
How revolving doors are more cost-effective than traditional doors - ilamont
http://sustainability.mit.edu/projects/revolving-doors
======
dmlorenzetti
This is closely related to my field of work, so I feel the need to be
pedantic.

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...

------
pasbesoin
At a number of commerical buildings I frequently, I... frequently see people
use the swinging doors located to the side of the revolving door (for ADA
compliance, if nothing else). They do this even when there is no traffic at
the revolving door.

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.

~~~
pasbesoin
My (very) first draft ended up being what I stuck with. I was going to
position the text, maybe add a border, etc. But when I printed this out, it
seemed a good combination of minimal and to the point.

I realize the value I quote is specific to the MIT environment studied, but
I'd rather not complicate things. It gets the point across, and the URL is
given for those who want to investigate further.

[https://docs.google.com/fileview?id=0B1boia8nkdobOWQzZWEwNTg...](https://docs.google.com/fileview?id=0B1boia8nkdobOWQzZWEwNTgtYTgyYS00OTQ1LWExYjEtYTE2Yjg3NDMzZDgw&hl=en)

(Not that I expect much credit for this simple approach. But now I have
something I can put in my bag, ready for the next opportunity.)

EDIT: Also, the term "use" might be considered vague or otherwise non-
specific. But it is brief and fits the intended tone of KISS (Keep It Simple
Stupid). In my mind, "use" doesn't create the mental 'stutter' that "consume"
or another verb might. And perhaps its repetition in the second sentence
provides a subliminal reinforcement. (While the use of "do" avoids repetition
within the same sentence to negative effect. Call the literary criticism
police; I'm out of control.)

~~~
arantius
I think "Swing doors waste ..." is more accurate. And perhaps easier to grasp.
Doors don't _use_ energy, unless they're motorized.

~~~
pasbesoin
I was attempting to address this in my "literary criticism moment". "The
average Joe" is, in my thinking, unlikely to be this specific in their
analysis. "Use" gets the point across without invoking more complex topics
(what does "consume" or "waste" mean) and/or words that may already be
politically and emotionally loaded.

As for the "Please consider" part (responding to the other response in this
branch of the discussion tree), I didn't want to be "telling" anyone what to
do. I thought it would be more productive / invoke a more positive response to
ask them to think things through for themselves. Also, since I'm not the
building owner nor manager, it's not really my place to dictate policy. I'm
making a suggestion to the individual reading the sign.

I don't go into more detail on the sign, because detail -- or the impression
of same -- tends to put people off. If anyone's really interested, the cited
URL is pretty simple and "MIT Energy Initiative" is pretty easy to remember
and google. (Also/instead, maybe I was just lazy.)

Thanks for the feedback, though. Valid points. I'm just explaining my
reasoning, not seeing them as invalid.

------
electromagnetic
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.

~~~
scott_s
I think you're making the analysis more complicated than it needs to be.
Revolving doors are more energy efficient because less inside air is exposed
to the outside. Or, from the article:

 _The revolving door stops conditioned air from moving freely. An open swing
door is like letting go of a balloon- the air rushes out of the opening. A
revolving door is never open- seals remain in contact with the walls of the
door at all times. Only the air in the chamber with the person going through
the door is transferred._

------
po
I often refer to revolving doors as parallel to serial converters. I my last
employer's building, when walking out in a group we had to form into a two by
two column to get out of the building through the two revolving doors.

------
city41
I wonder about this every time I go through a revolving door. I'm glad to see
a webpage speak to it.

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.

------
chaosmachine
Revolving doors scare me...

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

~~~
snprbob86
That looks like a fine example of sound safety engineering at work. All doors
are risky in highly windy environments. My neighbor is missing several finger
tips due to a wind-slammed door. I've also witnessed a sliding door dislodged
from its tracks and tumbling down the street. In this video, the safety glass
shattered as designed, leaving the man startled, but unharmed.

~~~
chaosmachine
From what I understand, it's actually a safety system malfunctioning. During a
fire, the 4 doors are supposed to collapse together, to let people go straight
through. For some reason, it tried to switch to fire mode with the guy still
inside.

~~~
snprbob86
Interesting... why would they collapse with that amount of force? It seems
like it is collapsing awfully fast to be by design, not wind.

------
wallflower
A fun thing to do (if you're not inconveniencing anyone) with automated
swinging doors (that swing out). Because of the finite state machine in the
door controller, if you step on the pad on the outside (where the door swings
to), you can block your friend inside.

------
klipt
Would save even more energy if they were attached to a generator...

~~~
jacquesm
You're probably just joking, but in case you aren't, no it would just cause
all the users of the door to have to consume that much more in calories.

~~~
pbhjpbhj
The door must be hinged, it also has a braking system to prevent it from
rotating too quickly. Adding resistance to drive a generator in place of
heat/sound generation seems not unreasonable. In cars I think they call it
regenerative braking.

Of course an analysis of the heat loss path will help to determine if this is
worthwhile or if the heat can be used more directly to aid heating the
building.

~~~
jacquesm
A regenerative system on a door that has brushes that cause friction with the
sides isn't going to make more power than it will cost to create a
regenerative braking system in the first place. It adds a whole layer of
complexity that will affect reliability and in the end it's going to 'save'
piddly little bits of power.

If you take the cost of an energy storage system you have to divide the price
of the unit by the amount of power that you can buy for that money discounted
with what you think power will cost over the lifetime of the unit.

This will most likely come out negative.

