>The cause of most comb collapses is probably due

> to an inability of the colony to cool the nest due to inadequate
> ventilation, water source, or radiated heat, a design change
> to the TBH would correct this.
>

The cause for such a comb collapse can actually be narrowed down.  It would
be due to the lower portion of the top bar reaching the temperature at
which the beeswax softens to the extent that it can no longer support the
weight of the comb below.  The more honey in that comb, the more
gravitational pull on the critical wood to wax juncture.


In most natural cavities, there is no direct solar irradiation to the upper
surface to which the combs are attached, so excessive heating of this
critical juncture would not be expected.  It is only in man made hives that
this would be expected to be an issue.

In a Langstroth hive with a dark-colored 3/4" wooden cover, I've measured
temperatures easily exceeding 160F on the top of the cover.  At such a
temperature, wax melts into liquid.  On the underside of that cover in an
empty (no bees) hive, the temp can reach 145F, and the temperature of the
top bars roughly 1/8" below can reach 122F.

But if there is a colony present in the hive, the bees manage to keep the
temperature of the underside of the cover to about 110F, and that of the
top bars to not much above 100F.  At that temp, the combs remain attached.

How do they do it?  If you look carefully when you remove the cover, you
can see how the bees place droplets of water over the top bars in order to
use evaporative cooling to keep the tops of the top bars (3/4" above the
wood to wax juncture) cool.  They apparently fan air across that 1/8" space
(through which they can barely squeeze their bodies).  I find this ability
to cool the top bars striking.

In a TBH, the bees do not have access to the tops of the top bars, and
unable to use such evaporative cooling there.  So as Joe suggests, the
design of the structure above those top bars is critical to keep them from
overheating.
-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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