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 Same as vapor compression but NO COMPRESSOR
Replace compressor

4. Absorption cooling cycle
Relatively simple thermodynamics with addition of mixtures (water – ammonia)
Rich solution of
Heat
H2O
H2O + NH3
Rich solution of
H2O
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 hfg Isotherms are ploted only in liquid region for H2O
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 diagram at the end of your textbook you will find these diagrams for 1) NH3-H2O 2) 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
H2O + NH3
Rich solution of
H2O
H2O + NH3

12. Mixing of two streams with heat rejection (Absorber)
=pure
NH3 (x2=1) m3
mixture of
H2O and NH3 m1 m3 m2 m1 2 Q
cooling
Heat rejection
Mixture of 1 and 2 3’
Mass and energy balance:
(1)
(2) 1 3
(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
sub cooled
liquid
mixture x1
Q12 m3
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 2 h1
=h2 T1 1 2 p1
Saturated liquid at p1
≠p2 T2 2L
Saturated
liquid m1
=m2 p1
≠p2 p2
Saturated liquid at x1
=x2 x1
=x2

17. Simple absorption system3V 3L
3LLP

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

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
sub cooled
liquid
mixture x1 x1
Q12 m3
Q12 m3

20. Absorption cooling with preheater improvement 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’’ 1
Saturated liquid at p1
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 6h
1’’’
mixing
Saturated liquid at p1’
isotherm
1’’
Useful
cooling
energy
(larger!)
1’’’L =2 4 1’
Saturated liquid at p1
2’ , 2’’ 4’ 5 1
Cooling
tower
(needs to cool more!)
Pumping
energy

24. System improvement #3 Generator with Enrichment of NH3 8V 9 8L 10 8LLP
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 m1
=m2 5 2
sub cooled
liquid
mixture
isotherm m3 2L
Q12 x1 x8

26. System improvement #1 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 m1
=m2 5 2
sub cooled
liquid
mixture
isotherm m3 2L
Q12 x1 x8

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 m1
=m2 5 2
sub cooled
liquid
mixture
isotherm m3 2L
Q12 x1 x8

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

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

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
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.

36. System with no pump (Platen-Munter system)
H2O-NH3 + hydrogen

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

38. Thermal storage Store heat Store cooling energy
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 ?