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Energy Saving Options Electricity. Electricity Generation.

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Presentation on theme: "Energy Saving Options Electricity. Electricity Generation."— Presentation transcript:

1 Energy Saving Options Electricity

2 Electricity Generation

3 During Electricity Generation, thermal energy is converted to work. The process is subject to the Carnot principle

4 Carnot Principle W = Q s -Q r Efficiency = W/ Q s = Q s -Q r Q s (Q = m c p T) So, Efficiency = T s -T r T s Heat Supplied, Q s at T s Heat Rejected, Q r at T r Work, W (Temperatures in degrees K)

5 Efficiency: Heat to Work If T s = 600 o C (steam) = 873 K and T r = 350 o C = 623 K Efficiency = = 28.6% Thus, 71.4% of the heat energy is rejected to the environment Heat Supplied, Q s at T s Heat Rejected, Q r at T r Work, W (Temperatures in degrees K)

6 Supply Capacity

7 The maximum kVA that can be taken from an electricity mains supply cable is limited by a fuse. Utilities charge a fixed amount monthly for each kVA of available supply capacity

8 Maximum Demand

9 The kVA being taken by the supply cable is measured continuously, or at given intervals. The user pays a premium to the electrical utility according to the maximum value of kVA (the maximum demand) which occurs during the month

10 The Reduction of Maximum Demand The user should monitor the kVA readings to ascertain when the peak occurs and its magnitude

11 The user will then be in a position to reduce maximum demand charges by identifying activities that contribute to maximum demand identifying activities that contribute to maximum demand rescheduling activities that occur at maximum demand time (peak lopping) rescheduling activities that occur at maximum demand time (peak lopping) staggerong start-up times staggerong start-up times using stand-by generators to peak-lop using stand-by generators to peak-lop maximising power factors maximising power factors switching-off plant when not required switching-off plant when not required

12 The Reduction of Maximum Demand It should be noted that each kW saved by electricity conservation, also saves 1 kVA of maximum demand charges

13 Electric Motors and Variable Speed Drives

14 Electric Motors ac Both the efficiency and the power factor of an electric motor vary with the load The largest potential savings with electric motors is to match motor to load so that the motor runs at maximum efficiency

15 Electric Motors ac A survey of all motors at a site should be made and efficiencies estimated. Those motors which are too large should be changed. Many times this involves swapping motors around the plant and buying only a few new motors

16 Variable Speed Drives ac In situations where the load on the motor fluctuates, the use of variable speed drives should be considered to avoid large heat losses at lower loads

17 Fans and Ducts FAN DUCT AIR

18 Fans and Ducts ac Power = flow rate of fluid x specific volume of fluid x pressure rise across fan /fan efficiency

19 To Reduce Power Requirements ac 1.Reduce flow-rate of fluid 2.Decrease pressure drop in the duct Fans and Ducts

20 Flow Control can be achieved in two ways: ac 1. A damper can be used to restrict the flow 2.The fan speed can be altered Fans and Ducts

21 Minimise bends and elbows restrictions, filters, dampers and frictional forces Fans and Ducts Reducing Head Losses (Pressure Drops)

22 Pumps and Pipes PUMP PIPE LIQUID

23 Pumps and Pipes feed water pumps feed water pumps chilled water pumps chilled water pumps condensate return pumps condensate return pumps oil pumps oil pumps process fluid pumps process fluid pumps cooling tower water pumps cooling tower water pumps

24 ac Power = flow rate of fluid x specific volume of fluid x pressure rise across pump / pump efficiency Pumps and Pipes

25 To Reduce Power Requirements ac 1.Reduce flow-rate of fluid 2.Decrease pressure drop in the pipe Pumps and Pipes

26 and similarly, Flow Control can be achieved in two ways: ac 1. A flow control valve can be used to restrict the flow, just as a duct damper 2.The pump speed can be altered just as the fan speed Pumps and Pipes

27 Considerations of selecting optimal pumps and speeds to match pipe flow rates are exactly as for fans and ducts. Pumps and Pipes

28 Reducing Head Losses (Pressure Drops) Minimise bends and elbows restrictions, orifices, valves vertical rises frictional forces Pumps and Pipes

29 Compressors

30 Compressors Work in = pressure energy + change in internal energy m c p dT =pV + m c v dT m c p dT =m R dT + m c v dT c p =R + c v for air, 1005 = J/kg K m = mass of gas cp,cv = specific heats at constant pressure and volume p = pressure dT = change in temperature R = characteristic gas constant

31 Thus 1005 units of work are required to produce 287 units of pressure energy, even at 100% efficiency of compression. Furthermore, the work (electricity) has been produced in the first place in the conversion of heat to work at 30% efficiency. Compressors

32 So it requires at least 3350 units of heat energy to produce 287 units of pressure energy, or 11.7 units of heat for 1 unit of pressure energy. Compressors

33 Compressed air is the most expensive energy commodity and should only be used as a last resort. Question every use for compressed air. It certainly should not be used for swarf blowing and cleaning purposes. Compressors

34 check conditions of plant check conditions of plant check efficiency check efficiency check position of inlet duct check position of inlet duct check maintenance procedures check maintenance procedures check control arrangements check control arrangements check the amount of compressed gas supplied check the amount of compressed gas supplied check delivery temperature and pressure check delivery temperature and pressure check for leaks check for leaks Compressors

35 check uses for compressed gas check uses for compressed gas check pressures at points of use check pressures at points of use reduce generating pressure to minimum reduce generating pressure to minimum consider interstage cooling consider interstage cooling consider interstage bleed-off at different pressures consider interstage bleed-off at different pressures consider the use of localised booster compressors consider the use of localised booster compressors switch off compressors when not in use switch off compressors when not in use Compressors

36 consider the introduction of compressed gas accumulation so that off-peak electricity can be used or to peak lop maximum demand consider the introduction of compressed gas accumulation so that off-peak electricity can be used or to peak lop maximum demand use outside air/water for cooling/intercooling use outside air/water for cooling/intercooling recover heat from cooling and intercooling recover heat from cooling and intercooling Compressors

37 avoid condensation and concomitant blockage of pipelines avoid condensation and concomitant blockage of pipelines reheat compressed gas to increase discharge pressure reheat compressed gas to increase discharge pressure meter compressed air usage meter compressed air usage look for heat recovery opportunities look for heat recovery opportunities Compressors

38 Lighting

39 check zonal lighting requirements check zonal lighting requirements zone lighted areas zone lighted areas check that parts of the building are not being lit unnecessarily check that parts of the building are not being lit unnecessarily use infra-red detectors/time switches use infra-red detectors/time switches check the maintenance procedures check the maintenance procedures replace lamps when their efficiency drops replace lamps when their efficiency drops check lighting controls check lighting controls use automatic controls use automatic controls Lighting

40 challenge the need for large areas of glazing challenge the need for large areas of glazing eliminate glazing eliminate glazing obtain economic balance of artificial lighting and day-lighting obtain economic balance of artificial lighting and day-lighting use separate circuits for day-lighted peripheries use separate circuits for day-lighted peripheries use separate circuits for use outside working hours use separate circuits for use outside working hours Lighting

41 check colours of room surfaces check colours of room surfaces check conditions and cleanliness of luminaires and windows check conditions and cleanliness of luminaires and windows keep windows and roof-lights clean keep windows and roof-lights clean avoid dark background colours avoid dark background colours never use low-efficiency filament lamps never use low-efficiency filament lamps use low-energy fluorescent or discharge lamps use low-energy fluorescent or discharge lamps look for heat recovery opportunities look for heat recovery opportunities Lighting

42 Refrigeration and Air Conditioning

43 check maintenance and operating procedures check maintenance and operating procedures evaluate load patterns and operating cycles evaluate load patterns and operating cycles check conditions of plant and equipment check conditions of plant and equipment check for and seal leaks check for and seal leaks check insulation levels and conditions of insulation check insulation levels and conditions of insulation consider the use of thermal (cold) storage consider the use of thermal (cold) storage Refrigeration and Air Conditioning

44 check operation of condenser fans check operation of condenser fans check cleanliness of heat transfer surfaces check cleanliness of heat transfer surfaces check water treatment systems check water treatment systems check cooling tower operation check cooling tower operation check control arrangements check control arrangements check operating temperatures and pressures check operating temperatures and pressures look for heat recovery opportunities look for heat recovery opportunities Refrigeration and Air Conditioning

45 Select proper design points - temperature and humidity - thermal comfort chart Select proper design points - temperature and humidity - thermal comfort chart Select minimum airchange rates - vent off pollutants at source Select minimum airchange rates - vent off pollutants at source check control arrangements check control arrangements check that heating and cooling systems cannot conflict check that heating and cooling systems cannot conflict reduce heating and cooling loads reduce heating and cooling loads check zonal requirements check zonal requirements Refrigeration and Air Conditioning

46 check for unoccupied areas check for unoccupied areas consider zoning, partitioning, false ceilings and destratifiers consider zoning, partitioning, false ceilings and destratifiers minimise infiltration minimise infiltration look for opportunities for heat recovery look for opportunities for heat recovery check insulation levels check insulation levels isolate system from the surroundings isolate system from the surroundings Refrigeration and Air Conditioning

47 On-site Cogeneration

48 Examine the annual heating and power requirements for the site and consider whether the on-site generation of power with use of the heat generated might be an economic option. Such a system could also produce refrigeration via an absorption refrigeration system using the heat rejected from the power generator


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