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re: plans for a passive solar, energy efficient two-story duplex?
4 aug 2003
ecnerwal   wrote:

>> a 32x32x8' tall house with r48 walls and ceiling and 96 ft^2 of r4 windows
>> with 50% solar transmission and 15 cfm of natural air leakage would have a
>> thermal conductance to outdoor air of 1024ft^2/r48 = 21 for the ceiling plus
>> 24 for windows plus 20 for walls plus 15 for air infiltration, a total of
>> 80 btu/h-f. 
>that's a very tight house, nick.  0.109 ach...

one local sip builder guarantees 0.2. the swedish standard is 0.025.
(how do they do that?)

>i believe that you'll want some active ventilation to make it livable...

sure. a reversing fan in a house partition might act as a "shurcliff lung."

>i've been running numbers for my 24x48x21 foot two story shop, located 
>in southwest vermont (albany ny is closest nrel data site).

with 700 btu/ft^2 on a south wall on an average 26.5 f december day.
>r33 sip walls (should be tight), r10 stemwall (aboveground 18", 
>insulated to the footings 4 feet underground...

drew gillett says there are at least 20 bad ways to do that. we just
got back from soldier's grove, where we saw pressure-treated plywood
over the concrete stemwall (ok), weedwhacked foamboard (not good),
frost-heaved foamboard (worse), etc. stucco seems ok, or metal

>...r38-ish ceiling, r5 or r10 under the slab (not sure if r10 is 
>worth it with the frostwall already insulated to r10, and drainage to 
>keep the soil inside the frostwall dry). the slab is not intended as 
>"passive solar storage", it's intended as a workshop floor, and will 
>have radiant heat tubing embedded.

might be your first mistake :-)

>the benefits of high temperature water storage have been successfully
>beaten into my head here over the years.

otoh, sunspace warm air is cheap, with a slow ceiling fan and overhead
lower-temp water.

>there's a 10x10 r17.5 door, and a mandoor which, if typical of mandoors 
>(r3.5), will suck almost as much heat from a 3x7 door. perhaps i can 
>find a better one or improve the one i have...

you might attach a couple of 4x8x3" sheets of latex-painted styrofoam
to the outside of the door, with a large mating flange on the building.
or use a steel door with magnetic weatherstripping.

>the windows i've looked at are r2.9 for double-insulated low-e ii argon fill;
>i'm currently guesstimating 192 square feet, skewed to the south...

...8.3% of the floorspace. how about 96 ft^2 on the south, with 48, 24
and 24 on the e/w/n, with some lightshelves or skylights for daylight?
you might look for r4 fiberglass windows with 50% solar transmission...

>the overall building envelope has an aggregate r value of 12.27 (434 
>btu/h-f) (including floor to ground, which does not have quite the 
>temperature difference to put up with that the walls and roof do). 
>neglecting the floor, the overall r value jumps to 20.4 (204 btu/h-f)

more slab insulation and less radiant heat might help.

>however, better doors and windows quickly get lost in the noise, because 
>already the ventilation heat requirement exceeds the radiation heat 
>requirement, at a ventilation rate of 1 ach. 

you need that much for your work, vs 15 cfm per occupant?
you might partition off the areas needing more ventilation. 
>on a -20f day (68f inside - extreme day for gesssing size of heating 

ashrae says albany is warmer than -6 f 99% of the time...

>the radiation heat loss is 24,401btu/hr, ventilation is 36,758. 
>(i'm crunching the ventialtion heat loss using numbers i was given in a 
>fish-farming course...

heavy breathers?

>...rather than run up the cost of the windows and man door a lot,
>i'm looking at an air-to air heat exchanger as being the most important
>next thing to consider spending money on for conservation.

perhaps a reversing fan in series with a humidistat. canadians use
coroplast air-air heat exchangers in pig barns...

>i have not yet run numbers on window gain. one 48x21 wall is more or 
>less due south (within 5 degrees) with deciduous trees providing some 
>summer shade, and less (but still a fair bit) winter shade. i like the 
>trees, i don't plan to remove them, though some thinning might happen.

prune them flush to the ground? :-)

>i intend to turn much of that wall (other than the windows) into a 
>low-cost solar collector.

good luck. you might add on half of a quonset-style lean-to greenhouse
covered with polyethylene film or a single layer of flat polycarbonate.


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