ASHRAE Journal - July 2023 - 46

TECHNICAL FEATURE
Tables 6.8.1-8 and 6.8.1-9 of Standard 90.1-2022
cover the minimum efficiencies for variable refrigerant
flow (VRF) products. For the small duct free products,
the previous metric was SEER. As of January 1, 2023, it
was changed to SEER2. For the larger VRF products, the
DOE completed a negotiated ruling in 2021 on the AHRI
1230 test procedure, resulting in a decrease in the full
load EER by 4.2% to 6.7% and a drop in the IEER by
12%. The levels for IEER were not changed in the 2022
standard, so effectively this resulted in a 12% minimum
efficiency increase.
HVAC Equipment Efficiency Ratings
New SEER2 and HSPF2 Metrics: SEER2 (cooling
performance during the cooling season) and HSPF2 (heating performance
during the heating season) are still calculated in much
the same way as with the previous performance metrics, SEER and
HSPF. What's new is that the input values are now obtained under
more realistic testing conditions-higher static pressures that better
simulate the effect of ductwork, resulting in greater fan energy use
and lower numeric ratings for both SEER2 and HSPF2. In addition,
for HSPF2, more low-temperature hours are included in the heating
performance testing. This results in a much greater percentage
drop in efficiency values for HSPF2 than for SEER2, compared to
the previous SEER/HSPF metrics. The change in SEER to SEER2
results in about a 5% drop in the rating and the change in HSPF to
HSPF2 decreases by about 16%.
IEER Metric: The IEER metric is an annualized metric based
on a U.S. climate zone weighted average for mechanical cooling
operating hours and weighted performance at 100%, 75%, 50%
and 25% of mechanical cooling capacity (excluding economizer
performance benefits.) It provides a more accurate representation
of mechanical cooling efficiency in a building but does not encompass
the system impacts of economizers or ventilation for IAQ.
The industry is working on further changes to the metric for future
updates.
ISMRE Metric: ISMRE is a metric that was developed for
DOAS and is covered by the AHRI 920 standard. It is an annualized
metric similar to IEER but is targeted to reflect the moisture
removal efficiency of the DOAS unit expressed in lb of moisture/
kW∙h. The metric is annualized based on four weighted average
part-load rating points. ISMRE2 reflects the changes in test procedure
issued through a DOE negotiated ruling and documented in
the AHRI 920 standard.
46
ASHRAE JOURNAL ashrae.o rg
J U LY 2023
Test procedures are the procedures that defined the
testing and rating requirements for products. As part of
the DOE ruling, several AHRI 1230 test procedures were
revised:
* Requirements for a new maximum Sensible Heat
Ratio requirement at 100% and 75% load;
* Addition of a control's verification test
requirement;
* Change in the DOE air-cooled metric for
>65,000 Btu/h from EER to IEER.
With the growing interest in electrification to reduce
environmental emissions, the use of larger chillerbased
heat pumps has been growing. This has prompted
AHRI 550/590 to add standardized rating conditions for
chiller heat pumps and heat recovery chillers. Similarly,
ASHRAE Standard 90.1-2019 included new requirements
for heat chiller heat pumps in Table 6.8.1-16. In
Standard 90.1-2022, in addition to making some necessary
corrections to the table, the table was modified with
expanded rating conditions to account for data centers.
Similar changes were made to standard chillers to cover
the higher chilled water temperatures now being used
by data centers.
Another equipment category that is getting more
use and interest is dedicated outdoor air units
(DOAS). DOAS products are covered by AHRI 920;
the minimum efficiencies are defined in Tables
6.8.1-13 and 6.8.1-14 of Standard 90.1-2022. As part
of another DOE negotiated ruling, some of the test
and rating requirements for DOAS equipment were
changed and improved; for example, static conditions.
Subsequently, the ISMRE metric was changed to
ISMRE2, and the associated efficiency tables were
updated. These changes were implemented in
Addendum cv to Standard 90.1-2022, now available for
download at ashrae.org.
The efficiency requirements for commercial dry
type transformers, as defined in Table 8.8.4, were
also updated to reflect new DOE-defined values.
Additionally, Table 6.8.1-5 for furnaces was updated and
reformatted to improve clarity. Lastly, gas hot-water
boiler systems for space heating in new buildings (with
a total system input of at least 1,000,000 Btu/h [293 kW]
but not more than 10,000,000 Btu/h [2931 kW]) must
now have a minimum thermal efficiency of 90% (condensing)
and a maximum return water temperature of
120°F (48.9°C).
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