Energy conservation in the greenhouse


Published on

Presented at the 2013 Utah Green Conference sponsored by the Utah Nursery and Landscape Association, 28 January 2013.

This lecture was recorded and you can see it at:

Published in: Education
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Energy conservation in the greenhouse

  2. 2. Managing Energy Expenses in the GreenhosueSteven E Newman, Ph.D., M.S. Greenhouse Crops Extension Specialist and Professor of Floriculture
  3. 3. Energy Dollars Heat = 70-85%
  4. 4. Natural Gas PricesContinue to Rise
  5. 5. Solar Energy Hot air from gable Solar Panels Under bench heat
  6. 6. Storage of low grade heat from solar gain in under-benchTES (Thermal Energy Storage) system
  7. 7. Air intake plenumGreenhouse earth solar thermal storageEAHE – Earth to Air Heat ExchangerSHCS – Soil Heating and Cooling System PARAMETERS Air DTi-o Pipe Depth Air return plenum Pipe Material Pipe Diameter Air Flow rate Soil T Soil H2O & texture
  8. 8. Fan/coil heat exchanger Greenhouse earth solar thermal storage SHCS – Soil Heating and Cooling System High Efficiency “variable scroll” compressor Ground Source Heat Pump“Slinky” type Can be combined withHeat Exchange Coil other recovery systems;trenched 5 ft deep Boiler economizers,UNDER greenhouse A/C condenser heatstructure Essentially an electric heater which captures solar gain and adds “heat of compression” Higher COP (SEER rating) = less $ for electric heating
  9. 9. The Hobbit House http://www.sunnyjohn. com:///index.html
  10. 10. Heat Storage Scott Skogerboe Greenhouse
  11. 11. Heat Storage Scott Skogerboe Greenhouse`
  12. 12. Heat Storage• Phase Change Materials – A phase change material is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. – Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.
  13. 13. Phase Change Salts
  14. 14. Phase Change Salts Exotherm "Tuneable" Phase Change Salt transitions @ 45F External Temp. 100 Temperature( F) Original 90 - 20%NaCl - 40%NaCl 80 water 70 60 50 40 8/3/08 12:00 8/4/08 0:00 8/4/08 12:00 8/5/08 0:00
  15. 15. Insulation• Opaque insulation – Rigid board insulation • North walls • Side walls up to bench height – Fiberglass • Protect from water – Sprayed-on urethane
  16. 16. Insulation• Transparent insulation – Aircap pads • Difficult to attach to glass • May be stapled • 12% reduction in light • On outside, watch snow
  17. 17. Insulation• Lap seal – Transparent caulking compound – Commercially applied to glass – More economical when done during construction – Less air exchange
  18. 18. Insulation• Tight covering reduces heat loss – Weather stripping on doors and vents – Good glass maintenance – Closing gaps under foundation – Lubricating vent louvers for good operation – Covering unused fans
  19. 19. Polyethylene Film• Double poly over glass – Energy savings up to 50% – Reduces light transmission – Less air exchange• Single poly over glass – Energy savings up to 40% – Difficult to inflate
  20. 20. Polyethylene Film
  21. 21. Single Polyethylene over Glass
  22. 22. Movable Nighttime Insulation• System Overview – Construct a frame / grid to move fabric on from truss to truss.• Support System -Supports The Drive System – Gear Motor – Rack & Pinion Chassis – 1-3/8” Steel Drive Shaft
  24. 24. Automated Heat Curtain
  25. 25. Heat Curtains
  26. 26. Heat Transmission Aluminized material Non-porous material Porous Cloth No curtain 0 0.2 0.4 0.6 0.8 1 U value, Btu/hr sq ft °F
  27. 27. Comparison of same house with similar Heating Degree Hours 3.0 Cumulative run time or theCum. heater run time (hours) 2.5 amount of time that the heating device was in operation during The heating degree days in a a heating cycle in hours. season are derived by 2.0 summing the difference between the average outdoor 1.5 temperatures above a base (e.g., 65 F) each 24 hours and 1.0 the base temperature. Heating degree hours (equal 0.5 to heating degree days x 24) are used in computing seasonal energy flows in a 0.0 building due to both 0 50 100 150 200 250 300 350 400 450 500 conduction and convection. Cum. heating degree hours
  28. 28. Comparison of same house with similar Heating Degree Hours Covered Uncovered 3.0 Heating began withCum. heater run time (hours) 2.5 less than 25 HDH 2.0 when curtains open 1.5 1.0 0.5 0.0 0 50 100 150 200 250 300 350 400 450 500 Cum. heating degree hours
  29. 29. Comparison of same house with similar Heating Degree Hours Covered Uncovered 3.0 Heating began withCum. heater run time (hours) 2.5 less than 285 HDH 2.0 when curtains closed 1.5 1.0 0.5 0.0 0 50 100 150 200 250 300 350 400 450 500 Cum. heating degree hours
  30. 30. Comparison of same house with similar Heating Degree Hours Covered 3.0 At 436 HDH and Uncovered curtains open, 2.69Cum. heater run time (hours) 2.5 hours of heater time were required 2.0 At 436 HDH and curtains 1.5 closed, 0.295 hours of heater time were 1.0 required 0.5 0.0 0 50 100 150 200 250 300 350 400 450 500 Cum. heating degree hours
  31. 31. Preliminary Results• At 436 heating degree hours – House with curtains open required 2.69 hours of heater time – House with curtains closed required 0.295 hours of heater time – Savings of 2.39 hours• Assuming a unit heater at 250,000 Btu/hr – Open curtains would required 672,500 Btus of fuel – Closed curtains would require 73,750 Btus of fuel
  32. 32. Active Cooling in the greenhouse
  33. 33. Greenhouse CoolingWhy is cooling needed?• Solar radiation is the “heat input” for the earth – Radiate as much as 277 Btu/ft2/hr onto the surface of the earth on summer day – Coastal and industrial areas, may only be 200 Btu/ft2/hr• Up to 85% of this radiation may enter the greenhouse – Most of the IR heat becomes trapped inside – Greatly increases the greenhouse temperature
  34. 34. Greenhouse CoolingActive Cooling Systems• Dry bulb temperature – Actual air temperature measured with an ordinary thermometer• Wet bulb temperature – The air temperature if enough water were to be evaporated into it to saturate the air
  35. 35. Greenhouse CoolingActive Cooling Systems• Wet bulb temperature is what the air can be cooled to if the evaporative cooling system is operating at 100% efficiency• Fan and pad systems – 80% efficiency
  36. 36. Greenhouse CoolingPhysics of Evaporative Cooling• Use evaporation of water to convert sensible heat into latent heat, thus reducing the temperature of the air• About 1,060 Btu’s of heat are “absorbed” out of the air for every pound of water evaporated
  37. 37. PsychrometricChart
  38. 38. Greenhouse Cooling• Air exchange rate (cfm) required – Standard recommendation is one exchange per minute – Remove and replace entire volume of greenhouse• Modify “standard” cfm as needed – Account for density of air (elevation) • FELEV – Maximum light • FLIGHT – Maximum temperature rise • FTEMP
  39. 39. Greenhouse CoolingDesigning a Fan and Pad System• Fan selection and placement – Total fan cfm = calculated cooling requirements – Fans should be equal to cfm required – Usually placed on the wall opposite the pads – Maximum distance between fans and pads is 200 feet – Place fans close to plant height – No more than 25 feet between fans, evenly spaced
  40. 40. Greenhouse Cooling 75 F 82 F Typically temperature rises 7 F from cooling pad to exhaust fan
  41. 41. Energy Expenses Heat Refrigeration ( 1%) Ventilation (10%) Soil Pasteurization (9%)
  42. 42. What Does a VFD Do?• A VFD controls the frequency sent to the motor• Motor RMP can be varied as cooling need changes• Reduces cold/moist air rush
  43. 43. What Does a VFD Do?• Reduces cold/moist air rush• Reduces heat stress• Increase crop uniformity• Create uniform growth environment
  44. 44. Precise Control of Fan SpeedDuring summer months, thecooling requirement can changedramatically throughout the day• Short Cycling• In-Rush Current• Soft Starting• Affinity law
  45. 45. In-Rush Current• Truly a “killer” of electronics• Creates unnecessary heat• Motor consumes up 10 times its normal full amp load for 500 ms during start up
  46. 46. In-Rush Current• Short cycling• Fans run for longer so in-rush is limited• Eliminated with Soft Start• VFDs could lengthen life of equipment
  47. 47. Micro-climate Uniformity• Slowly ramp up fan speed as needed• Limits cool air rush
  48. 48. Micro-climate Uniformity• Evaporative Cooling Pad• Running fans longer help create homogeneity
  49. 49. Energy EfficiencyAffinity law• Change in power is proportional to the cube of the change in speed• A fan running at 50% RPM only uses 12.5% power!
  50. 50. Energy Efficiency• Teitel et al. (2004) proposed variable speed drives to control fans according to the heat load on the greenhouse.• They showed that it is possible to reduce electricity consumption by 36%.• In their study, the average energy consumption with a variable speed system over a period of one month was about 0.64 compared with ON/OFF. Teitel, et al. 2004. Energy Conversion and Management 45:209-223
  51. 51. Temp/Humidity• Measured Temp/Humidity for one day.• VFD greenhouse showed reduced change in both humidity and temp. Teitel, et al. 2004. Energy Conversion and Management 45:209-223
  52. 52. Temp/Humidity• Measured Temp/Humidity for one day.• VFD greenhouse showed reduced change in both humidity and temp. Teitel, et al. 2004. Energy Conversion and Management 45:209-223
  53. 53. Research OverviewIdentify benefits using VFDs• VFD greenhouse vs. Non VFD greenhouse• Envirostep• Temperature• Crop uniformity• Water use• Amp clamp
  54. 54. Envirostep• Wadsworth Envirostep greenhouse controller• Modulated voltage output• Many Possibilities for VFD setup
  55. 55. Temperature• VFDs creates a more homogeneous environment• Maintaining set points will be a challenge• Uniform air flow ramped up and slowed down as needed to eliminate cool air rushes• Place temperature sensors around the greenhouse
  56. 56. Amp Clamp Power Cycle Data
  57. 57. Energy EfficiencyContinuous Energy Use Monitor• 3-Phase electricity monitoring at up to 10 locations.• Simultaneous monitoring between VFD and NON VFD Greenhouse.• KWh units and cost estimate• Current usage and accumulated• Web accessible
  58. 58. Fan Control Requirements• Voltage Modulated Output (0-10 VDC)• Managed as a percentage of the voltage output similar to a mixing or steam valve• Integrates easily into step controllers ramping up fan speeds based on temperature demand
  59. 59. Contact Information• Review and share this presentation:• Website:• eMail: