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Date: | Fri, 31 Jan 2020 10:50:33 -0500 |
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Good questions from Randy.
>That being the case, it's clear that moisture is not freely escaping by
convection. <
Perhaps not bulk convection, but outward diffusion of heat and moisture
from the cluster must occur. Over the course of winter many litres of
water (free water in the honey and metabolic water from consumption of
honey) are generated. It seems hard to imagine that all of this could be
retained indefinitely inside the cluster. Where I am with a winter mean
temp of about -10C /14F water release is about 3L/month, based on hive
scale data. When I have used top entrances, on some cold still mornings I
have seen a steady plume of condensed vapour exiting those entrances.
Either directly or indirectly this moisture is coming from the bees.
To some extent top entrances can be self-regulating in terms of allowing
airflow. When it gets very cold, hoar frost around the entrance reduces
the opening and can eventually block it off. It then thaws off again when
temperatures rise, allowing ventilation to resume.
The thermal analysis put forward by Mitchell (cited in recent posts) and
the observations of Seeley on natural nests is quite persuasive and argues
against 'extra' winter ventilation. But managed colonies are larger and
their winter state is quite likely different.
Although there seems to be general agreement (imagine that eh, beekeepers
agreeing :)) about the merits of some winter insulation in areas with cold
winters, published guidance usually says little about when to add it. I
think it is probably important to wait until after cold weather (sub zero C
for at least a week or two) to ensure the cluster has not only formed but
entered its low energy state. Otherwise the hive could remain too warm,
the bees too active, with too much food used and high moisture release.
Top entrances might help in such situations by reducing the internal
temperature.
Rob Hughes
Upper Kingsclear, NB
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