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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