Lecture Objectives:

• Introduce HW3

• Learn about sorption chillers

Sequence of operation(PRC research facility)

Control logic:

Mixture in zone 1: IF (( TM<TSP) & (DPTM<DPTSP) ) heating and humidifying Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heatingHumidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA)

decrease humid.

Mixture in zone 2: IF ((TM>TSP) & (DPTM<DPTSP) ) cooling and humidifying Cool. coil cont.: IF (TSP<TSA) increase cooling or IF (TSP>TSA) decrease

coolingHumidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA)

decrease hum.

Mixture in zone 3: IF ((DPTM>DPTSP) ) cooling/dehumidifying and reheatinCool. coil cont.: IF (DPTSP>DPTSA) increase cooling or IF (DPTSP<DPTSA)

decrease cooling Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heating

Set Point (SP)

Mixture 2

Mixture 3

Mixture 1

DBTSP

DPTSP

HW3

• Writhe a sequence of operation instruction list for the air handling unit from HW2 (problems: 3&4)

HW3• You will need to define:

A) what environmental variable/condition change- Temperature and RH of ambient air, Q cooling, Q heating, …..

B) which variables can you control -recirculation rate, recirculation position, Total flow rate, TCC,…

C) which variable will you control - …..

D) how are you going to “move” between different operation schemes E) writhe “if - else” set of instruction for different controlled devices while

considering different operation scheme (see the example I gave you in class)

Absorption CycleSame as vapor compression but NO COMPRESSOR

Replace compressor

Absorption cooling cycleRelatively simple thermodynamics with addition of mixtures (water – ammonia)

HeatRich solution of

Rich solution of

H2O

H2O H2O + NH3

H2O + NH3

Mixtures(T-x diagram)

For P= 4 bar

Dew point curve

Bubble point curve

Saturated vapor

Saturated liquid

Mixture of liquid and vapor

Impact of Pressure

h-x diagram

Isotherms are showmen only in liquid region

hfg for H2O

hfg for NH3

Composition of h-x diagramSaturated vapor line at p1

Equilibrium construction line at p1

x1

A

Adding energy

B

Isotherm

at P 1 and T 1

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’.

X1’mass fraction of ammonia in saturated vapor

1e

h-x diagramat the end of your textbook you will find these diagrams

for 1) NH3-H2O

2) H2O-LiBr

LiBr is one of the major liquid descantsin air-conditioning systems

Adiabatic mixing in h-x diagram(Water – Ammonia)

From the textbook (Thermal Environmental Eng.; Kuehen et al)

Absorption cooling cycle

HeatRich solution of

Rich solution of

H2O

H2O H2O + NH3

H2O + NH3

Mixing of two streams with heat rejection (Absorber)

QHeat rejection

m1

m2

m3

xx3

1

2

3’

3

Mass and energy balance:

From mixture equation:

(1)

(2)

(3)

Substitute into (2)

Substitute into (3)

From adiabatic mixing (from previous slide)

m1

m2

m3

=pure NH3 (x2=1)

Mixture of 1 and 2cooling

mixture of H2O and NH3

Change of pressure(pump)

1

2

p1 ≠p2

p2

p1Saturated liquid at

Saturated liquid at

m1=m2

x1 =x2

x1=x2

1

2

Saturated liquid at p1

Sub cooled liquid at p2

Heat transfer with separation into liquid and vapor (Generator)

Apply mass and energy balance In the separator :

Defines points 3 and 4 in graph

Heat

Sub cooled liquid Saturated

liquid

Saturated vapor

We can “break” this generator into 2 units

Q12

m1=m2

m4

m3

Separator

Apply mass and energy balance In the heat exchanger

defines point 2in graph

Q12 /m1

x1

sub cooled liquid

mixture

=2V

2L=

heating

Heat rejection with separation into liquid and vapor (Condenser)

m1=m2

Saturated vapor

m1

m2

1

Saturated vapor at

p1

Saturated liquid at

p1

x1=x2

2x1 =x2

p1 =p2

Q1-2/m1

heat rejection

Throttling process (Expansion valve)

m1=m2

x1 =x2

p1 ≠p2

1

2

x1 =x2

p1 ≠p2

p1

p2

h1 =h21

2

Saturated liquid at

Saturated liquid at

T2

T1

2V

2L

Saturated vapor

Saturated liquid

Simple absorption system

3L

3V

3LLP

Saturated vapor at p2=p3=p4

Saturated liquid at p2=p3=p4

Saturated liquid at p1=p5=p6=p3_LLP

Simple absorption system

1

2

3

3V

3L 4 5

1’

5L

65V

3LLP

mixing

Useful cooling energy

Needed thermal energy

Heat transfer with separation into liquid and vapor (Generator)

Q12

=m2

m3

x1

mixture

=2V

2L=

heating

Q12

m1=m2

m4

m3

Separator

Q12 /m1

x1

sub cooled liquid

mixture

=2V

2L=

How to move point 4 to right ?

Heat rejection with separation into liquid and vapor (Enrichment NH3 in the vapor mixture)

Q12

m1=m2

m3

SeparatorQ12 /m1

x1

sub cooled liquid

mixture

4=2V

1cooling

2

2L

5

Q45 /m4

6=5V cooling

78m8x8

x8

This is our point

isothe

rm