Arduino thermostat

Earlier I finished the piping for the the two additional zones.  A quick recap, one zone will allow  a boiler to heat the tank that is normally heated by solar.  The second zone is really not a zone but the piping and circulator pump that will add heated water from the chip boiler.

The solar water tank, or solar thermal store has two coils in it, the first coil is heated by the solar loop on the roof.  This coil is physically lower in the tank so that the heated water will rise and the sensor controlling this coil is lower as well.  This allows the maximum storage from the tank from solar at all times.  The second coil and sensor that is intended to be heated from the boiler is mounted higher.  The water at the top is  hottest and therefore the  least amount of energy will be needed and the maximum amount of free energy is used first.  Of course solar is not free, it still requires a circulator pump but I assume it to be negligible and therefore in this context free.

Knowing this and assuming that I am going to use an Arduino microcomputer in the process anyway, I am intending to implement the solution in two steps.  The first step to wire and shrink wrap a thermistor  and run the thermistor back to a breadboard, and display the temperature on an LCD.  If the temperature is below a certain value, digital write to a relay to turn on the circulator pump.  If the temperature is good, do nothing.

In the second iteration of the solution my plan is to add a time chip to the system and make the process more efficient.    The logic is this:

8am, no real need for hot water, and there is a good chance the solar will heat the water.

4pm, heat water and maintain until 8pm if needed.

8pm-8am maintain a minimum, lukewarm temp.  We’re not a shower in the morning family.  Of course on the weekend the program will have to be different.

To implement this 2nd iteration a real time chip will be required.  I have found a few, one at sparkfun.com

http://www.sparkfun.com/products/10160, $19.95

 

and a second one at

http://macetech.com/store/index.php?main_page=product_info&cPath=5&products_id=8

I am inclined to the second link, the board is cheaper with a built in battery holder and battery shipped with the product for $14.99

And the yourduino option for $9.00

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=48

http://adafruit.com/products/264

 

Also $9.00

Any opinions?


Progress-Goal for the week

Potato Harvest drying on floor

I harvested potatoes last weekend with the girls and the floor was covered.  I had to clean up so I could work without stepping on vegetables.  So that was job one on Sat morning, get more liquor boxes and get things cleaned.  Finally finished that with help from the girls on Sunday morning.  It snowed over the weekend so Sunday was spent plowing and going to a party at a friend’s house.  On Saturday,  with help from my 11 year old helper,I did get one half of the circulation loop for the heating of the solar tank installed.

Clean floor after Potato

Today’s goal is to finish installing the loop and run stub piping through the wall to where the chip boiler will be installed.  I want to install the loop in the solar water tank to allow for more energy storage.  This will allow more  flexibility when the microcomputer is deciding where to put the heat from the chip boiler.  Finishing the loop will also allow the Arduino Uno to be the thermostat controller hooked to the Boiler Boss. With a thermistor and LCD added to a relay board the Arduino can be the thermostat to run the zone.  It seems to me this would be a great way to test the Arduino since all that can happen if the thermostat fails to work is a cold shower.  Of course this assumes that the solar loop didn’t heat the water sufficiently and the solar can still heat the water hot enough for a shower on a good sunny day.

Return manifold with piping from heating coil in Solar tank and stub from chip boiler

The boiler boss is one central control unit that contains all the relays for the zones.   This box controls all the circulator pumps and the new circulator pump needs to be wired into this and the Arduino wired in as a thermostat.

Boiler boss with Cover removed

So this weeks goals are simple: 1)  Finish the solar hot water tank loop, wire it in and test with an Arduino controlling the zone, acting as the thermostat. 2)  Apply the sealant to the chip boiler and test for leaks.  3)  Work on the Chimney penetration through the rear wall of the shop for the chip boiler.  This will be a straight 4″ pipe out since there is forced draft.

I got some good comments from a friend concerned with the temperature of the return water so I got a fresh battery for my non contact thermometer and took some temperature measurements  of the zone water at the point  leaving the circulator and just above the return manifold  so here they are:  113 out and 98/99 back, not a lot of difference.  The outside temp is approx. 30 (all temps F).

I am having a difficult time removing the end plug for the upper manifold, this is a 3/4″ black iron plug, I am thinking of using heat, any other suggestions,  I am trying this plug with a 24″ pipe wrench, I am afraid if I try to use a cheater I will break something.


Preparing the tank, attempting to add a larger LCD

Good week of progress so far, I have on order the sealant to fix the remaining leaks in the chip boiler and have ordered the circulator pumps for to tie in the solar tank coil and the chip boiler.  But to make progress toward completion I have to do more than sit in front of the computer writing about pump sizing and ordering materials.  So time to get out the welder and add a good sized drain to the tank and create  the ability to rotate the tank to make the sealant process successful.  Pictures to follow.

On another note I am having trouble hooking up a 4 line LCD display, primarily because it seems to have different pinouts than a standard LCD and because it has two enable pins, one pin for each two lines.  So more research is required on that.


Sizing the circulator pump

Today my plan is to size the circulator pump from the chip boiler through the manifolds of the existing oil-fired boiler.  The formula is: Q = h/(Cp*p*Delta T) Where Q is the heat transfer in Gallons per minute, Cp is the specific heat capacity, a constant based on the fluid, in this case water, p (really rho, I need help figuring out how to add greek letters and subscripts) and an assumed temperature drop or Delta T.  Since it is my intention to run the chip boiler at 180°F and set the min temp on the oil burner at 130°F this will give me a 50°F temperature before the temp of the furnace requires it to fire.  By leaving myself enough room I am hoping the Arduino controller and good temperature monitoring will preclude the oil boiler from firing.  For the formula however I am going to assume a temperature difference of 20°F.  So, again assuming a 30,ooo Btu chip boiler,  a Cp for water of 1 BTU/Lbm/1°F, p (rho) the density of water, 62.34 lb/cu ft., Delta T=20°F and to convert BTU to gal/min 7.48 Gal/cu ft  Therefore Q=30,000(7.48 gal/cu ft)/((1 Btu/lbm/1°F)(62.34 lb H2O/cu ft)(60 min/hr)(20°F)=2.9997 GPM

http://www.engineeringtoolbox.com/water-flow-rates-heating-systems-d_659.html

This formula gives the flow rate and now I need to calculate the pressure drop or head loss.   The formula for this is:

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

HL = k x c x L x (f1.75)  Measuring the distance to the proposed location of the chip boiler, I get about 18′ of piping to and from the existing boiler and approx 10 of additional piping in the boiler, assuming 4 elbows.  Planning on using either 3/4″ pex tubing or 1/2″ copper.  Using Table 1 in the above link either 3/4″ pex or 1/2″ copper will be acceptable for a flow rate of 3 gpm.  I would prefer to use the 1/2′ copper since it is a relatively short run and will require less  hangers and difficulty doing a nice neat job through the utility room.    From Table 2 I see a equivalvent feet of 1.55 for each elbow so 4 x 1.55 ft= 6.2 ft  From Table 3,  k =.0159, From Table 4 Water at 180°F, c=0.933, finally the flow rate raised to the 1.75 power is 6.83.  So the total length is 18+6.2+13=37.2 ft.  I calculate a rough head loss of approx. H loss=.0159*37.2*.933*6.83=3.77 ft  Use the graph to find the correct pump having the conditions of 3 gpm  flow and 3.77 ft of head It looks like a Taco 003 or a Taco 006 pump will work just fine.   After some internet research using my normal internet heating component supplier I will probably use a Grundfos UPS 15-58FC, 3 Speed Circulator pump, 1/25 HP, 115 V

The lower manifold shown in the right hand picture is the cold return from the zones.  I am planning on adding the hot water from the chip boiler in at this point to prevent the oil-fired burner from starting.  This will also increase the heat reservoir by heating the water in the furnace as well.  Lastly I plan on adding a 4th zone onto the existing manifolds to take advantage of the existing 2nd heating coil in a solar hot water tank I have separately heated by solar evacuated tubes.  This will give additional options for the Arduino to dump heat.


Chip boiler Project

Hi!  I decided to write a blog about the fun things I like to do and how it I like to apply those things to my life.  I believe a balance is important, I feel it when I don’t have enough of something, exercise, money, sleep you name it.   My goal is to do something about all of those things and more with a welder, an Arduino application and a sense of humor.  My latest project is a homemade chip boiler that can burn either wood chips or pellets.  The plan is simple, develop a boiler to heat the entire house on the cheap.   The brains of the system is to be a Arduino microcomputer to control the boiler and the rest of the house in parallel with the existing oil fired boiler.

So the project is really split into two parts, the welding and design of the boiler and the control of the existing system and new boiler.  The chip boiler is a continuous burn unit probably producing 20-30k BTU.  Initial tests indicated 20-30k, I did these tests in the open air by weighing a pan of water and timing the time to boil.  This was a very crude method so the prototype boiler may yield different results.  The existing oil fired boiler is rated at 130,000 BTU.  So to get the two systems to work together will require a different paradigm, one requiring the circulator  pumps to work more intermittently and often .

But enough about the control theory for today,   The prototype boiler is 90% welded up and has been tested  for leaks.   The boiler was started from an over the road truck’s fuel tank.  The internal seams were never intended to be water tight and I am having trouble with welding up the all the internal weeps.    The tank under my house’s water pressure of  about 45 psi weeps,  I am intending to call and get some information on tank sealing paints today.  After a brief internet search I have seen several sealants that are intended to work with gas tanks for car restoration.  I plan to call and see if they will work with a water application  If this seems possible and good I plan to move onto the Arduino control application since I will no doubt be waiting a day or two for the materials to arrive and then apply the materials to the tank and wait the appropriate drying time.  Please feel free to weigh in on any suggestions on sealing the tank.