I attached my observation (data collection) from my 2 monitored hives. Unfortunately, it seems that one of my sensors failed. The one located just above the slatted rack. Fortunately I have 7 months worth of previous data on that location that I will be able to use.

The 2021-2022 Slatted Rack temperature profile looks identical to last years. This year I am measuring the same profile for a colony without a slatted rack. 

No Slatted Rack:
From the charts below you can clearly see that the colony without the slatted rack is running cooler and is more clustered. Still very loose considering that we hit -25C and more than 70% of the box top profile is above 10C. From the temperature lines you can see 2 distinct groupings. A high temperature choppy group (~15 to 18C) and a lower temperature smooth group (~5 to 9C). My interpretation is that the high T group is inside the cluster and the choppyness is due to the heater bees heating the interior. The smooth group is outside the cluster and therefore the outer cluster mantle emits constant heat.  The other interesting observation is the 2 sensors below the cluster on the bottom board and just inside the entrance. The entrance temperature is consistently higher than the temperature at the center of the screen bottom board. The third line is the temperature in my open crawl space below all of my colonies.  Humidity levels 15C at RH60%; -4C RH65% (bottom board center) and -1.5C RH75% (entrance). The bottom board RH and entrance are paralleling each other closely.

With Slatted Rack:
From the charts the cluster shape is very loose where more than 96% of the box top profile is above 10C. Overall running warmer (~19 to 22C) and the temperatures below the slatted rack are mostly identical to each other (Center Bottom Board = Entrance) and warmer to the colony without a slatted rack by 3 to 6C. Humidity RH are also the same. 

Last year my singles without a slatted rack consumed about 1/4 less honey 25 to 30lbs vs 40lbs than my singles with a rack. Too early yet to say, but that will likely also be the case if the profile continues. From my heat loss calculation, the rack colony is losing about 44% more heat out of the enclosure (3.93W 0.41lbs/week honey equiv vs 2.72W 0.28lbs/week honey equiv at -15C). When comparing the entrance temperatures there is clearly a difference. My guess is that the colony without a rack has more air stream mixing occurring (in vs out). Likely a form of heat recovery.

So my hypothesis: 
for this experiment will be that using a slatted rack in an insulated colony will actually cause the colony to run warmer, increase honey consumption and may actually not add any benefits. 

What do you think?

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