energy saving options electricity. electricity generation
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Energy Saving OptionsEnergy Saving Options
ElectricityElectricity
Electricity Electricity GenerationGeneration
Electricity GenerationElectricity Generation
During Electricity Generation, thermal energy is converted to work.
The process is subject to the Carnot principle
Carnot PrincipleCarnot Principle
W = Qs -Qr
Efficiency = W/ Qs
= Qs -Qr
Qs
(Q = m cp T)
So, Efficiency = Ts -Tr
Ts
Heat Supplied, Qs at Ts
Heat Rejected, Qr at Tr
Work, W
(Temperatures in degrees K)
Efficiency: Heat to WorkEfficiency: Heat to WorkIf Ts = 600oC (steam)
= 873 Kand Tr = 350 oC
= 623 KEfficiency = 873 - 623
873 = 28.6%
Thus, 71.4% of the heat energy is rejected to the environment
Heat Supplied, Qs at Ts
Heat Rejected, Qr at Tr
Work, W
(Temperatures in degrees K)
Supply Supply Capacity Capacity
Supply Capacity Supply Capacity
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
Maximum Maximum DemandDemand
Maximum DemandMaximum Demand
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
The Reduction of Maximum DemandThe Reduction of Maximum Demand
The user should monitor the kVA readings to ascertain
when the peak occursand its magnitude
The user will then be in a position The user will then be in a position to to reduce maximum demandreduce maximum demand charges charges
byby
identifying activities that contribute to identifying activities that contribute to maximum demandmaximum demand
rescheduling activities that occur at rescheduling activities that occur at maximum demand time (peak lopping)maximum demand time (peak lopping)
staggerong start-up timesstaggerong start-up times using stand-by generators to peak-lopusing stand-by generators to peak-lop maximising power factorsmaximising power factors switching-off plant when not requiredswitching-off plant when not required
The Reduction of Maximum DemandThe Reduction of Maximum Demand
It should be noted that each kW saved by electricity conservation,
also saves 1 kVAof maximum demand charges
Electric Electric Motors and Motors and
Variable Variable Speed DrivesSpeed Drives
Electric MotorsElectric Motors
acBoth the efficiency and the power factor of
an electric motor vary with the loadThe largest potential savings with electric
motors is to match motor to load so that the motor runs at maximum efficiency
Electric MotorsElectric Motors
ac
A survey of all motors at a site should be made and efficiencies estimated.
Those motors which are too large shouldbe changed.
Many times this involves swapping motorsaround the plant and buying only a few
new motors
Variable Speed DrivesVariable Speed Drives
acIn situations where the load on the motor
fluctuates, the use of variable speeddrives should be considered to avoid
large heat losses at lower loads
Fans and DuctsFans and Ducts
FAN
DUCTAIR
Fans and DuctsFans and Ducts
ac
Power = flow rate of fluid x specific volume of fluidx pressure rise across fan /fan efficiency
To Reduce Power Requirements To Reduce Power Requirements
ac1. Reduce flow-rate of fluid2. Decrease pressure drop
in the duct
Fans and DuctsFans and Ducts
Flow Control can be achieved in Flow Control can be achieved in two ways: two ways:
ac1. A damper can be used to restrict the flow
2. The fan speed can be altered
Fans and DuctsFans and Ducts
MinimiseMinimise
bends and elbowsbends and elbows
restrictions, filters, dampersrestrictions, filters, dampers
and frictional forcesand frictional forces
Fans and DuctsFans and DuctsReducing Head Losses Reducing Head Losses
(Pressure Drops)(Pressure Drops)
Pumps and Pumps and PipesPipes
PUMP
PIPELIQUID
Pumps and PipesPumps and Pipes
feed water pumpsfeed water pumps chilled water pumpschilled water pumps condensate return pumpscondensate return pumps oil pumpsoil pumps process fluid pumpsprocess fluid pumps cooling tower water pumpscooling tower water pumps
ac
Power = flow rate of fluid x specific volume of fluidx pressure rise across pump / pump efficiency
Pumps and PipesPumps and Pipes
To Reduce Power Requirements
ac1. Reduce flow-rate of fluid2. Decrease pressure drop in the
pipe
Pumps and PipesPumps and Pipes
and similarly, Flow Control can be and similarly, Flow Control can be achieved in two ways: achieved in two ways:
ac1. A flow control valve can be
used to restrict the flow, justas a duct damper
2. The pump speed can be alteredjust as the fan speed
Pumps and PipesPumps and Pipes
Considerations of Considerations of selecting optimal pumps selecting optimal pumps
and speeds to match and speeds to match pipe flow rates are pipe flow rates are
exactly as for fans and exactly as for fans and ducts. ducts.
Pumps and PipesPumps and Pipes
Reducing Head Losses Reducing Head Losses (Pressure Drops)(Pressure Drops)
MinimiseMinimise
bends and elbowsbends and elbows
restrictions, orifices, valvesrestrictions, orifices, valves
vertical risesvertical rises
frictional forcesfrictional forces
Pumps and PipesPumps and Pipes
CompressorsCompressors
CompressorsCompressors
Work in = pressure energy + change in internal energy
m cp dT = pV+ m cv dT
m cp dT = m R dT+ m cv dT
cp = R + cv for air,
1005 = 287 + 718J/kg K
m = mass of gascp,cv = specific heats at
constant pressure and volume
p = pressuredT = change in temperatureR = characteristic gas constant
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.
CompressorsCompressors
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.
CompressorsCompressors
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.
CompressorsCompressors
check conditions of plantcheck conditions of plant check efficiencycheck efficiency check position of inlet ductcheck position of inlet duct check maintenance procedurescheck maintenance procedures check control arrangementscheck control arrangements check the amount of compressed gas check the amount of compressed gas
suppliedsupplied check delivery temperature and pressurecheck delivery temperature and pressure check for leakscheck for leaks
CompressorsCompressors
check uses for compressed gascheck uses for compressed gas check pressures at points of usecheck pressures at points of use reduce generating pressure to minimumreduce generating pressure to minimum consider interstage coolingconsider interstage cooling consider interstage bleed-off at different consider interstage bleed-off at different
pressurespressures consider the use of localised booster consider the use of localised booster
compressorscompressors switch off compressors when not in useswitch off compressors when not in use
CompressorsCompressors
consider the introduction of consider the introduction of compressed gas accumulation so compressed gas accumulation so that off-peak electricity can be used that off-peak electricity can be used or to peak lop maximum demandor to peak lop maximum demand
use outside air/water for use outside air/water for cooling/intercoolingcooling/intercooling
recover heat from cooling and recover heat from cooling and intercoolingintercooling
CompressorsCompressors
avoid condensation and concomitant avoid condensation and concomitant blockage of pipelinesblockage of pipelines
reheat compressed gas to increase reheat compressed gas to increase discharge pressuredischarge pressure
meter compressed air usagemeter compressed air usage look for heat recovery opportunitieslook for heat recovery opportunities
CompressorsCompressors
LightingLighting
check zonal lighting requirementscheck zonal lighting requirements zone lighted areaszone lighted areas check that parts of the building are not being check that parts of the building are not being
lit unnecessarily lit unnecessarily use infra-red detectors/time switchesuse infra-red detectors/time switches check the maintenance procedures check the maintenance procedures replace lamps when their efficiency dropsreplace lamps when their efficiency drops check lighting controlscheck lighting controls use automatic controlsuse automatic controls
LightingLighting
challenge the need for large areas of challenge the need for large areas of glazing glazing
eliminate glazingeliminate glazing obtain economic balance of artificial obtain economic balance of artificial
lighting and day-lightinglighting and day-lighting use separate circuits for day-lighted use separate circuits for day-lighted
peripheriesperipheries use separate circuits for use outside use separate circuits for use outside
working hoursworking hours
LightingLighting
check colours of room surfaces check colours of room surfaces check conditions and cleanliness of check conditions and cleanliness of
luminaires and windows luminaires and windows keep windows and roof-lights cleankeep windows and roof-lights clean avoid dark background coloursavoid dark background colours never use low-efficiency filament lampsnever use low-efficiency filament lamps use low-energy fluorescent or discharge use low-energy fluorescent or discharge
lampslamps look for heat recovery opportunitieslook for heat recovery opportunities
LightingLighting
Refrigeration Refrigeration and Air and Air
ConditioningConditioning
check maintenance and operating check maintenance and operating proceduresprocedures
evaluate load patterns and operating cyclesevaluate load patterns and operating cycles check conditions of plant and equipmentcheck conditions of plant and equipment check for and seal leakscheck for and seal leaks check insulation levels and conditions of check insulation levels and conditions of
insulationinsulation consider the use of thermal (cold) storageconsider the use of thermal (cold) storage
Refrigeration and Air ConditioningRefrigeration and Air Conditioning
check operation of condenser fanscheck operation of condenser fans check cleanliness of heat transfer surfacescheck cleanliness of heat transfer surfaces check water treatment systemscheck water treatment systems check cooling tower operationcheck cooling tower operation check control arrangementscheck control arrangements check operating temperatures and check operating temperatures and
pressurespressures look for heat recovery opportunitieslook for heat recovery opportunities
Refrigeration and Air ConditioningRefrigeration and Air Conditioning
Select proper design points - temperature Select proper design points - temperature and humidity - thermal comfort chartand humidity - thermal comfort chart
Select minimum airchange rates - vent off Select minimum airchange rates - vent off pollutants at sourcepollutants at source
check control arrangementscheck control arrangements check that heating and cooling systems check that heating and cooling systems
cannot conflictcannot conflict reduce heating and cooling loadsreduce heating and cooling loads check zonal requirementscheck zonal requirements
Refrigeration and Air ConditioningRefrigeration and Air Conditioning
check for unoccupied areascheck for unoccupied areas consider zoning, partitioning, false consider zoning, partitioning, false
ceilings and destratifiersceilings and destratifiers minimise infiltrationminimise infiltration look for opportunities for heat recoverylook for opportunities for heat recovery check insulation levelscheck insulation levels isolate system from the surroundingsisolate system from the surroundings
Refrigeration and Air ConditioningRefrigeration and Air Conditioning
On-site On-site CogenerationCogeneration
On-site CogenerationOn-site Cogeneration
Examine the annual heating and power requirements for the site and consider whether the on-site generation of power with use of the heat generatedmight be an economic option.
Such a system could also produce refrigeration via an absorption refrigeration system using theheat rejected from the power generator