Greenhouse Cooling Concepts

1
Greenhouse CoolingConcepts
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 reach
  temperatures of 20F greater (or more) than the
  air temperature

3
Too HOT!!

• Loss of stem strength
• Reduction of flower size
• Delay of flowering
• Bud abortion

4
(No Transcript)
5
SUMMER COOLING
WINTER COOLING

• Active
• Fan-and-pad cooling
• Fog
• Passive
• ventilators

• HAF fans
• Convection tube cooling

6
Passive Cooling

• Percent of roof space ventilated has increased
  over time with design improvements
• Success is very crop specific
• Even fully retractable roof designs are now
  available
• Cheaper to operate than active cooling systems,
  but construction costs arent less expensive

7
Acta Hortic. 443 31-38
8
(No Transcript)
9
(No Transcript)
10
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

11
Evaporative Cooling

• Works well in most climates where might it not
  function effectively?
• Based on heat absorption during the evaporation
  of water
• Relatively inexpensive compared to other types of
  cooling

12
(No Transcript)
13
http//www.munters.com/home.nsf/FS1?ReadFormconte
nt/products.nsf/ByKey/OHAA-55GSWH
http//okfirst.ocs.ou.edu/train/meteorology/HeatTr
ansfer.html
14
Pad and Fan 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

15
(No Transcript)
16
(No Transcript)
17
Active Summer Cooling System Calculations (Basics)

• Fan-and-Pad system
• Rate at which warm air must be removed from the
  greenhouse
• Types of pads used
• Fan placement
• Path of the airstream

18
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
• Why are pads thick? and why do they have a cross
  fluted design?

19
(No Transcript)
20
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/ft2 a six inch 350 cfm/ft2
• By way of comparison excelsior pads can only
  support an airflow rate of 150 cfm/ft2
• You want vents over the exterior of the pads to
  seal the external air source off when active
  cooling isnt needed

21
(No Transcript)
22
More Details

• Water must be delivered to a 4-inch pad at the
  rate of 0.5 gpm per linear foot of pad
• For a 6-inch thick cellulose pad a 0.75 gpm per
  linear foot is required
• Longest recommended delivery pipe is 60ft for the
  4 inch system and 50 ft for the 6 inch system1/8
  inch holes every three inches are required for
  both systems
• Holes point upward and release water into an
  impingement cover water drips down onto a
  distribution pad

23
Rate of Air Exchange

• Measured in cfm (cubic feet per minute)
• NGMA uses 8 cfm/ft2 of floor space as astandard
• In warmer climates 1 volume per
  minuterecommended roughly 11-17 cfm/ft2
• As elevation increases so must the rate of air
  removal.  Why?

24
Other factors

• Light Intensity
• Temperature rise across the greenhouse
• Pad-to-fan distance

25
Calculating Air Removal Rate

1. Calculate the standard cfm Greenhouse area X 8
   cfm/ft
2. Correct for the standard rate of air removal
   using the larger of Fhouse or (Fvel)
3. Fhouse Felev X Flight X Ftemp
4. Total cfm standard cfm X (Fhouse or Fvel)
5. Select the fans to install

26
(No Transcript)
27
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
• Place fans on leeward side of the greenhouse
• Rules change with multiple houses
• Protect fans from weather and provide screening
  on both sides to protect workers, visitors, and
  wildlife
• Air movement can cause special problems in larger
  houses

28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
Fog Cooling

• 20-year-old technology
• High pressure water delivery system generates a
  fog of very fine water particles (lt10 microns)
• Drops evaporate in the air
• Even dispersal of the particles means cooling of
  throughout the greenhouse

http//www.valproducts.com/Air/EvapFog.html
32
Fog Cooling

• Initial cost usually close to that of fan and pad
  coolingsystems (water quality determining
  factor)
• 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
  waterdroplet size decreases.
• Systems allow near 100 percent cooling efficiency
  and wet bulb temperatures can essentially be
  obtained

33
(No Transcript)
34
(No Transcript)
35
Fog Cooling II

• Exhaust fans still used
• Fog nozzles installed just inside the
  inletventilators
• Roughly half the exhaust fan capacity of
  fan-and-pad cooling systems is necessary
• High water quality is critical
• Can also be used with plant propagation systems
• Disease occurrence much lest than with a
  mistsystem. Why?

36
Fog Cooling Advantages

• There is less electrical consumption
• Heat rise across the greenhouse is controlled
• Cooler average temperatures can be achieved
  across the greenhouse
• System is good substitute for mist systems on
  propagation benches.

37
Effectiveness of Winter Cooling

• Ventilators used to be the only way to winter
  cool problems
• Convection-tube and HAF eliminate horizontal
  temperature gradient problems
• Both modern systems circulate air in the
  greenhouse

38
(No Transcript)
39
Active Winter Cooling

• Convection tube cooling
• Exhaust fan turned on
• A louver opens in the gable
• A pressurizing fan in the end of the polyethylene
  tubes turns on
• Cool air mixes with greenhouse warm air and galls
  to thefloor cooling the plant growing area
• Pressurizing fan must move as much air as the
  exhaustfan.
• 2 cfm required

40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
HAF fans

• 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

44
(No Transcript)
45
(No Transcript)
46
Integrating of Heating andCooling Systems

• Remember there are some spring andfall days
  when you may have to use,summer heating, winter
  cooling andsummer cooling systems all on
  thesame day

47
BRINGCALCULATORSandTEXTBOOK on Thursday !!!!