Dave Cushman asks why upper ventilation is so important, and says that he
has over-wintered without upper ventilation without difficulty.  Jorn
Johanssen says he has successfully overwintered in Styrofoam (polystyrene)
hives in Denmark and reports beekeepers doing so in British Columbia,
Canada.  (He does not address whether upper ventilation is provided).

My initial comments on the subject were less than complete.  I will try to
do better.

If hives are constructed "tight", meaning little to no opportunities for air
circulation and exchange other than at the entrance, and the entrance is at
the bottom of the hives, internal condensation will probably occur where
bees are over wintered in cold climates.  This condensation will accumulate
until water drips onto the cluster, soaking the bees and eventually killing
them.

The bee cluster has an internal temperature of approximately 90 degrees F.
(32 C.)  The air within the cluster is, of course, of the same temperature
and picks up moisture from the honey.  As this warm air rises, it comes into
contact with the hive cover or crown board (inner cover).  Unless the top of
the hive is insulated, the hive cover or crown board will be approximately
the same temperature as the outside air.  In cold climates, there will be a
significant difference between the 90 F of the warm air inside the cluster
and the top of the hive.  This will result in quickly cooling the warm air,
which will mean that it can no longer hold as much moisture, which will
cause condensation to build on the hive cover or crown board.  If this
condensation continues to build, it will cause water to drip onto the bees
in the cluster, which do not have any means to dry themselves.  (The bees on
the outside of the cluster might be surviving at a temperature of 60 F (15
C) and the dripping moisture must be particularly dangerous for them.)

I don't know where Dave Cushman lives, but if he has not had difficulty with
condensation one or more of the following has to be true:
a. The winters do not have extreme cold.  I forget the temperature
differences required for condensation, but they are significant as the
typical 30 degree (F) difference between the inside and the outside of the
bee cluster does not result in condensation.
b. The hives are well insulated, so that there are not considerable
temperature differences between the cover(s) and the warm air generated by
the cluster.
c. There are, in fact, upper entrances that allow the warm, moist air to
escape before it condenses.  Such entrances might be as simple as corners or
covers that do not fit tight, small knot holes, etc.

To properly consider the success of the polystyrene hives in Denmark and
British Columbia, one must consider the average winter temperatures.  Jorn
says the average in Denmark is 0 degrees C, which is 32 F.  This is
considerably higher than winter temperatures in much of the US, and is much
like temperatures in Washington D.C.  I know from personal experience the
winter temperatures in British Columbia vary considerably.  Around the city
of Vancouver and on Vancouver Island it rarely snows and when it does the
snow melts the following day!  Further north is some of the most severe
weather in the world!  My guess is that where the bees are over-wintered in
nucs they have reasonably mild temperatures.

The polystyrene (Styrofoam) hives I have seen from Sweden and the nucs from
Canada are extremely well made and fit together very well.  Again, my
concern is whether they are too well made (for our climate) and will produce
considerable condensation.

Anyone have any experience with them in a climate where outside temperatures
are regularly in a range of 0F to-30F (-17C to -34C)?


Lloyd
Lloyd Spear, Owner, Ross Rounds, Inc.  The finest in comb honey production.
www.rossrounds.com