INTERPOLATION OF UTILITY AND ENVIRONMENTAL RESULTS FROM 

NEMS-BT OUTPUT 

LIST OF TABLES 

Table 14A.1 Set of Multipliers for Various Home Appliance Standards...................... 14A-2 

LIST OF FIGURE 

Figure 14A.1 An Example of Interpolation of a Trial Standard Level: Difference in 

Coal Capacity............................................................................................ 14A-3 

Figure 14A.2 An Example of Trial Standard Level: X1 Marginal NOx Emissions ....... 14A-4 

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EERE-2006-STD-0127 COMMENT 64.2
APPENDIX 14A. INTERPOLATION OF UTILITY AND ENVIRONMENTAL 

RESULTS FROM NEMS-BT OUTPUT 

The effects of proposed home appliances energy-efficiency standards on the electricity 

and natural gas industries were analyzed using a variant of the U.S. DOE/EIA National Energy 

Modeling System (NEMS) called NEMS-BT, together with some exogenous calculations. 

Because the relative size of the energy savings being implemented in NEMS-BT is too small to 

be seen in the context of the whole electricity and natural gas utility sector, NEMS-BT is not 

used directly. Rather, exploratory runs are conducted to estimate marginal effects, which are 

then used to calculate the small effects due to each proposed trial standard level. 

To run a simulation in NEMS-BT, the Residential Demand Module cooking load or the 

Commercial Demand Module water heating load is reduced annually according to the energy 

savings estimated by the National Energy Savings model (see Chapter 13) for a given trial 

standard level. These energy savings increase over time and are distinguished by fuel type 

(electricity, natural gas, LPG, and oil). 

The magnitude of the energy decrement that would be required for NEMS-BT to produce 

stable results safely out of the range of numerical noise is greater than even the most stringent 

standard under consideration. Therefore, it has been necessary, in both the utility analysis and 

environmental assessment, to estimate results in the range of the standard levels effects using 

interpolation. Interpolated values are derived from a series of higher decrement simulations 

based on the standard levels. The actual annual savings attributed to each standard level are 

compared between standard levels, and those with similar energy savings patterns over time are 

grouped together. One set of simulations is run for each of the savings groups. The standard 

levels for the residential and commercial home appliances analysis were modeled separately for 

each appliance: 

Residential Cooking Standard Level 4: used to model Standard Levels 1, 2, and 3. 

Residential Microwave Ovens Standard Level 4: used to model Standard Levels 1, 2, and 3. 

To preserve the pattern of energy savings over time for a trial standard level, savings in 

each year were multiplied by the same factor. This factor varies between standards because the 

magnitude of the savings changes. An appropriate set of multipliers was chosen to augment the 

savings to a magnitude that produces credible results. Using professional judgement, sets of 

three or four multipliers were selected for each of the modeled trial standard levels as shown in 

Table 14A.1. 

14A-1

EERE-2006-STD-0127 COMMENT 64.2
Table 14A.1 Set of Multipliers for Various Home Appliance Standards 

Cooking Trial Standard Level 4 25, 50, 60, 75 

Microwave Oven Trial Standard Level 4 50, 100, 150, 200 

The output for electricity generation and capacity by fuel type for each of the iterations 

(e.g., 25, 50, and 75 times the standard level) is then regressed, with the y-intercept forced 

through the origin, and the actual standard level forecast is interpolated along this regression line. 

The linear regression is forced through the origin because a zero change must be the case with no 

standard in place and because the target points of interpolation are close to the origin (i.e., at low 

energy decrements). 

Figure 14A.1 shows an example of the interpolation approach for a proposed trial 

standard level X1. The magnitude of the energy savings multiplier is plotted on the x-axis 

against the reduction in coal installed generating capacity for each reported year, as shown by the 

various plotted lines. In general, results for the various NEMS-BT runs are reasonably stable 

and linear, with the noisy behavior appearing below the first multiplier of the trial standard level 

savings decrement. 

The Department used the interpolated total fuel generation at each trial standard level to 

determine emissions savings. Wherever possible, the environmental assessment analysis used 

marginal emissions rates over average emissions rates. However, as will be discussed further in 

this appendix, difficulties arose with using marginal rates in all circumstances and alternative 

methods needed to be used. Marginal emissions rates incorporate both effects of the standards— 

the emissions saved by the reduction in total generation and the slight change in the emissions 

characteristics of the whole power sector that result from the slight change in dispatch and 

capacity expansion plan. The net effect on the entire system is very small and, typically, the 

overall effect on emissions can be fully attributed to the decremented generation. The annual 

marginal emissions rates at the trial standard level were extrapolated from these rates (at 

multipliers of the trial standard level savings) by taking a simple average. 

Figure 14A.2 shows an example of the extrapolation for NOx emissions rates for trial 

standard level X1. In this case, marginal rates for NOx emissions are shown for each year. As is 

evident in the figure, more stable results are produced at higher levels of demand decrement. At 

lower decrement levels (i.e., both on the left-hand side of the figure and in years with small 

standards impacts), the emissions rate is quite variable. The dashed lines show the earlier years 

of the imposed standard—those in which the decrements to demand are smallest. The constant 

emissions rates at higher decrement levels are therefore assumed to hold in the range of small 

decrements commensurate with the various standard levels and the implied marginal emissions 

rates are used to estimate emissions reductions. 

Wherever possible, the Department calculated annual marginal emissions rates for each 

of the simulations in each modeled standard level, based on the actual output from NEMS-BT. 

Total emissions savings in each year are the product of the annual marginal emissions rate and 

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EERE-2006-STD-0127 COMMENT 64.2
the reduction in generation (by fuel or collectively) for that year (as calculated by the 

interpolation method described above). 

-25.0 

-20.0 

-15.0 

-10.0 

-5.0 

0.0 

Multiplier 

GW 

2015 

2020 

2025 

2030 

2015 Regression 

2020 Regression 

2025 Regression 

2030 Regression 

No Std. Level 100x Std. 

Level X1 

200x Std. 

Level X1 

150x Std. 

Level X1 

50x Std. 

Level X1 

Figure 14A.1 An Example of Interpolation of a Trial Standard Level: Difference in 

Coal Capacity 

14A-3

EERE-2006-STD-0127 COMMENT 64.2
-1.0 

-0.8 

-0.6 

-0.4 

-0.2 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

Multiplier 

g/kWh 

2003 

2004 

2005 

2006 

2007 

2008 

2009 

2 0 10 

2 0 11 

2 0 12 

2 0 13 

2 0 14 

2 0 15 

2 0 16 

2 0 17 

2 0 18 

2 0 19 

2020 

2021 

2022 

2023 

2024 

2025 

2026 

2027 

2028 

2029 

2030 

50x Std. Level X1 100x Std. Level X1 150x Std. Level X1 200x Std. Level X1 

Figure 14A.2 An Example of Trial Standard Level: X1 Marginal NOx Emissions 

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EERE-2006-STD-0127 COMMENT 64.2