Building Architectural Elements as Integral Parts of the HVAC System

In my previous post, I discussed why I’ve come to feel
that developing an understanding
of  the interior architectural and structural elements in a
building
 like shafts, plenums, and stairwells is critical
to understanding how the building will function, as recapped
below.

As you will recall, the drawing is a section cut of a high rise
that I was working on that was drawn so that it hit every major
shaft in the building.  I made the section cut because I was
trying to understand how the air that came in through four, 30.000
cfm direct/indirect evaporative cooling AHUs made its way through
the building. After all, as Dr. Al Black, one of my mentors would
say, The Goes Intas gotta equal the Goes Outas and during
start up, we were faced with a situation where, since there were no
Goes Outas, we had fewer than the required Goes Intas and the ones
that we had were over-pressurizing the building.

The graphics below illustrate how air was intended to flow
through the building for two of the four systems (the other two
were similar to what is shown but served the other half of the
building). The Goes Inta path was fairly straight forward; each of
the systems introduced air to the public lobby it served via a duct
that ran down a mechanical shaft.

The Goes Outa path was a bit more complex, as illustrated
below. 

In general terms, on its way out of the building, the air
supplied to the public lobbies moved:

From the lobby to a return plenum
which was connected to a mechanical shaft.

The air flowed up the mechanical shaft to a common
return plenum
that also served as an equipment
room.

Some of the air exited the building from the return
plenum/equipment room
via the air to air heat
exchangers serving the direct/indirect air handling systems.

The majority of the air, which was
not not exhausted through the air to air heat exchangers,
moved down a different mechanical shaft to the 5th floor.

A transfer duct with fire/smoke
dampers
in it allowed the air to transfer through the
5th floor ceiling plenum to a different mechanical shaft.

Fans at the bottom of the mechanical
shaft
transfered the air to a different plenum which
allowed it to ventilate the parking garage located in the lower
levels of the building.

A garage exhaust fan moved the air
from the parking garage up yet another mechanical shaft to the
upper level of an adjacent office tower and ejected the air from
the building.

While complex, the arrangement was clever in that it allowed air
that would have normally been exhausted anyway to do double
duty.  Specifically, the air provided both cooling for
the public lobby areas via an evaporative process as well as
ventilation and some measure of temperature control for the
enclosed parking garage.

What we learned by making the section cut and then overlaying
the systems on the section cut (illustrated below) was that there
was a smoke damper in a transfer duct on the 5th floor that was
closed when it should have been open in the normal operating mode.
Compounding the confusion was the fact that the
normal (power off) position of the damper was
designed to occur in the worst case the building is on
fire
scenario, which was not the normal
operating mode for the building.

The bottom line was that the damper was closed when it should
have been open and as a result, obstructed the path that allowed
the air to exit the building under normal, non-emergency
conditions. A simple modification got the damper to be open for
normal building operation (which was not the position for normal
smoke evacuation operation) and closed in an emergency (the normal
smoke evacuation position).  The building section with the air
handling system superimposed on it was a critical diagnostic tool
for the commissioning team.  It has also served as a very
useful training and documentation tool for the ongoing operation of
the facility. 

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