A LOW CARBON DEFROST SYSTEM
Tom DAVIES , Robin CAMPBELL, Varun THANGAMANI
Frigesco Ltd., Innovation Centre, University of Exeter
Tom@frigesco.com
15th Intnl Refrigeration and Air Conditioning Conference, Purdue, 2014
EXISTING DEFROST METHODS
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•
•
•
•
Electric
Hot gas
Cool gas
Warm liquid
Reverse cycle
• ALL USE EXTRA ENERGY TO MELT ICE AND THEN TO RE-CHILL
• Some use thermal storage
FLASH DEFROST
• REQUIRES A HEAT STORE INSERTED
IN THE LIQUID LINE LEAVING THE
CONDENSER
• REQUIRES 3 SOLENOID VALVES +
PIPEWORK
• DOES NOT USE EXTRA ENERGY
NORMAL OPERATION & HEAT STORE
ON CHARGE
SUBCOOLING DURING CHARGE
START OF DEFROST
EVAPORATOR TEMP DURING DEFROST
HEAT STORE DEPLETED
HEAT STORE RECHARGED
POSSIBLE COLD CHAIN
APPLICATIONS
• LARGE SYSTEMS – WAREHOUSES
• TRANSPORT SYSTEMS
• SUPERMARKETS AND CONVENIENCE STORES –
WALK-INS
• RETAIL DISPLAY CABINETS (RDCs)
• DOMESTIC FREEZERS
• ______________________________________________
• PLUS
• AIR SOURCE HEAT PUMPS
TESTS ON:
Supermarket retail display cabinets 4.8m worldwide.
Cold Rooms - over 2.5m worldwide,
900k in large supermarkets, 300k in
fast food (MacDonalds, Starbucks, etc)
plus hospitals, schools, restaurants.
Air source heat pumps, rapidly growing
market. Over 2m units sold in Europe
in 2010.
RDC TESTS
• 2.6m HALF GLASS DOOR PLUS OPEN WELL (R404A)
• BOTH REFRIGERATION CIRCUITS MODIFIED TO TAKE
HEAT STORE MODULES
• COULD BE RUN WITH EITHER ELECTRIC DEFROST
OR FLASH DEFROST
• 24hr TESTS TO COMPARE ENERGY CONSUMPTION
TO EN23953:2005 STANDARD AT CC3.
• FLASH DEFROST REDUCED ENERGY CONSUMPTION
BY 40% WITH 6 DEFROSTS PER DAY.
RDC TESTS – AVERAGE PRODUCT
TEMPERATURES
WALK-IN TESTS
• 8m3 STOREROOM WITH SIMULATED LOADS
• REFRIGERATION CIRCUIT MODIFIED TO TAKE HEAT
STORE MODULE (R404A)
• COULD BE RUN WITH EITHER ELECTRIC DEFROST
OF FLASH DEFROST
• 24hr TESTS TO COMPARE ENERGY CONSUMPTION
• FLASH DEFROST REDUCED ENERGY CONSUMPTION
BY 20%
ELEMENTS OF WALK-IN RIG
WALK-IN TESTS – PRODUCT
TEMPERATURE SWINGS
DAILY ENERGY CONSUMPTION
WALK-IN
Electric defrost
Flash defrost
360
288
TEC (KWh/24h)
RDC
Electric defrost
Flash defrost
DEC (KWh/24h)
52.26
31.87
RECRC (KWh/24h)
66.66
39.03
TEC (KWh/24h)
118.92
70.90
BENEFITS OF FLASH DEFROST
• Flash defrost eliminates the use of electrical power for
melting ice
• Flash defrost limits the temperature rise in the air coil
• Flash defrost reduces temperature rises in the product
• Flash defrost reduces energy consumption in post-defrost
re-chilling phase
• Flash defrost creates the opportunity to operate at higher
evaporator temperatures
• Flash defrost allows more frequent defrosts
Questions?
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