Handbook of Energy Engineering Calculations features worked-out examples and enables you to obtain accurately results with minimum time and effort. HANDBOOK OF. ENERGY ENGINEERING. CALCULATIONS. Tyler G. Hicks, RE. Editor. International Engineering Associates. Member: American Society of. It was set in Times Roman by Each section of this handbook is designed to furnish comprehensive Standard Handbook for Mechanical Engineers - DoomzDay.
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Handbook of Energy Engineering, Sixth Edition · Read more Handbook Of Financing Energy Projects · Read more Handbook of Reliability Engineering. Now in its sixth edition, the Handbook of Energy Engineering is a valuable For the purposes of calculating life cycle cost calculations, the time period will. SOLVE ENERGY PROBLEMS QUICKLY AND ACCURATELYFilled with step-by- step procedures for performing hundreds of calculations, this practical guide.
Then, some state-of-the-art advances will be characterized so that their benefits and limitations are explicit. It is important to recognize when purchasing these compact fluorescent lamps that they provide the equivalent light output of the lamps being replaced. Total Operating Cost No. Hicks, P. The control function in a traditional facility is performed by a pneumatic controller which receives its input from pneumatic sensors i. There are a limited number of on and off cycles possible each day.
Subjects Technology Engineering Nonfiction. Energy conversion engineering Steam power generation Gas-turbine power generation Internal-combustion engine energy analysis Nuclear energy engineering Hydroelectric energy power plants Wind power energy design and application Solar power energy application and usage Geothermal energy engineering Ocean energy engineering Heat transfer and energy conservation Fluid transfer engineering Interior climate control energy economics Energy conservation and environmental pollution control.
Technology Engineering Nonfiction. Publication Details Publisher: Tyler G. More about Tyler G. Handbook of Energy Engineering Calculations Embed. Handbook of Engineering Tables. Low Energy Building Engineering. Handbook of Corrosion Engineering. Handbook of Optical Engineering.
Handbook of transportation engineering. Handbook of reliability engineering. Energy Conversion Mechanical Engineering. Handbook of engineering electromagnetics. Handbook of Carbohydrate Engineering. Handbook of Structural Engineering. Handbook of Recording Engineering. When used by itself as the principal criterion, it may result in choosing less profitable investments which yield high initial returns for short periods as compared with more profitable investments which provide profits over longer periods of time.
Example Problem An electrical energy audit indicates electrical motor consumption is 4 x lo6 kWh per year. Assuming an 8q: Solve the problem using the present worth, annual cost, and rate-of-return methods. Thus we see that taking into account a modest escalation rate can dramatically affect the justification of the project. In other words, for tax purposes the expenditure for an asset such as a pump or motor cannot be fully expensed in its first year. The original investment must be charged off for tax purposes over the useful life of the asset.
A company wishes to expense an item as quickly as possible. The Internal Revenue Service allows several methods for determining the annual depreciation rate. Straight-line Depreciation: Sum-of-Years Digits: Another method is referred to as the sum-ofyears digits. In this method the depreciation rate is determined by finding the sum of digits using the following formula: The declining-balance method allows for larger depreciation charges in the early years, which is sometimes referred to as fast write-off.
The rate is calculated by taking a constant percentage of the declining undepreciated balance. The most common method used to calculate the declining balance is to predetermine the depreciation rate. In this method the salvage value or undepreciated book value is established once the depreciation rate is pre-established. To calculate the undepreciated book value, Formula is used: Salvage value is 0. Gas and combustion turbine equipment used to produce electricity for sale is depreciated over a year period.
Equipment used in the steam power production of electricity for sale including combustion turbines operated in combined cycle with steam units , as well as assets used to produce steam for sale, are normally depreciated over a year period.
However, most electric and steam generation equipment owned by a taxpayer and producing electric or thermal energy for use by the taxpayer in its industrial process and plant activity, and not ordinarily for sale to others, is depreciated over a yearperiod.
Electrical and steam transmission and distribution equipment will be depreciated over a year period at the same percent declining balance rate. Energy Efficiency Equipment and Real Property Depreciation Energy conservation equipment, still classified as real property, is depreciated on a straight line basis over a recovery period.
Other real property assets are depreciated over the above period, depending on their residential or nonresidential character. Handbook of Energy Engineering 26 After-tax Analysis Tax-deductible expenses such as maintenance, energy, operating costs, insurance and property taxes reduce the income subject to taxes. For the after-tax life-cycle cost analysis and payback analysis, the actual incurred annual savings is given as follows: On the other hand, the depreciation allowance reduces taxes directly.
To compute a rate of return which accounts for taxes, depreciation, escalation and tax credits, a cash-flow analysis is usually required. This method analyzes all transactions including first and operating costs. To determine the after-tax rate of return, a trial and error or computer analysis is required. The present worth factors tables in the Appendix, can be used for this analysis.
All money is converted to the present assuming an interest rate. The summation of all present dollars should equal zero when the correct interest rate is selected, as illustrated in Figure This analysis can be made assuming a fuel escalation rate by using the gradient present worth interest of the present worth factor. Example Problem Comment on the after-tax rate of return for the installation of a heatrecovery system given the following: Correct iwhen ZP 0 I Figure The problem facing the energy engineer is how to forecast what the future of energy costs will be.
All too often no fuel inflation is considered because of the difficulty of projecting the future. In making projections the following guidelines may be helpful: Is there a rate increase that can be forecast based on new nuclear generating capacity?
In locations such as Georgia, California, and Arizona electric rates will rise at a faster rate due to commissioning of new nuclear plants and rate increases approved by the Public Service Commission of that state. What has been the historical rate increase for the facility? Even with fluctuations there are likely to be trends to follow.
What events on a national or international level would impact on your costs? New state taxes, new production quotas by OPEC and other factors will affect your fuel prices. What do the experts say? Energy economists, forecasting services, and your local utility projections all should be taken into account. Energy Economic Analysis 29 The rate of return on investment becomes more attractive when lifecycle costs are taken into account.
Tables A-9 through A can be used to show the impact of fuel inflation on the decision-making process. The effect of escalation is not considered. Calculate for 5-, lo-, , year life. The second component is a uniform series of 0. The sum of these two present worth factors must equal P. In the case of no escalation, the formula is 0. The results are indicated below. This figure can be used as a quick way to determine after-tax economics of energy utilization expenditures.
Effects of Escalation on Investment Requirements Note: An energy audit serves the purpose of identifying where a building or plant facility uses energy and identifies energy conservation opportunities.
There is a direct relationship to the cost of the audit amount of data collected and analyzed and the number of energy conservation opportunities to be found. Thus, a first distinction is the cost of the audit which determines the type of audit to be performed. The second distinction is the type of facility. For example, a building audit may emphasize the building envelope, lighting, heating, and ventilation requirements.
On the other hand, an audit of an industrial plant emphasizes the process requirements. Most energy audits fall into three categories or types, namely, walkthrough, mini-audit, or maxi-audit. Walk-through-This type of audit is the least costly and identifies preliminary energy savings.
A visual inspection of the facility is made to determine maintenance and operation energy saving opportunities plus collection of information to determine the need for a more detailed analysis.
Mini-audit-This type of audit requires tests and measurements to quantify energy uses and losses and determine the economics for changes. Muxi-uudi-This type of audit goes one step further than the mini-audit.
It contains an evaluation of how much energy is used for each function such as lighting, process, etc. It also requires a model analysis, such as a computer simulation, to determine energy use patterns and predictions on a year-round basis, taking into account such variables as weather data.
Data Acquisition This phase requires the accumulation of utility bills, establishing a baseline to provide historical documentation and a survey of the facility. All energy flows should be accounted for; thus all "energy in" should equal "energy out.
All energy costs should be determined for each fuel type. The energy survey is essential. Instrumentation commonly used in conducting a survey is discussed at the conclusion of the chapter. The life-cyclecosting techniques presented in Chapter 2 will be used to determine which alternative should be given priority.
A very important phase of the overall program is to continuously monitor the facility even after the ECOs have been implemented. Documentation of the cost avoidance or savings is essential to the audit. Remember, in order to have a continuous ongoing program, individuals must be made accountable for energy use. As part of the audit, recommendations should be made as to where to add "root" or submetering.
For an industrial facility the energy audit approach includes process consideration. Figures through illustrate how energy is used for a typical industrial plant. It is important to account for total consumption, cost, and how energy is used for each commodity such as steam, water, air and natural gas.
This procedure is required to develop the appropriate energy conservation strategy. The top portion of Figure illustrates how much energy is used by fuel type and its relative percentage.
The pie chart below shows how much is spent for each fuel type. Using a pie-chart presentation or nodal flow diagram can be very helpful in visualizing how energy is being used. Energy Use and Cost Profile Figure , on the other hand, shows how much of the energy is used for each function such as lighting, process, and building heating and ventilation.
Pie charts similar to the right-hand side of the figure should be made for each category such as air, steam, electricity, water and natural gas.
Figure illustrates an alternate representation for the steam distribution profile. Several audits are required to construct the energy use profiles, such as: Envelope Audit-This audit surveys the building envelope for losses or gains due to leaks, building construction, doors, glass, lack of insulation, etc.
Functional Audit-This audit determines the amount of energy required for a particular function and identifies energy conservation opportunities. Functional audits include: Steam Distribution Nodal Diagram Heating, ventilation and air conditioning Building Lighting Domestic hot water Air distribution Process Audit-This audit determines the amount of energy required for each process function and identifies energy conservation opportunities. Process functional audits include: Handbook of Energy Engineering 38 Utility Audit-This audit analyzes the monthly, daily or yearly energy usage for each utility.
Table Percent The residential sector consumed See Table The analysis estimates a major increase in the use of electricity by the building sector, increasing from These figures represent the source primary energy used to generate electricity. During this period, natural gas use is forecast to increase slightly from 7. The use of solar and renewable energy is ex'Source: Energy Auditing and Accounting 43 pected to more than double from 1.
The various types of instrumentation commonly used in the survey are discussed in this section. Infrared Equipment Some companies may have the wrong impression that infrared equipment can meet most of their instrumentation needs. The primary use of infrared equipment in an energy utilization program is to detect building or equipment losses. Thus it is just one of the many options available.
Several energy managers find infrared in use in their plant prior to the energy utilization program.
Infrared equipment, in many instances, was purchased by the electrical department and used to detect electrical hot spots. Infrared energy is an invisible part of the electromagnetic spectrum.
It exists naturally and can be measured by remote heat-sensing equipment. Within the last four years lightweight portable infrared systems became available to help determine energy losses. Differences in the infrared emissions from the surface of objects cause color variations to appear on the scanner. The hotter the object, the more infrared radiated.
With the aid of an isotherm circuit, the intensity of these radiation levels can be accurately measured and quantified. In essence the infrared scanning device is a diagnostic tool which can be used to determine building heat losses. An overview energy scan of the plant can be made through an aerial survey using infrared equipment. Aerial scans can determine underground stream pipe leaks, hot gas discharges, leaks, etc.
Since IR detection and measurement equipment have gained increased importance in the energy audit process, a summary of the fundamentals is reviewed in this section. The visible portion of the spectrum runs from. The infrared or thermal radiation begins at this point and extends to Handbook of Energy Engineering 44 approximately pm. Objects such as people, plants, or buildings will emit radiation with wavelengths around 10 p.
See Figure Electromagnetic Spectrum Infrared instruments are required to detect and measure the thermal radiation. To calibrate the instrument, a special "black body" radiator is used. A black body radiator absorbs all the radiation that impinges on it and has an absorbing efficiency or emissivity of 1. The accuracy of temperature measurements by infrared instruments depends on the three processes which are responsible for an object acting like a black body.
These processes-absorbed, reflected, and transmitted radiation-are responsible for the total radiation reaching an infrared scanner. The real temperature of the object is dependent only upon its emitted radiation.
Corrections to apparent temperatures are made by knowing the emissivity of an object at a specified temperature. The heart of the infrared instrument is the infrared detector. The detector absorbs infrared energy and converts it into electrical voltage or current.
The two principal types of detectors are the thermal and photo type. The thermal detector generally requires a given period of time to develop an image on photographic film.
The photo detectors are more sensitive and have a higher response time. Television-like displays on a cathode ray tube permit studies of dynamic thermal events on moving objects in real time. There are various ways of displaying signals produced by infrared detectors. One way is by use of an isotherm contour. The lightest areas of the picture represent the warmest areas of the subject, and the darkest areas represent the coolest portions. These instruments can show thermal variations of less than 0.
Energy Auditing and Accounting 45 The isotherm can be calibrated by means of a black body radiator so that a specific temperature is known. The scanner can then be moved and the temperatures of the various parts of the subject can be made. These instruments are described below.
Ammeter and Voltmeter To measure electrical currents, ammeters are used. For most audits, alternating currents are measured. Ammeters used in audits are portable and are designed to be easily attached and removed. There are many brands and styles of snap-on ammeters commonly available that can read up to amperes continuously.
This range can be extended to amperes continuously for some models with an accessory step-down current transformer. The snap-on ammeters can be either indicating or recording with a printout. After attachment, the recording ammeter can keep recording current variations for as long as a full month on one roll of recording paper. This allows the study of current variations in a conductor for extended periods without constant operator attention.
The ammeter supplies a direct measurement of electrical current, which is one of the parameters needed to calculate electrical energy. The second parameter required to calculate energy is voltage, and it is measured by a voltmeter. Several types of electrical meters can read the voltage or current.
A voltmeter measures the difference in electrical potential between two points in an electrical circuit. In series with the probes are the galvanometer and a fixed resistance which determine the voltage scale.
The current through this fixed resistance circuit is then proportional to the voltage, and the galvanometer deflects in proportion to the voltage. The voltage drops measured in many instances are fairly constant and need only be performed once. If there are appreciable fluctuations, additional readings or the use of a recording voltmeter may be indicated. Wattmeter and Power Factor Meter The portable wattmeter can be used to indicate by direct reading electrical energy in watts. It can also be calculated by measuring voltage, current and the angle between them power factor angle.
The basic wattmeter consists of three voltage probes and a snap-on current coil which feeds the wattmeter movement. The typical operating limits are kilowatts, volts, and amperes. It can be used on both one- and three-phase circuits.
The portable power factor meter is primarily a three-phase instrument.
One of its three voltage probes is attached to each conductor phase and a snap-on jaw is placed about one of the phases. By disconnecting the wattmeter circuitry, it will directly read the power factor of the circuit to which it is attached. It can measure power factor over a range of 1.
This range covers the large bulk of the applications found in light industry and commerce. The power factor is a basic parameter whose value must be known to calculate electric energy usage. Diagnostically, it is a useful instrument to determine the sources of poor power factor in a facility. Portable digital kWh and kW demand units are now available. Digital read-outs of energy usage in both kWh and kW demand or in dollars and cents, including instantaneous usage, accumulated usage, projected usage for a particular billing period, alarms when over-target levels are desired for usage, and control-outputs for load shedding and cycling are possible.
Continuous displays or intermittent alternating displays are available at the touch of a button for any information needed such as the cost of operating a production machine for one shift, one hour or one week. Footcandle Meter Footcandle meters measure illumination in units of footcandles through a light-sensitivebarrier layer of cells contained within them.
They are usually pocket-size and portable and are meant to be used as field instruments to survey levels of illumination. These meters differ from conventional photographic lightmeters in that they are color and cosine corrected. Several types of temperature devices are described in this section. Thermometer There are many types of thermometers that can be used in an energy audit.
The choice of what to use is usually dictated by cost, durability, and application. Three separate probes are usually provided to measure liquid, air or surface temperatures. Surface Pyrometer Surface pyrometers are instruments which measure the temperature of surfaces. They are somewhat more complex than other temperature instruments because their probe must make intimate contact with the surface being measured. Surface pyrometers are of immense help in assessing heat losses through walls and also for testing steam traps.
They may be divided into two classes: The low-temperature unit is usually part of the multipurpose thermometer kit. The high-temperature unit is more specialized but needed for evaluating fired units and general steam service.
There are also noncontact surface pyrometers which measure infrared radiation from surfaces in terms of temperature. These are suitable for general work and also for measuring surfaces which are visually but not physically accessible. A more specialized instrument is the optical pyrometer. Psychrometer A psychrometer is an instrument which measures relative humidity based on the relation of the dry-bulb temperature and the wetbulb tem- 48 Handbook of Energy Engineering perature.
Relative humidity is of prime importance in W A C and drying operations. Recording psychrometers are also available. Portable Electronic Thermometer The portable electronic thermometer is an adaptable temperature measurement tool.
The battery-powered basic instrument, when housed in a carrying case, is suitable for laboratory or industrial use. A pocket-size digital, battery-operated thermometer is especially convenient for spot checks or where a number of rapid readings of process temperatures need to be taken.
Thermocouple Probe No matter what sort of indicating instrument is employed, the thermocouple used should be carefully selected to match the application and properly positioned if a representative temperature is to be measured. The same care is needed for all sensing devices-thermocouple, bimetals, resistance elements, fluid expansion, and vapor pressure bulbs.
Suction Pyrometer Errors arise if a normal sheathed thermocouple is used to measure gas temperatures, especially high ones. The suction pyrometer overcomes these by shielding the thermocouple from wall radiation and drawing gases over it at high velocity to ensure good convective heat transfer. The thermocouple thus produces a reading which approaches the true temperature at the sampling point rather than a temperature between that of the walls and the gases.
By obtaining a good air-fuel ratio, substantial energy will be saved. Combustion Tester Combustion testing consists of determining the concentrationsof the products of combustion in a stack gas.
The products of combustion usually considered are carbon dioxide and carbon monoxide. Oxygen is tested to assure proper excess air levels. Energy Auditing and Accounting 49 The definitive test for these constituents is an Orsat apparatus.
This test consists of taking a measured volume of stack gas and measuring successive volumes after intimate contact with selective absorbing solutions.
The reduction in volume after each absorption is the measure of each constituent. The Orsat has a number of disadvantages. The main ones are that it requires considerable time to set up and use and that its operator must have a good degree of dexterity and be in constant practice.
Instead of an Orsat, there are portable and easy to use absorbing instruments which can easily determine the concentrations of the constituents of interest on an individual basis.
Setup and operating times are minimal and just about anyone can learn to use them. The CO, or 0, content, along with knowledge of flue gas temperature and fuel type, allows the flue gas loss to be determined off standard charts.
Boiler Test Kit The boiler test kit contains the following: The purpose of the components of the kit is to help evaluate fireside boiler operation. Good combustion usually means high carbon dioxide CO, , low oxygen O, , and little or no trace of carbon monoxide CO. Gas Analyzers The gas analyzers are usually of the Fyrite type.
The Fyrite type differs from the Orsat apparatus in that it is more limited in application and less accurate. The chief advantages of the Fyrite are that it is simple and easy to use and is inexpensive. This device is used many times in an energy audit. Three readings using the Fyrite analyzer should be made and the results averaged. Draft Gauge The draft gauge is used to measure pressure. It can be the pocket type or the inclined manometer type. Handbook of Energy Engineering 50 Smoke Tester To measure combustion completeness the smoke detector is used.
Smoke is unburned carbon, which wastes fuel, causes air pollution, and fouls heat-exchanger surfaces. To use the instrument, a measured volume of flue gas is drawn through filter paper with the probe.
The smoke spot is compared visually with a standard scale and a measure of smoke density is determined. Combustion Analyzer The combustion electronic analyzer permits fast, close adjustments. The unit contains digital displays. A standard sampler assembly with probe allows for stack measurements through a single stack or breaching hole.
Smoke pellets-limited use but very low cost. Considered to be useful if engineering staff has experience in handling. Anemometer deflecting vane -good indication of air movement with acceptable order of accuracy.
Anemometer revolvingvane -good indicator of air movement with acceptable accuracy. However, easily subject to damage. Pitot tube-a standard air measurement device with good levels of accuracy.
Considered essential. Must be used with a monometer. Impact tube-usually packaged air flow meter kits, complete with various jets for testing ducts, grills, open areas, etc. These units are convenient to use and of sufficient accuracy. Energy Auditing and Accounting 52 Heated thermocouple-these units are sensitive and accurate but costly. Hot wire anemometer-not recommended. Too costly and too complex. Temperature Measurement The temperature devices most commonly used are as follows: Glass thermometers-considered to be the most useful to temperature measuring instruments-accurate and convenient but fragile.
Engineers should have a selection of various ranges. Accuracy is good and they are reliable and convenient to use. Thermocouples-similar to resistance thermocouple but do not require battery power source.
Chrome-Alum or iron types are the most useful and have satisfactory accuracy and repeatability. Bimetallic thermometers-considered unsuitable. Pressure bulb thermometers-more suitable for permanent installation.
Optical pyrometers-only suitable for furnace settings and therefore limited in use. Thermogaphs-use for recording room or space temperature; gives a chart indicating variations over a or hour period. Reasonably accurate. Spring-wound drive. Pressure Measurement Absolute and Differential Common devices used for measuring pressure in W A C applications accuracy, range, application, and limitations are discussed in relation to HVAC work are as follows: Absolute pressure manometer-not really suited to HVAC test work.
Diaphragm-not really suited to HVAC test work. Micromanometer-not usually portable, but suitable for fixed measurement of pressure differentials across filter, coils, etc. Draft gauges-can be portable and used for either direct pressure or pressure differential. Manometers-can be portable. Used for direct pressure reading and with Pitot tubes for air flows.
Very useful. Swing vane gauges-can be portable. Usually used for air flow. Bourdon tube gauges-very useful for measuring all forms of system fluid pressures from 5 psi up.
Special types for refrigeration plants. Humidity Measurement The data given below indicate the type of instruments available for humidity measurement.
The following indicates equipment suitable for W A C applications: Psychrometers-basically these are wet and dry bulb thermometers. They can be fixed on a portable stand or mounted in a frame with a handle for revolving in air.
Dewpoint hygrometers-not considered suitable for W A C test work. Dimensional change-device usually consists of a "hair," which changes in length proportionally with humidity changes. Not usually portable, fragile, and only suitable for limited temperature and humidity ranges.
Very convenient to use. Electrolytic-as above, but for very low temperature ranges. Therefore unsuitable for HVAC test work. Gravimeter-no t suitable. It is important to quantify usage, fuel costs as a function of production. Figure illustrates a typical steam and utility cost report. This report enables the plant Energy Auditing and Accounting 53 manager to evaluate the total Btus of fuel consumed, the total fuel cost, and the total steam generation cost as a function of production.
This report is issued monthly. Since each plant has the same report, plant to plant comparisons are made and the effectiveness of the energy use is measured. Oil ' 7. Gas 8. Feedwater Temp. Equivalent Steam No.
Boiler Efficiency Total Fuel Cost No. Operating Supplies water, chemicals, etc. Maintenance Charges Other Miscellaneous Charges Total Operating Cost No. Total Steam Generation Cost No. Using energy more efficiently reduces the product cost, thus increasing profits. In order to account for the process energy content, all energy that enters and leaves a plant during a given period must be measured.
Figure illustrates energy content of a process report. The report applies to any manufacturing operation, whether it is a pulp mill, steel mill, or assembly line. This report enables one to quickly identify energy inefficient operations. Attention can then be focused on which equipment should be replaced and what maintenance programs should be initiated.
This report also focuses attention on the choice of raw materials. By using Btus per unit of production, measurable goals can be set. This report will also identify opportunities where energy usage can be reduced.
The energy content of raw materials can be estimated by using the heating values indicated in Table Example Problem Comment on energy content by modifying process No. Answer Process No. Total Btu's Per Unit Usage a. The first step is to analyze the billing structure. It may be possible to negotiate a better tariff rate with the local utility or modify the facility operation to qualify for a lower rate. In addition, specified charges or discounts for power factor, time of day or demand will determine if certain electrical efficiency measures are economicallyjustified.
This chapter reviews the basic parameters required to make sound energy engineering decisions. Billing Demand-The maximum kilowatt requirement over a , , or minute interval. Load Factor-The ratio of the average load over a designated period to the peak demand load occurring in that period.
Power Factor-The ratio of resistive power to apparent power. Traditionally electrical rate tariffs have a decreasing kilowatt hour kWh charge with usage. This practice is likely to gradually phase out. New tariffs are containing the following elements: Time of Day-Discounts are allowed for electrical usage during offpeak hours.
The billing demand will remain at that ratchet for 12 months even though the actual demand for the succeeding months may be less. The resistive portion of a load cannot be added directly to the reactive component since it is essentially 90 degrees out of phase with the other.
The pure resistive power is known as the watt, while the reactive power is referred to as the reactive volt amperes. To compute the total volt ampere load, it is necessary to analyze the power triangle indicated below. The relationships for line and phase voltages and currents are illustrated by Figure In order to relate the motor horsepower to a kilowatt kW , multiply the horsepower by.
Typical values are shown in Table To supply several small water users, a large pipe services the plant at a high pressure. Several branches from the main pipe service various loads. Pressure re- Electrical System Optimization 63 Table 4.
Similarly, a large feeder at a high voltage services a plant.