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Archdemon

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Reply with quote  #11 

I think its made out of leftover bricks and a layer of plastering facade? Not sure if thats the right word....

Yeah where the washroom and bedroom is today used to be a outer wall on the rightside, but now there is an extension with a space below you can crawl in, i guess i could just make some holes there to get some air in.

Same with techroom i guess.
Since the warm air will travel towards the bedroom in my estimation, this should create some hotpockets and positive airpressure as long as i can pull fresh air in the same route.

But maybe im better of just doing a matrix screen absorber, and one long piece with 2 outlets into the house rather than 2 separate ones.

Maybe could add like a fan controller to direct / control the heatflow to where i want it.
Anyone tried that?

What size of a fan is recommended? Or should i simply count CFM?
Dont want a to powerful fan in risk of cooling the air while pushing it.

 

stmbtwle

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Reply with quote  #12 
You can always slow down a too-big fan. Too small...

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Willie, Tampa Bay
Archdemon

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Reply with quote  #13 

Quote:
Originally Posted by gbwillson


More questions:

How Deep should a collector be?
Have you tried different depths with different results?

Glazing Variations? Most common seems to be polycarbonate, if so which thickness here?

How much insulation is needed at a minimum?

Black paint in the back or some reflective capability?

2 screens peaked ( in matrix design and ZP ) or could there be any benefit in running 3?

Any benefit from drawing (Cold) air in with a fan and sucking out the hot air with Another fan?

Will booster fans inside the setup just cool the air instead of move it? Or will they simply break from the heat. (Example; setup 2x 90mm fans in the bottom at low rpm just to move the air up.)

Rick H Parker

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Reply with quote  #14 

Glazing Variations? Most common seems to be polycarbonate, if so which thickness here?


Here is a page that has a lot of information on the pros and cons of different glazing materials.

 

Black paint in the back or some reflective capability?

 

Flat black, reflective is counter productive. You want to get as close to Blackbody as practical.

 

 

 

Any benefit from drawing (Cold) air in with a fan and sucking out the hot air with Another fan?

 

Fans in series will boost the total pressure but not the flow. Unless one fan does not have enough pressure to overcome the opposition to flow.

fansinseriesgraph.gif 

 Fans in parallel with boost the flow but not the pressure.

fansispargraph.gif 

Will booster fans inside the setup just cool the air instead of move it? Or will they simply break from the heat. (Example; setup 2x 90mm fans in the bottom at low rpm just to move the air up.)

 

Fans do not cool air. The cooling effect of a fan on a human is, sweat evaporating and carrying away heat .. evaporation cooling. Try this experiment, with a thermometer measure still air, turn on a fan measure the air going into and coming out of the fan … all three measurements are the same.

 

 



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Rick H Parker
Kansas, USA
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gbwillson

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Reply with quote  #15 
There is another reason you may want two fans, with one pushing and one pulling air through your collector. If your collector gets hot enough, you will need a lot of airflow to keep the excess heat under control or you are not running efficiently and wasting heat. So you need to have a large amount of air flowing through the collector box. A single, large capacity fan pushing or pulling may be able to control the excess heat and keep the collector running efficiently. But this single may cause the glazing to bulge in or out excessively. This may allow air to bypass the collector where it is not desired. It may also cause air leaks. Two fans may be able to give you the CFM needed to keep the output temps under control as well as greatly reduce the glazing deflection. You can also set up the fans so only one runs when the collector output temps are low or moderate. And the second fan kicks in when temps get too high.

Bottom line, you want a collector to heat the air as high as possible as it passes through the collector box, and the fan capacity to keep the output temps moderate for maximum efficiency. The output air temps should never get so high as to damage a second, exhaust fan.

The amount of insulation needed depends on types of winters you experience, and to a lesser extent who and where the unit is to be installed. Frigid winters like where I live in Minnesota, would require at least an inch of polyiso. You could get away with less if the unit was mounted to the wall of the house. But more than an inch would be better if the back of the unit was exposed to the winter winds. Insulation should also be made of polyiso or fiberglas which can handle the heat. Never use polystyrene unless it is covered with a layer of heat resistant insulation. Even a short stagnation event will cause polystyrene to melt unless protected.

How deep? Using common board sizes, such as a 1"x6" or 2"x6" for the side walls are almost always used, but nothing says you have to. I don't recall anyone testing performance one way or another to see if there is a measurable difference due to differing collector depths. But 4"-6" is a good working depth. Since the back insulation and any back cover may take a portion of that depth. Too shallow and it can make it more cramped to work inside. You also make everything inside the collector box that much closer to the cold glazing. Too deep, and your collector box may take slightly longer to warm in the morning and you use more materials which weigh more. 

If using three screen layers for a standard angled screen collector you will have more air flow resistance than if you had only two layers. So more airflow would be needed. Tests have shown little to no difference in performance between 2 or 3 layers. With a ZP, a 3rd layer of screen wouldn't make a difference in the flow and could potentially improve performance. BUT... a 3rd layer would also receive less sunlight, and move the hottest part of the absorber that much closer to the cold glazing. This might only be an issue if the collector were very shallow.

Greg in MN








Rick H Parker

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Reply with quote  #16 
If using three screen layers for a standard angled screen collector you will have more flow resistance than if you had only two layers. So more airflow would be needed.

More air pressure not airflow capacity would be needed to overcome the additional resistance and get the desired airflow. This is a case where two fans in series would make a difference.  Flow = Pressure (Force) /Opposition to flow (Resistance) up to the maximum airflow of the fan.

It is the same as batteries ... Batteries in series, the forces (Voltage, pressure) sum.  Batteries in parallel the flow capacity (current, airflow) sum.


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Rick H Parker
Kansas, USA
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JohnGuest

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Reply with quote  #17 
Increasing pressure to overcome resistance also increases running costs. If you gain the additional fan power back terms of additional heat gains then its all good. If you dont, you`ll reduce the COP [wink]
Rick H Parker

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Reply with quote  #18 
Increasing pressure to overcome resistance also increases running costs

Running two fans in parallel to increase the flow capacity does the same.

Which way to go depends of what is preventing one from getting the desired airflow. If one is getting way less the one fan is rated for in terms of CFM, more pressure (series) is the way to go. If the desired air flow is greater then the rated CFM of one fan, more flow capacity (parallel
) is the way to go.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
JohnGuest

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Reply with quote  #19 
Pressure always costs more than flow so, whenever possible, minimising resistance is the way to go [wink] 
gbwillson

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Reply with quote  #20 
"Resistance is futile"

Signed,

The Borg Collective

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