the real question was which one would score better, a plain double pane at R2 or a super fancy triple pane at R10, 1 sqft glass only considering the rest of the scenario is the same, while my location is about the same latitude as your example the mean daily temperature is much lower, we used some similar software from pvwatts and another site that had real historical records of sunshine, temperatures, solar trigonometry and such ( granted acuracy questionable just an axample ), the result we reached:

a plain cheap double pane had a higher net than the most expensive passiv house type tripple pane reason beeing the extra 15% of radiation lost due to the third pane far outweighed the energy saving due to the extra insulation, see below:

Crap, this arithmetic is wrong too. Let me go back to metric, but this time use the metric U value (5.6 times the Imperial)

1200 HDD in January is about a 40F gradient
= to 22.2C
My double pane with hard coat Low E has an American U value of 0.35, or 1.96 metric
Thus heat loss in watts is 22*1.96 = 43.5 watts, or about 1 kWh a day per square_meter.

OK, now I can see where Corwyn is coming from.
Now we can compare to triple pane:
U (imperial) is about 0.2 for fancy coated glass, or 1.12 metric
Now heat loss is 1.12*22.2 = 24.86 watts, a savings of (43.5 - 24.8) = 18.7 watts = 449 Wh a day per square meter.

How much heat gain have we given up ?
2 panes of clear glass in Jan in MI let in about 1800 Wh a day per square_meter;
3 panes will let in 2/3rds of that amount, or 1200 Wh a day per square_meter.

So, we reduce heat loss by 449 Wh per square_meter but reduce heat gain by 600 Wh per square_meter.

I think this is right, finally!
Which is better ? Double pane is cheaper, lighter, and has a (small) benefit in net solar gain compared to triple-pane, but would do much worse (almost twice the losses) in holding heat generated from inside the home from say a furnace (or from a ground heat pump.)

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I was just going back and reading through and althou I am still not serious about expensive windows for the weight and cost factor I think I found an error in your math still.

presumably double panes let in the 1800 WH, that is 0.85x0.85 =0.7225 of the total available which is 1800/0.7225 =2491wh now presuming a tripple lets in 0.85x0.85x0.85x2491 = 1530wh, the third pane filters 0.15 of the 1800 not 2 thirds so heat gain is only reduced 230wh, guess all those german scientists were on to something, go figure

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just a fictive calculation glass only into account, maybe you can settle it do the fancy tripples perform better overall?

Sorry, I don’t see any errors in my math. However, I am not sure how you are justifying using a 15% solar heat loss per layer of glazing. That seems like an overly simplistic rule of thumb that would be very inaccurate at best. You need to account for the solar angle of incidence to the fenestration glazing.

Why not just use the precise SHGC value published by the fenestration manufacturer for the specific fenestration that you are considering? Then the instantaneous clear sky solar heat gain (BTU/Hour) is the SHGC (%) times the fenestration area (SF) times the incident total irradiance (BTU/Hour-SF). The incident total irradiance (BTU/Hour-SF) can be very accurately determined for any given location and time/date using proven ASHRAE engineering methodology. You then integrate the instantaneous clear sky solar heat gain over the number of minutes per month that you actually receive irradiance at your location (i.e., accounting for roof overhang and local terrain obstacles) to determine the average instantaneous clear sky solar heat gain (BTU/Hour). The average monthly climatic solar heat gain (BTU/Day) is the average instantaneous clear sky solar heat gain (BTU/Hour) times the average monthly irradiance time (Hours/Day) times the climatic sunshine (%) for the specific location.

Our passive solar heat gain software does all the math and work. Here an excerpt from our software showing some of the details to give you a sense how this is properly done:

'Solar Heat Gain Calculations'

'Only perform these calculations if solar radiation is available at south wall at this time'
if (sra=='Yes'){

'Solar Angle of Incidence to Glass'
csaitg=Math.cos(saltadeg*rpd)*Math.cos((180+sazmadeg+swdftsdeg)*rpd);
saitgdeg=dpr*Math.acos(csaitg);

'Extraterrestrial Solar Irradiance'
esibtuphsf=433.3*(1+0.033*Math.cos(2*pi*(daynum-3)/365));

'Air Mass Ratio'
amr=1/(Math.sin(saltadeg*rpd)+0.50572*Math.pow(6.07995+saltadeg,-1.6364));

'Air Mass Beam Exponent'
ambe=1.219-0.043*bod-0.151*dod-0.204*bod*dod;

'Air Mass Diffuse Exponent'
amde=0.202+0.852*bod-0.007*dod-0.357*bod*dod;

'Beam Normal Irradiance'
bnibtuphsf=esibtuphsf*Math.exp(-bod*Math.pow(amr,ambe));

'Diffuse Horizontal Irradiance'
dhibtuphsf=esibtuphsf*Math.exp(-dod*Math.pow(amr,amde));

'Incident Beam Irradiance'
ibibtuphsf=bnibtuphsf*csaitg;

'Vertical/Horizontal Clear-Sky Diffuse Irradiance Ratio'
vhcsdir=Math.max(0.45,0.55+0.437*csaitg+0.313*Math.pow(csaitg,2));

'Incident Diffuse Irradiance'
idibtuphsf=dhibtuphsf*vhcsdir;

'Incident Ground Reflected Irradiance'
igribtuphsf=0.5*grc*(bnibtuphsf*Math.sin(saltadeg*rpd)+dhibtuphsf);

'Incident Total Irradiance'
itibtuphsf=ibibtuphsf+idibtuphsf+igribtuphsf;

'Instantaneous Clear Sky Solar Heat Gain'
icsshgbtuph=shgc*itibtuphsf*srabroper/100*wasf;

'Maximum Instantaneous Clear Sky Solar Heat Gain'
if ((icsshgbtuph>0) && (icsshgbtuph>micsshgbtuph)){
micsshgbtuph=icsshgbtuph;
}

'Sum of the Instantaneous Clear Sky Solar Heat Gain Samples'
if (icsshgbtuph>0){
numit=numit+1;
sicsshgbtuph=sicsshgbtuph+icsshgbtuph
}

'End SRA Logic'
}

'End Hour Iteration Loop'
}

'End Day Iteration Loop'
}

'Average Monthly Irradiance Time'
amith=numit*deltat/ndim;

'Average Instantaneous Clear Sky Solar Heat Gain'
aicsshgbtuph=0;
if (numit>0){
aicsshgbtuph=sicsshgbtuph/numit;
}

'Maximum Monthly Clear Sky Solar Heat Gain'
mmcsshgbtupd=aicsshgbtuph*amith;

'Average Monthly Climatic Solar Heat Gain'
amcshgbtupd=aicsshgbtuph*amith*ssper/100;

sorry for the confusion, I was refferin to the other felow I have been coresponding with, I need a minute to read through your notes, but long story short we were presuming a 15% shgc per pane, haven't yet considered any particular window just simply a theoretical exercise if you will, some of the sites and softwares involved in this include real data to calculate HDD, much like you sugested every 2 minutes, those softwares account for sun trigonometry historical sunshine data, etc, here's my latest:

5132 HDD in heating season november through february, 0.5 U value double pane clear glass window:
5132*0.5 = 2566 btu per SF per heating season
= 2566*10.76 = 27610 btu per square_meter per season
= 27610/120 = 230 btu per square_meter per day

Convert btu to Wh:
180/3.14 = 57 Wh (per square_meter per day)
27610/3.14= 8793 Wh/sqm/season?
hope I got this right

as for gain pvwatts say 322kwh solar radiation /sq m that is counting the shgc of 0.7225,

so what have I done wrong a 9kw loss compared to a 322kw gain, for plain double panes, I guess it does not apear too unrealistic



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Posted By sailawayrb on 01 Feb 2014 02:25 PM
I agree 100% Lbear, it is one thing to debate a subject with passion and quite another to just be a hostile bully making those kind of ignorant and unproductive personal attacks. I think some folks think that a high post count somehow makes them more of an expert than others. Research data has shown just the opposite to be true. Each post and debate stands on its own merit. We should all do our best to police this forum, call out offenders when needed, and ultimately drive out repeat offenders.

Thanks. The moderating on this forum is non-existent. Like you mentioned, we have to self-moderate.

 

So I have come to my senses if you will, provided due to my location normal double panes are a heat loss, and I have to have some high end glass, triples and up, which I won't afford a whole wall of, besides considering some loss gain calculations, I am working on a new drawing, more so geared towards Passiv Hause, lots of insulation reasonable glass and thermal mass, reduced demand in principle. So I was going over all your threads and the instructions on your website, one thing I am kind of stuck on at the moment is the full shade and full sun angle. In short I am kind of going backwords about it, I am trying to chose a window size based on the building, I'm not picky as long as it works, I'll post some pics soon, the overhang shades the south wall well above 8 feet in dec 21 and almost to the floor on June 21 so somewhere in there the window needs to be. Reading through your instructions looks to me your approach is a bit too modest granted the example you mention thou at about the same latitude is a world of difference, I believe you mention a daily temp of 47 in January, we don't see that till early April, so I recon I need a bit more aggressive approach selecting those dates for example I kind of get the full shade logic, sort of, 68 f for a high is still a cold day here, especially after sunset, so the idea was to incorporate some thermal mass to collect some heat during the day still at that point. I had a look at the weather website you mentioned in the instructions nov30 through march 5 th they label the cold season, the way I am looking at it with modest fenestration I could use all the sun I can get during this time, in theory our nightly lows never get above 70 when I pulled up my HDD s still had some values in July, in theory if I get this right won't need any cooling, so maybe a more involved thought process would be in order, one based on HDD rather than average high temp? Something along the lines where the btu input during the day matches the loss at night should be a begin to shade point? The opposite in the fall once the btu loss becomes grater than the possible gain have that full sun . In other words even the hottest day of the year the average between the daily high and nightly low is 75 F that is perfect to me, all I am saying maybe a different strategy picking those dates might be better suited if you have time look up Exeter, mi on the weather site it uses the monroe airport station, let me know what your take on it is. Thx George

I just looked up some angles based on the weather site and march 5th is 42.04degrees, I would be inclined to chose it as the full sun angle in other words time to start pulling the shades down, than September 20th hot season is over, I would be inclined to chose it as the full shade angle, temperatures are starting to drop time to start pulling the shades up, in the end not sure what dates those angles represent on the other side of the year as you explain it in your instructions, I'm looking into it, but it would probably end up similarity had I chose the dates as your instructions detail it, let me know what your take is on this.

George, it sounds like you are gaining a good sense of what is involved to properly design a passive solar building and you appear to be making good progress too. However, it also sounds like you have thus far only used our Passive Solar Altitude Angle and Passive Solar Roof Overhang Design software.

As explained in our passive solar software instructions, you should first take a wag at the roof overhang design using the historical temp approach as you indicated. Then you should use our Passive Solar Fenestration Exposure software to verify that your roof overhang design is indeed providing the shading and sun on the dates as you intended.

At this point you should then use our Passive Solar Heat Gain software to determine the passive solar heat gain BTUs that will occur with your design at your location. Don't neglect to include terrain obstacles as they can have a significant effect on your passive solar heat gain BTUs. You should have already used our Heat Loss Analysis software (or other similar software) to determine your expected building heat loss BTUs.

Once you have your heat gain and heat loss BTU data, you can then enter it plus your HDDs into our Integrated Heating Performance software to estimate your supplemental heating requirements and associated fuel usage. The goal here being to minimize your supplemental heating requirements without creating an overheat situation. As you get more aggressive with passive solar heat gain, you may need to use our Passive Solar Thermal Mass Performance software to buffer the heat gain to avoid a daytime overheat situation (i.e., reducing the daylight heat gain by storing some of it and releasing it during the night time).

So YES, passive solar design is all about determining and properly aligning the BTUs. You may need to go back and make some design refinements and then repeat this exercise several times to get a good design. And YES, passive solar building design can be a very iterative and often time consuming process. We use sophisticated software to automate this process and help us find the optimum fenestration area for a given set of design parameters. However, this software is a real number cruncher that would not run in JavaScript via your Internet Browser.

what drew me to the Earthship concept was self sustainability, and that might work out great in NM, even if they do get some cold nights, but that aproach in Michigan, is like getting a bigger furnace to keep up with the house, it served its purpose and got me started, it was not long till I realised that our solar input is not enough and plain glass will net negative, while at it came across the Passiv Haus standard and it's pretty obvious I need to combine both,
I haven't yet figured out the heat loss btu's for my building as I havent yet come up with a final design, I tinkered a bit on your website but for the most part some fields I was not sure what to input, there is a website I have come across before ( I'll post some links for the record ) which I am allready familiar with and it overlaps google maps satelite view graphics and stuff, I understand it a bit better, that's where I have been getting my solar angles from, and another felow pointed me to pv watts and some other sites, which have real weather stations data figured in the software calculations, so for the time beeing I was using them to kindof gage which way to take this.

the lot is on flat ground and thou in a wooded area, I checked it personally and also gathered solar angle data, ran the math the paper and pencil way, and determined how far to clear not to have any terain obstacles, or how big to the neighbours trees have to get for the shadow to touch the house,

for the most part I kindof took a backwords aproach, and made sure I can get all the sun available rather than calculate how much I am going to miss out on, this was a while back when I was considering the ond designs with a whole glass wall, I haven't finished the new one yet but the new south wall loocks like it's going to have a thin strip of glass a good 10 feet from the ground, I have seen a few houses done that way thought it was interesting now I know why, considering its not a slab anymore ( got a little to complicated trying to insulate it good enough ) so that give me even more clearence.

given the climate here, which honestly I like the North better than any other place and I traveled, the direction I am heading at the moment is to efficiently gather as much as I can in the cold months, and keep it in, I am not too concerned with overheating, that is a good thing, it will just have to be dealt with, be it thermal mass or if it gets down to it hidronic systems what have you, I would prefffer to keep it as passive as possible verry little if none mechanisms, since I am going the Passivhaus route now and HRV goes without saying so I can supplement warm glycol be it from solar colectors or an out door boiler or at least that is the idea at the moment.

my dilema at the moment is selecting the proper dates for my particular project, while reading through your instructions, I kindof got the hint ( for lack of a better word ) your aproach is " affraid " of the heat, you mention for the full solar angle an average low mid day temp of 4? F I think it was in november, I dont feel right about that whole concept for my location, that number is more like 20 F in januarry for me , not a good Idea to wait that long for full sun.

I lived in the north all my life and spent enough time in the elements, granted it changes a bit with every year we cant's take everything into account, but from my experience, octomber is still ok, I don't believe we are using our furnace yet ( kindof looking to match the overhang design with my current heating habbits ) somewhere there the shadow needs to start lifting and gets some gain, by november 1st mornings and evenings get a little too cold out in the open need to dress up if youre going hunting, by the 15th it is on, I spent a few mornings and evenings this year it was rough, I dont know how those critters do it all winter, at that point overheating is hot a concern any more staying warm is, same with the spring by may the furnace may be completely off, I'll keep an eye on it this spring see how it really goes and which day I actually turn it off,

you know what ? I think I got a record of my natural gas usage on my bills, that should be a good hint right there, I'll have to look it up and get back to it.

ok so how do I properly do this? looks like for my climate the climatic extremes are about a month behind the sun, ie coldest day is about a month behind the winter solstice so is the hottest day about a month behind the summer solstice, my main priority is full solar exposure during the winter months, guess I could use shades in the summer if need be, it works kind of odd if I go for full sun still by say march 5th, by sept 5th the window will be fully exposed again, august is still rather hot thou usually by the end of august evenings get cooler, put on a sweater time,
I drew some angles and so far looks like my windows would have to be a foot strip about 7 foot high, saw some designs like that I found it interesting, bit odd at the same time, my goal here is to design the house around the elements not the common practice looks first approach, a foot strip in comparison to roughly 16 foot deep floor works out to 6.25% pretty close to that rule of thumb, ironic,
I haven't gotten as far as calculating heat loss and gains as I am still deciding how to build. either way an initial thought I am now going for passiv haus standards or as close as I can get, I've considered double stud walls foot thick minimum still reading up on insulation options, but so far looks like R40 walls R60 ceiling, I may have to increase those numbers from what I have reading up so far, still working on that, any thoughts picking the proper full sun and full shade dates? the idea is to draw the windows based on the sun angles and the insulation by the heat gain, I may be going about it in a bad way too.

George

here is a copy of my gas bill usage over the past 2 years, it pretty much reflects the same data as the averages gathered on the weather spark site, it also reflects our personal habits and comfort levels, June, July, August, September, and October hardly any use mostly hot water, Going by the instructions on the Borst calculators, may 27th sounds like a good day for full shade, that works out great for the first half of the year problem comes couple months later by the end of july the shades will start to lift and august is still rather warm, same on the other end, waiting till January for full sun not such a great idea, well maybe, January 31st will have a similar angle with November 21st or there about, unlike the Oregon weather these winters are a bit rougher, however the following months after January 31st appear to be where most of the heating demand is, oh what to do?

Month starting,HDD,% Estimated
2013-02-01,1199,0.04
2013-03-01,1099,0
2013-04-01,718,0.03
2013-05-01,270,0.06
2013-06-01,105,0
2013-07-01,56,0
2013-08-01,65,0.03
2013-09-01,225,0
2013-10-01,529,0
2013-11-01,965,0
2013-12-01,1326,0.03
2014-01-01,1642,0

here's my HDD from http://www.degreedays.net/#generate, base temperature of 70F pretty much where we keep it except briefly in the evenings we may bump it a bit oddly enough very similar numbers with my gas bill, considering a the best window has the worst R value of the whole project by far, it would not be such a bad Idea to have them fully exposed well up to spring equinox, by April my heating demand diminishes to half of January so the shading may begin, that works out great but in retrospect 6 months later at fall equinox, I have full sun again, the month of October has about a third the heat demand of January, that seems to be a decent compromise between early spring and early fall gain.
the issue becomes the months before the fall equinox, having partial exposure , usually the last week of august nights get a bit chilly its the first part of august that concerns me, but I cant figure out a way to accomplish this in a passive manner, looks like shades will have to do, if I pick July 25 as full shade, that will coincide with an angle sometimes in mid may, so I would have full shade during, if I put that off till aug 22nd may work out better but it narrows the band up to equinox, leaving me with a thin strip of window, which is fine by me as long as that gets me the best use of it .

any thoughts picking the proper dates?

I have been tweaking this so much that it doesn't look anything like what I initially envisioned, and still not sure if more is needed but its cheap fun at this time. I read a pole building book last summer and the idea intrigued me since based on it's simplicity and open floor plan possibilities, these sheets are rather large at the moment best I can do is take some photos. Can barely see the grid on the pic but one small square is 6 inches for size, 13 feet pole spacing north to south 20 foot span counting the cantilever. I realized how difficult and costly insulating a slab could get so figured I'd look into a subfloor and took the same principle as double stud walls all around floor and roof too, a rough idea I have about 18 inches of cavity in the outer walls R 60 if cellulose, about 30 inches available for roof and ceiling, I got to look into it a bit more see how it all adds up some of these may need to be tweeked still put in principle the only thermal bridge are the poles, at 30 inches not too bad plus I reconed I should insulate them inside the building, so in theory heat loses should be minimal considering no windows east west and north. I have been scratching my head around the overhang and where the windows should go, so far I picked spring/fall equinox for full sun, it's still rather cold here in march, and jully 25 for full shade the hottest day, in reality may 18th has the same angle august will be kindof tricky might have to change that a bit but the goal here is to have most winter exposure, shades will have to do for the summer. just a rough guess at this moment my windows work out to be about 3 foot tall 6 feet above floor level, bit of an odd look but I'm fine with that, guess beauty is in the eye of the beholder and what works and it's simple to build looks good to me. granted I have yet to figure out the exact measurements, I did that a few times on previous drawings that ended up scraped so kindof playing with it for now till it's final. any thoughts on insulation/airtightness, I am loading up those poles considerably allready with double floors so I am considering two story spec poles to cope with that, I saw a owens corning gap sealer that looks much more environmentally conscious, further reading required, compared to foam, JM has this spider cellulose type a combination of the 2 maybe, kindof aiming for Passiv Haus now or as close as I can get, I think some rough figures called for R60 walls, R100 roof, I'll be doing some modeling in therm for sure. granted vapor barriers and such are a concern, I wonder what products are out there that may do double duty, saw a hammer and hand video about sheathing with vapor barrier built in another thought was to use Greenboard on the inside of outside walls, it has a barrier built in should help with the air sealing. any thoughts much appreciated still keeping an open mind and trying not to get too attached to one idea or another.

pictures suck i'll see about a better exposure but that's so far my idea of a window detail

how about a 2 story, I noticed most PH are 2 story and I am sure there is reasoning for that, I ran the numbers works out to less material, for the same square footage yet twice the wall per foundation foot. and than the wind forces, guess some compromises must be made somewhere.

Is a two story generally a better idea?

Two Story....

If its a true two story with no inset walls you eliminate 50% of your roof shingles, insulation and reduce hot Attic ceiling exposure ..... Your trusses you loose from cutting your roof in half sorta can be reapplied as floor joist for second floor. Your HVAC duct can be moved from the hot attic to your open web joist which is within the conditioned envelope. Your Plumbing and electrical runs can be shortened also in some cases. If solar gain is desired it opens up possibility for solar gains/storage much further back into the structure.

Negatives...
Requires the construction of stair case .... You loose some sq ft because of this, but can be converted to storage or what ever space underneath. Need to add square footage for HVAC on first floor.

I'm sure there is more, but thats what came to mind right off the bat.

kindof what I am coming to realize I just crunched the numbers and it is considerably less materials, however looking at a pole foundation, it would be sitting on 6 poles rather than 10 and it adds up to more weight per pole,

on the other hand the floor between the levels would make a good service cavity and it can be a simple floor where the roof I was looking at double rafters with lots of insulation I have to look into it the poles are supposedly good for 6 tons each, got to figure what all this adds up to