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stmbtwle

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Reply with quote  #111 
Yes you write your own code on your computer, then upload it to the Arduino.  It's really not that difficult.  Get an Arduino "starter kit" which will include the microprocessor, miscellaneous electrical components, and a manual with simple programs called "sketches" and basic circuits. Once you figure out how it acts you can build your own circuits, write your code and get it to do pretty much whatever you want.  

One of the nice things about the Arduino is you can get much closer temperature tolerances than you can with a snap switch, and you can run a small LCD display that will tell you what is going on with the collector.

A differential thermostat will also work.





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Willie, Tampa Bay

gregkn73

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Reply with quote  #112 
Hi again Willie,
Does the shape of the collector has any role to the general efficiency of Aretha ? For example will a 4*12 collector with hex always placed on top, will be better placed horizontal or vertical?
stmbtwle

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Reply with quote  #113 
To be honest there hasn't been that much research done on it.  Paolo in Italy always made a roughly square collector and they worked fine.  The earlier ones had the radiator and fan near the upper top, later ones it was in an upper corner with a channel down one side, and the hot air found its way back the best way it could.  For that matter the HEX assembly doesn't even have to be in the collector, they have built at least one where the HEX assembly was outside, connected by short ducts.  All of mine have had the HEX inside the collector.

Bear in mind that an ARETHA is at heart an AIR based collector, so anything that will work in an air collector will work in an ARETHA.  The only difference is that you need a return path for the air, so it's good to have the "input" and "outlet" close together.

I've tried a solar-screen dual pass, a cinefoil dual pass, and a ZP out and return, they all worked well.  However I live in Florida and I already have solar hot water and PV, so it's hard to justify spending a lot of money on a collector that I might use 2-3 months of the year.  The only ARETHA I have working now is heating my hot tub.  It does a good job at that but an ARETHA is not best for a hot tub because of the chlorine attacking the metal parts.  That wouldn't be an issue for a space heater or DHW.

I have made it a point of mounting the HEX at or near the highest part of the collector and the fan as low as practical.  I arrange my air flow so that the air goes through the HEX first, and the fan is running in (relatively) cooler air.  So far I've not had a fan fail.   

Were it mine I think I'd mount a 4x12 collector horizontally with the HEX and fan in the center, to keep the air paths short and reduce power requirements.  The small one I'm currently running works well like that.

Hope this is of help...

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Willie, Tampa Bay
gregkn73

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Reply with quote  #114 
Do you have a photo of the one with the dual pass solar screen, without the glazing , to see it inside ?I would like to see until what height you make the solar screen, what material for the solar.screen, how you stabilize-hang the hex inside the wooden box, etc
stmbtwle

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Reply with quote  #115 
Paolo's original Aretha. he makes no mention of a screen: https://simplysolar.supporttopics.com/post/show_single_post?pid=1282827101&postcount=32&forum=268123

My Aretha screen collector with the solar screen. Regular screen might have worked, I never tried it:

https://redirect.viglink.com/?format=go&jsonp=vglnk_150936413162013&key=ccc2217bc2b75c4bdf5f7e57267f0464&libId=j9e470wl010009xy000DA3phthe5o&loc=https%3A%2F%2Fsimplysolar.supporttopics.com%2Fpost%2Faretha-project-hot-air-collector-with-car-radiator-6882647%3Fhighlight%3Daretha%26trail%3D40&v=1&out=http%3A%2F%2Fs71.photobucket.com%2Fuser%2Fstmbtwle%2Flibrary%2FSolar%2520collector&ref=https%3A%2F%2Fsimplysolar.supporttopics.com%2Fpost%2Faretha-project-hot-air-collector-with-car-radiator-6882647%3Ftrail%3D30%26highlight%3Daretha&title=ARETHA%20Project%2C%20hot%20air%20collector%20with%20car%20radiator%20-%20Simply%20Solar&txt=http%3A%2F%2Fs71.photobucket.com%2Fuser%2Fstmbtwle%2Flibrary%2FSolar%2520collector



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Willie, Tampa Bay
stmbtwle

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Reply with quote  #116 
The ARETHA Project facebook page:
https://www.facebook.com/permalink.php?story_fbid=592557904229602&id=307885346030194

You might look at this if you haven't already:
https://simplysolar.supporttopics.com/post/willies-zp-aretha-8407113?highlight=aretha&trail=10

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Willie, Tampa Bay
gregkn73

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Reply with quote  #117 
Willie thank you very much, your photos were tremendous helpful. Two more questions. What did you use as a solar screen? Also I have a radiator with its fan from a Nisan Almera 1400cc benzine. From your experience how many square feet of collector, can the above radiator absorb heat?
stmbtwle

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Reply with quote  #118 
Sorry I have no experience in that regard, read Paolo's posts on the Aretha.  He said the radiator for a 130hp motor would work for up to about 5 sq meters (50 sq ft). 
https://simplysolar.supporttopics.com/post/aretha-project-hot-air-collector-with-car-radiator-6882647?highlight=aretha&pid=1290859301

Build it and see.  Make sure when you build it you allow for a larger radiator and/or fan if need be.
You can expect about a 20F (air) temperature drop through the HEX.  Also, the air leaving the HEX should be near the temperature of the water going in. You can get it down to near zero but that requires a 2-stage HEX.

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Willie, Tampa Bay
gregkn73

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Reply with quote  #119 

I red that willie but here http://www.meteoenergia.it/aretha/index_aretha.htm     sugest  "a car radiator for every 8-10 square meters (sqm), recovered from a car-wrecker". This was the reason i asked for your experience. Thank you any way for all your help.

stmbtwle

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Reply with quote  #120 
Car radiators vary in size according to the size of the engine, so that's not much use.  My choice for a large collector would be a Jeep Cherokee radiator, they're a long, skinny crossflow type and I figured out that I could arrange for the air to go through the radiator twice, for more efficiency.  I've also determined that I can get a brand-new all aluminum racing radiator online for about the same price as a used, questionable one from a local wrecker.

Also I found when experimenting that TWO heat exchangers "stacked" work better than one, the second acts as a "scavenger" or "preheater" depending on how you look at it.  It's definitely an improvement.

An HVAC water-to-air heat exchanger I think would be more durable as the coils are copper; they come in several "standard" sizes and are no more expensive than a good radiator.  I have one in my current unit.

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Willie, Tampa Bay
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