Earthships

Only in that you didn't include solar heat gains through the window... Or there could other things, I didn't convert to check, I am used to imperial units.

 

I was not calculating net gain, just heat loss based on the provided U value.

If 264 Wh/day is the correct heat loss per square meter at a 20C temp gradient, then it seems to me that windows will be a net heat gain into the home for all but the most severely clouded climates.

Then again, my physics skills are at best rudimentary and I might be way off base.

addendum: from wikipedia --

U is the inverse of R with SI units of W/(m2K) and US units of BTU/(h °F ft2);

 

Corwyn,

This study
http://web.mit.edu/parmstr/Public/NRCan/nrcc18674.pdf

measured net heat gain in the winter using different windows at locations in Canada. I'll call this a stress test of windows
Double pane were rarely net negative, even in Winnipeg*. The study is from 30+ years ago, so I'll presume U values are much better today. I know my fixed double pane (with air) have a U value of 0.31.

E.g. In December when the delta T was ~ 35C and the incident radiation a measly 340 MJ for the month ( ~ 3 kWh/day), the net heat gain was -28 MJ. The values are per square meter.

 

I recalculated again using a different method, and still conclude that double-pane windows for my home in Abq were a good choice, and the best value.

MI is most certainly not Abq though, so I am not in any way suggesting that what works here would be a good idea there. I am only suggesting that Blue can reach some decent conclusions with straightforward calculations. I used pvwatts to find out the incident radiation in my area, and assumed 70% transmission through the double pane glass. In fact, if you want to be lazy like me, set the DC rating to 0.8 and the derate to 0.7 to match solar insolation of about 800 watts/meter_squared and 70% light transmission, then you can directly read the kWh of solar heat gain per month per square meter from the generated table from the column labeled AC. Note that this is Heat_in only; heat loss has to be figured separately. Using this method, I find that my windows gain 3 kWh and lose 0.1 kWh per square meter each day.

For average outside temperature I added the average high to the average low for each month , and divided by two.

 

My double pane, fixed windows have a U = .31, = to an R of 3.22

 

Light transmission is not the stat you want, rather SHGC (Solar Heat Gain Coefficient), which is usually given on the tag of windows. Some double pane windows are down around 0.3 SHGC. Not right for me or 2007blueprius, but possibly for you.

Heating degree days (see: Heating & Cooling Degree Days - Free Worldwide Data Calculation ) are a better way of finding monthly heat losses. Simulations with actual weather are even better.

 

Corwyn,

Right about SHGC -- I used transmission loosely. My windows are about 0.7 (clear glass)
Heating degree days correlates very well with the average I calculated -- either way will do so long as a month at a time is considered.

 

Maybe.

Once you have decent windows on the outside, I would recommend forgetting the inner ones. Good windows on the outside make the hole in the wall, net positive. In other words they contribute to keeping the house warm. The inner windows are now blocking light, preventing solar heat gain, and cooling off the buffer room when it is cold outside. If you think of being in the middle of a bunch of insulation, the temperature halfway through is going to be halfway between the inside and outside temperature. That is what you will get (absent other considerations) in your buffer room. While without the windows, that space will be room temperature, at a cost of heat loss thorough the extra surface area (which can be made fairly small).

That's it exactly. Double studded walls are one of several styles, personally I prefer a Larsen truss made with i-joists over a standard 2x4 stud wall, with the outer sheathing of the standard wall taken as the air/vapor barrier. Details are important though.

 

Not in New England it won't.

 

I take your word for it -- I only checked the validity for my home.

Any idea why NE is different ?

 

A plain double pane window would be about R-2. Those triples are around R-10, selective coatings, gas filled, and with very small frames. Here is an example: Passive House Windows and Doors | Intus Windows | Residential U-PVC Windows and Doors

 

My rule of thumb: Each pane of clear glass blocks about 13 - 15% of incident radiation.

 

Here is another website for average temps and degree days at your location
Climate Averages by ZIP Code

Notice that if you multiply the (65 -average_temp) by 30, you usually get quite close to the degree days. Negative results in the summer are cooling degree days. If you want an even closer result, multiply by the actual days in that month (28 in Feb, 31 in Dec ...)

So e.g, January is your coldest month, and averages 25F outside. If you assume an interior temperature of 65F, the delta is 40F, = 22.2C.

A window with a U value of 0.3 (R = 3.3) will lose 0.3*22.2 = 6.6 watts per square meter of heat through the month, or 6.6*24*30 = 4752 Wh in the month. The last calc multiplies watts * (hours in a day) * (days in a month)

For you Imperial/American folks,
1000 Wh = 1 kWh
1 kWh = 3412 btu
1 square meter = 10.76 square feet

 

The average T outside in the summer is a modest 70F, so yeah, active cooling would seem to imply poor house design or use. I would just keep in mind though that for many people the AC is actually running to lower the humidity.

I know you said that you like humidity, but you must consider it for the sake of the house. Mold is a bitch. While we have been talking temps (and they *are* important), I suspect that your house will actually succeed or fail based on how well you deal with humidity and water infiltration of the home envelope. This is particularly true for a home that tries to implement passivhaus concepts.

Corwyn has hinted as much, but I"ll just be blunt and say it: the building technique is every bit as important as the design. If I was in your shoes, I would find a passivHaus builder in my area and volunteer on the construction site for the equivalent of a summer.

 

Ahh. No, R-values are also different in imperial units versus metric units. (And of course U-values as well).

1 U-value (BTU / (ft^2 * hour * °F) = 5.68 W / (m^2 * °K)

Sorry for the confusion.