[Greenbuilding] A Manitoba house

[nick pine]

Sean Rauch wrote:

-We live in Manitoba Canada and plan to build just outside of Winnipeg

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/International/pvwattsv1_intl.cgi 
says 3.13 kWh/m^2 (992 Btu/ft^2) of sun falls on a south wall on an average 
December day in Winnipeg.

The stat file at 
http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data3.cfm/region=4_north_and_central_america_wmo_region_4/country=3_canada/cname=CANADA 
says the average December temp is -14.1 C (6.6 F) with a -12.1 high.

-I'm working with a model right now that has 2000 square feet of living 
space spread out over two floors

... eg 32'x32'x16'-tall, with a 1024 ft^2 ceiling and 2048 ft^2 of walls.

-We're planning the basic south facing windows with thermal mass inside to 
collect as much winter sun as possible.

That could work. If the house has no internal heat gains and it's 75 F on an 
average day and 65 after 5 cloudy days in a row (with a 2^-5 probability), 
65 = 6.6 + (75-6.6)e^(-5x24/RC) makes time constant RC = 759 hours. With US 
R30 walls and an R60 ceiling  and  R30 night- and cloudy-day window 
insulation and a 1/R = G = 1024/60+2048/30 = 85 Btu/h-F cloudy-day 
conductance, it would need C = 759hx85Btu/h-F = 64.8K Btu/F of room temp 
thermal mass, eg 64.8K/25 = 2591 ft^3 of concrete or 4048 ft^3 of 
cylindrical rock gabions, about 25% of the house volume, or more, with less 
night window insulation.

-The house wont be off grid but I don't want to rely on the grid for any of 
the climate control demands of the house.

It might have a shiny massy ceiling heated by passive air heaters, with a 
thermostat and a slow low-power ceiling fan to mix down hot ceiling air as 
needed to keep the house exactly 70 F for 5 cloudy days, or 70 F during the 
day and 60 at night. Here's a nice air heater: 
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm 
With hot ceiling air and colder air outdoors, you might use R2 twinwall 
polycarbonate with 80% solar transmission instead of a single layer in balmy 
Montana. Gary Reysa and I tried this scheme in 2010, with one big mistake, 
an uninsulated partition wall that turned the air heater into an air cooler 
at night... http://www.builditsolar.com/Experimental/dCube/Barra/BaraBox.htm

With no windows (use flat screen TVs and outdoor cameras), the house would 
need about (65-6.6)85 = 5K Btu/h or 119K Btu/day (collect 20K Btu/h for 6 
hours) or 596K Btu for 5 cloudy days in a row. At (say) 160 F, a 1 ft^2 
twinwall air heater would gain 0.8x992-6h(160-6.6)1ft^2/R2 = 460 Btu on an 
average day, so the house could have 119K/460 = 260 ft^2 of air heater 
glazing, eg an 8'x32' south wall. A 1024 ft^2 ceiling with a 3 Btu/h-F-ft^2 
slow 2-sided airfilm conductance would be about 20KBtu/h/3KBtu/h-F = 7 F 
cooler than the hot air around it when collecting heat on an average day, 
and a 5.5"x32' air heater flow path with A = 14.7 ft^2 and H = 8' would make 
the air heater air (20K/(16.6x14.7sqrt(8)))^(2/3) = 9.4 F warmer than the 
air near the ceiling, so the ceiling would be 160-9.4-7 = 144 F on an 
average day.

A 1000 cfm ceiling fan could keep the house 70 F with a 
70+5KBtu/h(1/3K+1/1K) = 77 F ceiling, and (144-77)C = 596K makes C = 4.3K 
Btu/F for 5 cloudy days in a row, ie 4.2 psf, eg 0.8 inches of water, or 
deeper water in trays that cover less ceiling surface.

Have fun :-)

Nick