So you think the op needs to get some new boxes rather than worrying about how best to manage the ones he already has?Originally Posted by derekm
So you think the op needs to get some new boxes rather than worrying about how best to manage the ones he already has?
note: The actual calculation of lumped conductance is much more complicated because of external/internal convection, corners lack of floor etc...
its really best to experimentally measure or simulate using CFD
Last edited by derekm; 02-08-2015 at 08:38 AM.
you can reduce conductance with a drop over insulating cover of PIR, tape sealed inside and out.
So how many bees will that take?
I can tell you the physics the bees have to deal with... not how many bees is the lower limit , The physics shows you need very high levels of insulation for very small colonies not to increase thermal stress.
We have fullsize colonies in full size hives of 50mm PIR all year ... So the upper limit of insulation is not the worry. One experiment (not ours) with a very small colony used a tube of 140mm PIR with a 3 way folded frame.
500 bees can overwinter in an Apidea which has poly walls around 20mm thick.
The key factor is not the thickness of the walls, it is adjusting the number of bees to the volume of the box they live in.
500 bees would not overwinter in a national brood box even if the walls were 2 metres thick!
And that is a good way to demonstrate that thermal stress on its own means little, it is all to do with how thermal factors interact with all the others influencing the living colony. Bees can survive on comb out in the open, at least for a while. In winter, it is the interaction of insulation, the cavity size, ventilation, the proximity to food, in particular the proximity to food upwards where it is warmer, the size of the cluster, moisture availability, disease status of the bees, number of healthy young bees, state of the queen ..... and many other factors. If insulation in relation to winter survival bothers you then you need to consider the first seven of these (and probably more) which all interact in complex ways that vary through the winter.
More simply, bigger, well-provisioned colonies buffer their own environments. Smaller ones can only survive if their environment is right. Empirically, experience shows that bees overwinter better in well-designed polystyrene hives than in traditional wooden ones.
In my previous location, winter températures often went down to -20c , stayed negative over long periods,and I never needed to insulate walls to overwinter the bees. Perhaps I was wrong, but I think if we start to tinker with the hive climate we need more knowledge of all the parameters than I have.
I found that the most important factor in cold winters was the presence or lack of brood.No brood allows the bees to survive at lower températures, and they can go into a sort of coma where they certainly don't seem stressed. They also are in a fitter state for foraging at the beginning of spring.
What I don't like about wall insulation is that the bees risk to be out of sync.with the outside weather when the winter is coming to an end, and unnecessary flights can be a reason for consuming stores, not to mention the queen starting to lay too early.
Of course, different climates have different problems.
The volume of the cavity is not relavent its the the properties of the enclosure that inlfuence heat loss.
as regards thickness of wood you are correct the thickness of wood you would need to correct a colony mass reduction of a factor of 30 (15000 to 500) in a wooden national(dimensions ~ 300mm) is about 5 metres wood or 1 metre of PIR.
if you reduce to the box to 75mm square then you can use 1 metre of wood or 200mm of PIR.
The basic research on Bees is Southwick, E. E., 1982. Metabolic energy of intact honeybee colonies. Comparative Biochemistry &
Physiology 71, 71(2), pp. 277-281.
but i think its only valid down to 2000 bees.
the physics you can read up in
Incopra, DeWitt, Bergman & Lavine, 2006. Fundamentals of heat and Mass transfer. s.l.:John Wiley
and sons.
if you only reduce from 15000 to 2000 (7.5 reduction) bees then your wooden national sized box needs 200mm walls of wood or 40mm of PIR or 60mm of polystyrene.
a 75mm sized box need 55mm of wood
a 100mm sized box needs 75mm wood
if you want to have the same conditions as a poly national hive. then for a 15000 to 2000 reduction
Then all the numbers change. Then we are considering 140mm PIR or 200mm of polystyrene for a 2000 bees colony in a national box
a 75mm box 55 mm of poly
a 100mm box 75mm poly or 50mm PIR
Why dont you come to the SBA Autumn convention and we can talk in person.
Last edited by derekm; 02-08-2015 at 02:22 PM.
Ok then. I challenge you to overwinter 500 bees and a queen in a national size cavity. You can use whatever material and whatever thickness of walls which takes you fancy.
I have done it in an Apidea with 20mm poly walls. Good luck!
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