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jeharms

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Posts: 28
Reply with quote  #11 
Thanks for your comments and suggestions, Greg.

I used the Kill-a-Watt device to measure the power usage of the fans when I installed them. 
  • The smaller heater uses two Rona bathroom fans, each of which uses 31 watts.  When the temperature reaches 40 or so, the second fan kicks in.  So, most of the time, the smaller heater consumes 62 watts of power.  If it runs for 8 hours, that is approximately .5 kwh.
  • The larger fan (a used multi-speed furnace fan) uses 210 watts when running at low speed, and 280 watts when running at high speed.  So, most of the time, the larger heater consumes 280 watts of power.  If it runs 8 hours, then it should consume approx. 2.25 kwh.
  • Total power consumption for 8 hours at high speed (2.75 kwh).
The electricity cost is the cost to run the fans, not what it would cost to generate that amount of heat with electricity.  Actually, the costs are a little on the low side.  I was still using last year's rates of 7.8 cents/kwh.  They were recently increased to 8.196 cents/kwh (plus a flat rate of $8.08/month).  I will update the web calculations shortly.



Each time the temperatures are recorded in the database, it triggers a database calculation of the power consumption (in watt-hours) since the previous time that the temperatures were recorded.  This calculation is based on the time (in seconds) between the two recordings and the fan speed during that interval (which determines which power level).  The web page obtains the total power for a day by querying the database for a sum of the watt-hours for each heater during the 24-hour period.

If you have a suggestion for more power efficient blowers, I'd be happy to hear them.

I also noticed that the east end of the large heater remains hotter than the west end.  I agree that it is likely too long a path for the airflow.  Also, the sensors aren't in the middle of the airflow path.  They are just under the top airflow divider.  It could be that the airflow is considerably less than in the middle of the path.  I'm going to leave it like this for this winter, and will consider modifying the airflows next year.  I also think that one of the reasons for the east side remaining hotter is that the air flow going to the east side is split 50/50 for the two areas (one area being between the two windows and the other being to the right of the 2nd window).  If the air is travelling half as fast, it stands to reason that would not cool down as well as the west side.

As a matter of interest, when I was sheathing the heater (i.e., installing the polycarbonate), the sensors were already installed but the fan was not.  At that point, since there was no fan to cool it down, the temperature got up to 95 deg. Celsius. 

Seeing how hot it still gets with the fan running, I should have designed it with larger air flow space.  As indicated on the web-page, the upper heater has 8" round intake and exhaust vents, each with a back-draft damper.  The back-draft damper may impede the airflow somewhat.  Also, the long distance runs for the airflow through the heater probably add considerable resistance. Given the area of the vent ducts ( approx. 50 sq. in.), I designed the airflow to try to ensure that each side would have at least 25 sq. inches for the air to pass through.

Within the next few days, I hope to start a new "simply solar" project to describe how I setup up the Arduino to control the fans and record the data.





jeharms

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Posts: 28
Reply with quote  #12 
Rick, I just saw your reply about the furnace fan.  Would you suggest a duct booster fan instead?

The sensor for the outside temperature is under the deck at the far right side of the photo.   I placed it under the deck so it would never be in the sunshine.

Comparing the outside temperature readings with AccuWeather reports for Lac du Bonnet, I'd say that the sensor is pretty accurate.


Jake
gbwillson

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Reply with quote  #13 
Jake-

Before we get too far ahead of ourselves we should verify the CFM output from the exhaust of the current fans. The fact that the furnace fan you are currently using only uses 280watts leads me to believe it to be quite small, perhaps even an inducer fan. I have a furnace fan that I converted to an air cleaner in the workshop. On high, it used 750 watts in free air, outputting about 1,000 CFM. It's not a particularly large unit either, since it came from my old tiny furnace as my house in not very big. So you might simply have a very small furnace fan. My smallest collector fan uses 200 watts and has an output of about 350CFM in free air. Once you verify the CFM output, then you might consider alternatives. The chart below might come in handy at some point. In any case, you have a working unit, so maybe at some point you come across your anemometer. I myself have been looking at mixed-flow units on Amazon. They move a lot of air and handle static pressure well. Lots of choices and various prices. I found an 8" unit  that moves 735 CFM for $59+ free shipping! Right now all of my fans used in my collectors have been free or very close to it. Garage sales, thrift stores and catching the trash when an old furnace is being replaced are great sources. 

Greg in MN





jVlcj.png 



Rick H Parker

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Posts: 742
Reply with quote  #14 

Rick, I just saw your reply about the furnace fan.  Would you suggest a duct booster fan instead?

As Greg said, lets not get ahead of ourselves. The reason furnaces use a centrifugal fan is, static pressure does the lifting, power builds velocity. Your moving air vertically two stories against the natural flow, cold and denser air up, hot and less dense air down. If you don't have enough static pressure to lift the cold air to the top of the collector, there will be no air movement. 

It is like the difference between a semi truck and a race car. For as big as they are semi trucks don't have a lot of power 325 - 550hp. You can pull 80,000 Lbs up a mountain with a semi because, the semi has lots of torque but, you cannot pull 80,000 up mountain with a 600hp race car because the race car has a lot of power but not enough torque.

Static pressure and torque are forces. Force is how strong something is. Power is the rate (how fast) energy is transferred or converted. A 98 lb weakling fan maybe fast but if it cannot bench press the air to the top, there no accomplishment. Whatever fan is used must be strong enough to bench press the air to the top, that requires force (strength) not power.


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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
Rick H Parker

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Reply with quote  #15 
Is your furnace not coming on at all or is the time duration to short to display on graph?
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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
jeharms

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Posts: 28
Reply with quote  #16 
At this time the furnace isn't coming on at all. When it does, the sensor by the furnace vent will reach 35 degrees Celsius (if using the air conditioning system as a heat pump) or 60 degrees (if the 20kw auxiliary heating elements in the furnace are on).
gbwillson

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Reply with quote  #17 
Jake-

Looking at your output temps and the temps readings in the upper corners, I think you should STRONGLY consider covering part of each unit or installing booster fans ASAP! The temps WILL begin to cause damage over time! Polycarbonate will begin to be affected just over 80˚C.(176˚F). And who knows how the other materials, adhesives, and paints will react.

This time of year we still have the occasional warm day, and the collectors as you have them simply can't draw off enough of the hot air to keep the temps under control. 

Greg in MN[eek]
jeharms

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Posts: 28
Reply with quote  #18 
Thanks for the advice.  I'll follow up on it as soon as I can.
HauteGaronne

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Posts: 9
Reply with quote  #19 
Hi Jake,
can you please explain how your screen channels are designed around the turns? Ie do you have screen frames going all the way to the end of the turns? Like I have tried to draw here.
U-turn screens.png 

Or do they end before the turns like here?
U-turn screens Short.png 
Cheers

gbwillson

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Reply with quote  #20 
FYI-

Jake hasn't been around much since he posted about his cabin heaters. If you hold your cursor over a persons name you can see how long it has been since they last visited. you might try emailing him directly.

Greg in MN
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