Welcome to the Solar Collector
Brainstorming and Development Page!


 

Home

Hot Air Collector

Hot Water Project 1

Hot Water & Space Heating

Solar Electric

Solar Construction 101

FAQs

Best Collectors

Simply Solar
Sign up Calendar Latest Topics
 
 
 


Reply
  Author   Comment   Page 1 of 3      1   2   3   Next
Bartman

Registered:
Posts: 4
Reply with quote  #1 
Hello Everyone,

I must start by thanking Scott & Dan for all there great info.

I am looking to build collectors for my house in BC, Canada

It looks as if 90 degree vertical is a good choice.

I want to make a stiff Mylar reflector system that can fold up in summer.

I like the screen collector but my concern is the inside air coming in contact with the twinwall glazing. I am thinking that the downspout is the better way to go because the air only touches the heated metal and avoids the cold glazing.

I would love to find an answer.

Thanks,

Bart

gbwillson

Avatar / Picture

Registered:
Posts: 2,286
Reply with quote  #2 
Hi Bart-

I like your idea of using the mylar panels to increase output. Living in Minnesota, I had the same thoughts about the heated air touching the cold glazing. The downspout collector would certainly keep the heated air away from the glazing. Though many good designs with a high enough airflow should do the job. I built my 4'x16' ZeroPass collector that was quite effective at keeping the flow of air separate from the glazing. I have tested my ZP collector with pieces of yarn placed inside the collector box and my testing showed little to no air moving outside the air streaming through the collector. I also had the air velocity high enough(20+MPH) so that the air was inside the collector for less than half a second. The build is quite simple too. I helped a neighbor build his own ZP collector for his 20'x30' garage using my design. This past winter he didn't have to fire up the garage furnace the entire winter and had temps in the garage in the low 70's˚F on any given sunny day, even with the outside temps as low as -10˚F.

Below is a link to my ZeroPass collector:
http://simplysolar.supporttopics.com/post/gregs-new-zeropass-collector-7234542?trail=10

Greg in MN[wave]
Garage_Hermit

Avatar / Picture

Registered:
Posts: 2,240
Reply with quote  #3 
Quote:
the air only touches the heated metal and avoids the cold glazing


At least theoretically, whether the air touches the glazing or not is somewhat immaterial - the heat will still pass, due to radiation...

The overriding criterion is throughput - the greatest volume of air possible per unit area of glazing - and the air *velocity* - getting it out of the box ASAP...

This implies having correctly sized ducts and fan...

G_H

__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
SolarInterested

Avatar / Picture

Spam Stomper
Registered:
Posts: 1,050
Reply with quote  #4 
Some heat would be transferred to the glazing by conduction. In any case, the downspouts are a better choice than popcans but you might also consider a Cinefoil Tube Collector http://simplysolar.supporttopics.com/post?id=7059555

See the BuildItSolar site for a side by side heating performance test comparing a solar air heating collector that uses aluminum gutter downspouts for the absorber to a collector that uses two layers of black screen for the collector.

http://www.builditsolar.com/Experimental/AirColTesting/DownSpoutCol/110511TestDSCol/110511DSColTest.htm

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

Registered:
Posts: 4
Reply with quote  #5 
Hi Guys,

Thanks for the info and links.

1)comment.. downspouts are a better choice than popcans

Regarding Metal Mass in a collector. Is more (thicker) metal in the collector better? ie downspout vs screen vs Any test results for dryer vent?



2)On Garys flow tests...
I think the downspout manifold is choking the middle downspouts...

I made a drawing about the optimized manifold.
I was thinking of putting a screen in front of this, kind of a hybrid of the ZP and DS.

3) Anyone here every tried negative pressure between glazing and metal for vac insulation? (kinda Advanced topic)

4)Using Flex tubes in the back instead of Downspout?


Thanks,
Bart

 
Attached Files
pdf Thermal_Mass_Zero_Pass_1.pdf (45.36 KB, 24 views)

SolarInterested

Avatar / Picture

Spam Stomper
Registered:
Posts: 1,050
Reply with quote  #6 
Quote:
Originally Posted by Bartman
... Regarding Metal Mass in a collector. Is more (thicker) metal in the collector better?
It's thought that less is better.

Quote:
3) Anyone here every tried negative pressure between glazing and metal for vac insulation?
Given the glazing commonly used and the area involved it's probably not practical. Twin wall is one option for decreasing heat loss.

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

Avatar / Picture

Registered:
Posts: 2,240
Reply with quote  #7 
Regarding absorber MASS, interesting paper HERE ...

Apparently, per section 4.6, the thicker the metal of the absorber "risers", the more efficient the collector, since the thermal conductivity increases...

Thus a heavier downspout ought to be better.
Also, copper is better than aluminum is better than steel (I think everybody knew that already...).

G_H

__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
stmbtwle

Avatar / Picture

Registered:
Posts: 2,826
Reply with quote  #8 
I think the choice of copper/aluminum/steel is a matter of cost.
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
KevinH

Registered:
Posts: 560
Reply with quote  #9 
Regarding the original question, I haven't seen any side by side testing that isolates the outside temperature.  For example, compare a screen collector to a tube collector at 40F, 20F, 0F, -20F and plot the efficiencies.  Most testing involving tube collectors like the downspout and pop can have been done at fairly moderate outside temps.  Gary was going to do a cold weather comparison between the pop can and screen collectors, but I don't think it happened (original test was at 80F outside).  I have always thought that the performance would shift towards the tube collector as the outside temperatures drop.  That has been my own experience, but it is subjective and not based on a controlled side by side test.  Both collectors types are losing heat due to radiation out the glazing and conduction with the glazing, but in the tube design you have the dead air space which should act as an insulator (a little like a dual pane window).

G_H,
That was a surprising conclusion.  I would have expected a thicker tube to have more heat transfer resistance, but I haven't looked into the physics.  The study is based on a simulation (not real testing) so it depends on how good their model is.  It is also based on a hot water collector.  It is something that could be tested if the setup was good enough to detect a 15% difference.  Menards, for example, sells two grades of downspout (thick and thin).

Kevin H
Garage_Hermit

Avatar / Picture

Registered:
Posts: 2,240
Reply with quote  #10 
Yes, Kevin, it surprised me too, that is why I posted it !

I always thought, "Mass is Crass"...

I thought (think...) that a collector needs to be like a Low Thermal-Inertia Sunspace...
As the man himself says (Morris Dovey...), ideally, all the collector should be warming is AIR, not structure...

G_H

__________________
(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.

 

web statistics