Greenhouse Energy Efficiency

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• Greenhouse Energy Efficiency
• Scott Sanford
• Sr. Outreach SpecialistFocus on Energy / Rural
  Energy Issues
• Biological Systems Engineering
• University of Wisconsin Madison

This presentation is funded in part by the
Wisconsin Focus on Energy program
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Greenhouse Energy Use

• Energy
• 2nd largest cost behind labor
• 70-80 for space heating
• 10-15 Electricity
• The Economic-Energy Balance
• Light transmission for plant growth
• Environmental factors humidity, temperature
• Structure cost
• Operating costs

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Principles of Heat Loss

• Conduction
• Heat conducted through a material
• Convection
• Heat exchange between a moving fluid (air) and a
  solid surface
• Radiation
• Heat transfer between two bodies without direct
  contact or transport medium Sunlight
• Infiltration
• Exchange of interior and exterior air through
  small holes in building shell

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Greenhouse types
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Structure Efficiency

• Gutter Connected
• Lower heat loss / less surface area
• Better space utilization
• 1.5 ratio heat loss area to floor area (25,000
  sq. ft.)
• Stand alone (quonset, gable, gothic)
• Isolated growing conditions
• Natural Ventilation with open / roll-up side
  walls
• Heat as filled
• 1.7-1.8 ratio - heat loss area to floor area
  (3000 sq. ft.)

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Structural Efficiency

• Space heating comparison
• All Glazing Double poly IR
• 24,000 ft2 growing area
• Black fabric covered floor
• LP power vent unit heaters _at_ 78 seasonal
  efficiency
• Farm A Eight greenhouses 30 x 100 x 15H x
  3 side
• Energy use 1793 gallons LP per house (14,344
  gal. total)
• Farm B Gutter connected greenhouse
• 5 bay 30 (150) x 160 x 10H (15 peak)
• Energy use 11,929 gallons
• Energy savings 2415 gallons (18 savings)

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Common Glazing Materials

• Glass
• Acrylic
• Polycarbonate
• Fiberglass-reinforced plastic
• Polyethylene film

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Glazing Materials

• Heat loss
• Single pane glass
• Highest heat loss (1.1 Btu/sq. ft.-hr-F)
• Longest life (Unless large hail) 25 years
• Highest cost / Structure
• High light Transmittance
• Double Polyethylene Film
• Low heat loss ( 0.5 to 0.7 Btu/sq. ft.-hr-F)
• Shortest life 3-4 years (UV degradation)
• Low cost
• Lowest Light Transmittance

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Glazing Material Comparison
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Infrared Radiation

• Plants, soil greenhouse
• - absorb solar or short radiation
• Reradiate heat out - long wave radiation
• Glass and rigid plastic
• - inhibit loss of IR radiation (lt 4 loss)
• Polyethylene film
• - IR loss gt 50
• Polyethylene film with IR additives
• - reduce heat losses by 20
• - without loss of light transmission

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Infrared Radiation pathways
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Polyethylene film w/ IR additive

• Reduces heat loss by 15-20
• Incremental Cost 0.015 / sq. ft.
• Payback 2-3 months / one season
• Diffuses light
• AT Plastics Dura-Film 4 Thermal AC
• Dura-Film 4 Thermal AC Plus
• Tyco Plastics Tufflite Infrared
• Klerks K50 IRAC
• Green-Tek Sunsaver
• Ginegar Plastics Sun Selector AD-IR / Suntherm
• www.agra-tech.com/thermal_glazings.htm

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Glazing Materials vs Infiltration

• Infiltration Rates
• Louvers, doors, holes, laps in glazing
• Glass high (2x compared with double poly)
• Double Poly lowest
• Air Exchanges
• New Construction Per Hour
• Glass, fiberglass, polycarbonate, acrylic 0.75 to
  1.5
• Double-layer plastic film 0.5 to 1.0
• Old Construction
• Glass, good condition 1.0 to 2.0
• Glass, poor condition 2.0 to 4.0

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Infiltration Factors

• Glazing types
• Wind
• Still air versus 15 mph wind can double heat loss
• High infiltration reduces CO2 enrichment
  effectiveness
• Wind breaks
• Cut heat loss by 5 to 10
• Reduces risk of wind damage to structures
• Acts as snow fence

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Infiltration leaks

• Save 3-10 in heating costs
• Check Roof and wall vents - seal tight
• Tight Cover
• Glazing / lap seals on Glass
• Fix holes in cover
• Weather stripping around doors
• Door Sills
• Ventilation louvers close tight
• Dry Lubricant - use graphite
• Cover unneeded fans / vents during winter
• Foam and plastic
• Plug gaps around foundation
• Double/Single polyethylene over glass 40
  savings

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Factors effecting Light

• Light growth
• Greenhouse orientation
• Single span East/West maximize winter sunlight
• Multi span North/South gutter shadows move
• Glazing Transmittance
• Differences between materials
• Dust
• Anti-Dust additive
• Condensation can reduce light 25-50
• Anti-Condensate / Anti drip additive

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GE Lexan ZigZag

• Heat loss 20-40 less than single glass
• Light transmittance
• Glass 89-92 ZigZag 89 direct / 81 diffuse
• 4-6 more light to plants in winter faster
  growth
• Orientation
• East/West gutters - 2 light gain
• North/South gutters 4 light gain
• Less Support profiles than glass 2 light gain
• www.gestructuredproducts.com/sp1/LexanZigZag/LEX_E
  ng_Products_ZigZag2.html

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Greenhouse - Heat Loss

• Insulate walls to plant height
• North walls insulate all opaque surfaces
• and more?
• Perimeter 24 below ground 1 to 2 Foam
• New construction

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Night-time Heat Loss

• Night Curtains
• 80 of greenhouse heating at night
• Reduces night heating up to 50
• Double poly w/ internal thermal blanket
• 0.4 Btu/hr-F-ft2
• Curtain must be sealed to prevent chimney effect
• Double as summer shade system
• Automated curtains expensive for seasonal grower
• Manual open curtains? - Lower cost

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Thermal / Shade Curtains
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Types of Curtain Systems

• Gutter to Gutter
• Truss to Truss
• Flat
• At bottom of truss
• Reduces night time volume to be heated
• Slope - Flat Slope
• Follows roof profile part way
• Installed without moving equipment
• Slope Slope
• Minimizes cold air trapped above curtain

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Thermal / Shade Materials

• Porous curtains
• Allows condensate and rain leakage to drain
• Lower heat retention than nonporous materials
• Semi-porous materials (preferred)
• Allows moisture to migrate
• High heat retention
• Non-porous material
• Highest heat retention
• Impervious to water and air movement - can fail
  if water collects on top of curtain
• Shade in summer / heat retention
• Higher shading factor Higher heat retention

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Curtain Materials Semi porous Aluminized and
clear polyethylene woven fabric
100
75
65
55
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Shading Material Comparison
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Which shade to Choose?

• Heat of summer maximum sunlight (June, July)
• 10,000 footcandles
• Most bedding and flowering plants can tolerate
  4000 to 5000 footcandles of light
• Greenhouse glazing light transmission
• Glass 90
• Double Poly 80
• 10,000 fc x 80 x 55 LT 4400 footcandles
• 45 shading recommended (52 energy savings)

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Other Material parameters

• Flammability
• Roll up or folding
• Shading
• Day length control (blackout)
• Heat retention

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Curtain Installation Issues

• Plants hanging from rafters
• Irrigation hanging from rafters
• LOTS of Things hanging from rafters
• Heating pipes
• Poly tubes
• Heaters
• Gable or roof vents or open roof systems
• Fully drawn curtain will restrict summer air flow

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Greenhouse unit heats

• Low cost
• Low installation costs
• Easily staged
• Reliable
• Location / heat distribution system affects
  heating costs

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Unit heater Seasonal Efficiency

• TE Cost
• Gravity Vent heaters 80 858
• Power Vent Heaters 80 943
• Separated Combustion 82 1845
• TE Thermal Efficiency Combustion and heat
  transfer efficiency.
• Reference Gas-Fired Unit Heaters A guide to
  greenhouse heating strategies, Calalog
  10-115,Modine Mfg., September 1996.

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Unit heater Seasonal Efficiency

• TE SE
• Gravity Vent heaters 80 65
• Power Vent Heaters 80 78
• Separated Combustion 82 80
• TE Thermal Efficiency Combustion and heat
  transfer efficiency.
• SE Seasonal Efficiency Includes TE plus heat
  loss out exhaust vents when heater is idle.
• Reference Gas-Fired Unit Heaters A guide to
  greenhouse heating strategies, Calalog
  10-115,Modine Mfg., September 1996.

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Unit heater Cost per kBtu output

• 250,000 Btu input, 80 Thermal Efficiency
• Type SE Cost
  /kBtu out
• Gravity Vent 65 858 5.28
• Power Vent 78 943 4.84
• S Combustion 80 1845 9.23
• Heater cost / (Btu input x SE) x 1000

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Unit Heater cost justification Gravity Vent or
Power Vent?

• Greenhouse 30 x 96 located in Madison, WI
• Two 250,000 Btu Output LP Unit heaters
• Incremental cost for PV heaters - 85 /ea
• All other costs assumed the same
• Growing season Feb 1 to June/July
• Estimated Fuel consumption
• Gravity vent 2179 gallons
• Power vent 1816 gallons

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Unit Heater cost justification Gravity Vent or
Power Vent?

• Total Incremental heaters - 170
• Assumed LP Cost - 1.00 / gallon
• Fuel cost difference - 363 / season
• Simple payback 170 / 363 0.47 season
• Since this is based on the greenhouse being used
  5 or 6 months, the incremental cost is paid back
  in 3 months.

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Non-vented unit heaters

• Fuel savings 20

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Non-vented unit heaters

• MUST be used with fresh air intakes
• Oxygen depletion in tight greenhouses poor
  combustion
• 1 in2 air intake area per 1000 to 2000 Btu/hr of
  furnace capacity
• 2 to 3 diameter opening for a 250,000 Btu/hr
  heater
• Increases CO2 levels
• Good for plants
• Could be used in place of a CO2 generator
• Increases H2O levels
• Can increase / cause disease problems
• Increased condensation lower light levels
• Only recommend using NG or LP gas
• Combustion byproducts from oil / kerosene harmful
  to some plants (tomatoes)
• Ethylene, Sulfur Dioxide, Nitrous Oxide, CO

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Heating Maintenance

• Heat Equip. Maintenance
• Insulation of pipes and ducts in head-house
• Clean Air heat Exchanges
• Lubricate motors fans
• Remove Soot can reduce fuel consumption by 10
• Steam trap maintenance
• Burner tune up
• Change fuel filter
• Correct nozzle
• Thermostat Calibrate annually
• Up to 20 fuel savings
• Provide air intakes for Boilers and unit heaters
• Smell of combustion gases indicated lack of large
  enough air intakes

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Greenhouses - Heating

• 2 Heating system efficiency increase
• in 30 foot by 100 foot greenhouse
• Saves 200 gallons of Fuel oil
• or 330 gallons of Propane
• or 285 Therms of Natural Gas
• per year

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Greenhouses - Heating

• Heating System Distribution
• In-Floor heating w/ Floor growing system
• Concrete floor not needed
• Bench heating
• Lower heating costs 20-25
• Study - 7 increased yields for tomatoes
• Forced Air Under-bench distribution
• Poly tubes under bench
• Approximately equivalent to a 5F reduction in
  greenhouse temperature.

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Central Heating Systems

• High Efficiency Heating equipment 90
• Hot water systems - Munchkin Boiler 92 AFUE
• Radiant heating

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Environmental Controls

• Central Unit to control
• Heaters
• Fans
• Louvers / Vents
• Irrigation
• Lighting
• CO2
• Computer control ensures systems are not
  competing
• Example - Heater on while fan is running
• Computer tied to on site weather data
• Anticipates heating and ventilation needs

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Alternative Energy Sources

• Utilize Waste heat cogeneration
• Landfill gas
• Dane Co Landfill - 2 MW of waste heat
• Manure Digesters
• Power plant reject heat
• Wind Turbines
• Geo-Thermal

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Space Utilization

• Racking Systems
• Take advantage of different plant light and
  temperature requirements
• Bench Layout
• Longitudinal 59
• Peninsula 69
• Movable 81

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Bench LayoutSpace Utilization
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Greenhouses - Ventilation

• Energy-Efficient Fans
• Efficiency ranges from 12 to 27 CFM/watt
• Test data available at
• BESS Lab - http//www.bess.uiuc.edu/index2.htm
• Air Movement Control Association www.amca.org
• http//cart.amca.org/publications/product.asp?PN2
  62/ND
• 36 or 48 fans efficiency greater than 20 CFM
  / watt _at_ 0.1 H2O
• Fan Maintenance
• Shutter lubrication (dry lubricant graphite) /
  maintenance
• Belt tension / alignment Automatic tighteners
• Trim weeds shrubs
• Bearing lubrication

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Greenhouses - Ventilation

• Shade Cloth
• Aluminized shades 10ºF lower air temperatures
• Internal Shade cloth can double as thermal
  curtain
• Evaporative cooling
• Misting
• Roll-up side walls
• Open Roof Designs

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Supplemental lighting

• Shorten / predictable time to market
• Plant later Less heating
• Earlier Flowering
• T-8 Fluorescent lamps Growing Chambers
• HID lamps Greenhouse
• High Pressure Sodium most energy efficient
• Pulse Start Metal Halide more blue light
• Incandescent lamps inefficient, low output /
  lamp
• Lamp Controls
• Timer
• Light integral controller

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Supplemental Lighting

• Response and effect varies greatly
• Short-day plant
• Day-neutral plant
• Long day plant
• Plug and Liners more root development
• Greenhouse Veg. High daily light integral (DLI)
  requirements.
• Cut Flowers supplemental lighting common
• Use Off-Peak electric?
• Lighting Up Profits, Paul Fisher Erik Runkle,
  2004.
• www.pllight.com/horticultural/publications.php

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Greenhouse Tools / Resources

• Greenhouse audit tool
• AgEnergy Resource web site
• http//energy.uwex.edu
• Energy Conservation for Commercial Greenhouses,
  NRAES-3, Ithaca, NY, 2001.
• Greenhouse Engineering, NRAES-33, Ithaca, NY,
  1994.
• www.nraes.org
• National Greenhouse Manufacturers Association
• www.ngma.com

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Wisconsin Focus on Energy

• Public / Private partnership - goal to conserve
  energy
• Focus is on electricity and natural gas / propane
  
• Services are available to 85 of homes
  businesses in WI
• Promotes Energy conservation Renewable energy
• Program areas
• Residential
• Business
• Industry
• Funded by 16/yr fee per electric meter

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Wisconsin Focus on Energy Agricultural
Program

• Free Energy Audits
• Information collected via farm visit or by phone
  / mail
• Standardized model used to estimate energy
  savings
• GRANTS available to encourage installation of
  high
• efficiency equipment
• Consultants are independent dont sell
  equipment
• Must be serviced by a participating utility to
  receive
• grants
• Provide educational materials

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Focus on Energy

• www.focusonenergy.com
• 1-800-762-7077
• 1-608-273-0182 direct line to Ag program
• Renewable Energy program
• (wind, bio-gas, solar)
• 1-888-476-9534
• Larry Krom

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Contact Information

• Scott Sanford
• Sr. Outreach SpecialistFocus on Energy / Rural
  Energy Issues
• Biological Systems Engineering
• University of Wisconsin Madison
• 608-262-5062
• sasanford_at_wisc.edu
• www.focusonenergy.com 1-800-762-7077