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apollo

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Reply with quote  #1 
I have found aluminum downspouts already factory-coated in a flat black paint. Anything that will keep me from having to use a spray can is a plus. However, is there any benefit to purchasing an uncoated aluminum downspout and painting it black to purchasing coated aluminum downspouts as long as the paint is flat and not shiny? Well, besides the price, which is high for a coated downspout but worth it to get away from having to purchase multiple spray cans (very expensive) and spending hours painting (very tedious) and getting the overspray everywhere? Thank you for your response.

gbwillson

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Reply with quote  #2 
Hi Apollo-

Welcome! Since you already have the factory finished downspouts, use them. But if you need a few more for may reason don't hesitate to buy them from a local store and paint them yourself. Most in-stock downspouts from Home Depot or Lowes are made from rather thin aluminum, which is good as it helps transfer the heat all the way around to the shade side of the downspout. And if you buy the dark brown colored ones, only a very light coat of spray pain is needed to bring them to a nice dark black.

Greg in Minneapolis[wave]
pianoman8020

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Posts: 56
Reply with quote  #3 
Hi Apollo,

It's great that you found some reasonably priced downspouts. Now what to do with them. If I were to build a tube collector, I would reform them to say 1" x 8" by inserting a couple of 3/4" steel pipes in the tubes, laying a piece of plywood over it, and drive over it with a car. Now you can have a much thinner collector, better air agitation in the tubes, easier to fabricate tube headers and use half the number of tubes. I must admit that I have never tried this but such an arrangement should be just as efficient as a full sized tube collector.

Jim from IL
apollo

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Reply with quote  #4 
Greg in Minneapolis: Thank you for your reply. I had not considered that thin downspouts would be better collectors. That is information I will keep in mind when purchasing the downspouts. You're right. If I get a prefinished downspout in a dark color and the finish is too shiny, I can always give it a spritz of paint to dull the surface. That would be much less costly and time-consuming than painting a silver surface black. Which, ugh, is a real pain in the heinie.

Jim from Illinois: Aside from the fun I could have driving over the plywood, I was especially interested to read that turbulence would improve the efficacy of the collector. I know turbulence in water pipes is bad, so I wonder why turbulence in solar pipes would be good? Does it increase the heat gain by slowing the air flow? I was planning on using 3x4" downspouts and insulating the box with Rockwool. If I run the incoming air through one downspout to a plenum lined with Rockwool so I could turn the corner 180 degrees to run through two more downspouts for the heating, would that achieve the same effect of turbulence? I have another plenum designed for the bottom of the two downspouts so I can turn another 180 degrees and run back up to the outlet. More turbulence?

This is an interior installation in the windows of my sunroom so I won't have pipes leading away from the collector. I wanted to keep the cold-air intake low to separate it from the hot air outflow to avoid mixing the air, but if that is too many turns I can always redesign the intake to be toward the top and just have one cold-air plenum opening into the compartment for the outflow pipes. I am limited on the width I can build the collector. It can be no more than 26" wide and I'd prefer to keep the height to 30".

Thank you Greg and Jim for your comments. They have been most helpful. I am new at this, so I appreciate that you took the time to share your knowledge and experience.
gbwillson

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Reply with quote  #5 
Apollo-

Are you saying you are building a heater that will be placed INSIDE the window or house? 

Greg in MN
apollo

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Reply with quote  #6 
Greg,

Well, inside the house. Situation: I have a sunroom that is 60 ft long and 15 ft deep with a bank of 16 windows. In my climate the room gets cold. I want to build a heater(s) that will sit on a ledge in front of the window but not right against the window. I constructed a window screen heater as a test that sits on the ledge and it's doing a decent job. I don't want a blast furnace but I do want something that can put out some heat, especially because the sunroom is my primary source of heat. There is no central heating in the house. Opening the doors onto the sunroom helps to warm the living section of the house. I live in a berm home and it is easy to keep it warm once it has been warmed. This year there has been little sun and. therefore, little heat.

You seem somewhat concerned about the location. Is there a problem?

Thanks,
Apollo
pianoman8020

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Posts: 56
Reply with quote  #7 
Hi Apollo,

The more air turbulence in a tube the better for heat exchange reasons. Your common gas hot water has coiled steel straps (called a turbulator) inside the center fire tube. Some air conditioners use turbulators in their cooling coils.

From your description of collector size, I assume you are considering a inserting a small collector into a window space. Double pane windows are one of the biggest energy loosing points of a house. Typically, all the daytime energy gained is lost in the night time and is a net zero heater. Putting a solar heater into a window space would break this link but would also deprive you of the use the window with little payback.

Money would be better spent on sealing the house, better insulation and thermal shutters. A solar collector should be additive to the thermal profile of the house.

With that said, I would build a larger reformed downspout collector sized for below all windows of your sun room. I have a few ideas on general arrangements that could be used. Air inlets and outlets can be easily designed for.

Jim from IL
gbwillson

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Reply with quote  #8 
Apollo-

Not a problem in that you most certainly need some added heat with all those windows. The issue is the placement of the heater(s). With the heater inside the window, the sun has already entered the space you want to heat. Without the heater in the window, the sun's rays will warm whatever objects they hit. Those objects will in turn will slowly give back the warmth until they cool to room temperature. So whether the sun hits the floor, a wall, or another object in the room, the amount of BTU's entering the room is exactly the same. And this would include a heater placed inside the window. Now any dark objects will absorb more of that incoming heat, and lighter colored objects will absorb less.

What happens when you place a dark colored heater right next to the window pane is to concentrate the heat that has already entered the room through that window. So the BTU's that already entered now hit the dark surface right next to the cold window pane. And while it will feel warm if you put your hand in front of the air blowing out of the heater, the fact remains that the BTU's entering the room through the glass is the same. You might even lose a few BTU's due to the warm, dark surface having heat drawn from it by the cold window pane close to it.

My suggestion would be to look at building something to mount outside, perhaps against the wall below the windows. Here is a great example built by Irishvoyageur:

https://simplysolar.supporttopics.com/post/sullivans-solar-powered-solar-air-heater-10354289?&trail=10

P1410168.jpg 

A collector could be built to fit the heat output of your needs. With this unit, air is drawn from inside the room, passing through the heater and back into the room. Check out the PDF in the link above.


Greg in MN

SolarInterested

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Reply with quote  #9 
... or the sunroom could be used as the collector

Low Thermal Mass Sunspaces for Home Space Heating
https://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#LowMassSS

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

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Posts: 8
Reply with quote  #10 
Jim,

Thank you for your explanation about turbulence. I won't get much of that with a downspout collector. But, hmmm, I could make a tube of a short length large-mesh wire and insert it into the downspouts. That would certainly add turbulence!

I agree that with most houses, money spent sealing and insulating would be beneficial. The sunroom in my house is the only stick-built part. The main body of the house has concrete walls 15-inches thick and the walls and double T-beam roof are covered with dirt several feet thick. Not much chance of sealing that. Because the concrete does cool off as the dirt does, I am insulating with Rockwool as I remodel. It's a slow process.

I have been researching solar collectors for a few months now, but I'm sure I haven't seen everything out there. If you have links to view these ideas you mentioned, or want to detail them, I would be interested to look at them. Every new thing I learn helps me in my decisions.

Greg,

The explanation about BTUs was great. I will definitely take that into consideration.

I liked the idea from Irishvoyageur. I could adapt it to my situation but I have a few problems to overcome. That wall is only 12 inches high and I'd have to drill through 15 inches of concrete and rebar (and the tile-covered ledge under the window) to bring in the warm air. Let's not forget the raccoons, squirrels, and skunks that think everything that close to the ground has been put there for their entertainment. There are four wider walls between each bank of windows on which I am planning to install collectors higher above the ground to help heat the middle third of the house. That will thwart the raccoons and skunks, but nothing stops the gnawing of the squirrels. Unless I make the boxes out of metal. Ah the joys of living in the country.

The solar gain through the windows does warm the room. I wanted a bit more warmth that would waft into the middle third (no windows, one outside door) where most living takes place. That rarely gets above 60 degrees in the winter. 70 degrees in the summer, which is fantastic! I am planning on building large outside solar collectors to heat what I call The Cave - the back third of the house. Winter temperatures in that section are a brisk 45 to 50 degrees and heat from the sunroom can't reach it. No windows, one outside door. Drilling through the concrete for the plumbing is going to be fun.

SolarInterested,

The sunroom is currently my solar collector, and that room is pleasant when the sun shines no matter what the outside temperature (6 degrees this morning). The rest of the house, not so much. Right now I'm just testing collectors to find the best way to heat the house. It's not like I'm freezing, but I sometimes have to force myself to go into the back third of the house to exercise. I start out in a coat, gloves, and scarf until I warm up enough to shed them one by one. Nice place to exercise in the summer, though.

Jim and Greg and SolarInterested,

I really appreciate the time you have taken to answer my questions and improve my knowledge. I haven't seen a situation such as mine on any of the solar sites I've visited but with just a little thought I'm sure I can get something to work. Especially with the help you've given me. If you can think of anything else, I would be more than happy to hear it.

Sincerely,
Apollo

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