3. cooling a. introduction 1) definition reduce temperature of air entering greenhouse why?...
TRANSCRIPT
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