ASHRAE Journal - September 2023 - 40

TECHNICAL FEATURE
FIGURE 3 Cold-start CO oxidation comparison between (a) the OEM condensing furnace and (b) the
retrofitted condensing furnace with the Pt/Rh AGR.
500
450
400
350
300
250
200
150
100
50
Furnace On
CO
1,180
100
90
80
70
60
50
40
30
20
10
620
920
1,480
1,780
Furnace Off
Time (s)
2,080
2,380
2,680
2,980
Protection Agency (EPA) furnace
emissions requirements (Figure 2b).
Figure 3 shows how AGR enables
Furnace On
CO
1,220
Furnace Off
Time (s)
1,520
1,820
where it is connected into the third row of the
primary HX. The AGR catalyst is made from a ceramic
honeycomb substrate shown in Figure 1a. It adds a
limited pressure drop, but the tested results indicate
a regular induced draft fan installed in the furnace is
able to overcome the limited pressure drop penalty.
The AGR-enabled furnace experimental setup and
testing procedure followed the instrument and testing
requirements provided in ANSI/ASHRAE Standard 1032017.5
As a baseline, the OEM furnace was also tested.
The testing results show that the AGR catalysts are
capable of continuous NOx redox and oxidation of
CO/HC/CH4 and formic gases. Figure 2 shows the
condensate acidity, NOx emissions, and AFUE
comparison of the AGR-enabled condensing
furnaces-with the original commercial furnace
at 80,000 Btu/h (23 kW) heating capacity.
Compared with the acidic condensate of pH
~3.42- 3.76 in the OEM furnace, the AGR-enabled
furnace produced a neutral condensate of
pH ~7 (Figure 2a), 99.9% acidic content removal.
Moreover, the results show that AGR enables NOx
emission at levels ranging from 0 ng/L to 1 ng/J,
which is much lower than the 14 ng/J value for
the California new furnace emissions standards
and the 40 ng/J value for U.S. Environmental
40
ASHRAE JOURNAL ashrae.org S E PTEM B ER 2023
2,120
2,420
ultraclean CO emissions even at cold
starts, an advantage in the effort to
keep the public safe. Typically, a CO
concentration of 70 ppm is sufficient
to produce acute, negative effects in
healthy adults. In addition, although the
test furnace is certified to ANSI safety
standards with baseline CO emissions,
lower CO emissions would be preferred
to simplify passing ANSI certification
and to create larger margins to unsafe
operating conditions.
Moreover, the oxidation of CO/HC/CH4
and formic gas can recover energy from
the emissions and slightly improve
the AFUE of the furnace, as shown in
Figure 2c. Compared with the Pt AGR,
the Pt/Rh AGR with low precious metal
loading achieved better results in NOx reduction and
AFUE improvement. Thus, significant opportunities
exist to optimize AGR catalysis at low cost.
The AGR catalyst is also capable of continuously
trapping SOx. The typical sulfur concentration in the
U.S. natural gas pipeline (1 ppm to 4 ppm) is low;
therefore, a furnace would need to run several years
to degrade the AGR capability for SOx trapping. The
authors' previous results conservatively demonstrated
the need for a regeneration event every three years or
more.2 Once the AGR degrades, the AGR component can
be disassembled from the furnace for regeneration and
FIGURE 4 (a) The condensate acidity and (b) NOx of the Pt AGR-enabled furnace before
and after the 400 hour test.
14
13
12
11
10
9
8
7
6
5
4
3
2
1
40
35
30
25
20
15
10
5
 Retrofitted Furnace (Fresh Pt AGR)  Retrofitted Furnace (400 h Pt AGR)
CO Emissions (ppm)
CO Emissions (ppm)
pH
NOx(ng/J)

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ASHRAE Journal - September 2023

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