[BLDG-SIM] "Chimney Effect" modeling, have any ideas

[Tom Anderson]

I know one of the ASHRAE handbooks has some calculations for calculating stack
effect for buildings... not sure which handbook, or possibly the ASHRAE
Heating/Cooling load calc book.

Here in Vermont our tallest building is something like 12 stories high.
However, a few years ago I helped a client with a 250,000 sq. foot hospital
wing, 8 stories high.

The basic problem was excessive infiltration at the main entrance lobby,
especially in severe Winter conditions.  There were several elements at play,
but these were the most significant:

Six elevator shafts, running from lobby elevation to rooftop,  with a machine
room above the shafts.  Each shaft had an opening in top of shaft with a grate
between shaft and machine room.  The grated opening is required by code for
smoke evacuation.  The machine room had a propellor exhaust fan blowing out,
with fresh air louvers on opposite wall.

So much heat gain from elevator motors kept that exhaust fan running almost all
the time, even in Winter.  The fan was sucking large volumes of air out of the
shafts, and was assisted by the thermal Winter stack effect (chimney effect),
even though the make-up air louvers were sized porperly and functioning normal.

To solve the shaft opening problem, I installed UL smoke dampers in the grated
opening.  Damper were pneumatic, Normally Open (N.O.).  The dampers stayed
closed all the time, except when fire alarm activated, when the pneumatic EP
would relieve air pressure, opening the dampers.

The State of Vermont accepted the scheme..... it conformed to the code intent.

Look closely at the top of an open elevatror cab and you will see a 3 to 4 inch
gap between open door and shaft wall.

Also,  entrance vestibules should have enough distance between the two sets of
doors so one door set is always closed..  Very hard to accomplish in high
traffic areas.  This is how I learned why those big New York style high rise
buildings use revolving doors....  prevents infiltration.

Infiltration from stack effect is usually difficult to solve as well as
difficult to calculate.  A lot of variables, and many are hard to pin down.

Not sure if this addresses your atrium problem...... hope this helps.

Tom Anderson
South Burlington, Vermont, USA


"Spurlock, R. Bruce" wrote:

> > We have been working with Marriott on modeling the HVAC and ventilation at
> > the Marriott Marquis downtown.
> > We had a presentation  to Marriott, which went very well.... but we told
> > them we did not have a good way to model the atrium (this is the one with
> > a 50 floor atrium downtown.)  They said have several similar hotels (in
> > particular one in New York City almost exactly like the Atlanta hotel.)
> >
> > It seemed to me that this is somewhat similar to cooling towers and
> > smokestack chimney effect problems.... is there some software or expertise
> > out there that would help us on this?
> > This is not a crisis, but it would be nice to know if there was a good way
> > to estimate these effects.
> >
> > In general, they try to plug any holes at the top to minimize the effect,
> > but it still occurs.
> >
> > Bruce Spurlock
>
> ======================================================
> You received this e-mail because you are subscribed
> to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe
> from this mailing list send a blank message to
> BLDG-SIM-UNSUBSCRIBE at GARD.COM



======================================================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM