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Energy efficiency in Refrigeration Systems

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HVAC and refrigeration systems consume a lot of electricity in Nepalese Industries. Therefore, improving the efficiency of these systems can lead to huge cost savings. This presentation was held in ...

HVAC and refrigeration systems consume a lot of electricity in Nepalese Industries. Therefore, improving the efficiency of these systems can lead to huge cost savings. This presentation was held in the context of energy auditor training in Nepal in 2012 that was supported GIZ/NEEP Programme.

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  • As mentioned earlier, we can see the difference in power consumption between various cooling mediums. The lower the temperature to be attained the higher is the power consumption.
  • Energy savings in refrigeration needs application of common sense. The first thing to look for is in the process. There may be a stream which is cooled from 50 O C to 25 O C. In this case the stream can first be cooled by cooling water upto say 30 O C and further cooling can be effected by chilled water. Chilled water is costlier than cooling water. There could also be process streams to be cooled and other stream requiring heating. In such cases proces to process heat exchange can reduce chilled water requirements as well as steam. Similarly in an air conditioning application, minimising/ eliminating unwanted loads can bring down energy consumption. Once load reduction options have been explored, we can move to refrigeration plant to try and optimise the system.

Energy efficiency in Refrigeration Systems Energy efficiency in Refrigeration Systems Presentation Transcript

  • ENERGY EFFICIENCY INENERGY EFFICIENCY IN REFRIGERATION SYSTEMREFRIGERATION SYSTEM D.PAWAN KUMAR D.PAWAN KUMAR
  • INTRODUCTIONINTRODUCTION Refrigeration deals with the transfer of heat from a low temperature level at the heat source to a high temperature level at the heat sink. Air conditioning for comfort Refrigeration for process
  • TON OF REFRIGERATIONTON OF REFRIGERATION 1 ton of refrigeration = 3024 kCal/hr heat rejected. The cooling effect produced is quantified as tons of refrigeration.
  • VAPOUR-COMPRESSION REFRIGERATION SYSTEMVAPOUR-COMPRESSION REFRIGERATION SYSTEM (R-22)(R-22)
  • VAPOUR – ABSORPTION REFRIGERATION SYSTEMVAPOUR – ABSORPTION REFRIGERATION SYSTEM EVAPORATOR CONDENSOR PUMP GENERATOR ABSORBER STRONG SOLUTION WEAK SOLUTION COOLING WATER IN HOT WATER OUT THROTTLING VALVE Regulating Valve Waste Heat/ Direct Fired Heat load In
  • PERFORMANCE ASSESSMENTPERFORMANCE ASSESSMENT The specific power consumption kW/TR is a useful indicator of the performance of refrigeration system. By messing refrigeration duty performed in TR and the Kilo Watt inputs measured, kW/TR is used as a reference energy performance indicator. The refrigeration TR is assessed as TR = Q ⋅Cp ⋅ (Ti – To ) / 3024 Where TR is cooling TR duty Q is mass flow rate of coolant in kg/hr Cp is coolant specific heat in kCal /kg / 0 C Ti is inlet. Temperature of coolant to evaporator (chiller) in 0 C. To is outlet temperature of coolant from evaporator (chiller) in 0 C.
  • OVERALL ENERGY CONSUMPTIONOVERALL ENERGY CONSUMPTION Compressor kW Chilled water pump kW Condenser water pump kW Cooling tower fan kW Overall kW/TR = sum of all above kW/ TR
  • EFFECT OF VARIATION IN EVAPORATOR TEMPERATUREEFFECT OF VARIATION IN EVAPORATOR TEMPERATURE ON COMPRESSOR POWER CONSUMPTIONON COMPRESSOR POWER CONSUMPTION Evaporator Temperature (0 C) Refrigeration Capacity (tons) Specific Power Consumption Increase in kW/ton (%) 5.0 67.58 0.81 - 0.0 56.07 0.94 16.0 -5.0 45.98 1.08 33.0 -10.0 37.20 1.25 54.0 -20.0 23.12 1.67 106.0 A 10 C raise in evaporator temperature can help to save almost 3 % on power consumption.
  • EFFECT OF VARIATION IN CONDENSER TEMPERATUREEFFECT OF VARIATION IN CONDENSER TEMPERATURE ON COMPRESSORON COMPRESSOR POWER CONSUMPTIONPOWER CONSUMPTION Condensing Temperature (0 C) Refrigeration Capacity (tons) Specific Power Consumption Increase in kW/TR (%) 26.7 31.5 1.17 - 35.0 21.4 1.27 8.5 40.0 20.0 1.41 20.5
  • EFFECT OF POOR MAINTENANCEEFFECT OF POOR MAINTENANCE ON COMPRESSOR POWER CONSUMPTIONON COMPRESSOR POWER CONSUMPTION Condition Evap. Temp (0 C) Cond. Temp (0 C) Refrigeration Capacity (tons) Specific Power Consumption (kW/ton) Increase in kW/Ton (%) Normal 7.2 40.5 17.0 0.69 - Dirty condenser 7.2 46.1 15.6 0.84 20.4 Dirty evaporator 1.7 40.5 13.8 0.82 18.3 Dirty condenser and evaporator 1.7 46.1 12.7 0.96 38.7
  • ENERGY SAVINGS OPPORTUNITIESENERGY SAVINGS OPPORTUNITIES Cold Insulation Process Heat Loads Minimisation Flow optimization and Heat transfer area increase to accept higher temperature coolant Avoiding wastages like heat gains, loss of chilled water, idle flows Frequent cleaning / de-scaling of all heat exchangers
  • AT THE REFRIGERATION PLANT AREAAT THE REFRIGERATION PLANT AREA Ensure adequacy of chilled water and cooling water flows, avoidance of bypass flows by valving off the idle equipment. Minimize part load operations by matching loads and plant capacity on line, adopting variable speed drives for varying process load. Ensure efforts to continuously optimize condenser and evaporator parameters for minimizing specific energy consumption and maximizing capacity. Adopt VAR system where economics permit as a non CFC solution
  • SELECT THE RIGHT COOLING MEDIUMSELECT THE RIGHT COOLING MEDIUM Type of cooling Power Consumption 1. Cooling tower water 0.1 KW/TR 2. Chilled water System at 10o C 0.7 KW/TR 3. Brine System at -20o C 1.8 KW/TR Order of preference Cooling water ChilledWater Brine
  • ENERGY SAVINGS IN REFRIGERATION SYSTEMSENERGY SAVINGS IN REFRIGERATION SYSTEMS There are two broad ways by which energy can be conserved 1.By decreasing the load 2.By optimising the refrigeration system
  • CALCULATING THE OPERATING LOAD OF ACALCULATING THE OPERATING LOAD OF A CHILLER PLANTCHILLER PLANT Refrigeration plant Refrigeration plant Hot well 12O C Cold well 8O C Process Chilled water flow – 100 m3 /hr Refrigeration TR - 100,000 kg/hr x 1 x 4 3000 - 133.33 TR Efficiency- Power drawn by compressor, kW TR m Cp 120 133.33 - = 0.9 DT
  • EFFICIENT OPERATION & MAINTENANCEEFFICIENT OPERATION & MAINTENANCE The suction temperature, pressure delivery pressure of compressors should be kept at optimum level Ensure all indicators are working properly Keep record of oil consumption Condensers Remove scale and algae and adopt suitable water treatment Give periodic purging of non-condensable gases Lesser the water temperature more the COP Routine defrosting of Cooling coils Stop condenser water pump when compressor not working 5O C rise in condensing temperature increases 10 % power consumption 5O C rise in evaporating temperature increases 10 % power consumption
  • ENERGY SAVING MEASURES IN REFRIGERATIONENERGY SAVING MEASURES IN REFRIGERATION Look for process modifications to reduce the cooling load Use cooling water to remove the maximum heat before using chilled water Provide VSD for condenser water pumps to vary the cooling water flow to maintain 4o C difference across the condensers Avoid primary pump operation Normally two pumps are operation (Chilled water supply pump from cold well and return water pump from hot well) Modify to operate only return water pump Provide VSD for efficient part load operation Explore ‘Ice-bank’ system for Maximum demand reduction Explore application of vapour absorption with cost economics Replace old systems with modern energy efficient systems
  • COLD INSULATIONCOLD INSULATION Thumb rules for cold Insulation Chilled water pipe insulation (Provide 2 to 3 inch thickness) Duct insulation (Provide 1 to 2 inch thickness) Suction line refrigerant pipe insulation(Provide 2 to3 inch thickness) Difference in temperature between ambient and surface Heat ingress kCal/m2 /hr Exposed area per tonne of refrigeration 5 35 86 10 73 41 15 113 27 20 154 19 Basis: Ambient temperature - 35O C, emissivity – 0.8, still air conditions Allowable heat ingress – 10 –15 Kcal/m2 /hr