Energy saving in airports by trigeneration. Part II: Short and long term planning for the Malpensa 2000 CHCP plant

Energy saving in airports by trigeneration. Part II: Short and long term planning for the Malpensa 2000 CHCP plant
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  Energy saving in airports by trigeneration. Part I: Assessingeconomic and technical potential E. Cardona  * , A. Piacentino, F. Cardona DREAM – Department for Energy and Environmental Researches, Faculty of Engineering, Universita`  di Palermo,Viale delle Scienze, 90128 Palermo, Italy Received 24 March 2005; accepted 27 January 2006Available online 20 March 2006 Abstract Airports are very energy-intensive areas, because of the large buildings (both terminals and non-passengers areas) equipped with heat-ing and air-conditioning systems, the high power demand for lighting and electric equipment and the energy requests from many facilitieswithin the airport area. The contemporaneous and high demand for power and heat makes cogeneration to represent a viable solutionfor energy saving; in southern climate zones, however, combined heating, cooling and power (CHCP) systems can lead to even betterresults. This paper constitutes the first part of a work in two parts; starting from an analysis of typical energy demand profiles in airports,economical and technical criteria to assess the feasibility of trigeneration plants are proposed. Typical results for large airports are alsopresented. Part II of this work presents an in-depth analysis for the Malpensa 2000 airport, oriented to optimize the design and the oper-ation of the CHCP system.   2006 Elsevier Ltd. All rights reserved. Keywords:  Trigeneration; Airports; Energy saving; Feasibility 1. Introduction Energy consumption in airports depends on a largenumber of factors, so that any attempt to define generalcriteria for efficiency increase is hazardous.Energy demand depends on both structural (surface,volume, building orientation, external and roof thermalinsulation, double glazing, etc.) and operational variables(number of passengers per year, average occupancy levelsin air-conditioned areas, seasonal fluctuations in numberof passengers, etc.) related to the size of the airport. Also,the climatic conditions play a primary role, dependingheating and cooling loads on the fluctuations of externaltemperature.A significant contribution to the overall energy demandderives from the facilities usually situated within the air-port area, like restaurants, shopping centres, baggagestores, etc.Even if energy cost accounts for only 3–5% of airports’variable cost, the absolute values of energy consumptionare very significant; thus, large margins for increase inenergy efficiency exist, which have been analysed by manyexperts in transportation and energy systems [1,2]. A sys-tematic approach to energy saving requires a qualitativeand quantitative analysis of heat, cooling and power loads.The actions oriented to increase the overall energy effi-ciency in airports can be classified as follows: •  Low or no-cost actions: abatement of inefficiencies inenergy transportation and use (heat losses in pipelines,malfunction of control and regulation system, etc.),training of new skills in energy management amongemployees or improvements in the monitoring and tar-geting system, with sophisticated controls and periodicalenergy auditing. Investigations for UK airports [1]revealed a significant potential for such actions. 1359-4311/$ - see front matter    2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.applthermaleng.2006.01.019 * Corresponding author. Tel./fax: +39 091 236113. E-mail address:  cardona@unipa.it (E. Cardona). www.elsevier.com/locate/apthermeng Applied Thermal Engineering 26 (2006) 1427–1436  •  High cost/long term actions: actions based on retrofit-ting the technology with major changes in the philoso-phy of energy conversion, like the adoption of a CHPsystem or the use of thermal wheels and run-aroundcoils in place of traditional energy systems. Large bene-fits can be achieved, but these actions are very expensiveand risky and should be considered after implementingthose in the above two categories.In this paper the economic and technical feasibility of CHCP plants in airports is discussed.Today, CHP and CHCP plants are operating in manyairports all over the world; best examples are the90 MW e  CHP plant at the JFK airport (New York), the50 MW e  CHP plant at Heathrow (London), the 50 MW e CHCP plant at Malpensa (Milan) and the 40 MW e  CHCPplant at Kuala Lumpur. However, we will show that air-ports are very suitable for CHCP applications and a largerspread can be expected. 2. Energy demand in airports Because of the large differences in energy demandamong airports, a feasibility study should be performedfor each case study with ad hoc considerations. However,in this work some outlines on CHCP applications in air-ports are proposed, starting from a statistical distributionof available energy consumption data.Energy demand in airports is correlated to many factors;among these, heat losses by air infiltration and lossestrough windows and roofs (and thus related to the heatedor air-conditioned surface and volume) are prevalent. InTable 1 average values for installed capacity and yearlyenergy consumption are presented [3].In Table 2 characteristic data for a restricted number of airports in Italy are presented.The wide ranges indicated for the specific energy con-sumption in Table 1 are due to the large differences in ther-mal transmittance of walls and roofs, in the use of highefficiency lighting systems, etc. Furthermore, energydemand in airports can widely vary year by year, depend-ing on eventual variations in the number of passengersand facilities: most airports are growing much faster thanthe economy as a whole, and this requires large efforts toforecast demand [4] and frequent increases in the energysupply as well. Therefore, when designing a CHCP plantfor airports a modular approach should be adopted, likein most of CHCP installations in airports all over the world Nomenclature ATD aggregate thermal demandATD boil  fraction covered by the auxiliary boilerATD CHP  fraction covered by heat recovery from the en-gine C   cost C  cool  cooling demandCHP combined heat and powerCHCP combined heat cooling and powerDGH distributed generation with heat E   electric demand E  exch.  energy exchange with the gridEI energy intensity F   fuelFLOT full load operation time H   heat production H  LV  lower heat value [MJ/kg or MJ/Nm 3 ] i   interest rateIC specific installed capacityMP E  market price for electricity purchase [  € /kWh e ]MP fuel  market price for fuel [  € /kg or  €  Nm 3 ]MP exch.  electricity price, coincident with MP el  when pur-chased from the grid, negative when soldNCC net cash flow N  tr  number of transits [passengers/year]pax passengerPHR user  power to heat ratio, on the demand sidePHR primemover  ratio between power and heat recoveryfrom prime mover S  opt.  optimal size S  s  spark-spreadTDD thermal demand for direct usesTDM, EDM thermal and electric demand managementTPEC total primary energy consumptionYEC specific yearly energy consumption Greek letters g e,av.  average efficiency of the national generation sys-tem g e  electric efficiency g t  thermal efficiency Subscripts marg marginal (CHCP system over conventional one)energy related to energy flowsmaint maintenanceamortization related to amortization of investment Table 1Typical values of specific installed capacity and energy consumption inairportsElectricity Heat CoolingIC 0.5–0.8 kW e /pax 50–160 W t /m 2 50–200 W c /m 3 YEC 4.5–5.8 kW h e /pax 30–55 kW h t /m 3 20–40 kW h c /m 3 1428  E. Cardona et al. / Applied Thermal Engineering 26 (2006) 1427–1436   which usually consist of several small groups to cover thegrowing energy demand. In the meantime, a modularapproach enhances the reliability of supply, which is amain concern for airports.Another important aspect when sizing the plant regardsthe shape of energy demand profiles. A regular profilethroughout the year favours the CHCP feasibility, allowingto operate the plant at high load levels in CHCP mode formost of the year. As said, number of passengers (whichinfluences both the electrical demand and the internal loadfor air-conditioning), heat transfer trough the buildingenvelope and lighting are the main factors contributing tothe overall energy demand. In Fig. 1a and b the passengerstraffic in six airports all over the world is presented. InFig. 1a very large international airports are presented, withover 25 million passengers per year, whilst those to whichFig. 1b is referred are smaller airports, with less than 11million passenger per year. As evident, the traffic trendsof large airports is more regular, while large fluctuationscan be observed in the small airports’ traffic, due to theinfluence of seasonal tourism.Basing on our experience, we can thus affirm that inlarge airports major opportunities for CHCP applicationsexist, because of the higher required capacity and the moreregular demand profiles. CHCP applications in small air-ports usually lead to longer payback periods; however,each case should be investigated separately, because alsoin small airports CHCP can represent a viable solution infavourable tariff contexts. In Fig. 2a–c the energy demandprofiles in the Italian airports referred to in Table 2 are rep-resented on monthly basis.In Fig. 2a, bars in black and in white-dotted respectivelyrepresent the direct thermal loads and the heat consump-tion for feeding an absorption chiller covering the wholecooling demand; this indirect heat demand makes the over-all heat demand profile much more regular. The electricdemand monthly profile, represented in Fig. 2c, is also very Fig. 1. Monthly passenger traffic in (a) large international airports: New York—JFK, Rome—Fiumicino, London—Heathrow, (b) small airports:Palermo—Falcone–Borsellino, Malaga, Nice-Coˆte d’Azur.Table 2Main data of the examined airportsPassengersper year(2003)(10 3 units)Heated andair-conditionedareas (m 2 )LatitudeAirport no. 1:Malpensa 2000,Milan26.000 329.000 45  39 0 NorthAirport no. 2:Fiumicino,Rome27.900 285.000 41  46 0 NorthAirport no. 3:Falcone andBorsellino, Palermo3.400 38  11 0 North E. Cardona et al. / Applied Thermal Engineering 26 (2006) 1427–1436   1429  regular because electric load is related to quite constantactivities 12 month a year.The daily demand profiles (not represented here) forheat and cooling are quite regular (variations up to+20%/  20% with respect to the average value), with littleincreases during morning or afternoon, depending on thebuildings’ orientation. The electric load daily profile ischaracterised by higher power requests during the evening,with a demand leap when the lighting system of runwaysand control tower lights up. Obviously, some electric loadsrequire a very high safety of supply; hence, dedicatedengines or inverter groups (consisting of a rectifier, a stor-age battery package and an inverter) are usually availablefor energy supply in case of power grid failures.Despite this quantitative analysis of energy consumptioninairports,aqualitativeanalysisisneededtoassesswhethera CHCP system can comply with all energy requests. Mostairports are provided with central systems for hot or warmwater production (usually natural gas or diesel oil fuelledboilers) and for cooling (large electric chillers); power isusually purchased at 15–20 kV. All-air systems are mainlyadopted, with air-treatment units where temperature andhumidity are adjusted; a typical range of temperature forthe heat exchanges in such units is 85–70   C.Water temperature in the cooling jacket circuit of recip-rocating engines typically exceeds these values, being suffi-cient for feeding the air-heating system; heat recoveryfrom this circuit amounts to 20–30% of the energy input Fig. 2. Monthly energy consumption for (a) heat, (b) cooling, (c) electricity.1430  E. Cardona et al. / Applied Thermal Engineering 26 (2006) 1427–1436   by fuel. In gas turbines the whole heat recovery is fromexhaust gases, at a much higher temperature. Dependingonthecoolingdemandlevels, asingleoradoubleeffectlith-ium bromide absorption chiller can be installed, producing5–7   C cold water for the air-treatment units. Single effectabsorption chiller require super-heated feeding water at120–130   C or low pressure steam (typically 70–90 kPa);only high temperature heat recovery from exhaust gases iscompatible with the temperature required by absorptionchillers. 3. Technical feasibility of CHCP in airports When retrofitting a conventional plant with a CHCPsystem, the existing components and equipment must beintegrated with the new ones. In this section a typicalenergy system for airports and the required lay-out changesare examined, as plotted in Fig. 3; in the same figure, newcomponents or major changes are represented by hatchedlines.When a conventional system is converted into a CHCP,the existing boilers and chillers can be used as auxiliary sys-tems to cover the peaks of demand (when it exceeds theCHCP plant capacity). As concerns the infrastructures,when a centralized all-air system for heating and coolingexists, the same pipelines can be conserved; eventually,improvements in the water distribution network could beneeded, as represented in Fig. 3 where two different con-ventional central systems were serving different areas.The delivery distance for warm and cold water must becompatible with the maximum heat losses acceptable; inthis sense the warm fluid circuit is not critical, becausethe temperature range between delivery and return circuitsis constant (in case of control systems which intervene onthe flow rate) and not inferior to 15   C. The cooling systemalso operates at constant temperatures (regulation on theflow rate); here, however, attention should be paid becauseof the only 5–6   C gap between delivery and return temper-ature (typical values for air-conditioning systems are 5– 7   C inlet and 12–13   C outlet temperature). Hence, theinsulation of pipelines is selected on the basis of the maxi-mum losses in the cooling circuit.A connection between the internal and the public grid isprovided by an automatic parallel panel; it allows the bi-directional power exchange, also ensuring system’s safetywhen starting or switching off the prime mover and in caseof frequency or voltage anomalies on the grid. A CHCPplant requires much larger spaces than a conventionalone and it should be far enough from the runway andthe tower control to avoid any electromagnetic interfer-ence. However, to find an appropriate site is not difficult,being most airports situated in large and flat sites.Evidently, no technical obstacles exist for CHCP appli-cations in airports and an effective integration with the Terminal 1Terminal 2 T      e    r   m   i     n    a   l      3      Parking area  External facilities(restaurant, laundry etc.) Cargo area Boilersandchillers 1 chillersandBoilers 2Centralair-treatmentunitsCentralunitsair-treatmentCentralunitsair-treatment  u   n   i      t     s    a   i     r   -   t    r    e     a    t    m    e    n    t     C      e    n    t    r    a   l      air-treatmentunitsCentral  CHCP plant Warm waterCold waterpipelinepipeline Highvoltagegrid Controltower 3 ~ Mediumvoltageuses 3 ~ Low   voltageuses LH Automaticparallelpanel warm/cold air pipelines warm/cold water pipelines Fig. 3. Simplified representation of a CHCP plant retrofit for airports. E. Cardona et al. / Applied Thermal Engineering 26 (2006) 1427–1436   1431
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