Australian Solar Cooling Interest Group (ausSCIG ......Australian Solar Cooling Interest Group...

Australian Solar Cooling Interest Group (ausSCIG) Conference 2013 www.ausSCIG.org

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Day 2 – Solar Cooling Conference - 12/04/2013Venue: CSIRO, North Ryde, Sydney

Timothy AndersonTimothy AndersonTimothy AndersonTimothy Anderson1111 ,Mike Duke,Mike Duke,Mike Duke,Mike Duke2222, and James Carson, and James Carson, and James Carson, and James Carson2222

1 School of Engineering, Auckland University of Technology

2 School of Engineering, University of Waikato


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� Demand for cooling can be more significant than for heating in Australia

� Unglazed solar collectors have often been used a means of providing low cost heating to swimming poolsto swimming pools

� Under night conditions when there is no solar radiation and the sky temperature is low, unglazed collectors can radiate heat to the sky


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� Unglazed collectors are typically polymer style “mats” that are laid on top of a roof, often leading to poor often leading to poor aesthetics due to their lack of integration

� Want to integrate into the building not ontothe building

www.sunwindpowerinc.com


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� Long run metal roofing is widely used for domestic, commercial and industrial applicationsapplications

� Can be used for low temperature pool heating through to domestic water heating

� High emissivity polyester paint surface


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� Long run roofing made of coloured steel

� Cooling trough added to profileadded to profile

� Channels formed in the trough are enclosed forming a riser tube having an inlet and outlet at opposite ends


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� Grey absorber

� 1-D steady state thermal model

� In the absence of solar radiation the collector radiation the collector acts as a radiator

� Steady state outdoor thermal test

)(4 3Spmap TTTS −= σε

ParameterParameterParameterParameter SymbolSymbolSymbolSymbol ValueValueValueValue UnitUnitUnitUnitEmittance of plate εp 0.95System flow rate m 340 l/hCollector Area A 6.3 m2

Absorber thickness t 0.5 mmTube Hydraulic

Diameterdh 8.5 mm

Tube Spacing W 0.22 mInsulation Conductivity k 0.045 W/mK

Back Insulation Thickness

Lb 0.1 m

Absorber Conductivity kabs 50 W/mK

( )( )32

2

00028.00035.00224.01

)100/(73.0)100/(56.0711.0

nnn

TT dpdps

+−+×

++=ε

ass TT 25.0ε=


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� Collectors coupled to a cylinder which was heated during the day then cooled at night

� In the absence of any 0

10

20

30

40

50

Tem

pera

ture

(°C

)

TankAmbient

� In the absence of any radiation, there is a net heat loss from the collector of ~50 W/m2

-200

-100

0

100

200

300

400

0 4 8

12

16

20 0

Hea

t G

ain

/Loss

(W

/m2)

Time (h)

0

0 4 8

12

16

20 0

Time (h)


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� Potential to use large areas of collector to operate in heating mode during daytime, 40

60

80

100

Ra

dia

nt

He

at

Lo

ss (

W/m

2)

Experiment

Modelled

during daytime, with storage in a “hot” cylinder and at night with storage in a “cold” cylinder

0

20

40

20:00 21:00 22:00 23:00 00:00

Ra

dia

nt

He

at

Lo

ss (

W/m

Time (h)


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� Four cities chosen for examination, Auckland, Sydney, Brisbane and Perth

� Sky temperature is 1500

2000

2500

3000

3500

4000

Ho

urs

Pe

r Ye

ar

Auckland

Sydney

Brisbane

Perth

� Sky temperature is typically 15-20° below ambient for all cities 0

500

1000

0 5 10 15 20 25 30 35

Ho

urs

Pe

r Ye

ar

Tambient - Tsky

ass TT 25.0ε=( ) ( )322 00028.00035.00224.01)100/(73.0)100/(56.0711.0 nnnTT dpdps +−+×++=ε


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� Sky temperature depression ignores the influence of convective heat transfer

� Stagnation temperature 2000

2500

3000

3500

4000

Ho

urs

Pe

r Ye

ar

Auckland

Sydney

Brisbane

Perth

� Stagnation temperature below the ambient temperature

� Perth and Sydney seem most suitable

( )3

44

4 apc

asapastag Th

TTTT

σεεσε

+−

−=

0

500

1000

1500

0 5 10 15 20

Ho

urs

Pe

r Ye

ar

Tambient - Tstagnation


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� Able to achieve cooling in the order of 50W/m2 (temperatures of ~10ºC observed)

� Well suited for moderate cooling loads under summer conditions if storage used

� Sydney and Perth a system area of 100m2� Sydney and Perth a system area of 100m2

averaging a radiant heat loss of 50W/m2 may be able to be used for approximately 2000h annually; this would lead to cooling of approximately 10000kWh/annum.


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Australian Solar Cooling Interest Group (ausSCIG ......Australian Solar Cooling Interest Group...

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