Hybrid Car – More Fun with Less Gas

Re: Finally back from Missouri

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Posted by nicksanspam on October 23, 2005, 1:26 pm
 


A silver lining.


Hurricanes, relatives, cost of living, house prices, culture, jobs...


Here's some NREL long-term climate data:

                      - - - January - - -        - - - July - - -
               HDD    avg/max  sun    SDD  CDD   avg/min  hum rat w
                                
Asheville      4308   36/47F   1180   37   787   73/63F   0.0144
Cape Hatteras  2698   45/52    1130   49  1638   78/72    0.0169
Charlotte      3341   39/49    1140   39  1582   79/70    0.0147
Greensboro     3865   37/47    1140   37  1253   77/67    0.0148
Raleigh        3457   39/49    1130   39  1417   78/68    0.0149
Wilmington     2470   45/55    1170   51  1926   80/72    0.0168
Roanoke        4360   35/44    1110   34  1052   76/65    0.0134

Land to the west of Asheville is cheap. It's cooler, but solar fuel is free.
All these climates need dehumidification for comfort, by ASHRAE standards,
but not much cooling. An airtight house wouldn't need much dehumidification.
Opening windows or running a whole house fan at night looks good for a house
with a long time constant, ie lots of thermal mass and insulation.

The "SDD" (sun per degree day) column is the amount of solar heat that falls
on a square foot of south wall on an average January day divided by
the difference between an indoor temp of 68 F and the 24-hour average
outdoor temp, eg 1180/(68-36) = 37. Higher SDDs make solar heating easier.

A 40'x60'x8' tall house with R30 walls and an R40 ceiling and 192 ft^2
of R4 windows and 0.2 ACH and a thermal conductance of 192/4 = 48 Btu/h-F
for windows + 1408/30 = 47 for walls + 2400/40 = 60 for the ceiling +
0.2x40x60x8/60 = 64 for 64 cfm of air leakage totaling 219 would need
about 24h(68-36)219 = 168K Btu of heat on an average Asheville January day.

A square foot of R1 sunspace glazing or polycarbonate "solar siding"
with 90% solar transmission might gain 0.9x1180 = 1062 Btu and lose about
6h(100-42)1ft^2/R1 = 348 on an average day, for a net gain of 714, so
168K/714 = 235 ft^2 of glazing (eg 8'x32' of siding) might provide all
the heat, with no electrical use or sun into windows.

If sunspace air keeps a ceiling mass C in the living space 100 F on
an average day and it provides heat for 5 cloudy days as it cools to 75,
C(100F-75F) = 5dx168K makes C = 33600 Btu/F, eg 539 ft^3 of water in
a 2.7" layer under the ceiling, or less, with a big tank on the ground,
or less than that, with fin tubes under the ceiling.

The ceiling might have a low-e surface below the mass to allow night
setbacks and avoid overheating the house, with slow ceiling fans and
room temp thermostats and occupancy sensors to control room air temps.

Nick


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