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: http://youtu.be/79oNfUG43XA

1. BEST INDUSTRY PRACTICE: ENERGY CONSERVATION
Steve Newman

2. Managing Energy Expenses in the Greenhosue
Steven E Newman, Ph.D., M.S.
Greenhouse Crops Extension
Specialist and Professor of
Floriculture

3. Energy Dollars
Heat = 70-85%

4. Natural Gas Prices
Continue to Rise

5. Solar Energy Hot air from
gable
Solar Panels
Under bench
heat

6. Storage of low grade heat from solar gain in under-bench
TES (Thermal Energy Storage) system

7. Air intake plenum
Greenhouse earth solar thermal storage
EAHE – Earth to Air Heat Exchanger
SHCS – 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. 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 with
Heat Exchange Coil other recovery systems;
trenched 5 ft deep Boiler economizers,
UNDER greenhouse A/C condenser heat
structure
Essentially an electric heater which captures solar gain and adds “heat of compression”
Higher COP (SEER rating) = less $ for electric heating

9. The Hobbit House
http://www.sunnyjohn.
com:///index.html

10. Heat Storage
Scott Skogerboe Greenhouse

11. Heat Storage
Scott Skogerboe Greenhouse`

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. Phase Change Salts

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. Insulation
• Opaque insulation
– Rigid board insulation
• North walls
• Side walls up to bench height
– Fiberglass
• Protect from water
– Sprayed-on urethane

16. Insulation
• Transparent
insulation
– Aircap pads
• Difficult to attach to
glass
• May be stapled
• 12% reduction in light
• On outside, watch
snow

17. Insulation
• Lap seal
– Transparent caulking
compound
– Commercially applied
to glass
– More economical
when done during
construction
– Less air exchange

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. 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. Polyethylene Film

21. Single Polyethylene over Glass

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

23. Retractable Curtains 1-3/8” PUSH
TUBE
ALUM.
ANGLE
7/8” ALUM.
LEAD EDGE
GALV. 2” SQ. TUBING
INT. TRUSS MEMBER
GALV. ANGLE
IRON ALUM.
ANGLE
STATIONARY INTERMEDIATE
LINES ROLLER BRACKETS
COVERING MATERIAL

24. Automated Heat Curtain

25. Heat Curtains

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. Comparison of same house with similar Heating Degree Hours
3.0
Cumulative run time or the
Cum. 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. Comparison of same house with similar Heating Degree Hours
Covered
Uncovered
3.0
Heating began with
Cum. 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. Comparison of same house with similar Heating Degree Hours
Covered
Uncovered
3.0
Heating began with
Cum. 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. Comparison of same house with similar Heating Degree Hours
Covered
3.0
At 436 HDH and Uncovered
curtains open, 2.69
Cum. 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. 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. Active Cooling in the greenhouse

33. Greenhouse Cooling
Why 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

35. Greenhouse Cooling
Active 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

36. Greenhouse Cooling
Active 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

37. Greenhouse Cooling
Physics 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

38. Psychrometric
Chart

39. 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

40. Greenhouse Cooling
Designing 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

41. Greenhouse Cooling
75 F 82 F
Typically temperature rises 7 F
from cooling pad to exhaust fan

42. Energy Expenses
Heat
Refrigeration ( 1%)
Ventilation (10%)
Soil Pasteurization (9%)

46. 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

47. What Does a VFD Do?
• Reduces cold/moist air rush
• Reduces heat stress
• Increase crop uniformity
• Create uniform growth
environment

48. Precise Control of Fan Speed
During summer months, the
cooling requirement can change
dramatically throughout the day
• Short Cycling
• In-Rush Current
• Soft Starting
• Affinity law

49. 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

50. In-Rush Current
• Short cycling
• Fans run for longer so in-rush
is limited
• Eliminated with Soft Start
• VFDs could lengthen life of
equipment

51. Micro-climate Uniformity
• Slowly ramp up fan speed as needed
• Limits cool air rush

52. Micro-climate Uniformity
• Evaporative Cooling Pad
• Running fans longer help create homogeneity

53. Energy Efficiency
Affinity 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!

54. 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

55. 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

56. 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

57. Research Overview
Identify benefits using VFDs
• VFD greenhouse vs. Non VFD
greenhouse
• Envirostep
• Temperature
• Crop uniformity
• Water use
• Amp clamp

58. Envirostep
• Wadsworth Envirostep
greenhouse controller
• Modulated voltage output
• Many Possibilities for VFD
setup

59. 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

60. Amp Clamp Power Cycle Data

61. Energy Efficiency
Continuous 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

62. 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

63. Contact Information
• Review and share this presentation:
http://www.slideshare.net/snewman7118
• Website:
http://www.greenhouse.colostate.edu
• eMail:
Steven.Newman@Colostate.edu