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HolgerB

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Posts: 13
Reply with quote  #1 
Hi all,

1st of all thanks for this forum

I should have know it earlier when I learn all the stuff about solar air heater and even bought some construction manuals from a german guy which lives from selling build-kits for hot air collectors. After seeing all those different variants I ended up building a collector which is some sort of mixture of different modells.

I hope you bare with me since I am no native English speaker. In other words: Those who find spelling errors, can keep them

My hot air collectors is not a high tech model. I build it as straight forward as possible. Main material used is massive Siberian larch because this wood is know for being very weather resistant.

The main frame is constructed from massive planks (measurement 27x143 mm). The back side is made by deals (measurements 20x144 mm) which have tongues and grooves (hopefully this is the right translation). I screwed everything together and added a few massive metal brackets. The part between the frame and the backside was sealed with silicone. Then I build an inner frame with roof lathes (24x48 mm). This frame was later filled up with scrunched newspaper for isolation. I added a layer of aluminum foil for further reflection of any IR radiation inside the collector. Then I added a layer of pressboard which I screwed to the roof lathes. Everything was painted black afterwards. I am using a simple black aluminum blind (240x90 cm) as absorber. The air intake are several 3 cm big holes in the bottom of the collector. I am using Acrylc double-chambered sheets (16 mm thick) to cover the collector. Transparent silicon sealing tape is used in between. The front sheet is kept in place by some metal brackets which apply slight pressure to it. I used thin aluminum
sheet as roof to seal gaps between the frame and the back wall. I am using standard 100 mm Polypropylene tubes (ususally waste pipe) as it can withstand temperatures above 90°C.

Inside my house I use a thermostat with external sensor (inside the collector) which controls a small 12V DC / 2A power supply. A standard PC fan (120x120 mm) is used to suck the air into the house. I used a PC fan because they have a higher operating temperature compared to the cheaper fans you get from the hardwarestore (which usually can only take up to 40°C). My fan is rated with 80 m3/h airflow and needs 1W of power. May be I will need a stronger fan but for first testing this one should do.

Things I learned so far:
- Interestingly there is always airflow from the collector even without sun and inactive fan. Seems to be some sort of chimney effect. I need to build a hatch to cover the tube from the collector in Summer / Winter.

- In the Summer the sun can cause temperatures inside the collector above 70°C causing a massive warm airstream into the house. Unless you like to have a sauna in your house, a hatch should be used
With above 30°C in the shadow the airstream feeled like hair blower.

- Never build your collector too massive. We had to use the car pulling it upwards with a thick rope to put this thing into place (about 2.2 m above the ground).

Currently I am building a wooden frame with a hatch, which will both provide a solid mounting for the 120 mm fan to the wall as well as holding the hatch in place. A small magnetic switch (called Reed contact in Germany) will only close the fan circuit when the hatch is open. I will do this to avoid the fan blowing against the closed hatch. I will add pictures later as soon as the hatch is mounted. I was thinking about an electric actuated hatch which is controlled by the thermostat as well but this makes things overly complicated plus motorized "fan jalousies" are way too expensive (> 100€) for such a pet project.  If everything turns out as I expect, I will build a second collector with 2.5 m² as well which uses fly mesh as absorber. The results I have seen here look promising. I will then chain the two collectors in row (1st collector feeds the warmed air into the second collector).

Here is a link to my Google Picasa gallery:
https://plus.google.com/u/0/photos/106197940058137636835/albums/5900438705710925921?authkey=CLWL29_367OFbA

The descriptions are in German but I guess the pictures are quite obvious. Feel free to ask questions as they arise.

Best regards,
Holger

SolarInterested

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Reply with quote  #2 
Holger welcome to our forum. Do you know how much your collector weighs?
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Both temperature rise and airflow are integral to comparing hot air collectors
HolgerB

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Reply with quote  #3 
Good question:
I was able to move it with my wife or a friend.
Educated guess ~ 60-70 kg
EcoMotive

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Reply with quote  #4 
That's a great looking solar heater Holger. Your english translation was very good and thank you for the interesting account of how it was built and mounted.

I must say it's quite refreshing to see some pictures of work done all the way over from Germany and to see metric units being used

P.S. That's a nice VW Golf you got there... and welcome to the forum.

Lance in Newfoundland

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 “Only primitives & barbarians lack knowledge of houses turned to face the winter sun.” 
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SolarInterested

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Reply with quote  #5 
Holger you mentioned "using a simple black aluminum blind (240x90 cm) as absorber". Is there a picture of just this? I think I see it in some of your photos behind the glazing but that may just be corrugations in the glazing.

Your collector is heating outside air which is good if you want fresh air. Did you consider drawing air from inside so it didn't need to be warmed so much?

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Both temperature rise and airflow are integral to comparing hot air collectors
HolgerB

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Reply with quote  #6 
@EcoMotive:
Thanks for the nice words ! Hopefully it is not too hard to translate metric values to inch, feet, etc.
Our VW Golf is quite old but still in good shape. I hope it will last another few year

@SolarInterested: I am not shure if blind is the right translation. In German we call this "Jalousie". I mean like this:
http://www.hornbach.de/shop/Alu-Jalousie-schwarz-40x175-cm/3420868/artikel.html
I saw another guy buidling several big hot air collectors covering one complete face of his house using "Jalousies" as absorber. Since he had big temperature gains, I thought that a Jalousie would make a nice absorber. Especially since my jalousie was not expensive (~ 40€) and quite easy to install. Since it was already in dim black no further work was required.  There is a picture showing a friend of mine where the collector is mounted at the wall but still open. There you can see the Jalousie fully extended prior we mounted the glazing.

It is picture #26.

I did indeed consider drawing inside air into the collector but then switched to the outside air concept for several reasons.
#1: We live in a massive brick house. So making holes in the wall mean going through 70 cm bricks which is not exactly fun. One hole was quite some work and I did not feel like adding a second hole.

#2: We love fresh air. So having something that brings in fresh, pre-heated air seemed more logical to me than circulating used air from the house. Both concepts have their strenghts and their weaknesses.

#3: I was afraid of condensing humidity when the warmer inhouse air touches possibly colder surfaces in the outer collector. May be I am a bit over cautious here because we hade severe issues in our house with mold.

#4: Circulation you inhouse air means you need good intake and exaust points to enforce air circulation in your house. Since we live on two floors I could imagine this would require me to suck colder air from the upper floor and push in heated air in the lower floor. Not quite easy to do






solardan1959

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Reply with quote  #7 
Holger,
   The Blinds are something I have been wanting to try since reading The ZEN of passive Solar Collectors. http://www.iedu.com/Solar/Panels/#Absorber
  He uses something that works out like an upside down and backward blind and claims that works best.
  I am not sure what you are doing with the outlet vent.  It seems to be in the middle and not at the top of the collector.  How are you channeling the air through the collector from the input to the output as the usual configuration is input at the bottom and output at the top?
  This wooden hatch, does this also stop and seal the flow to prevent reverse thermo syphoning?  It needs to seal to prevent it from sucking the warm air out of your house at night.  A backdraft preventer can also be used like this so it opens and closes automatically.
http://www.homedepot.com/p/t/202907125?productId=202907125&storeId=10051&langId=-1&catalogId=10053&MERCH=REC%2d%5f%2dproduct%2d1%2d%5f%2d202907128%2d%5f%2d202907125%2d%5f%2dN#.UgywjNco6po

Welcome to the group and thanks for contributing your project!
Dan
HolgerB

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Posts: 13
Reply with quote  #8 
Dan,

thanks for the welcome ! I can not exactly agree with the concept of the Zen of passive heating. Adding something whichs stores heat to the collector like a thin layer of slate which stores heat can extend the time period where you extract heat from the collector. At least in my case the backwall of my collector seems to heat up as well since I usually get another 1.5 to 2 hrs after dawn where still warm air is drawn from the collector. This might change though in spring and autumn when the sun does have less power than in the summer and the outside temperatures are lower. Also I have to add that this is only theoretical and might be different between active and passive collectors.

For input I use several holes in the bottom of the collector (see pic #13). The exhaust is a PP-tube with a diameter of 100 mm in the top of the collector (seep pic #15 and #16). It was first in the middle at the top of the collector but I had to move it to the top right corner because my breaktrough which I made from inside the house was much closer to the window as I thought

I do not exactly know what thermo syphoning means but the hatch will close the whole to avoid cold air flowing into the house. First I thought that warmer air from inside the house would stream out through the whole if the inside temeratures are lower but vice versa is happening. As soon as the hole is not covered cold air from outside streams into our house. This seems unlogical to me since cool air is heavier than warm air. So I had rather expect an airflow from inside to outside as the collector gets cooler...strange...

Thanks for posting a link to the flowback damper but it is not clear to me how it works. Unless there is a bi-metal spring which acutates the damper flaps when temperature changes, I guess it is kept close by a spring unless enough airflow takes place. The later method causes similar issues like I had with fan "jalousie" I wanted to use in the first place:
http://www.amazon.de/Edelstahl-Abluftgitter-LG-5015-Rohranschluss-L%C3%BCftungsgitter/dp/B0062X90SC/ref=pd_sim_sbs_diy_4

My weak fan is not strong enough to push the flaps open. I do not want a big fan requiring 40-100W for simply drawing a small defined amount of air from the collector. I am open to suggestions for a cheap solution to this issue though

Regards,
Holger

SolarInterested

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Reply with quote  #9 
Quote:
Originally Posted by HolgerB
...  There is a picture showing a friend of mine where the collector is mounted at the wall but still open. There you can see the Jalousie fully extended prior we mounted the glazing.

It is picture #26.


Thanks

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Both temperature rise and airflow are integral to comparing hot air collectors
HolgerB

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Posts: 13
Reply with quote  #10 
You are welcome !
BTW: What is the right translation for this ? Is it jalousie in English as well ?
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