9-i

CHAPTER 9. EMISSIONS ANALYSIS

TABLE OF CONTENTS

9.1 INTRODUCTION ........................................................................................................... 9-1

9.2 AIR EMISSIONS DESCRIPTIONS AND REGULATION........................................... 9-2

9.3 GLOBAL CLIMATE CHANGE..................................................................................... 9-4

9.4 ANALYTICAL METHODS FOR AIR EMISSIONS..................................................... 9-8

9.5 EFFECTS ON POWER PLANT EMISSIONS ............................................................. 9-10

9.6 EFFECTS ON UPSTREAM FUEL-CYCLE EMISSIONS .......................................... 9-14

9.7 SUMMARY OF EMISSIONS IMPACTS .................................................................... 9-14

LIST OF TABLES

Table 9.3.1 Reduction in Cumulative Energy-Related Emissions of CO2 over the 

analysis period for ASHRAE Energy Conservation Standards* ......................... 9-7

Table 9.5.1 Power Sector Emissions Projection from AEO2011 Reference Case................ 9-10

Table 9.5.2 Power Sector Emissions Impacts Forecasts for Water-Cooled and 

Evaporatively-Cooled Product Efficiency Levels ............................................. 9-11

Table 9.5.3 Power Sector Emissions Impact Forecasts for VRF Water-Source Heat 

Pump Efficiency Levels..................................................................................... 9-12

Table 9.5.4 Power Sector Emissions Impact Forecasts for Computer Room Air 

Conditioner Efficiency Levels........................................................................... 9-13

Table 9.6.1 Estimated Upstream Emissions of Air Pollutants as a Percentage of Direct 

Power Plant Combustion Emissions.................................................................. 9-14

Table 9.7.1 Cumulative Emissions Reductions Under ASHRAE Efficiency Levels* ......... 9-15
9-1

CHAPTER 9. EMISSIONS ANALYSIS 

9.1 INTRODUCTION

This chapter describes potential changes to emissions of carbon dioxide (CO2) and three 

air pollutants that may result from energy conservation standards for water-cooled and 

evaporatively-cooled products, VRF water-source heat pumps, and computer room air 

conditioners. The impacts on air emissions are largely driven by changes in power plant types 

and quantities of electricity generated under each of the considered standard levels. Changes in 

electricity generation are described in the utility impact analysis in chapter 11. 

DOE analyzed the effects of its amended standard levels on the electric utility industry 

using a variant of the DOE/Energy Information Administration (EIA)’s National Energy 

Modeling System (NEMS).a

 NEMS is a public domain, multi-sectored, partial equilibrium 

model of the U.S. energy sector. Each year, DOE/EIA uses NEMS to produce an energy forecast 

for the United States, the Annual Energy Outlook (AEO). The AEO for 2011 (AEO2011) 

forecasts energy supply and demand through 2035. 1

 DOE used a variant of this model, referred 

to as NEMS-BT,b

NEMS-BT has several advantages that have led to its adoption as the forecasting tool in 

the analysis of energy conservation standards. NEMS-BT uses a set of assumptions that are well 

known and fairly transparent, due to the exposure and scrutiny each AEO receives. In addition, 

the comprehensiveness of NEMS-BT permits the modeling of interactions among the various 

energy supply and demand sectors, producing a complete picture of the effects of energy 

conservation standards. Perhaps most importantly, NEMS-BT can be used to estimate marginal 

effects, which yield a better estimate of the actual impact of energy conservation standards than 

considering only average effects.

to account for the impacts of energy conservation standards for water and 

evaporative cooled products, VRF water source heat pumps, and computer room air conditioners. 

DOE’s analysis consists of a comparison between model results for the AEO2011 Reference 

Case and for cases in which standards are in place, and applies the same basic set of assumptions 

as the AEO2011. The AEO2011 reference case corresponds to medium economic growth.

 

a For more information on NEMS, refer to the U.S. Department of Energy, Energy Information Administration 

documentation. A useful summary is National Energy Modeling System: An Overview 2003, DOE/EIA-0581(2003), 

March, 2003. 

b DOE/EIA approves use of the name NEMS to describe only an official version of the model without any 

modification to code or data. Because this analysis entails some minor code modifications and the model is run 

under various policy scenarios that are variations on DOE/EIA assumptions, DOE refers to it by the name NEMSBT (BT is DOE’s Building Technologies Program, under whose aegis this work has been performed). NEMS-BT 

was previously called NEMS-BRS.
9-2

9.2 AIR EMISSIONS DESCRIPTIONS AND REGULATION

This analysis considers three pollutants: sulfur dioxide (SO2), nitrogen oxides (NOX), and 

mercury (Hg). An air pollutant is any substance in the air that can cause harm to humans or the 

environment. Pollutants may be natural or man-made (i.e., anthropogenic) and may take the form 

of solid particles (i.e., particulates or particulate matter), liquid droplets, or gases.c DOE’s

analysis also considers carbon dioxide (CO2). 

Sulfur Dioxide. Sulfur dioxide, or SO2, belongs to the family of sulfur oxide gases 

(SOx). These gases dissolve easily in water. Sulfur is prevalent in all raw materials, including 

crude oil, coal, and ore that contains common metals like aluminum, copper, zinc, lead, and iron. 

SOx gases are formed when fuel containing sulfur, such as coal and oil, is burned, and when 

gasoline is extracted from oil, or metals are extracted from ore. SO2 dissolves in water vapor to 

form acid, and interacts with other gases and particles in the air to form sulfates and other 

products that can be harmful to people and their environment.1

Nitrogen Oxides. Nitrogen oxides, or NOX, is the generic term for a group of highly 

reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the 

nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide 

(NO2), along with particles in the air can often be seen as a reddish-brown layer over many urban 

areas. NO2 is the specific form of NOX reported in this document. NOX is one of the main 

ingredients involved in the formation of ground-level ozone, which can trigger serious 

respiratory problems. It can contribute to the formation of acid rain, and can impair visibility in 

areas such as national parks. NOX also contributes to the formation of fine particles that can 

impair human health.2

Nitrogen oxides form when fossil fuel is burned at high temperatures, as in a combustion 

process. The primary manmade sources of NOX are motor vehicles, electric utilities, and other 

industrial, commercial, and residential sources that burn fossil fuels. NOX can also be formed 

naturally. Electric utilities account for about 22 percent of NOX emissions in the United States.2

Mercury. Coal-fired power plants emit mercury (Hg) found in coal during the burning 

process. While coal-fired power plants are the largest remaining source of human-generated Hg 

emissions in the United States, they contribute very little to the global Hg pool or to 

contamination of U.S. waters.3 U.S. coal-fired power plants emit Hg in three different forms: 

oxidized Hg (likely to deposit within the United States); elemental Hg, which can travel 

thousands of miles before depositing to land and water; and Hg that is in particulate form. 

Atmospheric Hg is then deposited on land, lakes, rivers, and estuaries through rain, snow, and 

dry deposition. Once there, it can transform into methylmercury and accumulate in fish tissue 

through bioaccumulation. 

Americans are exposed to methylmercury primarily by eating contaminated fish. Because 

the developing fetus is the most sensitive to the toxic effects of methylmercury, women of 

 

c More information on air pollution characteristics and regulations is available on the U.S. Environment Protection 

Agent (EPA)’s website at www.epa.gov.
9-3

childbearing age are regarded as the population of greatest concern. Children exposed to 

methylmercury before birth may be at increased risk of poor performance on neurobehavioral 

tasks, such as those measuring attention, fine motor function, language skills, visual-spatial 

abilities, and verbal memory.4

Carbon Dioxide. Carbon dioxide (CO2) is not a criteria pollutant (see below), but it is of 

interest because of its classification as a greenhouse gas (GHG). GHGs trap the sun’s radiation 

inside the Earth’s atmosphere and either occur naturally in the atmosphere or result from human 

activities. Naturally occurring GHGs include water vapor, CO2, methane (CH4), nitrous oxide 

(N2O), and ozone (O3). Human activities, however, add to the levels of most of these naturally 

occurring gases. For example, CO2 is emitted to the atmosphere when solid waste, fossil fuels 

(oil, natural gas, and coal), wood, and wood products are burned. In 2007, over 90 percent of 

anthropogenic (i.e., human-made) CO2 emissions resulted from burning fossil fuels.5

Concentrations of CO2 in the atmosphere are naturally regulated by numerous processes, 

collectively known as the “carbon cycle.” The movement of carbon between the atmosphere and 

the land and oceans is dominated by natural processes, such as plant photosynthesis. While these 

natural processes can absorb some of the anthropogenic CO2 emissions produced each year, 

billions of metric tons are added to the atmosphere annually. In the United States, in 2007, CO2

emissions from electricity generation accounted for 39 percent of total U.S. GHG emissions.5

Particulate Matter. Particulate matter (PM), also known as particle pollution, is a 

complex mixture of extremely small particles and liquid droplets. Particle pollution is made up 

of a number of components, including acids (such as nitrates and sulfates), organic chemicals, 

metals, and soil or dust particles.

PM impacts are of concern due to human exposures that can impact health. Particle 

pollution - especially fine particles - contains microscopic solids or liquid droplets that are so 

small that they can get deep into the lungs and cause serious health problems. Numerous 

scientific studies have linked particle pollution exposure to a variety of problems, including: 

increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty 

breathing, for example; decreased lung function; aggravated asthma; development of chronic 

bronchitis; irregular heartbeat; nonfatal heart attacks; and premature death in people with heart or 

lung disease.

DOE acknowledges that particulate matter (PM) exposure can impact human health. 

Power plant emissions can have either direct or indirect impacts on PM. A portion of the 

pollutants emitted by a power plant are in the form of particulates as they leave the smoke stack. 

These are direct, or primary, PM emissions. However, the great majority of PM emissions 

associated with power plants are in the form of secondary sulfates, which are produced at a 

significant distance from power plants by complex atmospheric chemical reactions that often 

involve the gaseous (non-particulate) emissions of power plants, mainly SO2 and NOx. The 

quantity of the secondary sulfates produced is determined by a very complex set of factors 

including the atmospheric quantities of SO2 and NOx, and other atmospheric constituents and 

conditions. Because these highly complex chemical reactions produce PM comprised of different 

constituents from different sources, EPA does not distinguish direct PM emissions from power 
9-4

plants from the secondary sulfate particulates in its ambient air quality requirements, PM 

monitoring of ambient air quality, or PM emissions inventories. For these reasons, it is not 

currently possible to determine how the amended standard impacts either direct or indirect PM 

emissions. Therefore, DOE is not planning to assess the impact of these standards on PM 

emissions. Further, as described below, it is uncertain whether efficiency standards will result in 

a net decrease in power plant emissions of SO2, and of NOx in many States, since those pollutants 

are now largely regulated by cap and trade systems. 

Air Quality Regulation. The Clean Air Act Amendments of 1990 list 188 toxic air 

pollutants that EPA is required to control.6 EPA has set national air quality standards for six

common pollutants (also referred to as “criteria” pollutants), two of which are SO2 and NOX. 

Also, the Clean Air Act Amendments of 1990 gave EPA the authority to control acidification 

and to require operators of electric power plants to reduce emissions of SO2 and NOX. Title IV of 

the 1990 amendments established a cap-and-trade program for SO2, in all 50 states and the 

District of Columbia (D.C.), intended to help control acid rain.

6 This cap-and-trade program 

serves as a model for more recent programs with similar features.

In 2005, EPA issued the Clean Air Interstate Rule (CAIR) under sections 110 and 111 of 

the Clean Air Act (40 CFR Parts 51, 96, and 97).d 70 FR 25162–25405 (May 12, 2005). CAIR 

limited emissions from 28 eastern States and D.C. by capping emissions and creating an 

allowance-based trading program. Although, CAIR was remanded to EPA by the U.S. Court of 

Appeals for the District of Columbia Circuit (D.C. Circuit), (see North Carolina v. EPA, 550 

F.3d 1176 (D.C. Cir. 2008),) it remained in effect temporarily, consistent with the D.C. Circuit’s 

earlier opinion in North Carolina v. EPA, 531 F.3d 896 (D.C. Cir. 2008). 

On July 6, 2010, EPA issued the Transport Rule proposal, a replacement for CAIR. 75 

FR 45210 (Aug. 2, 2010). On July 6, 2011, EPA promulgated the final Transport Rule, entitled 

“Federal Implementation Plans: Interstate Transport of Fine Particulate Matter and Ozone and 

Correction of SIP Approvals,” but commonly referred to as the Cross-State Air Pollution Rule or 

the Transport Rule. 76 FR 48208 (Aug. 8, 2011). On December 30, 2011, however, the D.C. 

Circuit stayed the new rules while a panel of judges reviews them, and told EPA to continue 

enforcing CAIR (see EME Homer City Generation v. EPA, No. 11-1302, Order at *2 (D.C. Cir. 

Dec. 30, 2011)).

On December 21, 2011, EPA announced national emissions standards for hazardous air 

pollutants (NESHAPs) for mercury and certain other pollutants emitted from coal and oil-fired 

EGUs. 76 FR 24976. The NESHAPs do not include emissions caps and, as such, DOE’s energy 

conservation standards would likely reduce Hg emissions.

9.3 GLOBAL CLIMATE CHANGE

Climate change has evolved into a matter of global concern because it is expected to have 

widespread, adverse effects on natural resources and systems. A growing body of evidence 

 

d See http://www.epa.gov/cleanairinterstaterule/.
9-5

points to anthropogenic sources of greenhouse gases, such as carbon dioxide (CO2), as major 

contributors to climate change. Because this rule, if finalized, will likely decrease CO2 emission 

rates from the fossil fuel sector in the United States, the Department here examines the impacts 

and causes of climate change and then the potential impact of the rule on CO2 emissions and 

global warming. 

Impacts of Climate Change on the Environment. Climate is usually defined as the 

average weather, over a period ranging from months to many years. Climate change refers to a 

change in the state of the climate, which is identifiable through changes in the mean and/or the 

variability of its properties (e.g., temperature or precipitation) over an extended period, typically 

decades or longer. 

The World Meteorological Organization and United Nations Environment Programme 

(UNEP) established the Intergovernmental Panel on Climate Change (IPCC) to provide an

objective source of information about climate change. According to the IPCC Fourth Assessment 

Report (IPCC Report), published in 2007, climate change is consistent with observed changes to 

the world’s natural systems; the IPCC expects these changes to continue.

7

Changes that are consistent with warming include warming of the world’s oceans to a 

depth of 3000 meters; global average sea level rise at an average rate of 1.8 mm per year from 

1961 to 2003; loss of annual average Arctic sea ice at a rate of 2.7 percent per decade, changes in 

wind patterns that affect extra-tropical storm tracks and temperature patterns, increases in intense 

precipitation in some parts of the world, as well as increased drought and more frequent heat 

waves in many locations worldwide, and numerous ecological changes.

8

Looking forward, the IPCC describes continued global warming of about 0.2 °C per 

decade for the next two decades under a wide range of emission scenarios for carbon dioxide 

(CO2), other greenhouse gases (GHGs), and aerosols. After that period, the rate of increase is 

less certain. The IPCC Report describes increases in average global temperatures of about 1.1 °C 

to 6.4 °C at the end of the century relative to today. These increases vary depending on the model 

and emissions scenarios.

8

The IPCC Report describes incremental impacts associated with the rise in temperature. 

At ranges of incremental increases to the global average temperature, IPCC reports, with either 

high or very high confidence, that there is likely to be an increasing degree of impacts such as 

coral reef bleaching, loss of wildlife habitat, loss to specific ecosystems, and negative yield 

impacts for major cereal crops in the tropics, but also projects that there likely will be some 

beneficial impacts on crop yields in temperate regions. 

Causes of Climate Change. The IPCC Report states that the world has warmed by about 

0.74 °C in the last 100 years. The IPCC Report finds that most of the temperature increase since 

the mid-20th century is very likely due to the increase in anthropogenic concentrations of CO2

and other long-lived greenhouse gases such as methane and nitrous oxide in the atmosphere, 

rather than from natural causes. 
9-6

Increasing the CO2 concentration partially blocks the earth’s re-radiation of captured 

solar energy in the infrared band, inhibits the radiant cooling of the earth, and thereby alters the 

energy balance of the planet, which gradually increases its average temperature. The IPCC 

Report estimates that currently, CO2 makes up about 77 percent of the total CO2-equivalente

global warming potential in GHGs emitted from human activities, with the vast majority (74 

percent) of the CO2 attributable to fossil fuel use.8 For the future, the IPCC Report describes a 

wide range of GHG emissions scenarios, but under each scenario CO2 would continue to 

comprise above 70 percent of the total global warming potential.9

Stabilization of CO2 Concentrations. Unlike many traditional air pollutants, CO2 mixes 

thoroughly in the entire atmosphere and is long-lived. The residence time of CO2 in the 

atmosphere is long compared to the emission processes. Therefore, the global cumulative 

emissions of CO2 over long periods determine CO2 concentrations because it takes hundreds of 

years for natural processes to remove the CO2. Globally, 49 billion metric tons of CO2 –

equivalent of anthropogenic (man-made) greenhouse gases are emitted every year.f Of this 

annual total, fossil fuels contribute about 29 billion metric tons of CO2.

9

Researchers have focused on considering atmospheric CO2 concentrations that likely will 

result in some level of global climate stabilization, and the emission rates associated with 

achieving the “stabilizing” concentrations by particular dates. They associate these stabilized 

CO2 concentrations with temperature increases that plateau in a defined range. For example, at 

the low end, the IPCC Report scenarios target CO2 stabilized concentrations range between 350 

ppm and 400 ppm (essentially today’s value)—because of climate inertia, concentrations in this 

low-end range would still result in temperatures projected to increase 2.0 °C to 2.4 °C above preindustrial levelsg (about 1.3 °C to 1.7 °C above today’s levels). To achieve concentrations 

between 350 ppm to 400 ppm, the IPCC scenarios present that there would have to be a rapid 

downward trend in total annual global emissions of greenhouse gases to levels that are 50 to 85 

percent below today’s annual emission rates by no later than 2050. Since it is assumed that there 

would continue to be growth in global population and substantial increases in economic 

production, the scenarios identify required reductions in greenhouse gas emissions intensity 

(emissions per unit of output) of more than 90 percent. However, even at these rates, the 

scenarios describe some warming and some climate change is projected due to already 

accumulated CO2 and GHGs in the atmosphere.10

The Beneficial Impact of the Rule on CO2 Emissions. It is anticipated that the Rule will 

reduce energy-related CO2 emissions, particularly those associated with energy consumption in 

buildings. The U.S. Energy Information Administration (EIA) reports in its 2011 Annual Energy 

 e GHGs differ in their warming influence (radiative forcing) on a global climate system due to their different 

radiative properties and lifetimes in the atmosphere. These warming influences may be expressed through a common 

metric based on the radiative forcing of CO2, i.e., CO2-equivalent. CO2 equivalent emission is the amount of CO2

emission that would cause the same- time integrated radiative forcing, over a given time horizon, as an emitted 

amount of other long- lived GHG or mixture of GHGs.

f Other non-fossil fuel contributors include CO2 emissions from deforestation and decay from agriculture biomass; 

agricultural and industrial emissions of methane; and emissions of nitrous oxide and fluorocarbons.

g IPCC Working Group 3 Table TS 2
9-7

Outlook (AEO2011)

11 that U.S. annual energy-related emissions of CO2 in 2009 were about 5.4 

billion metric tons, of which 1.2 billion tons were attributed to the residential buildings sector

(including energy-using products such as space cooling products). Most of the greenhouse gas 

emissions attributed to residential buildings are emitted from fossil fuel-fired power plants that 

generate electricity used in this sector. In the AEO2011 Reference Case, EIA projected that 

annual energy-related CO2 emissions would grow from 5.4 billion metric tons in 2009 to 6.3 

billion metric tons in 2035, an increase of 16 percent, while residential emissions would grow to 

from 1.17 billion metric tons to 1.23 billion metric tons, an increase of 5 percent. 

The estimated cumulative CO2 emission reductions from energy conservation standards

(shown as a range of alternative Efficiency Levels) for water and evaporatively cooled products, 

VRF water source heat pumps, and computer room air conditioners, during the 30-year analysis 

period are indicated in Table 9.3.1. Estimated CO2 emission reductions in Table 9.3.1 only come 

from electricity generation (i.e., power plants). The estimated CO2 emission reductions from 

electricity generation are calculated using the NEMS-BT model.

Table 9.3.1 Reduction in Cumulative Energy-Related Emissions of CO2 over the analysis 

period for ASHRAE Energy Conservation Standards*

Efficiency Levels

Level 1 Level 2 Level 3 Level 4 Level 5

Million Metric Tons 

Water-cooled and 

Evaporatively-cooled Products 0.099 0.096 0.253 0.363 0.371

VRF Water-source Heat Pumps 0.000 0.054 0.823 1.96 3.58

Computer Room Air 

Conditioners 0.177 2.14 8.06 18.7 31.1

Total 0.276 2.29 9.13 21.1 35.1

Percent of Total Cumulative 

Emissions Reduction compared 

with the AEO2011 Reference 

Case in 2014-2043

0.00 0.00 0.01 0.03 0.05

*The analysis period for water-cooled and evaporatively-cooled products runs from 2013 through 2043.

The analysis period for VRF water-source heat pumps runs from 2013 through 2042.

The analysis period Computer Room Air Conditioners runs from 2012 through 2042.

The Incremental Impact of the Rule on Climate Change. It is difficult to correlate 

specific emission rates with atmospheric concentrations of CO2 and specific atmospheric 

concentrations with future temperatures because the IPCC Report describes a clear lag in the 

climate system between any given concentration of CO2 (even if maintained for long periods) 

and the subsequent average worldwide and regional temperature, precipitation, and extreme 

weather regimes. For example, a major determinant of climate response is “equilibrium climate 

sensitivity”, a measure of the climate system response to sustained radiative forcing. It is defined 

as the global average surface warming following a doubling of carbon dioxide concentrations. 
9-8

The IPCC Report describes its estimated, numeric value as about 3 °C, but the likely range of 

that value is 2 °C to 4.5 °C, with cloud feedbacks the largest source of uncertainty. Further, as 

illustrated above, the IPCC Report scenarios for stabilization rates are presented in terms of a 

range of concentrations, which then correlates to a range of temperature changes. Thus, climate 

sensitivity is a key uncertainty for CO2 mitigation scenarios that aim to meet specific temperature 

levels. 

Because of how complex global climate systems are, it is difficult to know to what extent 

and when particular CO2 emissions reductions will impact global warming. However, as Table 

16.3.1 indicates, the rule is expected to reduce CO2 emissions associated with energy 

consumption in buildings. 

9.4 ANALYTICAL METHODS FOR AIR EMISSIONS 

For each of the considered Efficiency Levels, DOE calculated total power-sector 

emissions based on output from the NEMS-BT model.

NEMS provides reference case load shapes for several end uses. The model uses predicted 

growth in demand for each end use to build up a projection of the total electric system load growth 

for each region, which it uses in turn to predict the necessary additions to capacity. DOE uses 

NEMS-BT to account for the implementation of energy conservation standards by decrementing the 

appropriate reference case load shape. For ASHRAE products the cooling end use load shape was 

selected, and the NEMS was decremented with commercial sector energy savings. The energy 

decrements are also divided amongst the nine U.S. Census divisions based upon the share of energy 

end use consumption in each division, as given in NEMS.

DOE used the site energy savings developed in the national impact analysis (chapter 8) for 

each Efficiency Level as input to NEMS-BT. The magnitude of the energy decrement that would be 

required for NEMS-BT to produce stable results out of the range of numerical noise is larger than the 

highest efficiency standard under consideration. Therefore, DOE estimated results corresponding to 

each Efficiency Level using interpolation. DOE ran higher energy use reduction levels in NEMS-BT, 

representing multipliers of each Efficiency Level, and used these outputs to linearly interpolate the 

results to estimate actual changes in generation and capacity due to the standard.

Although the current time horizon of NEMS-BT is 2035, other parts of the energy 

conservation standards analysis extend through the year 2043. It is not feasible to extend the forecast 

period of NEMS-BT for the purposes of this analysis, nor does DOE/EIA have an approved method 

for extrapolation of many outputs beyond 2035. While it might seem reasonable to make simple 

linear extrapolations of results, in practice this is not advisable because outputs could be 

contradictory. An analysis of various trends sufficiently detailed to guarantee consistency is beyond 

the scope of this work, and, in any case, would involve a great deal of uncertainty. Therefore, all 

extrapolations beyond 2035 are simple replications of year 2035 results. To emphasize the 

extrapolated results wherever they appear, they are shaded in gray to distinguish them from actual 

NEMS-BT results.
9-9

Coal-fired electric generation is the single largest source of electricity in the United 

States. Because the mix of coals used significantly affects the emissions produced, the model 

includes a detailed representation of coal supply. The model considers the rank of the coal as 

well as the sulfur contents of the fuel used when determining optimal dispatch.

Within the NEMS-BT model, planning options for achieving emissions restrictions in the 

Clean Air Act Amendments include installing pollution control equipment on existing power 

plants and building new power plants with low emission rates. These methods for reducing 

emission are compared to dispatching options such as fuel switching and allowance trading. 

Environmental regulations also affect capacity expansion decisions. For instance, new plants are 

not allocated SO2 emissions allowances according to the Clean Air Act Amendments. 

Consequently, the decision to build a particular capacity type must consider the cost (if any) of 

obtaining sufficient allowances. This could involve purchasing allowances or over-complying at 

an existing unit.

For this analysis, DOE used the version of NEMS-BT based on AEO 2011, which 

assumes the implementation of CAIR. Thus, DOE’s analysis assumes the presence of nationwide 

emission caps on SO2 and caps on NOX emissions in the 28 States covered by CAIR. DOE 

expects that the NEMS-BT based on AEO 2012 will incorporate implementation of the Transport 

Rule.

SO2 emissions from affected Electric Generating Units (EGUs) are subject to nationwide 

and regional emissions cap and trading programs, and DOE has determined that these programs 

create uncertainty about the standards’ impact on SO2 emissions. The attainment of emissions 

caps is typically flexible among EGUs and is enforced through the use of emissions allowances

and tradable permits. Under existing EPA regulations, any excess SO2 emissions allowances 

resulting from the lower electricity demand caused by the imposition of an efficiency standard 

could be used to permit offsetting increases in SO2 emissions by any regulated EGU. However, if 

the standard resulted in a permanent increase in the quantity of unused emissions allowances, 

there would be an overall reduction in SO2 emissions from the standards. While there remains 

some uncertainty about the ultimate effects of efficiency standards on SO2 emissions covered by 

the existing cap and trade system, the NEMS-BT modeling system that DOE uses to forecast 

emissions reductions currently indicates that no physical reductions in power sector emissions 

would occur for SO2.

h

The CAIR established a cap on NOx emissions in 28 eastern states and the District of 

Columbia. All these States and D.C. have elected to reduce their NOx emissions by participating 

in cap-and-trade programs for EGUs. Therefore, energy conservation standards for water and 

evaporatively cooled products, VRF water source heat pumps, and computer room air 

 

h In contrast to the modeling forecasts of NEMS-BT that SO2 emissions will remain at the cap, during the years 2007 

and 2008, SO2 emissions were below the trading cap. This raises the possibility that standards could cause some 

reduction in SO2 emissions. However, because DOE does not have a method to predict when emissions will be 

below the trading cap, it continues to reply on NEMS-BT and thus does not estimate SO2 emissions reductions at 

this time.
9-10

conditioners may have little or no physical effect on these emissions in the 28 eastern States and 

the D.C. for the same reasons that they may have little or no physical effect on SO2 emissions. 

With respect to Hg, in the absence of emissions caps, a DOE standard would likely 

reduce Hg emissions and DOE uses NEMS-BT to estimate these emission reductions.

9.5 EFFECTS ON POWER PLANT EMISSIONS

Table 9.5.1 shows AEO2011 Reference Case power plant emissions in selected years. 

The Reference Case emissions are the emissions shown by the NEMS-BT model to result if none 

of the Efficiency Levels are promulgated (the base case). 

Table 9.5.1 Power Sector Emissions Projection from AEO2011 Reference Case

NEMS-BT Results 2010 2015 2020 2025 2030 2035

CO2 (million metric tons) 2,303 2,138 2,225 2,360 2,444 2,526

NOX (million tons) 2.57 1.98 1.98 2.00 2.01 2.03

Hg (tons) 40.5 26.8 26.8 28.0 28.7 29.3

Table 9.5.2 through Table 9.5.4 show the estimated changes in power plant emissions of 

CO2, NOX, and Hg in selected years for each of the Efficiency Levels considered in this 

rulemaking. As in Table 9.5.1, values for CO2 are given in metric tons, while values for NOX and 

Hg are given in short tons.
9-11

Table 9.5.2 Power Sector Emissions Impacts Forecasts for Water-Cooled and 

Evaporatively-Cooled Product Efficiency Levels

NEMS-BT Results* Difference from AEO2011 Reference Case

Total

2010 2015 2020 2025 2030 2035 2040 2042 2043 2013-2043

ASHRAE

CO2 (Mt/yr) 0.00 0.00 0.00 -0.01 0.00 0.00 0.00 0.00 0.00 -0.099

NOx (1,000 tons/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -0.081

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.001

13 EER (Water)/12.5 EER (Evap)

CO2 (Mt/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -0.096

NOx (kt/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -0.079

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.001

14 EER (13.1 Evap)

CO2 (Mt/yr) 0.00 0.00 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.253

NOx (1,000 tons/yr) 0.00 0.00 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.208

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.003

15 EER (13.1 Evap, 14.8 VL Water)

CO2 (Mt/yr) 0.00 0.00 -0.01 -0.02 -0.02 -0.02 -0.02 -0.02 -0.02 -0.363

NOx (1,000 tons/yr) 0.00 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.298

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.004

Max Tech

CO2 (Mt/yr) 0.00 0.00 -0.01 -0.02 -0.02 -0.02 -0.02 -0.02 -0.02 -0.371

NOx (1,000 tons/yr) 0.00 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.305

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.004

*CO2 results are in metric tons, NOX and Hg results are in short tons.

Extrapolation
9-12

Table 9.5.3 Power Sector Emissions Impact Forecasts for VRF Water-Source Heat 

Pump Efficiency Levels

NEMS-BT Results* Difference from AEO2011 Reference Case

Total

2010 2015 2020 2025 2030 2035 2040 2041 2042 2013-2042

ASHRAE

CO2 (Mt/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000

NOx (1,000 tons/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Level 1

CO2 (Mt/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -0.054

NOx (kt/yr) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -0.044

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.001

Level 2

CO2 (Mt/yr) 0.00 0.01 -0.02 -0.03 -0.04 -0.04 -0.04 -0.04 -0.04 -0.823

NOx (1,000 tons/yr) 0.00 0.00 -0.01 -0.03 -0.03 -0.04 -0.04 -0.04 -0.04 -0.675

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 -0.001 -0.001 -0.001 -0.001 -0.009

Level 3

CO2 (Mt/yr) 0.00 0.01 -0.04 -0.08 -0.08 -0.10 -0.10 -0.10 -0.10 -1.96

NOx (1,000 tons/yr) 0.00 0.01 -0.03 -0.07 -0.07 -0.08 -0.08 -0.08 -0.08 -1.60

Hg (ton/yr) 0.000 0.000 0.000 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.022

Max Tech

CO2 (Mt/yr) 0.00 0.02 -0.07 -0.14 -0.15 -0.19 -0.19 -0.19 -0.19 -3.58

NOx (1,000 tons/yr) 0.00 0.02 -0.06 -0.12 -0.13 -0.15 -0.15 -0.15 -0.15 -2.93

Hg (ton/yr) 0.000 0.000 0.000 -0.001 -0.002 -0.002 -0.002 -0.002 -0.002 -0.040

*CO2 results are in metric tons, NOX and Hg results are in short tons.

Extrapolation
9-13

Table 9.5.4 Power Sector Emissions Impact Forecasts for Computer Room Air 

Conditioner Efficiency Levels

NEMS-BT Results* Difference from AEO2011 Reference Case

Total

2010 2015 2020 2025 2030 2035 2040 2041 2042 2012-2042

ASHRAE

CO2 (Mt/yr) 0.00 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.177

NOx (kt/yr) 0.00 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.145

Hg (ton/yr) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 -0.001

Level 1

CO2 (Mt/yr) 0.00 0.01 -0.04 -0.09 -0.10 -0.10 -0.10 -0.10 -0.10 -2.14

NOx (1,000 tons/yr) 0.00 0.01 -0.04 -0.08 -0.08 -0.08 -0.08 -0.08 -0.08 -1.76

Hg (ton/yr) 0.000 0.000 0.000 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.023

Level 2

CO2 (Mt/yr) 0.00 0.05 -0.16 -0.35 -0.38 -0.40 -0.40 -0.40 -0.40 -8.06

NOx (1,000 tons/yr) 0.00 0.05 -0.14 -0.30 -0.32 -0.32 -0.32 -0.32 -0.32 -6.62

Hg (ton/yr) 0.001 0.000 -0.001 -0.004 -0.005 -0.005 -0.005 -0.005 -0.005 -0.087

Level 3

CO2 (Mt/yr) 0.00 0.12 -0.38 -0.81 -0.89 -0.92 -0.92 -0.92 -0.92 -18.7

NOx (1,000 tons/yr) 0.00 0.11 -0.34 -0.69 -0.73 -0.74 -0.74 -0.74 -0.74 -15.4

Hg (ton/yr) 0.002 0.001 -0.002 -0.008 -0.011 -0.012 -0.012 -0.012 -0.012 -0.203

Max Tech

CO2 (Mt/yr) 0.00 0.20 -0.63 -1.35 -1.48 -1.53 -1.53 -1.53 -1.53 -31.1

NOx (1,000 tons/yr) 0.00 0.18 -0.56 -1.14 -1.22 -1.23 -1.23 -1.23 -1.23 -25.6

Hg (ton/yr) 0.003 0.002 -0.003 -0.014 -0.018 -0.020 -0.020 -0.020 -0.020 -0.337

*CO2 results are in metric tons, NOX and Hg results are in short tons.

Extrapolation
9-14

9.6 EFFECTS ON UPSTREAM FUEL-CYCLE EMISSIONS

Upstream fuel-cycle emissions refer to the emissions associated with the amount of 

energy used in the upstream production and downstream consumption of electricity, including 

energy used at the power plant. Upstream processes include the mining of coal or extraction of 

natural gas, physical preparatory and cleaning processes, and transportation to the power plant. 

The NEMS-BT does a thorough accounting of emissions at the power plant due to downstream 

energy consumption, but does not account for upstream emissions (i.e., emissions from energy 

losses during coal and natural gas production). Thus, this analysis reports only power plant 

emissions.

However, previous DOE environmental assessment documents have developed 

approximate estimates of effects on upstream fuel-cycle emissions. These emissions factors 

provide the reader with a sense of the possible magnitude of upstream effects. These upstream 

emissions would be in addition to emissions from direct combustion. 

Relative to the entire fuel cycle, estimates based on the work of Dr. Mark DeLuchi, and 

reported in earlier DOE environmental assessment documents, find that an amount 

approximately equal to eight percent, by mass, of emissions (including SO2) from coal 

production are due to mining, preparation that includes cleaning the coal, and transportation from 

the mine to the power plant.12 Transportation emissions include emissions from the fuel used by 

the mode of transportation that moves the coal from the mine to the power plant. In addition, 

based on Dr. DeLuchi’s work, DOE estimated that an amount equal to approximately 14 percent 

of emissions from natural gas production result from upstream processes. 

Emission factor estimates and corresponding percentages of contributions of upstream 

emissions from coal and natural gas production, relative to power plant emissions, are shown in 

Table 9.6.1 for CO2 and NOX. The percentages provide a means to estimate upstream emission 

savings based on changes in emissions from power plants. This approach does not address Hg 

emissions.

Table 9.6.1 Estimated Upstream Emissions of Air Pollutants as a Percentage of Direct 

Power Plant Combustion Emissions

Pollutant

Percent of Coal

Combustion Emissions

Percent of Natural Gas

Combustion Emissions

CO2 2.7 11.9

NOX 5.8 40

9.7 SUMMARY OF EMISSIONS IMPACTS

Table 9.7.1 summarizes the estimated emissions impacts for each of the Efficiency 

Levels for water and evaporatively cooled products, VRF water source heat pumps, and 

computer room air conditioners. It shows cumulative changes in emissions for CO2, NOX, and 
9-15

Hg for 2014 through 2043 for each of the Efficiency Levels. Cumulative CO2, NOX, and Hg 

emissions are reduced compared to the Reference case for all Efficiency Levels. For comparison, 

the cumulative power sector emissions in the AEO2011 Reference case, over the period 2014 

through 2043, are 71,472 Mt for CO2, 60,127 kt for NOx, and 855 tons for Hg.

Table 9.7.1 Cumulative Emissions Reductions Under ASHRAE Efficiency Levels*

Level 1 Level 2 Level 3 Level 4 Level 5

Water-cooled and Evaporatively-cooled 

Products

 CO2 (Mt)

 NOX (kt)

 Hg (t)

0.099

0.081

0.001

0.096

0.079

0.001

0.253

0.208

0.003

0.363

0.298

0.004

0.371

0.305

0.004

VRF Water-source Heat Pumps

 CO2 (Mt)

 NOX (kt)

 Hg (t)

0.000

0.000

0.000

0.054

0.044

0.001

0.823

0.675

0.009

1.96

1.60

0.022

3.58

2.93

0.040

Computer Room Air Conditioners

 CO2 (Mt)

 NOX (kt)

 Hg (t)

0.177

0.145

0.001

2.14

1.76

0.023

8.06

6.62

0.087

18.7

15.4

0.203

31.1

25.6

0.337

* Values for CO2 are given in metric tons, while values for NOX and Hg are given in short tons.
9-16

REFERENCES

 

1. U.S. Environmental Protection Agency, Sulfur Dioxide, 2011. 

http://www.epa.gov/airquality/urbanair/

2. U.S. Environmental Protection Agency, Nitrogen Dioxide, 2011. 

http://www.epa.gov/air/nitrogenoxides/

3. U.S. Environmental Protection Agency, Mercury, 2011. http://www.epa.gov/mercury/

4. Trasande, L., C. Schechter, K.A. Haynes, and P.J. Landrigan,, Applying Cost Analyses to 

Drive Policy That Protects Children : Mercury as a Case Study. Annals of the New York 

Academy of Sciences, 2006. 1076

5. U.S. Environmental Protection Agency, 2009 U.S. Greenhouse Gas Inventory Report, 

2009. http://www.epa.gov/climatechange/emissions/usinventoryreport.html

6. U.S. Environmental Protection Agency, Clean Air Act. 1990. http://www.epa.gov/air/caa/

7. Intergovernmental Panel On Climate Change, IPCC WGI Fourth Assessment Report: 

Climate Change 2007: The Physical Science Basis, 2007. Geneva. http://ipccwg1.ucar.edu/wg1/docs/WG1AR4_SPM_PlenaryApproved.pdf

8. Intergovernmental Panel On Climate Change, Climate Change 2007 – Impacts, 

Adaptation and Vulnerability. http://www.ipcc-wg2.gov

9. Intergovernmental Panel On Climate Change, IPCC Special Report on Land Use, LandUse Change And Forestry, 2000. 

http://www.grida.no/publications/other/ipcc_sr/?src=/Climate/ipcc/land_use/index.htm

10. Intergovernmental Panel On Climate Change, IPCC Fourth Assessment Report Climate 

Change 2007: Working Group III Report "Mitigation of Climate Change", 2007. 

http://www.ipcc.ch/pdf/assessment-report/ar4/wg3/ar4-wg3-ts.pdf

11. Energy Information Administration, Updated Annual Energy Outlook 2011. Report No. 

DOE/EIA-0383(2011). http://www.eia.gov/forecasts/aeo/

12. DeLuchi, M. A., Emissions of Greenhouse Gases from the Use of Transportation Fuels 

and Electricity, Volume 2: Appendixes A-S, November, 1993. Argonne National 

Laboratory. Argonne, IL. Report No. ANL/ESD/TM-22-Vol.2.