Subject: | |
From: | |
Reply To: | |
Date: | Wed, 17 Nov 2021 12:46:07 -0500 |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
Do you hypothesize the lack of heat recovery from the air mixing can
account for all of the 44% additional heat loss?
During the odd warmer winter days where entrances warmed up, the colonies without a rack were more active. Hence the reason I thought 2 of my colonies with racks had not made it through the winter. (ultra quiet, and minimal hive front mortality. Both did well this season. The mixing likely allows the lower section below the cluster to warm faster.
The heat loss I calculated is that of the heat loss through the enclosure walls using inside and outside temperatures, the thermal properties and geometry of the hive body. The heat loss via the entrance/bottom of the hive is a lot more complicated. The slatted rack likely has an impact on the internal natural convective current. It also reduces the effective exposed area below the cluster.
Impact on spring broodrearing?
I remove my racks in early spring because of the colder nights. The area below the slatted stays too cold for my bees to effectively exit. Once morning temps are warmer I replace them. It gives me a chance to clean them. In very cold climates weaker double colonies get locked into the top box when the population is too small (8 frames of bees vs 16 frame of bees). My early spring routine is to remove the "frozen" bottom box. This is the only downside to insulation vs solar gain. However, -30C mornings in April are not unheard of, so the insulation is required to ensure early brood is protected from the elements. My experimental "n" was too small last year (2 of each), both colonies without the rack had larger brood nests early on for the reasons I mentioned above. The results for the rack colonies were split. Hence the reason for this years monitoring comparison. If I don't do it who else will.
Another set observation from last winter are heating events during really cold days where the colony lights up and quickly heats up the interior (no outside disturbances). The interior maintains its heat for periods of 3-4 days similar to my previous calculation around the impact of human disturbances. This effect also occurred but was sustained after I added pollen patties early April. The bees just have a much easier time maintaining internal temperatures. https://drive.google.com/file/d/1RKV08ZX0KA-KtRCzdI-qVzUPOdc6oC0b/view?usp=sharing
Background:
I agree that bees do cluster when exposed to cold temperatures , the set point is just different when heat loss is significantly reduced.
From the literature we know that the cluster mantle density is proportional to the local temperature where clustering begins below 15C and will be at its tightest around -10C. Typically all the research assumes the "local temperature" equals the "outside temperatures". This is clearly not the case when the enclosure is well insulated and heat loss is reduced.
Bees cannot defy the laws of physics (energy cannot be destroyed it has to go somewhere), the literature also states that bees clusters generate 5 to 20 Watts (broodless or minimal brood) of heat depending on the local temperature and much higher when late winter broodrearing is initiated. The heat loss from an insulated hive is less than that value at outside temperatures much lower than 10C therefore the heat stays inside keeping the local temperature higher. Hence the conclusions found by D Mitchell where he states that clustering happens at much lower temperatures. I have observed the same over the last few years. The slower heat loss thus slow down the bees natural instinct to protect itself from the cold as the local temperature is higher than the triggering temperature. Generated heat comes from honey, less heat is required therefore we have lower consumptions. Not using a top entrance makes my boundary conditions easier to model as heat loss above the entrance is driven by good old simple formulas. I could throw in thermal lag (<1hr vs >6-8 hrs) and the improved performance of thermal sinks (honey frames) in
***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html
|
|
|