Solar air heating NO south facing wall or roof - options

[Spiral_72]

Thank you for your time. I'll consider it all and plan to post pictures.

I'm dying to try some wind power too, but that'll likely go on the back burner till I get this "Easier " stuff worked out.... Besides, we do not see that much wind around here.

[J.P.M.]

Since you ask:

1.) I doubt if you'll see much diff. in heat production base strictly on whether the units are horizontal or vertical. Going back to prior comments, usually, the faster the air flows through the unit(s) the more efficient the heat transfer with the same caveats about more fan/duct noise, drafts and lower outlet temps (but probably more heat at a lower temp.) and more pumping power used. There ain't no free lunch.

2.) For what sounds like your application (winter heating), laying panels horizontal will cost you. Approx. best tilt is about latitude + 10 to 20 deg. or so. Laying them horizontal will cost you big time in the winter heat production dept. Besides, you'll never get the snow off them. It'll melt, refreeze and cause problems in general.

3.) As for vertical, or other orientation for that matter, with vertical probably the most severe, wind loadings and considerations are a BIG concern. 3' X 7' anything presents a big surface to the wind. Look out for and account for wind loads. If they haven't got you yet, they will.

[Spiral_72]

Yes, I read back through the replies on this topic and believe it or not I've been considering where to get reasonably priced aluminum or steel shapes to make a frame. I know a guy with a large metal brake but I'd rather not drive 200miles round trip...... so yes I have every intention of replacing the wood thanks to your recommendation. Thank you so much. The double pane idea is borderline brilliant. I'd not considered that.

At the moment I'm wondering if the 3' wide, 7' tall screen collector I'm using now has the same output as a 7' wide, 3' tall. Obvioulsy the screen will have to tilt appropriately. The collector area is the same. I can't find any instances of this idea on the internet though I'm sure they exist. I did see an aluminum roofing absorber used in this orientation, not tilted, but wider than tall. I'm figuring the total heat output would be the same, maybe not as elevated as a temp though assuming air flow is the same for both panels.

I'm working on a drawing to lay three 7' wide , 3' tall collectors on my roof, standing straight up. Two rows of three will work as well, but the rear row will be in the shade until about 11am so I'd do good to run two separate fans and duct so I don't heat then cool the air in the shaded collectors. I guess I could lay them all flat on the roof, however I don't think that'll work very well for this panel style.

Let me know what you think please.

[J.P.M.]

Just a brief update. The panel is still pumping heat into my house. I do have my first bit of maintenance though, instead of putting my fancy controller in there I just run the fan off a power supply you plug in. While I was at work "Someone" forgot to plug it in, the insulation melted and now I have a panel that works 50% I bought some new / different insulation but haven't installed it yet. How's that for lazy?

I do now have three single pane sliding glass doors and two double pane sliding glass doors to build more heaters though. It'll be interesting to see the difference. I hope to get to all that soon.

Welcome back.

Not lazy to me. Sounds like Murphy's law as applied to self induced foulups. Folks who never made a mistake probably never did anything.

A word of caution: Depending on collector materials - mostly the non metallic parts like wood frames, etc. common to DIY efforts - repeated and lengthy exposure to warm/hot air in an air cooled collector will cause the materials to dry out. This can cause problems, particularly when a collector has been stagnating in the sun, and especially when someone then turns the fan on. Depending on materials, wood may have had its kindling temp. lowered to below the collector stagnation temp. by the drying process and combustion may occur - and made more rapid when air is forced through the collector(s) when the fan is turned on.

FWIW, that drying process took several months in my first air cooled design and it did cause combustion under some unusual circumstances. No real damage but a real eye opener for me.

A suggestion which you may already be well aware of: If you plan on more air cooled collectors, consider using the double pane units as the last ones in the flow path in either a series or parallel or combination arrangement. Reason: Double pane units lose less heat. The hottest air will be farther along the collector flow path. Put the units with the lower heat loss where the temp. is the highest --->> better efficiency.

[Spiral_72]

Just a brief update. The panel is still pumping heat into my house. I do have my first bit of maintenance though, instead of putting my fancy controller in there I just run the fan off a power supply you plug in. While I was at work "Someone" forgot to plug it in, the insulation melted and now I have a panel that works 50% I bought some new / different insulation but haven't installed it yet. How's that for lazy?

I do now have three single pane sliding glass doors and two double pane sliding glass doors to build more heaters though. It'll be interesting to see the difference. I hope to get to all that soon.

[russ]

As J.P.M. said - Thanks for the update!

Russ

[J.P.M.]

A quick note. We're still seeing about a $20-$30 drop in out energy usage every month so far with one panel. Duke sends out usage comparison reports to us that compares our energy use with other homes in the area. We've fallen to almost "Most efficient". The house is fairly well insulated but I couldn't have expected this much. It helps the wife permits me to warm the house to 75F during the day so the heat is long delayed coming on until early morning.

I haven't worked on the project since I last posted. I just sits there pumping out heat all day and sending me updates over the internet. That's cool!

I'm going to gut the panel to install copper pipe next. Maybe we can heat the hot tub with it, then if that works as well as I hope.... the hot water for the house. I've been working on copper pipe with an aluminum flashing wing.. We'll see.


Take care!

Thanx for the update.

No wet blanket here, but be careful about tubing, fins, expected heat transfer expectations vs. reality. Contrary to intuitive and common wisdom, simple clamping/wiring of fins to tubes gives poor heat transfer. Solder/weld/braze, other metallurgical bonding is much better - which brings up the situation of bonding dissimilar metals, not only from metallurgical but mechanical standpoint, mostly thermal expansion considerations. Don't be intimidated, but look before you leap. Bonding copper-->> aluminum may be a problem. Also, the thermal expansion differential Cu -->> Al and its cyclic nature will lead to early failure w/out some innovative design tricks. As for DHW applications, check local code requirements and always think safety first, and safety 2d, 3d, etc.

Keep having fun.

Regards,

[Spiral_72]

A quick note. We're still seeing about a $20-$30 drop in out energy usage every month so far with one panel. Duke sends out usage comparison reports to us that compares our energy use with other homes in the area. We've fallen to almost "Most efficient". The house is fairly well insulated but I couldn't have expected this much. It helps the wife permits me to warm the house to 75F during the day so the heat is long delayed coming on until early morning.

I haven't worked on the project since I last posted. I just sits there pumping out heat all day and sending me updates over the internet. That's cool!

I'm going to gut the panel to install copper pipe next. Maybe we can heat the hot tub with it, then if that works as well as I hope.... the hot water for the house. I've been working on copper pipe with an aluminum flashing wing.. We'll see.


Take care!

[Spiral_72]

You are all very kind. I'm working on the next panel design. I'd like to have the next three panels built before it gets warm again.

It was unusually warm, maybe 60F today, partly cloudy. The panel made 105F when it quit raining about 11am till about 3:30, then 90F till about 4:30. The house got too warm really at 72F when I got home from work at 7pm and the heat still hasn't come on yet. It really works well but I'm running out of cold weather here

[russ]

Alright sir. Such as it is. The picture taken in the shop was prior to painting the inside. I drilled about ten 3/4" holes in that 1x2 middle divider to pass heat. I also included the web monitor page.

Looks good - thanks!

[J.P.M.]

Alright sir. Such as it is. The picture taken in the shop was prior to painting the inside. I drilled about ten 3/4" holes in that 1x2 middle divider to pass heat. I also included the web monitor page.

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That looks a whole lot better than anything I ever did.

[albert436]

Pretty amazing.

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[Spiral_72]

Sounds nice, any chance you could post some pictures?

Alright sir. Such as it is. The picture taken in the shop was prior to painting the inside. I drilled about ten 3/4" holes in that 1x2 middle divider to pass heat. I also included the web monitor page.

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[J.P.M.]

Sounds nice, any chance you could post some pictures?

JPM, {respectfully} you are a



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I know less than .01% about anything and get dumber by the hour.

[J.P.M.]

JPM:

The house air is circulated through the panel. I would eventually like to build enough heat that I can heat fresh air at the expense of 20-30F.

Thank you for the caution about wood, I thought I had considered everything. In that case I will try to come up with an alternative. I saw a guy use steel wall studs for his frame. I plan to use duct board for insulation on the next panels. The R value is 4+ while the temp rating is 250 degrees, rigid and has a mylar skin. Best of all it's inexpensive.

I could build a frame off the roof to rotate the panels 45 degrees, but I'm worried about wind then, which requires more bracing, more holes in the roof, more spacing between the panels to avoid the next panel's shadow, etc.etc. AH!

I see your point about facing the panels dead south. SE is covered with trees so I'd lose 2hrs of my energy window. I'll have to go SW which puts the panels off the roof at the front of the house, YUCK. or maybe on the wall of the attached garage with long duct. Or maybe I can rotate my entire house 45 degrees? Hmmmm.

I definitely planned on running the panels in parallel FOR efficiency. I could be wrong, but I figured four panels raising 70F to 120F was better than four panels in series raising 70F to 180F or 200F.

Albert:

I'll post pictures of the controller, MAYBE the panel but the panel's exterior isn't painted. It was intended as a test (with great results) rather than a permanent installation. I used 6in insulated flex duct run down the wall outside so it looks like a set from a cheesy science fiction movie. Heck I only have $40 in the panel, but since it works I will proceed with a nicer built unit.

For the controller I used Arduino Uno, a Seeed Ethernet controller, a 13.5V 3A wall wart, LM7805 for system power, a MOFSET driven by PWM from the Arduino to vary the fan speed to keep the incoming air a constant temp regardless of sun. I don't remember what temp sensor I used but it's a linear Fahrenheit-voltage. I can look if you want. I cut up a CPU heat sink and bonded that to the sensor to keep the temp reading more constant. The fan is the largest computer type fan I had on hand..... it's tool large for a computer, I dunno where I got it. I don't count the cost of the controller and related because I already had the stuff on hand from other projects.

I'll post a link to my monitor website once I remove the control buttons. I don't want people diddling with the fan controller y'know.


Thank you for your thoughts and your information.

Short reply: Thanx for the return.
Re: parallel vs. series. For the same flowrate, series will probably give slightly more efficiency. Reasons are not complicated but depend on one another in funny ways at times. Basically, heat transfer is usually better when things are moving faster. Also, keep in mind that the goal is to produce heat, not high temperatures for their own sake. 400 cfm increasing from 100 to 110 deg. will move as much heat as 100 cfm going from 100 to 140 deg. the 400 cfm however will mean a lower collector temp. and so less heat loss to the surroundings, hence, more heat to the dwelling and higher efficiency, but the lower temps may feel "drafty". If it's 400 cfm, series vs. parallel flow, the picture is a bit more complicated, but series flow may be a bit more efficient still because of higher flow velocity over the absorber, but at the expense of higher pumping cost and probably more noise. Let the tradeoffs begin.

Having fun yet ?

Regards,