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Author Topic: Top vs Bottom ?  (Read 7752 times)
T Beek
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« Reply #80 on: January 18, 2013, 08:46:17 AM »

I have always wondered why some BK wrap there hives in black tar paper??

I can understand the wind shielding aspect, but heating the hive on sunny winter days will cause the ball of bees to break prematurely and result in a higher consumption of winter stores.

Studies that I read show that a steady constant hive temperature makes things easier for the bees to maintain a warm bee ball in wintertime.
The bees need a quiet stable environment.

mvh edward  tongue



"Different strokes for different folks." 

Most BEEKs will try most anything they "think" might benefit their bees or themselves.  We need only consider some of the crazy things BEEKs have done in the past (and present) to bees, intentionally or not, rational or not.

As I (hate) to say whenever asked "what's killing the bees?"  'We' are killing the bees (you can replace bees with your own favorite species).

"To be a friend of the Earth you must be an enemy of the people"  TC Boyle
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"Trust those who seek the truth, doubt those who say they've found it."
piarelal
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« Reply #81 on: February 15, 2013, 04:37:25 AM »

Hello everyone!..All this brainstorming and washing is being invaluable to me! shocked grin 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! afro 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.

BlueBee  Smiley, 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!




















« Last Edit: February 15, 2013, 05:55:51 AM by piarelal » Logged
T Beek
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« Reply #82 on: February 15, 2013, 08:51:08 AM »

piarelal;

Wow, what an excellent analysis.  We'd Better be on our toes.  You out there BlueBee?  

Welcome to the BeeMaster Forum, hope we hear from you often.

I especially liked your description of the value in creating 'empty space' under hives, as its something I've done all along.
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"Trust those who seek the truth, doubt those who say they've found it."
BlueBee
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« Reply #83 on: February 15, 2013, 10:45:08 AM »

Yes, I will have to keep on my toes.  Some good thoughts from piarelal.

I’m sure bee keepers will debate the pros and cons of top vs bottom entrances and vents for eons.  In an insulated full sized hive, I’ve been successful with top entrance hives and bottom entrance hives.  From a thermal perspective, I completely agree that a bottom entrance (heat bubble) design is going to be more thermally efficient.  The main reason I went with a top (actually a mid) entrance with my full sized hives is because of these:



I don’t know if you have skunks in India or not, but they are a real menace to bees where I live.  Where I live you need to keep the entrances at least a half meter off the ground or the skunks will claw up my polystyrene hives and kill the bees.  So I either have to put my hives on stands or go with a mid entrance.  I chose the mid entrance option since its cheaper (no stands) and easier on my back (lower to ground) to lift supers. 

My full sized hives do have an empty space below them where I can monitor for mites.  The bottom of the bee’s home is screened, and that sits on another box that is about 12cm tall.  My nucs do not have such empty spaces though.
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piarelal
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« Reply #84 on: February 18, 2013, 04:04:03 AM »

Hei Man, your pictures are great! They perfectly visualize the flow of winter air at the top of the hive. Warm humid and CO2 laden air must rise on top of the bees, that's why when you open the hive there is no condensation in the central area; As this air move away from the centre it must become cooler and denser and therefore, in a well insulated hive, will tend to descend at the side without condensing, while opening the hive cool further this already relatively cool air under its dew point and forces its condensation.
Well  angel grin Now I'm tripping! The more I look into this and the more sci-Fi  become the world of the bees..

From Wikipedia page on Natural convection:
"As the temperature difference between the top and bottom of the fluid becomes higher, significant differences in fluid parameters other than density may develop in the fluid due to temperature. An example of such a parameter is viscosity, which may begin to significantly vary horizontally across layers of fluid. This breaks the symmetry of the system, and generally changes the pattern of up- and down-moving fluid from stripes to hexagons,as seen at right. Such hexagons are one example of a convection cell."

A great article I found on the Warrèbeekeeping forum :
"Flow currents and ventilation in Langstroth beehives due to brood
thermoregulation efforts of honeybees" by Rangarajan Sudarsan, CodyThompson, Peter G.Kevan, Hermann J. Eberl. So long..
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derekm
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« Reply #85 on: February 18, 2013, 06:50:31 AM »

Hei Man, your pictures are great! They perfectly visualize the flow of winter air at the top of the hive. Warm humid and CO2 laden air must rise on top of the bees, that's why when you open the hive there is no condensation in the central area; As this air move away from the centre it must become cooler and denser and therefore, in a well insulated hive, will tend to descend at the side without condensing, while opening the hive cool further this already relatively cool air under its dew point and forces its condensation.
Well  angel grin Now I'm tripping! The more I look into this and the more sci-Fi  become the world of the bees..

From Wikipedia page on Natural convection:
"As the temperature difference between the top and bottom of the fluid becomes higher, significant differences in fluid parameters other than density may develop in the fluid due to temperature. An example of such a parameter is viscosity, which may begin to significantly vary horizontally across layers of fluid. This breaks the symmetry of the system, and generally changes the pattern of up- and down-moving fluid from stripes to hexagons,as seen at right. Such hexagons are one example of a convection cell."

A great article I found on the Warrèbeekeeping forum :
"Flow currents and ventilation in Langstroth beehives due to brood
thermoregulation efforts of honeybees" by Rangarajan Sudarsan, CodyThompson, Peter G.Kevan, Hermann J. Eberl. So long..
be careful with this last paper as it assumes that the shell of the hive is a perfect insulator (section 3.4 boundary conditions)
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If they increased energy bill for your home by a factor of 4.5 would you consider that cruel? If so why are you doing that to your bees?
piarelal
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« Reply #86 on: February 18, 2013, 10:45:13 AM »

Hello Dereckm, thanks for the tip!
What would be different in a real hive? The only obvious thing I can think of is that the real hive,when it's cold, would dissipate some heat to the surroundings and so the thermal gradient between the brood area and the rest of the hive, would diminish..slower flow..-without taking into consideration the effects of concentration of Co2 and water vapour!;or during a hot summer day the real hive would heat up speeding up things..
I am on the right path? What are the implications?
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derekm
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« Reply #87 on: February 18, 2013, 02:11:45 PM »

You get additional internal convective flow due to the surface  heat loss creating  negative buoyancy.
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If they increased energy bill for your home by a factor of 4.5 would you consider that cruel? If so why are you doing that to your bees?
piarelal
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« Reply #88 on: February 19, 2013, 10:33:13 AM »

The surface heat loss must be inversely correlated to the R value of the insulated hive; do you know at what value of R this heat loss become appreciable enough to create negative buoyancy?

I presume that you agree that negative buoyancy in this case would depend on the fact that when the porosity of the brood area bee cover or the winter cluster decreases,i.e. the cluster contract as when the temperature drops, the dissipation of heat in this areas decreases too, which in turn decreases the flow of air from the cluster to the opening of the hive. In this conditions of slower flow, the air region right underneath the bees will start sinking because of its high concentrations of CO2 and water vapour. But when the bee cluster expands again, increasing its porosity, the heat released will rise and and with it the air flow...The hive breath!!! shocked grin

Dereckm have you read the study of Thomson Cody posted above? ..Thanks to Little John for this link... He was also a member of the team that modelled the Langstroth hive study.
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piarelal
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« Reply #89 on: February 19, 2013, 10:47:45 AM »

hey Dereckm, do you have any idea how a circular nest or hive might influence the flow? Thanks for the help!
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