Solar Window Inserts

Free heat with minimal investment. Having a serious interest in renewable energy, I recently got the urge to try and create a solar insert that would simply slide into my existing window casings to help with the heating of my 1996 mobile. I saw on the local news one night how a local man built a solar thermo siphon (TAP) air panel to do just that using black aluminum window screen and plywood. OK, that's fine if you don't mind living in a cave as it totally blocked the view and incoming light through the window. The concept is fine and it works. He made a comment about how much he saved on heating, but I don't remember what he said. Having seen many designs on the internet of solar space heaters using black window screen, I decided to test the idea last winter as I had a difficult time believing window screen could possibly generate much heat. So, I grabbed a couple of screens I just happen to have and attached them to the front door with magnets salvaged from a micro wave. Amazing!! I think I was getting over 120 deg. I didn't write it down so I am relying on my (poor) memory.

Anyway, I wasn't too keen on losing the view or light so I set my mind to wandering and came up with the idea of using poly film instead of plywood. The first prototype was made using poly film and the initial test gave me 90 - 94 deg. with the sunlight hitting about 60% of the window screen. Not bad. OK. Now, how can I improve this? If I can reflect the sunlight onto the backside of the screen, it should generate more heat. Aluminum foil? You would need a substrate to attach it to and it would also eliminate the view and light. Then it hit me! Aluminized Mylar (emergency blanket, rescue blanket etc.)!! I recalled that as I was playing with other solar projects that these blankets reflect light and heat yet are also semi transparent, so I tried it. Super! It is like having polarized windows and it boosted the output temperature about 4 deg. This winter will tell the tale.

Now, on with the instructions...

What you need:
3/4" square molding for basic framework
Black window screen - the window screen I see around here isn't really black but Charcoal. Still dark enough to serve as solar absorber.
1/4" X 3/4" molding for attaching film to frame, screen bead molding?
Saw - table saw or miter box
Drill motor
Screwdriver or power driver
wood glue - optional
a sharp utility knife to trim excess film
heavy duty scissors or tin snips for cutting window screen - you might also consider gloves when working with aluminum screen
#6 X 1-1/2" wood screws - I used 8 per frame
#6 X 3/4" wood screws for attaching trim molding
countersinking drill bit for the above screws
Staple gun and staples - 1/4" - 3/8"
POly drop cloth, emergency blanket or other transparent sheet to enclose air chamber and for anti siphon flap valve. Another option that may improve efficiency would be a thin polycarbonate sheet screwed to the frame.

Step 1: Build the frame

Measure your window opening and cut 3/4" square molding accordingly. My windows are 29" X 59" so, two pieces 28-15/16" for top and bottom frame, 2 pieces 57-7/16" for side frames and two pieces 27-716" for inlet/outlet frames. I cut the pieces for the main frame 1/16" short for a slip fit into the window opening. A tight seal isn't really necessary unless you have serious air infiltration around your windows. In that event, I would either properly seal the leaks or make another frame that you can seal tightly against the existing window and cover it with plexiglass/polycarbonate.

assemble the top and bottom rails to the ends of the upright rails using one #6 X 1-1/2" wood screw at each joint. Here is where we might add wood glue for a more durable joint. Make sure your frame is relatively square and fits well into your opening. Not too tight and not too loose. A competent woodworker might dado the frames for a more professional look.

Now, add the inner rails that will create your inlet/outlet openings. Considering my window size and emergency blanket size (52" X 84") if I make the inner opening 50-1/2" high, I can use the 52" width of the blanket with minimal waste. That makes my vent openings 2-3/4" high by the width of the frame. There is a formula for determining the vent size but me and formulas don't get along too well. Some percentage of total collector area.

Now you might paint or stain your frame if desired.

Comments

[Wepwopper]

Great idea! I was just writing my group about our simple frames. Hubby and I made double sided frames from 1"x 2" wood frames and stapled clear vinyl shower curtains over both sides. (bought cheap at $1.00 ea). We put them in all the windows. The one in the bathroom is getting ragged and we just put it in anyway. The upper flap flopped down and when I reached up to tuck it back in I felt warm air rising up out of the thing! When I have time I want to revise these to include the screen on one side and clear vinyl inside with an upper flap to allow hot air to pour out. :)

[spring97]

After reading all the discussion about thebriguy's solar panels and WhoTookMudshark (and others) comments, I had to get my two cents worth in.
Is it possible for everyone, including the practicalists and the thermodynamicists to be right? I think it is.
First of all, it is obvious that putting up a solar panel is not going to cause any more light (and therefore heat) to come into a room. As was pointed out, that is controlled by the size of the window. As was also pointed out, all that light bouncing around the room is being absorbed by carpet, furniture, your bobblehead collection, etc.
The thing is, neither the carpet nor the chair is a very good re-radiator of heat and so the chair feels nice and warm if you sit in it because of CONDUCTION and the carpet feels warm (if you have your shoes off) because of CONDUCTION, not radiation.
In another vein, folks usually keep their windows covered with drapes in cold weather to reduce heat loss through CONDUCTION, unless they have double or triple pane windows in which case they might not need a solar panel in the first place. The other reason for closing the drapes is so that UV rays don't discolor or rot the chair fabric (or fade the bobbleheads).
Thermodynamics aside, thebriguy did the one thing the body can relate to. He heated the air. Therefore, with the solar panel installed, while the furnishings
might not be warm, the air is, and that makes people in the room feel warmer as well. And, not to be taken lightly, the solar panel probably keeps some room heat from being conducted outdoors through the glass.
I think we could all be happier if we agreed that thebriguy's panel does not make the absolute room temperature any hotter, but it does convert the available heat energy into a form that the human body likes best. AHHHH, pass sthe hot chocolate.

[celalboz]

Hi, Bit off topic but can I buy my own land with 10-20 bushes  and place a motor home on it?
IS there any laws against it? zonning etc. Since bushes will hide it from plain view from a far?
or I can only have one in a trailer park like I hear mostly?
thanks a lot.
Al Boz

[O-Budd-1]

You need to check your local zoning laws and you may need to have utilities supplied to the property before you can place a mobil or manufactured home on it.

Budd

[littleangels]

You should monitor you fresh air intake to make sure that you are getting enough 'fresh air' as not to fall victim to carbon monoxide poisoning.
I live i a mobile home as well, and these are not built as "houses". The gas pipes are right under your floor, and although the homes are built to have 'give', gas pipes aren't.... So you may have small gas leaks and not even be aware.
Just be careful.
Fantastic idea, though!

[rlarios]

This looks like a nice project and relatively easy to undertake. I wonder how it worked during 2009-2010 Winter and what your outside temperatures were.

Good work, sir !

[gramcraker]

That's pretty cool. I didn't notice, have you had a cold winter to try this out yet? I would suggest making the upper inner rail a bit taller(or the trim a bit shorter) leaving a little more room for the upper control vent to seal across the frame's width without needing to be as precisely placed.

[Slezridr]

Actually, it is late Oct. and winter is just starting, but I do have some performance input.
Since I have such a snug fit in the window frame, I decided to cover the insert's exterior facing frame with the clear heat shrink window covering kit. I believe it increased the efficiency considerably, as it is heating just the existing room air and not the cold window air. Just the other morning, at 10:00 am, the outside temp. was in the low 40's and I was getting 96 deg. out of the window insert, while getting 84 deg. from the external solar panel. I have noted 110 deg. from the insert from earlier observations. At that time, the external panel was contributing 180 deg. to my bedroom and the room temp reached 75 deg. (heaven). I have a really low tolerance for cold temps.

[sendie61]

What is the REAL amount of energy you can take out of such a panel?
I read in a review on some DIY solar panel guides that they use  awesome examples but that in fact this is nonsense.
Here is where the reviews are: http://energy.e-bookz.info
Anyone an opinion?

[smessud]

Just to add a 2cent advice.
As some said, there are two different things :

the amount of "heat" (energy)
the temperature of the different elements of the room (air, walls, floor)

For those who are not trained in thermodynamics, it is easy to understand the difference.

Compare energy-heat with a VOLUME of liquid in a bucket (say 3 litres)
and compare temperature with the LEVEL OF WATER in this bucket (say 6 cm).

If you take another bucket (smaller in diameter) and put your 3 litres in it, the height of liquid (temperature) will be higher.

This is why it takes longer to heat metal (large diameter bucket) than plastic. It will take more heat to reach the same temperature.

In the case of this instructables, people are talking about 10° increase in room temperature. This is in fact air temperature. If they check the walls, they may find a much lower temperature. Air temperature is the real measure of "how good we feel", but it is a wrong measure of "how warm is the full room with walls and floors".

I think what is happening is when you don't have the screen, you heat walls and floor. The concrete needs a lot of heat to warm up, so the light coming directly from the window does not heat air and doeas not increase much the concrete temperature.

With the screen the heat entering the room is first CONCENTRATED in the air. It is logical that a (air) temperature increase be registered and that occupants feel better.

Of course, the air will then heat walls and ceiling (remember, hot air goes up), so the net effect is physically zero. But as the nervous system of occupants is concerned, they will feel better, as long as they don't touch walls and floor.

[Grady]

Well, I'd like to send you some of this Florida Heat !

[WhoTookMudshark]

I hate to be the bearer of bad news, but if you use an existing window it is physically impossible to have any impact on the heating. The sun coming in that window was already being absorbed by everything in your house and converted into heat energy. :)

[resago]

if that were true, nobody would be able to see into your house because of 0 reflected light(if it were all converted to heat)

[WhoTookMudshark]

You're splitting hairs! Of course some light makes its way out, but not anymore than the light that leaks out after this project is completed. I was generalizing to avoid being too wordy. :)

[neuralstatic]

maybe even worse: the mylar material is actually reflective, so more of the light will be reflected out of the house before it can even warm the interior?

[Slezridr]

Yeah, that's a common statement in the solar circle and I understand the thoughts behind it, but I'm a prove it to myself kind of guy and will see what happens this winter.

[karossii]

Yes and no... while you are correct in a larger sense (and I would never recommend someone try to heat their house with one of these 'solar heaters')... depending on the energy efficiency of the windows, they allow light (and heat) to escape out of the house. If you set up a solar over inside the window, and circulate the air through it, you get a much higher efficiency of light to heat conversion, and more importantly, retention.

Thus you could save pennies per month in your energy bills by retaining a bit more solar heat - and you would also feel the noticeable stream of warm air which would convince many people it is functioning much better than it actually is.

Of course, the solar inserts in this Instructable would have next to no impact on said retention; in fact it will likely lessen the retention and reflect out more heat than you had before, as it has no proper chamber to heat the air or circulation of said heated air.

You probably know this already and are simplifying to get your point across; but if you explain where the myth/misinformation is rooted, people are much more likely to both believe, and more importantly, understand.

[Slezridr]

Of course, the solar inserts in this Instructable would have next to no impact on said retention; in fact it will likely lessen the retention and reflect out more heat than you had before, as it has no proper chamber to heat the air or circulation of said heated air.

In essence there are two air chambers in these inserts one between the window and the insert, and another between the screen and mylar film. The cooler air enters at the bottom and weaves through the screen on its way up and out the top vent. I don't have a suitable graphics program to create a diagram of the process, but if you check out the "Solar Barn" at Home Power.com, there is a good explanation of the thermo siphon process.

[thebriguy]

Thank you for your polite explanation. The value is more in comfort than a heating bill - for my children's room - It will warm a room (I should have not deleted my previous posting). The best designs of these utilize the exterior of the home without obstructing the window.

[Slezridr]

Yes, a panel mounted outside on a wall would be more effective, in fact I have a panel mounted outside as well, but then you are cutting holes through the walls which is somewhat discomforting to me. I have had over 200 degrees coming from that panel and I need to re-vamp it a little to increase the air flow and bring that temperature down. Then, there is Mother Earth News "Heat Grabber". I had considered trying one of those, but it is rather bulky and you would need a large storage area when it is not in use. I will monitor my inserts this winter and post the results here. I have five windows to fit these to, 3 on south side and 2 on east side.

[bobby sissom]

speaking of mother earth news heat grabber,i built one simular with material i had on hand i was very pleased with the output.I recorded temps as high as 190 coming out in a steady flow on icy cold days with snow covered ground,the more heat it put into my home the less my electric heaters kicked on. i was so pleased i showed my brother the results and he now has one on his home as well

[bobby sissom]

as for storing it in the summer i simply built an add on box at the top to turn it into a solar dehydrater, great for jerky
just as a side note sitting in yard not attached to anything ,snow and ice on the ground ,i recorded tempt with a digital temp. at 70 degrees it was 22 degrees outside at the time

[thebriguy]

(removed by author or community request)

[WhoTookMudshark]

Whenever light hits anything, it is converted to heat. Black converts all of it, and white reflects most of it. If it does happen to get reflected, it just keeps bouncing around until it hits something that DOES absorb it. The sun's energy doesn't just vanish if it hits something not-quite-black. In reality, heating up a medium so close to the window actually makes it worse. It heats up the warm side of the window instead of the floor, so temperature contrast on the window is higher, and more heat sneaks out as a result. I am ALWAYS getting into arguments on this site when it comes to thermodynamics. Nobody seems to understand how light and heat work. Just think about it! The same amount of sunlight is coming in that window no matter what. What it hits is irrelevant, its the same sunlight and it will create the exact same amount of heat unless you place a mirror in the window and bounce it all right back out. briguy you should really edit your post to avoid spreading misinformation! :)

[thebriguy]

Your wrong - experience proves this. I've made a few variations on this item and they do warm a room. Please explain why this does work, WhoTookMudshark, before criticizing why "it is physically impossible" without ever building one yourself. Your impoliteness comes off a bit snobby (you sound like the typical kid who thinks they are smarter than they are...). No amount of knowledge is more valuable than experience ~ in my OPINION.

[WhoTookMudshark]

This is the response I was expecting. I think my avatar makes me look like a "typical kid" and most people don't take me seriously. You have the right idea with your 6:30AM post, though! An exterior panel hanging on the side of the house with a system to move the heat indoors would definitely be a big help.

I don't doubt that the device makes the area around the window more comfortable (and usually that's the draftiest and most uncomfortable part, so that is a big advantage) but the net effect on the average temperature in the room (and the heating bill) is the same. The heat is just being caught on the device instead of the floor or drapes or what-have-you.

[MrBoB]

Actually, WhoTookMudshark is correct. The Solar Window Inserts are doing two different things, which combine to give the results that are described. First, energy from the sun is being trapped between the window and the insert, locally warming the air in that area. I'm sure that they do feel an increase in heat near the window. HOWEVER, this means that the energy from sunlight which does reach the rest of the room is reduced by the amount removed by the insert. So while the area near the insert will be warmer, due to solar energy being concentrated there, the rest of the room will be cooler, due to a reduced amount of energy available. This brings me to point two. The solar insert is undoubtedly providing an insulating effect on the room, both by reducing the amount of airflow across the window pane, and also by reflecting heat and light back into the house that would otherwise escape through the window. It isn't that the device doesn't work, it's that it doesn't work the way you think it does. I would guess you could get the same results by covering your windows with clear plastic sheet.

[trebuchet03]

I think you're confusing someone that disagrees with you with someone that is insulting you. Not once did Who take on an impolite stance ;)

[trebuchet03]

I am ALWAYS getting into arguments on this site when it comes to thermodynamics.

I feel your pain :p One of the more confusing bits is that somewhere along the line, schools stopped teaching that there's a difference between heat and temperature. I think that's what's going on here.

And, I support your post :)

[thebriguy]

Actually - I see this all the time. People quoting 'Laws' and reasons why peoples work 'shouldn't work but never explain why they do work. I've noticed a lot of heady people that think too much and do too little - try it before stating 'facts' that don't always hold up. Designs like these actually DO heat up the average size bedroom by 5 to 10 degrees. How does this happen if 'the laws of thermodynamics' don't allow it.

[trebuchet03]

In retrospect - I shouldn't have said "poor measurement skills" and instead should have said "Poor measurement methodology" :)

[trebuchet03]

Poor Measurement skills ;)

The amount of heat entering isn't changing. What is changing is the what is being heated. Instead of adding heat to concrete (for example) , we're adding heat to this screen. Concrete has a much higher specific heat capacity than this screen.

I'm not saying you can't thermo siphon air like this (I don't think anyone is claiming that) - but what you can't do is bring more heat into the room. Your heat source is the sun - which has (for our purposes) a fairly constant output. Our heat collector is this window, which has constant dimensions. Adding something behind the window does not somehow increase the amount of solar output.

---

People quoting 'Laws' and reasons why peoples work
Oh please - you're the only one dropping thermo laws. I think the words you're looking for are heat flux:
http://en.wikipedia.org/wiki/Heat_flux

[resago]

its a net positive effect because less light is bouncing off non-black items in the room and back out of the window WITHOUT being converted to heat. I think this is what WhoTookMudshark was missing. To reiterate, the more light that hits a dark surface and is turned to heat, the less that gets reflected back out the window in the form of light and uncaptured heat.

[resago]

but I would leave out the mylar as well, you don't want to relect, just absorb.

[justinhyp]

Cool idea, maybe you could hang something out the window as to not block sunlight.

[got2bskilled]

Nice! I was expecting it to be transparent.. but still pretty darn cool- I mean HOT!

[Slezridr]

Actually, it is semi-transparent. if you lok at the opening photo, you might notice the railing for my fathers handycap ramp outside the window, and a few trees. That was one of my concerns when I came up with this.

[SinAmos]

Try colored water. Absorption rates are different.

[l8nite]

That is pretty cool.or is it hot? = ) for more solar projects check out www.motherearthnews.com

[stephenniall]

hmm pretty cool