1、358 2010 ASHRAEABSTRACTThe efficient use of energy reduces both energy costs andgreenhouse gas (GHG) emissions, and the mix of energysources can also affect GHG emissions. In the United States,the building sector comprises about one third of GHG emis-sions 1, presenting an attractive opportunity for
2、 utilizingadvanced design, operation and control strategies to minimizeenergy consumption and emissions while optimizing overallsystem performance through the implementation of cogene-ration, heat recovery, adaptive controls and other advancedtechniques. This paper presents an approach for controlli
3、ngGHG emissions and energy consumption through improvedcommunication between energy consumers and suppliers, andadvanced energy management systems. A specific exampleinvolving cogeneration is detailed to demonstrate the concept.INTRODUCTIONModern society is built on energy technologies to providea c
4、omfortable and safe environment, and to produce desirablegoods and services. There are many different ways to identify,categorize and subdivide energy consuming sectors. Twoexamples are on the basis of end use, such as heating, cooling,lighting or manufacturing, or on the basis of the general classo
5、f activity, such as transportation, industrial or buildings.However, regardless of how the energy consumption is cate-gorized, the efficient use of energy is desirable. Focusing onenergy efficiency as a means to control energy usage, ratherthan a simple reduction in energy consumption, allows us tom
6、eet our broader economic goals without sacrificing perfor-mance desired from the activity. The link between energy efficiency and GHG emissionsis clear. The principal GHG of concern is CO2, a product ofcarbon-based fuels combustion. Thus, both the efficiency offuel burning devices and the efficiency
7、 of devices that useenergy produced by other devices that burn fuel, affect GHGemissions. Taking a broader view, the efficiency of all the vari-ous processes in an energy conversion chain influences thetotal energy requirements, and therefore the associated GHGemissions. ENERGY MANAGEMENT SYSTEMSThe
8、re are multiple factors which can influence energyefficiency and performance. The efficiencies of combustionand mechanical energy conversion equipment and systems canvary with load and other operating conditions, both at thesupplier and consumer ends of the supply chain. As a result,maintaining effi
9、cient system operation usually requires anenergy management system (EMS) which can measure andmanipulate essential system parameters 2. Modern EMSsmay also be capable of communicating with utilities, weatherforecasters, and other entities in order to perform sophisticatedcontrol actions, including l
10、oad shedding, fuel switching, andother proactive measures. In order to make proper decisionsand maintain optimum system operation, the EMS must beable to access the required information and have a means toevaluate various modes of operation and manipulate operatingconditions. This capability implies
11、 a level of intelligence thatis certainly feasible, but only recently seeing increased imple-mentation. EMS optimization goes beyond simple feedback controlof individual processes, or even cascaded loop control, andventures into intelligent hierarchical control strategies that canconsider overall sy
12、stem performance, and adjust, activate orEnergy Systems Management and Greenhouse Gas ReductionStephen J. Treado, PhD, PE David Holmberg, PhDMember ASHRAE Member ASHRAEStephen Treado and David Holmberg are mechanical engineers with the National Institute of Standards and Technology, Gaithersburg, MD
13、.OR-10-039 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted w
14、ithout ASHRAEs prior written permission. ASHRAE Transactions 359terminate processes as required 3. Some of the EMS-basedstrategies to reduce energy usage and GHG emissions include:Controlling equipment and systems for higher efficien-ciesReducing loadsShifting loads to off-peak time periodsEnergy st
15、orageHeat recoveryEnergy source selectionMethods such as cogeneration (combined heat andpower), heat recovery and fuel switching can have a largeimpact on GHG emissions. Determining the optimum operat-ing conditions requires careful consideration of many factors,including the carbon content of the f
16、uel sources, emissionscharacteristics, and the efficiencies and controllability of thevarious systems and components. The link between EMS and GHG reductions lies in theability to monitor the critical source and site parameters thataffect energy usage, energy efficiency and emissions. Some ofthese o
17、pportunities can be implemented in a straightforwardmanner without any special or advanced features or capabili-ties. For example, reducing energy consumption by reducingloads or increasing energy efficiency will reduce GHG emis-sions. Switching from higher to lower carbon content energysources will
18、 also reduce GHG emissions. If various energysource alternatives are available onsite, their selection can bebased on information that is readily available locally. If,however, the energy source alternatives include one or moreoffsite sources, in addition to the algorithms required tocompare the sou
19、rce emissions, a communications capabilitythat provides access to energy source carbon content or emis-sions characteristics would be required. The key point is thatthe EMS would not be simply monitoring and maintainingoperating conditions such as temperatures and airflows, butwould be continuously
20、evaluating energy source alternativesto minimize emissions, or some combination of emissions,energy usage and energy costs. UTILITY INTERACTIONS AND SMART GRIDA relatively recent, and ongoing, development involvesreal-time communication between the building EMS andutilities via the internet, private
21、 network or other securechannel, a concept know as smart grid. This type of tech-nology would enable end users (consumers) to obtaincurrent information from different utilities regardingparameters such as pricing and emissions, including CO2, asshown in Figure 1. In this figure, each utility could h
22、ave adifferent average rate of CO2production per unit of electri-cal power, (kg/s-kW)(lb/s-kW), since the power could becoming from a different mix of sources including fuel-firedplants or renewable resources. These values could also varywith time of day, weather conditions and operationalfactors, s
23、o a continuous updating would be required to staycurrent. There may also be merit in providing a value for themarginal CO2emissions for the utility, since that wouldcorrespond to the emissions associated with providing anadditional increment or decrement of electrical power,however the use of this f
24、actor would be complicated sinceoverall utility power demand is constantly changing, and themarginal contribution of each power source, along with thecombined marginal value, might be difficult to determine.Armed with the relevant emissions information along withother real time data such as costs, o
25、ne way or another endusers could elect to obtain their electrical power from thesupplier they deem to be most appropriate, based on energycost, emissions or other relevant parameter, or alternativelywhere available, generate their own electrical power. Figure 1 Communicating emissions information be
26、tween utilities and end users.C 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital fo
27、rm is not permitted without ASHRAEs prior written permission. 360 ASHRAE TransactionsASHRAE BACnet is addressing the tools that enable thecommercial building or facility to communicate with utilities.ASHRAE and many other organizations are together involvedin a collaborative process to address commu
28、nication standardsunder the NIST-lead smart grid effort. NIST was given themandate by the 2007 EISA legislation to coordinate smart gridstandards interoperability. NIST has outlined the informationcontent into a knowledge base, and brought together expertworking groups to address the process for ach
29、ieving standardsinteroperability. Details of the process and status of this effortcan be found on the NIST website at: http:/www.nist.gov/smartgrid/. Some of the standards that are being addressed thatare pertinent to consumers include pricing and quality. Qualityhas different aspects including sour
30、ce characteristics, voltageregulation (peaks, mean, frequency, phase), and prediction ofnear-term quality.ENERGY USE AND GHG EMISSIONSThe total energy used by an enterprise may be composedof a number of components, but typically consists of a combi-nation of electrical power and thermal energy resul
31、ting fromon-site or external combustion of fossil fuels. In some cases,there may also be a source of electrical power from a renew-able resource such as solar photovoltaic or wind power, orpossibly a renewable heated fluid source, such as geothermalor solar thermal power. Another option is the on si
32、te genera-tion of electrical power from a fuel source, such as a gasturbine or diesel engine, which may be accompanied by abyproduct source of heated fluid, a strategy called cogenera-tion. A schematic representation of offsite power generationwith onsite heat source, compared to a cogeneration syst
33、em, isgiven in Figure 2. The GHG emissions that are associated with each of theseenergy sources can vary substantially, both compared to eachother, and over time, as a function of the carbon content of thefuel. For example, electrical power generated by a coal-firedpower plant would have a high CO2e
34、mission rate, whilehydroelectric power would have essentially zero, while a natu-ral gas fired generator would fall somewhere in between. Thecombined CO2emission rate is a function of the particular mixof generating technologies in operation at any given time.When trying to evaluate the GHG emission
35、s associatedwith the use of electrical power generated remotely, it is neces-sary to know the effective carbon content or emissions char-acteristics of the mix of power generation sources. Thisevaluation is largely an accounting exercise, since power is fedinto utility and regional power grids from
36、many sources, andextracted by multiple consumers. It should be possible for autility to obtain an estimate of the percentage contributions ofeach type of power generation, and from that determine therate of CO2production as a function of electrical powerproduced, as well as a value for the marginal
37、emissions.However, these values can vary with time as different reservesare brought online to meet varying power demand 4. Typicalvalues for coal fired power plants are about 0.95 kg/kW-h(2.1 lb/kW-h), 0.90 kg/kW-h (2.0 lb/kW-h) for oil fired, and0.6 kg/kW-h (1.3 lb/kW-h) for gas fired, while the U.
38、S. aver-age is only 0.61 kg/kW-h (1.3 lb/kW-h) due to the contributionfrom non-emitting sources (hydro, nuclear and renewable).As mentioned above, average or marginal values could beused to represent emissions. Similar values can be obtained foreach primary energy source (i.e. each fuel source) for
39、on sitecombustion. By comparing the CO2emission rates of the vari-ous energy sources, along with the conversion efficiencies, themix of energy sources that minimizes GHG emissions can bedetermined. As a side note, it would also be possible to opti-mize total energy usage, energy cost, or any combina
40、tion ofthe three parameters.As an example of a change in operation in response to realtime utility data is shown in Table 1, referring to Figure 1. Util-ity emissions indicators are monitored and as they change overtime, the most favorable source can be selected.HEAT RECOVERY, ENERGY STORAGE AND REN
41、EWABLE ENERGY SOURCESOne of the advantages of on site power generation is thepotential for combined heat and power systems (cogenera-tion). The large-scale electrical power version of this conceptis known as district heating 5. In either case, a fuel is burnedto generate heat which powers a generato
42、r, and subsequentlythe waste heat is utilized for water, space or process heating.The combined efficiency of such a system exceeds that ofpower generation alone. Depending on the circumstances, theuse of cogeneration may result in lower GHG emissions, espe-cially when the CO2emission rate of the ele
43、ctric utility is high,and there is a need for the waste heat from the power genera-tion. This scenario will frequently be the case for industrialinstallations, since process heating requirements can be verylarge. This approach would not be favored, however, for indus-trial applications that have hig
44、h electrical power requirementsrelative to heating requirements, since the heat rejected by thepower conversion system would not be in demand.Energy storage is another concept that can be particularlybeneficial. Whenever heating loads are variable and do notnecessarily coincide with the availability
45、 of thermal energy,heat storage can increase overall system efficiency by allow-ing thermal energy to be stored and recovered for later use,thereby moving it from the waste to the useful category.Energy usage can also be shifted to times when the carboncontent of the energy source is lower.Renewable
46、 energy sources are always beneficial from aGHG reduction perspective, since they are assumed to have nonet contribution to CO2production, and the energy theyproduce will substitute for energy sources that do emit GHGs.While higher renewable energy conversion efficiencies arebeneficial, the actual e
47、fficiency has only an indirect effect onemissions due to the substitution of carbon-free renewableenergy for non-renewable fossil fuels. Since renewablesources such as wind and solar radiation are essentially free, 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
48、 (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, 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. ASHRAE Transactions 361Figure 2 Schematic diagram of al
49、ternative system configurations for providing electrical power and heating energy.Table 1. Building Operation Response to Real time Utility Emissions DataTime1(mass/s-kW)2(mass/s-kW)3(mass/s-kW) Utility Selection1 2.64 (10-4) 2.5 (10-4) 1.67 (10-4) Utility 32 2.64 (10-4) 2.0(10-4) 1.8(10-4) Utility 33 2.64 (10-4) 1.9 (10-4) 2.0 (10-4) Utility 24 1.6 (10-4) 1.8 (10-4) 2.2 (10-4) Utility 1C C C 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only
