The recent discussion of water in hives prompts the following notes.
                The air in the winter hive can be crudely likened to a
floating bubble, a 'warm air balloon'.  Forced ventilation, notably wind at
the entrance or mesh floor, is a major influence on the turnover of this
'bubble'.  Bodily movement of air masses can be a far greater influence on
the water regime in the hive than the effects on gas densities caused by
admixing into the air both water vapour (tending to decrease the density)
and carbon dioxide (tending to increase it).
        The temperature of the 'warm air balloon' is influenced also by
that anomalously large quantity, the latent heat of evaporation of water
(same thing, with a minus sign, as the heat given out when water
condenses).   If a hive is struggling for heat, it will keep warmer if
water vapour actually condenses from the air before the air leaves the
hive; the problem then becomes to ensure that the liquid runs away
harmlessly.
        If ventilation is inadequate, some fanning may be organised  -
anyone studied this?  We are all familiar with the little dears excercising
just outside (one side of) the entrance on a summer evg, to create an
inverted-U scavenging loop of air to evaporate water; does any such
arrangement get organised to relieve excess moisture from the hive in some
winter conditions?
        What this discussion brings into focus is the potential of mesh
floors to improve ventilation (tho' I'm sure in cold winds this could be
too much) as well as to allow varroa to fall out.  Always nice to do two or
more functions with the one component  -  and no moving parts!

R