No more Tin on Roof for me??

[Karol]

Your reply could be misleading to others . So for their sake I will clarify

Assume bees like 34C so +100C is the same temp differential as -66C.
the heat flow is still only 6W.

As regards "heatsink".. If the surface area has not been increased, or the emissitity or refectivity been not been signifcantly adversely changed, the description "heat sink" does not fit unless you are attaching extra passive or active air moving features.(didnt notice that being mentioned)

Further A tight fitting cleanish aluminum roof reduces heat loss and heat gain rather than increase it
However The emissivity and reflectivity of the rubber is probably no different to tar paper.
Thus the rubber roof with insulation underneath is within the range of conditions that bees are subject to

Tree nests.

The bulk cooling is at the leave stomata where the water evaporates thats 10m+ of oak away so is irrelavent.

The water flow is through the vascular cambium which is in the outmost layers and this flow stops in winter.

This part of the tree is relatively uninsulated and the water flow can be regarded as being at ambient temperature by the time it gets to 5m (typical bee nest height) and is therefore insignificant.

The bulk insulating the bees is secondary xylem which has water content but no water flow.

How do I allow myself to get drawn into these things?

The evaporative process cools the leaves and is remote from the trunk - that much I agree with. However, that's not what I was getting at. It's the evaporative process which is the engine that draws the water through the tree (coupled with capillary action) which in turns helps cool the tree - bit like a 'cold' running water in a heat exchanger. By the time that the water reaches the leaf the temperature differential has dropped through warming (during transport) which helps evaporation at the leaf.

Anyway, if rubber rooves aren't a problem then they aren't a problem - just so long as the bees are happy and don't have to work too hard to cool themselves.

 

[Little John]

Just want to chuck this observation into the pot ...

One of my National tops has a copper top (made from an old hot water cylinder). It's very old and the copper was dark, almost black in places.
Last year we had a couple of hot, sunny days - but not many I grant you. It was on one of those days that I put my hand on the copper and almost burnt it - there was no way I could have held my hand on there. But before stripping-off the copper and getting drunk on the scrap metal proceeds, I decided to paint it off-white. On the next hot, sunny day, it felt barely warm to the touch.

Now I've got enough science degrees to know all about colour and heat absorption and so on .. but the difference was so dramatic, that knowing the theory didn't even come close to doing that first-hand experience justice.

Colour and the choice of underlying material makes a helluva difference.

LJ

 

[Robbie & Jans Bees]

Thank You for all the replys. First I construct the roof from 18mm ply then I am talking to the company they say they can produce white rubber, I am hoping that it will be at the right price and afordable like most bee keeps I try and build out of anything I can beg, barrow or get without paying. The first roof I am going to try is with black rubber the advantage is I can fould it over any surface I am putting a 5mm bead on top of the ply then a 2mm ply before adding the rubber this will leave an air pocket to prevent I hope over heating. Will put up photos at end of march? Robbie

 

[user 6228]

How do I allow myself to get drawn into these things?

The evaporative process cools the leaves and is remote from the trunk - that much I agree with. However, that's not what I was getting at. It's the evaporative process which is the engine that draws the water through the tree (coupled with capillary action) which in turns helps cool the tree - bit like a 'cold' running water in a heat exchanger. By the time that the water reaches the leaf the temperature differential has dropped through warming (during transport) which helps evaporation at the leaf.

Anyway, if rubber rooves aren't a problem then they aren't a problem - just so long as the bees are happy and don't have to work too hard to cool themselves.

The heat exchanger effect is not significant by the time its gone 5m because the heat exchanger is so effective it done its job before it reaches the bees. 15 sq metres of area with the liquid 10 mm or so below the surface gets the 250L /day,(for this hypothetical 1m diameter oak tree) close to ambient quickly.

Thanks for the discussion as I need to have my ducks in a row for a lecture on this.

 

[user 6228]

Just want to chuck this observation into the pot ...

One of my National tops has a copper top (made from an old hot water cylinder). It's very old and the copper was dark, almost black in places.
Last year we had a couple of hot, sunny days - but not many I grant you. It was on one of those days that I put my hand on the copper and almost burnt it - there was no way I could have held my hand on there. But before stripping-off the copper and getting drunk on the scrap metal proceeds, I decided to paint it off-white. On the next hot, sunny day, it felt barely warm to the touch.

Now I've got enough science degrees to know all about colour and heat absorption and so on .. but the difference was so dramatic, that knowing the theory didn't even come close to doing that first-hand experience justice.

Colour and the choice of underlying material makes a helluva difference.

LJ

Nothing beats an experiment... my hives are silver from being made out of foil backed PIR. In summer the bricks on top of the hive get hot in the sun but the foil roof feels cool. On dull winter days the brick feel cold but roof is warm to the touch. I get a buzz out of simple experiments that work

 

[nubee 61]

fibre glass roof

Had'nt thought of using Kevlar weave before, hmmm I suppose I could make the whole roof out of it.... got loads lying around the workshop... interesting.

I think though that the rubber will perish the same as felt does, the UV light wont be kind to it. If you've ever seen an old tyre lying around you'd understand what I mean.

Think the Tin might still have the edge... but Kevlar hmmm We use the GRP most places offshore because its rugged and dosen't have the same problems with the UV that other materials do... I feel an experiment coming on.

i have been using 18mm ply sheathed in fibre glass for a couple of years seems to be fine

 

[Dishmop]

I've just built my 1st hive (a copy of a layens hive i bought), i've fitted it with a tin roof, but i'm concerned about the amount of heat it will generate in summer. (i live in southern spain, where the summers are scorching)......I've just had an idea, i could fit a piece of rubber car mat over lid, or will this insulate the hive more making it hotter inside?

Paint it white.

 

[Karol]

The heat exchanger effect is not significant by the time its gone 5m because the heat exchanger is so effective it done its job before it reaches the bees. 15 sq metres of area with the liquid 10 mm or so below the surface gets the 250L /day,(for this hypothetical 1m diameter oak tree) close to ambient quickly.

Thanks for the discussion as I need to have my ducks in a row for a lecture on this.

If you're talking lectures then things are more complex than first meets the eye when it comes to trees. It might be worth remembering that fluid moves in both directions in a tree so the heat exchanger effect is considerable throughout the whole height of the tree. I used the term 'climate controlled' rather loosely when in reality (as I understand it) trees regulate their temperature much more precisely.

You might find this link interesting:

http://www.treeworld.info/f29/trees-regulate-leaf-temperature-2846.html

Also, thermoscanning is a technique used to identify diseases/rot in trees which would only be possible if temperatures within tree trunks are fairly uniformly distributed/graduated. Interestingly, cavities within trees are generally colder than the surrounding live tissue.

In any event, tree trunk cavities provide 'climate controlled' habitats for bees which I would suggest are probably more 'comfortable' from extremes of cold and heat than man made hives. (Bearing in mind that bark does also provide insulation during winter when fluid transport within trees has arrested).

Good luck with the lecture

 

[Tom Bick]

Nice looking hives particularly like the painted rooves

 

[user 6228]

If you're talking lectures then things are more complex than first meets the eye when it comes to trees. It might be worth remembering that fluid moves in both directions in a tree so the heat exchanger effect is considerable throughout the whole height of the tree. I used the term 'climate controlled' rather loosely when in reality (as I understand it) trees regulate their temperature much more precisely.

You might find this link interesting:

http://www.treeworld.info/f29/trees-regulate-leaf-temperature-2846.html

Also, thermoscanning is a technique used to identify diseases/rot in trees which would only be possible if temperatures within tree trunks are fairly uniformly distributed/graduated. Interestingly, cavities within trees are generally colder than the surrounding live tissue.

In any event, tree trunk cavities provide 'climate controlled' habitats for bees which I would suggest are probably more 'comfortable' from extremes of cold and heat than man made hives. (Bearing in mind that bark does also provide insulation during winter when fluid transport within trees has arrested).

Good luck with the lecture

Bee nests are typically long way from the leaves(so leaf theromoregulation is irrelavent) and the roots.
Any differential to ambient is down to thermal mass and thermal conductance effects not heat transfer to/from the leaves or roots(done the maths). Are you saying the bark is producing significant heat energy from the leaf generated nutrient flow, or directly from photosynthesis?

Tree thermography.
The wood has high thermal mass(2390 Jkg-1K-1) and is moderately insulating(0.14 ~ 0.17 Wm-1k-1) . The wood will be warmer than the surroundings on a cold day colder on a warm day. Parts of Trees without cavities will have higher or lower surface temperature because of the higher thermal mass and conductivity(the voids have lower thermal mass and conductivity) (and less surface area if the cavity is exposed).
Areas of trees with disease will have differences in thermal conductivity and or thermal mass. This paper says its thermal properties (http://www.treethermography.it/papers/20.pdf)

I agree that trees are very much better than hives just not the detail of your reasoning
Trees insulating and thermal mass properties predominate in providing a more stable and energy conserving environment for bees

 

[Karol]

Bee nests are typically long way from the leaves(so leaf theromoregulation is irrelavent) and the roots.
Any differential to ambient is down to thermal mass and thermal conductance effects not heat transfer to/from the leaves or roots(done the maths). Are you saying the bark is producing significant heat energy from the leaf generated nutrient flow, or directly from photosynthesis?

Tree thermography.
The wood has high thermal mass(2390 Jkg-1K-1) and is moderately insulating(0.14 ~ 0.17 Wm-1k-1) . The wood will be warmer than the surroundings on a cold day colder on a warm day. Parts of Trees without cavities will have higher or lower surface temperature because of the higher thermal mass and conductivity(the voids have lower thermal mass and conductivity) (and less surface area if the cavity is exposed).
Areas of trees with disease will have differences in thermal conductivity and or thermal mass. This paper says its thermal properties (http://www.treethermography.it/papers/20.pdf)

I agree that trees are very much better than hives just not the detail of your reasoning
Trees insulating and thermal mass properties predominate in providing a more stable and energy conserving environment for bees

I understand the 'physics' of heat distribution but this is not enough to explain the temperature profile seen in trees. If roots and leaves did not influence heat distribution (other than locally) then there would be a temperature gradient running from the ground to the crown which by and large there isn't. My understanding (for what it is worth) is that there are homeostatic mechanisms at play of which heat exchange is one.

Basically, the trunk represents a tube which is (very efficiently) insulated by a layer of bark. Heat exchange then occurs between the rising and falling liquid which is 'driven' by photosynthesis and transpiration (stomatal evaporation). The heat exchange is an internal circulatory exchange - not so much an exchange to the external environment.

At this point I have exhausted my very limited knowledge of this subject.

 

[Hombre]

Nice looking hives; I particularly like the white insulation that you have put on the top . . .