On-Farm Refrigeration for Small Scale Produce Growers · (cheap garden hose) Pressure Differential...

On-Farm Refrigeration for Small Scale Produce Growers

Nils Johnson

WSU Stevens Co. Extension

Ag and Food Systems Coordinator

11/3/18

All rights Reserved, Nils Johnson, WSU Stevens County Extension, 11/3/18

Outline

• The thermal energy family…

• Basics of heat transfer

• Thermal characteristics of fruit and vegetables

• Example systems

• Reference material

• Contact Info

All rights Reserved, Nils Johnson, WSU Stevens County Extension, 11-3-18

Thermal Energy FamilyMom, Dad, and the First Child…

• Temperature• Commonly measured in degrees (Farenheight, Celcius, Kelvin)

• Is a “potential” measured between one point and another

• Zero temperature does exist (-273 degrees Celcius)

• Heat flow rate• Commonly measured in Watts, BTU’s per hour, Horsepower

• Is “Power”

• Energy• Commonly measured in Watt-hours, BTUs, Calories

• Energy = Heat flow rate X Time


Thermal EnergyThe integral of Heatflow with respect to time

• Where does Temperature come in?• Temperature differential is the “force” that makes heat flow happen


Thermal Energy = 𝑡𝑖𝑚𝑒 1

𝑡𝑖𝑚𝑒 2𝐻𝑒𝑎𝑡 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒

Yay! Calculus…

Technically…

Thermal EnergyThermal Resistance

• Tends to resist thermal flow

All rights Reserved, Nils Johnson, WSU Stevens County Extension,11-3-18

UniformTemperature

Thermal Resistance

Cool Area

Thermal EnergyThermal Resistance

• Tends to resist thermal flow


Thermal Energy Source Thermal Energy Flow

Co

ol S

ide

Ho

t Si

de

Thermal Resistance

Temperature Differential

Cool Area

Thermal EnergyThe Water Analogy

• Temperature is like Water Pressure• It’s the force that causes flow to happen.

• Is measured as a differential between one point and another

• Thermal Power flows like Water flowing through a hose• If there’s Pressure (Temperature) flow happens

• Thermal Resistance is like a small diameter garden hose• Water slows more slowly out of a hose than from an open spigot


Water AnalogWater flow resistance

• Tends to resist water flow


Water Pressure Source Water Flow

Ho

se O

utl

et

Spig

ot

Sid

e

Flow Resistance(cheap garden hose)

Pressure Differential

Puddle

Thermal EnergyInsulation and Thermal Conductors

• High thermal resistance: Insulation• Examples:

• Expanded Polystyrene sheeting

• Fiberglass batts

• Low thermal resistance: Thermal conductor• Example:

• Aluminum sheeting

• Stone

• Soil


Cool Area

Thermal EnergyCalculating Heat Flow (Power)

• Example: Polystyrene Sheeting• R-Value: 8 Hr·Ft_sq·°F/BTU

• Equation

BTU/Hr = Temp H-C x Area ÷ R Value

• Calculation

Flow Rate = 50 F° x 32 Ft_sq ÷ 8 Hr·Ft_sq·°F/BTU

= 200 BTU per Hr


4 Ft

8 Ft

Thermal Energy Source

The

rmal Flo

w 90 F°

40 F°

90 – 40 = 50Temp H-C = 50 F°

Surface Area = L x W4 ft x 8 ft = 32 Ft_sq

Outline

• Thermal energy family



• Example systems


• Contact Info


Heat TransferFour ways for heat to move

1) Conduction• Solid objects make physical contact and transfer thermal energy between them

2) Convection• A fluid (or gas) transfers thermal energy to something else

3) Radiation• An object transfers thermal energy through electromagnetic radiation

4) Mass Transfer• An object moves into an area or out of an area, moving thermal energy with it

All of these only happen if there’s temperature difference between objects or substances




• Example• You burn your leg on the chrome exhaust pipe of a motorcycle

• The exhaust pipe was hot

• Your leg was cool

• When the two touched thermal energy transferred to your leg




• Example• Hot exhaust gas from the motorcycle heated the exhaust pipe

• Hot exhaust gas came out of the engine

• It traveled through the cooler exhaust pipe

• Thermal energy transferred into the metal of the exhaust pipe

• The thermal energy heated the pipe




• Example• The sun radiates thermal energy on you (it’s a sunny day)

• You absorb thermal radiation and your temperature rises

• You feel hot despite the fact that the air temperature is mild

• You decide to put on shorts and ride your motorcycle




• Example• You run cold water on your burned leg

• Your leg is hot

• The water is cold

• Through convection, thermal energy transfers from your leg to the water

• Through Mass Transfer, thermal energy in the water moves away onto the ground


Heat TransferFour ways for heat to move - Recap





Exercise: Think of examples with produce storage


Outline

• The thermal energy family



• Example systems


• Contact Info


Thermal CapacityEnergy it takes to heat a particular substance

• Specific Heat• Standard Units: BTU per Lb - F°

• Metric Units: Joules per Gram - C° (1 Joule = 1 Watt-Second)

• Examples


Conversion Factor4.18 joule per °C – gram = 1 Btu per °F – pound (https://www.translatorscafe.com/)

Specific Heat By Mass

Produce Item BTU per Lb - °F Joules per Gram - °C

Steel 0.12 0.50

Aluminum 0.22 0.92

Polystyrene 0.33 1.38

Wood 0.44 1.84

Pears 0.86 3.60

Peaches 0.91 3.81

Cabbage 0.94 3.93

Lettuce 0.96 4.01

Zucchini 0.97 4.04

Water 1.00 4.18

0.12 0.220.33

0.44

0.86 0.91 0.94 0.96 0.97 1.00

Specific Heat By Mass

https://www.translatorscafe.com/unit-converter/en/specific-heat-capacity/4-15/kilojoule/kilogram/K-Btu (IT)/pound/%C2%B0F/

Heat of RespirationEnergy given off by produce as it decays

• Units: • Standard units: BTU per Lb - Day

• Metric units: Watts per Gram - Second

• Examples:


Heat of Respiration

Produce Item BTU per Lb-Day BTU per Lb-Hour

Steel - -

Aluminum - -

Polystyrene - -

Wood - -

Pears 0.52 0.04

Peaches 0.56 0.05

Cabbage 0.97 0.08

Lettuce 1.43 0.12

Zucchini 1.36 0.11

Water 0.00 0.00

Outline

• The thermal energy family



• Example systems


• Contact Info


Real Life ExamplesLow cost refrigeration

CoolBot Controller

• Heats the AC unit thermometer “tricking” it into cooling below 60°F

• Is easy to install

• Works on most AC units that have a digital display

• Costs about $350

• More information on the CoolBot Website


Real Life Example20-Foot Insulated Shipping Container

• Size• 20 Ft long

• 8 Ft wide

• 8 Ft tall

• Insulation• 4” Expanded polystyrene

• R-Values

• Walls and Roof: 20

• Floor: 15

• Refrigeration Unit• 23000 BTU per Hour AC Unit

• CoolBot controller



• Size• 20 Ft long

• 8 Ft wide

• 8 Ft tall

• Insulation• 4” Expanded polystyrene

• R-Values

• Walls and Roof: 20

• Floor: 15


• CoolBot set to cool at 38°F

• Contents• 500 Lbs of Cabbage


Example20-Foot Insulated Shipping Container

Contents: 500 lbs of Cabbage at 80°F

Cooling Unit: 23,000 BTU/Hour

1) Field Heat to Remove: = 500 Lbs x 0.94 x (80° - 38°)= 19,740 BTU

2) Thermal Gain from Air, Ground & Sun: = 2173 BTU/Hr

3) Thermal Gain from Respiration: = 500 Lbs x 0.08 = 40 BTU/Hr


Sun

The

rmal Flo

w

120 °F

Air: 90 °F

Ground: 70 °F

Real Life ExampleHome Built Farm Cooler – Meadowlark Farm

• Located inside packing shed

• Size• ~8 Ft long

• ~8 Ft wide

• ~8 Ft tall

• Plywood outside

• FRP inside

• Insulation• 3 1/2” Fiberglass




DistributionPlan

Farm to Food Pantry Program (2017)

Local Farmers Contract

Donations

Gleaners

Donations

GleaningSchedule

8000 Lbs

2000 Lbs

11,000 Lbs

$7000

20000 Lbs

Pickup & Delivery

Average Cash Cost: 31¢ per Lb

Average Wholesale Produce Price:

$1.95 per Lb

Hunger

Coalition

Schools

All rights Reserved, Nils Johnson WSU Stevens County Extension, 6-22-18

Trailer – Design Specifications

Food Pantry and On Farm Refrigeration • Final Design Criteria

• Small enough to pull behind a small car• Holds 25 banana boxes on a pallet

• Runs on a 2000 Watt generator• Forkliftable on and off the trailer

Original Cool Pup Trailers - 2 Trailer Versions

Two Mini-Sized Refrigerated produce trailers…• DIY Version

• ~$6000 Mobile• ~$3400 Stationary (no trailer or generator)

• Factory made Version)• Prices TBD but approximately $8500

Real Life ExampleCoolPup Refrigerated Trailer

• Portable Self-Contained

• Size• ~51 inches long

• ~45 inches wide

• ~45 inches tall

• Plywood outside

• Plywood underlayment inside

• Insulation• 4 1/2” Polystyrene board



• Honda EU2000i Generator


Reference MaterialOutside sources of information

• Refrigeration and Controlled Atmosphere Storage for Horticultural Crops – NRAES-22,Cooperative Extension, Northeast Regional Agricultural Engineering Service, 1984, James A. Bartsch, Dept. of Agricultural Engineering, Cornell University, G. David Blanplied, Dept. of Pomology, Cornell University

• Farm Structures Factsheet, Order No. 306.300-1, British Columbia Ministry of Agriculture and Food, May 1989, Agdex 730, Erich Schultz

• Pack-N-Cool Manual-2, North Carolina State University, Dr. Penelope Perkins-Veazie

• Forced-AirCoolingSystemsForFreshOntarioFruitsAndVegetables, Ontario Ministry of Agriculture,Food, and Rural Affairs


../../../Storage/e1914-ND-NRAES-22-Refrigeration-and-Controlled-Atmosphere-Storage-for-Horticultural-Crops.pdf

../../../Storage/RefrigerationRequirementForFuritsAndVegetables_BC_Gov_306300-1.pdf

../../../Grants/NW_FarmCreditServies_RuralCommunityGrant_10-1-15/NCStateU_PacNCool_Info/PackNCool-Manual2.pdf

../../../Storage/Forced-AirCoolingSystemsForFreshOntarioFruitsAndVegetables.pdf

• Nils JohnsonStevens County WSU Extension Ag Program Coordinator

Phone: (509) 684-2588

Mobile/Text: (509) 680-8659

Email: [email protected]

• Stevens Co. Extension Office:986 S. Main, Suite D, Colville WA

Contact Information


mailto:[email protected]

On-Farm Refrigeration for Small Scale Produce Growers · (cheap garden hose) Pressure Differential...

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