6/11/2015. Forced Air Cooling. Temperature Variation During. Divide Airspace Between Coolers

Transcription

1 Jim Thompson P.E. Bio. & Agricultural Engineering Dept. UC Davis Temperature ( F) Product Temperature during Air /2 3/ 7/8 5/6 Cool Peaches at.5 cfm/lb Hours of Cooling 3 2 Temperature ( C) Temperature ( F) /2 3/ 7/8 5/6 Cool Peaches at.5 cfm/lb Hours of Cooling first fruit mass average last fruit C 3 2 Divide Airspace Between Coolers Temperature Variation During Large diameter melons Uncooled centers Airflow Block warm air from uncooled fruit from affecting fruit that has begun cooling.

2 Temperature Variation During Temperature Measurement Airflow Small diameter blueberries Uncooled near air exit Reversing Airflow Direction Vertical Cooler with Flow Reversal closed open closed open 9 Effect of Product Diameter 7/8 Cooling Time (hr) Cantaloupe, dia.=6. Peaches, dia.=3.25" Cherries, dia.=." 2 3 Air Flow Rate (cfm/lb or m 3 /s MT) Airflow (cfm/lb) Pressure Drop vs. Airflow..... Pressure drop across pallet (in wc) Strawberries, >% vent Tomato, % vent Canatloupe, 6% Pears, 5% vent Plums % vent Pears, 2% vent Vent area should be greater than 5% for airflow > CFM/lb (m 3 /s MT) 2

3 Pressure Drop vs. Airflow Airflow Pressure Drop (in.) 3 2 Pear Grape 2 3 Air Flow (cfm/lb, m 3 /s MT) Interior packaging has a big effect omn pressure drop (mm) 3 Maximum airspeed 5 fpm (7.5m/s) Refrigeration Capacity Calculations Evaporator Capacity for product cooled by each unit Compressor/condenser Capacity for sum of all evaporators Refrigeration capacity limit Evaporator Capacity Refrigeration capacity (tons/ lb of product (kw/mt)) Capacity (% of maximum) 7/8ths cooling time (min) Unlimited 2.3 (9) 5 Average for.8 () 7 55 first /2 cooling period Average for 7/8 cooling.5 () 6 65 Based on cooling 2 pallets of broccoli with 32 F ( C) air and 68 F (2 C) initial temperature. Refrigeration load for product only. Energy Coefficient Energy Coefficient = Cooling Work / Electricity Use Product cooled per billing period (lbs) Temperature drop in cooling ( F) Electricity use (kwh) High EC = more cooling for less electricity Forced Air Cooler Efficiency Season Cooler Average EC Strawberry A.68 Strawberry E. Strawberry C.33 Strawberry D.33 Strawberry B.23 Grape C.9 Grape B.9 Grape A.3 Oldest facility 3

4 Electricity Use in Electricity Use (%) Product 36 Fans 3 Lights 6 Walls Lifts 9 Energy Coefficient FA coolers are inefficient at low product throughput rates Strawberry cooler B Capacity (lb/month-ft 2 ) Strawberry cooler A Maximize Use of Refrigerated Volume Use racks or stack pallets Consolidate Divide storage and refrigerate only space needed Shut down HID Lighting Options High Bay Fluorescent

5 Replace W HID lamps with High Bay Fluorescent Cold Storages are Hard to Light Location Unit cost ($) Use (hr/da) Payback (days) Outside Cold Storage Cold Storage w/ motion sensor Task Lighting Improve refrigeration system efficiency. Refrigeration System Efficiency Increase suction pressure. Floating suction pressure control Decrease discharge pressure. Install more condenser capacity Speed control for screw compressors. Proper compressor sequencing. Optimum control of system. Refrigeration System Efficiency 25 to % Reduction in electricity use 5

6 Improve refrigeration system efficiency. Minimize exterior heat gain. Minimize Heat Gain Install rapid acting doors. Use high reflectivity exterior surfaces. Add wall or roof insulation. Insulate exterior refrigeration piping. Improve refrigeration system efficiency. Minimize exterior heat gain. Minimize fan electricity use. Fan Electricity Use Reduce fan speed near the end of cooling? In storage, reduce airflow when evaporators operate a partial capacity. Fan cycling Slow motor speed. Forced Air Cooler Cost (Tunnel cooler in an existing cold room, no high side) Approximate Forced Air Cooler Cost (22 data) lift truck rental electricity 22% repair capital % New designs < energy use << lower labor cost capital cost $/pallet ( hr/day day/yr) 2 5 Standard tunnel Vertical, double channel Flow through labor 6% 5 6