This is the first time I have over-wintered a double brood box and with temperatures dropping last night to 1C and not planned to rise above 5C most of the day, I thought today would be a good chance to see the impact of taking off a Bee Cosy.
In this test, I have a temperature sensor on the top of the hive roof in the centre, one measuring outside temperature and two sensors in the hive - one on the crown above the cluster and another in the corner of the crown board. The hive has an open mesh floor with the varroa tray fitted.
Between 1:30pm and 2:30pm with only a brood and a half Bee Cosy fitted the outside temperature was around 3C and the air captured in the Bee Cosy consistently 2.5C warmer than the outside temperature.
The weather for the test was still, cold and foggy although the sun did try and burst through at 2:30pm as I removed the Bee Cosy.
The graph below shows the benefit of the warmer air around the hive from the Bee Cosy quickly disappearing when the Bee Cosy was removed at 2:30pm. The crown board temperature remains relatively stable as the colony adjusts to the changing conditions - interestingly the sensor above the cluster showed a short increase of 0.5C to around 7.5C as the colony quickly began to use more energy to cope with the fall in temperature before re-adjusting.
This test took place in still still conditions without rain and without a double brood Bee Cosy in place. I plan to carry out further temperature tests each week in different weather conditions to test how the Bee Cosy responds to different hive arrangements and weather conditions.