Cob: New to this list and the idea of cob

[Darel Henman]

Dtebb,

If you don't have a lot of sunshine up there cob may not be a good idea,
unless you insulate it on the outside.

dtebb wrote:
> 
> I live in Vancouver, British Columbia. The climate here may be considered
> moderate, not as cold as Minnesota. I have been talking with an energy
> engineer here who has "significant concerns" about cob as an insulator.
> This engineer was unwilling to endorse cob unless it was an un-heated
> building or used for interior walls. The r-values are just way too low and
> he is not convinced that in as cold a climate as we have here, that the
> thermal mass would work so well.

You'd need to get your solar insolation figures for the 12 months of the
year on a vertical surface (per ft^2 or meter^2) from some agency.  In
America its freely available.  Can you orient the structure to face
solar south?



> We hardly get sun here in the winter, so
> forget solar gain.
You might have him look into PAHS, (Passive Annual Heating System), I
think it is, where you also use the mass of the land around you. 

At what depth does you soil's temperature remain constant all year round
up there?  At what depth is it?

 He talked at length about technical issues that i barely
> understood. He is also very intrigued by cob as low in embodied energy in
> terms of no manufacturing of the material, the abundance of the material,
> low cost and ability of almost anyone to learn this method. He did suggest
> that a type of foam insulating layer would be something worth researching
> or doing as they do with ramed earth.He would even support from a technical
> side the research. How this may affect breathability and thermal mass is
> not known but perhaps worth trying.
> 
> Now, there are a number of cob structures here in B.C. now and those living
> in them report that they are comfortable. It would be very valuable
> information to know how much energy they are using per sq. ft. to heat. It
> is still possible that with good double or triple glazed windows, a well
> insulated ceiling and other energy design features together with a good
> thermal mass design, that minimizes loss in r-value. I came across some
> data in a building book I have that states that infiltration (flow of air
> in and out of the home through cracks) acounts for 55% of the heating load.
> Whether accurate or not, it is something very important to consider.
> 
> So the question I have is how can we determine when and how the thermal
> mass cancels out the loss in r-value? Where is the balance between the two?
> How cold is too cold? How can we design for maximum thermal mass capability?

Ian, you need to calculate your thermal mass's storage value.  For this
you'd need the "specific heat" factor for cob, which you'll probably
have to build up from compact soil or adobe type specifi heat factors
available.  In America it's units are   btu / pouond per deg_F    It is
the number of heating units that the material will store before rising
it's temperature one degree.  Specific heat values are also available in
metric. 

Try something along this line.

Specific heat for your cob in:                   (btu / pound per deg F)

Then get the denisty of cob, again here I use:        (pounds/ft^3)    

Then calculate the number of cubic feet of cob you have (ft^3)

then   cubic_feet * density * specific_heat_facter  =   btus per deg_f
temperature differential.

So the wall will give off this many btus and loss just one degree of
sensible heat.

The btus per square foot of solar insolation might be useful to see how
charged up the walls can get.

Along with so many btus / hour per person.  Include your refridgerat's
heat output, its = wattage.
And so on....

This can be reversed and though of as a heat sink to, if you have hot
summers.  But, I don't think that you do up there.

Darel