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In window thermosyphon working nicely.

Tony Jennings

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Hi all,

I just finished building a thermosyphon panel to cover a window in the back room of the house and test out how well it works... and although my design leaves much room for improvement, it works very nicely.

This is based on The Zen of Passive Solar Heating but using a much simpler method and scrap wood I had around the property.

Rather than tearing out a wall to build it, I just built an overlay that I attached to the inside window frame.

After installing it today I came back two hours later... and instead of having the room colder than the rest of the house it was already 10 degrees warmer.

The air coming out of the air output vent at the top was almost 120 degrees and the air was moving pretty nicely.

Now that I know it works I'm going to invest in materials to do it right and correct short comings of the prototype:

* Foil the window facing side and spray it black
* Add rounded corners to the internal cold air backflow block
* Sand the interior surfaces to reduce air friction
* Use proper metal slats completely across the panel

I might also set some thermal batteries in the window before attaching the panel (bricks, water containers, etc.).

Anywise, I figured I'd share as these work way better than I expected... and if one can afford black aluminum blinds for the in window side then one could also control the heat output... to ensure things don't get way too hot.

I'll do a full write up as I build the second version out. This one was just quickly thrown together from scrap plywood, 2x4 panels, and a bit of strong tie and air vent ties.

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Pearl Sutton

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Looks good!!
And good results :)
My compliments!

I have thought those work so well, I'm surprised they aren't building them into windows like they build blinds into them.

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Tony Jennings

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My test was mostly to see if I should build them into the sun facing wall of the addition in between windows... and to build them into the bottom half of the green house wall when I get around to building it... placing them below the windows/sheeting that is going into the top half of the wall. I may still go with a pure cob base but will likely build at least two of these into the lower half.

I'd never seen them before and although the physics makes perfect sense I wanted to see just how well a simple version would work.

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Tony Jennings

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Pearl Sutton wrote:
I have thought those work so well, I'm surprised they aren't building them into windows like they build blinds into them.

If they built them into windows the energy companies would lose millions of dollars per year...

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Pearl Sutton

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Tony Jennings wrote:
If they built them into windows the energy companies would lose millions of dollars per year...

True that!!

Building them into the house wall is wise :) There are types that use more thermal mass, depending on where you are, they might be worth considering. I'd also make sure they open for maintenance or modification when built. I saw someone hard build them in, then have to put a lot of work into removing it to fix a problem.

Cool! Love to see people doing good things!
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Pearl Sutton wrote:Looks good!!
And good results :)
My compliments!

I have thought those work so well, I'm surprised they aren't building them into windows like they build blinds into them.

They don't build them into windows because there is no net gain from them. The amount of heat coming in through the window is the same.

If you build one of these with vents cut top and bottom, and place it on the wall where there is no window, then you gain from it. It will pull cooler air in from the bottom vents in the room, heat the air, and vent it into the room through the top vents. If you don't block the top vents at night, it will do the opposite and cool your room because the flow will reverse.

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Tony Jennings wrote:

Pearl Sutton wrote:
I have thought those work so well, I'm surprised they aren't building them into windows like they build blinds into them.

If they built them into windows the energy companies would lose millions of dollars per year...

They really wouldn't. The only person that would lose money would be the consumer that bought the device. If it doesn't have a collector larger than the window, there is no gain.

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L Goodwyn

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Don't paint your wood your getting some nasty chemicals. If you own a
torch char the surface of the wood.

I've seen a few of these using aluminum cans as the heat transfer tubes.

My idea was to use a cheap solar pv panel to power a dc fan
(i.e. computer fan 5v- 12v) for more air flow. Flexible dryer duct to the floor for
a cold air intake.

Cool idea, what you have done is awsome.

Peace.

Pearl Sutton

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Trace Oswald wrote:

Pearl Sutton wrote:
They don't build them into windows because there is no net gain from them. The amount of heat coming in through the window is the same.

If you build one of these with vents cut top and bottom, and place it on the wall where there is no window, then you gain from it. It will pull cooler air in from the bottom vents in the room, heat the air, and vent it into the room through the top vents. If you don't block the top vents at night, it will do the opposite and cool your room because the flow will reverse.

I mean build them in right. Double paned glass,then slats, then one more pane of glass, that has the vents in it. Could even put the vents on a thermostat or timer to make them work right. This could be done right easily and just built into the window.

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I understand the idea Pearl. It's just that it doesn't work that way. Only a certain amount of heat can enter through a certain size window. Nothing you build into that window can make more heat than you get through the window already. Building a thermosiphon into the window adds cost but no heat gain.

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Tony Jennings

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Trace Oswald wrote:

Pearl Sutton wrote:Looks good!!
And good results :)
My compliments!

I have thought those work so well, I'm surprised they aren't building them into windows like they build blinds into them.

They don't build them into windows because there is no net gain from them. The amount of heat coming in through the window is the same.

The amount of heat coming in is the same. However, between the inserted metal, dark coloring, and possibly other things such as thermal mass that energy is used much more efficiently. Personally, I wouldn't build them into windows because I like sunlight. That being said, one could get some of the sun by installing interior black aluminum inset blinds and use a plexi glass box instead of a wood box.

You may not believe there is a difference but that room never gets above 70ish when it is only 60ish outside. Today with the door closed the room was almost 90 while it was 60ish outside. The other interior window in that room had condensate forming on it because of the temperature difference. It was as hot in that room as it normally is when the wood stove is going full bore... and the next room (with the stove) was still only just about 60 (there is a door between the rooms).

(the following was edited in after posting)
I expect that the rapid churning of air also has something to do with the heat gain.

Of course, if you live in a cob house with dark floors and not a modern wood house or trailer then perhaps the gain wouldn't be nearly as significant.
(end edit)

Trace Oswald wrote:If you build one of these with vents cut top and bottom, and place it on the wall where there is no window, then you gain from it. It will pull cooler air in from the bottom vents in the room, heat the air, and vent it into the room through the top vents. If you don't block the top vents at night, it will do the opposite and cool your room because the flow will reverse.

My goal is to put it onto the wall... but simply building (a very inefficient) one onto an existing window made a very large gain.

Because it has a heat lock in the middle ( what I put against the window was basically a box with an intake at the bottom left, a vertical divider up the center about 80% of the way, and the intake to the window at the top right) the reverse air flow should not happen at night. It would have been simpler to test without the air lock but I wanted to make sure that works as described.

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It seems you have your mind made up, so I will just say this. There are people that have made thermosiphons that fit into windows and attempted to market them. The reason you don't see these units for sale at every Wal-Mart is because they don't work. If you go to any of the many YouTube videos showing the various attempts, and read the comments, you will find engineers and physicists that have taken the time to explain the reasons why they don't work in painstaking detail. The first one I built was much simpler than yours. I took a piece of foil backed insulation board the size of the window, cut out a vent at the top and bottom, taped a piece of plastic bag over the top vent to stop the flow from reversing. I painted the window side black. 120 degree air came out the top vent. A fun experiment but not a way to hear my house. The builditsolar site goes into working models and in-depth testing for more information.

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Tony Jennings

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Trace Oswald wrote:It seems you have your mind made up, so I will just say this.

I don't have my mind made up. I built a simple one and the result was pretty impressive (20 degrees hotter in that room than normal).

I'll trust my own experience over some high priced experts every day of the week.

The initially linked site explains quite well how they work. If they are no more efficient than a large window then having big windows in their place should have worked just as well.

Anywise, not going to get sucked into a big argument, just sharing my own experience tinkering with these for others interested.

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If i am understanding this, you took a window and made a trombe wall. Heated air goes up which sucks cooler air from the bottom.

If the assertions are true about not getting a gain, i can see a better mixing of the air in that room from the current created. Similar to what a ceiling fan would do. If this is whats happening, you are getting a gain in the area that you occupy (ground to 6ft up).

If that seems reasonable, could you quantify it? Take this room and another room, measure temp at ground, midway, and at ceiling height.

This is interesting....

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It's good to test. Sometimes it's hard to see what's going on, though. You can have the same energy input and distribute it or use it differently. The difference may be more pleasing or effective than the original situation without being in any way more efficient. If you end up with a more pleasing and comfortable arrangement, that's a win regardless if the energy sums zero out.

For me, I like light coming through windows, so something like this would definitely need to go in a wall. What happens in different seasons?

Regards,
Rufus

Tony Jennings

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wayne fajkus wrote:If i am understanding this, you took a window and made a trombe wall. Heated air goes up which sucks cooler air from the bottom.

If the assertions are true about not getting a gain, i can see a better mixing of the air in that room from the current created. Similar to what a ceiling fan would do. If this is whats happening, you are getting a gain in the area that you occupy (ground to 6ft up).

If that seems reasonable, could you quantify it? Take this room and another room, measure temp at ground, midway, and at ceiling height.

This is interesting....

Yep, that is pretty much it.

Of course, the metal slats and dark surface color help to reflect the sunlight multiple times and absorb more of it.

The room next door (same house, same day, more sun facing window space (3 times as much... but the room is twice as large)) was over 20 degrees cooler even though the room I put the thermosyphon in is the most leaky room in the house (the hot tub room... which is currently empty but not insulated and very ventilated).

Outside temperature: 60 degrees
Temperature in unheated rooms of the house: 59 degrees
Temperature in the hot tub room (no water in the tub, way worse ventilation than any other room): almost 90 degrees

I didn't measure the temperatures at ground, midway, and ceiling... and temperatures (except air output) were taken at eye level. I'll take measurements for different rooms tomorrow around noon and see what they are.

We live in a trailer with rooms added on (both parents are carpenters, dad passed a while back) and mom prefers the look of modern houses to the earthy cob style so I'm experimenting with things that would help her heat the house without 9 cords of wood per year. Obviously, getting some thermal mass in (I'm making bricks right now), insulating her wood stove and maybe creating a rocket stove inside of it or doing a level or two of masonry on top between it and the riser, etc. will help... but we don't have much to work with so I'm starting with things that I can do with scraps that her and dad have collected over the years.

This worked way better than expected... even though the design was very sub optimal. Now I need to build a version that can be tinkered with (variable sized input/output ports, etc.).

Any yes, the gain is the entire room... pretty certain that is because of the circulation it is creating. It may not reach the floor to get the coolest air but as more air gets hotter the movement will cause it to mix with the cooler air and eventually cause that to warm up as well. Now only if that room had some thermal mass in it... hrmm... fill the hot tub...

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Tony Jennings

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Rufus Laggren wrote:It's good to test. Sometimes it's hard to see what's going on, though. You can have the same energy input and distribute it or use it differently. The difference may be more pleasing or effective than the original situation without being in any way more efficient. If you end up with a more pleasing and comfortable arrangement, that's a win regardless if the energy sums zero out.

For me, I like light coming through windows, so something like this would definitely need to go in a wall. What happens in different seasons?

Regards,
Rufus

Thanks. I completely agree. But I suspect that the difference is akin to the difference between a light wood colored bowl in a light wood box covered by a piece of glass and a metal box with reflective internal coatings holding a dark metal bowl with water and the box being covered by a piece of glass. Other solar oven improvements could obviously be incorporated.

The air flow is definitely a solid bonus as it seems to force the lower cold air to mix and get heated itself.

The air stop built into the box should prevent it from cooling the room (acting in reverse) and potentially give a bit better insulation than a window. With the proper angles on the metal slats and the proper overhang this shouldn't cause any extra gain during the summer in hot areas (if it does plug the vents) and should provide more heat in winter (if sun facing). The originally linked article goes into pretty good detail on why he uses slats and why he ended up building an air trap. Aluminum blinds could be adjusted during different times of the year to provide more or less heat as wanted.

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Morris is a very good guy and very happy to discuss this type of thing over email. Maybe ask him about your idea of putting the thermosiphon in the window. He can give you a much more exact answer than I can as to it's efficiency. He is one of those high-priced experts you are talking about though.

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Tony Jennings

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Trace Oswald wrote:Morris is a very good guy and very happy to discuss this type of thing over email. Maybe ask him about your idea of putting the thermosiphon in the window. He can give you a much more exact answer than I can as to it's efficiency. He is one of those high-priced experts you are talking about though.

I get the feeling you are being honest and really appreciate the feedback and ideas.

I'm going to continue running tests and experimenting and posting what I find here for others (with more detail). I know enough about how the mind works to know that I could be skewing my perception... but I don't believe that to be the case at this point.

I'll be making a second thermosyphon insert for the addition and gathering a lot more information before installing it. I was a bit dubious myself about it... but I've been pleasantly surprised with the results. If that one works out then I'll definitely be adding some between the windows on the sun facing wall in the addition and using them at around ground level in the green house. Otherwise I'll be more than happy to admit my mistake as science is supposed to be about experimenting and observing... not convincing or adhering to currently believed ideas.

I've gained so much from places like this and simply want to give something back. Most of what i've gleaned over the past decade and a half has already been posted here in various forms. This is one of the few things I haven't seen more than a few references to here... and it is working so far for me.

And, again, if we lived in a cob house with earthen floors I'd expect the only difference to be from the quicker cycling of air... but we live in a leaky trailer with decently insulated additions and relatively little thermal mass... so even minor improvements tend to make a respectable difference. Maybe I'll get mom to let me rip out the null wall (empty outside air between two rooms) between the front room and the living room and put in a cob rocket stove... that would make a massive difference in how much wood she needs each year.

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Capturing heat in a thermal mass, and moving it to where you want it via heated air, plus box adding protection vs air infiltration, all seems better than a window into an empty room.

Trombe wall or low mass sunsace, it works.

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I'm not saying thermosiphon heaters don't work. They work wonderfully and I use them in my shop. Morris has the best design I've seen. His are made to very exacting standards and are harder to build than some. He is a great guy and a couple years ago I exchanged emails with him when I had some questions. Ultimately, i decided to go with a design that was easier to build. The one I used is shown in full detail on the build it solar site. A man built it onto his shop in Idaho. It uses black window screen as a collector and simple plastic flaps to stop air flow from reversing at night rather than Morris' air trap. I'm not at all trying to dissuade Tony from doing this. They are a great idea. But they need to be built onto the wall, or in such a way that they make the collector area bigger than the window or there is no more gain that the window itself provides. Storing the heat or moving it don't have anything to do with whether the heat comes in through a thermosiphon or through the window. For best results, if I were Tony, I would build the thermosiphon on the wall to get the extra heat in, and make an insulated curtain for the window that I could roll down in the evening to trap the heat in the room. Just my opinion of course.

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Tony Jennings

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Trace Oswald wrote:... I would build the thermosiphon on the wall to get the extra heat in, and make an insulated curtain for the window that I could roll down in the evening to trap the heat in the room. Just my opinion of course.

This is definitely what I'll be doing. The in window version is simply a quick way to be able to test, adjust, and play with it without having to take a section of wall out... and to show my mom the results in order to get her comfortable with the idea of putting some of these into the south facing walls.

Like many modern houses her house is designed very poorly from a sun usage standpoint... and a few changes should make a huge difference in the amount of fire wood she needs each year to keep the house semi warm.

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If any of my previous posts came off as argumentative, please accept my apologies. I think it's great that you are trying to help your mother save wood and be more comfortable. I posted because it seems you are traveling the same path that I was 7 or 8 years ago, and I hoped to save you some steps. I'm all for experimenting and really enjoy it. Who knows, you may come up with something entirely new, or a better way to do something existing. I absolutely don't want to dampen your enthusiasm. I would again like to recommend the build it solar site. There are people doing really great things there.

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alternative to blocking windows.

The one I used is shown in full detail on the build it solar site. A man built it onto his shop in Idaho. It uses black window screen as a collector and simple plastic flaps to stop air flow from reversing at night rather than Morris' air trap.

Couldn't find my link to the specific one he mentioned but it IS a very nice design & simpler to build. Poke around builditsolar to find it. Well worth investigating.

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Trace Oswald

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Mike Barkley wrote: alternative to blocking windows.

The one I used is shown in full detail on the build it solar site. A man built it onto his shop in Idaho. It uses black window screen as a collector and simple plastic flaps to stop air flow from reversing at night rather than Morris' air trap.

Couldn't find my link to the specific one he mentioned but it IS a very nice design & simpler to build. Poke around builditsolar to find it. Well worth investigating.

I found it. Very nice build and more within my skill-set than Morris' beautiful design.

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Tony, congrats on your success! I look forward to your report on the final, or at least 2.0 version. Do you have any projected costs or bill of materials planned out yet? I would love to build something similar for an unheated guest room and a very leaky un-insulated barn. I'm not expecting magic in the barn, but it would be nice to be able to keep water in its liquid state.

Are you planning a full production model similar to the Zen of Passive Solar Heat, or a more DIY-esque style?

On your prototype, what did you use for the fins? I tried to figure it out, but I'm not able to recognize them from the pictures.

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Tony Jennings

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Quick thermal scanner measurements from today:

Outside Temperature: 64 degrees

In another south facing room (twice as large with 2ce as much window space and better insulated)
- at floor level: 62 degrees
- at eye level: 64 degrees
- at ceiling level: 64 degrees

In the room I put the thermosyphon in:
- at floor level: 82 degrees
- at eye level: 86 degrees
- at ceiling level: 90 degrees

For materials and such I just used some things we had lying around:
- a piece of 5/8 inch siding (rough side facing the window, used wood putty to seal in the ends)
- for the box spacer I just used 2x4s (cut them, added glue to get it air tight, then screwed them in)
- for the back of the box I used a piece of 1/8th inch wood panel (sanded it down first)
- for the slats, I used 3/4 inch aluminum duct strap (cut with tin snips) mounted in some extra cedar fencing slats (cut slots with a jig saw using a blade having a kerf slightly larger than the strap)
- to get an air tight seal with the wall I just used a piece of pipe insulation cut into three pieces length wise and compressed them between the panel and the window trim when I screwed the panel to the wall.

Mine is all DIY from common materials that are cheap. When I do the in wall panel the main changes will be:
- 1 1/4 to 1 1/2 inch wide metal duct strap
- UV resistant poly for the outward face
- caulking for external sealer (the panels are going to stick out of the outside of the wall)
- adjustable/closeable vents

And thanks for the link Trace Oswald. Much appreciated. And no need to apologize... but appreciated none the less. Always hard to determine tone over the internet.

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