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Potato Storage Ventilation and Humidification. Roger Brook Extension Engineer Michigan State University. Potato Storage Ventilation. main function is to control temperature of potatoes in storage remove field heat and heat of respiration supply and/or control humidity

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potato storage ventilation and humidification

Potato StorageVentilation and Humidification

Roger Brook

Extension Engineer

Michigan State University

potato storage ventilation
Potato Storage Ventilation
  • main function is to control temperature of potatoes in storage
  • remove field heat and heat of respiration
  • supply and/or control humidity
  • provide oxygen and remove CO2
  • dry wet potatoes
  • warm up cool potatoes
slide3

Respiration

“ Respiration is, in a way, the opposite of photosynthesis. Energy stored in sugars is now released for use in maintenance of the tuber.”

6CO2 + 6H2O + Energy

6O2 + C6H1206

(85% is heat)

Oxygen

Glucose

Carbon

Dioxide

Water

respiratory changes over time
Respiratory changes over time

100

sprouted

tubers

80

60

40

20

0

SEP

NOV

JAN

MAR

MAY

the effect of temperature on respiration
The effect of temperature on respiration

5

5

mg/g Sucrose

mg/g Reducing sugars

0

0

30

35

40

45

50

55

60

65

gas exchange in potato tubers
Gas exchange in potato tubers

O2

H20

O2

CO2

O2

H20

H20

O2

CO2

H20

CO2

O2

H20

CO2

O2

Lenticel and epidermis of potato tuber

the effect of stress on respiration
The effect of stress on respiration
  • In general, any type of stress causes respiration to increase.
  • Stresses to watch for:
    • lack of fresh air (O2, CO2)
    • handling
    • temperature fluctuations
    • exhaust gases (CO, C2H4)
wall cross section
Wall cross-section

vapor barrier

steel cladding

Plywood

1" extruded polystyrene

house wrap

Insulation and structural

TYPICAL WALL SECTION

temperature profile in wall cross section

50°F

49.1°F

48.4°F

41.9°F

1.8°F

0.3°F

3.4F

0°F

Temperature profile in wall cross-section
psychrometrics in potato storage
Psychrometrics in potato storage
  • Psychrometrics is the study of dry air-water vapor mixtures (moist air) and how mixtures are affected by varying amounts of water vapor and changing temperatures
relative humidity
Relative humidity
  • The ratio of the actual amount of moisture in the air to the maximum amount of moisture the air could hold at that temperature. Relative humidity (RH) is expressed as a percentage
relative humidity terms
Relative Humidity Terms
  • Dry bulb temperature
    • measured by ordinary thermometer
  • Wet bulb temperature
    • measured by a thermometer with the bulb covered by a water moistened wick in a moving stream of ambient air
  • Dewpoint temperature
    • temperature at which moisture starts to condense from cooled air
effect of warming air on rh
Effect of warming air on RH

50 oF

95% RH

55oF

78% RH

60 oF

66% RH

surface temperature and condensation
Surface temperature and condensation
  • condensation occurs at dewpoint temperature
  • potatoes or ceiling may be cooler than surrounding air; result can be “wet” surface.
  • Remedy: circulate air above bin or add insulation to ceiling.
slide15

Where to measure Relative Humidity

100 FT

30 FT

Distribution Ducts

Loading

and

Work

Area

8ft. c/c

Plenum

Fan Room

relative humidity measuring devices
Relative Humidity measuring devices
  • Dial hygrometers
  • Sling psychrometers
  • Aspirated psychrometer
  • Electronic RH sensors
humidification systems
Humidification Systems
  • High humidity
    • critical for curing process
    • minimal weight loss
    • maximum quality out of storage
  • Need 1 gal. water per 800 - 1000 cfm of design air flow
example of humidification required
Example of humidification required

System has two 5-HP fans:

need ~ 1 gal / 800-1,000 cfm airflow

To determine humidifier capacity:

water = 32,000 cfm/1,000 cfm/gal = 32 gal.

water = 32,000 cfm/800 cfm/gal = 40 gal.

weight loss vs relative humidity
Weight loss vs. Relative Humidity

12

10

75%

8

85%

% Weight Loss

6

95%

99.50%

4

2

0

0

1

2

3

4

5

6

7

8

9

10

Months in storage

centrifugal humidifier
Centrifugal humidifier
  • also known as “spinning disk”
  • most common; moderate cost
  • low to moderate maintenance
  • low operating cost
  • excess water in plenum
  • prone to mineral buildup
high pressure nozzles
High pressure nozzles
  • moderate cost
  • moderate maintenance
  • some excess water in plenum
  • moderate operating cost
  • prone to nozzle plugging
high pressure air water nozzles
High pressure air/water nozzles
  • high cost
  • high maintenance
  • low excess water in plenum
  • high operating cost
  • noisy
  • excellent humidification
air washers
Air washers
  • high initial cost
  • may require additional humidifier
  • may provide added cooling