Windows for Passive Solar Sunroom

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PASun
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Windows for Passive Solar Sunroom

#1 Post by PASun »

Hi,

There is a lot of great information here, so thanks for everyone sharing!

I am adding a 21' wide x 16' deep passive solar sunroom to the back of my home here in Whitehall Pennsylvania, plant growing zone 6b. The south wall of the sunroom will face southeast (slightly more south than east). The sunroom will have a 4" thick paver floor that along with the concrete block back wall of the house will serve as thermal mass to absorb sun energy and then radiate heat to help warm the space when temperatures drop. Right now my back door will be the only opening into the sunroom and I intend on leaving that door open to allow the sunroom to help warm up the house during sunny days during fall/winter. My plan is to use the least amount of glazing that I can to have enough sunlight to heat and light the space. The structure will have a gable frame shingle roof with cathedral ceilings and insulated concrete foundation walls that extended 2' above grade. The roof will be vented via ridge vent and soffits. Insulation values in the roof and walls will be higher than code since my goal is to retain solar gains on sunny days during the winter when the sun's solar angle is never more than 37 degrees and keep out the heat during summer. Roof overhangs will help block glazing to keep things cooler during warmer months. I will be starting many vegetable seedlings during late winter/early spring and propagating trees in the sunroom but this will not be a greenhouse year round. Sunlight will be beneficial for plants too but glazing will only exist along the south wall and part of the west wall and will not exceed a 20% glazing-to-floor area ratio

I am still undecided about the type of windows I will use but since casements are very efficient when it comes to air leakage, I am leaning towards using them and possibly awning windows below the casements I think this combination would help a lot with ventilation too. I have done a lot of research about passive solar, the use of thermal mass, ventilation techniques, glazing etc. I have learned about high SHGC glazing made by glass manufacturers like Cardinal and Guardian but I am having a hard time finding window manufacturers that use high SHGC glass. ClimaGuard 80/70 looks like it would be ideal as does Cardinal's i89 4th surface coating on a double pane combined with a LoE - 180 on the 2nd surface. Unless I am not talking to the right people, high SHGC glass is not used in windows that are readily available here even in the northeast. I knew when I talked to window companies it would be uncommon that a customer ask if they offer windows with a code required U-factor and a SHGC in the 60-70 range. Sunrise does not offer this and I talked to a window company owner who installs/carries Okna and he had never been asked this kind of question before and had to get back to me after speaking with Guardian. He called back saying he can't supply a window with that type of SHGC then proceeded to tell me that my sunroom would be getting too hot with such glazing lol. Despite my initial explanation of the sunroom build, controlling direct gains with window shading, storing heat gains to prevent overheating etc I don't think he understood passive solar concepts.

I welcome thoughts and expertise regarding the sunroom I am going to build and if anyone knows if there are some good window manufacturers that offer high SHGC windows without having to buy from Canadian manufacturers?

Thanks,

Chris

WindowsDirectCinci
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Re: Windows for Passive Solar Sunroom

#2 Post by WindowsDirectCinci »

We had some beautiful flowers draping over copper planters attached to our back deck, my wife went out of town and I was responsible for taking care of the plants.... They almost died so I'm not sure about the needs your requiring lol. But I do know that you should look for windows that don't have a low e coating, I know they are available through probably any major glass manufacturer. When comparing shgc make sure to know whether they are speccing the whole window unit or just the glass. The window includes the frame also. I know cardinal glass low-e 180 has a shgc of .69 and is available from sunrise, they call it p2100. I also see no reason to pair that with i89 as the extra coating should reduce the shgc

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toddinmn
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Re: Windows for Passive Solar Sunroom

#3 Post by toddinmn »

Clear glass may be the way to go , depends on what minimal glazing is . May want to check code for u factor requirements , might need an exception to use clear glass.

PASun
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Re: Windows for Passive Solar Sunroom

#4 Post by PASun »

Thanks for the replies.

WindowsDirectCinci where can I find the P2100 information? A few weeks ago I looked into the Sunrise P2100a recommended for windows in the northern zone and in their frame it his a SHGC of .49 but U-factor of .30. Looks like their P2210 brings the U-factor to within a code acceptable .25 and has a SHGC of .48. https://www.sunrisewindows.com/low-e-gl ... hern-zone/.

Tinted windows are not good for plant growth. However, many Low-e coatings don't reduce VT that much, they reduce infrared. Plants use mostly visible light and Low-e coatings reduce the amount of the visible spectrum transmitted (through glass) by less than 5% (they reflect heat - not light). The visible portion of the spectrum is the part that is necessary for plant growth. They are always coming out with new types of coatings and use combinations of these coatings. Some tinted coatings alone can block a 2/3 of the visible light spectrum.

Todd I do have several patio door tempered glass panels that I could use that don't have a Low E coating. I was hoping to use glazing that could be opened and not just picture framed windows.

WindowsDirectCinci
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Re: Windows for Passive Solar Sunroom

#5 Post by WindowsDirectCinci »

That is the same glass the a just means it will have argon, the numbers I quoted are the numbers for the glass not including the window frame. As you can see the numbers are drastically different when the frame is included. Unless you put in glass units directly into the opening I think that’s about as close as your going to get

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Windows on Washington
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Re: Windows for Passive Solar Sunroom

#6 Post by Windows on Washington »

You have done some pretty good research on this. A double pane 180 with an i89 surface 4 coating will give you pretty solid performance on the thermal resistance along with the higher SHGC numbers.

Anything that is PassivHaus is going to incorporate thermally insulated shades for the overnight lows to help with energy loss when the sun is down.

https://www.cardinalcorp.com/technology ... nce-stats/

Anyone that deals in Cardinal glass "should" be able to order the 180/i89 package...they just are familiar with it is all. You are correct and the vendor you spoke to is wrong. SHGC of 0.56 on the glass, assuming the overhangs that you describe, will be fine in that case.

PASun
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Re: Windows for Passive Solar Sunroom

#7 Post by PASun »

Thanks Windows on Washington I really appreciate the information.

Are some window manufacturers locked into not being able to use any glass from their glass provider? The Okna business owner told me he called Guardian and it's not something they can put in their windows. I did talk to the northeast rep for Guardian and she said she would get back to me with some window manufacturers that would make windows that I could use in my sunroom that could contain their ClimaGuard 80/70

Right now I am just seeing the SHGC of the glass itself. Is it possible to get a SHGC of 60 or more once in a frame?

What window manufacturers would you recommend for casements with high SHGC?

Thanks

Chris

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Windows on Washington
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Re: Windows for Passive Solar Sunroom

#8 Post by Windows on Washington »

Only thing that will get you to 60 and above in a window that is in a frame is clear glass in all likelihood. You have to figure that the SHGC in all the frame components and sash is "0" so that is going to drop the average pretty quickly.

PASun
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Re: Windows for Passive Solar Sunroom

#9 Post by PASun »

ok, that makes sense. I did not realize the sash and frame were averaged in at 0 to give the actual SHGC of the window.

PASun
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Re: Windows for Passive Solar Sunroom

#10 Post by PASun »

Are casement windows really helpful for the passive solar sunroom I have described? I had originally thought that the superior air seal that casements provide when compared to double hung windows would help retain heat gains much better during winter nights when there is no sun that day or no sun for several days. How much better and is it worth having casements for my purposes?

I now know that a SHGC in the mid 50's when in a window frame is what I should be looking for. That being said, what window manufacturers make good quality windows for what I am looking for in the sunroom?

Chris

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Windows on Washington
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Re: Windows for Passive Solar Sunroom

#11 Post by Windows on Washington »

If the DH is a well regarded brand and airtight, the difference is negligible. The casement typically more well suited for what people envision for a sunroom.

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HomeSealed
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Re: Windows for Passive Solar Sunroom

#12 Post by HomeSealed »

Windows on Washington wrote: Tue May 07, 2019 6:52 am If the DH is a well regarded brand and airtight, the difference is negligible. The casement typically more well suited for what people envision for a sunroom.
Exactly. Casements will provide the best seal "out of the box", there are a couple of things to add:
1) As alluded to, there are some very tight double hungs on the market that get the same air leakage rating.
2) While a compression seal (casement) is still theoretically superior to a friction seal (dh), casements WILL sag over time. There are adjusters built in to newer models, and those products with better engineering won't see it as severely (although size and usage also play a role), but its still a bit of an inherent issue with casements.

I would not recommend against casements for those reasons, although I'd only say that the advantages that a casement presents at the time of install (superior seal) may even out over time. Ultimately, both config's can be very good, I just wouldn't choose a casement for the primary reason of getting a better seal.

PASun
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Re: Windows for Passive Solar Sunroom

#13 Post by PASun »

Thanks Homesealed! It looks like DH windows may be the way to go for several reasons. Most importantly, the sunroom will be a closed off from the house and the advantages of casement windows appear to be minimal when compared to well sealed double hung windows.

I am now considering just a 3rd surface LoE coating like Cardinal's 180. I had been splitting hairs between retaining heat in the sunroom with using a 4th surface coating like i89 in addition to a 2nd surface LoE and having a higher SHGC if using a 3rd surface LoE only. This does not even take into consideration the additional expense of windows with an added 4th surface coating. What would I be missing out on by using just a 3rd surface high SHGC LoE for my purposes?

A double hung window like Pella's NaturalSun seems like a good option. Sunrise is a brand mentioned a lot here. Any other brand recommendations that offer what I am looking for?

Chris

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HomeSealed
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Re: Windows for Passive Solar Sunroom

#14 Post by HomeSealed »

Personally I'd try to avoid a 4th surface coating even if it helps to achieve your ideal SHGC. In cold climates like yours that surface 4 coating will keep the inside surface temp of the glass colder, reducing the condensation resistance. This is even more concerning in a sunroom, where these windows will be colder than normal, but the there will still be moisture present from the home's interior. Sunrooms are known for condensation on the windows in general, and that will only make it worse.

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Windows on Washington
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Re: Windows for Passive Solar Sunroom

#15 Post by Windows on Washington »

+1.

If you are going to be running some thermal shades, surface 4 coatings are a mixed bag.

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