Download viii. air circulation

VIII.
AIR CIRCULATION
A. Definition - movement of air within
greenhouse
B. Circulation importance
1. Uniform air movement
2. Prevent temperature layering
Leaf
CO2
H2O
Heat
3. better air exchange around
plant
a. replace CO2 depleted air
b. remove high humidity
c. reduce temperature of leaf
surfaces
C. Circulation requirements
– 40 ft/min minimum up to 100 ft/min
– Slight movement of leaf
Low
Circulation:
Photosynthesis
vs rate of air
movement
around leaves
High turbulence
Low turbulence
High
D. When to Circulate
– When
– Night:
• continuous all year
– Day:
• winter
– only when min. ventilation off
– during medium
or
– max ventilation
• summer - usually off
E. Problems
– Uniform air movement
– Moving air through plants
F. Types of Systems
1. Horizontal Air Flow
(HAF)
a. Description
b. Requirements
– Fan capacity:
1/4 vol.
– Placement:
• 25' x 100'
four fans
• 20’ x 50’ two
fans
c. Better than
poly tube
Circulation: HAF
HAF
2. Plastic (poly) tube system
a. Description
b. Requirements
–fan capacity = 1/4 house
volume
–cross sectional area of tube =
1 sq ft/100 cuft/min, capacity
of fan
–total area of all holes = 1.5 to 2
times cross sectional area
–30' wide house: two fans
–100-150' long: two fans
Circulation: Polytubeminimum ventilation and
heating
Circulation: Polytube
Circulation: Polytube
air
Polytube circulation