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Federal Register / Vol. 86, No. 127 / Wednesday, July 7, 2021 / Proposed Rules
revisions to ANSI/AHRI 9202015 will refer to the same table for return airflow ESP. AHRI, No. 11 at p. 15 DOE
received no other comments on this issue.
Consistent with the AHRI comment, section 6.1.5.6 of AHRI 9202020 does include different ESP requirements for supply and return airflow, thereby resolving the identified issue.
Accordingly, DOE is proposing to adopt the ESP requirements set forth in AHRI
9202020 section 6.1.5 Supply and Return Airflow Rates, as enumerated in section 2.2.1c of the proposed Appendix B.

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iv. Target Return Airflow Rate In the July 2017 ASHRAE TP RFI, DOE noted that for testing DDXDOAS
units equipped with VERS, Tables 2 and 3 in ANSI/AHRI 9202015 provide return airflow temperature conditions and indicate that the temperature conditions apply to units with energy recovery at balanced airflow. 82 FR
34427, 34437 July 25, 2017. It is unclear from ANSI/AHRI 9202015
what airflow streams should be balanced, how to determine if they are balanced, and within what tolerances they should be balanced. In the July 2017 ASHRAE TP RFI, DOE requested comments on which airflow streams should be balanced and whether balanced airflow is representative of field use. Id.
On this topic, AHRI raised a number of issues with testing DDXDOAS
equipped with VERS generally, as previously discussed. AHRI also stated that using balanced airflows is consistent with the test procedure for rating VERS described in ANSI/AHRI
10602018. AHRI further commented that in field operation, unbalanced flows may be needed to maintain positive building pressure; however, most equipment selection is done at or near balanced airflows. AHRI, No. 11 at pp. 1415
Subsequent updates to the industry consensus test standard at AHRI 920
2020 shed further light on this issue.
Specifically, section 6.1.5 of AHRI 920
2020 specifies the return airflow rate must be within 3 percent of the measured supply airflow rate. Based on DOEs review of DDXDOAS product literature and consideration of the AHRI
comment, it has become apparent that there is no clear optimal ratio of supply airflow to return airflow for DDXDOAS
testing to be representative of field use.
Therefore, DOE has tentatively concluded that the provision in AHRI
9202020 is appropriate.

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i. Demand-Controlled Ventilation DDXDOAS units are often used in demand-controlled ventilation DCV
operation, which regulates the building ventilation requirement based on parameters such as building occupancy.
Typically, a DCV system monitors the concentration of carbon dioxide CO2 in the return air or in the building and regulates the supply airflow rate accordingly. During periods of nonoccupancy, which could represent a significant portion of field-use, the DCV
system controls the unit to operate at a low airflow rate, thereby reducing the units overall energy use. DDXDOASes using DCV systems are typically equipped with variable-speed supply fans that can be adjusted to meet changing ventilation needs. In the July 2017 ASHRAE TP RFI, DOE sought comments on whether to include operation under DCV conditions i.e., low supply airflow conditions to be included as part of DOEs test procedure. 82 FR 34427, 34437 July 25, 2017.
In response to this issue, the Joint Advocates encouraged DOE to adopt an efficiency metric that captures the benefits of DCV. The Joint Advocates stated that adopting such a metric could provide more field-representative equipment ratings and better inform consumers when purchasing equipment.
Further, the Joint Advocates argued that capturing the benefits of DCV would promote adoption of variable speed fans, provide more flexibility in building operation, and reduce energy use. Joint Advocates, No. 9 at p. 2, 4
AHRI and Carrier commented that the performance of the DXDOAS under DCV operation must be characterized prior to developing a test procedure and that adopting provisions to address DCV
operation could significantly increase the cost and complexity of testing. AHRI
further stated that DCV operation is primarily controlled by building operators. Carrier stated that performance would depend highly on the building type, occupancy, and site requirements for demand ventilation.
AHRI, No. 11 at p. 14; Carrier, No. 6 at p. 4
DOE reviewed the comments and considered whether to adopt testing conditions to account for the energy use profiles of models with low supply airflow rates that are typically experienced by units with DCV.
Incorporation of the airflow modulation that would be enabled by DCV might provide more representative efficiency ratings, help in consumer decision making, and potentially promote the market penetration of variable speed
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fans. However, DOE is not aware of representative field data regarding the typical DDXDOAS duty cycle when operating with DCV and, thus, agrees with the comments of AHRI and Carrier that characterization of DCV
performance would be an important first step in integrating this control feature into the test procedure. DOE further agrees that adopting additional testing requirements to capture the effect of DCV could significantly increase testing cost and complexity, as noted in comments provided by AHRI and Carrier. Given the lack of data on infield performance and the anticipated additional testing burden of such a test, DOE has tentatively decided not to include performance under DCV
operation in its proposed test procedure for DDXDOASes at this time.
j. Tolerances for Supply and Return Airflow and External Static Pressure DOE noted in the July 2017 ASHRAE
TP RFI that Table 1 of ANSI/ASHRAE
1982013 includes operating and condition tolerances of 5 percent for airflow rate. 82 FR 34427, 34439 July 25, 2017. It includes a test operating tolerance for ESP equal to 0.05 in H2O
and a test condition tolerance for ESP of 0.02 in H2O. As provided in section 5.2.2 of ANSI/AHRI 9202015, the airflow rate and ESPs are set at Standard Rating Condition C dry-bulb temperatures without the refrigeration systems and energy recovery if applicable in operation. ANSI/AHRI
9202015 states in section 5.2.2.4 that once the airflow rate is set, the fan speeds shall not be adjusted for the remaining tests. DDXDOAS units that are for use with air ducting are required by the industry test standard to be set up with ESP requirements in Table 4 of ANSI/AHRI 9202015, and units tested as if they would be installed without ducts are tested with 0 in H2O ESP.
DOE notes that while operating in dehumidification mode, the airflow rates and ESPs may fluctuate more than for dry operation as condensate accumulates and then drains from the cooling coil. In addition, for dehumidification and heating tests, the density of supply air may be different, which may change fan performance, and, thus, the ESP. These factors could cause the supply air ESP to fluctuate more than the operating tolerances specified in Table 1 of ANSI/ASHRAE
1982013, and/or to deviate from the specified ESP by more than the test condition tolerance. Likewise, the airflow rates could fluctuate more than the specified operating tolerances, and the average airflows could deviate by more than the test condition tolerances
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