[Greenbuilding] Passivhaus propaganda

Tue Dec 3 11:31:18 CST 2013

Passivhaus standard with little cost penalty if carefully designed.
par ex. Oakmeadow
Primary school, Wolverhampton in England built for the same budget
as a basic thermal regulation UK standard school.

Note Passivhaus is just an energy standard, any style will work.

http://blog.emap.com/footprint/2011/11/02/first-look-two-passivhaus-schools-by-architype/

Good video technical presentation
https://www.youtube.com/watch?v=MffKNX5qlLw&playnext=1&list=PLAD94D448BBA00BB9&feature=results_main

regards

John Daglish
Paris, France
www.batirsain.org

2013/12/3 nick pine <nick at early.com>:
> "Shrink That Footprint" (a Passivhaus Astroturf lobby?) at
> http://cleantechnica.com/2013/11/26/value-well-insulated-house/#BvfyIGJDp0mUmBxC.99
> says:
>
>> The leaky house has solid walls, poor loft insulation, an uninsulated
>> floor, single glazed windows, and lots of draughts. Because of this, it
>> needs 300 kilowatt-hours of heating for each square meter of space per year
>> (kWh/m2a) just to stay warm.
>
>
> How large a house? How warm? In what climate? Maybe the UK, with lots of
> draughts. It is unwise to believe everything one reads on the internet.
>
>> The modern house has insulation in the wall cavity and loft, an insulated
>> floor, double glazing, and some draught excluders. Because of its better
>> insulation, it needs just half the heating of the leaky house, 150 kWh/m2a,
>> to maintain a similar internal temperature.
>
>
> How much insulation in the wall cavity? Similar to what internal
> temperature?
>
>> The passive house has superb insulation in all materials, triple-glazed
>> windows that face the equator to maximize solar gains, and is so air tight
>> that it uses a ventilation system to keep the air fresh. It needs just 15
>> kWh/m2a of heating.
>
>
> How superb? :-)
>
>> What does this mean in simple terms? The leaky home's heating bill might
>> be $1,500 a year, $750 for the modern, and $100 for the passive house.
>
>
> Might? What's the cost per kWh? Why not  less  than 15 kWh/m^2 per year?
>
> Would a 2400 ft^2 (223 m^2) Passivhaus near Philadelphia require 223x15 =
> 3346 kWh/year or $100/($0.168/kWh) = 595 kWh/year of $0.168/kWh PECO
> electricity?
>
> Germany has no sun. Why do we have to build houses like they do? In my
> opinion, this anonymous research group spent too much money insulating and
> making this mythical Passivhaus airtight, and not enough on solar air
> heaters.
>
> Where I live near Phila (4954 HDD with 65 F base), an average-sized
> 40'x60'x8' tall pre-McMansion with 4000 ft^2 of wall and roof surface with
> no windows and no air leaks and no heat loss down through the floor could be
> heated to 65 F with 595 kWh/year (about 2.03 million Btu/year, like 200
> gallons of oil) with a 4954x24x4000/2.03M = R234 wall and roof R-value, eg
> 47 inches of R5 per inch Styrofoam :-)
>
> A few inexpensive PVs and a minisplit heat pump with a COP of 5 would allow
> a zero-energy house with R47 walls and roof, but Passiv purists (eg Hudson
> at http://hudsonpassiveproject.com/about.html ) refuse to use such "external
> technologies."
>
> Let's assume that all of the 2.03 million Btu/year backup fuel helps heat a
> direct gain house with no night or cloudy-day window insulation in December
> and January with 2.03M/62 = 32.7K Btu/day, and the house solar heats itself
> with no fuel during the rest of the year. And let's cram lots of room
> temperature thermal mass into the house: a 20K Btu/F 4" slab +
> 3000x8"/12"x25 = 50K Btu/F 8" solid concrete walls + 10K Btu/F of
> furnishings, totaling 80K Btu/F. With this huge thermal mass, how much
> insulation do we need to heat the house for $100/year?
>
> An average January day in Phila is 30 F. A house with a G Btu/h-F
> conductance would have an RC = C/G hour time constant. C = 80K Btu/F and G =
> 200 Btu/h-F makes RC = 400 hours. The house would cool from 70 to 60 F after
> Dc = -RCln((60-30)/(70-30))/24h = 0.012RC cloudy days, eg Dc = 0.012x400 =
> 4.8 days, using the numbers above. With a coin-flip cloudy day model, this
> makes the average January solar heating fraction f = 1-2^-Dc, eg 0.964
> above. On a cloudy day, with no stored heat, the house needs B = 24h(65-30)G
> = 840G Btu/day of fuel, eg 840x200 = 168K Btu, using the numbers above. So
> the house above needs Y = 62(1-f)168K = 375K vs 2.03M Btu/year of fuel.
> Oops. This Passivhaus is way too good. We spent way too much money on
> thermal mass and insulation and airtightness.
>
> Let's try G = 350. Then Dc = 0.012RC = 959/G = 2.74 days and Y = 62(1-f)840G
> = 52KGx2^(-959/G) = 3.32M vs 2.03M Btu/year. Oops. This Haus is too bad.
>
> Y = 2.03M = 52KGx2^(-959/G) makes G = -959ln(2)/ln(39/G) = -665/ln((39/G).
> Plugging in G = 300 on the right makes G = 326 on the left. Repeating makes
> G = 313, 319, 316, 318, and 317. This Haus is just right.
>
> It needs 24h(70-30)317 = 304.3K Btu to stay 70 F on an average January day,
> when 1000 Btu/ft^2 of sun falls on a south wall in Phila... 304.3K/500 = 609
> ft^2 of R4 argon triple-glazed direct gain south windows with 50% solar
> transmission (what do they cost?)
> http://www.greenbuildingadvisor.com/blogs/dept/musings/choosing-triple-glazed-windows
> and no night insulation could provide that, altho that's 27% larger then the
> south wall area :-)
>
> The windows would have a 609/4 = 152 Btu/h-F conductance, leaving 317-152 =
> 165 for the rest of the house, or 165-2400/40 = 105 for the walls, given an
> R40 ceiling. So the walls need a (1600-609)/105 = 9.4 R-value, which seems
> oddly reasonable for a Passivhaus, until we recall the huge thermal mass and
> the assumptions that it is absolutely airtight and there is no heat loss
> through the floor.
>
> Removing the windows and their conductance would make G = 165 Btu/h-F, so
> the house would need 24h(70-30)165 = 158.4K Btu to stay 70 F on an average
> January day. A 1 ft^2 80 F air heater with R2 glazing with 80% solar
> transmission would gain about 0.8x1000-6h(80-30)1ft^2/R2 = 650 Btu/day, so
> we could heat this Haus with 158.4K/650 = 244 ft^2 of air heaters over the
> 480 ft^2 south wall.
>
> With an R40 ceiling and R30 wall insulation, G = 2400/40+1600/30 = 113
> Btu/h-F and f = 0.9998 and Y = 1213 Btu/year (way too good :-) This house
> could have 24(70-30)113/650 = 167 ft^2 of air heaters.
>
> A less expensive house could have less concrete. G = 113 makes Y =
> 5.89Mx2^-Dc = 2.03M Btu, which makes 2^-DC = 0.345 and Dc = -ln(0.345)/ln(2)
> = 1.54 days, ie 36.9 hours, with RC = -36.9/ln(0.75) = 128 hours = C/113, so
> C = 14.5K Btu/F. IIRC, an average house contains about 7K Btu/F of building
> materials and furnishings. We could add a slab, or a concrete wall, or
> (14.5K-7K)/5 = 1500 concrete blocks and boards for a bookcase, or 2 shallow
> pebble beds above and below a few 55 gallon water drums, which could help
> heat water for showers.
>
> Nick
>
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