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Green Energy Living

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Hello, has anybody ever used or have the test results or temperature output or temperature rise of a horizontally mounted 4 foot by 6 foot size 4 foot by 8 foot aluminum dryer vent hot air collector?. the reason why I'm asking is I just basically want the least expensive easiest to build highest temperature output horizontally mounted panel so I can put it on a roof without it being so high. 4 ft high is okay. Just in my mind it seems that the aluminum dryer vent would be easy inexpensive and have a decent temperature output. What would be the design or performance of a screen collector mounted horizontally?. Thank you

gbwillson

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GEL-

From what we've seen there is very little difference in performance between vertical and horizontal heater designs. It takes very little effort to overcome the buoyancy of warm air to rise. That being said, if a design has airflow that is too low, the warmest air would tend be towards the upper parts of a collector. Or, in the case of a serpentine aluminum dryer vent, the upper part of a given section of dryer duct. For ease of build and low cost for a 4x8(or 8x4) heater I think either the dryer vent of 2-screen collector should give you roughly 4,000-5,000 BTU's per hour, which is about the same as a household electric space heater.

Greg in MN
Green Energy Living

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Thanks Greg, I appreciate it, good information. Do you know anybody who has a output temperature for a aluminum flex duct heater? When I did a screen absorber collector I was able to get a hundred and ninety-to 220° on a 50-degree day.
gbwillson

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GEL=

There have been a few people who have built a solar heater using aluminum venting as the absorber. Kevin H built one. You can find a few more examples if you sue the search terms drier and dryer. 

When you state you got a 200˚F temperature on a 50 degree day, what was the amount of air flowing through it at the time you took the temperature? Something very important to keep in mind is that the achieving the maximum output temperature is NOT the goal to strive for. What you are looking for is the maximum temperature gain from input to exhaust, along with the highest airflow to maximize BTU output. Output temperature without knowing the amount of air flowing through a collector means nothing. Think of it this way: If someone told you they did 200, what does that mean? 200 what? 200 pushups? 200 miles per hours? 200 points? 200 degrees? You need to know the context of the 200 and what it represents. You will see a bunch of solar heaters bragging up the output temperature of a collector they built. But unless you know how much airflow(Cubic Feet Per Minute or equivalent) the output temps mean nothing. 

The airflow should be measured at the exhaust. You can't use the rating of a fan because fans are normally rated in free air. A collector will have resistance so your output will always be lower than the free air rating of the fan. An empty black box with no intake or exhaust will also have a very high temperature inside.

The ultimate goal of a solar heater is to have the highest possible temperature increase AND a fan strong enough to extract the maximum amount of BTU's. A large amount of lukewarm air will provide far more BTU's than a trickle of hot air. 

Greg in MN
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Reply with quote  #5 
Quote:
Originally Posted by Green Energy Living
... Do you know anybody who has a output temperature for a aluminum flex duct heater?


Not flex duct but BIS does test aluminum soffit, downspout and pop can collectors:

http://www.builditsolar.com/Experimental/AirColTesting/Index.htm

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Both temperature rise and airflow are integral to comparing hot air collectors
Green Energy Living

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Reply with quote  #6 
I understand what you're saying Greg, I saw Scott Davis's video on designing the ultimate collector. The temperature was measured at the exhaust while running a typical 4 inch CPU fan.
gbwillson

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Reply with quote  #7 
GEL-

I'm glad you saw Scott's video. As an example, my current collector averages a 40˚F  temp increase, with about 400 cubic feet of air passing through it. The intake draws air off the basement floor which is about 60˚F. This means I'm exchanging 400CFM of 60˚F air with roughly 100˚F air! This is equivalent to the heat output of 3 - 4 electric space heaters. 

Greg in MN
Green Energy Living

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Reply with quote  #8 
Awesome, that's very good, do you have pictures or videos or description for a link to the build?. Thank you. I'd like to check it out.
gbwillson

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Reply with quote  #9 
GEL-

You can read up on the ZeroPass heater build here:
https://simplysolar.supporttopics.com/post/the-zero-pass-hot-air-collector-6611426?trail=10
gbwillson

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Reply with quote  #10 
GEL-

It's a newer collector design, but there have been several built in the last few years. The ZP is a great unit if you need lots of heat. The downsides are that it likes a long configuration and needs LOTS of airflow. 

Do a search using the words such as  zero, pass, zero pass, zp, and zeropass. Here you can explore individual builds.

Greg in MN

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