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Energy Efficient Refrigeration

Energy Efficient Refrigeration

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Energy Efficient Refrigeration

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  1. Energy Efficient Refrigeration Jane Gartshore, Cool Concerns Ltd

  2. Outline • Revision - the basics • Component operation • Factors effecting efficiency • load reduction • operating conditions • The low hanging fruit

  3. Revision • Common principles • How a system works • Importance of operating conditions: • evaporating temperature • condensing temperature • superheat • subcooling

  4. A Simple System

  5. A Simple System COSP = capacity / total power input

  6. COSP • What do you expect the COSP to be?

  7. COSP • What do you expect the COSP to be? Typically … • LT ~ 0.5 to 1.5 • HT ~ 2 to 4 • AC ~ 4 to 6

  8. Superheated gas high pressure Superheated gas low pressure Subcooled liquid high pressure Saturated liquid high pressure Saturated mixture low pressure A Simple System Saturated mixture high pressure

  9. How Many Times Round the Circuit?

  10. How Many Times Round the Circuit? 20,000

  11. Compressor Most efficient if: • compression ratio low • suction superheat low • cooling adequate

  12. Evaporator Evaporator effectiveness depends on ... • evaporating temperature / pressure • size / condition of evaporator • temperature of cooled space / fluid • degree of useful superheat • degree of subcooling

  13. Condenser Condenser effectiveness depends on ... • condensing temperature / pressure • size / condition of condenser • cooling medium • temperature of cooling medium • head pressure control

  14. Superheat Useful superheat • in evaporator • aim for ~ 5K Non useful superheat • in suction line • minimise Refrigerant arriving at compressor must be superheated (but not too much!)

  15. Subcooling • 10K subcooling ~ 7% capacity increase • natural cooling or by subcooler • insulate liquid line when using a subcooler • No subcooling ~ ??% capacity reduction • condensing temperature too low • liquid line passes through hot area • loss of refrigerant

  16. Expansion Valve • Subcooled liquid at entry • Useful superheat setting important • TEV, minimum 6 bar pressure drop • EEV, minimum 4 bar pressure drop

  17. Central Plant Systems • Several smaller compressors for better capacity matching to load • Can be unevenly sized • Controlled on suction pressure

  18. Central Plant Systems

  19. Central Plant Control EV EV EV EV S S S S

  20. Evaporator Temperatures -8 -12 -8 -6 EV EV EV EV S S S S

  21. An Efficient System ... • has minimum load • has minimum temperature lift • uses an efficient combination of components • is well controlled

  22. Keeping the Load Low

  23. Load - Door Management Open door: Freezer, £6/h Chiller, £3/h

  24. Load - Product Loading

  25. Load - Defrost • Does the defrost work? • Is it controlled correctly • Defrost on demand can improve efficiency

  26. Load - Auxiliaries Switching off fans can save up to 14%

  27. Load - Sec. Ref. Pumps • Contribute twice to energy use • direct electricity consumption • heat into secondary fluid • Variable Speed Drive • will reduce pump power, e.g. by 25% • will reduce heat load

  28. Load - Insulation Cold store / cabinet insulation Secondary fluid pipe work insulation • ensure in good condition • ensure sufficient thickness • ensure well joined / sealed Suction line Liquid line

  29. Temperature Lift • Evaporating temperature • Condensing temperature • Control 1°C = 2% to 4%

  30. Evaporating Temperature • Cooled space / fluid temperature - as high as possible e.g. increasing frozen food store temperature from -25°C to -20°C saves over 10% (and reduces breakdown)

  31. Evaporating Temperature

  32. Evaporating Temperature • Ensure evaporator is clean • Ensure evaporator is clear of frost

  33. Evaporating Temperature • Refrigerant charge is critical • leak test • repair • re-charge

  34. Reduce Leak Potential • Brazed joints • Minimum charge • Minimum pressures • Charge monitoring • Effective leak testing

  35. Condensing Temperature • Ensure condensers are clean

  36. Condensing Temperature What’s the problem here?

  37. Condensing Temperature

  38. Condensing Temperature

  39. Condensing Temperature • Recommend replacement • take opportunity to fit larger condenser

  40. Condensing Temperature Non condensable gases increase condensing temperature • Purge air / nitrogen • use an automatic (refrigerated) air purger • portable versions available

  41. Control • Highest possible evaporating temperature • thermostat / controller (LP) setting • Lowest possible condensing temperature • minimum head pressure control • Appropriate useful superheat • TEV / EEV adjustment • Optimum compressor strategy

  42. Low Hanging Fruit • Cold store air change load reduction • Auxiliary load reduction • Reducing refrigerant leaks • System control • Re commissioning • Maintenance £££'s

  43. Air Change Reduction • Heat and moisture • Door management • Strip curtains / air lock • Try dehumidification • e.g. 8% reduction

  44. Aux Load Reduction Double impact / saving • Evaporator fan motors • E.g. 14% reduction on HT area • Process fluid pump control

  45. PPM 300 250 200 150 100 50 0 3 6 9 12 15 18 21 3 6 9 12 15 18 21 3 6 9 12 15 18 21 3 6 9 12 15 18 21 Tuesday Wednesday Thursday Friday 05/02/2002 06/02/2002 07/02/2002 08/02/2002 Leak Reduction 15% leakage doubles power input • Maintenance • Leak test method • Regime • Fixed leak detection • Charge monitoring

  46. Control • Suction and discharge pressure optimisation • ~10% savings • Defrost on demand • ~2.5% savings • Floating head pressure • ~ 7% savings

  47. Re Commissioning Re set suction & discharge set points Example savings: • 21.2% on HT pack • 13.6% saving on LT pack • 6.9% on total site energy

  48. Maintenance is Vital Ensure there is a maintenance regime which at least … • cleans condensers and evaporators • checks for leaks (and repairs them!) • does an eyes & ears system check

  49. Energy Efficient Refrigeration Jane Gartshore, Cool Concerns Ltd