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jeharms

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Reply with quote  #1 
Today is the first day of my fully functional solar heating system near Lac du Bonnet, Manitoba (just north of the 50th parallel).  I'm celebrating by sharing the info with my fellow DIYers in this forum.

heaters.jpg 

My system consists of the following:
  • Heater 1 (8' wide by 9'6" high) zero-pass screen
  • Heater 2 (34' wide by 7' high) zero-pass screen
  • Arduino controller with an ethernet shield
Air movement in Heater 1 is powered by two 90 cfm bathroom fans.  I programmed the controller to turn one fan on when the heater temperature (near the exhaust) is 5 degrees Celsius warmer than the interior.  If the heater gets above 40 degrees C., the second fan switches on.  It has two 4" inlets and two 4" outlets that share the same airflow path.

Air movement in Heater 2 (mounted on the 2nd storey, south-facing wall) is powered by a used 3-speed furnace fan. The fan is located in the crawlspace and pushes the air into the heater via an 8" duct.  The heat is exhausted through another 8" duct back down to the crawlspace where there is a screed coat of concrete over a 2" layer of SM rigid insulation.  The idea is for the concrete floor to act as a heat sink and dissipate the heat overnight into the main floor by radiation and by allowing the cold air intake of the central air furnace to access the heated crawlspace.  The furnace fan switches from OFF to LOW when the temperature in the heater is more than 8 degrees warmer than the crawlspace and from LOW to HIGH when the heater temperature exceeds 40 degrees Celsius.

I created a website to monitor the results:
http://jeharms.ca/cottage/index.php

The Arduino controller takes temperature readings from 8 sensors every minute or so and updates the database (for the website) about every 10 to 15 minutes.

My hope is that the solar heater will be the main heater for the cottage (approx. 2000 sq. ft.) and that my 20kw electric furnace will serve as the backup heater.

I welcome your comments and questions.

Jake


SolarInterested

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Reply with quote  #2 
Jake, very nice and thanks for sharing the details of your setup.
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jeharms

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Reply with quote  #3 
I thought I'd add something about the design of these heaters.  boxes.JPG 
The upper floor heater was a bit of a challenge for two reasons:
  1. the layout inside the house put limits on where I could place the 8" ducts from the crawlspace to the heater.  The upper duct is in a chase in the very corner of a bedroom, and the lower duct is inside the bathroom vanity.  They both travel along the same chase through the downstairs bathroom to the crawlspace.
  2. the placement of the windows put limits on the ability to have evenly spaced airflow partitions.
The glazing on the heaters is the clear polycarbonate sheathing that matches the 9 - 36 profile of metal sheathing (a diamond rib every 9").







gbwillson

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Reply with quote  #4 
Very nice setup Jake!

Looking at the readings, I see 3 readings for heater #2, but only one for heater#1. And is the non-exhaust reading the intake temp for each heater? What is the CFM output for the two heaters? And what did you use for the size of the screen gap? 

I also had a chuckle when looking at the total BTU's for today. Kinda hard to read as numbers run together and might be a bit easier if you added a comma where needed. But that might mess up the formatting. But in any case, you have lots of BTU's. Is there any way to break out the collector data separately between the two heaters? They are so much different in size, shape, and CFM I think it would be interesting to better judge the specific performance. I do like seeing the average and total for the day for each of the units. Very helpful information, and it really shows you just how many BTU's the main heating system DOESN'T have to run.

Thanks for sharing. I'll be checking the data regularly.

Greg in Minnesota

PS:I'd also love to see more about your Arduino setup. Might be better in a separate topic though.
jeharms

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Reply with quote  #5 
Thanks for the feedback and questions, Greg.
I have separate data for the heaters, so I'll just work at presenting it separately for each heater.
I'd be happy to share my arduino setup on this forum.  Should I start a new "member's project" for that?

There are 3 sensors for Heater 2:
  • one 15" from the top near the east end
  • one 15" from the top near the west end
  • one right in the exhaust vent.
The one in the exhaust vent is needed to get the temperature of the air that is re-entering the building.  Because of its proximity to the building air (separated by a back-draft damper) it will not necessarily reflect heater temperature.  For instance, at night, it is several degrees warmer than the temperature at the other two sensors.  Also, as it is right near the top of the heater (under the 42" overhang), it might not get as much sun as the other sensor locations.  I use the average of the east and west sensor readings to trigger the fan, but I use the exhaust/output sensor for calculating BTUs.

I wanted a sensor at each end of the upper heater to get a sense of the airflow.  As I expected, the gap at the top of the windows is too small for even airflow. When the fan is on, the sensor at the east end (past the 2nd window) stays several degrees hotter than the sensor at the west end.

The other heater only has one sensor, right at the top between the two 4" exhaust portals.  I might still add another one at the top in the middle (so that the reading at night is not affected by the heat coming from the house into the exhaust vents).

Both heaters are situated under a 42" eave (overhang).  This means that, for the top heater which is closer to the eave and is only 7 feet high, at the peak of summer the sun should touch only the bottom 12" of the heater.  I should be able to get by without covering that heater in the summer.  I might have to cover part of the lower heater because it is taller and starts well below the eave.  I suspect the bottom 4 feet of the heater will be exposed to the mid-summer sun.

For the BTU calculations, I'm guessing at the cfm.  I misplaced my anemometer to measure the airflow rate, and I hope to find it or get a replacement soon.  I'm pretty confident about the airflow rate for Heater 1 because the fans are identical to the fans used on my experimental panels on the guest cottage.  I measured their airflow rate with the anemometer a couple of years ago.  I'm less confident about the airflow rate for Heater 2.  Reading up on multi-speed furnace fans, I saw rates like 400 and 600 cfm for low and medium speeds and 1200 cfm for high speed.  At the moment, my formula is using 320 cfm on low speed and 400 cfm for high speed (medium-high on the fan motor).

I'll let you know when I've been able to measure the airflow rate.

Cheers,
Jake


jeharms

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Posts: 28
Reply with quote  #6 
Further in response to Greg in Minnesota, I have now redesigned the web page to improve the display of BTU data. 
  • added 'thousands' separator
  • show the hours and BTUs/hr for each heater separately
I also changed the representation of power usage from watt-hours to kwh (kilowatt-hours).

Here is the link again for the web page: http://jeharms.ca/cottage/index.php

I'm happy to see your interest in this project.
gbwillson

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Reply with quote  #7 
Jake-

Thanks for the changes to the output table. It's helpful to see how the different units are performing.

As the sun gets lower in the sky your performance should improve, at least for a few weeks. But the running time will get shorter. And both collectors should see some gain from the reflection off the snow. 

Greg in MN
Rick H Parker

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Reply with quote  #8 
Oct 13
3.05 kilowatt hour = 10,407  Btu
Heat collected 155,669 Btu.
Ratio 155,669/10,407 = 14.96/1

15 units of energy for every unit of energy overhead.  Gain ratio= 14:1.




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gbwillson

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Reply with quote  #9 
Jake-

Could you post 7-10 days or more of data? Even a months work would be awesome! I'd love to watch for trends over time, especially as the season changes and the sun gets lower in the sky.

A few observations:

-I'm only able to point out the points below because the great data you are collecting which is very informative. I thank you greatly for sharing!

-I think the output temps are too high in both units. You are currently outputting 60C or more(140˚F) and the sun is still quite high in the sky so I would expect the output temps to continue to rise. With a 20˚C input that gives you a DeltaT 40˚C(70˚F) or more! And as the outside temps drop, there will be a greater difference between the outside air and the collector. So there will be a lot more heat loss through the glazing. A small booster fan could help the airflow needing to change primary fan. 

-I've noted that the upper East corner is quite a bit warmer than the upper West. This tells me that it is likely there is not enough air moving in that corner. Actually both upper corners are much hotter than the exhaust vent. Rounding those corners may have helped eliminate the hot spots. While adding a booster fan may also correct this. It also could be that the length of the duct run to the far East corner is too long. If you have easy access to the innards, you might try making small adjustments to the flow where the air rises between the windows. Making this opening a bit smaller should force more air to the upper East corner. If easy access isn't possible at this point can move the divider that splits the intake air to have a little more air directed to the East end? Also, without an accurate CFM reading, the numbers could be off.

-Is there any possibility that air is bypassing the dividers? Even small gaps would allow the air to miss the channel at the cost of lost heat. 

-I'm not sure I follow when you show the cost of electricity. Does your electricity have tiered pricing?Or are you trying to show how much electricity it would have cost had you produced the BTU's with electricity? I ask because if Rick is correct that on the 13th it cost you 3.05kwh to produce 155,669BTU's, then something seems off. That's an awful lot of electricity! Yes, you are getting plenty of BTU's, but at the cost of over 90kwh for a month. Heck, my entire house averages about 500kWh for a entire month! So maybe the charting is off, labeled wrong, or the big fan uses a heck of a lot of juice. Have you check your fans with a Kill-a-Watt? I would shoot for a ratio of energy used to energy produced of 50/1 or more. Though it may not be possible depending on the cost per kWh.

Again, thank you for sharing sure great data. I'd love it if you could start a topic showing you assembled the Arduino unit and how you used it to log this great data.

Greg in MN

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Rick H Parker

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Reply with quote  #10 
That's an awful lot of electricity!

It is his Centrifugal fan, the 3-speed furnace fan. Centrifugal fans are great for boosting pressure and a producing a smooth air flow but, the electrical power to air power conversion is low ... all them changes in direction as the air is pushed through robs power.  Axial fans are better at moving large volumes of air efficiently.

What I find weird is the outside temperature rises and falls with the collector output. Sensor too close to the collector?

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Rick H Parker
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