Screened bottoms?

[Bigfoot]

Alright all you top bar beekeepers out there I need some input. I have been reading different forums and conversing on this page about screened bottom boards in a TBH. I myself have a TBH with a screened bottom board in it, I noticed about a week ago when I pulled out the bottom board a fairly large amount of pollen on the board, so I pretty much swore I wouldn't use screened bottom boards again... until this afternoon, I went out to check my hive and I noticed a lot of bees swarming around the entrance, when I viewed the bees through the observation window they were going crazy in the hive, when I removed the bottom board almost immediately the hive calmed down even the bees swarming around the entrance calmed down. I think I need to rethink the screened bottom unless I can find another way to vent the hive. any suggestions?

[Michael Bush]

The natural way a hive ventilates is like breathing.  They push a bunch of air into the hive raising the pressure there and then they let it escape.  To do this they need one entrance.  With a vertical hive having one at the top and the bottom creates a chimney.  This is good to a point as it may save them the work of the other method, but if there is too much ventilation it can make it difficult for them to cool the hive in the summer as well as heating it in the winter.  The indications you have, though, are they appeared to need more ventilation than they were getting.  Perhaps.  You could, of course proved a vent at the bottom at one end and the top a the other and get a little of the chimney effect.

[FRAMEshift]

They push a bunch of air into the hive raising the pressure there and then they let it escape.  To do this they need one entrance.

I think it's very cool that they can adjust the period of their ventilation to match the cavity they are in.  They pulse and synchronize their fanning to match the pressure resonance when they are forced to do so by having only one entrance.... since with one entrance, continuous fanning won't work to exchange air.  But I would still think that continuous fanning would be more efficient, as long as it's possible to do it.   On the other hand, if you live in a hollow tree with thick wood all around, you probably don't need as much ventilation.

I use a screened bottom in a long hive, but I do have it blocked on three sides so that wind (hot or cold) doesn't overwhelm the bees control over ventilation.

[caticind]

FRAMEshift and I differ on this one.  I keep the exact same design of long hive, but I leave the screened bottom board completely open to the ground, with just an edge so I can put in a mite drop board if I need to.  We will see over the next couple of years if there is a difference in thriving.  I definitely see less bearding and fanning behavior than he does.  Granted, we live in a very mild climate.  I couldn't do it if we had wind like the midwest or temps staying below freezing.

[Bigfoot]

Thanks for the input folks I really do appreciate it.

[Danger Brown]

Thanks from me too! I didn't know about the pulsed ventilation from a single entrance. Fascinating!