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 Latest Topics
 
 
 


Reply
  Author   Comment   Page 4 of 4      Prev   1   2   3   4
johnfmonroe

Registered:
Posts: 43
Reply with quote  #31 
I have been bouncing all around designs for my hot air collector. It comes down to low weight, ease of building with high efficiency. I always considered wood in my collector as being too heavy for holding the screen system. A lite wood is Western Cedar I could use for the screen. I could use a thin 3/4" x 1 3/8" & the spacers would stabilize the frame. 

Another question. Those of you that have used steel stud track for the frame of your collector, did you build it slightly wider than 4 feet to allow for the 4 x8 feet of polyisy insulation board not jamming? Like 1/4 " wider.  ilu.jpg 



gbwillson

Avatar / Picture

Super Moderator
Registered:
Posts: 2,414
Reply with quote  #32 
John-

I think having only 5/8" between the glazing and the top screen is too little distance. I wouldn't go with anything less than an inch between the screen and the glazing. What if you stole 3/8" from the back of the collector and added it to the front? That would give you 1" distance between the glazing and the screen. It would reduce the distance between the bottom screen and the back insulation to 1/4", but that distance is less critical because it still allows airflow around the back screen and the polyiso, which has an R-value several times greater than the glazing. 

Another option would be to move the polyiso outside of the stud track as Don drew up in post #1 of this topic. 

Having what is your primary heating surface, the front screen, in such close proximity to the cold glazing, will greatly reduce heat gain. 

Greg in MN
johnfmonroe

Registered:
Posts: 43
Reply with quote  #33 
Thanks, Greg. I have changed my spacer to 1 inch at the top & 1/4" at the bottom. Let me ask you another question, with the three-screen system, one a layer at the top & two on the bottom do you think that would be an additional heat grabbing addition. And could the two screens at the bottom just be laid flat on the polyiso with no spacer & a 1 1/4" spacer at the top? In other words, why is a spacer even needed at the bottom? Just spray the polyiso black, lay the two screens on it with a bead of caulk to hold it down as a 0-inch spacer. 

John in IN
gbwillson

Avatar / Picture

Super Moderator
Registered:
Posts: 2,414
Reply with quote  #34 
John-

I used two layers for the back screen layer thinking that it would be better to stop more light from getting to the polyiso and keeping the most energy right where it's needed, in the screen gap. Yes, you can lay the screen right on the back, but you will lose a bit in that any airflow can't move in and around the back screen layer. air can only move in front of it. But as tight as space is inside if you use stud track, it could be worth the tradeoff. Look at Irishvoyager's build where he did that very thing. 

Again, none of this is set in stone. But it does make sense to allow a bit of air to better interact with the back screen layer(s). Even as little space as 1/4" behind the back screen layer would be enough. But as long as you break up the laminar flow within the screen gap, I think either way would work just fine. The only way to prove otherwise would be to build two identical collectors, with the only difference being the distance of the back screen layer from the polyiso.

Greg in MN
johnfmonroe

Registered:
Posts: 43
Reply with quote  #35 
Once again, Thanks. I wasn't thinking clearly, as I need spacers on the bottom to keep the bottom part of the screen stretched tight width-wise.

John in IN
dbc

Registered:
Posts: 303
Reply with quote  #36 
John - I think it's a good idea to build the collector frame slightly over-sized.  I added 1/8 inch.  This was not so much for the polyiso insulation - you want a tight fit there anyway, and the edges will squish a little if they have to - but rather for the glazing.  The glazing I used was exactly 4 ft. wide.  I didn't want it overhanging the frame anywhere, because I secured the glazing to the frame with angle pieces fastened into the side of the frame.

late edit - John, your drawing showed cedar being used in the screen assembly.  Not sure about cedar there; it may have unpleasant (or unhealthy) out-gas components.  I have read that poplar out-gasses the least of commonly available wood species.  I have used poplar as well as garden-variety pine or fir without problems.
johnfmonroe

Registered:
Posts: 43
Reply with quote  #37 
Sad story. A neighbor lady nearby is pretty poor, has no heat for several reasons, the house is old & wiring is very bad. I & other neighbors help her as much as we can. This is what I am thinking to get some heat on the cheap. 2 x 4 x 12' treated lumber bolted to the side of the house. Polyiso fastened in & sprayed black. A 6-inch inlet & outlet. Perhaps twin glazing. No snap switch, she would plug & unplug it since if she gets a couple of different things going it blows a fuse. Any advice on this without getting too expensive & complicated. 

John in IN IMG_0145_LI.jpg 

SolarInterested

Avatar / Picture

Moderator
Registered:
Posts: 1,092
Reply with quote  #38 
What about the window screen absorber? An empty black box does not perform well.
__________________
Both temperature rise and airflow are integral to comparing hot air collectors
gbwillson

Avatar / Picture

Super Moderator
Registered:
Posts: 2,414
Reply with quote  #39 
John--

How kind you and the other neighbors to help this person out.

Depending on what is in the basement, you might consider using the two basement windows for access. That way the ground floor windows won't get blocked and allow the sunshine to enter.

I would build the collector using 1x6's rather than 2x4. It would give you more room and would weigh the same. But if you want the strength of 2x material, build the sides using 2x6's. Again, 2x4 walls don't allow enough space inside.

I'd STRONGLY recommend using a snap switch. Consider it a safety switch. Not only does it automate the unit, but imaging what will happen if she forgets to turn the unit on. If a home circuit is tripped with the addition of the fan, I'd rather see her unplug the collector fan for a few seconds, and then plug it back in a minute later. She's far less likely to forget. These collectors heat up in seconds! The fan doesn't have to use a lot of amperage to achieve good airflow. You might also consider powering the fan using a PV panel. 

Greg in MN
johnfmonroe

Registered:
Posts: 43
Reply with quote  #40 
First I need to check out her wiring. I am getting almost too old for this, but maybe I could run her a new line or two of 12 gauge 3 wire with 20 amp breakers. The house was built in the late 1880s so I suspect the wiring is the old knob type of wiring. Thanks Greg. & gbwillson. 



gbwillson
 
I am familiar with yellow popular & it is heavier than Cedar. This lady's electric circuits cannot run her microwave & washing machine without popping the circuit breaker. I think a snap only makes sense if she has a good electric line.
So I may have to set aside my hot air collector & see what I can do for her. 

John in IN


Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.

 

web statistics