Presentation given during ProGreen EXPO in Denver Colorado 10 February 2012 http://www.progreenexpo.com

1. BEST INDUSTRY PRACTICE: REDUCE YOUR POWER LOAD
Matthew Schreiner and Steve Newman

2. Reducing Your Electric Power Consumption Using Variable-
Frequency Drive Controllers on Your Exhaust Fans
Matthew Schreiner
M.S. Floriculture Graduate Student
Steven E Newman, Ph.D., M.S.
Greenhouse Crops Extension Specialist and
Professor of Floriculture
ProGreen EXPO
10 February 2012
10:30 am – 11:30 am

3. Active Cooling in the greenhouse

4. 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

6. 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

7. 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

8. 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

9. Psychrometric
Chart

10. 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

11. 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

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

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

17. 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

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

21. 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

22. 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

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

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

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

26. 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!

27. 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

28. 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

29. 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

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

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

32. 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

33. HOBO temperature
Temperature Sensors data loggers

34. Hanging Lysimeters
• Water use
• Weighing Lysimeter
• Determine water use across greenhouse
to determine how air flow rates impact
plant growth

35. Hanging Lysimiters

36. Energy measurements
Amp Clamp
• Measures amperage
every 30s
• Connects directly
around power wire
• Very accurate
• Simultaneous amp
data between VFD
and On/Off

37. Amp Clamp Power Cycle Data

38. 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

39. 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

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