Solar Collector Design

Solar Collector Design

I set out to make a solar hot water heater design this year based on the builditsolar.com $1000 solar hot water heater design.  My goals were to make it based on that design, but try to modify it to make it even more cost effective, without degrading performance.  I am shooting for around $500 cost for the entire unit.

2/20/10

Well I started work on the solar collector portion of the design this weekend.  My daughter's friend had just replaced their windows and had the old ones leaning against their fence when I happened to see them and asked if I could have some of them.  I ended up getting 6 windows, each 24" x 48" casement type, for free.  Here are some of them leaning against the fence.


Next step was getting the nice window out of the frames.  This was really pretty easy.  Pound off the sill, open the window all the way so its past 90 degrees open, then take a screw driver and remove the metal straps and brackets holding it in the frame.  That takes about 10 minutes for each window.  Hereis a picture of the first window removed from its frame.


Being the salvager I am, I took off all the hardware and saved the wood screws.  There were lots of nice metal
straps, angle brackets, latches and screws from the job.  Here's my collection after all the windows were done.



Now I've got to build these windows into frames and add the solar collector material and PEX tubing to the back.
I have 48 sq ft of glazing to work with, which I think I will build into two 6x4 collectors.

Updated 3/14/10

Worked on building 1st collector.  First step was building a simple frame for three windows out of 2x4s.  Here's the frame
with a couple windows on checking for fit.


Next I mounted the windows to the frame with some screws.  I pre-drilled the windows to make sure I didn't split the wood.  I just put a screw in each corner so it would be easy to take apart if necessary.


Next I caulked all the joints, removes some loose paint and put a coat of Kilz sealer/primer paint on he box and called
that done until final painting and adding some final flashing around the windows.

Next I started working on the back panel.  1st thing was too cut some slats to create the runners that will be used to hold the pex in place on the backboard.  I bought some 1x4 and ripped them on the table saw to make 1x2s and the cut them to length for the runners.  Here are the runners all cut and predrilled for screw mounting.



Next I tried to figure out how to run the 1/2" PEX tubing on the board and make maximum use of my cut flashing pieces
that are 10"x11".  I installed the bottom runner on the board first, making sure I gave it some slope to ensure it would
have no trouble draining back when the pump is off.  I gave it a 1/2" of slope for each run of pex.  Here is a picture
of installing the 1st runner.

I noticed the runner had some bend in it and ending up fixing the ends in place then installing the middle screws
after aligning the runner to my straight metal ruler.



After installing the bottom runner, I installed the upper half of the channel by placing the pex tubing in between the two
and making sure they were snug together before screwing down.  I am figuring I will be able to press the PEX and the
thin aluminum sheets in this channel.  Here's a picture of putting in the top part of a channel.



Here is a picture after all the runners are in place and I have laid in the PEX tubing into the channel to see how its going
to work.


Last thing I did was check how my aluminum flashing pieces were going to fit and realized I needed a few more since I
ended up adding the fifth run of PEX.  Here is a picture of the small pieces of flashing laying on the board.  The rest of
this will need to wait till I get the rest of my flashing sheared.


3/22/10 - Update

Next thing was to preform each piece of aluminum with a simple form.  Here is the form, a piece of the flashing, a piece of the PEX and a 2x4 to press the PEX and flashing into the form.


Here are some of the preformed pieces on the back panel.


Since the flashing is so thin, it didn't hold its form.  I decided to mount it as follows.  Lay silicon caulk down the furrow where the PEX will be pressed on a row. Then press the PEX down into the form and use some large staples to hold the PEX down tight in the furrow. I had to do one piece at a time and kinda stand/kneel on my 2x4 foot press while nailing in the large staples.  I just put them in tight enough to just deform the PEX a tiny bit.


Here is the all the rows stapled in. 


Notice the fins of each piece are sticking up a bit.  From here I just put in some
small staple gun staples in the center of each piece into the furring strips to bring them flat.  Here is a picture of
everything stapled down.  The last thing I did was use some metal tape to cover all the PEX and provide some
heat transfer to the top of the PEX tubing. 


I added a small thermistor I built for sensing the temperature on the panel.


From there I just spray painted it flat black and screwed it into my window frame to give it a quick test.  Here it is
in the backyard.  Notice all the trees in the glass reflection.  I don't have a really sunny spot all day to test the unit.  I end up with shading for most of the afternoon.  This will be reduced when I trim back some trees.


Unfortunately, there was only a few 5 minute periods of sunny on the most cloudy day.  I managed to get it up to about 145F in about 5 minutes before it got cloudy.  Will run this on my diffferential temperature controller next weekend and take soem thermal recordings of units performance.  One thing I noticed is that some of the staples that were holding the flashing flat pulled loose when it got hot, so I will need to add a few more staples to secure the flashing.  I also need to add some insulation to the back and sides. 

Lastly it seems like if it get set on or near the ground, a white / reflective footing might help increase the incident light on the collector.

Well, that's it for now.

3/24/10

I ran it for a day connected to my homemade temperature controller.  Here's a picture of the temperature controller I built to test it.  The
temperature controller performs the differential temperature control needed for solar hot water collecting as well as records temperature data
for 4 temperature sensors I built to go with it out of NTC thermistors and ring lugs.



The temperature probes on T3 and T4 were unconnected and have bogus readings.  Temperature Sensor T1 was the inside of the collector and T2 was the outside ambient.  Managed to get up to around 180F with no insulation on the back or even caulked up tight on the back panel.  Looks like it works good enough to try running some water thru it with the pump and storage tank.  Here is some capture from the run.  I got a dip later in the afternoon due to trees shadowing it, so I'm not sure how hot it could have gotten in the mid-day sun.

myDTC Deluxe v1.2
s)Status  c)Config  t)Set LogTick  f)Freeze Mode
0)Set SI Units  1)Mode_R1  2)Mode_R2  3)SP_R1
4)SP_R2  5)Bump Minutes  6)Bump Hours
7)DeltaT  8)LowT  9)HighT  m)Menu  r)Rules
>c
 DTMP   LTMP   HTMP  MODE1   MODE2   LOGTICK  SP_R1  SP_R2 FRZMODE
 01 F   05 F   60 F  DTC_R1  DTC_R2  5 MIN    25 F   25 F  ALLOFF
>t
Logging Tick :5 MIN
(u)Up (d)Down (e)Set (m)Menu
>d
1 MIN
(u)Up (d)Down (e)Set (m)Menu
>e

Saved!
>
Time          Tick  T1  T2  T3  T4  R1  R2  R1TIME R2TIME
000:09:30  666  66  59 212  24 ON  ON  002.4   014.8
000:09:31  667  66  59 212  24 ON  ON  002.4   014.8
000:09:32  668  68  59 212  24 ON  ON  002.4   014.8
000:09:33  669  68  59 212  24 ON  ON  002.4   014.8
000:09:34  670  68  59 212  24 ON  ON  002.4   014.9
000:09:35  671  66  59 212  24 ON  ON  002.4   014.9
.......
000:10:02  698  95  60 212  24 ON  ON  002.9   015.3
000:10:03  699  97  60 212  24 ON  ON  002.9   015.3
000:10:04  700  99  60 212  24 ON  ON  002.9   015.4
000:10:05  701 100  60 212  24 ON  ON  002.9   015.4
000:10:06  702 100  62 212  24 ON  ON  003.0   015.4
000:10:07  703 102  62 212  24 ON  ON  003.0   015.4
000:10:08  704 102  62 212  24 ON  ON  003.0   015.4
......
000:10:46  742 138  66 212  24 ON  ON  003.6   016.1
000:10:47  743 138  66 212  24 ON  ON  003.6   016.1
000:10:48  744 140  66 212  24 ON  ON  003.7   016.1
000:10:49  745 142  66 212  24 ON  ON  003.7   016.1
000:10:50  746 142  66 212  24 ON  ON  003.7   016.1
000:10:51  747 144  66 212  24 ON  ON  003.7   016.1
000:10:52  748 144  66 212  24 ON  ON  003.7   016.2
.........
000:11:45  801 174  71 212  24 ON  ON  004.6   017.0
000:11:46  802 176  69 212  24 ON  ON  004.6   017.1
000:11:47  803 176  71 212  24 ON  ON  004.6   017.1
000:11:48  804 176  71 212  24 ON  ON  004.7   017.1
000:11:49  805 176  71 212  24 ON  ON  004.7   017.1
000:11:50  806 180  71 212  24 ON  ON  004.7   017.1
000:11:51  807 180  71 212  24 ON  ON  004.7   017.1
000:11:52  808 176  71 212  24 ON  ON  004.7   017.2
000:11:53  809 180  71 212  24 ON  ON  004.7   017.2 -- 180F inside temp at 11:53 with outside 71F.
000:11:54  810 176  71 212  24 ON  ON  004.8   017.2
000:11:55  811 176  71 212  24 ON  ON  004.8   017.2
000:11:56  812 176  69 212  24 ON  ON  004.8   017.2
000:11:57  813 176  71 212  24 ON  ON  004.8   017.2
000:11:58  814 172  69 212  24 ON  ON  004.8   017.3
.......
000:12:20  836 163  71 212  24 ON  ON  005.2   017.6
000:12:21  837 163  71 212  24 ON  ON  005.2   017.6
000:12:22  838 160  71 212  24 ON  ON  005.2   017.7
000:12:23  839 160  71 212  24 ON  ON  005.2   017.7
000:12:24  840 160  71 212  24 ON  ON  005.3   017.7
.......
000:13:30  906 138  71 212  24 ON  ON  006.4   018.8
000:13:31  907 135  71 212  24 ON  ON  006.4   018.8
000:13:32  908 131  71 212  24 ON  ON  006.4   018.8
000:13:33  909 129  71 212  24 ON  ON  006.4   018.8
000:13:34  910 126  71 212  24 ON  ON  006.4   018.9
000:13:35  911 126  71 212  24 ON  ON  006.4   018.9
.......
000:14:50  986 140  73 212  24 ON  ON  007.7   020.1
000:14:51  987 142  73 212  24 ON  ON  007.7   020.1
000:14:52  988 142  73 212  24 ON  ON  007.7   020.2
000:14:53  989 145  71 212  24 ON  ON  007.7   020.2
000:14:54  990 147  73 212  24 ON  ON  007.8   020.2
......
000:15:55  051 138  73 212  24 ON  ON  008.8   021.2
000:15:56  052 135  73 212  24 ON  ON  008.8   021.2
000:15:57  053 133  73 212  24 ON  ON  008.8   021.2
000:15:58  054 131  73 212  24 ON  ON  008.8   021.3
000:15:59  055 131  73 212  24 ON  ON  008.8   021.3
000:16:00  056 131  73 212  24 ON  ON  008.9   021.3

I am really happy with the temperature sensor performance and the differential temperature controller operation.  Will know better once I have a pump to run with it and can get some collector efficiency numbers and measure the amount of heat I'm collecting in the tank and the tank losses.

Cost Info for 2 of these Solar Collectors:

Here is a workup of the cost of this solar collector (includes costs to build two of them).

48 SqFt Solar Collector Cost

48 SqFt Solar Collector Cost



Next step is too build up a solar storage tank and get the pump so I can run some testing to see how well the collector transfers the heat to the water.

4/11/10

Performance Testing the 24 SqFt Collector

I did some testing of this collector with a 5 Gallon tank to see how many BTUs it was
putting out.  Here is the test data.  The 1st sheet is calculations of how many BTUs
I should be available for water heating after collector losses.  The 2nd sheet is test
data for two separate tests I ran. I was able to get 2250 BTU/Hr out of this collector during
the test.  I think its possible to bring this up to around 2500 BTU/Hr by adding some more
insulation to the 2x6s inside and insulating and minimizing the PEX tubing length outside
the collector.


Thermal Calculations for Solar Collector and Tank

Thermal Calculations for Solar Collector and Tank



Here are some pictures from testing.  Basically the test setup consisted of:

1.  24 Sqft Solar Collector
2. 5 gallon bucket filled with water and insulated with some R-13 insulation
3. Submersible pump and some PEX tubing to pump water from the bucket, thru the collector,
and back into the bucket.
4. Some temperature sensors and my temperature controller to record the collector temps and water temps.
5.  All tests were run for one hour and BTUs and water heating recorded.  This data is recorded in the
spreadsheet above.

The first test I ran, the collector didn't have any insulation on the back of it.  I added it after trying to figure
out why the output was low.  Adding the insulation helped a great deal. 

Here's a picture of the pump I used for the testing.  I ended up turning the flow down some due to some
bad PEX to PEX fittings that had a slow leak.  I figure I was running about 1/2 rate, maybe 165gph.


Here is the collector and 5 gallon water tank with insulation under the work bench.  The pump is inside the
bucket.  A computer above is recording temperature via my temperature controller. The return is on the other
side.


Here is a picture from the second days test were I've added some insulation to the back of the collector.  In the
picture above there is no back insulation.  You can also see just a piece of the PEX return tubing that goes back to
the tank.



This is a link to the storage tank I am going to use with this collector initially built out of a
food storage plastic drum and some insulated walls.

http://sites.google.com/site/brianssolarwaterheater/home/solar-hot-water-storage-tank


Email:  smith100griggs@gmail.com


Thanks for looking.





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