Alternative Alternative evaporative coolingevaporative cooling

and and naturally naturally ventilated double roof ventilated double roof

systemsystem for for environmental environmental

controlled controlled dairy barndairy barn located in tropical located in tropical

and subtropical and subtropical regionsregionsWei Fang, Ph.D., Professor

Dept. of Bio-Industrial Mechatronics EngineeringNational Taiwan University

Part I. Alternative evaporative cooling

Evaporative coolingEvaporative cooling

Pad and FanPad and Fan

Pad and Fan system is Pad and Fan system is PowerfulPowerful

But it require But it require proper design, proper design, proper installatioproper installatio

nnandandproper maintenaproper maintena

nce.nce.

Poor Poor design/install/maintenandesign/install/maintenan

cece

Poor Poor design/install/maintenandesign/install/maintenan

cece

ElectrolysisElectrolysis

Coated PadCoated Pad

Pad substitutes - Palm tree Pad substitutes - Palm tree fibersfibers

Pad substitutes – Rolling Nets

Dry bulb Temperature, oC

Rela

tive

mil

kin

g

perf

orm

an

ce

1998, ASAE fundamentals

Effect of wind speed Effect of wind speed on milking performance on milking performance

of Holstein cowof Holstein cow

Wind SpeedWind Speed 10 10 ooCC 26.7 26.7 ooCC 35 35 ooCC

0.18 m/s0.18 m/s 100 %100 % 85 %85 % 63 %63 %

2.44 m/s2.44 m/s 100 %100 % 95 %95 % 79 %79 %

4.02 m/s4.02 m/s 100 %100 % 95 %95 % 79 %79 %

1998, ASAE fundamentals

25~70 Pa pressure dropη =70 % for 15 cm pad

2.5 m/s

Multi-layer nets with Multi-layer nets with sprayingspraying

View from insideView from outside

Fogging is better than spraying

Multi-layer nets with Multi-layer nets with foggingfogging

Multi-layer nets with Multi-layer nets with foggingfogging

ComparisonComparison

OutdoorOutdoor

TTdbdb 32 32 ooCC

RH 55%RH 55%

TTdb db

After Pad After Pad Wind speedWind speed

m/sm/s

EfficiencyEfficiency

10 cm Pad10 cm Pad 26.37 26.37 ooCC 1.5-2.51.5-2.5 75 %75 %

28.25 28.25 ooCC 4.04.0 50 %50 %

Multi-Net with Multi-Net with foggingfogging

25.0 25.0 ooCC 8.08.0(3 AC/min)(3 AC/min)

92.5%92.5%

Part II. Naturally ventilated double

roof system

Materials for Roofs Materials for Roofs

Porous galvanized Porous galvanized steel platesteel plate

Traditional galvanized steel Traditional galvanized steel plate with PU attachedplate with PU attached

Learn from the mother Learn from the mother naturenature

Tiny holes on roof mimicking stomata of leaf

Porous double roofPorous double roof

Air gap between two layers provides driving force when heated by solar radiation.Such driving is self adjusted according to the intensity of outdoor solar radiation

Roof materialsRoof materials

Traditional single Traditional single layer galvanized layer galvanized steel plate + PUsteel plate + PU

DisadvantageDisadvantage Non-recycleNon-recycle PU burnablePU burnable Hot air trap insideHot air trap inside

Porous double layer Porous double layer galvanized steel plategalvanized steel plate

AdvantagesAdvantages Can be recycledCan be recycled Fire proofFire proof Provide roof opening allow Provide roof opening allow

hot air escape from roofhot air escape from roof Heated air layer enhance Heated air layer enhance

natural convectionnatural convection

Galvanized steel plate (GSP)

GSP + PU

Double Porous GSP

Code 11 is house 1 & sensor at location 1: 0.5 m from ceiling height (with no ceiling installed) , code 36 is

house 3 & sensor location is 3 m from roof

Comparison on peak Comparison on peak temperaturestemperatures

Single roofSingle roofPorous Double roofPorous Double roof

45.5 oC

38.3 oC 38.3 oC

41.1 oC

Galvanized steel plate (GSP) GSP + PU

34.9 oC

37.6 oCDouble Porous GSP

No ceiling installed

Another experimentAnother experiment

Single layer galvanize Single layer galvanize steel platesteel plate

Single layer galvanize Single layer galvanize steel plate +PUsteel plate +PU

Porous double layer Porous double layer galvanize steel plategalvanize steel plate

Single layer galvanize Single layer galvanize steel plate + white paintsteel plate + white paint

Reflective white paint Reflective white paint increase reflectivityincrease reflectivity

Wavelength, nm

Refl

ecti

vity

Galvanize steel plate painted with Reflective

white pain

Galvanize steel plate (light

green color)

Positions of T sensorsPositions of T sensorsDL porous

SL & PU SL + paint

SLOutside surface

Inside surface

Center air

Outside surface

Inside surface

Center air

Avg. T during Avg. T during 10:00-10:00-14:0014:00

T ofT of center center airair

T ofT of outside outside surfacesurface

T ofT of inside inside surfacesurface

SLSL 37.0037.00 53.9153.91 48.9748.97

SL + PUSL + PU 37.1337.13 64.2564.25 46.3646.36

DL porousDL porous 32.4232.42 52.2352.23 36.7136.71

SL + paintSL + paint 33.3233.32 49.6649.66 35.2535.25

△T = 5 oC △T = 15 oC △T = 13 oC

ConclusionsConclusions Multi-layer nets fogging system provides good evaporative

cooling efficiency even under high air velocity. Double layer porous roof provide naturally ventilated roof

vent. It also has the capability of self adjusting according to outdoor solar radiation.

Roof materials painted with Reflective white paint absorbed 30% of solar radiation, yet other roof absorbed 70% of solar radiation.

An experimental daily barn was build based on above findings.

50 m x 15 m x 2.5 m， 50 cows

Wind speed 2.5 m/s

Air exchange 2 times/min

Porous double layer galvanized steel plate

Thank you for your attention