I’m interested in the thermal performance of bee cozies. 

I did a word search of BEE-L for “bee cozy,” “cozy,” and “cozies” which didn’t turn up much of interest.

I also had a look at manufacturer information sheets which weren’t particularly helpful. E.g., 
http://nodglobal.com/faq-bc/
http://nodglobal.com/wp-content/uploads/2017/08/Booklet-Bee-Cozy-2016.10.19.pdf

I am interested in the extent to which solar radiation penetrates bee cozies to warm the woodenware hive bodies underneath.  Can anyone point me to data on this topic?

I’ve just started a little data-collection myself with 12 colonies, six wrapped with black plastic wrap and bee cozies, and six only with black roofing felt.

My measuring instrument is a bit crude, I’m afraid, namely, a digital poultry thermometer. The probe is meant to be stuck into a roasting turkey with a heat resistant wire to the circuitry on the outside of the oven.

I shoved the temperature probe in under the roofing felt or the black plastic wrap (inside the bee cozy) and waited a couple of minutes for the temperature reading  to stabilize.  The probe was situated in the middle of the second (top) deep, on top of the wood outer surface of the deep.

Apiary air temperature was +4.5 deg. C. Weak sunshine, thin overcast. All hives were sun exposed.  Gusts of breeze periodically.  Only a few colonies had a small number of bees flying but these were all from the roofing felt hives. None of the bee cozy hive colonies were flying.

Preliminary results – the average temperature of the exterior hive bodies (upper deeps) of the bee cozy hives was ~6 degrees C colder that the roofing felt hives.  ~ 6 deg C versus ~12 deg C.

Also, when I cracked open the inner covers, pretty much none of the bee cozy bees were clustered on the sunward SW side of the hives.  I could see one cluster on the opposite side.  In hives where the feed paste was half eaten, the clusters were more in the centre of the hive.  In contrast, all of the roofing felt hives had clusters on the sunward SW side, which is the side I insert feed paste/fondant into.  

More data are required.  I will add a digital infrared thermometer to the data collection so that I can measure the temperatures on the outside of the wraps directly opposite the temperature probes on the inside.

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