Solar air heating NO south facing wall or roof - options

[Spiral_72]

Good afternoon. I'd like a little advice please. I have referenced these and other forums many times to build what I would consider to be a very successful solar air heater panel. I've been lurking, reading and gathering information for some time.

The panel is 36x80 with single panel glass, two layers of black aluminum screen in an insulated box. I live in SC where it has been fairly cold recently. The panel has been running for one month. It noticeably warms the living room and kitchen (400sqft) which were previously the coldest rooms in the house. I built my own fan controller using Arduino which posts updates on the internet for me to watch from work during it's operation. Yea, I am proud of the controller I calculate the panel makes about 850btu/hr of heat on an average day, ranging from 0btu on a cloudy day to near 1000btu/hr on a ~70degree say with full sun. I used a 13gal bag to estimate the airflow.

I installed the panel in the one location on the entire house that was reasonably accessible, would permit a temporary mount (since this is a prototype) and could be piped into a window to avoid drilling 5in holes through brick walls. Since the panel works so well I acquired three more panes of glass to build more panels and wish to permanently mount and duct them.

The trouble is, I have no south facing walls of roof. The house is near 45degrees off of south which makes mounting very difficult. I pretty much have to install the panels on the roof due to the layout, roof, trees, shadows etc. A south facing panel means it needs to be mounted off the roof on stilts which stinks.

Do y'all have any thoughts? Any links to people that have had the same problem with a solution? I can't find a solution I'm especially fond of.

Thank you.

[J.P.M.]

Good afternoon. I'd like a little advice please. I have referenced these and other forums many times to build what I would consider to be a very successful solar air heater panel. I've been lurking, reading and gathering information for some time.

The panel is 36x80 with single panel glass, two layers of black aluminum screen in an insulated box. I live in SC where it has been fairly cold recently. The panel has been running for one month. It noticeably warms the living room and kitchen (400sqft) which were previously the coldest rooms in the house. I built my own fan controller using Arduino which posts updates on the internet for me to watch from work during it's operation. Yea, I am proud of the controller I calculate the panel makes about 850btu/hr of heat on an average day, ranging from 0btu on a cloudy day to near 1000btu/hr on a ~70degree say with full sun. I used a 13gal bag to estimate the airflow.

I installed the panel in the one location on the entire house that was reasonably accessible, would permit a temporary mount (since this is a prototype) and could be piped into a window to avoid drilling 5in holes through brick walls. Since the panel works so well I acquired three more panes of glass to build more panels and wish to permanently mount and duct them.

The trouble is, I have no south facing walls of roof. The house is near 45degrees off of south which makes mounting very difficult. I pretty much have to install the panels on the roof due to the layout, roof, trees, shadows etc. A south facing panel means it needs to be mounted off the roof on stilts which stinks.

Do y'all have any thoughts? Any links to people that have had the same problem with a solution?

Thank you.

FWIW, sounds sorta familiar and nicely done. I'd easily believe 1000 BTU/hr. in sun, -->> ~ 25-40% thermal eff. maybe a fair amount more depending on flowrate, outside air temp. and other stuff. 850 BTU/day average seems a bit low. Is house air recirculated ? Does the ducting have a backflow damper ? Panels need not face dead south. I'm not sure this qualifies as a solution but, given a choice and weather patterns, facing more SE if possible may help take the chill off in the A.M. and you may wind up w/ ~~70% or so of the south orientation production. SW orientation will work but maybe create an overheat problem, the house probably being warmer by afternoon. The solar collector police won't come if the panels are off south some. For additional panels, ducting in parallel will get you lower pressure drop - smaller blower, lower pumping costs and probably quieter operation (which can be a big deal), but lower air velocity --->> less efficient heat transfer - less output -->>lower performance. It's the no free lunch thing and usually results in a bunch of design tradeoffs. A friendly caution which you probably know, or will soon learn, here first hopefully: Solar air heater boxes made of wood products dry out rather quickly. When they do, the kindling temp. of that wood based material is reduced. A stagnant collector may achieve temps. in excess of that reduced kindling temp. creating a fire hazard and /or an actual fire, especially if the controller decides to turn the blower on and light things up like a blast furnace.
I used spray painted steel wool for my original design many years ago. The next iteration used 4-6 layers of folded alum. screen sprayed flat black. 3d iteration used the screen, 2 glazings, and return flow to the collector ducted in a rather funky way that took it between the 2 glazings to preheat the air some on its way to the screen absorber material and also reduce the cover loss if the ambient temp. wasn't too cold. It worked well but was a bit impractical. Eff. improvement was slight but measureable, I think. Biggest unknown was flowrate, which I was never able to nail down beyond a swag. I had a lot of fun and learned some stuff. I found no right/wrong answers, the technology pretty forgiving, and I got a rush every time I felt the result of the warm power of the sun at the outlet.

Good luck. Stay curious. Regards,

[albert436]

Sounds nice, any chance you could post some pictures?

JPM, {respectfully} you are a

wonk noun \ˈwäŋk, ˈwȯŋk\
: a person who knows a lot about the details of a particular field (such as politics) and often talks a lot about that subject

Wonk.jpg

[Spiral_72]

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.

[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,

[J.P.M.]

Sounds nice, any chance you could post some pictures?

JPM, {respectfully} you are a



[ATTACH=CONFIG]3769[/ATTACH]

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

[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.

0217141730.jpg0217141733.jpg1124131726.jpgmonitor.jpg

[albert436]

Pretty amazing.

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[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.

[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!

[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

[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!

[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,

[russ]

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

Russ

[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.