ASHRAE Journal - September 2020 - 9

LETTERS

tool, even in terms of the simple
Carnot cycle equation, in presenting and comparing other feasible
design alternatives beyond boilers
and chillers.

Birol Kilkis, Ph.D., Fellow ASHRAE, Cankaya, Turkey

The Author Responds
Thank for your kind words on
the article and for sharing your
perspective on the exergy of the system. Of all the questions I thought
the article might generate, solving
the age-old question of exergy vs.
energy was not one I expected.
You obviously know the topic well,
so I won't delve into the accuracy of
the calculations.
Long ago I let go of the skills for
those calculations, about the time
I was taught 1 Btu (1 match completely burned as per my article)
could lift a 1 lb weight 778 ft into the
air. I still can't comprehend that is
the equivalent amount of energy,
but I accept it as fact.
To address your observation, ﬁrst
let me say that the entire premise of
the article was based on the goal of
"electriﬁcation" and an efﬁcient carbon emissions-free building, with
all energy coming from carbon-free
sources. So from that respect, your
solution of a much higher exergy
system using combustion at the site
is a nonstarter. Besides not including all the upstream exergy losses
of getting and delivering that fossil
fuel to the site, you are ignoring the
downstream implications of the
emitted CO2.
However, your analysis highlights
an interesting point in the age-old
debate. Your explanation correctly
points out the ﬁrst and second
laws of thermodynamics and then
goes on to apply it to a certain type

of energy, namely fossil fuels, of
which we have a limited supply
and that have sizable long-term
consequences. However, the renewable sources of energy supplied
to the Earth each day is massively
beyond our needs, limited only
by our ability to collect and store
it. If we look at the exergy of the
renewable sources, much of the
incoming energy is radiated back to
space which, as I understand it, is
an incalculable loss of exergy, or at
least incalculable for me.
So the realization I come to is,
in respect to electriﬁcation and
renewables, exergy may not be as
important a metric, since it will
all be either used by nature or
wasted away. Fossil fuels are a ﬁnite
resource, the creation of which took
millions of years to form and concentrate into a stored form. Their
unique "high level" and energy density will surely be needed for things
like aviation, for which we have
yet to invent a viable carbon-free
solution.
True, there indeed are other applications of using the "high level" of
electrical energy we collect, and for
that I say let's collect more. But to
preclude it from being used in a way
that satisﬁes the need to remove
carbon-emitting combustion from
our buildings, based on the "loss"
of exergy that will be lost anyway,
doesn't seem prudent.
Yes, if the grid is not all carbon
free, there is some shifting in where
emissions occur, but the grid is
likely to get to low or very low carbon before all buildings and certainly before transportation. Thanks
again for your comments.
Mark MacCracken, P.E., Life Member ASHRAE,
Miami Beach, Fla.

Makeshift
Negative Pressure
Patient Rooms

ASHRAE's efforts and publications
regarding the response to COVID-19
are exactly what membership needs
ASHRAE to do.
As a practicing Florida engineer,
we have an eleventh lesson learned
following the 10 in the July 2020
ASHRAE Journal article "Makeshift
Negative Pressure Patient Rooms
in Response to COVID-19" by Frank
Shadpour, P.E., Fellow ASHRAE, and
Stefanie Johnson.
Stated simply, existing facilities quickly run out of conditioned
makeup air for added exhaust to
transform positive pressure ICU
rooms into negative pressure rooms.
In California outside makeup air
has "no" humidity, and the addition
of exhaust may create a negative
pressure building, but without the
associated high humidity problems
we see in more humid regions. All
would agree that 100% exhaust is
the better solution, but when the
building lacks capacity for additional makeup air, HEPA recirculation is a viable option allowed by the
guidelines and CDC.
Additionally, HEPA units can be in
short supply and other than an Ofﬁce
of Statewide Health and Planning
and Development (OSHPD) alternate, codes do not require HEPA ﬁltration of AII room exhaust.
In light of this, it would be of
interested to learn what discussion
the authors' ﬁrm had with facility
infection control risk assessment on
the recirculation option using HEPA
ﬁltration for temporary negative
pressure rooms.

SEPTEM BER 2020

Grady Burch, P.E., Member ASHRAE, Oakland, Fla.
ashrae.org

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ASHRAE Journal - September 2020

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