Energy Saving Options Electricity. Electricity Generation.

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


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


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


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


To Reduce Power Requirements

ac1. Reduce flow-rate of fluid2. Decrease pressure drop in the

pipe


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


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.


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


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.


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.


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.


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


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


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


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


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


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


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


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

Energy Saving Options Electricity. Electricity Generation.

Documents

Transcript of Energy Saving Options Electricity. Electricity Generation.