Same as Michael.
I’ve almost rid my apiary of screened bottoms and I leave the reducer on the 5" setting all year. In the winter I just put mouse protection in front of the reducer. I couldn’t imagine trying to condition the air in my house with the floor removed and replaced with screen and seeing the ground below lol.
So with a solid floor and the entrance reduced to 5 inches do you leave a hole open in the crown board?
I ask because every time I have put the inspection trays ( your corflute) in especially when there is nectar being brought in, I get condensation under the crown board
All of my crown boards (inner covers) have a hole in the middle so bees can come up from below and they have a 1" notch that leads to the outside. That notch is protected from the elements by the outer, telescoping cover.
hmm,
I have found- if I try an research something about bees- invariably I find two opposite opinions about any given question. The problem is the various arguments are usually logical and are based on direct experience. Part of this comes down to geographical differences, different types of bees, types of beekeeping, etc. However much of the controversy cannot be explained by these factors.
Concerning screened bottoms - I started looking into it- and early on I read this:
This article is strongly in favor of screened bottoms- with no coreflute at all even in winter The theory revolves around beetle control- but also on ventilation in the hive. The idea is that you must have very little to no ventilation from the top of the hive and an insulated roof. This means the ceiling remains the warmest surface in the hive so when hot moist air rises it does not condense on the warm surface. Instead the stale moist air flows down the sides of the hive and exits and is replaced by fresh air at the bottom. According to the author bees can tolerate cold air- the problem they have is stale moist air.
This makes a lot of sense- I prefer fresh air too even if it is cold. I always leave a bedroom window ajar in winter.
However I also follow Michael’s logic perfectly- no-one wants a cold damp drought in winter either. I just wonder if you avid the ‘chimney affect’ by having no ventilation at the top of the hive- then even if the bottom is wide open - the warm air in the hive acts like a barrier to the drought entering the hive- kind of like fresh water forms a barrier against salt water - a halocline. The author of the article was surprised to hear that many beekeepers didn’t even see the need for a shield at the bottom to stop wind gusts disturbing the open hive.
The author claims even hives in snow country were reported to fare better with open screened bottoms than less well ventilated hives. This type of design would seemingly work best with no top entrances, no hole in the inner cover or ventilation in the roof at all, and with an insulated roof.
Anyhow this afternoon we did our first check of the hive after winter: the bees survived winter VERY well. Hive was full of brood in all stages, pollen and two outer frames of completely capped honey. Every frame was covered in bees and we saw the queen- she looked older and larger than last year but strong and good. We removed the two capped frames of honey- put in two new frames for them to draw out- and added the flow super. Within two minutes bees were all in the flow super. There were no signs of any pets or diseases at all- really superb brood pattern- and many bees returning with big loads of pollen. No sign of queen or swarm cells either.
We fed the bees a few ounces of nectar we robbed in August and froze to ‘compensate’ for the two frames of honey we took (7kg’s!). The bees were bringing in
And- we had the coreflute in the Upper slot all winter 
I put it in the lower slot this afternoon. Did I do right? Who knows.
a side note - if your hives are in an area with heavy wasp (primarily Yellow Jacket) populations, an open SBB just attracts them more with the mix of honey, bees and dead bees, so keeping the board in is definitely helpful in controlling their attraction
Here is an update on this modification because it is relevant to the discussions on the SBB. My SHB trap with its mixture of vinegar and vegetable oil is very effective at catching my bees which escape through the screen. I can also find bees sitting on the corflute board.
So my concern is not that my trap is not capable of catching the beetles, it is that so many of my beetles are getting out through the screen, are attracted to the trap and drowning.
Consequently, i am wondering if my SBB screen size is apprpriate? I recall there was some discussion on this some months ago.
There is a complicating factor with bee air con. It needs a good flow of air to work as it is evaporative not refridgerative.
Evaporative air con you have to leave the doors and windows open… otherwise it gets humid and stops working. Thats why the bees are busting a gut at the front of the hive… they’ve got to get all that moisture out of the hive. The correct airflow is difficult to get right… if there are loads of bees at the front beating their wings its probably too little… none and its too much. Theoretically one could help the bees by controlling how open the cor flute was but i suspect its difficult in practice.
I certainly found that with the corflute out, i didnt have bearding, even on +40 days but i took other measures like shading with a wet towel as well so dont know how much the corflute impacted it.
Evaporative cooling requires controlled ventilation and in particular the bees need to dispose of moist air. Moist air rises. Letting it out the top is a good plan, but if you don’t, you should at least restrict the air coming in so the bees can control it. Unlimited ventilation makes cooling impossible.
Why would moist air rise? It would be cooler and denser?.
All in the physics. I think we had discussed it some time ago.
Basic facts.
I dont think the pIysics works like that… warm air can hold more moisture but doesnt necessarily contain it, you can have humid air or dry air depending on the contexf.
Evaporative cooling works by liquid water converting to gaseous utilising the energy available in the warm air. This cools the warm air down as well as increasing it’s humidity. This is the basis of wet bulb temperature… the max amount evaporation can cool the air by. The hot dry air and water reach an equilibrium between a cooler temperature and maximum humidity.
When bees bring water in to cool the hive and when they ripen honey this effect will be in play, cooling the hive down and causing down currents locally. However… respiration is a different matter… here the bees body adds heat into the mix… so they exhale warm moist air, which presumably rises where the bees are most concentrated.
If i was a bee in hot weather… i’d want to ripen honey in the outer upper frames and release water where the air is drawn into the hive. This should draw cooled air through the centre of the brood up to the top and down the sides.
If you open the top you will get better air flow in the centre but not at the walls. So bees wont have to work as hard at cooling the hive but will have to work harder at ripening honey… bit of a trade off. If the bees cant keep up providing water to match the airflow you will end up making the hive warmer due to hot air being drawn through the hive and the opposite at night.
Opening the screened bottom board will have a similar effect provided the bees release the water at the right point, below the brood and not at the entrance. But it will cause more air flow down the sides of the hive.
I’m going to experiment a bit this summer with different arrangements to see how the bees cope with hot days.
Watch the video @JeffH posted, City of Bees, they actually show in the hive how well the bees move air around the hive, and the why/how
If you google it, there are thousands of meteorologists who would love to explain the physics of why moist air rises. The fact is, it does. That’s why it ends up in the sky where it rains down on us… fog, is not moist air, it is water droplets and they are heavier than air. Once they evaporate into the air again, they rise too.
Yep what busso says is true Dunc, have a read of this.
Perhaps I was a little simplistic but this is not the forum for debate on this.
Google: “Latent Heat” for an understanding on endothermic and exothermic processes and the phase change from liquid to vapour.
Important to note that there is no change in kinetic energy during the phase change but there is potential energy changes. The energy in the form of heat.
My basic understanding of bees cooling and warming the hive is more about movement or transfer of heat rather endothermic or exothermic processes. There will be phase changes but only as a consequence, much the same as a fan cools the skin. But I need to research it further.
Edit: Thought just occurred that the evaporation (phase change) of water in the honey will cause changes of temperature within the hive.
Its a great video.
Humidity has a tiny impact on density… at beehive temps 100% humidity is 3% water.
Temperature has a big impact on density. Some examples…
40C dry air is 1.13 g/L, once humidified it drops to 15C 100% humidity and the density is 1.22. By comparison 100% humidity 40C air is 1.10g/L.
Bee breath is about 1.13g/L.