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Compressed Air System
Air Is Free !!!
Compressed Air Is Free !!!Not
Compressed Air Efficiency:60 to 80% of the power of the prime mover is converted into an
unusable form of energy (HEAT)And to a lesser extent, into friction, misuse and noise
Approximately 10% gets to the
point of use!!
A typical compressed air system
Types of Air Compressors
There are three basic types of air compressors:Reciprocating (Recip)Rotary Screw (Screw) Rotary Centrifugal (Centrifugal)
These types are further defined by:the number of compression stages method of cooling (air, water, oil) drive method (motor, engine, steam, other) how they are lubricated (oil, oil-free) packaged or custom-built
Positive-Displacement Compressors –Reciprocating
A piston, driven through a crankshaft and connecting rod by an electric motor reduces the volume in the cylinder occupied by the air or gas, compressing it to a higher pressure. Single-acting compressors have a compression stroke in only one direction, while double-acting units provide a compression stroke as the piston moves in each direction. Large industrial reciprocating air compressors are double-acting and water-cooled. Multi-stage double-acting compressors are the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units. Reciprocating compressors are available in sizes from less than 1 hp to more than 600 hp.
Positive-Displacement Compressors -Rotary compressors
Most commonly used in sizes from about 30-200 hp. Most common type of rotary compressor is the helical twin screw-type (also known as rotary screw or helical lobe). Male and female screw-rotors mesh, trapping air, and reducing the volume of the air along the rotors to the air discharge point. Rotary screw compressors have low initial cost, compact size, low weight, and are easy to maintain. Rotary screw compressors are available in sizes from 3-600 hp and may be air- or water-cooled. Less common rotary compressors include sliding-vane, liquid-ring, and scroll-type.
Dynamic Compressors -centrifugal
These compressors raise the pressure of air or gas by imparting velocity energy and converting it to pressure energy. The centrifugal-type is the most common and is widely used for industrial compressed air. Each impeller, rotating at high speed, imparts primarily radial flow to the air or gas which then passes through a volute or diffuser to convert the residual velocity energy to pressure energy. Some large manufacturing plants use centrifugal compressors for general plant air, and, in some cases, plants use other compressor types to accommodate demand load swings while the centrifugal compressors handle the base load.
Dynamic Compressors –Axial and mixed flow
Axial compressors consist of a rotor with multiple rows of blades and a matching stator with rows of stationary vanes. The rotating blades impart velocity energy, primarily in an axial plane. The stationary vanes then act as a diffuser to convert the residual velocity energy into pressure energy. This type of compressor is restricted to very high flow capacities and generally has a relatively high compression efficiency. Mixed flow compressors have impellers and rotors which combine the characteristics of both axial and centrifugal compressors.
General Selection Criteria for Compressors
Capacity (m3/h) Pressure (bar) Type of Compressor
From To From To
Roots power compressor single stage
100 30000 0.1 1
Reciprocating - Single / Two stage 100 12000 0.8 12 - Multi stage 100 12000 12.0 700 Screw - Single stage 100 2400 0.8 13 - Two stage 100 2200 0.8 24 Centrifugal 600 300000 0.1 450
SYSTEM COMPONENTSIntake Air Filters : Prevent dust and atmospheric impurities from entering compressor. Dust causes sticking valves, scored cylinders, excessive wear etc.Inter-stage Coolers : Reduce the temperature of the air (gas) before it enters the next stage to reduce the work of compression and increase efficiency. They can be water-or air-cooled.After Coolers : Reduce the temperature of the discharge air, and thereby reduce the moisture carrying capacity of air.Air-dryers : Air dryers are used to remove moisture, as air for instrument and pneumatic equipment needs to be relatively free of any moisture. The moisture is removed by suing adsorbents or refrigerant dryers, or state of the art heatless dryers.Moisture Traps : Air traps are used for removal of moisture in the compressed air distribution lines. They resemble steam traps wherein the air is trapped and moisture is removed.Receivers : Depending on the system requirements, one or more air receivers are generally provided to reduce output pulsations andpressure variations.
DryersWhen air leaves an aftercooler and moisture separator, it is typically saturated. Any further radiant cooling as it passes through the distribution piping, which may be exposed to colder temperatures, will cause further condensation of moisture with detrimental effects such as corrosion and contamination of point-of-use processes. This problem can be avoided by the proper use of compressed air dryers. The most common types are:
Refrigerant-type dryers cool the air to 35 to 40F and then remove the condensed moisture before the air is reheated and dischargedDeliquescent-type dryers use a hygroscopic desiccant material with a high affinity for water. The desiccant absorbs water vapor and is dissolved in the liquid formed. Dew point suppression of 15 to 50F degrees can be expected when the proper bed level is maintainedTwin tower regenerative-type dryers use a desiccant which adsorbs water vapor in the air stream. Adsorb means that the moisture adheres to the desiccant, collecting in the thousands of small pores within each desiccant bead. The composition of the desiccant is not changed and the moisture can be driven off in a regeneration process by applying dry purge air, by the application of heat, or a combination of both. Regenerative desiccant-type dryers typically are of twin tower construction. One tower dries the air from the compressor while the desiccant in the other tower is being regenerated, after the pressure in the tower being regenerated has been reduced to atmospheric pressure. The purge air requirement can range from 10 to 18% of the total air flow, depending on the type of dryer. The typical regenerative desiccant dryer at 100 psig has a pressure dew point rating of -20F to -40F
Air ReceiverReceivers are used to provide compressed air storage capacity to meet peak demand events and help control system pressure. Receivers are especially effective for systems with widely varying compressed air flow requirements. Where peaks are intermittent, a large air receiver may allow a smaller air compressor to be used and can allow the capacity control system to operate more effectively and improve system efficiency. An air receiver after a reciprocating air compressor can provide dampening of pressure pulsations, radiant cooling, and collection of condensate. Demand-side control will optimize the benefit of the air receiver storage volume by stabilizing system header pressure and "flattening" the load peaks.
Heat Recovery with Water-CooledCompressors
Heat recovery for space heating is not as common with water-cooled compressors because an extra stage of heat exchange is required and the temperature of the available heat is lower. Since many water-cooled compressors are quite large, however, heat recovery for space heating can be an attractive opportunity. Recovery efficiencies of 50-60% are typical.
Traps and DrainsAutomatic condensate drains or traps are used to prevent the loss of air through open petcocks and valves. Drain valves should allow removal of condensate but not compressed air. Two types of traps are common: mechanical and electrical. Mechanical traps link float devices to open valves when condensate rises to a preset level. Electric solenoid drain valves operate on a preset time cycle, but may open even when condensate is not present. Other electrical devices sense liquid level and open to drain only when condensate is present. Improperly operating or maintained traps can create excessive air usage and waste energy
Air Distribution SystemsThe air distribution system links the various components of the compressed air system to deliver air to the points of use with minimal pressure loss. The specific configuration of a distribution system depends on the needs of the individual plant, but frequently consists of an extended network of main lines, branch lines, valves, and air hoses. The length of the network should be kept to a minimum to reduce pressure drop. Air distribution piping should be large enough in diameter to minimize pressure drop. A loop system is generally recommended, with all piping sloped to accessible drop legs and drain points.
When designing an air distribution system layout, it is best to place the air compressor and its related accessories where temperature inside the plant is the lowest. A projection of future demands and tie-ins to the existing distribution system should also be considered.
Reciprocating compressor
Screw compressor
Centrifugal Compressor
Compressor efficiency
( )( ) ( ) ⎥⎦
⎤⎢⎣
⎡⎟⎠⎞
⎜⎝⎛× 1 - P
P 0.612 / P Q 1-KNK / NK1-K
s
dsTheoretical kW =
N = No. of stagesK = Ratio of specific heats (1.35 for air)Ps = suction pressure in kg/cm2
Pd = Discharge pressure in kg/cm2
Q = Actual air flow (m3/min.)Actual kW = √ 3 V I × PF as measured
Efficiency of compressor and motor combination = kWActual
kW lTheoretica100 ×
Energy Efficiency practices in compressed air systems
Effect of Intake Air temperature on Power Consumption
Inlet Temperature (0C)
Relative Air Delivery (%)
Power Saved (%)
10.0 102.0 + 1.4 15.5 100.0 Nil 21.1 98.1 - 1.3 26.6 96.3 - 2.5 32.2 94.1 - 4.0 37.7 92.8 - 5.0 43.3 91.2 - 5.8
Every 40C rise in inlet air temperature results in a higher energy consumption by 1 % to achieve equivalent output. Hence, cool air intake leads to a more efficient compression.
pAir Inlet Filter on Power
Consumption
Pressure Drop Across air filter
(mmWC)
Increase in Power Consumption (%)
0 0 200 1.6 400 3.2 600 4.7 800 7.0
For every 25 mbar pressure lost at the inlet due to choked filters, the compressor performance is reduced by about 2 percent.
ElevationPercentage Relative
Volumetric Efficiency Compared with Sea Level
Altitude Meters
Barometric Pressure
Mbar At 4 bar At 7 bar
Sea level 1013 100.0 100.0 500 945 98.7 97.7
1000 894 97.0 95.2 1500 840 95.5 92.7 2000 789 93.9 90.0 2500 737 92.1 87.0
It is evident that compressors located at higher altitudes consume more power to achieve a particular delivery pressure than those at sea lvel, as the compression ratio is higher.
Efficacy of Inter and After Coolers
Details Imperfect Cooling
Perfect Cooling
Chilled Water Cooling
1 Stage inlet temperature 0C 21.1 21.1 21.1 2 Stage inlet temperature 0C 26.6 21.1 15.5 Capacity (m3/min) 15.5 15.6 15.7 Shaft Power (kW) 76.3 75.3 74.2 Specific energy consumption kW (m3/min)
4.9 4.8 4.7
Percent Change + 2.1 - - 2.1
It can be seen from the table that an increase of 5.50C in the inlet to the second stage results in a 2 % increase in the specific energy consumption. Use of cold water reduces power consumption.
Cooling Water Requirement
Compressor Type
Minimum quantity of Cooling Water required
for 2.85 m3/min. FAD at 7 bar (lpm)
Single-stage 3.8 Two-stage 7.6 Single-stage with after-cooler 15.1 Two-stage with after-cooler 18.9
Power Reduction through Pressure Reduction
Pressure Reduction Power Reduction (%)
From (bar) To (bar)
Single-stage
Water-cooled
Two-stage Water-cooled
Two-stage Air-
cooled
6.8 6.1 4 4 2.6
6.8 5.5 9 11 6.5
A reduction in the delivery pressure of a compressor would reduce the power consumption.
Expected Specific Power Consumption of Reciprocating Compressors (based on motor
input)
Pressure bar No. of Stages Specific Power kW/170 CMH
1 1 6.29 2 1 9.64 3 1 13.04 4 2 14.57 7 2 18.34 8 2 19.16 10 2 21.74 15 2 26.22
Energy Wastage due to Smaller Pipe Diameter
Pipe Nominal
Bore (mm)
Pressure drop (bar) per 100 meters
Equivalent power losses (kW)
40 1.80 9.5 50 0.65 3.4 65 0.22 1.2 80 0.04 0.2
100 0.02 0.1
Typical acceptable pressure drop in industrial practice is 0.3 bar in mains header at the farthest point and 0.5 bar in distribution system
Discharge of Air through Orifice
Gauge Pressure
Bar 0.5 mm 1 mm 2 mm 3 mm 5 mm 10 mm 12.5 mm
0.5 0.06 0.22 0.92 2.1 5.7 22.8 35.5 1.0 0.08 0.33 1.33 3.0 8.4 33.6 52.5 2.5 0.14 0.58 2.33 5.5 14.6 58.6 91.4 5.0 0.25 0.97 3.92 8.8 24.4 97.5 152.0 7.0 0.33 1.31 5.19 11.6 32.5 129.0 202.0
Cost of Air Leakage
Orifice Size mm
KW Wasted
* Energy Waste (Rs/Year)
0.8 0.2 8000 1.6 0.8 32000 3.1 3.0 120000 6.4 12.0 480000
* based on Rs. 5 / kWh ; 8000 operating hours; air at 7.0 bar
Heat Recovery
As noted earlier, compressing air generates heat. In fact, industrial-sized air compressors generate a substantial amount of heat that can be recovered and put to useful work. More than 80% of the electrical energy going to a compressor becomes heat. Much of this heat can be recovered and used for producing hot water or hot air.
Typical uses for recovered heat include supplemental space heating, industrial process heating, water heating, makeup air heating, and boiler makeup water preheating. Recoverable heat from a compressed air system is not, however, normally hot enough to be used to produce steam directly.
As much as 80-93% of the electrical energy used by an industrial air compressor is converted into heat. In many cases,a properly designed heat recovery unit can recover anywhere from 50-90% of this available thermal energy and put it to useful work heating air or water
Heat Recovery with Air-Cooled Rotary Screw Compressors
Air-cooled packaged rotary screw compressors are very amenable to heat recovery for space heating or other hot air uses. Ambient atmospheric air is heated by passing it across the system's aftercoolerand lubricant cooler, where it extracts heat from both the compressed air and the lubricant that is used to lubricate and cool the compressor.
Since packaged compressors are typically enclosed in cabinets and already include heat exchangers and fans, the only system modifications needed are the addition of ducting and another fan to handle the duct loading and to eliminate any back pressure on the compressor cooling fan. These heat recovery systems can be modulated with a simple thermostatically-controlled hinged vent. When heating is not required -- such as in the summer months -- the hot air can be ducted outside the building. The vent can also bethermostatically regulated to provide a constant temperature for a heated area.
Hot air can be used for space heating, industrial drying, preheating aspirated air for oil burners, or any other application requiring warm air. As a rule of thumb, approximately 50,000 Btu/hour of energy is available for each 100 cfm of capacity (at full-load). Air temperatures of 30 to 40oF above the cooling air inlet temperature can be obtained. Recovery efficiencies of 80-90% are common
Steps in simple shop-floor method for leak quantification
Shut off compressed air operated equipments (or conduct test when no equipment is using compressed air).Run the compressor to charge the system to set pressure of operationNote the sub-sequent time taken for ‘on load’ and ‘off load’cycles of the compressors. For accuracy, take ON & OFF times for 8 – 10 cycles continuously. Then calculate total ‘ON’ Time (T) and Total ‘OFF’ time (t).The system leakage is calculated as System leakage (cmm) = Q × T / (T + t)Q = Actual free air being supplied during trial, in cubic meters per minuteT = Time on load in minutest = Time unload in minutes
Leak test: exampleCompressor capacity (CMM) = 35Cut in pressure kg/SQCMG = 6.8Cut out pressure kg/SQCMG = 7.5On load kW drawn = 188 kWUnload kW drawn = 54 kWAverage ‘On-load’ time = 1.5 minutesAverage ‘Unload’ time = 10.5 minutes
Comment on leakage quantity and avoidable loss of power due to air leakages.
a) Leakage quantity (CMM) =
= 4.375 CMMb) Leakage per day = 6300 CM/dayc) Specific power for compressed air generation=
= 0.0895 kwh/m3
d) Power lost due to leakages/day = 563.85 kWh
( )( ) ( ) 35
5.105.11.5
×+
( )CMH6035kWh 188
×
Capacity Assessment in Shop-floor
Isolate the compressor along with its individual receiver being taken for test from main compressed air system by tightly closing the isolation valve or blanking it, thus closing the receiver outlet.Open water drain valve and drain out water fully and empty the receiver and the pipe line. Make sure that water trap line is tightly closed once again to start the test.Start the compressor and activate the stop watch.Note the time taken to attain the normal operational pressure P2 (in the receiver) from initial pressure P1.Calculate the capacity as per the formulae given below :
Min./NM TV
PPP
Q 3
0
12 ×−
=Actual Free air discharge
Where
P2 = Final pressure after filling (kg/cm2 a) P1 = Initial pressure (kg/cm2a) after bleeding P0 = Atmospheric Pressure (kg/cm2 a) V = Storage volume in m3 which includes receiver,
after cooler, and delivery piping T = Time take to build up pressure to P2 in minutes
ExamplePiston displacement : 16.88 CMMTheoretical compressor capacity : 14.75 CMM @ 7 kg/SQCMG Compressor rated rpm 750 : Motor rated rpm : 1445Receiver Volume : 7.79 CMAdditional hold up volume, i.e., pipe / water cooler, etc., is : 0.4974 CMTotal volume : 8.322 CMInitial pressure P1 : 0.5 Kgf / SQCMGFinal pressure P2 : 7.03 Kgf / SQCMGAtmospheric pressure P0 : 1.026Kgf/cm2A
Compressor output CMM :
( )2 1P P Total VolumeAtm. Pressure Pumpup time
− ××
( )4.021.0261
8.322 5.003.7×
×−
= 13.17 CMM
How Air Amplifiers Work
Compressed air flows through the inlet (1) into an annular chamber(2). It is then throttled through a small ring nozzle (3) at highvelocity. This primary air stream adheres to the coanda profile (4),which directs it toward the outlet. A low pressure area is createdat the center (5) inducing a high volume flow of surrounding airinto the primary air stream. The combined flow of primary andsurrounding air exhausts from the Air Amplifier in a high volume,high velocity flow.
HVAC and Refrigeration System
Ton of refrigeration
The cooling effect produced is quantified as tons of refrigeration.
1 ton of refrigeration = 3024 kCal/hr heat rejected.
Conceptual view of a chilled-water air-conditioning system
CFCs Are On The Way OutEighty percent of today’s existing chillers are centrifugal chillers that use R-11 as refrigerant. The newer, non-CFC alternative to R-11 is HCFC-123. Some centrifugal chillers use R-12; its non-CFC alternative is HFC-134a. Unitary A/C units typically use R-22, which will be phased out in the future.
Phase-Out DatesRefrigerants Action
1996 R-11, R-12, R-500, HCFC-152A, CFC-114
Production of these refrigerants is stopped. Equipment using these refrigerants is no longer manufactured.
2010HCFC-22 Manufacture of equipment using this refrigerant is stopped.
2020HCFC-22 Production of this refrigerant is stopped.
2020HCFC-123 Manufacture of equipment using this refrigerant is stopped.
2030HCFC-123 Production of this refrigerant is stopped.
Introduction
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 comfortRefrigeration for process
Vapour compression System
How do the chillers work ?
1. Boiling point of the water is a function of pressure. At atmospheric pressure water boils at 100 deg. C. When maintained at high vacuum, water will boil and subcool itself. The boiling point of the water at 6 mmHg (abs) is 3.7 deg. C.
2. Lithium Bromide (LiBr) has the property to absorb water due to its chemical affinity. At higher concentration and lower temperature LiBr absorbs water vapour (refrigerant vapour) very effectively.
How do the chillers work ?
3. As Lithium Bromide becomes dilute it loses its capacity to absorb water vapour. It thus needs to bereconcentrated using a heat source. Heat source may be Steam or Flue gases or even Hot water.
How do the chillers work ?
Vapour absorption chillers: Types
Single effect steam fired (0.4 to 2 kg/cm2)Steam Consumption for 200 TR = 8.5 Kg/hr/TR
Double effect steam fired (3 to 9 kg/cm2)Steam Consumption for 200 TR = 4.5 Kg/hr/TR Cost of m/c = Rs. 12000 to 15000 per TR
Low temperature hot water fired (75 – 100oC)High temperature hot water fired (110 – 145oC)Direct fired (oil, gas, kerosene)
HSD/LDO Consumption = 0.313 lit/hr/TRKerosene Consumption =0.326lit/hr/TRCost of m/c = Rs. 20,000 to 25000 per TR
Properties of Commonly used Refrigerants
Enthalpy * Refrigerant
Boiling Point
** (oC)
Freezing Point (oC)
Vapor Pressure * (kPa)
Vapor Volume * (m3 / Kg)
Liquid (kJ / Kg)
Vapor (kJ / Kg)
R - 11 23.82 -111.0 25.73 0.61170 191.40 385.43
R - 12 -29.79 -158.0 219.28 0.07702 190.72 347.96
R - 22 -40.76 -160.0 354.74 0.06513 188.55 400.83
R - 502 -45.40 --- 414.30 0.04234 188.87 342.31
R - 7 (Ammonia)
-33.30 -77.7 289.93 0.41949 -808.71 487.76
COP = (H2-H1)/(H3-H2)
Performance 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 / 0C Ti is inlet. Temperature of coolant to evaporator (chiller) in 0C.To is outlet temperature of coolant from evaporator (chiller) in 0C.
Overall energy consumption
Compressor kWChilled water pump kWCondenser water pump kWCooling tower fan kW
Overall kW/TR = sum of all above kW/ TR
Effect of Variation in Evaporator Temperature on Compressor Power Consumption
Evaporator Temperature
(0C)
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 10C raise in evaporator temperature can help to save almost 3 % on power consumption.
Condenser Temperature on Compressor Power Consumption
Condensing Temperature
(0C)
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 Maintenance on Compressor Power Consumption
Condition Evap. Temp (0C)
Cond. Temp (0C)
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 OPPORTUNITIES
Cold InsulationBuilding EnvelopBuilding Heat LoadsProcess Heat Loads Minimisation
Flow optimization and Heat transfer area increase to accept higher temperature coolantAvoiding wastages like heat gains, loss of chilled water, idle flowsFrequent cleaning / de-scaling of all heat exchangers
At the Refrigeration A/C Plant Area
Ensure regular maintenance of all A/C plant components as per manufacturer guidelines.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 Medium
Type of cooling Power Consumption
1. Cooling tower water 0.1 KW/TR2. Chilled water System at 10oC 0.7 KW/TR3. Brine System at -20oC 1.8 KW/TR
Order of preferenceCooling water ChilledWater Brine
Energy 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 a chiller plant
Refrigerationplant
Refrigerationplant
Hot well12OC
Cold well8OC
Process
Chilled water flow – 100 m3/hr
Refrigeration TR - 100,000 kg/hr x 1 x 43000
m Cp ∆Τ
- 133.33 TR
Power drawn by compressor, kWEfficiency -
TR
120 - = 0.9
133.33
Energy saving measures in A/c System
Comfort conditions: 25OC, 55 % RHMinimize heat load through glass windows
Provide sun control film, Use double glassInsulate roof top in A/C Building
Provide under deck insulation of 50 mm, Provide lawns at roof topOptimize fresh air supply into a/c room
Conduct CO2 study to optimize fresh air quantity10-15 cfm/person or 0.25 cfm/sq..ft as per ASHRAE
Minimise artificial lightingUse natural lighting , 3.5 kw lighting consumes 1.0 TR load
Provide controlsinstall thermostat to control peak and base loadProvide VSD for AHU with return air temp.sensor-set at 25oC
Air tight the building envelopprevent cold air leakage, Provide door closures
Avoid heat producing equipments inside the roomkeep away UPS Battery , ovens, other loads
Efficient operation & maintenance
The suction Temperature, pressure delivery pressure of compressors should be kept at optimum level
Ensure all indicators are working properlyKeep record of oil consumption
CondensersRemove scale and algae and adopt suitable water treatmentGive periodic purging of non-condensable gasesLesser the water temperature more the COPRoutine defrosting of Cooling coils Stop condenser water pump when compressor not working 5OC rise in condensing temperature increases 10 % power consumption5OC rise in evaporating temperature increases 10 % power consumption
Energy saving measures in refrigeration
Look for process modifications to reduce the cooling loadUse cooling water to remove the maximum heat before using chilled waterProvide VSD for condenser water pumps
to vary the cooling water flow to maintain 4oC difference across the condensersAvoid 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 pumpProvide VSD for efficient part load operation
Explore ‘Ice-bank’ system for Maximum demand reductionExplore application of vapour absorption with cost economicsReplace old systems with modern energy efficient systems
Cold InsulationDifference in temperature between ambient and surface
Heat ingressKcal/m2/hr
Exposed area per tonne of refrigeration
5 35 86
10 73 41
15 113 27
20 154 19
Basis: Ambient temperature - 35OC, emissivity – 0.8, still air conditionsAllowable heat ingress – 10 –15 Kcal/m2/hr
Thumb rules for cold InsulationChilled 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)
End
Fans and Blowers
Difference between fans, blowers and compressors
Equipment Specific Ratio Pressure rise (mmWg)
Fans Up to 1.11 1136
Blowers 1.11 to 1.20 1136 – 2066
Compressors more than 1.20 -
As per ASME the specific pressure, i.e, the ratio of the discharge pressure over the suction pressure is used for defining the fans, blowers and compressors as highlighted below :
Typical centrifugal fan operation
Fan types
Axial fanCentrifugal fan
Centrifugal Fan: Types
Backward CurvedPaddle Blade (Radial blade)
Forward Curved (Multi vane)
Axial Flow Fan: TypesTube Axial
Vane Axial
Propeller
Fan Types and Efficiencies
Centrifugal Fans Peak Efficiency Range
Airfoil, backwardly curved/inclined 79-83 Modified radial 72-79 Redial 69-75 Pressure blower 58-68 Forwardly curved 60-65 Axial fan vanaxial 78-85 Tubeaxial 67-72 Propeller 45-50
Axial-flow Fans Centrifugal Fans
Type Characteristics Typical Applications Type Characteristics Typical
Applications
Propeller
Low pressure, high flow, low efficiency, peak efficiency close to point of free air delivery
Air-circulation, ventilation, exhaust
Radial High pressure, medium flow, efficiency close to tube-axial fans, power increases continuously
Various industrial applications, suitable for dust laden, moist air/gases
Tube-axial
Medium pressure, high flow, higher efficiency than propeller type, dip in pressure-flow curve before peak pressure point.
HVAC, drying ovens, exhaust systems
Forward-curved blades
Medium pressure, high flow, dip in pressure curve, efficiency higher than radial fans, power rises continuously
Low pressure HVAC, packaged units, suitable for clean and dust laden air / gases
Vane-axial
High pressure, medium flow, dip in pressure-flow curve, use of guide vanes improves efficiency
High pressure applications including HVAC systems, exhausts
Backward curved blades
High pressure, high flow, high efficiency, power reduces as flow increases beyond point of highest efficiency
HVAC, various industrial applications, forced draft fans, etc.
Airfoil type Same as backward curved type, highest efficiency
Same as backward curved, but for clean air applications
System characteristic curve
System curve
Fan Laws
Flow ? Speed Pressure ? (Speed)2 Power ? (Speed)3
1 1
2 2
Q NQ N
= 2
1 1
2 2
SP NSP N
⎛ ⎞= ⎜ ⎟⎝ ⎠
3
1 1
2 2
kW NkW N
⎛ ⎞= ⎜ ⎟⎝ ⎠
Varying the RPM by 10% decreases or increases air delivery by 10%.
Varying the RPM by 10% decreases or increases the static pressure by 19%.
Varying the RPM by 10% decreases or increases the
power requirement by 27%.
Where Q – flow, SP – Static Pressure, kW – Power and N – speed (RPM)
Fan static pressureFan Static Pressure SP = SP (Fan outlet) – SP (Fan outlet)
SP (Fan outlet) – Static pressure at fan outlet, inches WCSP (Fan outlet) – Static pressure at fan inlet, inches WC
SP = 0.05 – (-10)= 10.05 in W.C.
Static Pressure Profile of the System
Static pressure drop and rise across entire system
Fan behaviour
Speed vs Power
% Speed % Power
100
90
80
70
60
50 13
100
73
51
34
22
Flow control
Damper - Most PopularVariable Speed Drive
Recirculation
Damper 100
VFCPower 75
50
VFD25
Ideal25 50 75 100
Flow
Impact of speed reduction
Use of VSD: Boiler ID fan case study
Use of VSD: Boiler ID fan case study(contd.)
Energy audit of fan
• Collect fan and motor specifications with ducting network
• Measure motor power input• Measure fan and motor speed• Measure static pressure at various points in the
duct• Measure total and static pressure and compute
flow• Estimate the system efficiency and check fan
operating point
What to Look for in the FieldOverall system efficiency will be determined by the type of fan or blower, its interaction with the air distribution system, and the method of control.
•Determine whether the right type of fan or blower is used for an application. Is your fan or blower is providing the best efficiency and performance in a given application.
•The efficiency of a system depends on the number and type of bends and restrictions. Sharp bends, especially, increase the resistance the fan or blower must overcome. Bends and restrictions near the inlet or outlet seriously degrade capacity and efficiency.
•With a properly selected fan or blower and well-designed air distribution system, the method of control is the main thing determining energy efficiency. In systems requiring constant air volume, the speed of a belt-driven fan or blower should be adjusted by proper selection of pulley sizes, and equipment should operate only when needed. In systems requiring variable airflow, an adjustable-speed control is most efficient.
Energy conservation in fans
• Match fan capacity to demand– downsizing, pulley change, VSD..
• Avoid unnecessary demand– excess air reduction– idling
• Reduce pressure drops– Remove redundant ducts– Modify ducting with minimum bends
• Drive system – Provide direct drive where possible– Replace V-belt by flat belt
• Replace with energy efficient fans• Regular preventive maintenance
Energy saving in Boiler ID fan by speed reduction through pulley change
8”10” 26 kW
1470 RPM 1181 RPM
14 kW 6” 10”
1470 RPM 882RPM
End
Pumps and Pumping Systems
End
Energy Balance for a Typical Pumping System
ELECTRICITY100%
12% LOSS
2% LOSS
24% LOSS
9% LOSS
11% LOSS
MOTOR
COUPLING
PUMPS
VALVES
PIPES
WORK DONE ON WATER
Centrifugal pump
Static head
Friction head or Dynamic head
System with high static head
System with low static head
Pump curve
Pump operating point
Typical pump characteristic curves
Effect of Throttling
HeadMeters
82%
Pump Curve at Const. Speed
Full open valveSystem Curves
Flow (m3/hr)
Operating Points
A
500 m3/hr300 m3/hr
50 m
70 m
Static Head
42 m
Effect of Throttling
HeadMeters
Pump Efficiency 77%
82%
Pump Curve at Const. Speed
Partially closed valve
Full open valveSystem Curves
Flow (m3/hr)
Operating Points
A
B
500 m3/hr300 m3/hr
50 m
70 m
Static Head
C42 m
Centrifugal Pump Performance Chart
Efficiency Curves28.6 kW
14.8 kW
Power Requirement for PumpYou can use any of the following formulas to make your calculations:
Power calculations
Assume that we need to pump 68 m3/hr. to a 47 meter head with a pump that is 60% efficient at that point.
Liquid Power - 68 x 47 / 360 = 8.9 KwShaft Power - 8.9 / 0.60 = 14.8 KwMotor Power - 14.8 / 0.9 = 16.4 Kw
Using oversized pump !As shown in the drawing, we should be using impeller "E" to do this, but we have an oversized pump so we are using the larger impeller "A" with the pump discharge valve throttled back to 68 cubic meters per hour, giving us an actual head of 76 meters.
Now our Kilowatts look like this:
Liquid Power - 68 x 76 / 360 = 14.3 KwShaft Power - 14.3 / 0.50 = 28.6 KwMotor Power - 28.6 / 0.9 = 31.8 Kw
Losing Energy
Subtracting the amount of kilowatts we should have been using gives us:31.8 - 14.8 = 17 extra kilowatts being used to pump against the throttled discharge valve.
Extra energy used - 8760 hrs/yr x 17 = 1,48,920 kw.= Rs. 5.95 lacs/annum
In this example the extra cost of the electricity could almost equal the cost of purchasing the pump.
Flow vs Speed
If the speed of the impeller is increased from N1 to N2 rpm,the flow rate will increase from Q1 to Q2 as per the given formula:
The affinity law for a centrifugal pump with the impeller diameter held constant and the speed changed:
Flow:Flow:Q1 / Q2 = N1 / N2
Example: 100 / Q2 = 1750/3500
Q2 = 200 GPM
Head Vs speed
The head developed(H) will be proportional to the square of the quantity discharged, so that
Head:Head:
H1/H2 = (N12) / (N22) Example: 100 /H2 = 1750 2 / 3500 2
H2 = 400 Ft
Power Vs Speed
The power consumed(W) will be the product of H and Q, and, therefore
Power(kW):Power(kW):
kW1 / kW2 = (N13) / (N23) Example: 5/kW2 = 17503 / 35003
kW2 = 40
The affinity law for a centrifugal pump with the speed held constant and the impeller diameter changed:
Flow:Q1 / Q2 = D1 / D2Example: 100 / Q2 = 8/6Q2 = 75 GPM
Head:H1/H2 = (D1) x (D1) / (D2) x (D2)Example: 100 /H2 = 8 x 8 / 6 x 6H2 = 56.25 Ft
Power(kW):kW1 / kW2 = (D1) x (D1) x (D1) / (D2) x (D2) x (D2) Example: 5/kW2 = 8 x 8 x 8 / 6 x 6 x 6kW2 = 2.1
Pumps in parallel
Cooling Tower TheoryHeat is transferred from water drops to the surrounding air by the transfer of sensible and latent heat
Water Drop with Interfacial Film
How cooling tower works ?• Heat and Mass transfer• 1 kg of water on evaporation removes approximately 530
kcals of heat• The heat given up by the water falling inside the tower
equals the heat gained by the air rising through the tower• The hot water entering the tower is distributed within the
structure in a manner that exposes a very large water surface to the air passing through.
• Water distribution is accomplished by means of spray nozzles or distribution pans and by means of various types of “fill.”
• This fill increases the exposed water surface to maximize contact with the air, increasing the rate of heat transfer.
Tower Size vs Approach
Thermal Performance• Thermal performance of an evaporative tower is primarily
dependent upon the entering air wet bulb temperature (WBT) and relative humidity (RH).
• The entering WBT is an independent variable that dictates cooling tower selection.
• It is both the theoretical limit to the leaving cold water temperature and the only air parameter involved in cooling tower selection.
• The difference between the WBT and the tower leaving or cold water temperature (CWT) is called the approach temperature or the approach.
• Approach temperatures generally fall between 5 and 20 F.• The difference between the tower leaving or hot water
temperature (HWT) and the CWT is called the range• Range, heat load, and WBT also affect tower size
Water losses in cooling tower
Water losses include evaporation, drift (water entrained in discharge vapor), and blow down (water released to discard solids).
Drift losses are estimated to be between 0.1 and 0.2% of water supply.
Evaporation Loss = 0.00085 x water flow rate x (T1-T2)
Blow down Loss = Evaporation Loss/(cycles-1)
where cycles is the ratio of solids in the circulating water to thesolids in the make-up water
Total Losses = Drift Losses + Evaporation Losses + Blow down Losses
End
Lighting
SyllabusLighting System: Light source, Choice
of lighting, Luminance requirements, and Energy conservation avenues
Basic Terms in Lighting System and FeaturesLamps:Lamp is equipment, which produces light. • Incandescent lamps: Incandescent lamps produce light by means of a filament heated to incandescence by the flow of electric current through it. The principle parts of an incandescent lamp, also known as GLS (General Lighting Service) lamp include the filament, the bulb, the fill gas and the cap. • Reflector lamps:Reflector lamps are basically incandescent, provided with a high quality internal mirror, which follows exactly the parabolic shape of the lamp. The reflector is resistant to corrosion, thus making the lamp maintenance free and output efficient. • Gas discharge lamps: The light from a gas discharge lamp is produced by the excitation of gas contained in either a tubular or elliptical outer bulb.The most commonly used discharge lamps are as follows:
Fluorescent tube lamps (FTL) Compact Fluorescent Lamps (CFL)Mercury Vapour Lamps Sodium Vapour Lamps Metal Halide Lamps
Most commonly used lamps
• Fluorescent lamps (FTL) • Compact Fluorescent Lamps (CFL) • Mercury Vapour Lamps • Sodium Vapour Lamps • Metal Halide Lamps
Luminaire Luminaire is a device that distributes, filters or transforms the light emitted from one or more lamps. The luminaire includes, all the parts necessary for fixing and protecting the lamps, except the lamps themselves. principles used in optical luminaire are reflection, absorption, transmission and refraction.Control GearThe gears used in the lighting equipment are as follows: § Ballast:A current limiting device, to counter negative resistance characteristics of any discharge lamps. In case of fluorescent lamps, it aids the initial voltage build-up, required for starting.§ Ignitors:These are used for starting high intensity Metal Halide and Sodiumvapour lamps.
Illuminance This is the quotient of the illuminous flux incident on an element of the surface at a point of surface containing the point, by the area of that element. The illuminanceprovided by an installation affects both the performance of the tasks and the appearance of the space.
Lux (lx): This is the illuminance produced by a luminous flux of one lux, uniformly distributed over a surface area of one square metre. One lux is equal to one lumen per square meter.
Luminous Efficacy (lm/W)This is the ratio of luminous flux emitted by a lamp to the power consumed by the lamp. It is a reflection of efficiency of energy conversion from electricity to light form.
Colour Rendering Index (RI)Is a measure of the degree to which the colours of surfaces illuminated by a given light source confirm to those of the same surfaces under a reference illuminent; suitable allowance having been made for the state of Chromatic adaptation.
Lighting System Approach
Ceiling Fixture
Lamps (light source)Ballast
Lens or Diffuser
Floor
Switch
Work SurfaceThe Requirement
Walls
Lighting Quality
• Illumination level.• Uniformity• Absence of glare.• Colour rendering index (CRI).
Luminaire
• This is a device that distributes, filters or transforms the light emitted from one or more lamps.
• The luminaire includes, all the parts necessary for fixing and protecting the lamps, except the lamps themselves.
• In some cases, luminaires also include the necessary circuit auxiliaries, together with the means for connecting them to the electric supply.
• The basic physical principles used in optical luminaire are reflection, absorption, transmission and refraction.
Gear
• Ballast– A current limiting device, to counter negative
resistance characteristics of any discharge lamps. In case of fluorescent lamps, it aids the initial voltage build-up, required for starting
• Ignitors– These are used for starting high intensity Metal
Halide and Sodium vapour lamps
Illuminance
• Is the quotient of the illuminous flux incident on an element of the surface at a point of surface containing the point, by the area of that element.
• The illuminance provided by an installation affects both the performance of the tasks and the appearance of the space.
• Lux (lx)– Is the illuminance produced by a luminous flux of one
lux, uniformly distributed over a surface area of one square metre.
Luminous Efficacy (lm/W)
Is the ratio of luminous flux emitted by a lamp to the power consumed by the lamp is a reflection of energy efficiency of conversion from electricity to light form
Colour Rendering Index (RI)
• Is a measure of the degree to which the colours of surfaces illuminated by a given light source confirm to those of the same surfaces under a reference illuminent; suitable allowance having been made for the state of Chromatic adaptation.
• The "color rendering index" (CRI) measures the effect of light on the perceived color of objects. To determine the CRI of a lamp, the color appearances of a set of standard color chips are measured with special equipment under a reference light source with the same correlated color temperature as the lamp being evaluated. If the lamp renders the color of the chips identical to the reference light source, its CRI is 100. If the color rendering differs from the reference light source, the CRI is less than 100. A low CRI indicates that some colors may appear unnatural when illuminated by the lamp.
Luminous Performance Characteristics of Commonly Used Luminaries
Lum / Watt Type of Lamp
Range Avg. Color Rendering
Index Typical Application Life (Hours)
Incandescent 8-18 14 Excellent Homes, restaurants, general lighting, emergency lighting
1000
Fluorescent Lamps
46-60 50 Good w.r.t. coating
Offices, shops, hospitals, homes
5000
Compact fluorescent lamps (CFL)
40-70 60 Very good Hotels, shops, homes, offices
8000-10000
High pressure mercury (HPMV)
44-57 50 Fair General lighting in factories, garages, car parking, flood lighting
5000
Halogen lamps 18-24 20 Excellent Display, flood lighting, stadium exhibition grounds, construction areas
2000-4000
High pressure sodium (HPSV) SON
67-121 90 Fair General lighting in factories, ware houses, street lighting
6000-12000
Low pressure sodium (LPSV) SOX
101-175 150 Poor Roadways, tunnels, canals, street lighting
6000-12000
Recommended Illuminance Levels for Various Tasks / Activities / Locations
Scale ofIlluminance:
The minimum illuminance for all non-working interiors, has been mentioned as 20 Lux (as per IS 3646). A factor of approximately 1.5 represents the smallest significant difference in subjective effect ofilluminance. Therefore, the following scale of illuminances is recommended.
20–30–50–75–100–150–200–300–500–750–1000–1500–2000, … Lux
Illuminanceranges:
Because circumstances may be significantly different for different interiors used for the same application or for different conditions for the same kind of activity, a range of illuminances is recommended for each type of interior or activity intended of a single value ofilluminance. Each range consists of three successive steps of the recommended scale of illuminances. For working interiors the middle value (R) of each range represents the recommended serviceilluminance that would be used unless one or more of the factors mentioned below apply.
Lighting Controls• On/off flip switches
• Timer control & auto timed switch off
• Presence detection
• Luminary grouping / Group Switching
• Day light linking, blinders, corrugated roof sheets
• Dimmers , Lighting voltage controllers
• Photo sensors
METHODOLOGY OF LIGHTING SYSTEM ENERGY EFFICIENCY STUDY
Step-1 : Inventorise the Lighting System elements, & transformers in the facility as per following typical format.
S. No.
Plant Location
Lighting Device
& Ballast Type
Rating in Watts
Lamp & Ballast
Population Numbers
Use / Shifts as I / II / III shifts /
Day
Energy savings in lighting System
• Make maximum use of natural light (North roof/translucent sheets/more windows and openings)
• Switch off when not required• Modify lighting layout to meet the need• Select light colours for interiors• Provide timer switches / PV controls• Provide lighting Transformer to operate at reduced voltage• Install energy efficient lamps, luminaries and controls• Clean North roof glass, translucent sheet and luminaries
regularly
Energy Saving in Lighting
• Separate lighting Transformer– To isolate from power feeder– To avoid voltage fluctuation problem– Energy saving at optimum voltage
• Install Servo stabilizer if separate transformer is not feasible
• High frequency electronic ballast's(30khz)– Energy savings 30 to 35%– Less heat load into A/C room
• Metal halide in place of Mercury and SVL lamps• CFT in place of incandescent lamps
End
DG set systemDG set systemSyllabusDiesel Generating systemFactors affecting selectionEnergy performance assessment of diesel conservation avenues
Typical Diesel CycleTypical Diesel Cycle
Specific fuel consumptionSpecific fuel consumptionThe specific fuel consumption has come down from a value of 220 g/kWh in the 1970s to a value around 160 g/kWh in present times.
Slow speed diesel engine, with its flat fuel consumption curve over a wide load range (50%-100%), compares veryfavourably over other prime movers such as medium speed diesel engine, steam turbines and gas turbines.
With the arrival of modern, high efficiency turbochargers, it is possible to use an exhaust gas driven turbine generator to further increase the engine rated output. The net result – lower fuel consumption per kWh and further increase in overall thermal efficiency. Turbocharger
A.C. GeneratorA.C. Generator ControlsControlsDiesel EngineDiesel Engine LoadLoad
AccessoriesAccessories
Excitation Control
Fuel Control
Foundation
Fig-9.2 DG Set System
DG Set as a SystemDG Set as a System
A diesel generating set should be considered as a system since its successful operation depends on the well-matched performance of the components, namely:
a) The diesel engine and its accessories.b) The AC Generator.c) The control systems and switchgear.d) The foundation and power house civil works.e) The connected load with its own components like heating,
motor drives, lighting etc.
Advantages of adopting Diesel Advantages of adopting Diesel Power Plants are:Power Plants are:
Low installation costShort delivery periods and installation periodHigher efficiency (as high as 43 -45 %)More efficient plant performance under part loadsSuitable for different type of fuels such as low sulphur
– heavy stock and heavy fuel oil in case of large capacities.Minimum cooling water requirements, Adopted with air cooled heat exchanger in areas
where water is not availableShort start up time
Sizing of a GensetIf the DG set is required for 100% standby, then the entire
connected load in HP / kVA should be added. After finding out the diversity factor, the correct capacity of a DG set can
be found out.
Example :Connected Load = 650 kWDiversity Factor = 1.86(connected load / demand)Max. Demand = 650/1.86 = 350 kW% Loading = 70Set rating = 350/0.7 = 500 kWAt 0.8 PF, rating = 625 kVA
High Speed Engine or High Speed Engine or Slow/Medium Speed EngineSlow/Medium Speed Engine
Factor Slow speed engine High speed engine
Break mean effective pressure -therefore wear and tear and consumption of spares
Low High
Weight to power ratio- therefore sturdiness and life
More Less
Space High Less
Type of use Continuous use Intermittent use
Period between overhauls* 8000 hours 3200
Direct operating cost (includes lubricating oils, filters etc.
Less High
Comparison of Various power Comparison of Various power generation optionsgeneration options
Description Units Combined GT & ST
Conventional Steam Plant
Diesel Engine Power Plants
Thermal Efficiency % 40 - 46 33 - 36 43 - 45
Initial Investment of Installed Capacity Rs./kW 8,500 - 10,000 15,000 -18,000 7,500 - 9,000
Cooling water requirement with once through cooling
(Lt/kWh)
Space requirement 125 % (App.) 250 % (App.) 100 % (App.)
Construction time Months 24 - 30 42 - 48 12 - 15
Project period Months 30 - 36 52 - 60 13 - 12
Auxiliary Power Consumption % 2 - 4 8 - 10 13 - 21
Plant Load Factor kWh/kW 6000 - 7000 5000 - 6000 7200 - 7500
Range of Control of Electrical output on Heavy oil
% 0 - 100 42 - 100 25 - 100
Start up time from cold minutes about 10 120 - 180 15 - 20
Altitude and Intake Temperature CorrectionsAltitude and Intake Temperature Corrections
Correction Factors For Engine Output
Altitude Correction Temperature CorrectionAltitude Meters over
MSL
Non Super Charged Super Charged Intake oC Correction
Factor
610 0.980 0.980 32 1.000
915 0.935 0.950 35 0.986
1220 0.895 0.915 38 0.974
1525 0.855 0.882 41 0.962
1830 0.820 0.850 43 0.950
2130 0.780 0.820 46 0.937
2450 0.745 0.790 49 0.925
2750 0.712 0.765 52 0.913
3050 0.680 0.740 54 0.900
3660 0.612 0.685
DeratingDerating due to Air Inter Cooler Water due to Air Inter Cooler Water Inlet TemperatureInlet Temperature
Water Temperature
oCFlow % Derating %
25 100 0
30 125 3
35 166 5
40 166 8
Power Factor:Power Factor:
The load power factor is entirely dependent on the load. The A.C. generator is designed for the power factor of 0.8 lag as specified by standards. Lower power factor demands higher excitation currents and results in increased losses. Over sizing A.C. generators for operation at lower power factors results in lower operating efficiency and higher costs. The economical alternative is to provide power factor improvement capacitors.
− Unbalanced Load: Unbalanced loads on A.C. generator leads to unbalanced set of
voltages and additional heating in A.C. generator. When other connected loads like motor loads are fed with unbalanced set of voltages additional losses occur in the motors as well. Hence, the load on the A.C. generators should be balanced as far as possible.
− Transient Loading: On many occasions to contain transient voltage dip arising due to
transient load application, a specially designed generator may have to be selected.
− Special Loads:Special loads like rectifier / thyristor loads, welding loads, furnace
loads need an application check. The manufacturer of diesel engine and AC generator should be consulted for proper recommendation so that desired utilisation of DG set is achieved without any problem.
Energy BalanceEnergy Balance& & Waste Heat Recovery in DG SetsWaste Heat Recovery in DG Sets
A typical energy balance in a DG set indicates following break-up:
Input : 100% Thermal EnergyOutputs : 35% Electrical Output
: 4% Alternator Losses: 33% Stack Loss through Flue Gases
: 24% Coolant Losses: 4% Radiation Losses
Typical Flue Gas Temperature and Flow Typical Flue Gas Temperature and Flow Pattern in a 5Pattern in a 5--MW DG Set at various MW DG Set at various
LoadsLoads
100% Load 11.84 kgs/Sec 370oC
90% Load 10.80 kgs/Sec 350oC
70% Load 9.08 kgs/Sec 330oC
60% Load 7.50 kgs/Sec 325oC
If the normal load is 60%, the flue gas parameters for waste heat recovery unit would be 320oC inlet temperature, 180oC outlet temperature and 27180 kgs/Hour gas flow. At 90% loading, however, values would be 355oC and 32,400 kgs/Hour, respectively.
Energy Saving Measures for DG Energy Saving Measures for DG SetsSets
a) Ensure steady load conditions on the DG set, and provide cold, dust free air at intake
b) Improve air filtration.c) Ensure fuel oil storage, handling and preparation as per manufacturers’
guidelines/oil company data.d) Consider fuel oil additives e) Calibrate fuel injection pumps frequently.f) Ensure compliance with maintenance checklist.g) Ensure steady load conditions, avoiding fluctuations, imbalance in phases,
harmonic loads.h) For base load operation, consider waste heat recovery system steam generation or vapour absorption system adoption.
i) consider partial use of biomass gas for generation. Ensure tar removal from the gas for improving availability of the engine in the long run.j) Consider parallel operation among the DG sets for improved loading .Carryout regular field trials to monitor DG set performance, and maintenance planning as per requirements.
Typical Format for DG Set MonitoringTypical Format for DG Set Monitoring
DG Set No.
Electricity Generating Capacity (Site), kW
DeratedElectricity Generating
Capacity, kW
Type of Fuel used
Average Load as % of DeratedCapacity
Specific Fuel Cons. Lit/kWh
Specific Lube Oil
Cons. Lit/kWh
1. 480 300 LDO 89 0.335 0.007
2. 480 300 LDO 110 0.334 0.024
3. 292 230 LDO 84 0.356 0.006
4. 200 160 HSD 89 0.325 0.003
5. 200 160 HSD 106 0.338 0.003
18. 880 750 LDO 78 0.345 0.007
19. 800 640 HSD 74 0.324 0.002
Energy Efficient Technologies
Maximum Demand
MD controller
Automatic Power Factor Controllers
Energy Efficient Motors
Design changes
Table 10.1 Watt Loss Area and Efficiency Improvement {PRIVATE}Watts Efficiency Improvement 1. Iron Use of thinner gauge, lower loss core steel reduces eddy current
losses. Longer core adds more steel to the design, which reduces losses due to lower operating flux densities.
2. Stator I 2 R Use of more copper and larger conductors increases cross sectional area of stator windings. This lowers resistance (R) of the windings and reduces losses due to current flow (I).
3. Rotor I 2 R Use of larger rotor conductor bars increases size of cross section, lowering conductor resistance (R) and losses due to current flow (I).
4. Friction & Windage Use of low loss fan design reduces losses due to air movement. 5. Stray Load Loss Use of optimised design and strict quality control procedures
minimizes stray load losses.
Technical aspects of Energy Efficient Motors
• Energy-efficient motors last longer, and may require less maintenance. At lower temperatures, bearing grease lasts longer; required time between re-greasing increases. Lower temperatures translate to long lasting insulation. Generally, motor life doubles for each 10°C reduction in operating temperature.
• Electrical power problems, especially poor incoming power quality can affect the operation of energy-efficient motors.
• Speed control is crucial in some applications. In polyphase induction motors, slip is a measure of motor winding losses. The lower the slip, the higher the efficiency. Less slippage in energy efficient motors results in speeds about 1% faster than in standard counterparts.
• Starting torque for efficient motors may be lower than for standard motors. Facility managers should be careful when applying efficient motors to high torque applications.
Soft Starters
Characteristics
Variable Frequency Drives
Motors connected to VFD provide variable speed mechanical output with high efficiency. These devices are capable of up to a 9:1 speed reduction ratio (11 percent of full speed), and a 3:1 speed increase (300 percent of full speed).
Variable Torque Vs. Constant Torque
• Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications.
• Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio.
Typical full-load efficiencies are 95% and higher
Fluid coupling
Energy Efficient Transformers
1600 kVA AmorphousCore Transformer
Electronic Ballast
Energy Efficient Lighting Controls
• Occupancy Sensors• Timed Based Control• Daylight Linked Control• Localized Switching
