3. Cooling

a. Introduction

1) Definition• reduce temperature of air entering

greenhouse• Why?–Reduce stress–Uniformity–Better growth

2) Types of systems

a) refrigeration system

b) evaporative cooling

• pad and fan

• high pressure mist - fog

b. Evaporative/cooling

Evaporative cooling

1) Principal– Energy Required

– H2O (liquid) + Warm air (energy) > H2O (gas) + cooler air

– 1000 BTU to change 1 lb liquid H2O to gas (water vapor)

2) Factors determining cooling– Temperature: outside

air– Relative humidity:

outside air– Temperature: inside

air– air movement– shading– structure– Covering

Evaporative Cooling

c. Pad and fan system

– 80% to 90% of difference

between wet and dry

bulb

– Temp increases from

inlet to outlet

– higher moisture

(outside) reduces temp

decrease

80% to 90% of difference between wet and dry bulb

Cooling efficiency

1) design of system

• pad and fan system

– Equipment

• Separate house

• Ridge and

furrow

– Fan and pad size

• fans, same as

for ventilation

– pads, based on fan

size and material

2) Important points in operation

– Eliminate leaks • through pads • around pads • other areas

– Uniform wetting • holes clogged • Detergent

– Algae • CuSO4

d. Unit coolers

e. High pressure mist - fog

– Small droplets• Nozzles

– 150-200 psi up to 500 psi

– special pump

– Problems• salt deposits• poor air movement

Fog evaporative cooling

Compare pad and fan to fog cooling