I never thought of revolving doors as a way to save energy through heating. I wonder if this is due to the fact that revolving doors have significantly larger '

I never thought of revolving doors as a way to save energy through heating. I wonder if this is due to the fact that revolving doors have significantly larger 'footprint' that means the actual door mechanism doesn't interfere with the natural convection currents of a building. Simply think about how convection works (in the winter) in a building it circles from 'warm' interior walls to 'cold' external walls (especially if they're glass), which at ground level causes cold air to move along the ground towards the interior of the building. Now what happens when you open a door to the frigid outside? The cold external air will hijack the convection current and be drawn inside. The opposite holds true in summer when the interior is colder than the exterior, however with the convection currents reversed the system is hijacked again and warm air rises from the door and up the interior wall, similarly cooled air from the buildings interior now flows through the open door, further enhancing the cycle. I've seen these convection patterns many times inside buildings, especially with steam during cooking. For instance, boil a kettle in front of a window (especially a large, or poorly insulated window), if it's summer the steam will roll up the wall and billow across the roof, in winter the steam will get dragged down over any counter tops and to the floor (if you're lucky, you can sometimes see the steam rise in the middle of the room, or conversely in summer it may sink at the centre of the roof). Incidentally, I never thought being an avid tea drinker would actually contribute to my scientific knowledge.