I think it would be a waste of effort to do what you are planning, and without the inert gas you will create moisture problems from the condensation that will outweigh any insulation benefits.

 

When it's subzero the humidity level of our air is around 10%. I expect that over several months of gradually cooling weather most of the humidity trapped between the panes would drop to the bottom of the cavity and escape into the air.

I'm mainly concerned about finding the optimal distance between the panes and the r-Value each cavity plus pane.

I could flood the cavity with CO2 or argon easily enough but that's not what I'm interested in for now.

 

Wy_white_wolf gave a nice link to some science behind the ideal spacing. Looks like temperature variation between outside and inside determines the correct spacing, as does frame material/glass coating/fill gas. Should note, in their experiment, they seal between panes to limit convection. Seems 13mm (1/2") was ideal. Basically, the Rayleigh Number is at play.
Glass manufacturers have gotten better at sealing between panes...I remember ripping apart the sealing joint in old double pane windows and seeing beads (Silica gel desiccants?). Back then, they used square aluminum tubing (with pinholes facing inward) filled with desiccant. And the rubber compound on sides of Al tubing held glass together. Basically, they accounted for their inability to keep space between panes perfectly sealed, and any moisture would be sucked up by desiccant. Moisture between panes is the killer of good R value (or inverse, U value) of windows, as we know water conducts way better than dry air.
Argon, being heavier than air, is used because it has a higher Rayleigh Number than air (less convection).

So, leaving a hole between panes (for drainage) is not the way to go...imho. I know your naturally trying to 'desiccate' between panes using cold weather, but I think you could do better with desiccate. And silicone as a sealer would be my last choice...consider something used by glaziers. https://www.hbfuller.com/en/product...cts-and-technologies/markets-and-applications/building-and-construction/windows

 

Here is a study on window pane spacing and the effectiveness of multiple pains.

http://www.solarme.uwaterloo.ca/DownloadPDFs/PaneSpacing_SESCI.PDF

Multiple panes is one of those diminishing return items./ Just because 2 pains reduces heat loss by 50% does mean a 3rd or 4th pain will give you the same results.

Optimum spacing seems to more dependent on the heat difference between inside and outside than anything else.

Here's another that tries to explain why 2cm (~3/4 inch) is accepted as optimal for pane spacing.

https://ask.metafilter.com/116058/Why-do-doublepaned-windows-have-a-2cm-gap

WWW

 

I hate it when someone posts an answer that really isn't an answer, but here goes. I priced out some double pane insulated glass replacement glazing a while back and while I forget the details, they were not all that expensive. You might consider that as an option.

 

Great! Thanks guys. This is the information I was looking for.

 

For the windows I want to open I'll use 2 crank outs in each frame.

 

My walls and ceiling are going to be insulated with 16" of cellulose so I will have lots of room for adding additional window panes.

If I were to seal all the panes in place and leave 2 temporary holes in each space between the panes on top of the window and then add an inert gas that is heavier than air into one of the holes wouldn't it force the air out of the other hole and replace it with the inert gas?

I've heard about people who are storing food for long periods in sealed containers. To purge the oxygen out of the grain they put a block of dry ice on top of the grain and as it turns to gas the heavier than air gas sinks into the grain and supposedly forces the air (oxygen) up and out of the grain.

 

I'm sure that your plan for the gas would probably work, but there is no way to know that you got all the ambient air out. I'm used to dealing with units with a 10 year warranty so the manufacturer has a very carefully defined process and procedure to make sure that the ambient air is evacuated and a specific amount of inert gas is introduced and the seal is intact and to make sure they meet ANSI standards. Inert gases are an expense, and manufactures strive to control expenses. You would end up wasting inert gas that is of little consequence to you, but adds up for manufactures.

Be careful with an inert gas. They have no oxygen in them and are odorless and colorless. One of the common gases used is Argon. We had to start jumping through all kinds of hoops a few years back with Argon because of a death caused by a leak displacing breathable air and an individual suffocated. Keep the area you are working in well ventilated.

 

Thanks. I read something about argon and they said that it would settle to the bottom of the lungs and replace the air. Over time it would completely fill the lungs and the person would suffocate.

If I go with argon it shouldn't be a problem because I would be doing it outside. I would think that CO2 would be a viable option considering that it is heavier than air.

 

Use argon, not CO2. Since CO2 has oxygen in it, there is the potential of having issues with condensation. In addition, CO2 will cause corrosion and tarnishing to Lo-E coatings if you are using them in your windows. Lo-E is worth the price premium because it blocks over 80% of the infrared from entering your space. Multiple panes and inert gas prevent heat transfer through thermal conduction but Lo-E works because it prevents the sun's rays from causing heat to build up in your space. If you stand in front of a conventional window on a 95 degree day you will soon start sweating and everything near the window will be warm to the touch. With a Lo-E window, you can stand right in front of it and the only effect is you will have to squint because of the sun. Everything near the window that the sun is shining on will be cool to the touch. The load it takes off your cooling system is incredible.

 

That's interesting about the Lo-E coating. Depending on where I settle down I'll probably design the roof to exclude the summer sun and allow the winter sun to come inside the house. I did that with my present house and it works well.