How to control green house environment.

1. Controlling Green HouseControlling Green House
EnvironmentEnvironment
Active Summer Cooling,Active Summer Cooling,
Active Winter Cooling,Active Winter Cooling,
Ventilation,Ventilation,
AndAnd
ComputersComputers..Prof. S. D. TidkeProf. S. D. Tidke
Modern college, PuneModern college, Pune

2. Why Cool Greenhouses ?
Most places have a summer climate that
requires greenhouse cooling – even Vermont
A greenhouse must be capable of cooling in
the winter and summer
With passive cooling greenhouses can
maintained temperature.

3. Too HOT!!
Loss of stem strength
Reduction of flower size
Delay of flowering
Bud abortion

4. ACTIVE SUMMER COOLINGACTIVE SUMMER COOLING
 Fan-and-pad system
 Fog system
ACTIVE WINTER COOLINGACTIVE WINTER COOLING
 HAF fans
 Convection tube

5. ACTIVE SUMMER COOLINGACTIVE SUMMER COOLING
• Also called Evaporative Cooling system.
• Works well in most climates.
• Based on heat absorption during the
evaporation of water.
• Relatively inexpensive compared to
other types of cooling.

6. Effectiveness of Summer Cooling
Fan and pad cooling can lower to 80% of
the difference between the wet and dry bulb
temperatures
Fog cooling can lower the temperature by
nearly all of the difference
Both of these systems are most effective at
low humidity

8. Fan and Pad CoolingFan and Pad Cooling
Available for almost 50 years
Most common system for summer cooling
Originally the pad was composed of wood
shreds
Today it is composed of cellulose
Exhaust fans are placed on the opposite wall

9. Pad Types and Specifications
 Excelsior pads (Wood fiber) had to be framed in wire
mesh for support; required annual replacement
 Cross-fluted cellulose is the most popular today, can
last up to 10 years
– Should be kept from heavy rains
– Only move if dry
 Other types of pads include aluminum fiber, glass
fiber, and plastic fiber

14. Cross-fluted cellulose pads
Come in height increments of ft
Available in 2, 4, 6, and 12 inches thick
A 4-inch-thick pad will handle an air intake of
250 cfm; a six inch 350 cfm. (cubic feet per
minute)
By way of comparison excelsior pads can only
support an airflow rate of 150 cfm.

16. EXHAUST FAN

17. Exhaust Fan Placement Rules
• Should not be more than 25 ft apart
• If the end of the greenhouse is 60 ft wide you
will need at least 3 fans
• Fans should be evenly spaced at plant height
• Rules change with multiple houses
• Protect fans from weather and provide
screening on both sides to protect workers,
visitors, and wildlife

21. Fog Cooling systemFog Cooling system
• 20-year-old technology
• High pressure water delivery system generates a
fog of very fine water particles (<10 microns)
• Drops evaporate in the air
• Even dispersal of the particles means cooling of
throughout the greenhouse

22. Fog Cooling
• Initial cost usually close to that of fan and pad
cooling systems.
• Operating cost less than fan-and-pad cooling
• Dispersion of water particles in the greenhouse air
where they extract heat from the air as they
evaporate.
• Rate of cooling increases proportionately as water
droplet size decreases.
• Systems allow near 100 percent cooling efficiency

24. Active Winter CoolingActive Winter Cooling
• Excess heat can be a problem during the winter.
• The actual process in winter cooling is tempering the
excessively cold ambient air before it reaches the plant
zone. Otherwise, hot and cold spots in the green house
will lead to uneven crop timing and quality.
• This mixing of low temperature ambient air with the
warm inside air cools the green house in the winter. .

25. Effectiveness of Winter Cooling
• Ventilators ‘used’ to be the only way
to winter cool
• Convection-tube and HAF eliminate
horizontal temperature gradient
problems
• Both modern systems circulate air in
the greenhouse

26. Active Winter Cooling
Convection tube cooling
•A polyethylene convection tube with air distribution holes,
a pressurizing fan to direct air in to the tube under
pressure, and an exhaust fan to create vacuum.
•When the air temperature inside the green house exceeds
the set point, the exhaust fan starts functioning thus
creating vacuum inside the green house.
•The louver of the inlet in the gable is then opened through
which cold air enters due to the vacuum.
•The pressurizing fan at the end of the clear polyethylene
convection tube, operates to pick up the cool air entering
the louver..

30. HAF fans (Horizontal air flow)
Similar to convection-tube-system
Requires HAF fans in the place of
convection tubes
HAF fans can be used for air
circulation when neither heating nor
cooling is in operation

32. VENTILATION SYSTEMVENTILATION SYSTEM
• Definition - a means of changing the air in an
enclosed space to :
Keep fresh air for
respiratory system
Preserve correct level
Of Oxygen in the air Control Carbon Dioxide
Control the moisture level Lowering the heat level Remove dust and odors

33. Requirements for an acceptable amount of fresh air
supply in buildings will vary depending on the nature of
occupation and activity.
Air changes per hour or ventilation rate is the
preferred criteria for system design.
SYSTEM OF VENTILATION

34. Definition - the process of supplying and removing
air through an indoor space without using
mechanical systems.
It refers to the flow of external air to an indoor
space as a result of pressure or temperature
differences
The benefits of natural include:-
Improved Indoor air quality (IAQ)
Energy savings
Reduction of greenhouse gas emissions
Increased worker productivity
Natural ventilation

35. WIND EFFECT STACK EFFECT COMBINATION
EFFECT

36. Acta Hortic. 443: 31-38

38. MECHANICAL VENTILATION SYSTEMS
Definition - Circulate fresh air using ducts and fans rather than relying
on airflow through small holes or crack’s in a home’s wall, roof or
windows.
Benefits of using mechanical ventilation:-
Better indoor air quality –can remove pollutants, allergens, and
moisture that can cause mold problems
More control – provide proper fresh air flow along with appropriate
locations for intake and exhaust
Improved comfort – allow a constant flow of outside air into the
home and can also provide filtration, dehumidification, and
conditioning of the incoming outside air.

39. • Now-a-days, computer control systems are common in
greenhouse
• Computer systems can provide fully integrated control
of temperature, humidity, irrigation and fertilization,
CO2, light and shade levels.
• A computer can control hundreds of devices within a
green house by utilizing dozens of input parameters,
such as outside and inside temperatures, humidity,
outside wind direction and velocity, CO2 levels and
even the time of the day or night.
COMPUTERSCOMPUTERS

40. • Computer systems receive signals from all sensors, and
send appropriate commands every minute to each piece
of equipment in the greenhouse.
• A computer produces graphs of past and current
environmental conditions both inside and outside the
greenhouse complex..
• Computers can only assist by adding precision to the
overall greenhouse production practice, and they are
only as effective as the software it runs and the
effectively of the operator.