[Greenbuilding] font foibles

[Clarke Olsen]

Nick,
Your detailed contributions are hampered by the, um.. demanding font  
in which they appear.
Is it possible to zoom it a notch for readability?
Clarke Olsen
373 route 203
Spencertown, NY 12165
USA
518-392-4640
colsen at fairpoint.net




On Jan 11, 2011, at 4:04 PM, nick pine wrote:

> RT <ArchiLogic at yahoo.ca> writes:
>
> > Once a house is well insulated/air-sealed and its massing,  
> orientation and
> > landscaping have been reasonably well considered, the building  
> heat load
> > will be so minimal that occupancy gains and solar gains should  
> provide
> > most of it (speaking "typical"-sized houses, say 1600 - 2800 sf)  
> in Cold
> > Climate Regions, say, > 7500 HDD/yr)
>
> Bullshit.
>
> Then again, Sustainable Building Industry Council masonry salesmen say
> reasonably well considered lukewarm sunspaces with LOTS of thermal  
> mass
> (bricks, according to SBIC Brick Institute of America members :-)  
> can give
> a max 60% solar heating fraction, even here in PA, with a mere 4954  
> FHDD.
>
> Then again, "most" can leave a lot. If a department store sells a  
> $1000 shirt
> with a 60% discount, it's still a $400 shirt. Direct gain houses  
> with minimal
> fuel bills in cold climates cost a lot, because windows on living  
> spaces lose
> heat on cloudy days. It's better to focus on absolute fuel  
> consumption than
> fractional savings.
>
> If cloudy days are like coin flips (a reasonable assumption,  
> according to my
> TMY2 simulations) a house that can keep itself warm for N cloudy  
> days in a row
> has a 1-2^-N solar heating fraction, eg 50% for 1 day, 75% for 2,  
> and so on...
> 90% requires -ln(1-0.9)/ln(2) = 3.3 days, 95% requires 4.3...
>
> A direct gain house in Minneapolis (7981 FHDD) in December will  
> cool from
> 70 to 60 F in -RCln((60-17.9)/(70-17.9)) = 0.213RC cloudy hours,  
> where RC
> is the house time constant in hours, so a 95% solar fraction  
> requires RC
> = 4.3x24h/0.213 = 484 hours = C/G, where C is the house thermal  
> mass in
> Btu/F and G is the house conductance in Btu/h-F (with nicely  
> cancelling
> units: C/G = (Btu/F)/(Btu/h-F) = h.)
>
> A 40'x60' house fully-loaded with room temperature thermal mass  
> might have
> a 6" floorslab with 6"/12"x40x60x25 = 30K Btu/F plus 2(40+60)x8x5 =  
> 8K Btu/F
> hollow concrete block walls, with C = 38K Btu/F and G = C/484 = 78  
> Btu/h-F.
>
> With A ft^2 of U0.25 south windows with 50% solar transmission (a  
> low U-value
> to maximize cloudy day heat storage) and 820 Btu/ft^2 of sun on the  
> south wall,
> 24h(70-17.9)(0.25A+Gmax) = 410A makes A = 12.8Gmax, where Gmax only  
> includes
> the ceiling and wall and ventilation conductances and 0.25A+Gmax <  
> 78, which
> makes Gmax < 5.7 Btu/h-F, with A = 72 ft^2 of south windows. In a  
> perfectly
> airtight house, a 30 cfm 90% ERV adds about 0.1x30 = 3 to Gmax,  
> leaving 2.7
> for walls and ceiling, eg 5928 ft^2 of 5928/2.7 = R2196 walls and  
> ceiling,
> eg R5/inch Styrofoam walls and ceiling, 36.6 feet thick :-)
>
> > the remaining auxiliary heating requirement will be so small that
> > a wee woodstove is quite adequate as the auxiliary heat source.
>
> After a few cloudy days, the wee woodstove needs to supply all the  
> house heat.
> How much wood do you have to feed it over a 7981 FHDD Minniapolis  
> winter, if
> the house walls are less than 36 feet thick? :-)
>
> > True, one could probably get close to 100% of the building's heat  
> load
> > from occupancy/solar gains by making the house look like one of Nick
> > Pine's wet dreams, but curiously enough, most people seem to like  
> having
> > windows on their homes and have their houses look like houses  
> rather than
> > Grade 6 science experiments gone awry.
>
> It's fun to live in science experiments gone awry :-)
>
> Nick
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