VIII. AIR CIRCULATION

A. Definition - movement of air within greenhouse

B. Circulation importance1. Uniform air movement2. Prevent temperature layering

3. better air exchange around plant

a. replace CO2 depleted air

b. remove high humidity

c. reduce temperature of leaf surfaces

Leaf

CO2 H2O Heat

C. Circulation requirements

–40 ft/min minimum up to 100 ft/min

–Slight movement of leaf

Circulation: Photosynthesis

vs rate of air movement

around leaves

Low High

High turbulence

Low turbulence

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. Descriptionb. Requirements– Fan capacity:

1/4 vol.– Placement:• 25' x 100'

four fans• 20’ x 50’ two

fansc. Better than

poly tube

Circulation: HAF

HAF

2. Plastic (poly) tube systema. Descriptionb. 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: Polytube- minimum ventilation and

heating

Circulation: Polytube

Circulation: Polytube

air

Polytube circulation