you should look into district heating solutions. For your application the lengths are quite small so you probably can get away with using an air duct and a fan to push the air through.
However, a better way is (probably optimal) to actually use a air/liquid heat pump which extracts the heat (cools down the air in one building), and heats up water which is used to transfer the heat to the other building.
The benefits of the second solution are:
- smaller diameter ducts (heat capacity of water is significantly greater)
- less cost on insulation (the diameter of the ducts will be limited)
- you can distribute the heat transfer medium (water) easier to different location of the building without worrying too much about losses, and then use fan coils to distribute the heat.
- Some minor safety concerns, e.g.: in case of a fire into building A (hot), the smoke will not be driven into building B.
The main drawback of the second solution, is the higher initial cost.
A few additional question clarifications:
- Would the first solution also require insulation around the air duct, however large?
Yes, both solutions would require significant insulation. The problem with the airduct, due to its larger cross-section it would require more insulation.
- Looking at solutions online, there are a lot of liquid-to-air pumps, though I guess I need two pumps to 1) capture the heat in building A, 2) convert to liquid, 3) deconvert back to air, 4) heat building two?
I am not sure what you mean exactly here, but you'd need at least one. However if you use fan coils you can just divert the hot water directly to them.
- Is there a way to prevent a duct from transferring smoke (and possibly fire, though that would seem like a long stretch) in the case that there is a fire issue with the first building in the first solution.
You could use filters (probably HEPA but I am not an expert), but the type of filters and the frequency that they would need replacing -IMHO- are going to be too costly over the long run.