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Insulating hives Oct 24

Insulating hives Oct 24

EDBK winter meeting 2024

A talk by Derek Mitchell, Hives and Insulation: Fact or Fiction?

Held at Kilmington Village Hall, 3rd October

Derek is a Research Fellow at the Institute of Thermofluids, School of Mechanical Engineering, University of Leeds. He first became interested in bees after attending a talk at Buckfast where he learned that bees are ‘engineers’, in that they refine sugars and adjust the environment of their homes by controlling heating, cooling and ventilation. This set him on a course to find out more through research, aided by his wife Elaine, who is a beekeeper.

Why?

Because what he was told about bees and their hives didn’t add up. From an engineering perspective, bees collect honey (energy) and maintain temperature in the hive, an energy expensive process. So where was the insulation? This prompted his research on the Thermofluid Engineering of the Honey bee nest.

At the heart of this work are computer models of heat and airflow. This requires Computer Aided Design (CAD) drawings of the whole hive, allocating physical parameters to each part. These models can then be used to visualize the hive and its environment. The components can be further split into small ‘cells’ to improve accuracy of predictions, including splitting air spaces into cells to visualize air flow. At this point, it is just a question of solving five basic equations for each of the 6 million cells created! The equations may be run for 18,000 iterations with different scenarios, rather like weather prediction algorithms. A super computer is required for this.

CAD drawing
Components divided into smaller cells

The next stage of the research is verification by experiment, obviously difficult to do with live bees! So, model ‘hives’ made from materials with similar properties to the real thing are substituted. Derek has even made model trees to simulate colonies in natural nests.

TRUE or FALSE?

Trawling through the available literature on overwintering bees, Derek has found “six statements”, some dating back as far as 1915, that he has challenged.

  • “We can ignore radiation”
    – Experiments show this accounts for 50% of total energy use!
  • “We only need to insulate the top as heat rises, sides not important”
    – air flow experiments show heated air goes up AND around AND between hive parts.
  • “Open mesh floors only loose heat from drafts”
    – actually, there is a lot of heat loss from drafts and Derek demonstrated radiation loss by showing an infrared video of bees on the open mesh floor. This may account for up to 25% of total radiation loss.
  • “Top bee space (under crown board) is not a problem”
    – hot air moves across the top and can disappear through any holes in the crown board. Better off with no top bee space.
  • “Bees heat the cluster, not the hive”
    – The reasoning for this is that the measured temperature difference between the outside and inside of the hive wall is small (see diagrams below).

    In the 1970s, Charles Owens published his Thermology of Bees, which showed diagrams of concentric temperature gradients within the cluster. Essentially, the outer mantle surface was 10 to 12°C and the inner core boundary was around 20°C. As the ambient temperature dropped, the cluster shrank until it could shrink no further. At this point the colony need to produce enough energy to maintain the outer mantle surface bees at 8 to 10°C, otherwise they fall off and die. There is a continual exchange of cold bees coming back into warmer areas and warm bees moving into the mantle. Owens’ work stopped at this point.

    Derek has revisited Owens’ scenarios using his computer models and shown that poly hives are much better insulators than wooden hives, and PIR hives (polyisocyanurate building insulation) are even better. The conclusion is that, for better hive insulation, go big.
  • “The cluster mantle is insulation”
    – Actually, the insulation effect of clustering bees will fall by a factor of 11 as the cluster shrinks! This is to do with the speed of heat loss as the density of the cluster changes. As an analogy, solid plastic will have poorer insulation than the same thickness of foamed plastic. The small bubbles of air cannot move by convection, so reduce the speed of heat loss. In the cluster, convection stops when the bees are ½ a bee-width apart, but the closer together the bees are, the higher will be heat loss by conduction. Thus, insulation falls as the cluster forms and tightens. The conclusion is, clustering does NOT form good insulation, but it seems that decreased insulation during clustering fortuitously allows higher heat transfer to keep the bees in the mantle alive.

    Clustering is an emergency survival device to enable the mantle bees to survive by transferring heat from the centre to the perimeter. In an insulated cavity, clustering is looser or does not happen.

None of these statements stand up to scrutiny. However, there are some beekeeper’s quick fixes that will improve the situation.

  • Putting hives in the shade avoids the stress of overheating.
  • Use aluminium foil coated hives (reduces radiation losses and evaporative cooling losses).
  • Use an aluminium hat which sheds rain away from the hive wall. Reduces evaporative cooling of hive surface. Could use white painted roof/sides in the summer.
  • Insulate the walls at the front and back of a National hive. This can be done with polystyrene sheet and aluminium-backed sticky tape (as used in building insulation). See image of heat loss below. The side with most heat loss is cold way to the frames.
  • Easy to mask mesh floors with Correx sheet. Do not stick down as moisture still needs to escape.
  • Top bee space air flow can be reduced with a flush crown board or thin frame sheet. Bees will propolise this but a flexible sheet is easy to remove. Open vents or matchsticks under the crown board should be avoided.
Owens hive

Owens hive temperatures

Cluster temperatures

Cluster temperatures

Heat loss

Heat loss from National hive

Convection in brood box

Convection in brood box

The downside of clustering

  • Increases stress
  • Reduces resistance to disease
  • Has a high energy cost to the colony.

The Beekeepers fix

  • The beekeeper can provide additional insulation which, in turn, will reduce stress, improve resistance to disease and lower the bees’ use of winter stores.
  • Radiation heat loss from a normal wooden hive is significant, so improving insulation as described will make a big difference.
  • GO BIG WITH INSULATION

The National vs the ideal hive

Professor Seeley showed that wild bees have, on average, an internal cavity diameter of 200mm, an external diameter of 500mm, a cavity of 40 litres, a bottom entrance, preferably 5m off the ground.
We have provided internal 372mm, external 460 mm, cavity 37 litres, bottom entrance, 0.5m off the ground

The ideal hive would look something like this, although it is questionable if it would be viable.

Conclusion: all bees do thermal engineering so we need to listen to the ‘client’ when designing hives. Building Regs are a better guide than books.

References

Thomas D. Seeley – The Lives of Bees. The untold story of the honey bee in the wild.

Statutory guidance.
Conservation of fuel and power: Approved Document L
Building regulation in England setting standards for the energy performance of new and existing buildings.
https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l

For an alternative view and further background information see the BBKA News October 2024 article by David Wilkinson, a BBKA member with 50+ years experience. To view the article online you will need to enter your BBKA membership number and your postcode.