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

transcript

On-Farm Refrigeration for Small Scale Produce Growers

Nils Johnson

WSU Stevens Co. Extension

Ag and Food Systems Coordinator

11/3/18

Outline

• The thermal energy family…

• Basics of heat transfer

• Thermal characteristics of fruit and vegetables

• Example systems

• Reference material

• Contact Info

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

UniformTemperature

Thermal Resistance

Cool Area

Thermal EnergyThermal Resistance

• Tends to resist thermal flow

Thermal Energy Source Thermal Energy Flow

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

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

Thermal Energy Source

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

0.86 0.91 0.94 0.96 0.97 1.00

Specific Heat By Mass

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

rmal Flo

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

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

20000 Lbs

Pickup & Delivery

Average Cash Cost: 31¢ per Lb

Average Wholesale Produce Price:

$1.95 per Lb

Hunger

Coalition

Schools

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

• ~45 inches wide

• ~45 inches tall

• Plywood outside

• ~45 inches wide

• ~45 inches tall

• Plywood outside

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

• Nils JohnsonStevens County WSU Extension Ag Program Coordinator

Phone: (509) 684-2588

Mobile/Text: (509) 680-8659

Email: nils.johnson@wsu.edu

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

Contact Information

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

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