ASHRAE Journal - July 2014 - 8

letters

Duct Cleaning

The Author Responds

I found May's HVAC Applications column by Dan Int-Hout very interesting
until I read, "In practice, most lined
ductwork is best left untouched, as
duct cleaning has been shown to create
more issues than it solves." As the president of the National Air Duct Cleaners
Association (NADCA) and owner of
an HVAC cleaning company, I said,
"What? Where did that come from?"
Nowhere in ACCA Standard
6-2007, ASHRAE/ACCA Standard
180-2008, NAIMA-AH122 and
NADCA Standard ACR 2013 is there
any indication that "lined ductwork
is best left untouched." In fact,
there are sections in each of these
standards addressing the proper
cleaning and restoration of fiberglass lined or duct board ductwork.
NADCA ACR 2013, 4.18 - 4.21.5 specifically covers proper cleaning and
resurfacing of fibrous glass surfaces.
Another sentence in the column
says, "You may be surprised to learn
just how much misinformation
there is in the market today." All
1,100-plus NADCA member companies would agree that is absolutely
true. Let me break down the facts.
Fiberglass lining (or for that matter any material used inside ducts)
can be cleaned and restored without
creating more issues than it solves if
proper procedures are followed.
Fiberglass lining often detaches,
breaks away, peels, flakes off and/
or delaminates, and at the time of
cleaning, those conditions should
be identified and the lining cleaned,
repaired and restored. With proper
engineering controls (ACR 2013,
Section 3), any risk associated with
the cleaning can be mitigated.

I agree that duct cleaning can be
done safely and effectively. My experience is that many times, neither
of the two above criteria is met. So
while I would support the comment,
it is with a caution that simply "getting the duct cleaned" is often worse
than leaving it alone, if not done
very carefully using trained personnel. I apologize for not being clearer
in my column.

Bill Benito, President, NADCA

ASHRAE JouRnAl

ashrae.org

Dan Int-Hout, Fellow ASHRAE, Richardson, Texas

VAV vs. Radiant
I found the system comparison of
the office building in Hyderabad
(May's "VAV vs. Radiant") very
interesting and commend the owners and authors on developing,
measuring, and reporting the comparative energy uses.
The 50% AEDG for Small to Medium
Office Buildings has recommendations
for both radiant and high performance VAV systems. The results
were modeled (not measured), but
the savings were 52% for radiant
and 50% for high performance VAV.
It would be beneficial for readers to
know any differences between the
article's "...optimized variable air
volume (VAV) system," and AEDG
recommendations. (www.ashrae.
org/freeaedg).
Space Conditions The article implies
that air-moving fans are included in
the radiant system. Were temperature setpoints for the radiant system
allowed to be warmer than the VAV
system?
Ventilation Airflow Given the warm 46°F
chilled water, were the ventilation airflows for the radiant system increased to allow for proper
humidity control? Did the VAV
system use the same ventilation

J u ly 2 0 1 4

airflows as the radiant system, which
would be higher than required by
ASHRAE Standard 62.1? If so, overventilating of the VAV system would
account for decreased CO2 levels,
but significantly increase energy use
in such a hot and humid climate.
VAV System For comparison, what were
the parameters for the Hyderabad
VAV system? (AEDG recommendations are shown in parentheses.)
Maximum Fan Power (0.72 W/cfm)
External Static Pressure (2 in. w.c.)
Energy Recovery (80% sensible, 70%
latent, 75% total)
Fan Pressure Optimization (Yes, required
by Standard 90.1 since 1999)
Supply Air Temperature (50°F, reset to
58°F for economizer effectiveness)
Demand Controlled Ventilation (Zone DCV
in response to occupancy)
System Ventilation Reset (Using ASHRAE
Standard 62.1 multiple space equation and diversity)
DX System Also, it was noted that
the radiant system's original DX
dehumidification system was not
adequate. Would inclusion of a lowtemperature chiller increase the cost
of the radiant system above that of
the VAV system?
Economizing Finally, the comparison
was made in a climate where there
are limited hours for airside economizing, and perhaps little part-load
operation, two characteristics that
further enhance VAV system efficiency. In other climates, with more
part-load operation and opportunities for economizing, the results may
be significantly different.
Mick Schwedler, P.E., Member ASHRAE

The Author Responds
Thanks for your letter. We always
appreciate another engineer who
likes to dig into the details. We

ASHRAE Journal - July 2014

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