains is limited to what linkages can be removed or replaced with half links and adding a slack tension device on the slack side of the roller chain. With this complete the LCD problems appear to be fixed. Without proper tension the chain did not ride on the sprockets smoothly and the tension could take up suddenly adding a jerk to the system. Without this mechanical jerk in the system the motor can work more smoothly allowing the LCD to not get the power fluctuations that garble the display. The feed problems appear to be fixed but in the last test the unit ran for four days without fail and at this point although there is a marked improvement that time has not been surpassed. Next on the list is the hopper extension to allow feeding of two bags of pellets. This will allow 16 hours of run time without any software improvements.
Last night I went over the remaining issues with my girlfriend. So here is the list and the possible fixes and approaches to each item.
1) Smoke. There is still some remaining minor smoking issues. Possible fixes, better caulking, stronger fans, a wind baffle, burner redesign? Pipe cleaning? I think I will start with a wind baffle and some better caulking, next furnace will have a better gasket design. I also have ordered a Magnehelic to help determine the normal static pressure so that a baseline can be established and tested against. The boiler is working so ordering fans without more facts would be a expensive trial and error process.
2) Feed issues. There continues to be an occasional feed issue. So much so that today I am going to take the burner off the boiler and see if I can determine the binding issue. Possible solutions? Increase in torque, already ordered more sprockets.
3) LCD issues. The problem has been traced to the relay and I think needs some old fashioned power regulation, no doubt involving a capacitor to remove the spike when the relay is released. Possible fixes, ordered an LCD backpack to free up some IO and also allow only one power and ground to go to the LCD.
4) Hopper Extension. 3 bags per day means a bag every 8 hours, no all that conducive to being able to leave for a day long event.
5) Data logging. Tuning the machine is always the fun part and so dependable data logging needs to happen. I ordered a SD card writer. This should allow the internal Arduino software to work with the card independently of Windows XP which seems to have problems with continual or repeated Arduino upload. I also plan to test the upload and communication with a Linux operating system.
Back to work! Today I built the wind baffle and so after the auger is clear back to the experiment.
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.
After having the issues described in the last post the decision was made to reconfigure the feed for the third time. Hopefully the third time is the charm. The feed is now horizontal again with a reconfigured air box and single fan blowing along with the exhaust fan. The auger was extended into the burn area to allow the pipe to be mounted flush to the inner surface of the mounting plate and so that the auger will push the burning pile down the burner trough. After some minor glitches the burner is up and running. I made some minor changes to the software to allow the burner to run more at a lower temperature and changed the setpoint to 140°F from 135°F. Minor changes but all part of the tweaking and learning process.
The goal for this coming week will be to monitor the fuel usage and see if the system can keep up with the predicted below zero temperatures forecast for tonight.
The increased air from the second fan did improve the smoke and make the inlet fuel pipe even cooler. It also enabled me to have a viewing port to see if there is flame or if the fuel was adding as expected. But two things happened, the fuel did not flow out of the way so at the bottom of the pipe there was a scree field of pellets which did not move until the previously feed fuel had burned. This situation makes the feeding control very critical. The pace of the feed must be the same as the pace of burning. This alone makes the design unworkable, the process must be more robust than to require advanced combustion calculation, measurement or observation.
The second problem observed was the area of combustion across the pellet field is limited the area of the roughly trapezoidal shape that was formed. This area is significantly smaller than the area of the burner trough. Consequently two things are learned. One the area naturally formed by the falling pellets is insufficient to maintain the water temperature required for my needs, as evidenced by the boilers inability to get past a temperature of approximately 130°F. This alone also requires the redesign since the whole idea is to heat the house. The second conclusion is the area is directly related the heat making capability and thus sizing a burner to a house and feed system is probably quite doable. This seems obvious in statement however, I was thinking that factors such as air volume and burner efficiency would play a larger role. At this point I think I can tailor the BTU’s by burner size and design. I think I will start with the more modest goal of getting the damn thing to work for more than a day.
I’ll admit to being a bit discouraged, however, as January’s calendar said, ” Character consists of what you do on the third and fourth tries”.
To the side see a shot of the burner on the bench in my messy shop. You can see in this shot the approx size of the pellet field that would be burning vs. the potential size of the pellet field if the entire trough was filled.