Furnance Duty Cycle

   The primary motivation for putting in the solar panels has been to reduce oil consumption and the ultimate success or failure will be judged by the oil savings.

    But measuring oil consumption is slightly difficult and very low resolution.  The truck comes to your house and fills the tank about 8 times per year. It is difficult to know how much oil is used in any given month and you can forget about seeing any consumption data on a daily basis in a way that is easily possible for metered products like electricity.

   However, I have found another way to measure oil consumption.  The technique has two parts.  First, the furnace supposedly uses 1.0 gallon per minute when it is on.  Secondly, there are data recorders (data loggers) that can measure when a motor is on.

   The data logger that I used is called a HOBO from manufactured by a company called Onset.  This is a great product.  You can log one year's worth of data.  It only uses one CR2032 watch battery, attaches to the motor with a magnet, and remotely senses the motor state based on fluctuating magnetic fields.  It has a USB port and the data can be downloaded to the HOBO software.  It is about $100 for the data logger and another $100 for the software. 

  What was a slight pain was parsing the data in Excel.  What I really want to know is Duty Cycle, or the percentage of time that the furnace is on in a given day.  What I start with is a bunch of time events that indicate when the motor turned on or off.  I spent a few hours writing a VBA macro in Excel to parse the data the way I wanted.  The biggest problem is splitting events that happen just before or just after midnight.  But the result is just what I wanted.

The chart is a little complicated so let me walk you through it.  On the horizontal axis is time, about one year starting at the beginning of heating season around October 7.  The black dots are data points for the duty cycle.  If the duty cycle was 50% it means that the furnace was firing half of the time.  I have almost a full year's worth of data.
   Since the data is a little noisy, I fit it with two curves.  One curve is parabolic and represent the heating season.  The second curve is linear and represents the summer season.  This gives a clearer representation of the two uses of the furnace 1) domestic heat, and 2) domestic hot water.  It seems reasonable to assume that the domestic hot water is fairly consistent throughout the year.  In fact, it looks like there is a baseline usage of about 5% or roughly 1 gallon of oil every day.
    The oil usage might rightly be broken down into three usage
1) Domestic home heating
2) Domestic hot water
3) Idle losses
Even if no one was in the house and it was summer, my furnace would still consume oil due to the old fashion "tankless" water heater.  The tankless heater requires the furnace to maintain temperature 24/7/365 just in case someone wants some hot water.

    It is difficult to separate hot water usage from idle losses so I have grouped them together in one group in the graph.  Hot water and idle losses represent about 40% of the oil consumed or 377gallons.  Of that, probably half is hot water and half is idling losses.  So a big win for the solar hot water system will be for it to make enough hot water to allow me to shut off the furnace in the summer.  If oil is $4/gallon, then 377 gallons/year means $1508/year, but I will never achieve that much savings because it is not sunny every day and I am not sure how to automatically shut the furnace off and I might also need to bypass the furnace to get this system to work, something I have yet to figure out how to do. Step-by-Step.

  For domestic heating, an estimated 555 gallons (60%) are used per year.  So perhaps I should have spent my money on a more efficient furnace rather than solar water heater system.  But then again, perhaps I can do the furnace upgrade in the future.

  The estimate shows about 932 gallons/year total oil consumption.  This number is quite good because in the 2009-2010 season I used 942 gallons, so the estimate might be within +/-5%.  The insight gained from the data logger information more than makes up for the possible +/-5% error.

   Hopefully in a year, we will have lower duty cycle numbers to share with you.

Up and Circulating

Once all the plumbing was in place, I was more than a little nervous about whether or not the system would hold pressure.  One bad solder joint could make my life very difficult.  So I set about the process of filling the system.

In order to fill the system, I purchased a 1/2 hp "jet pump" that is used for wells.  The pump would be used to draw water (or propylene glycol) from a bucket and pump it into the system.  Of course, like everything else, this meant taking a trip to Home Depot to figure out the appropriate fittings.  The inlet of the pump was a massive 1 1/4" NPT thread but the outlet was only a 3/4" NPT thread.  These would need to be adapted to "hose bib" fittings.    I found a 1 1/4" to 3/4" adapter so that the inlet and outlet were now both the same and I also found two 3/4" npt to 3/4" hose bib adapters.  Also purchased a couple of washing machine hookup hoses to connect the pump in to the solar pumping station.

  The water could then be pumped out of the orange buckets and into the system.  The fluid was then returned back to the bucket in one continuous loop.

     Unfortunately, I had two leaks. SIGH.  The first leak was between two of the solar panels.  It looks like I was not careful enough when installing the panels and one of the o-rings got pinched between the brass surfaces.  The o-ring was damaged and had to be replaced.  The second leak was one of the copper unions that I had placed above the hot water tank to facilitate service.  This union had a large open pore (void) in the surface where sealing was to occur (Thanks Cello).  So I purchased a new union from Home Depot for $17 rather than the $9 I had spent on-line for the other ones, but anyway it was replaced.
    Now to deal with the broken O-ring.  After having spent more than $3000 with Heliodyne, you might think they would have included a spare O-ring, but no.  Strike 1.  But should be simple enough to find a replacemtn.  It is a 1.250×3/32" o-ring.  So I go to Home Depot, Strike 2, they only have o-rings for kitchen faucets.   Go into work where there is a huge selection of o-rings.  There is a 1.250×1/8" but no 3/32".  Strike 3.  Drive to Sears Hardware in Ashland because I knew the Sears Hardware in Delaware (near where I formerly worked) had drawers full of o-rings.  But Sears Hardware Ashland doesn't have o-ring drawers.  Strike 4, but the Sears salesman does give me a tip to look at Ace hardware (which was closed at the time).  On the way home, I went to Lowes which also does not have o-rings despite the Lowes salesmen sending me on a wild goose chase. Strike 5 with four hours wasted.  The next day, I went to Lexington Ace Hardware near my house and purchased the needed o-ring for 59 cents.  Sigh.

   With the leaks fixed, I charged the system with water and it held.  Then I flushed the system with a water and TSP (tri-sodium phosphate) cleaner for several hours.   Next I flushed TSP out of the system with 20 gallons of clean water.  The jet pump moves the fluid at more than 5 gallons per minute.  Very impressive to see a 5 gallon bucket emptied that quickly.

   One small problem is that the flowmeter on the pumping station stopped working some time during this process.  The flushing had liberated some steel (or aluminum but not copper) shavings that got caught up in the flowmeter.  That required removing the flowmeter and removing the metal with tweezers.  Put the flowmeter back in and things were up an running.

Circulating on its own.

  It is all very well and good to use the charge pump, but the system should function with its own internal DC eco-circ pump.  First several attempts to do this failed.  There did not seem to be enough power coming from the solar panels.
     The process was very frustrating.  The eco-circ has its own built in controller that only takes as much power as is available from the solar panel and can supposedly run on as little as 8 watts.  Since I had a 20 watts of solar panels, it seemed like the pump should run.  The power from the solar panels was sent to both a charge control AND to the pump (switched through a relay).   My hope was that the charge control and the pump would each only take what they needed and share the power.  But this may have been a vain hope.  Even directly connecting the solar panel to the motor didn't seem to work.  I think there just is not enough power to get the motor started.  Even if the pump motor might be capable of running from 8 watts, perhaps it cannot start from 8 watts.
   So I needed a new plan.  One quick trip down to You-Do-It Electronics in Natick and I was back in business with a 50 W 24VDC power supply.  This did the trick and the pump started moving.  However, it was unreliable.
    Quickly I figured out that the problem was with air in the lines.  There are two air traps in the system which work great, except they can only do their job if the water is circulating.  Unfortunately, the water could not circulate because there was too much air in the lines.  Specifically, there was air trapped in the space where the motor impeller is located just before a check valve.  So there is a Catch 22.  The air traps cannot do their job if the water is not circulating but the water cannot circulate if there is air at the motor.

     By trial and error I found that by increasing the pressure  in the system (using the external charging pump) I could get the small circulator pump to start the water circulating.  The system has a flow meter with a glass window and massive quantities of air bubbles could be seen moving around.  Eventually, the bubbles worked their way to the air traps and could be purged from the system.  Then the some water was drained from the system to get the water pressure back down to about 12 psi.  All and all, I was happy to get to this point.  The system was holding pressure.  The water was circulating.  Not only is it circulating but it is circulating at more than 5 gpm (gallons per minute) which is twice the necessary 2.5 gpm.  Unfortunately it is taking 50 watts to get to 5 gpm, but hopefully it can get to 2.5 gpm for 25 watts.

    Clearly larger solar panels are needed so I ordered two 20 watt (40 watt total) solar panels from Amazon for $150 with $3.99 next day shipping..  Hopefully this will fix the issue with the pump.  I debated getting larger panels (like 60 watt total) but I really shouldn't need that much.


The Installation Tour

   So let me give you a tour of the installation now that it is almost complete.

The image above shows the South wall of my basement which contains most of the inside solar equipment.
1) Solar pumping station.  The front of this is the differential controller responsible for turning on and off the pump at the right time.  It is connects to thermistors (temperature sensors) on the solar panel and in the hot water tank.  Behind the controller is the pump and a large number of other components.
2) These Taco zone valves, when open, allow water (heat transfer fluid really) to flow to the hot water tank.  I doubled up on them to increase the amount of flow but in hind-sight this was probably unnecessary.  Although the connections to the valves are 1" the valve itself is probably less than 1/2".
3) These Taco zone valves, when open, allow water to flow to the heat dump.  Again they are doubled up.
4) This box contains A) charge controller, B) 24 V NiMH battery, C) 24 VDC to 12 VDC converter, D) some relays.
5) Some additional relays were needed to turn on the pump.  Unfortunately the controller is 12VDC but the pump is 24VDC so some relays were needed.
6) Expansion tank to take up the extra fluid when the water expanses when heated up.
7) These two pipes connect the pumping station to the solar panels
8) These two pipes connect the pumping station to the hot water tank.

  The picture above shows the 1/2 hp jet pump used for charging the system with fluid.  The fluid comes out of the bucket and is pumped into the solar system.  About 10 gallons is needed to fill the system.  The charging system is temporary and will be removed once the system is commissioned.

     The jet pump connects to the fill and drain ports on the solar pumping station (shown above) using garden hoses.

  Looking at the installation from another angle, we can see the solar pumping station (1) on the right, the piping (2) above, and the hot water tank (3) on the left.

       The overhead piping needed to be supported.  But most brackets would crush the insulation.  So I cut out a piece of aluminum (8x4"), painted it black, and placed it underneath the bracket to spread the load.  I also painted the bracket both black and white to match the insulation and ceiling as needed.
  

   On the other side of the room is the hot water tank.  The 80 gallon tank is manufactured right here in Massachusetts by Heat-Flo which is pretty cool.  There are a couple of nice things about the tank.  Firstly is that it is made of stainless steel which should assure a very long life time.  Secondly, all the connections are on the top of the tank which makes for a very clean installation. 

   The connections through the top of the tank were made through copper unions and full port valves. This setup allows the tank to be isolated from the rest of the system for servicing.

The wire for the thermistor was routed down the front face of the tank and secured with cable clamps that I pop-riveted to the plastic outer shell of the tank.

  Lastly, the solar PV panels were temporarily attached to the hot water panels using some 2x2" pressure treated lumber.  I felt there was a good chance that they would need to come off again, so I didn't attach them more permanently.  They will soon be replaced by larger panels and if those work out I will get some aluminum extrusions on which I will mount them more permanently.

  Next step, see if I can get Sweet Plumbing in to connect the hot water tank to the domestic hot water supply.

Plumb, Plumb, Plumb away.

With the pumping station and solar panels in place, all that remained was to get the hot water tank and piping in place and that is what I did.

  To make sure that the heat dump was well soldered, I put together a pressure test gauge as shown in the picture.

The gauge uses a tee that connects 1) pressure gauge, 2) tire valve stem, and 3) the pipe under test.  In this case I used "shark-bite" fittings from Home Depot.  The "shark-bite" fittings slide right on to the end of a pipe, but cannot be removed without a tool.  To check the integrity of the pipe, I filled the heat dump with compressed air.
     I found that overnight, there was some slight loss of pressure which was worrying.  So I decided to mostly fill the heat dump with water and then add air to create pressure.  This revealed that some leaking was occurring in the 1/4 NPT fittings.  Once I tightened the fittings, the leaking stopped.

    Plumbing is not difficult work, but it requires patience and attention to detail.  There is a lot of measuring, cutting, deburring, sanding, dry-fit, mark, disassemble, flux, solder, cool, clean, and repeat.  The parts have to be absolutely clean.  Flux needs to be applied to every square millimeter of both mating surfaces and solder must be applied to the full 360 degrees of the joint.
    The images below will give you a sense of the process for the return line for the solar panels.

    The first part of the piping required a 180 degree turn which I made with two "long radius" 1" copper elbows.  Those connected to the solar panels via a union (half) that was purchased from Heliodyne.  The union connects to the panel using an O-ring so that it can be disassembled easily.  I sloped the pipe leading to this area down in this direction.  If I need to drain the system I can just disconnect the union from the panel.  I considered adding a drain valve at this location, but I didn't.  

 That pipe connects to a second using a 90 degree long radius elbow.  These "long radius" elbows create dramatically less flow resistance than a standard elbows.  The pipe is then routed up at 45 degrees right underneath the panels.  I worked to minimize the visual impact of the piping by hiding them behind the panels.

 The pipe then transitions through a 45 degree elbow toward the house.

 

That pipe goes straight through the one of the holes in the sills.

 And then sticks into the basement.

 And curves down to the pumping station mounted on the wall.   The special high temperature/UV resistant UT Solaflex Insulation that I purchased from "Alt E" was not slit.  The insulation had to be slid onto the copper tubes which presented a bit of a logistics problem.  The joints in the 6' long insulation tubes had to be planned to be near solder joints.  The insulation could be compressed away from the jointed and held with a clamp during soldering.  To aid in installing the insulation, I applied baby power to the copper tubing and then slid the insulation onto the pipes.  The "long radius" elbows made it quite easy to make the insulation slide around the turns.  However, it is easy to poke your finger tip into the insulation, so I learned to work mostly with my palms.

 After soldering, the insulation could be pushed back into position.

 That should give you a better sense of the plumbing process.  The same process was repeated for the supply line to the solar panels and then connections made to the heat dump and the hot water tank.

   Speaking of the hot water tank, there is my buddy Doug dropping it off at my house.  Better go help him unload it.