Friends,
allow me an ilustrative remark. I keep bumblebees and if qeen should
be activated in autumn or winter one of the ways to do this is the CO2
narcosis. In such a case queens usually are put in an Erlenmayer's glass
and CO2 is added untill they are motionless. If the glass isn't closed
tightly, e.g. with some buch of fine paper only, gueens wake up
surprisingly soon, evidently as a result of diffusion of the CO2 through
pores in the plug. This responds to the Avogadro's law that a gas in the
mixture of gases expands like if there were no other gases present. I would
say that in wintering cluster of bees currently not the production of CO2
is a problem, but the condensation of water.
 
On the other hand, as I could see during spells of wery could weather what
in our county are the subzero temperatures 20 - 30 C, the lack of oxygen
may be more serious problem. If a colony has limited bottom entrance only,
and the autside temperature is falling, bees tend to remain in contact
with the soure of air - they must generate more heat, what causes an
increased respiration since more sugars must be burned. Under such
circumstances the cluster may lose its contact with stores. If the cold
spell lasts some weeks, such a colony may die even with plentifull stores
some cm above the cluster. Larger colonies have the known advantage of
continuous contraction of  cluster whereas the smaller ones are forced to
generate heat sooner.  The result of this fact is that the smaller the
colony the higher the relative need in oxygen, and the comparatively larger
the winter entrance (under severe cold outsiede!).
According to my experience colonies need warm upper cover. I would guess
for northern conditions as much as 5 - (8?) cm of styrofoam or similar
material would be needed. This is substantial help for colonies during
wintering (and in any time in the year). Small colonies need also warm
walls. During the winter two entrances are good together with the vertical
orientation of the hive space. Stores should be mostly above the upper
entrance. Bees must have enough time to addopt themselves to this
arrangment (from august).
Best regards,
Vladimir Ptacek
[log in to unmask]                    phone: .42/5/41129 562
Fac. Sci., Dpt. Anim. Physiol.        fax:   .42/5/41211 214
Masaryk University.
611 37 Brno, Czech Republ.