[Greenbuilding] Near-infinite Scandinavian breathingwall R-values

Fri Feb 13 20:40:41 CST 2009

I spoke to Prof Timusk today. He was in his country home that was built over 20 years ago as a dynamic wall house. He has done more real research on this than anyone, including the Scandinavians and Scots. 
The house is no longer running as a dynamic wall because of the operational difficulties. He still thinks the idea has real merit but it needs work to create a uniform flow around the house. Each side needs three or four zones to accommodate variable pressure fields. 
Short answer: good idea on theory but several unsolved practical obstacles. Not impossible but presently impractical. 
Alas, more research needed. 

John Straube
519 741 7920
Sent via BlackBerry

-----Original Message-----
From: Lawrence Lile <LLile at projsolco.com>

Date: Fri, 13 Feb 2009 11:57:43 
To: Nick Pine<nick at early.com>; greenbuilding at listserv.repp.org<greenbuilding at listserv.repp.org>
Subject: Re: [Greenbuilding] [BULK] Re: Near-infinite Scandinavian breathing
 wall R-values

Ah- this puts the idea into better focus.

> -----Original Message-----
> From: Nick Pine [mailto:nick at early.com]
> Sent: Friday, February 13, 2009 6:01 AM
> To: greenbuilding at listserv.repp.org
> Cc: Lawrence Lile
> Subject: Re: [BULK] Re: [Greenbuilding] Near-infinite Scandinavian breathing wall
> R-values
>
> Lawrence Lile writes:
>
> >OK.  Heat doesn't leave the space by convection.  If you don't count
> >the heat you added to the furnace making the breathing air, it looks
> >great!  But you did heat that air, and that energy does count, and that
> >heat DOES leave the breathing air channel by convection and conduction.
> >And  the inside of the wall, just behind the moving air breathing
> >thing, is still 72F, and the outside is still (say) zero.  Heat still
> >moves by conduction, just about the same rate as it did in the
> >conventional wall, driven by the 300 year old formula.
>
> Picture cold outdoor air entering the outside of a wall, as in Fig.
> 1.1(b) in:
>
> http://www.cibse.org/pdfs/8cimbabi.pdf
>
> The paper says "As cool ventilation air is drawn into a warm building
> through the breathing wall, air flows inwards in the opposite direction
> to the heat being conducted outwards as shown in the figure below. The
> contra-flow of mass versus heat fluxes results in the cool air picking
> up heat that would normally be lost through conduction, effectively
> yielding a reduction in the dynamic U-value of the wall and higher
> overall insulation efficiency..."
>
> (Equation (1) on page 4 for dynamic U-value is wrong in the paper above,
> and corrected in
> www.environmental-building.com/documents/Ecocity_paper_2008_final.pdf)
>
> So we still have to supply heat to the air in the room, but the wall
> R-value increases, so the room needs less total heat than a room with
> non-breathing walls and the same amount of ventilation air entering
> directly from the outdoors.
>
> Picture an 8' USR13 cube with 15 cfm of ventilation air. With no
> breathing walls, its conductance (ignoring the floor) is 5x8'x8'/R13 =
> 24.6 Btu/h-F. Keeping it 72 F inside on a 32 F day with no air-air heat
> exchanger requires about (72-32)(24.6+15) = 1584 Btu/h. If 15 cfm flows
> in throught the walls and ceiling, V = 15cfm/(5x8'x8') = 0.047 fpm, ie
> 0.00024 m/s, with a static metric R-value 13/5.68 = 2.29 m^2K/W, which
> makes Rd = (e^(1200VR)-1)/(1200V) =  3.23 m^2K/W, ie USR18.35, so the
> cube's thermal conductance is only 5x8'x8'/R18.35 = 17.4 Btu/h-F, and it
> only needs about (72-32)(17.4+15) = 1297 vs 1584 Btu/h, ie 18% less
> total heat.
>
> But it seems to me we can save more by dividing the cube in 2 parts with
> a periodically-reversing fan in the partition wall that turns the
> breathing walls into bidirectional heat exchangers. This would be like
> breathing through a scarf on a cold day. Breathe out, and the scarf
> material captures some of the heat and moisture. Breathe in, and it
> gives it back. How can we model this? Residential low-density fiberglass
> insulation has about 0.5 lb/ft^3. The ASHRAE HOF lists the specific heat
> of "glass wool" as about 0.16 Btu/lb-F, so 1 ft^2 of 3.5" unfaced
> fiberglass might have 0.5x0.16x3.5/12 = 0.023 Btu/F, with lots of
> surface. Warming it from 32 to 72 takes about 1 Btu. If 0.047 fpm flows
> into a wall and 0.047cfm(72-32) = 2 Btu/h, so this seems like the right
> ball park.
>
> Dan Antonioli writes:
>
> >One thing that would be helpful to the list is to remember that this
> >isn't an engineering forum. It's a green building discussion list.
>
> Same thing :-)
>
> >If you want to work with engineering formulas and math, please explain.
> >Just like your teachers asked you to do.
>
> My old Latvian friend Lisa used to say "Dahlink, never apologize, never
> explain." John Wayne said it in 1949 (in "She Wore a Yellow Ribbon.")
> Oxford teacher Benjamin Jowett said it on October 7, 1893.
>
> Don Eyermann writes:
>
> >Math
>
> This reminds me of another quote:
>
>    When we play tennis or walk downstairs we are actually solving whole
>    pages of differential equations, quickly, easily and without thinking
>    about it, using the analogue computer which we keep in our minds.
>    What we find difficult about mathematics is the formal, symbolic
>    presentation of the subject by pedagogues with a taste for dogma,
>    sadism and incomprehensible squiggles.
>
>           from Structures: Why Things Don't Fall Down, by J. E. Gordon
>
> Nick

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