MODELLING AND SIMULATION OF

ABSORPTION SOLAR AIR CONDITIONING SYSTEM

Teclemariam NemariamDepartment of Technology,Royal Institiute of Technology,Stockholm, Sweden

email: nemariam@egi.kth.se

Aim

• To obtain best system performance of a solar assisted absorption cooling system– Solar fraction– Overall system efficiency– Total cost

• Initial cost•Maintenance cost•Operational cost

Methodology

• TRNSYS simulation program– Transient Systems Simulation Program

• EES– Engineering Equation Solver

System Description

• Energy source Refrigeration Load cycle

System Description

• Solar collector• Thermal storage tank• Auxiliary heater • Absorption

refrigeration chiller with cooling tower

• Building• Diverter• Tee-piece• Relief valve• Piping system

relief valve

storagetank

absorptionchiller

building

tee-piece

heater

collector

sun

diverter

pump

pump

Trnsys Block Diagram

C o llec to rT Y P E 1

T Y P E 7 1

P ressu rere liev e v a lv e

T Y P E 1 3

T h erm a l sto ra g eta n k

T Y P E 3 8

T ee-p ieceT Y P E 1 1 h

A u x ilia ryh ea ter

T Y P E 6

A b so rp tio nch iller

T Y P E 7

B u ild in gT Y P E 1 9

D iv e rte rT Y P E 1 1 b

P u m pT Y P E 3

P u m pT Y P E 3

C o n tro lle rT Y P E 2 b

co o lin gto w er

Absorption Refrigeration System

g e n e ra to rc o n d e n se r

a b so rb e re v a p o ra to r

h e a t e x c h a n g e r

o u tp u th ea t

in p u th ea t

o u tp u th ea t

in p u th ea t

e x p a n s io nv a lv e

p u m p

s tro n gso lu tio n inre fr ig era n t

w ea k so lu tio nin re fr ig era n t

v a lv e

va p o u rre fr ig era n t

vapourrefrigerantP con

P ev

Tev Tcon, Tab Tg

liq u idre fr ig era n t

Absorption Refrigeration System

• Refrigerant– water

• Absorbent– Lithium

bromide

• Stages– Single-effect

• G. temp 80 – 100 C• COP 0.6 – 0.8

– Double-effect• Gen. Temp 100 – 160 C• COP 1.0 – 1.2

– Triple-effect• Gen. Temp 160 – 240 C• COP ABOUT 1.7

Absorption Refrigeration System

pure

refri

gera

nt (x

=1)

pure

refri

gera

nt (x r

)

pure

refri

gera

nt (x p

)Pressure

P 1

P 2

t2 tabs=t1 tgen

evaporator absorber

condenser generator

crys ta llisa tion

Strong refrigerant Poor refrigerant

Absorption Refrigeration System

• Drawbacks– Water

• Temperature greater than zero• High water vapour pressure

– Large volume

– Lithium bromide• Precipitate at low temperature

Building

• Details of a building are:– Location: latitude, longitude, altitude– Type: Office, recidential, hospital,...– Size: volume, area of walls, roof, floor,

windows, door, ..etc – Types of construction materials– Outside design conditions– Inside design conditions– Internal gains

Work done so far

• More than 75% course work• More than 80% literature survey• Modelling and simulation of a

complete system using standard TRNSYS components

Sample Simulation Results

• Solar collectors:– Evacuated collector, high quality flat plate

collector and ordinary flat plate colector

• Storage tank: cylinderical, vertical stand• Heater: gas fired• Single-effect absorption machine

– Refrigerant water and absorbent lithium bromide

– Capacity 24.44 kW

Sample Simulation Results

• Building:– Location: Assab, Eritrea. Latitude 13.07

N, longitude 42.6 E, altitude sea level– Type: two storey office – Size: volume, area of walls, roof, floor,

windows, door, ..etc are given in detail– Types of construction materials– Outside design conditions– Inside design conditions– Internal gains

• Every detail is given

Sample Simulation Results

• System Optimization– e.g. collector slope

0.00E+00

5.00E+07

1.00E+08

1.50E+08

2.00E+08

2.50E+08

0 10 20 30 40 50 60

collector slope (degree)

sola

r en

erg

y g

ain

(kJ

)

ESC DGC SGC

Sample Simulation ResultsSolar fraction as a function of colector area and storage volumee.g. using evacuated collector

0

10

20

30

40

50

60

70

80

10 20 30 40 50 60 70 80

collector area (m 2)

so

lar

fracti

on

(%

)

V1=1.0m3

V2=2.0m3

V3=3.0 m3

V4=4.0m3

V5=5.0m3

Sample Simulation Results• System efficiency as a function of

colector area and storage volume– e.g. using evacuated collector

0

10

20

30

40

50

60

10 20 30 40 50 60 70 80

collector area (m2)

syst

em e

ffic

ien

cy (

%)

V1=1.0m3 V2=2.0m3V3=3.0 m3 V4=4.0m3V5=5.0m3

Sample Simulation Results

• Solar fraction and system efficiency as function of collector area for a given storage volume

0

10

20

30

40

50

60

70

10 20 30 40 50 60 70 80

solar collector (m 2)

eff

icie

ncy

ESC syseff ESC solfr DGC syseffDGC solfr SGC syseff SGC solfr

Sample Simulation Results

• Yearly insolation energy, max possible solar heat gain and cooling load

0.00E+00

5.00E+06

1.00E+07

1.50E+07

2.00E+07

2.50E+07

3.00E+07

3.50E+07

4.00E+07

1 3 5 7 9 11

time (month)

en

erg

y (

kJ)

QIRT ESC DGC

SGC QLOAD

Notice

• The sample simulation result is extracted from a paper presented in the ISES Conference June 14-19 2003 in Götemberg, Sweden.

• If you have more interest please refer the paper.

• Thank you.