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Kostika

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Reply with quote  #1 
Hello, i am new to solar projects. I would like to build an aluminium screen solar air heater.

I really need to know how many screen layers should i use?
Also, the heat pipe of the collector is going to my basement so it needs a fan. The fact of pushing the hot air down is a good or bad idea? Just like this case.
[P1020290] 

SolarInterested

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Reply with quote  #2 
Quote:
Originally Posted by Kostika
Hello, i am new to solar projects. I would like to build an aluminium screen solar air heater.

I really need to know how many screen layers should i use? 


Two seems to work well.

http://www.builditsolar.com/Experimental/ScreenAbsorber/ScreenAbsorber.htm

"the two layers of screen have done about as well or better than other more complex absorber configurations tried so far."

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

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Reply with quote  #3 
Kostika-

There are currently two main configurations using screen as the absorber. Either the air passes through the screen layers, or passes between the screen layers. A 4'x8' collector can use either configuration with similar results. But when you build a larger collector and desire maximum BTU output, passing the air between the two screen layers is more effective. This configuration is referred to as a ZeroPass, or ZP for short. 

I agree with SolarInterested in that two layers is often the norm. If air has to pass through many layers of screen, it creates a lot of airflow resistance. With the ZP configuration, air passes between the layers, so the flow resistance minimal. Although often the bottom screen layer is doubled up, which helps keep the sun from passing to the back surface of the collector.

As far as pushing or pulling air, larger ZP units do better with pushed air, otherwise either way works fine. It takes very little air movement to overcome the buoyancy of warm air. My current ZP collector blows air off of the basement floor, through the collector and back into the basement. So it not only warms the entire basement, but the main floor above.

Greg in MN

PS: Please tell me the photo above is from last winter, and not last week. I'm not ready!

Kostika

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Reply with quote  #4 
Thank you very much for your reply.
Kostika

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Reply with quote  #5 
Thank you very much for the reply, what can you say about this design

https://cdn.instructables.com/F6Y/UD5C/IR3ZMAAR/F6YUD5CIR3ZMAAR.LARGE.jpg?auto=webp&fit=bounds

https://www.instructables.com/id/Screened-Solar-Air-Heater/

The high air flow resistance is good or not for the heat absorption,pump to circulate air?
gbwillson

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Reply with quote  #6 

Kostika-

There are a lot of heater designs on the internet, and the all work to one degree or another. But many of these make extraordinary claims about how hot they get. What they often don’t mention is just how little air is flowing through the collector. So high output temperature claims by themselves mean nothing. 

A heater design with lots high resistance is fine as long as you can more enough air through it to make it efficient. Hot collector temps also waste a lot of heat through the glazing as the greater the difference between the interior and exterior collector temps speeds heat loss. Looking at the design in your post, it’s easy to see why this design produced so little heat was produced. I think you noticed why as well…too much resistance. The air would have to pass through what looks like 48 layers of screen, with only a small 4” fan for air movement. But with that many screen layers, along with 4” ducting, even a large fan wouldn’t move much air. I do like the pleats, but maybe they should have been in the direction of the airflow, instead of perpendicular to it.

To compare the effectiveness of a design, three bits of information are needed to access the performance of a solar heater: input temperature, output temperature, and airflow. With these numbers, the actual BTU’s being produced can be calculated. Your linked collector had all three, and assuming he did his calculations correct, he states his BTU output for the day was 2,400. Think about that for a moment. He simply couldn’t get enough air through the collector to capture the heat he was collecting. An average electric space heater you may have at home will produce about 5,000 BTU’s per HOUR! Of course, an electric heater would cost a small fortune to run all day, while a solar air heater might cost as little was a 100 watt light bulb to operate.

My 4x16 ZP heater design, provides my home with over 15,000 BTUs per HOUR on a sunny day, regardless of the outside air temperature. Since I first built the ZP, others have built their own ZP heaters, some with improvements.  There’s always improvements to be found.

Greg in MN

“Any heater you build will give you more heat than the heater still on the drawing board.”

 
SolarInterested

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Reply with quote  #7 
Kostika you seem to be quoting posts without adding your response. Let us know if you need any help on posting.

Mike

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

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Reply with quote  #8 
SolarInterested, i dont fully understand how this forum works.
Gbwillson can you please provide to me a tutorial how to make a zero pass collector, what about air pump,glazing (in my country the only type i can find is polycarbonate sheet), pipes material etc?
gbwillson

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Hi Kostika-

Think of a forum as if you were writing a letter or email to a friend. You have the name of the person at the top, the body of the letter, and perhaps a signature of sorts. If the post is long or has many questions, it can help to break up large amounts of text using paragraphs or a list of questions. You can add photos, diagrams, hyperlinks, and more.

It's not as fast as an actual "chat room" or instant messaging, but it is as quick as an email, and as versatile. I rarely quote people unless I need to, well, quote something specific someone said because maybe there is a lot to explain or the quote saves me from typing a long rehash of someones post. Normally, I either hit either reply, or I just add a new post to the same thread. What you did was pressed the little pencil icon in the upper right hand corner of a given post. That allows you to select a specific quote about what someone said. But without a little editing on your part, it will include the entire post so you will want delete all but the important quote. If you simply want to reply to a post, you can hit the reply button in the lower right corner of a post. This is good if there have been several posts on the thread since you last responded. Your last post to both SolarInterested and myself in the same post is fine too, as long as you identify the individual parties. This method works great for answering several posts at the same time. 

Please don't hesitate to ask questions about how to use the site. Others likely have the same questions, but never asked. You won't have to wait very long for an answer, as many of us check in several times per day and even at night(insomnia).[sleep]

I hope this helps,

Greg in MN    


gbwillson

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Kostika-

There isn't a step by step tutorial, per say, on how to build a ZeroPass collector. However, the build is essentially the same as the standard angled screen collector with a couple of minor changes. I'll link to a simple screen collector build video below and point out the minor differences. 

But first, being you live in another country(where?), It will help to go over a few terms so we are on the same page. All solar air heaters have most components in common. You start with a box, insulate it, paint it black, add air intake and exhaust openings and cover it with glazing. Glazing can be glass or plastic. Glass is heavy and can shatter. Plastic glazing is usually either acrylic, or polycarbonate. Polycarbonate is preferred as it is lightweight, and shatter resistant. Acrylic tends to yellow and cracks rather easily compared to polycarbonate. You will want your plastic glazing to be UV protected to make it last longer. Some polycarbonate sheets come in what we call twinwall which is 2 or 3 layers connected together. This is often found in greenhouses and adds R-value to the glazing which is usually the biggest source of heat loss. Air Pump(we call it a fan) This is used to move the air through the ductwork, into the collector, and back again. These can often be found for little or no cost. A centrifugal fan is most commonly used as opposed to a radial fan as it handles static resistance, or the resistance to airflow, better. What you call pipes, we usually call ducts when in reference it home heating and air conditioning. Ducts are either thin aluminum or galvanized metal. You can also use flex duct, which allows ease of installation, at the cost of increased air flow resistance. 

Anyway, I hope the above gets you a little more familiar with a few of the terms we use. There are more, and we tend to use abbreviations and such during discussions. But you can't figure out something by the context, don't hesitate to ask. 

Okay, below is a link on how to build a simple screen collector. Once you have a better understanding of the basic build, I'll explain the minor changes for the ZP build.

Greg in MN

Below is a link from Gary Reysa's outstanding DIY solar site. Here he builds a basic screen heater.

https://www.builditsolar.com/Experimental/AirColTesting/ScreenCollector/Building.htm


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