1、2011 ASHRAE 974ABSTRACTAccording to the Carbon Trust of the United Kingdom,“CHP for industrial, commercial and domestic applicationshas the potential to make a significant contribution to energyefficiency improvements and to reducing CO2emissions. It isa key technology needed to help meet the UKs gr
2、eenhouse gasemission reduction targets and begin the transition to a lowcarbon economy” (CTUK 2002). CHP has the potential toreduce a facilitys CO2emissions provided there is good powerand thermal load matching and a credible means to calculatethese potential CO2emissions savings. The Regional Green
3、house Gas Initiative (RGGI) is thefirst mandatory, market-based effort in the United States toreduce greenhouse gas emissions. Ten Northeastern and Mid-Atlantic states will cap and then reduce CO2emissions from thepower sector by 10% by 2018. Midwestern and West Coaststates have created similar orga
4、nizations and are expected tomonetize carbon emissions. President Obamas intentions arefor sweeping changes in how Americans use energy, and he hasmade it clear that the United States will participate in talks onthe successor to the United Nations Kyoto Protocol. The engineering community is increas
5、ingly called upon tocalculate the carbon emissions impact of applying a CHPsystem at the design stage. This paper explores important data-set choices when comparing fuel use and CO2, SO2,and NOxemissions at the design stage for CHP systems with the electricgrid in various locations throughout the Un
6、ited States. INTRODUCTIONCalculating carbon emission from a particular buildingdesign is becoming important, as policymakers appear to bemoving toward monetizing these emissions. This presents aninteresting problem when evaluating the energy and emissionsimpact of designing a building using a CHP sy
7、stem.Calculating full fuel cycle1emissions from fuel input intoa CHP system is relatively straightforward. Calculating fullfuel cycle emissions saved by thermal energy recovered fromthe CHP generator and used by the building (e.g., for heating,hot water, chilled water, etc.) requires knowledge of th
8、e ther-mal system, the served load, and the technology that was notneeded as a result of the CHP system (displaced by the recov-ered thermal energy). Finally, displacing electricity from thegrid requires an understanding of the electric grids operation,likely power plant(s) that would provide power
9、to the buildingsite where the proposed CHP plant is to be located, and thetype of power plant whose electricity would be displaced bythe electricity generated by the CHP plant (e.g. nuclear, base-load coal, hydro, combined-cycle, cycling coal, oil and gas,peaking plants, etc.).The complexity of Amer
10、icas electric grid presents a diffi-cult problem for the engineering community to find a reliableand repeatable methodology to evaluate the carbon impact ofconsuming electricity on site. This task is further complicatedwhen attempting to calculate the carbon impact of applying aCHP plant that genera
11、tes electric power and useful thermalenergy. The federal government2has developed an onlineCHP Emissions Calculator (CHP-EC) (EPA 2009) to assessthe impact of applying a CHP system to thermal and electrical1.Full-fuel-cycle measure of energy consumption includes, in addi-tion to site energy use, the
12、 energy consumed in the extraction,processing, and transport of primary fuels such as coal, oil, andnatural gas; energy losses in thermal combustion in power-gener-ation plants; and energy losses in transmission and distribution tobuildings.Applying a Fuel and CO2Emissions Savings Calculation Protoc
13、ol to a Combined Heat and Power (CHP) Project DesignRichard S. SweetserMember ASHRAERichard S. Sweetser is president of EXERGY Partners Corp., Herndon, VA.LV-11-0302011. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions
14、, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAES prior written permission.2011 ASHRAE 975loads in a facility. The CHP-EC estimates the net air pollutionemissions (NOx, SO2, and CO2) fr
15、om CHP systems. The netemissions are calculated from the following three primarycomponents:On-site emissions from the CHP systemDisplaced emissions from on-site thermal production(i.e., steam)Displaced emissions from off-site generation of electric-ity, including transmission lossesThe net emissions
16、 equal the emissions from CHP minusthe displaced emissions from thermal production and electric-ity production:(1)The CHP-EC uses the Emissions note 427 hours annually have been allocated for planned maintenance5. CHP: Does the system provide heating or cooling or both?Cooling only A function of the
17、 application6. CHP: Fuel Natural gas A function of the application8. CHP: What is the CO2emission rate for this fuel? 117 lb/MMBtuDefault value for natural gasPounds per million Btu of energy input9. CHP: What is the heat content of this fuel? (Enter a value in only ONE of the boxes)1020Defaultcould
18、 vary somewhat by natural gas distribution company and location12. CHP: Electric efficiency 32.4% Engine manufacturer13. CHP: Base power to heat ratio 0.8141Basis is 1.4 MMBtu/h; thermal output used as input to the absorption chiller 403 kWthdivided by power output 328 kWe= 0.81414. CHP: NOxemission
19、 rate 0.6 gm/hph Engine manufacturer19. Cooling: Does the CHP provide cool-ing?Yes For comparative20. Cooling: Type of absorption chiller used?Typical single-effect absorption chiller, COP = 0.7The default COP equals the manufacturers rating for this application21. Cooling: What is the cooling capac
20、ity of the system?80 RT Driven by case study load22. Typical single-effect absorption chiller, COP = 0.70.80 kW/ton (COP = 4.4) Average new rotary screw compressor, water-cooled, 150 tons capacityCase study 29. Displaced electricity: Generation profile eGRID average fossil 2005 See displaced power g
21、eneration section of this paper.30. Displaced electricity: Select U.S. aver-age or individual state/NERC region for EGRID dataeGRID subregions See eGRID subregions section of this paper.31. Displaced electricity: Transmission losses7%Program default value; actual values could be higher or lower and
22、impact results up to 5%2011 ASHRAE 979yielding low cost electricity with no direct carbon emissions.Therefore, it is unrealistic to believe that nuclear or hydro-power would ever be displaced, for a multitude of reasons,leaving a fossil blend as the logical choice.A second matter of significant impo
23、rtance is to the deter-mine generator supply mix that actually delivers electricity tothe site. Many smaller countries solve this problem by usingnational averages. Figure 3 demonstrates the problem withusing national averages (eGRID Average Fossil 2005) byshowing results comparing the CHP plant in
24、terms of percentannual savings of CO2, NOxand SO2emissions, as well as fuelconsumption to the national average electric grid and variousstates. When comparing the CHP plant emissions to thenational average results, there is a reduction in CO2/carbonemissions by 48%, NOxemissions by 47%, SO2emissions
25、 by100%, and fuel consumption by 18%. However, whencompared to California averages, the CHP plant increases localNOxemissions by 294%, while reducing SO2emissions by98%, CO2/carbon emissions by 11%, and fuel consumption by6%. Using South Dakota values, the modeled CHP plantreduces local NOxemissions
26、 by 85%, SO2emissions by 100%,CO2/carbon emissions by 59%, and fuel consumption by 31%. Table 4 provides a compelling case to use state-basedemissions for power generation versus the national averagedata. California data shows 76% less CO2savings versus thenational grid, while South Dakota shows a 2
27、3% increase incarbon savings. This is due to the widespread use of naturalgas-powered generation in California versus coal-poweredgeneration in South Dakota.Figure 3, as well as Figures 4 through 9, demonstratesvariation in emissions and fuel usage resulting from the CHPplant designed in the case st
28、udy with the apparent exception ofSO2emissions. The reason for apparently no variation in SO2Figure 3 Annual percent emissions and fuel reduction using case study CHP system.Figure 2 Comparative CHP plant emissions and electricgrid fuel consumption and emissions.980 ASHRAE Transactionsemissions can
29、be found in Figure 2, which shows the naturalgas-based CHP plant SO2emissions to be less than 16 poundsper year. The best-case scenario in this assessment for grid-based SO2 emissions would be the California average fossilcomparison where the grid electricity would produce 840pounds of SO2, in this
30、case yielding a 98% SO2 reduction. Thesame assessment in Massachusetts would yield 14,800 poundsof SO2per year where the CHP plant would have a virtually100% SO2reduction. Figure 4 presents state CO2emissions from combustionpower plants located within each state and the national averagefrom all comb
31、ustion power plants (gray far right). There iswide variation in these results. However, these data are basedon generation and not consumption of electricity. For exam-ple, Vermont has virtually no combustion power plants;however, siting the CHP plant in Vermont will reduce CO2emissions over 3600 ton
32、s per year. This is because Vermont isa net importer of power, and a significant portion of thisTable 4. Percentage Reduction Deviation from U.S. AverageCalifornia U.S. Average South DakotaPercent ReductionPercent Less than U.S. AveragePercent ReductionPercent More than U.S. AveragePercent Reduction
33、NOx(tons/year) 294% 728% 47% 81% 85%SO2(tons/year) 98% 2% 100% 0% 100%CO2(tons/year) 11% 76% 48% 23% 59%Carbon (metric tons/year) 11% 76% 48% 23% 59%Fuel consumption (MMBtu/year) 6% 65% 18% 73% 31%Figure 4 Annual percent emissions and fuel reductionU.S. average and NERC regions.2011 ASHRAE 981import
34、ed power is produced from combustion of fossil fuels.California, Idaho, Oregon, and Washingtons low CO2emis-sions results show their use of natural gas, combined-cycle,and other high-efficiency combustion of fossil fuels to gener-ate electricity within their respective states. State-based datawould
35、appear not to be an accurate measure of emissionsbecause many states either import or export electricity to otherstates.The next logical step is to examine a Power Control Area(PCA). A PCA is a portion of an integrated power grid forwhich a single dispatcher has operational control of all electricge
36、nerators.North American Electric Reliability CorporationThe North American Electric Reliability Corporation(NERC) is a self-regulatory organization, subject to oversightby the U.S. Federal Energy Regulatory Commission andgovernmental authorities in Canada.NERC works with eight regional entities to i
37、mprove thereliability of the bulk power system. The members of theregional entities come from all segments of the electric indus-try: investor-owned utilities; federal power agencies; ruralelectric cooperatives; state, municipal, and provincial utilities,independent power producers, power marketers,
38、 and end-usercustomers. These entities account for virtually all the electric-ity supplied in the United States and Canada. The United States is divided into three main grids thathave few connections and little energy transfer between them.The Western Electricity Coordinating Council (WECC) andthe T
39、exas Regional Entity (TRE) form independent grids fromthe remainder of the NERC regions shown in Figure 5. Using NERC regions as the source of electric supply canmake sense in todays modern electric grid, since generatorsnow sell their power into wholesale markets operated byregional transmission or
40、ganizations. For example, the PJMInterconnection is a regional transmission organization thatcoordinates the movement of wholesale electricity in all orparts of Delaware, Illinois, Indiana, Kentucky, Maryland,Michigan, New Jersey, North Carolina, Ohio, Pennsylvania,Tennessee, Virginia, West Virginia
41、, and the District of Colum-bia. PJM acts as a neutral, independent party, operating acompetitive wholesale electricity market and manages thehigh-voltage electricity grid to ensure reliability for more than51 million people. The PJM Interconnection is largely repli-cated by the RFC NERC region. The
42、refore, all dispatchedpower generators supplying electricity to these states isblended into PJM. Examining the CHP case study system performanceacross the NERC regions in Figure 6, one can see that theMidwestern U.S. has older coal-based power plants, meaningthat the CHP plant fairs best here; howev
43、er, these older powerplants provide very low-cost electricity, which generallymeans the economics are not favorable for CHP. Texas standsout in that its high percentage of natural gas generating plantsand small NERC region, which includes only most of Texasand no other state, yields low carbon and N
44、Ox emissions andhigh fuel efficiency. Using the NERC regions dramatically narrows the spreadin results with the Midwest PCA by 20% greater CO2savingsversus the U.S. average, and the Northern Power PCA by 23%less than the U.S. average. (Note that the Western PCA has 8%less CO2savings versus 71% CO2sa
45、vings for generatingplants within California). eGRID SubregionsIn order to estimate the environmental attributes of theelectricity consumed in a particular facility, eGRID dividedthe electric grid into 27 subregions (Figure 7). These subre-gions represent a portion of the U.S. power grid that iscont
46、ained within a single NERC region, and generally repre-sent sections of the power grid that have similar emissions andresource mix characteristics, and may be partially isolated bytransmission constraints.Traditionally, CHP systems have been competitive insupplying energy in New Jersey, New York, Ne
47、w England,Texas, and California. Opportunities exist in other states withopportunity fuels (biomass, landfill gas, digester gas, wasteheat recovery, etc.). Figures 8 and 9 examine the NERC NPCCregion and associated eGRID subregions and the NERCWECC region and associated eGRID subregions.Figure 8 sho
48、ws logical CO2emissions deviation betweenthe subregions and clearly demonstrates expected NOxandfuel consumption shifts between the subregions. Figure 9 shows agreement between Colorado powergeneration data and the eGRID subregion, indicating in-stategeneration closely follows the eGRID subregions e
49、missionsand fuel savings. Washington state and the NWPP closelytrack for CO2 and fuel savingswith increasing NOxdeviationlikely due to imported power. The state of California and theCAMX subregion data results track in the same general direc-tion with only a significant NOxdeviation. Figure 5 NREC regions.982 ASHRAE TransactionsThe composition of non-state level aggregations levelsmay not be geographically obvious. The deviation between thestate of California and CAMX is largely due to the Intermoun-tain Power Project plant in the state of Utah is operated by andfor the Ci
