Hello everyone!..All this brainstorming and washing is being invaluable to me!
I'm writing from the Kullu Valley in the indian Himalaya where at around 2000mt I'm in the company of a colony of Apis Cerana Cerana housed in a Warre circular hive,and thanks to most of your posts on hive insulation in the last couple of years I'm starting to appreciate the paramount importance of the thermoregulation of the hive to the thriving of the bees in the temperate climates of the world,and I look agape at the complexity,the mystery,the spiritual beauty, and the wisdom that the bee superorganism adaptations and behaviours entail and which, with your help, I, quite flabbergasted!
start now to comprehend.
I would like to comment on Bluebee fotos of the plastic sheet applied to the top of his hives for the observation of condensation;
There is a lot to talk about, but let's start about this:
Professor Jurgen Tautz in the amazing The Buzz About Bees pag.217 states that a strong colony of Apis Mellifera, presumably Ligustica and hived in a conventional Langstroth or Dadant, can produce 300kg of honey during a summer, although only a small proportion of it is present at any time in the hive. The 4/5 of it, 240kg, are literally "burned" to regulate the temperature of the brood both in winter and summer and to warm the winter cluster (2 million K joules for brood rearing and another 2million Kj for the winter cluster; the combustion of 1kg of honey produces 12000kj). This means that building a hive that is only 3 to 6% more energy efficient could save the 7.5kg of honey that according to the same author the bees consume to build the 1200gr of wax combs of a typical nest..making a hive 10% more efficient would not also increase the honey yield for the beekeeper, but would also profitably allow, if we are a bit intelligent, the bees to build their combs, the exoskeleton of the superoganism -fondamental organ of its immune system- and to be fed only honey.
, this method for observing the hive activities influences what you see,and your fotos are not indicating how different hives prevent or facilitate the formation of condensation! By opening the hive you
force the condensation of the warm and humid air at the top of the hive,as the thin plastic sheet readily dissipate the heat to the cold air above. If the top is properly insulated the warm air underneath will retain its moisture and will be eventually transported outside thanks to the air circulation established by the temperature gradient between the warm cluster and the air outside; within an adequately insulated hive this "exhaled" air will shed some of its moisture only when it meet the cold drought of air entering from the hole.
What your picture are showing is that in a hive with a bottom entrance, the air above the cluster is warm and humid and the bees are scattered on the combs, maybe just relaxing, conserving energy (cfr."Outdoor Wintering of Bees" by E.F. Phillips, link by dereckm )while in a hive with a top entrance the air at the top,whose residence time is short by design, is cold and dry -that's why when it come in contact with the cold plastic sheet there is no condensation- and the bees ,as a result,cluster, insulating themselves and consuming thus abundant energy. Since the brood seem to require a relative humid -not wet!-environment, with a relative humidity,as far as I have gathered, between 40 and 70%- and since it seems thermodynamically efficient to create a "heat bubble" around the brood area and the cluster, your fotos illustrated to me the convenience of a bottom entrance.
In this amazing MSc thesis, "A CFD STUDY INVESTIGATING THE INFLUENCE OF BOTTOM BOARD GEOMETRY" by Cody Grant Thomson, the link of which was posted somewhere in the insulation threads, is explained how honeybees influence hive ventilation by adjusting the packing density of the winter cluster -incredibly important!- and how the addition of an empty space under the hive entrance creates a vortex of air that influences in a very positive way the rate of ventilation inside the hive,the removal of humidity and CO2 and all this especially when the temperature difference between the hive interior and the outside is small, i.e. in warm, humid days when it is most needed. To most Warrè beeks this extra space is known as Sump and it mimics the space found under the entrance of many of the natural bee nests investigated by Seeley and Morse (1976).
Thanks again to all of you for your invaluable help!