Lecture Objectives:

1. Lecture Objectives: • Continue with Sorption Cooling • Thermodynamics of mixtures • T - x diagram • H- x diagram

2. Combined heat and power(cogeneration CHP or three generation CCHP) Here, we use thermal energy for heating and/or cooling

3. Absorption Cycle Replace compressor Same as vapor compression but NO COMPRESSOR

4. Absorption cooling cycle Relatively simple thermodynamics with addition of mixtures (water – ammonia) Rich solution of Heat H2O + NH3 H2O H2O Rich solution of H2O + NH3

5. Mixtures(T-x diagram) Dew point curve Saturated vapor Mixture of liquid and vapor Saturated liquid Bubble point curve For P= 4 bar

6. Impact of Pressure

7. h-x diagram hfg for H2O hfg for NH3 Isotherms are ploted only in liquid region

8. Composition of h-x diagram Saturated vapor line at p1 Equilibrium construction line at p1 1e Used to determine isotherm line in mixing region! Start from x1; move up to equilibrium construction line; move right to saturated vapor line; determine 1’; connect 1 and 1’. Isotherm at P1 and T1 Adding energy B A x1 X1’ mass fraction of ammonia in saturated vapor

9. h-x diagramat the end of your textbook you will find these diagramsfor 1) NH3-H2O2) H2O-LiBr LiBr is one of the major liquid descants in air-conditioning systems

10. Adiabatic mixing in h-x diagram(Water – Ammonia) From the textbook (Thermal Environmental Eng.; Kuehen et al)

11. Absorption cooling cycle Rich solution of Heat H2O + NH3 H2O H2O Rich solution of H2O + NH3

12. Mixing of two streams with heat rejection (Absorber) m2 =pure NH3 (x2=1) m3 mixture of H2O and NH3 m1 m3 m2 2 m1 Q cooling 3’ Mixture of 1 and 2 Heat rejection Mass and energy balance: (1) 1 3 (2) (3) x3 x From mixture equation: Substitute into (2) Substitute into (3) From adiabatic mixing (from previous slide)

13. Change of pressure(pump) Sub cooled liquid at p2 2 Saturated liquid at p1 1 p1 ≠p2 m1 =m2 p2 Saturated liquid at x1 =x2 2 p1 Saturated liquid at 1 x1=x2

14. Heat transfer with separation into liquid and vapor (Generator) Saturated vapor Heat =2V Sub cooled liquid Saturated liquid We can “break” this generator into 2 units heating m4 Q12 /m1 2L= m1 =m2 Separator mixture sub cooled liquid x1 m3 Q12 Apply mass and energy balance In the separator : Apply mass and energy balance In the heat exchanger defines point 2 in graph Defines points 3 and 4 in graph

15. Heat rejection with separation into liquid and vapor (Condenser) Saturated vapor at p1 m1 Saturated vapor 1 heat rejection m2 Q1-2/m1 m1 =m2 Saturated liquid at p1 x1 =x2 2 p1 =p2 x1=x2

16. Throttling process (Expansion valve) Saturated vapor 1 2V 1 2 T1 h1 =h2 2 p1 Saturated liquid at p1 ≠p2 T2 2L Saturated liquid p2 m1 =m2 p1 ≠p2 Saturated liquid at x1 =x2 x1 =x2

17. Simple absorption system 3V 3L 3LLP

18. Simple absorption system Saturated vapor at p2=p3=p4 3V 6 3 5V mixing 1’ Needed thermal energy Useful cooling energy 4 3L 5 3LLP 2 Saturated liquid at p2=p3=p4 Saturated liquid at p1=p5=p6=p3_LLP 1 5L

19. Heat transfer with separation into liquid and vapor (Generator) How to move point 4 to right ? =2V =2V heating m4 Q12 /m1 2L= 2L= =m2 m1 =m2 mixture Separator mixture sub cooled liquid x1 x1 m3 Q12 m3 Q12

20. Absorption cooling with preheaterimprovement 1 Rich ammonia vapor 4 5 Refrigeration and air conditioning (Ramesh et al)

21. Absorption cooling with preheater Saturated vapor at p1’ 1’’’V=3 Major heat source 6 1’’’ mixing isotherm 6h 1’’ Useful cooling energy 1’’’L =2 4 5 1’ Saturated liquid at p1’ 2’ , 2’’ Saturated liquid at p1 1 Cooling tower Pumping energy COP= Q cooling / Q heating (Pump ???)

22. Use of precooling(system improvement #2)

23. Absorption cooling with precooling Saturated vapor at p1’ 1’’’V=3 Major heat source 6’ 6 1’’’ 6h mixing Saturated liquid at p1’ isotherm 1’’ Useful cooling energy (larger!) 1’’’L =2 4 1’ Saturated liquid at p1 4’ 2’ , 2’’ 5 1 Cooling tower (needs to cool more!) Pumping energy

24. System improvement #3 Generator with Enrichment of NH3 Different 8V 9 8L 10 8LLP 11

25. Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 5 m1 =m2 2 mixture isotherm sub cooled liquid m3 2L Q12 x8 x1

26. System improvement #1Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 5 m1 =m2 2 mixture isotherm sub cooled liquid m3 2L Q12 x8 x1

27. Ammonia Vapor Enrichment Process(Rectification)

28. Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture) This is our point cooling 1 4=2V Separator 6=5V Q12 /m1 cooling Q45 /m4 x8 m8 8 7 5 m1 =m2 2 mixture isotherm sub cooled liquid m3 2L Q12 x8 x1

29. Absorption system with Enrichment (no preheater nor precooler) Saturated vapor at p2 3V 8V mixing 3 11 8L 1’ Useful cooling energy 8LLP 10 2 3L 9 Saturated liquid at p2 Saturated liquid at p1 1

30. For Real energy analysis you need real h-x diagram! hfg for H2O hfg for NH3

31. Example of H2O-NH3 System • Text Book (Thermal Environmental Engineering) Example 5.5 • HW: • Solve the problem 5.6 from the textbook • Beside example 5.5, you will need to study example 5.6 and 5.7

32. LiBr-H2O Systems

33. LiBr-H2O Systems

34. Twine vessel LiBr-H2O Systems

35. Useful information about LiBr absorption chiller • http://www.cibse.org/content/documents/Groups/CHP/Datasheet%207%20-%20Absorption%20Cooling.pdf Practical Tips for Implementation of absorption chillers • Identify and resolve any pre-existing problems with a cooling system, heat rejection system, water treatment etc, before installing an absorption chiller, or it may be unfairly blamed. • Select an absorption chiller for full load operation (by the incorporation of thermal stores if necessary) as COP will drop by up to 33% at part-load. • Consider VSD control of absorbent pump to improve the COP at low load. • Consider access and floor-loading (typical 2 MW Double-effect steam chiller 12.5 tons empty, 16.7 tones operating). • Ensure ambient of temperature of at least 5°C in chiller room to prevent crystallization. • http://www.climatewell.com/index.html#/applications/solar-cooling

36. System with no pump(Platen-Munter system) • H2O-NH3 + hydrogen http://www.youtube.com/watch?v=34K61ECbGD4

37. Thermal storage for adjustment production to consumption We need a thermal storage somewhere in this system !

38. Thermal storage • Store heat • Many issues to consider (∆T, pressure, losses,…. ) • Store cooling energy • Chilled water • For cooling condenser • For use in AHU (cooling coils) • Ice storage • Compact but… • Other materials (PCMs) that change phase the temperature we need in cooling coils • Many advantages, but disadvantages too!

39. On-Peak and Off-Peak Periods This profile depends on the type of building(s) !

40. Chilled water tank Use of stored cooling energy Store Use

41. Which one is better ? • Depends on what you • want to achieve: • Peak electric power reduction • Capacity reduction • …..

42. Downsizing the Chiller • Lower utility costs • Lower on-peak electrical consumption(kWh) • Lower on-peak electrical demand (kW) • Smaller equipment size • Smaller chiller • Smaller electrical service (A) • Reduced installed cost • May qualify for utility rebates or other incentives

43. Sizing storage system (use Annual Cooling-Load Profile) How often you need to use it? What are the cost-benefit curves ? What is the optimum size ?