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Thesis CHP

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Thesis CHP

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  1. Comparison of Waste Heat Driven & Electrically Driven Cooling Systems for High Temperature, Off-grid Application Christopher Horvath April 20th, 2012 Center for Environmental Energy Engineering Department of Mechanical Engineering University of Maryland College Park, MD 20742-3035

  2. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems (AS) • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  3. Project Motivation [1] • Off-grid location requirements • Electricity • Cooling • High fuel consumption issues • Safety • Reliability • How to reduce this fuel consumption? • Combined heat and power (CHP)

  4. Project Objectives • Investigate CHP alternatives which: • Reduce fuel consumption • Reduce weight & volume • Meet the design criteria

  5. Design Point Conditions Picture References: [2] – [4]

  6. Design Conditions Non-Cooling (Hotel power) Electricity Runs ~ 24 hrs 0.75 kW – 4.6 hrs 1.5 kW – 7.25 hrs 2.25 kW – 7.25 hrs 3 kW – 4.6 hrs

  7. Design Conditions Weather profile (Meteonorm data) [4a] • Abu Dhabi, UAE • Hottest week, Aug 13th - 20th (+7°C)

  8. Design Conditions Weather profile (Meteonorm data) • Abu Dhabi, UAE • Full Year (+7°C, between 3,960 & 6,840 hours)

  9. Design Conditions Cooling load: • 5.275 kW at 51.7°C • Derived value for transient conditions • 2 occupants • Electrical equipment in cooling space • Ventilation, infiltration, and solar/conduction

  10. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems (AS) • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  11. Lit Review Thermally activated cooling technologies [5a] • Adsorption, absorption, solid/liquid desiccant cooling systems LiBr/Water AS flexible applications [5b] • Consistent COP • Limited by crystallization • Suggestions: pressurized absorber, cascaded, additives [5c] Commercial availability • Yazaki ACH-8 (Additives) [5d] • Rotartica (Mechanical enhancement) [5e]

  12. Approach Typical genset configuration (10 kWe) Powers VCS Alternative configuration (5 kWe) Powers Absorption System

  13. Modeling Approach Simulation summary

  14. Modeling Approach • Absorption system • Water/LiBr, air-cooled HXs • Utilizes engine exhaust heat • Address crystallization issue • Model overall systems in TRNSYS [6a] • Supporting components • Load profiles • Weather profiles • Characterize cooling system • Model in EES [6b] • Provide curve fits

  15. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems (AS) • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  16. Legacy System • Vapor compression system (VCS) • EES modeled • Design point COP – 1.06 • Physically based on AirRover model ULCR24BA [7]

  17. Legacy System 10 kW Genset Design point electricity ~ 8 kW

  18. AS Technology Overview [8] “Absorption Chillers and Heat Pumps” Absorption chillers Water/LiBr Simple case, 2 pressure levels Solution circulation and refrigerant circulation Desorber – driving heat input Evaporator – cooling

  19. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  20. Crystallization Characterization Tcond . . msol Tabs Crystallization (Boryta 1970) Tevap [9] Gluesenkamp et al. (2011)

  21. Anti-crystallization: CPA • Compressor-pressurized absorber prevents crystallization: • Pressure ratio of 2.3 • Parasitic electrical power ~ 250 W • Challenges: • Finding a suitable compressor • Separating the evaporator/absorber unit for compressor inclusion

  22. Anti-crystallization: SSLC • Separate sensible and latent cooling (SSLC) • Strategy • Small supplemental VCS • Split AS evaporator for 2 streams • Raise AS evaporator pressure • Removes crystallization • ISHPC 2011 paper [10] • Design temperature – 49°C • High COP – 2.91 • Low load – 446 W • Challenges: • Changing one variable (i.e. percent ventilation) changes everything else • Appropriate control strategy • Not pursued further

  23. Anti-crystallization: Cascaded • Strategy • Small supplemental VCS • Raise AS evaporator pressure • Advantages • Avoids crystallization • Small temperature lift <10°C • Small pressure ratio ~ 2 • High COP ~ 6.4 • Requirements • Water loop and pump • Bypass loop & extra HX • Electrical load ~ 800 W

  24. Anti-crystallization: MIAE • Membrane Integrated Absorber Evaporator • Strategy • Replace evaporator/absorber unit with membrane based unit • Requirements • Proprietary design • Water loops • Extra pump power consumption • Extra HXs [11]

  25. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  26. Baseline Absorption System Baseline absorption system • AS, engine, duct burner (DB) • Does not include anti-crystallization strategy

  27. Baseline Absorption System Inputs • Model based on textbook example [8] • Air-cooled HXs • HX UA values specified • Desorber temperature limited – 135°C • AS evaporator temperature – 16°C • Solving method - DB on or off • DB off – 4 kW heat input, 2.3 kW cooling • Curve fits • COP, DB on & off • Parasitic power, DB on & off • Solution inlet temperature to desorber

  28. Baseline Absorption System Parasitic loads AS, pumps & fans [16-20] – 482 W DB fuel pump [15] – 150 W

  29. Baseline Absorption System Curve fits • TableCurve 3D [21] • Functions of • Ambient temperature • Engine exhaust temperature (indicates part load)

  30. Cascaded Absorption System Modified from baseline AS EES model Water loop and pump Supplemental VCS Bypass loop (below 45°C) AS evaporator T raised – 20°C Higher evaporator load – 6 kW

  31. Cascaded Absorption System Supplemental VCS Modified from Legacy VCS Included as EES module COP - 6.4 Power input ~820 W

  32. Cascaded Absorption System HX diagram for water loop AS evaporator heated Chilled water cooled, then heated VCS condenser cooled

  33. Cascaded Absorption System HX diagram for VCS evaporator VCS refrigerant heated Air side cooled

  34. Cascaded Absorption System Parasitic loads Additional water loop pump [22] Supplemental VCS ~ 820 W Duct burner pump – 150 W

  35. MIAE Absorption System Modified from baseline AS EES model 2 water loops and pumps 2 additional internal pumps

  36. MIAE Absorption System Parasitic loads 2 Additional water loop pumps [23] – [25] 2 Internal pumps Duct burner ~150 W

  37. AS’s Overall Comparison Effectiveness definition [8]

  38. AS’s Overall

  39. Systems Overall

  40. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  41. Legacy System TRNSYS model

  42. Engine Component [26] – [27] Experimental engine performance for component basis Rated air temperature of 35°C DRS power solutions 3 kW Genset Engine – Yanmar L70

  43. Engine Component • Engine – Yanmar L70 [28] • 3600 RPM fixed speed • 320 cc/revolution • 4 cycle, air-cooled, • Volumetric η = 85% • Constant air density of 1.075 kg/m3 • Fuel density: 832 kg/L, LHV: 43 MJ/kg • Resulting exhaust flow rate – 0.00908 kg/s for 3 kW engine • Exhaust scaled linearly – 0.03027 kg/s - 10 kW

  44. AS TRNSYS Modeling

  45. AS Engine

  46. Model Verifications One week, steady state simulation Rough calculations:

  47. Model Verifications Rough calculations

  48. Outline • Background • Motivation & Objectives • Literature Review & Approach • Technology • Legacy System • Absorption Systems • Anti-crystallization Approaches • Modeling in EES • TRNSYS Modeling • Results • Conclusions • Future Work

  49. Results – Fuel Consumption

  50. Results – Fuel Consumption *Baseline AS does not contain anti-crystallization approach Tmargin = 12K, and Xmargin = 1.05% concentration

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