# Success and Thanks (Pics)



## MoonRiver (Sep 2, 2007)

Solar heater is built and installed. Putting out about 125 degrees after about 30 minutes.

I was able to use PVC male adapters and steel locknuts for my bulkheads to tie the PVC pipe to the heater. 

Here's how I access the house. I removed 1 brick and ran 3 pieces of 2" PVC pipe through the hole. Drilled holes in 2 1"x4" boards to hold the pipe in place. It looks a little lopsided, I forgot to take into account I was putting couplers on the end, so to get them on I had to stagger the pipe a little. 










Here's what the holes look like inside the house. I plan on building a box around each set of holes and putting a fan in the exhaust box rather than in the heater itself. You can see the thermometer reading about 120 degrees.










And here is a picture of the heater installed. It is 4' tall by 3' wide. The cylinders are aluminum down spouts filled with soda cans.










The 2 antenna on the top are actually vents. They have a screw cover that I can remove to vent the hot air out the top of the heater. I want to see if I can use that feature next summer to draw hot air out of the house.

The reason it is so close to the window is because I wanted the holes to be where the shutter used to be. That way, if I take down the heater, I can put the shutter back up to cover the holes.


----------



## deaconjim (Oct 31, 2005)

Nice job. How much air flow can it produce?


----------



## MoonRiver (Sep 2, 2007)

deaconjim said:


> Nice job. How much air flow can it produce?


How do I calculate it? The box itself is about 4 cu ft. On my prototype, the temperature inside the heater was over 220 degrees.


----------



## deaconjim (Oct 31, 2005)

To be honest, I've forgotten how to calculate flow through a pipe, but you'd have to be able to measure pressures, etc. to do that anyway. I'm just curious to know how much heating capacity it has.


----------



## MoonRiver (Sep 2, 2007)

deaconjim said:


> To be honest, I've forgotten how to calculate flow through a pipe, but you'd have to be able to measure pressures, etc. to do that anyway. I'm just curious to know how much heating capacity it has.


One of the articles I read said a 4' x 4' box should heat about 400 sq ft.


----------



## fishhead (Jul 19, 2006)

Looks good.

Maybe to get hot air out of the house you could put the intake near the ceiling by putting a 90 degree on your intake and extending it upward.


----------



## deaconjim (Oct 31, 2005)

fishhead said:


> Looks good.
> 
> Maybe to get hot air out of the house you could put the intake near the ceiling by putting a 90 degree on your intake and extending it upward.


I've seen a similar setup where the "box" used the entire wall, with vents at the top and bottom, on both inside and out. The vents were configured depending on the time of year.


----------



## Nevada (Sep 9, 2004)

Do you find that you need to block circulation at night to prevent losing heat during very cold weather? Do you have a convenient way of doing that?


----------



## MoonRiver (Sep 2, 2007)

Nevada said:


> Do you find that you need to block circulation at night to prevent losing heat during very cold weather? Do you have a convenient way of doing that?


I can't tell yet, but I don't seem to be getting a lot of draw. I kept the "holes" I cut out of the 1" x 4"s and put round head screw in them as a handle. I can slide these into the holes to block them off if I need to.

Today it is completely overcast and the air coming out of the heater is still almost 30 degrees warmer than the outside temperature.


----------



## Roadking (Oct 8, 2009)

Very nice, and it looks good to boot. Hope it works well for you. I still use my thermosyphone jobs with a PV panel as a collecting plate...heater (oil) never runs in those rooms.
Again, nice job and forethought with the window shutters.
Matt


----------



## Ed Norman (Jun 8, 2002)

Do the soda cans still have the ends on them?


----------



## Big Dreamer (Aug 6, 2010)

Nice job. I am not sure I understand the concept of the soda cans on the inside of the tubes could you maybe explain that a little further? I do like the fact of being able to take it down and put your shutter back up so again nice job.


----------



## TnAndy (Sep 15, 2005)

Big Dreamer said:


> I am not sure I understand the concept of the soda cans on the inside of the tubes could you maybe explain that a little further?


Increase in surface area = more heat absorbed= increased efficiency.


----------



## meanwhile (Dec 13, 2007)

Really nice. Do you have more photos of building process? I would love to see photos of how you put together the tubes. And, is there clear cover over the black tubes?


----------



## MoonRiver (Sep 2, 2007)

Ed Norman said:


> Do the soda cans still have the ends on them?


I drilled a hole in the bottom of each can.


----------



## MoonRiver (Sep 2, 2007)

meanwhile said:


> Really nice. Do you have more photos of building process? I would love to see photos of how you put together the tubes. And, is there clear cover over the black tubes?


I didn't take pictures of the entire build. There are several great videos on youtube that I used to get ideas.

[ame="http://www.youtube.com/watch?v=pXYaO596cgY"]down spout heater[/ame]
[ame="http://www.youtube.com/watch?v=Jzxw1j-dzY4"]pop can heater[/ame]

I used plexiglass as the cover (bought at Home Depot). I think glass might work better. On the prototype heater I built, the plexiglass got brittle and cracked.


----------



## SolarGary (Sep 8, 2005)

MoonRiver said:


> I didn't take pictures of the entire build. There are several great videos on youtube that I used to get ideas.
> 
> down spout heater
> pop can heater
> ...



Hi,
Just a couple comments on the two youtube videos.

- A high outlet temperature on a solar air collector (more than around 110F) indicates its not getting enough airflow and its operating inefficiently. The heat output is proportional to (temp rise from inlet to outlet)*(airflow rate).
The collector will be most efficient when the temp rise is just high enough to be useful for heating and the air flow rate is high. The reason for this is that the hotter the collector absorber runs the more heat it loses out the glazing -- heat lost out the glazing is heat that does not get to the room you are heating.

- Have to say I'm skeptical of the pop cans inside the down spouts. If you build the collector with just the downspouts, the solar radiation heats the down spouts, and you can get efficient transfer of heat from the downspout to air moving through the downspouts. The downspouts already provide about twice the heat transfer area of a flat plate absorber. 

By adding the pop cans inside, it seems to me that you reduce the airflow directly over the inside of the downspout surface just by having the cans there. Granted some of heat may be transferred from the downspouts to the pop cans and then to the air, but it seems unlikely to me that you would come out ahead of just having good, unrestricted airflow directly over the downspouts. It would be nice if someone could build one with each approach, and then measure true heat output (not just outlet temperature, which tells you nothing).
It would not surprise me if the cans in downspouts produces higher outlet temps, but this just means that it has more air resistance, and is slowing the flow down -- for the reasons discussed above, this is not a good thing.


If you want good technical advice on making solar collectors, the Yahoo discussion groups Simply Solar and Solar Heat are good and are populated by people who have built collectors AND understand the physics.
The solar stuff on youtube can be good, but much of it is just awful.

Just my 2 cents 

Gary


----------



## wy_white_wolf (Oct 14, 2004)

Thanks Gary

I had the same thoughts about the cans just not the words or time to explain it properly.

WWW


----------



## Windy in Kansas (Jun 16, 2002)

Up to a point the cans would act similar to the fins of a radiator, i.e. more surface area for the air to pass over. However would there be enough heat transfer to the cans to make a difference.

Whether the most efficient or not or could be boosted by more air flow, the main thing is that MoonRiver has done what some only think about doing, and that is harnessing some solar energy for heating.


----------



## gobug (Dec 10, 2003)

I learned some things from the comments above. Thanks MoonRiver for the photos, thread and input from others. 

I am in the process of building my 2nd solar air panel. On the first panel I used aluminum cans which I sliced off top and bottom and aluminum taped them together to make tubes. The glass is safety glass, and hence the dimensions are fixed (22" x 64"). I used 3/4" poly isocyanurate foam to line the box and support the tops and bottoms of the tubes. The air enters at the bottom, then snakes horizontally back and forth up to the top.

The air inlet and outlet are 1 aluminum can each (2 9/16"). Since it an off grid garage on a CO mountain, I attach a 12 volt muffin fan to the bottom. Not enough air comes out to keep the space comfortable when it gets cold. (50 degrees in, 105 degrees out)

Based on the comments above, my plans for box 2 are improvements over box 1. I am increasing the number of tubes and increasing the size of the inlet and outlet. Rather than running the tubes horizontally snaking up 64" I will turn the glass sideways and run the tubes vertically.

Now my questions:
Since I have short term limitations on being able to use high cfm fans, how big should the inlet and outlet be to take the best advantage of convection?

How much volume (which impacts how many tubes) should the box have? I made a box as an attempt to have a cold frame here in Denver. It was not intended to be a solar heater. It was 4 foot long by 2' wide and 2' high. The window is at 45 degree angle and is 1'x4'. The greenhouse window spring did not fit. I did not use it as a cold frame because it was 170 degrees when it was 30 degrees outside. That differential relates to this question since the solar exposure area is significantly smaller than my solar air panels.


----------



## Ed Norman (Jun 8, 2002)

I'd think some kind of simple adjustable outlet hole cover would be great for controlling air temp and flow at exit. A slider would be easiest, or wood bushings cut with a hole saw might work. 

I'd like one of these for my work shack.


----------



## gobug (Dec 10, 2003)

I agree that inlet and outlet holes need removable covers. I like your adjustable sliding cover idea. I am not always there, so a slider would allow me to shut off the whole thing until I return, or in the summer. However, an automatic closer, like a solar greenhouse window opener, may keep the living space comfortable whether I am there or not. The living space inside the garage is 16x24 insulated with good southern exposure. If a 4x4 panel will heat 400 sq ft, then 2 of my 22"x64" panels should do a good job of heating my living space in the garage.

My living space walls are 2x4 spaced 24". That translates into my next panel covering 2 wall voids. My inlet and outlet can be 48" wide (with a 2x4 in the middle). I suspect the height of the ideal opening size would be influenced by the volume of the panel and the cfm of the fan. Since I must cut through the plywood siding (inside and out) to make the inlet and outlet openings prior to the mounting of the panel, and construct the panel to have matching inlets and outlets, I need to decide soon.


----------



## Fat Charlie (Sep 9, 2010)

MoonRiver- That's a really nice looking finished product. Do you have any pictures or can you tell us about the manifolds?


----------



## MoonRiver (Sep 2, 2007)

gobug said:


> I agree that inlet and outlet holes need removable covers. I like your adjustable sliding cover idea. I am not always there, so a slider would allow me to shut off the whole thing until I return, or in the summer.


If you go with the standard 4" hole that most seem to use, you can use a dryer vent as long as you have enough draw to blow open the flapper. 

Something like this.


----------



## MoonRiver (Sep 2, 2007)

Fat Charlie said:


> MoonRiver- That's a really nice looking finished product. Do you have any pictures or can you tell us about the manifolds?


The manifolds are just aluminum down spouts. Drilled a hole to match each riser plus hole(s) to exit the heater. I didn't seal the manifolds to the risers, just made everything fit tight.


----------



## MoonRiver (Sep 2, 2007)

I've got the fans installed and running off the solar panel. Seems to be putting out a steady 100 degrees from around 9 am to 4 pm.


----------



## SolarGary (Sep 8, 2005)

MoonRiver said:


> I've got the fans installed and running off the solar panel. Seems to be putting out a steady 100 degrees from around 9 am to 4 pm.


That sounds good -- sounds like you have just about the right airflow through the collector.

What kind of fans did you use?

Gary


----------



## MoonRiver (Sep 2, 2007)

SolarGary said:


> That sounds good -- sounds like you have just about the right airflow through the collector.
> 
> What kind of fans did you use?
> 
> Gary


They are computer fans. 

Ultra Performance 120mm Case Fan
RPM: 2100
Air flow: 79.3 cfm

I installed them at input and output rather than inside the heater.


----------



## gobug (Dec 10, 2003)

I have purchased several different computer fans mostly because they are 12 volts. Some have 3 wires, are temperature sensitive (they turn on when it gets hot). I don't know what to do with the third wires, but the fans still work. I also got 2 squirrel cage computer fans. They were all cheap.

Yesterday I bought an attic fan at home depot. It says 500 cfm and comes with a 10 watt solar panel. The fan is 15" diameter, but the blade can be removed and replaced. Reducing the diameter of the fan tube will reduce the cfm output, and/or reducing the diameter of the blade will reduce the cfm. I have a friend who just had a solar attic fan which puts out 850 cfm on a 10 watt solar panel. The price ($450) was triple what I spent.

I figure I could use such a fan on more than one solar panel by using rectangular furnace ductwork to go from the fan to the boxes. I will be completing my second solar panel in the coming week prior to Thanksgiving, so I will post my progress.


----------



## PD-Riverman (May 24, 2007)

Alot of the small fans with 3 wires are 2 speed fans. One wire will be the ground, the other 2 will be the high or low speed wire, choose one and it will hook to the positive. I have had alot of bad luck with the ones I bought using the "Lower" speed. It burns out, so I only use the high speed now and if I want it to turn slower, I lower the voltage to the fan with a resistor or a voltage regulator. Have not had any more problems. I just cut off the lower voltage wire or tape it up where it is out the way. The "temperature sensitive" Fans I have turn faster as the heat increases.




gobug said:


> I have purchased several different computer fans mostly because they are 12 volts. Some have 3 wires, are temperature sensitive (they turn on when it gets hot). I don't know what to do with the third wires, but the fans still work. I also got 2 squirrel cage computer fans. They were all cheap.
> 
> Yesterday I bought an attic fan at home depot. It says 500 cfm and comes with a 10 watt solar panel. The fan is 15" diameter, but the blade can be removed and replaced. Reducing the diameter of the fan tube will reduce the cfm output, and/or reducing the diameter of the blade will reduce the cfm. I have a friend who just had a solar attic fan which puts out 850 cfm on a 10 watt solar panel. The price ($450) was triple what I spent.
> 
> I figure I could use such a fan on more than one solar panel by using rectangular furnace ductwork to go from the fan to the boxes. I will be completing my second solar panel in the coming week prior to Thanksgiving, so I will post my progress.


----------



## gobug (Dec 10, 2003)

If my panels are ~10 sq ft, and I deepen them to 1ft deep, a 500 cfm fan will refill the panel 50 times an hour. That is about once a minute. If I put two panels onto ductwork connected to the input fan, and if the fan volume is lowered because it is shared by 2 panels (plus a reduction in the size of the fan to the size of the air inlet duct) then I might get down to fresh air in each panel about every 5-10 minutes. 

What is the best difference between input air temperature and output air temperature?

Does air volume of the collector influence the airflow required. Or is it better to control the airflow to adjust the temperature out?

If I have a 15" fan blowing air into a box with a 4" out duct, what does that do to the air volume out?
thanks
gary


----------



## SolarGary (Sep 8, 2005)

Hi Gary,
Heat output is proportional to (airflow rate)*(temperature rise) --
So, you can make the same amount of heat with lots of flow and a little temp rise, or with lots of temp rise and a little flow.

The panels will be more efficient with the lots of flow with little temp rise. The reason is just that this will make the absorber run cooler, and it will lose less heat out the collector glazing -- heat lost out the glazing is heat that does not get to heat your room. But, most people aim for a temp rise of about 50F -- if you go much lower than this, the air coming out will not feel warm to people, and the collector may tend to short cycle early in the morning or late in the afternoon when there is less sun on it.

So, I'd aim for a flow rate that gives about a 50F temp rise.

I don't see any advantage in making the panels deeper. Not sure what the thinking is there?

One thing to be aware of is that a fans are often rated at their maximum output with no back pressure. When you add the collector and ducting flow resistance, the fan cfm will drop -- sometimes it will drop dramatically depending on the fan.

Gary


----------



## gobug (Dec 10, 2003)

Thanks Gary. 
The thought regarding depth was first based on the coldframe box prototype, which was more volume and less glass surface area. The inside (no airflow) was 140 degrees higher than the outside temperature. The inside of the panel with convection air flow through a serpentine 2 1/2" aluminum tube that is 30' long (no airflow into the panel air space) was about 70 degrees difference. I realize the airflow took away some of the heat. 

I am wondering if there is an optimum air volume through the panel, or if the surface area exposed to the sunlight is more important.

The second thought regarding depth or volume was related to air flow volume. More air could flow if the number of aluminum tubes is increased (and the serpentine air flow canceled). That is only if the airflow is through the aluminum tubing, instead of around it. I suspect every tube needs to get some sunlight. Although the aluminum tubing does transmit heat well, so a warm higher volume space may still warm unexposed aluminum.

I think that the btu's generated will be essentually the same regardless of cfm. So the more air volume, the lower the temperature gain. Is this a straight line proportionality or a curved proportionality? 

One advantage I see to a higher air volume is the more efficient distrubution of btu's around the living space. If there is adequate solar air panel to heat the space, and adequate air flow to circulate the heated air, is the temperature differential fairly flexible? 

I don't know how to adjust the air flow after assembly. I don't know how to estimate what the temperature differential will be. Based on what I have learned from this thread so far, I will proceed without increasing the volume, but eliminating the snake. I will connect 2 panels using rectangular furnace duct with 2 4" ducts per panel. I will alter the snake panel on my mtn property to have the air flow both through and around the aluminum tubes. Then I will measure the difference.

How do I measure air volume output?

One more question. What is the number of times fresh air should circulate in a living space?


----------



## gobug (Dec 10, 2003)

After a bit of googling for the amount of fresh air required for a healthy environment inside a superinsulated structure is 10CFM for each room except master bedroom and basement which are 20 CFM. So a one bedroom, kitchen, dining and living space would require 50CFM if airtight and super insulated. 

I don't know how accurate that is. If my mtn living space is 400 x 8 = 3200 cubic feet, the 50 cfm means 64 minutes to replace all the air in the space. That almost implies my solar hot air panel should be bringing fresh air inside, rather than recycling.


----------



## Jim Bunton (Mar 16, 2004)

Gary, when you say "most people aim for a temp rise of about 50F" are you talking about the difference between inflow and outflow of air or the difference between outside temperature and inflow of air? Sorry if this is too simple of a question but I am not sure what to expect.

Jim Bunton


----------



## pancho (Oct 23, 2006)

Just a question I have that some one might answer and save me a lot of work.

I have some 4'x8' sheets of glass. I wonder if bigger is really better for a solar heater?
Could I use stove pipe sandwiched between these sheets of glass and expect any heat?


----------



## SolarGary (Sep 8, 2005)

Jim Bunton said:


> Gary, when you say "most people aim for a temp rise of about 50F" are you talking about the difference between inflow and outflow of air or the difference between outside temperature and inflow of air? Sorry if this is too simple of a question but I am not sure what to expect.
> 
> Jim Bunton


Hi Jim,
I was talking about the difference between the collector inlet (from the room) and the collector outlet (to the room). That is, ideally you might pick up room air at 65F, run it through the collector, and deliver it back to the room at around 110 to 120F.

The main reason for this is just that air blowing from an outlet does not feel warm unless its substantially warmer than room temperature. 

The collector itself will work more efficiently if you pump more air through it as this keeps the absorber temperature down, which in turn results in less heat loss from the absorber out the collector glazing. The downside of more airflow is the need for a bigger fan and the bit about not getting enough temperature rise for the air to seem warm as it comes out of the collector and into the room. A backflow collectors, a happy compromise is about 2 cfm per sqft of collector, and a flow path through the collector that is about 15 to 20 ft long -- for collectors that don't naturally have a 15 to 20 ft path, add baffles to make the path that long.

Its not critical to get all this stuff right on the money, but one sure sign that a collector is not operating efficiently and not getting enough airflow is that it puts out very high temperatures -- eg 140F and above. 

Gary


----------



## SolarGary (Sep 8, 2005)

pancho said:


> Just a question I have that some one might answer and save me a lot of work.
> 
> I have some 4'x8' sheets of glass. I wonder if bigger is really better for a solar heater?
> Could I use stove pipe sandwiched between these sheets of glass and expect any heat?



Hi,
The heat output from a solar collector is directly proportional to the size of the collector, and most homes have heat losses that are high enough that you will run out of space to add collectors and/or money to build them before you add to much collector area.

I can give you a method to work through to see how much collector would heat your house, but the answer is almost always that the house will take as much collector as you can install. The exceptions might be for people living in a mild climate, or very very well insulated homes.

For the stove pipe approach to be effective, you would need to run the stove pipes right next to each other. The pop can collectors are sort of like a lot of small stove pipes, and they work OK -- see some of the entries in this section:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm#ActiveAir

You might be able to smush the stove pipes down some so that they get wider and you need fewer of them to cover a given width.


Gary


----------



## jwal10 (Jun 5, 2010)

My panels are 4' wide and 6' tall. I built a box with a 4" plenum at the top and bottom, lined it with black insulation board and installed 2"x3" aluminium downspouts vertically, 2" apart with cellular greenhouse panels for glazing. One is mounted on the wall of my 6'x8' south facing leanto greenhouse and one outside the airlock entry of my 400 sq ft. cabin. Air comes in at floor level, through the 4"x42" plenum and exits the top plenum, no fans just thermosyphon. I can control the air volume at the top. The air lock entry has a ceiling heat tray with duct work and seperate fans to the greatroom and bedroom. It gets warm enough in the greenhouse on a sunny winter day to open a colestory window to heat my shop also....James


----------



## byexample (Aug 28, 2009)

Really nice looking solar air heater.


----------



## Jim Bunton (Mar 16, 2004)

SolarGary said:


> Hi Jim,
> I was talking about the difference between the collector inlet (from the room) and the collector outlet (to the room). That is, ideally you might pick up room air at 65F, run it through the collector, and deliver it back to the room at around 110 to 120F.
> Gary


Thanks Gary,

Just wanted to make sure I understood you. Thought that is what you meant but thinking has gotten me in trouble before.


Jim


----------

