3. Cooling

1. 3. Cooling a. Introduction 1) Definition • reduce temperature of air entering greenhouse • Why? • Reduce stress • Uniformity • Better growth

2. 2) Types of systems a) refrigeration system b) evaporative cooling • pad and fan • high pressure mist - fog b. Evaporative/cooling

3. 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)

5. Evaporative Cooling 2) Factors determining cooling • Temperature: outside air • Relative humidity: outside air • Temperature: inside air • air movement • shading • structure • Covering

6. 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

7. Cooling efficiency 80% to 90% of difference between wet and dry bulb

8. 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

9. Important points in operation • Eliminate leaks • through pads • around pads • other areas • Uniform wetting • holes clogged • Detergent • Algae • CuSO4 d. Unit coolers

10. e. High pressure mist - fog • Small droplets • Nozzles • 150-200 psi up to 500 psi • special pump • Problems • salt deposits • poor air movement

11. Fog evaporative cooling

12. Compare pad and fan to fog cooling