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Author Topic: Top vs Bottom ?  (Read 6816 times)
little john
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« Reply #20 on: December 26, 2012, 07:20:47 AM »

Water vapor has a specific gravity of 0.6218.  That's 1 third lighter than air which has a specific gravity of 1.000.

http://www.engineeringtoolbox.com/specific-gravities-gases-d_334.html


Yep - I found that out just this morning.  Got the following from a hot-air ballooning site:
Quote
Moist Air - In the real world the air always contains some moisture. The addition of water vapour to a mass of air makes it less dense. Whilst this may appear a bit odd at first this occurs because the molecular mass of water (18) is less than the molecular mass of air (29).

It seems that in life sometimes it's necessary to stick your neck out and get something wrong, in order to learn from that mistake.

What you write is true - moisture-laden air is LESS dense than dry air, and thus will rise. Even the Wiki on this (http://en.wikipedia.org/wiki/Density_of_air) describes it as 'counter-intuitive'. Indeed, just about everybody I know who uses bottom entrances - including myself - does so in the belief that moisture-laden air is heavier, and thus will fall to the bottom of the hive and exit.

The only explanation I can offer for this confusion comes from the oft-quoted paper by Thur, who recommends the idea of 'upper integrity' (my words) thus implying that entrances should only be at the bottom of the hive. He writes:
Quote
Only the used air of respiration drops downwards, laden with carbon dioxide, and at the open bottom margins of the comb it is exchanged with fresh circulating air. .

CO2 of course has a molecular weight of 44, which will make air containing it heavier - but the same air will also contain water moisture, making it lighter.

Looks like it's time to get the calculator out ...

'best
LJ

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derekm
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« Reply #21 on: December 27, 2012, 11:20:11 AM »

... Indeed, just about everybody I know who uses bottom entrances - including myself - does so in the belief that moisture-laden air is heavier, and thus will fall to the bottom of the hive and exit.

The only explanation I can offer for this confusion comes from the oft-quoted paper by Thur, who recommends the idea of 'upper integrity' (my words) thus implying that entrances should only be at the bottom of the hive. He writes:
...
The issue is people jump on a single facet of a conclusion without understanding what is beneath it and then try to apply  that conclusion to circumstances where it doesnt apply.
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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?
beehappy1950
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« Reply #22 on: December 27, 2012, 12:41:56 PM »

My 2 cents worth. I use an inner cover year round. I take a saw and cut the lip on one end. Take out a chunk so I have an opening about 1 in. wide and 3/16ths deep. I turn them with hole down in winter and up in summer. Works great.
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Michael Bush
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« Reply #23 on: December 28, 2012, 09:09:02 AM »

>The issue is people jump on a single facet of a conclusion without understanding what is beneath it and then try to apply  that conclusion to circumstances where it doesnt apply.

Or it applies only somewhat.  Reality is not just one simple measurable thing, but a complexity of things.  In this discussion we have brought out that CO2 is heavier than air and water vapor is lighter than air.  Which wins out?

There are many things like this where what we think is the measurement for something is only one aspect of it.  Which would you prefer, a sunny calm, dry, 10 F day or a blowing, humid, rainy 40 F day?  You'll be warmer when it's 10F, sunny and calm even though we think temperature is how you measure cold...
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Michael Bush
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derekm
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« Reply #24 on: December 28, 2012, 09:22:03 AM »

... even though we think temperature is how you measure cold...


That is exactly the wooly thinking I'm talking about which has "Damp kills bees not cold" as one of its sayings
Heat flow confused with temperature.

And the Co2 vs H20 question is in the same trap
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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?
little john
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« Reply #25 on: January 01, 2013, 11:28:26 AM »

Just found an interesting idea - from:
http://www.uoguelph.ca/canpolin/Publications/ThompsonCody_MSc2011_edited.pdf

The thesis itself is a tad disappointing from a practical beekeeping point-of-view, in that nothing definitive emerges - but there is some confirmation that having a cavity beneath a bottom entrance (which I interpret as being the same as raising the bottom entrance a few inches) may be a beneficial strategy. Something to do with a vortex being created around or near the entrance.

The bloke goes into some pretty hairy maths: fluid dynamics, boundary layers, that kind of thing - the sort of stuff usually applied to modelling jet aircraft wings - I only hope that bees appreciate how scientifically advanced they are Smiley - but it may be worth mentioning that the original idea for this thesis came from someone's intuitive beekeeping practices.

LJ
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BlueBee
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« Reply #26 on: January 05, 2013, 03:40:34 PM »

Hereís an update on my top vs bottom entrance winter study.  Photos taken today about 3pm.  Weíve had an extended period of seasonably cold weather here in Michigan and virtually no sun.  A couple of nights down to single digits and no days above freezing.  The kind of weather that takes out hives. 









My hives with the heat bubble designs (only a bottom entrance) show LOTS of condensation and my hives with a top entrance show virtually none.  My observations of bee activity in the various designs (I have plastic tops to watch them) lead me to believe the heat bubble designs are indeed a bit warmer (as theory suggest).  However when I weight the risk of cold vs wet on the bees, I think wet is a much more deadly threat. 

If we ever get back above freezing here, I might go out with the drill and make some mods to a couple of my heat bubble designs to see if I canít improve the condensation problems.
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edward
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« Reply #27 on: January 05, 2013, 06:15:10 PM »

How big are your entrances, and do you have any other ventilation other than the entrances?

mvh edward  tongue
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BlueBee
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« Reply #28 on: January 05, 2013, 09:09:37 PM »

Edward, Iím experimenting with a few different configurations this winter but each hive has either a bottom entrance or a top entrance; never both.  No top vents with bottom entrances. 

If there is a entrance on the bottom and a hole at the top, youíre going to create a convection current (chimney effect) right through the hive which is going to make it simpler for heat to escape.  That defeats the value of insulation to some degree.  Probably doesnít make a bit of difference in most American wood hives since they have virtually 0 insulation value to begin with.  However a convection current could put my 38mm of polystyrene to waste!   I sure donít want that to happen; so no chimney effects in my hives. Smiley

Most of my hives have entrances that are about 9mm tall by 75mm (3Ē) to 100mm (4Ē).  I didnít want to close them down too much for fear of trapping too much CO2 inside.  On the big hives, the bees chew out the entrance reducers.
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edward
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« Reply #29 on: January 05, 2013, 09:42:27 PM »

So if I understand it your entrances are 9mm high and 75-100mm wide ?, no other ventilation?

And either top or bottom placement, with no other ventilation?

mvh edward  tongue
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BlueBee
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« Reply #30 on: January 05, 2013, 09:44:56 PM »

That is correct.

My goal is to inhibit the loss of heat via air infiltration while at the same time allowing for sufficient exchange of gases.  I'm not claiming I'm doing it right, mind you!  I'm just reporting what my goal is. grin
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edward
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« Reply #31 on: January 05, 2013, 09:47:42 PM »

OK, what are your highs and lows in winter temperatures and how long is your winter, or how long do the bees not fly out of the hive.

mvh edward  tongue
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BlueBee
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« Reply #32 on: January 05, 2013, 09:58:19 PM »

Michigan is located near the middle of North America and as such we have a continental weather pattern.  In the winter, cold air from Canada normally dominates our weather, but we usually do get breaks in the cold if high pressure set up on the east coast and pushes warm air from the Gulf of Mexico up this far north.  First freeze is typically Oct 15th.  Last frost is typically early May.  Looks like our temps have been a little cooler than Helsinki lately.

Because our weather is so variable, it is hard to predict how often the bees can make a cleansing flight.  I would say it would be rare for the bees to be cooped up for more than 3 solid months without a cleansing flight.  Spring doesnít really start to arrive here until Mid April.
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edward
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« Reply #33 on: January 05, 2013, 10:36:38 PM »

Ok that about what I have were I live in Sweden.

The way I and many others keep our bees in poly hives is with no ventilation in the top and ventilate with a metal screen over 70% of the bottom and an open entrance that wont allow mice to crawl in.

I myself and many other have a Swedish raised bottom board called universalbotten  http://www.pixonia.com/universalbotten2011.pdf     It has a metal ventilation grid in the rear that works like the back wall of your fridge and attracts moisture.
The front entrance is also open so air can flow freely across the bottom so the moisture ventilates out.

In the winter time with freezing temperatures the air is often very dry and helps keep hives dry.

None of my hives have the amount of condensation I have seen in your pictures and never over the hibernating bees, eventually a little moisture or frost on the outer skirts of the ball of bees.
All though I haven't looked at them on a continual basis under the whole winter. Just now and then in extreme causes.

In a nut shell our hives have a warm winter cap and a drafty floor to get rid of moisture, the walls may bee wet with condensation that run down and out of the hive.

This is just info on how most of us do it here  Smiley

Hope you learn a lot with your experiments and they work out, if not you have some more ideas to play with next winter  Wink

mvh edward  tongue

PS if the link doesn't work you can google " universalbotten " and look at the pdf file or google pictures and you can see the different bottom types.
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edward
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« Reply #34 on: January 05, 2013, 10:40:49 PM »

Also your condensation could be from the limited ventilation or the small nucs have a hard time keeping the hive warm.

mvh edward  tongue
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BlueBee
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« Reply #35 on: January 05, 2013, 11:17:52 PM »

Thanks for the ideas Edward.  I do have 4 nucs with open bottoms in my bag of experiments too.  2 are now dead.  The other 2 had a bunch of dead bees under them the last time I checked (not a good sign), but they were still alive. 

I liked the theory behind the ďheat bubbleĒ design that Derekm is fond of, and I wanted to experiment with various versions of that this winter.  If the condensation problem could be solved, that should be the most energy efficient design there is. 

Iím not real comfortable with the idea of an open bottom due to thermal reasons.  Do houses in Sweden have crawl spaces or basements?  A lack of insulation underfoot makes for a cool room!  Iím not saying it doesnít work overall;  I just donít like the idea of wasting heat.  However if it comes down to wasting heat vs a cold shower for the bees, Iíll go with wasting heat.
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Maryland Beekeeper
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« Reply #36 on: January 06, 2013, 02:15:08 AM »

very interesting and well said Edward, Blue Bee I have a hive with glass sides that illustrates Edwards descriptions I'll post, the condensation line stays below the cluster assuming they have the bodies to generate the heat to push the cold down that low
Cheers,
Drew
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BlueBee
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« Reply #37 on: January 06, 2013, 11:11:03 AM »

That would be interesting to see. 

Unfortunately my hives are not instrumented so I donít know exactly what the temperature profiles inside are, but based on the condensation Iím observing, itís pretty clear (at least in my hives) that the top comb temps in a double decker is below the dew point and no matter what I do in that design water is going to condense over the bees heads.  I could probably at 100mm foam on top of the double deckers and it wouldnít make a bit of difference.   When the bees are in the bottom box, those top combs are not going to be real warm.

In my hives wintering in a single box, it might be possible to get the condensation to move over to the side walls as you suggest Drew.  Itís almost there already. 

Where the condensation forms is going to depend upon how warm your hive is in the first place (insulation value) and where your bees are located (top vs bottom box).  If the upper part of your hive is warm enough (above the dew point), then you would not have condensation up there.  My 8 frame nuc (with all the water you can see in the photo) has 38mm thick foam walls.  The odds are that nuc is better insulated than 97% of beeks in North America.  So if Iím getting condensation without a top vent, the odds are everybody else is too. Smiley   
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derekm
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« Reply #38 on: January 06, 2013, 06:49:54 PM »

Thanks for the ideas Edward.  I do have 4 nucs with open bottoms in my bag of experiments too.  2 are now dead.  The other 2 had a bunch of dead bees under them the last time I checked (not a good sign), but they were still alive. 

I liked the theory behind the ďheat bubbleĒ design that Derekm is fond of, and I wanted to experiment with various versions of that this winter.  If the condensation problem could be solved, that should be the most energy efficient design there is. 

Iím not real comfortable with the idea of an open bottom due to thermal reasons.  Do houses in Sweden have crawl spaces or basements?  A lack of insulation underfoot makes for a cool room!  Iím not saying it doesnít work overall;  I just donít like the idea of wasting heat.  However if it comes down to wasting heat vs a cold shower for the bees, Iíll go with wasting heat.

if your hive is insulated the condensate will not be much colder than the dew point. the dew point is likely to be high not low ... Condensation does not necessarily mean cold....jus a surface lower in temp than than the dew point. Condensation inside the hive rather than outside means heat gain to the hive rather than heat loss.
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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?
derekm
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« Reply #39 on: January 06, 2013, 06:51:17 PM »

Thanks for the ideas Edward.  I do have 4 nucs with open bottoms in my bag of experiments too.  2 are now dead.  The other 2 had a bunch of dead bees under them the last time I checked (not a good sign), but they were still alive. 

I liked the theory behind the ďheat bubbleĒ design that Derekm is fond of, and I wanted to experiment with various versions of that this winter.  If the condensation problem could be solved, that should be the most energy efficient design there is. 

Iím not real comfortable with the idea of an open bottom due to thermal reasons.  Do houses in Sweden have crawl spaces or basements?  A lack of insulation underfoot makes for a cool room!  Iím not saying it doesnít work overall;  I just donít like the idea of wasting heat.  However if it comes down to wasting heat vs a cold shower for the bees, Iíll go with wasting heat.

if your hive is insulated the condensate will not be much colder than the dew point. the dew point is likely to be high not low ... Condensation does not necessarily mean cold....jus a surface lower in temp than than the dew point. Condensation inside the hive rather than outside means heat gain to the hive rather than heat loss.
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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?
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