For those of you who like a little math, I thought I would provide some equations for estimating the temperature inside your hives. Did I hear a collective sigh and a moan? There goes BB again with his heated hives? Not exactly. The math applies to wood hives too. I agree with the crowd that bees don’t set out to warm up their entire hive
, however depending upon the R value of the hive and air infiltrations, the bees heat CAN end up heating a hive rather substantially.
The hive temp equations are simplest if you calculate the hive temp based on a perfect R value and then adjust it later for air infiltration losses and solar gains. The equations for heat transfer were discovered by Newton 300 years ago (http://en.wikipedia.org/wiki/Convective_heat_transfer
). Using modern building materials, the differential nature of Newton’s equation can be simplified to a simple energy relation equation we can all understand.(Hive Surface Area/ R value) x (Temperature Inside – Temperature Outside) = BTUs of bee heat.
A full colony of bees can generate somewhere between 20 and 40 watts according to the literature I’ve seen and my casual observations. 1watt = 3.41 BTU/hour. A wood hive has a R-value of about 1.
A 2 deep hive has a surface area of about 14.5 sq feet. Plugging these numbers in the heat loss equation we have:
(14.5/R1) x Delta T = 20watts x 3.41
Delta T = 4.7F. Where Delta T is the temperature delta ABOVE the outside air temp.
A perfect wood hive with bees making 20 watts of heat would be at most 4.7F warmer than the outside air before accounting for air infiltration loses. When you take those into account, then the math agrees very closely to what people believe; “ bees don’t heat the hive, they only heat the cluster”.Now let’s run those same numbers with a foam hive having R10 insulation.
14.5/R10 * DeltaT = 20watts x 3.41
DeltaT = 47F.
A perfectly insulated R10 foam hive will be up to 47F above the outside temperature if the bees are making 20watts of heat in the cluster. In this case, the bees DO end up heating the hive along with the cluster.
This winter it got down to -6F here. The math says a wood hive got down to -2F inside. The math says a foam hive got down to 41F inside. If you were a bee, which house would you prefer? My bees are all alive; they seemed to prefer 41F over -2F.