The Solar Porch- Passive Solar Retrofit

The solar porch acts on principles of passive solar thermosiphon to pull up cool air from my basement and deliver warm air into my main living space.  A convection loop with no moving parts (aside from the windows.)

Construction details:
Walls: I enclosed a 17x6 foot area of my south-facing front porch with 16mm R-2.5 triple-wall greenhouse panels. The tops of the panels insert into channel aluminum and are removable in the summer. Bottoms are held with screws and nylon washers. A Metal drip guard guides moisture off the decking.
Door: (not pictured) just a panel set in aluminum channel so that is slides.
Floor: Insulated with 1 inch R-6 rigid foam simply laid on the original decking and covered in 1/2 inch treated plywood, screwed down.
Ceiling: Added R-13 foil backed fiberglass insulation between the existing ceiling joists
Basement air box: a chute covering a basement window constructed with 3/4 treated plywood and insulated with spray foam, 1 inch rigid foam scraps, and foil bubble insulation.

Operation:
Activation: I simply wait until the temps reach around 70 degrees F in the porch, then open the basement window and the top of the main floor window. Upon opening the windows, the air flow starts almost immediately.
Temperatures: Porch temps typically stay around 90 degrees on a sunny day (even with sub freezing temps outside), rising to 104 if I don't open the house windows to capitalize on the heat.
Deactivation: The windows get closed at night at about the same temp of 70 degrees, or just when I get to it.
Main heat: The house thermostat (typical forced air electric heat) is set at 66. I have no way of measuring the heat generated. It just acts as a supplement to the furnace and the furnace runs less. I will be able to compare energy usage after a couple more months.

Other/future uses:
-Makes a great sun sauna and the diffused light through the panels feels great!
-After more time studying the temp swings, I'll decide how useful this is for plants. It does stay at least 10 degrees warmer than outside overnight.
-I'd love to automate the house windows but doubt I could do so aesthetically.
-Maybe a rocket heater could fit into this equation, but only if I can't talk my wife into letting me put one in the main living space :)
-I might add a thermostatically controlled shutter or automatic hydrolic greenhouse vent to dump heat in an emergency overheat situation.
-I completed this with the input from some of you fine Permie folks in other threads, thanks!

Matt Todd wrote:The solar porch acts on principles of passive solar thermosiphon to pull up cool air from my basement and deliver warm air into my main living space.  A convection loop with no moving parts (aside from the windows.)

This looks great. I saw a video where Matt Walker was explaining that in a rocket mass heater, once the air left the barrel, it would behave like water but upside down.  In your design, the cold air from the basement fills up the lower part (like water) before pushing the warmer air in the window. I wonder if it would work even better if you only opened the top of the porch windows into the house.  

I am not sure if the porch would support it, but if you had some water barrels painted black they might keep the greenhouse warmer for plants in the night

The photo of the ratchet for the rope is not clear, can it be improved please?

John C Daley wrote:The photo of the ratchet for the rope is not clear, can it be improved please?

The "rope ratchet" doesn't appear to be in this view, probably mounted to the floor/joist above. Visible is the slack end of the rope, and a carabiner clip clipped onto a sash lift handle.

The rope ratchet device, is some sort of cam or chock device that grips the rope (similar to how Venetian blinds operate) with a hook for mounting.
When pulled in one direction, the rope slips through, but is prevented from returning by the cam. It may be released by a redirection of the slack end? (sideways and out of the grip?) or by unloading the cam and moving it aside.

They come in various sizes, for paracord and for ropes.

Tk Gillman wrote:
I wonder if it would work even better if you only opened the top of the porch windows into the house.  
I am not sure if the porch would support it, but if you had some water barrels painted black they might keep the greenhouse warmer for plants in the night

Originally, I did only open the top of the window. Then one day I opened the bottom too so the cat could go enjoy the sunshine and I noticed it only increased the volume of air pushing in.  I figure, as long as the porch air is warmer than the house air it will push in, whether that's at bottom or top window height.  Wish I had more ways to quantify and measure besides just my strip of paper indicator.

I do intend to add water drums at some point, but want to get some extra support under the porch first. Luckily there's an old sidewalk under there which will make a good foundation for support.

John C Daley wrote:The photo of the ratchet for the rope is not clear, can it be improved please?

I'll let someone elses photo in better lighting show the concept. I love these things! Mine is a smaller version.
Entirely unnecessary here since a hook and nail would do just as well, but I had it on hand and my wife is short so this is easier since she's the one that has to open it every mid-morning while I'm at work  :)

One way to make it automatic would be the sort of air flappers they use on homemade solar thermal air units (sometimes made from aluminum cans).  They use a very thin piece of plastic (garbage bag) that is draped over a piece of hardware cloth or other mesh.  That goes over the opening.  When the air flows in the direction you want (up into the sunroom), the flap opens and lets the air move.  When it gets cold and the air tries to reverse direction, the plastic is pressed against the mesh and blocks off the air flow.  Basically a check valve for air.

So you could put it on either window (likely the basement one) and just leave the other window open all the time.

Visual for the flapper (called a back draft damper in this link): https://www.builditsolar.com/Projects/SpaceHeating/VacationHome/PipeFreeze.htm

You can use "wax window openers", which reply on temperature of the wax inside a piston attached to a window to generate piston pressure, and these are used for automatic opening windows based on a temp range with no electrical use: https://orbesenteknik.com/more/window-openers/

You could mount one to the porch ceiling, with the piston pushing open the top pane at say 75-80 since it's hotter at the top, and the lower window could open at a lower temp to match opening times.

I've seen these used on a geodesic dome greenhouse, it was attached to one of the top triangles as well as one or two panels at the bottom. Some have springs and others a screw that allows you to adjust the temp when it will start to expand/open.

Thanks for sharing.
I have toyed with same idea for some time and keep wondering and wondering what is the best way in my context.

QUESTION -
RE: cool air being sucked upwards into the cavity as the air moves higher and into the open interior window.

What is the principle at play?

In the case of no basement and no crawl room under my stumped house, I have pondered this concept before and now wonder the following....

Could I use a hole under the floor of the PASSIVE Solar heated room?
Or does there have to be a greater depth of the cold air draw?

Also I wonder....
I have a two step drop /split level in my home.
The passive heated sun room is on the higher side of the split level lower room.
I wonder... is there any reason I could not successfully somehow make this happen, after navigating the no crawl room understory for the 5meters between the origins of the drawing cold in and the entry to the passive heated sun room?
The draw level difference would only be 1 ft or does that not matter?

Joyce Harris wrote:
RE: cool air being sucked upwards into the cavity as the air moves higher and into the open interior window.
What is the principle at play?

Thermo-convection I guess you'd say. The hot air wants to rise and expand, so it's happy to move into the high opening of the interior window.

Joyce Harris wrote:
In the case of no basement and no crawl room under my stumped house, I have pondered this concept before and now wonder the following....
Could I use a hole under the floor of the PASSIVE Solar heated room?
Or does there have to be a greater depth of the cold air draw?

Stumped, like up on legs? You could put a hole under the solar room, and it would still heat the incoming air from the floor. BUT this would only be practical for heating the outside air a few degrees. It would not effectively heat cold winter air and there would be no closed loop to promote flow and heat build.
Now if you ran a duct from the floor in the back of your house to the floor of the solar room, then you'd close the loop and generate heat and flow.

Joyce Harris wrote:
I have a two step drop /split level in my home.
The passive heated sun room is on the higher side of the split level lower room.
I wonder... is there any reason I could not successfully somehow make this happen, after navigating the no crawl room understory for the 5meters between the origins of the drawing cold in and the entry to the passive heated sun room?
The draw level difference would only be 1 ft or does that not matter?

I'm having trouble visualizing the details of this, but as long as you give cold air a path from a low spot in the house into the bottom of the solar room and out the top then you should get some flow.

Matt Todd wrote:

Joyce Harris wrote:
RE: cool air being sucked upwards into the cavity as the air moves higher and into the open interior window.
What is the principle at play?

Thermo-convection I guess you'd say. The hot air wants to rise and expand, so it's happy to move into the high opening of the interior window.

Joyce Harris wrote:
In the case of no basement and no crawl room under my stumped house, I have pondered this concept before and now wonder the following....
Could I use a hole under the floor of the PASSIVE Solar heated room?
Or does there have to be a greater depth of the cold air draw?

Stumped, like up on legs? You could put a hole under the solar room, and it would still heat the incoming air from the floor. BUT this would only be practical for heating the outside air a few degrees. It would not effectively heat cold winter air and there would be no closed loop to promote flow and heat build.
Now if you ran a duct from the floor in the back of your house to the floor of the solar room, then you'd close the loop and generate heat and flow.

Joyce Harris wrote:
I have a two step drop /split level in my home.
The passive heated sun room is on the higher side of the split level lower room.
I wonder... is there any reason I could not successfully somehow make this happen, after navigating the no crawl room understory for the 5meters between the origins of the drawing cold in and the entry to the passive heated sun room?
The draw level difference would only be 1 ft or does that not matter?

I'm having trouble visualizing the details of this, but as long as you give cold air a path from a low spot in the house into the bottom of the solar room and out the top then you should get some flow.

THANKS Matt.

I am contemplating something very similiar on my home, although more "lean-to" against a South wall. I have 3 questions that I hope you can help me with
1) Does the volume of the warm air space matter? I am looking at my sun space only being about 2 feet wide (long story)
2)Would hanging something black, like fiberglass window screen within the space make a significant difference in the amount of heat generated?
3) Could it work to pull cold air from the frigid 2nd story rooms thru a pipe down to the basement and thru the opening? Would it require something mechanical to move the cold air from the 2nd story?

Ok, one more question.... Do you plan to dismantle this for summer?
Thanks in advance for any advice!!!

Laura Trovillion wrote:
1) Does the volume of the warm air space matter? I am looking at my sun space only being about 2 feet wide (long story)

I don't think it matters. They make passive solar collectors and Trombe wall designs that are only inches deep. I only went so wide because that was the width of the porch/overhang.

Laura Trovillion wrote:
2)Would hanging something black, like fiberglass window screen within the space make a significant difference in the amount of heat generated?

It would likely make a positive difference. At the very least, less light reflected out means more heat to use.

Laura Trovillion wrote:
3) Could it work to pull cold air from the frigid 2nd story rooms thru a pipe down to the basement and thru the opening? Would it require something mechanical to move the cold air from the 2nd story?

Your cold air is going to happily sink down on its own as long as it has open stairways or floor grates to move through. We're getting too deep into design specifics to say exactly how it would work without knowing a lot more details. Generally speaking, as long as you are producing hot air it will rise up and cold air will be displaced down.

Laura Trovillion wrote:
Ok, one more question.... Do you plan to dismantle this for summer?

I definitely made it with that in mind, but might be lazy and just take the end panel off and leave the door open (or removed) in the summer.

It's impressive you've actually DONE this.  

Can I ask where you got the triple wall greenhouse panels and do you have to buy a particular kind of aluminum channel for them to fit into?  

I love the idea of being able to put it up (for cold weather) and take it back down (for warm weather).  

Can we come live at your house ... just so we could see how it works ... (just kidding of course).  Hubs does not like the cold and gettin' older all the time.  Just to have a warm porch in winter would be wonderful.  

Jenn Lumpkin wrote:
Can I ask where you got the triple wall greenhouse panels and do you have to buy a particular kind of aluminum channel for them to fit into?  

Thanks! One downside is that it won't work for raising transplants because it gets too hot. Supposedly anything over 90 is no good for things like tomato sprouts. But it does warm the house and the cats absolutely love it. One of them cries for the window to be opened, and we can't explain to him that it does not work when it is cloudy! Can't blame him, it's real nice to sunbathe in winter.

The triple wall came from Menards, and the aluminum channel is just stock 3/4 material from the metal section.

Thanks!  We'd have to travel a bit to get to a Menard's but not super far.  
We've been thinking about enclosing part of our back deck;  our house isn't exactly set north/south/east/west though;  for us, the "west" side (slightly facing south) would probably be the warmest in winter, and there's only a bay window on the "west" side.    

I had made some PVC-pipe little greenhouses years ago, with greenhouse plastic, so I know well how warm the sun can make things even in winter;  but the sun has to be shining;  otherwise, no, (or not much) greenhouse effect.  

I really like the "temporary" idea, that you can put it up and take it down.  The seasons change so much, from cold-cold to hot-hot, you really need the option to use it sometimes and NOT use it other times, I've thought for a long time.  And for the "in-between" times like spring and fall, you can just open the side door like you said, to regulate the heat.  That's NICE.

Nice too, you're aware of your cat's desires.    He oughtta know he's a LUCKY cat, to be able to sit in heat, in winter, at all!