Alan Riach said:

> So the question is - with screened bottoms should the top be
> open or closed or does it matter.

I'd strongly suggest "open", screened bottom board or not, for all
locations except the most frigid.  Its not the heat, its the humidity!
Moisture kills bees, not cold.

Some may dismiss this as "a lot of hot air".  I could not agree
more.  "Hot air" is the only ventilation mechanism one needs to
keep one's bees dry in winter.  Lucky for us, the bees make the
hot air at no extra charge.

I want LOTS of airflow.  I cut "extra" holes near the "rear" of my
inner covers, and staple 8-mesh over them to insure better airflow.
(See below for details).  I also notch not one, but TWO upper
entrances into the "thick side" of my inner covers at the front.
(George Imirie may have been the first to do this, I'm not sure.)

I will try to explain my reasoning below.  If doubtful, one could borrow
a thermal-imaging unit of the sort used to find insulation problems in
homes, and shoot pictures of one's hives this winter to "prove" all this
to oneself.

> The practice of putting on absorbent top covers to soak up moist air
> seems to work and is basically sound since water vapour is lighter than
> air and therefore will rise - all other things being equal.

I'm not sure I agree at all with that approach as applied to the not
terribly cold winters of Scotland (or Virginia, where I keep bees).  While an
absorbent material of some sort may seem a good idea at first, I don't like
it one bit in light of a long and expensive education in physics:

a)  Your "water-vapor" is lighter than "other" air simply because it is
     warmer.  Hot air rises.  Moisture itself has no effect on air's ability
     to "rise".  Warmer air is CAN carry more moisture than colder air.
     To test this, go outside on a day when you can "see your breath".
     Spray a fine mist of water from an atomizer.  Your breath has less
     water content than the spray from the atomizer, but your breath
     makes a "cloud", while the spray from the atomizer does not.

     I'll say it again.  Hot air rises.  Hot air also just HAPPENS to be
     able to carry a larger "moisture payload" than cold air.

b)  Given (a), why trap moisture in the hive?  I submit that, at best,
     it will raise the overall moisture level above the level possible
     when ventilating the hive (since a well-ventilated hive would
     roughly equal the exterior temperature and humidity, and winters
     tend to be drier and colder overall than other seasons).
     I want that moist air out, not "absorbed".

c)  What happens to this absorbed moisture when there is a
     sudden drop in temperature?  I submit that the moisture
     will condense out of the material and drip, or freeze, later
     to melt, and drip down.  It is clear that a drop in temperature
     would cause water to condense, and re-absorption of melted ice
     would be limited in a nearly freezing mass of absorbent
     material.  (Try it in your own freezer versus not in freezer with
      wet and dry cloths)

d)  How MUCH absorbent material might one need?  If one does not
     have enough, it would become saturated, which would be even
     more of a mess than (b) or (c).  How much moisture do 50,000
     bees generate?  I dunno.

I want to get the moisture OUT of the hive as quickly as it is produced.
I certainly do not want to keep moisture IN the hive, not even for a short
period.

> What about reports then of practices of putting on non
> absorbent/insulated top covers. Well at least they will stop the rising
> (and probably slightly warm) water vapour from condensing back into
> water when it contacts the cold top cover.

If there is sufficient ventilation, the warm(er), moist(er) air will
CONTINUE to rise, straight out the ventilation holes.  I do not
want it to collect against the inner cover at all!   Now, I agree that
the skimpy little hole in the middle of "standard" inner covers is
not big enough to insure that this happens, creating the problem of
the "soaked" el-cheapo (masonite) inner cover, but this is easy to fix.
Make more holes, or make the hole bigger!  While you are at it,
scrap the masonite, and replace it with plywood.

I think that the "porter bee escape" sized hole in inner covers is
about as relevant to modern beekeeping as the skep.  It is also
clearly the limiting factor in how much ventilation your bees have.
It not even as large as your hive entrance, let alone the area of a
screened bottom board.

As far as the utility of insulation, when people actually measured with
thermocouples, they found that the temperature inside the hive, but away
from the cluster was roughly the same as the outside air, contradicting the
"commonly held misconception" that the bees heat the entire interior of the hive.
This makes much more sense to me than the traditional view, and fits with
the fact that bees cluster within the hive.  (Think about it - if they heated the
whole hive, clustering would gain them nothing!)

The insulation seems to be a non-issue for all but the arctic locations
where wrapping of hives is required.  I want lots of airflow above all else.

> If a screened bottom board is used, the natural drafts caused by passing
> wind outside the hive, probably cause enough air currents inside the hive
> to overcome the gentle upward rise of the water vapour coming off the cluster,

If you have a hive without good top ventilation, the "natural drafts" across the
bottom screen are unlikely to get rid of the warmer, moist air.  Hot air rises, and
the warm moist air rising off the cluster will go to (and get stuck at) the top of
the hive.  The air near the bottom of the hive may exchange with the external
air, but a good model can be constructed with an upturned drinking glass and
a lit smoker.  Puff some smoke into the glass.  Blow as hard as you like across
the bottom of the upturned glass, and see what happens to the smoke at the top
of the glass.  Nothing much.  Cover the bottom of the glass with 8-mesh, and
you will get even less "tubulence effect".

> and the water vapour probably gets flushed out through the screened
> bottom by these relatively stronger currents.

Given the experiment above, the air would have to sink below the
cluster to exchange through the screen bottom alone.  If the water
vapor-laden air was cold enough to sink below the cluster, the water
would no longer be as moist.  Some (much?) water would have already
condensed out, and dripped onto the bees, which would be very bad.
The dewpoint (the measurement of the actual amount of moisture in air)
goes up and down with temperature, and only colder air "sinks".

   Example:  Contrast 30-degree air with a relative humidity of 100%
                   with 72-degree air, also at 100% relative humidity.
                   In both cases, the relative humidity is 100%, but the
                   colder air's dewpoint is 30 degrees and the warm air's
                   dewpoint is 72 degrees.  The higher the dewpoint
                   temperature, the more moisture is in the same volume of air.
                   (This is why cold winter air dries out the inside of your nose.)
                   Therefore, when temperature drops, moist air must give off
                   some of its moisture, creating "rain" just as clouds do.

> I guess extreme cold conditions (well below freezing) maybe also favour
> some top insulation.

I have zero experience with sub-zero beekeeping.  Anyone want to address
the case at "Ice Station Zebra"?  Clearly it is different, since entire seminars
are dedicated to the arcane art of "wrapping hives for winter".


HACKING AWAY AT INNER COVERS  (YES, YOU CAN BE A HACKER!)

First, let me explain that my hives are "sideways", with the longer side facing
South, and an entrance that runs the entire length of the long side.  I like it
much better, as one can stand behind the hive when working.  Except for
the bottom boards, my woodenware is identical to what one can buy, and
most of my supers are second-hand "store-bought" woodenware.

I cut two triangular openings with a saber saw, roughly 3 inches on a side,
at the two "rear" corners of the inner cover.  They simply cannot be too
big, but they can be too small, so be generous.

What's the "rear"?  The end that does not have the upper entrances
notched into it!

The triangles are roughly 1/2 inch from the edges, equidistant from the corners.
They are covered with 8-mesh, which is staple-gunned to the plywood with the
shallow 1/8-inch deep staples.

My only use for the "porter escape" hole (that oblong hole in the center) is
for my bucket-type feeders , so I block it in winter with a "plug" of 1/2-inch
plywood with a "flange" that is wider than the hole.  It just "sits in the hole",
and can be removed for summer or feeding at whim.

Why make vents at the rear and close the vent in the center?  Think about the
sun, which will shine on the FRONT of your hive, and warm the wood.  The bees
are sure to cluster near the front surface of the hive, so the vents want to be at
the REAR, behind, and not above the cluster.  The airflow will insure that the moist
air moves above and behind the cluster.  (Open up a hive this March, and look
at the cluster - betcha you will see a daytime cluster towards the front, just like
I did every time I looked.)

Now, here's where it gets tricky - you want to shim up the outer cover at the
REAR, not the front.  Keep the exhaust to the rear!

        jim

        A member of the "Society for Not Only The Obedience,
            But the Enjoyment of the Laws of Physics")