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Jimmy

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Reply with quote  #11 
Not a problem.
I can easily reprogram the uC to behave as a snap switch.

First I have to change the power supply I use. This is from an old notebook and it is not enough to go for higher rpms - flow rates - with the fan I use.
So I have bought yesterday a used ATX power supply which could output enough current.

stmbtwle

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Reply with quote  #12 
Jimmy I like your idea of the microcontroller to turn the fan on and off. It will give you many more options than a simple snap disk.
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Willie, Tampa Bay
Jimmy

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Reply with quote  #13 
Quote:
Originally Posted by stmbtwle
Jimmy I like your idea of the microcontroller to turn the fan on and off. It will give you many more options than a simple snap disk.


Thanks. [smile]
I'm just thinking about the best SW.
I'll try to pwm controll the fan depending on the temp differences.
A low flow rate when the output is just say 20C warmer then input.
Medium in case of a 30C difference, max if delta T is even more.
And then I can also use it to log temps.
Garage_Hermit

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Reply with quote  #14 
Jimmy,

If you did not discover it yet, there is some ARDUINO stuff HERE that you might find interesting...

http://www.simplysolar.supporttopics.com/post/arduino-links-and-discussion-6250231?highlight=arduino&pid=1286182190#post1286182190

G_H

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(2) It's wrote, "voilà" unless talking musical instruments...
Jimmy

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Reply with quote  #15 
After some trial and error with this single panel I've decided to enlarge my collector and make it (at least) twice the size.
Only thing I won't do is to drill 2 other holes in the wall so I'd like to use the existing ones. Maybe I can enlarge them a bit. They are 4" (10cm)
I think I would try the ZP or back pass set up.

So my first question would be how to make an even air flow in a 2m x 2m (or maybe even 3m wide) panel if the air enters in the bottom middle or enters in one bottom corner
and exists on the top similarly. (You can see pictures about the current set up in the first posts.)
solardan1959

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Reply with quote  #16 
Jimmy,
   The 4 inch holes will still work with the larger panel but 6 inch vents would be a whole lot better for getting good flow.  Greg, (gbwilson), has used a zero pass with a four foot wide collector so you should be able to push that to 6 foot.  He feels higher flow is preferred for the zero pass which would also point for the need for larger vents.  Still the traditional two slanted screen would also work well.  I'm not real clear on how you had the 4 1x6 meter panels in your current collector, was that a single layer or was each panel two layers?
Dan
Jimmy

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Reply with quote  #17 
The 1st setup was on the pictures. It had 4 frames inside (1m x 0,6m) covered on both sides (double layer). Those frames were inside the box with some overlapping. First attempt was to blow from bottom side than I've also tried to suck through from the bottom.
Unfortunately I was not able to measure the air flow but it had a 30-40C temp increase.
I use a blower from a Suzuki Ignis I think and it has 3 levels. With this 1st setup sometimes I had to switch to 3rd to keep the incoming air around 40C. But that setup had a big flow resistance as the air had to pass trough the 4 frames.
Than last summer I've changed to the ZP setup used by Greg. But as the construction was not that good I had to realise that the layer over the absorber was not streched enough and touched it.
So I have removed this lower layer and now it is a back pass if I'm right.
This setup works with the same blower but on level 1. And the temp increase is a max. 30C. (But I do not have a reflector. My dog could not stand it. [smile] )
So I'm not sure if I can make any comparism. My only chance is that I'm logging my collector to the net. So I can compare that in January of this year and last year what was the temp increase in the garage after a full sunny day. (Which I haven't had recently.)

So I think this blower is powerful enough for a bigger ZP, but of course I can change to a 6" one.
The first question is what manifold setup should I build in to have an even flow.
gbwillson

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Reply with quote  #18 
Jimmy-


As Dan mentioned, the ZP takes advantage of higher flow rates far better than many other designs. And unlike your first build, there is very little resistance as the air never has to pass through layers of screen. It also allows it to work best in a long configuration, compared to a square. That being said, it will still allow you to have higher, more efficient air flow rates. One way you can see just how much resistance your many layers of screen add to your collector is to compare output air flow with the screens, and compare that with the screens removed.

As far as the manifold, or specifically the intake manifold the with shouldn't be an issue. As long as the CFM are high enough to create an overpressure(slight) in the manifold, and the air leaves the manifold evenly through the narrow screen slot. Your fan sounds like it has a lot of flow, but as you mentioned, the 4" duct will cause a restriction. In any case, don't worry about the Delta-T(temp increase) so much as long as you have enough flow to control the temps should they get too high. I'm often running with only a 25-30˚ temp rises, which us usually more efficient than being much higher, since high output temps can lead to heat being lost through the glazing and ducts. 

Greg in MN
solardan1959

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Reply with quote  #19 
Jimmy,
   If I am understanding what you described, you have a metal absorber on the back and a screen some distance from that, (maybe three inches), that the flow is going through.  The glazing is another inch or so from the screen.  I was recently talking about such a set up only using a wavy metal absorber but now I'm getting off track.  If my guesses above are correct, it would work as you have found out but definitely could be improved upon.  Unless I missed something that is not a back pass, a back pass would have the absorber closer to the glazing and the flow would only be behind the absorber leaving no flow between the absorber and the glazing.  (back pass has the flow passing by the back of the absorber only)  A dual pass would have air on both sides of the absorber.  So it appears like you do mainly have a zero pass, just not a full screen one like Greg's.  All of the above designs work but I think you could make yours work better several ways.
add a layer of screen to the back even if you lay it on the absorber.
close the gap on the screens to about 1 inch between the layers.
build a plenum/header on the input and output to force the air between the screens, (which was one of your main questions)
Here is one of Greg's photos from his 2nd zero pass build Solar Web Page > Categories > Member Projects! > Greg's New ZeroPass Collector
[image] 

What I'm not finding is a good photo showing the manifold in the real collector he built but it was just a hole like you have, a rectangular section on each end, and boards or something above and below the screen channel to force the air to flow between the screens.
The 90 degree change from you input duct will be your biggest restriction but has you have already found out, you can still get good flow out of your unit even with you 4 inch ducts.  If you do some of the above steps you should increase your temps which will allow you to leave as is and increase your flow.  Ideally you can run at the highest speed and still see your 30 C but have a much higher flow rate.
Dan

edit, here is an example of one I built, I used flashing to block the flow above and below the screen channel.
[image] 

from: Categories > Member Projects! > SolarDan's Zero Pass/Dual Pass Long Screen Collector but that is a long story and this was the last design of that build.
Dan
Jimmy

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Reply with quote  #20 
Thanks Greg,

 question is how to measure the output air flow? My idea was to put a DC fan in the output and measure the indicated voltage. But it is not exact at all. And as I have already missed that with the old design what I can still compare is the measured data of temp increase.

Since using the ZP I think sometimes even the 1st level of my blower is too high. So I might further reduce it with some resistance or using PWM.

Hi Dan,

 sorry you are right it is not a back pass just a ZP where the lower screen was removed. As it was touching the absorber. And my idea was that it just blocks some light to be able to touch the surface of the absorber. So right now I have only one layer about an inch behind the glazing.
Other thing is the absorber. As I'm not able to find Polyiso board with Al layer here in Hungary I'm using some thin heat reflector foil painted to black. So it could be that I should change to some better absorber. The first collector only had some 3mm mdf board painted to black as absorber. I do not know if it was better or worse.

 Jimmy
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