How revolving doors are more cost-effective than traditional doors

Please note my criticisms should not be taken to knock the thrust of the work itself. The research question had to do with social effects, while I am criticizing the modeling behind the infiltration estimates.

First of all, the "stack effect" is not the most important driver of flow in modern buildings (especially not ones that have revolving doors). Mechanical systems are designed to dominate stack and wind-driven flows, precisely because engineers want to control the flows in the building. The analysis presented on the web page and in the research report discussed only stack and wind effects.

Second, the equations shown in the figure on the web page are from a steady-state "multizone" modeling approach. Steady-state models don't represent swinging doors well, because of several important transient effects: (1) momentum effects associated with the intermittent nature of the flow (makes airflow smaller than a steady-state model would suggest; and (2) active pumping by the door (makes airflow larger than a passive transient model would suggest).

Third, I think the blanket statement that "heating is less efficient than cooling" is just flat-out wrong. Heating is pretty easy-- just plug in a lightbulb, and 100% of the electricity it burns gets converted to heat. For this reason, many buildings have core zones that require cooling year-round.

Fortunately, I don't think any of these criticisms affect the broad validity of the work. Their modeling seems to have been driven largely by experimental studies, not by the material described on their web page and in their paper. Therefore one can assume they got the right order of magnitude (one might also note that the cited papers are from 1958 and 1961-- in other words, the basic technical part here is not new, and it's unlikely they botched it too badly).

One final criticism. MIT has a very good faculty that specializes in building energy issues. Any of them could have pointed out these problems, and helped guide a much stronger technical analysis. Unfortunately, none of that faculty seems to have been consulted for this study (the acknowledgments list a bunch of urban studies and management faculty, plus people from the facilities department). I know this was just a class exercise, but it seems to me representative of the sorts of analyses that can result when management people start mucking about in technical matters...

Often, they will hit the button to automatically open the doors. This is even worse than using the door manually, as the timer that controls the door motion usually leaves the door open for many seconds -- presumably to accommodate a slower user or one with a wider configuration, e.g. a wheelchair -- before beginning to close. Mind you, these are people who appear to be fully mobile and not unduly hindered or handicapped.

Quite often, I'll see people use the swinging doors to exit, where they just hit the crash bar and proceed. Presumably, they find this quicker (by a matter of a second or three) and more convenient.

(The cynic in me says: And after all, if they are even aware of the difference in efficiency, they are not personally paying the heating bill and cooling bills.)

I wonder whether a brief, one page "flyer" version of the linked information could be effective in altering behavior. I wouldn't ask permission to post them; I'd just engage in a guerrilla campaign of slapping them up when and where I can get away with it. Preferably, the flyer would have a professional appearance and the salient information would be encapsulated in an easily scanned sentence or three in large font. There might be more detail below, and hopefully also an eye-catching graphic.

I'm no graphics artist, but maybe I'll give it a go.

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.

You can also speak to anyone who works near both revolving and regular doors, such as building receptionists. They will quickly tell you the revolving door lets far less cold in, and will probably tell you with a good deal of frustration how much they hate the regular doors.

http://www.youtube.com/watch?v=ACtW09PT7fY