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Federal Register / Vol. 86, No. 110 / Thursday, June 10, 2021 / Proposed Rules TABLE IV.6BOILER ENERGY USE DUE TO UFHWST HEAT LOSSES IN 2025 MMBTU/YR 12
Capacity US gal EL
50

0
1
2

175

1.76
1.55
1.41

375

2.78
2.39
2.13

750

4.71
3.97
3.48

1500

8.59
7.32
6.48

3500

11.44
9.63
8.42

21.09
17.45
15.02

5000
25.27
20.80
17.83

TABLE IV.7SAVINGS IN BOILER ENERGY USE DUE TO REDUCED UFHWST HEAT LOSSES IN 2025 MMBTU/YR
Capacity US gal EL
50
1
2

khammond on DSKJM1Z7X2PROD with PROPOSALS

3. Additional Sources of Uncertainty As discussed in section IV.B.2 of this document, the inputs to DOEs tank thermal loss model were primarily based on publicly-available information, DOEs previous knowledge of UFHWSTs, and feedback from manufacturers received during interviews conducted under NDAs. To validate the model, DOE compared the results produced by the model to results of testing previously conducted to evaluate the performance-based test procedure proposed for UFHWSTs in the May 2016 CWH TP NOPR, which was largely based on the standby loss test procedure for commercial storage water heaters. The proposed test procedure included a standby loss test that would be conducted as the mean tank water temperatures decay from 142 F to 138 F at a nominal ambient temperature of 75 F. 81 FR 28588, 28603 May 9, 2016. Standby loss tests were conducted on 17 UFHWSTs with an advertised insulation level of R12.5
and storage volumes of 40, 80, or 120
gallons in order to gather data on whether measured standby losses were consistent with what would be expected from tanks insulated to their rated and/
or advertised insulation levels, to assess the repeatability and sensitivity of the proposed test procedure, and to gather data on the potential burden in conducting the testing.
DOE used the same analytical model described in this section to calculate the expected losses from each of these tanks, using their measured dimensions and actual number of ports. As discussed, the internal water temperature 140 F and ambient air temperature 75 F used for the analytical model were the same as the 12 The projected value for Boiler Efficiency Boilern is 0.922 in 2027, see section IV.F.2 of this document for more details.

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Jkt 253001

0.21
0.35

175

I

0.39
0.64

375

I

0.74
1.23

average temperatures seen during the physical testing. The same assumptions about insulation details e.g., R-values for different materials and the use of fiberglass around ports were used as were used for the baseline R12.5
units in DOEs thermal loss model. The average predicted rate of standby losses for these tanks were 73 percent of the measured standby losses and ranged from as low as 58 percent of the measured losses up to 90 percent of the measured losses. Because the estimated standby losses are significantly lower than the measured losses, this suggests that DOEs thermal loss model undercounts the actual standby losses that would occur in the field.
Furthermore, the wide range in calculated standby losses as compared to measured standby losses indicates that the accuracy of the thermal loss calculations in predicting the standby losses of a particular model will be somewhat unpredictable, thereby adding additional uncertainty.
Furthermore, when DOE conducted standby loss tests of UFHWSTs, it found that tanks with identical storage volumes, dimensions, number of ports, and nominal insulation levels differed by up to 8.5 percent, whereas DOEs model would predict the same level of standby losses for these tanks. This finding suggests that there may be variations in the extent of R12.5
coverage between units, even between units from the same manufacturer. As discussed in section IV.B.2 of this document, it may not be practical to insulate all surfaces of UFHWSTs with polyurethane foam due to the nature of the insulation application process or the need to retain access to certain ports.
Differences in manufacturers tank designs, manufacturing processes, or their interpretations of the R12.5
insulation requirement could lead to variations in the amount of tank surface
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750

1500

1.26
2.10

I

I

1.81
3.02

3500

I

3.64
6.07

5000
4.47
7.44

area that is actually insulated with R
12.5. Therefore, tanks that appear to have the same attributes and insulation may have different levels of standby losses in the field. This source of potential variation in standby losses further supports DOEs conclusion that there may be additional sources of thermal losses that vary between tanks and that are not adequately captured in its current thermal loss model. This variation also makes it very difficult for DOE to characterize the representative performance of a baseline UFHWST, or the expected performance at any potential amended standard level, with a high degree of confidence since there is significant variation in thermal energy losses at a given efficiency level Rvalue that cannot be readily predicted or otherwise accounted for in the analysis. Due to these potential variations in insulation coverage and because DOE has not been able to verify its thermal loss model against its physical test results, there is significant uncertainty as to the validity of its energy use analysis.
D. Life-Cycle Cost and Payback Period Analysis To determine whether a standard is economically justified, EPCA requires DOE to consider the economic impact of the standard on manufacturers and consumers, as well as the savings in operating costs throughout the estimated average life of the equipment compared to any increase in price, initial charges, or maintenance expenses of the equipment likely to result from the standard. 42 U.S.C.
6313a6BiiIII The effect of new or amended energy conservation standards on individual consumers usually involves a reduction in operating cost and an increase in purchase cost. To evaluate the economic impacts of potential energy conservation
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