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IX. REDUCING GREENHOUSE TEMPERATURE A. temperature regimes –range 50-80 deg, stress above 90 deg.

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Presentation on theme: "IX. REDUCING GREENHOUSE TEMPERATURE A. temperature regimes –range 50-80 deg, stress above 90 deg."— Presentation transcript:

1 IX. REDUCING GREENHOUSE TEMPERATURE A. temperature regimes –range deg, stress above 90 deg

2 Greenhouse effect

3 B. Temperature in greenhouse determined by: 1. Solar energy –Greenhouse effect: Solar energy- short wave radiation passes through glass Thermal radiation- longer waves trapped –shading in greenhouse –time of year –time of day

4 2. Exterior ambient temperature 3. Moisture transpired –Temperature in empty greenhouse greater than in greenhouse with plants 4. Evaporation of water from soil, walls etc.

5 C. Techniques to reduce temperature 1.Shading - reduce energy absorbed a.Shading compound Permanent shade after application Removed Aug – Sept b.Shade curtain Remove during cloudy weather

6 2. Greenhouse ventilation a. Definition movement of outside air through greenhouse b. Characteristics of ventilation system 1) capacity to reduce temperature 2) uniform temperature 3) automated 4) minimum and maximum ventilation

7 c.Time of year 1)Winter ventilation Late fall, winter, early spring: outside air cool Minimum to maximum ventilation usually adequate 2)Summer ventilation 1)Temperature control difficult Shading and ventilation Maximum ventilation

8 d. Types of Systems 1) Natural ventilation –Establish convection currents Ridge vent and side vents Open area -40% of floor space Removable side wall Removable roof

9 Natural ventilation

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13 2) Motorized Systems - minimum Mix cold with warm ghs. air Poly tube system with vent Low speed fan with vent One fan or several turned on, with vent 3) Motorized systems – maximum Outside directly into greenhouse Temperature dependent Air flow rate -3/4 to 1 1/4 air ex. /min -7-8° rise

14 Air exchange vs temperature

15 e. Control of Systems 1) Natural ventilation Manual Automatic Thermostat Computer 2) Motorized ventilation –thermostats –fan(s) 1 or 2 speed –Vents Fully open or closed modulating

16 3) End wall ventilation 1) Fans on one end wall 2) Vents on other end wall 3) Fan spacing 25’ 4) 1 air exchange/min

17 4) Side wall ventilation –problem mixing cold air –Air exchange rate vs velocity 1 exchange 30’ x 100’ -end wall ft/min -side wall - 30 ft/min –Fan spacing- max 25 ft

18 Side wall ventilation

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21 Natural ventilation


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