Heating systems use a heater fan attached to a permanent-magnet, variable-speed blower motor to force warm air into the passenger compartment. The higher the voltage applied to the motor, the faster it runs.

A switch mounted on the instrument panel controls the blower operation. In most heating systems, the switch controls blower speed by directing the motor ground circuit current through or around the coils of a resistor block mounted near the motor.

When the switch is off, the ground circuit is open and the blower motor does not run. (Some systems used in the 1970s, however, were wired so that the blower motor operated on low speed whenever the ignition was on). When the switch is turned to its low position, voltage is applied across all of the resistor coils and the motor runs at a low speed.

Moving the switch to the next position bypasses one of the resistor coils. This allows more current to the blower motor, increasing its speed. When the switch is set to the highest position, all of the resistors are bypassed and full current flows to the motor, which then operates at full speed.

In some GM systems, a relay is used between the high switch position and the blower motor. Ford incorporates a thermal limiter in its resistor block.

Current flows through the limiter at all blower speeds. If current passing through the limiter heats it to 212 F (100 C), the limiter opens and turns off the blower motor.

When this happens, the entire resistor block must be replaced.

In summary:

1. The fan control switch routes current through paths of varying resistance to control motor speed.

2. An electric motor drives the heater fan.

3. Blower motor resistors are installed on a “block” near the motor. Some resistor blocks have a thermal limiter.


Lighting design ranges from following a cookbook to a high-level art form. It is not the responsibility of the HVAC designer, but lighting imposes far-reaching consequences on the HVAC design.

Nearly all lighting is derived from electricity. Only a fraction of the power is transformed to light, and virtually all the lighting-related energy is released to the space or ceiling plenum, where it must be addressed by the HVAC system.

The HVAC designer should tell the lighting design team, and the other design team members, including the owner, about the possible impact of lighting layouts on the HVAC system. In the first half of the twentieth century, most lighting was of the incandescent type.

At that time, lighting levels were spartan, relative to system cost, operating cost, and availability of power. With the advent of fluorescent lighting in roughly the time period of World War II, it was perceived that productivity could be improved with increased levels of lighting in the workplace.

The 1950s and 1960s then became a time of excess in lighting design, with high levels of illumination and consequent average imposed lighting loads of 4 to 6 W/ft2, even more in some cases. The energy constrictions of the early mid-1970s called quick attention to the problem of conspicuous energy consumption for lighting.

Public sensitivity combined with cost factors has helped reduce expectations and bring new lighting products to market. Common lighting designs for office space will now average 1.5 to 2.0 W/ft2 of connected load. Multiple-level switching of lamps may reduce this even further for much of the time.

There is still the problem of high-intensity lighting using incandescent lamps for retail display and fine visual work. The incandescent lamp seems to offer a color spectrum that is closer to that of the sun than other lighting types.

Where the lighting quality is truly important to the function of the space, incandescent fixtures should be questioned, but accepted. The consequence is the increased cooling capacity requirement and higher cost of power for lighting.

To quantify the impact of lighting power, 1 W/ft2 extra will require approximately 0.15 ft3 /(min # ft2) extra cooling air (15 to 20 percent more than average) and will require an additional 0.25 ton of cooling per 1000 ft2 of building space.

This is 25 to 30 tons of added cooling capacity to a 100,000-ft2 building, related to only 1 W/ft2 of lighting. Savings in HVAC equipment cost will often more than pay for improved lighting equipment.


While most HVAC designers will have the support of a competent electrical design staff, it is important to understand certain fundamentals of electricity, power distribution, and utilization, because so many HVAC system devices are mechanically driven and controlled.

In building construction, HVAC design is interwoven with the electrical design, and each discipline needs to be conversant with the other. Electrical-mechanical interfaces need to be fully communicated for complete designs to be achieved.

The HVAC designer should have a working background in the fundamentals of electricity and electric control. Full presentation of the electrical needs of the HVAC system must be part of the HVAC design work, as must a complete understanding of the impacts of electrical heat releases on the building environment.

In rooms where electric devices consume electricity and give off heat, some sort of ventilation for cooling is required. Electronic installations may require mechanical refrigeration.

Natural convection ventilation usually assumes a 10 to 20#F rise in the space which allows calculation of the probably required ventilating airflow quantities, assuming that the heat release can be estimated. The following estimating factors may be helpful.

Assume that 3 to 5 percent of the active load will be dissipated in transformation. This may drop to 2 to 3 percent for more efficient units.

Elevator machine rooms:
Figure all the elevator motor horsepower times a factor for the estimated percentage of time in use. Peak-use hours approach 100 percent.

Consult the elevator vendor for temperature constraints and secondary losses from control panels, etc.

Motor control centers:
These units generate some heat from control transformers and starter holding coils. This equipment does not hold up well in hot environments. Carry this observation over into plant design considerations.


On a number of issues the HVAC designer must interface with the electrical designer, each sharing information and responding appropriately.

Motor loads: Motor sizes and locations derive from the HVAC equipment selections and equipment layouts.

Motor control features: HVAC control schemes determine many of the needed starter characteristics, e.g., hand-off-auto or start-stop, auxilary contact types and number, pilot light requirements, and control voltage transformer size if external devices needing control power are involved. Be sure to coordinate the specification and control of two speed motors and motor starters.

Fire and smoke detection and alarm: The electrical designer is usually responsible for fire detection and alarm, if such is required. But building codes require smoke detectors in the airstream of recirculation fan systems larger than 2000 ft3 /min.

If smoke is detected, fan systems are required to shut down. Similarly, if the building detection systems go into alarm, the fan systems must turn off. Further sophistication gets into smoke control in buildings, a separate topic by itself.

Lighting systems: The HVAC designer must fully understand the building lighting systems to be able to correctly respond to the cooling loads which develop.

Any inordinately high lighting loads may stimulate discussion and evaluation of lighting fixture selection. Automated lighting control may be included as a feature of a building automation system.

Transformer vaults: Electric transformers typically lose 2 to 5 percent of the power load (winding losses) to the ambient air. Building transformers may wind up in underground vaults, in secure rooms, in janitor closets, or in ceiling spaces.

Dissipation of the heat with ventilation is often a challenge. Note that even though the load may decrease, transformers seldom sleep; 24 h/day ventilation is required.

Building HVAC systems which follow a time-clock schedule are inadequate for transformer rooms. Some electronic monitoring and control devices cannot tolerate ambient air temperatures above
about 100 deg F.


Commissioning is an old idea, but, as a formal concept, is of fairly recent origin. In the ASHRAE Handbook the term first appears in the Applications, 1995 volume. The activities it includes are those that have been found necessary—beyond the actual construction process— for achieving a complete and working HVAC system, which satisfies the requirements of the design and the needs of the owner.

The term ‘‘quality assurance’’ is sometimes used. The ideal, from owner’s viewpoint, is that the commissioning team, selected by and working for the owner, will assist in the design phase as well as the construction phase, ensuring that the owner’s needs are met by the design.

This is rarely the case except for those owners who have staff personnel with these capabilities. And many owners do not desire the extra expense, although this expense is compensated for in the long run by better system performance and more user satisfaction.

The objectives of commissioning are:

# To ensure that the system design satisfies the owner’s needs.
# To ensure that the system performs in accordance with the design intent.
# To require complete and detailed documentation of operation and maintenance requirements, including reference and training manuals.
# To provide basic training for operators and maintenance personnel.
# To observe, coordinate, and document all system performance tests (TAB). This is especially desirable in connection with DDC control technology, to prove the proper operation of the DDC software.
# To assist in the resolution of disputes, subject to the terms of the contract documents.
# To ensure compliance with all code requirements.
# To advise the owner when each part of the work has been satisfactorily completed and can be accepted.

For these purposes the commissioning team should be selected and paid by the owner and operate separately from the design and construction teams.

Commissioning can also be applied to existing systems with sometimes amazing results in improved performance and better use of energy. This usually happens as a study with recommendations for redesign and upgrade, followed by implementation of the recommendations.


In the process of construction, nearly always a condition will arise that is inadequately or incorrectly defined by the contract documents. Often this will be the result of conflicts with other trades, due to lack of coordination among designers.

A classic case of this occurred when the HVAC inspector caught a deep concrete beam, ready to pour, without the slot required to allow a large duct to pass through. (Fortunately the forms were adjusted to provide the slot.) Hopefully, the condition will be encountered before the constraints are cast in concrete or fabricated in steel.

Upon identifying the problem, the construction team—designers and constructors—will seek a solution. Often an adjustment can be made which incurs no additional cost to the contractor, and the work proceeds.

Sometimes correction of the problem creates additional cost and effort for the contractor, who then seeks added compensation. Such is granted by change order to the contract.

A change order involves a documented scope of work, a price, and a time, and it becomes part of the contract when it has been agreed to by all parties. The pricing mechanism is sometimes awkward since the element of competitive bidding is gone.

Even as some owners will try to obtain more service than the documents truly define, some contractors will seek compensation beyond the value or cost of the added work. In a field review, the designer must work hard to see that equity is maintained.

When a design error is involved, the contractor is not interested in covering the cost, and some owners become an immediate designer’s adversary. Design fees are typically inadequate to provide contingency funds, even for small items.

Errors-and-omissions insurance protects against major lawsuits, but there is a cost range where designers must fend for themselves. Fortunate is the designer who works with an owner who realizes that no set of construction documents is perfect, that 2 to 3 percent of basic cost for added clarification is reasonable, and that openly working through problems is better than trying to hide or barter them away. Construction budgets should contain a percentage, typically 10 percent, to allow for changes.


The concept of indoor air quality (IAQ) is not new. Publications as far back as the early 1800s discuss the subject and suggest ventilation as the solution.

These early writers mostly recommended a minimum of 5 ft3 /min of outdoor air per person, but later writers increased that number. The present ASHRAE Standard 62 value is 20 ft3 /min for
normal situations.

Most of this early work was done in England, where a number of public buildings were provided with heating and ventilating systems, including the House of Commons. Centrifugal fans were developed, using small steam engines for motive power.

Schools were a prime target for ventilation, and by the early part of the twentieth century the schoolroom unit ventilator was developed and advertised. Electric motors were available by then. A three-story elementary school, built in 1916, included an outdoor air-ventilation system with a direct current motor-driven supply fan (rheostat control provided manual variable volume!) and cast iron steam-heating coils in the ventilation air for winter use.

When the new science of air cooling came along, the value of introducing outdoor air through the cooling/heating system was obvious. And, as the material in the previous parts of this book shows, present technology allows us to control outdoor air ventilation very accurately.

Negative Effects of Poor Air Quality
Two terms are important: building related illness (BRI) and sick building syndrome (SDS). BRI relates to individual illness due to poor IAQ. Much of this relates to allergens, to which some people are more sensitive than others.

SBS means that many people become sick in the building environment, and this, of course, causes loss of production and, perhaps, lawsuits. In addition, there are problems with odors (including those caused by smoking) and problems with high or low humidity.

High humidity may allow mold growth and deterioration of the building or furnishings. Excessive air movement (drafts) is a common complaint. When people are sick or complaining, they are not producing.

Positive Effects of Air Quality
Many studies have shown an increase in productivity of 10 percent or more, when the air quality and other environmental factors are optimized, and there is less time off for sickness and fewer complaints.

Housekeeping and cleaning are made easier and less expensive. Thus, good IAQ is economically advantageous, and it improves the morale of the people who work and live in the building.



It is the ratio of ultimate strength of the material to allowable stress. The term was originated for determining allowable stress. The ultimate strength of a given material divided by an arbitrary factor of safety, dependent on material and the use to which it is to be put, gives the allowable stress.

In present design practice, it is customary to use allowable stress as specified by recognized authorities or building codes rather than an arbitrary factor of safety. One reason for this is that the factor of safety is misleading, in that it implies a greater degree of safety than actually exists.

For example, a factor of safety of 4 does not mean that a member can carry a load four times as great as that for which it was designed. It also should be clearly understood that, even though each part of a machine is designed with the same factor of safety, the machine as a whole does not have that factor of safety.

When one part is stressed beyond the proportional limit, or particularly the yield point, the load or stress distribution may be completely changed throughout the entire machine or structure, and its ability to function thus may be changed, even though no part has ruptured.

Although no definite rules can be given, if a factor of safety is to be used, the following circumstances should be taken into account in its selection:

1. When the ultimate strength of the material is known within narrow limits, as for structural steel for which tests of samples have been made, when the load is entirely a steady one of a known amount and there is no reason to fear the deterioration of the metal by corrosion, the lowest factor that should be adopted is 3.

2. When the circumstances of (1) are modified by a portion of the load being variable, as in floors of warehouses, the factor should not be less than 4.

3. When the whole load, or nearly the whole, is likely to be alternately put on and taken off, as in suspension rods of floors of bridges, the factor should be 5 or 6.

4. When the stresses are reversed in direction from tension to compression, as in some bridge diagonals and parts of machines, the factor should be not less than 6.

5. When the piece is subjected to repeated shocks, the factor should be not less than 10.

6. When the piece is subjected to deterioration from corrosion, the section should be sufficiently increased to allow for a definite amount of corrosion before the piece is so far weakened by it as to require removal.

7. When the strength of the material or the amount of the load or both are uncertain, the factor should be increased by an allowance sufficient to cover the amount of the uncertainty.

8. When the strains are complex and of uncertain amount, such as those in the crankshaft of a reversing engine, a very high factor is necessary, possibly even as high as 40.

9. If the property loss caused by failure of the part may be large or if loss of life may result, as in a derrick hoisting materials over a crowded street, the factor should be large.


Most oxides can be considered close packings of oxygen ions with the cations occupying the tetrahedral and/or octahedral sites in the structure. As an example, a-alumina (a- Al2O3) consists of an hep packing of O2~ with two thirds of the octahedral sites occupied by Al3+ in an orderly fashion.

Since for each O2" there exist one octahedral and two tetrahedral sites, in Al2O3 there would be three octahedral sites in which two Al3+ are placed thus two-thirds of the octahedral and none of the tetrahedral sites are filled.
The compound is electrically neutral, since 2 X (3+) (Al) = 3 X (2-) (O). If the Al is shared by six O's, then 3/6 = l/2 of its charge is contributed to each O. For the charge on each O to be satisfied, four Al's need to be coordinated to each O, since 4(1A) = 2.

A notation to indicate the coordination scheme for a-Al2O3 is 6:4—each Al is coordinated to six O's and each oxygen is coordinated to four Al's.

The structure of silicates is complicated, but the basic unit is the SiO4 tetrahedron. The three polymorphs of SiO2-quartz, tridymite and cristobalite—have different arrangements for the linking of all four vertices of the tetrahedron.

Each Si is bonded to four O's and each O is bonded to two Si's. In the layer silicates such as micas, clays, and talc, only three of the vertices are linked. The result is a laminar structure in which the bonding between layers is a weaker ionic bonding, hydrogen bonding, or van der Waals bonding, respectively, for mica, clay, and talc.

Of particular importance in semiconductors is the diamond structure. In this structure, each atom is tetrahedrally coordinated to four other atoms. The predominant covalent bonding of the structure is manifested by the high degree of directionality in the bonding.

In addition to diamond, Si and Ge have this structure, as do other semiconductors that have been doped with other elements.


Coal is a sedimentary rock formed by the accumulation and decay of organic substances derived from plant tissues and exudates that have been buried over periods of geological time along with various mineral inclusions. Coal is classified by type and rank. Coal type classifies coal by the plant sources from which it was derived.

Coal rank classifies coal by its degree of metamorphosis from the original plant sources and is therefore a measure of the age of the coal. The process of metamorphosis or aging is termed coalification.

The study of coal by type is known as coal petrography. Coal type is determined from the examination of polished sections of a coal sample using a reflected-light microscope.

The degree of reflectance and color of a sample are identified with specific residues of the original plant tissues. These various residues are referred to as macerals. Macerals are collected into three main groups: vitrinite, inertinite, and exinite (sometimes referred to as liptinite).

Coal rank is the most important property of coal, since it is rank which initiates the classification of coal for use. Rank is a measure of the age or degree of coalification of coal. Coalification describes the process which the buried organic matter goes through to become coal.

When first buried, the organic matter has a certain elemental composition and organic structure. However, as the material becomes subjected to heat and pressure, the composition and structure slowly change.

Certain structures are broken down, and others are formed. Some elements are lost through volatilization while others are concentrated through a number of processes, including being exposed to underground flows which carry away some elements and deposit others. Coalification changes the values of various properties of coal.

Thus, coal can be classified by rank through the measurement of one or more of these changing properties. In the United States and Canada, the rank classification scheme defined by the American Society of Testing and Materials (ASTM) has become the standard. In this scheme, the properties of gross calorific value and fixed carbon or volatile matter content are used to classify a coal by rank.

Gross calorific value is a measure of the energy content of the coal and is usually expressed m units of energy per unit mass. Calorific value increases as the coal proceeds through coalification. Fixed carbon content is a measure of the mass remaining after heating a dry coal sample under conditions specified by the ASTM.

Fixed carbon content increases with coalification. The conditions specified for the measurement of fixed carbon content result in being able alternatively to use the volatile matter content of the coal measured under dry, ash-free conditions as a rank parameter.

The rank of a coal proceeds from lignite, the “youngest” coal, through subbituminous, bituminous, and semibituminous, to anthracite, the “oldest” coal. Others prefer to classify such deposits as graphite.

Graphite is a minimal resource and is valuable primarily for uses other than as a fuel.) According to the ASTM scheme, coals are ranked by calorific value up to the high volatile A bituminous rank, which includes coals with calorific values (measured on a moist, mineral matterfree basis) greater than 14,000 Btu/lb (32,564 kJ/kg). At this point, fixed carbon content (measured on a dry, mineral matter-free basis) takes over as the rank parameter.

Thus, a high volatile A bituminous coal is defined as having a calorific value greater than 14,000 Btu/lb, but a fixed carbon content less than 69 wt%. The requirement for having two different properties with which to define rank arises because calorific value increases significantly through the lower-rank coals, but very little (in a relative sense) in the higher-ranks, whereas fixed carbon content has a wider range in higher-rank coals, but little (relative) change in the lower-ranks. The most widely used classification scheme outside of North America is that developed under the jurisdiction of the International Standards Organization, Technical Committee 27, Solid Mineral Fuels.


Other important properties of coal include swelling, caking, and coking behavior; ash fusibility; reactivity; and calorific value.

Calorific value measures the energy available in a unit mass of coal sample. It is measured by ASTM Standard Test Method D 201 5M, Gross Calorific Value of Solid Fuel by the Adiabatic Bomb Calorimeter, or by ASTM Standard Test Method D 3286, Gross Calorific Value of Solid Fuel by the Isothermal-Jacket Bomb Calorimeter.

In the absence of a directly measured value, the gross calorific value, Q, of a coal (in Btu/lb) can be estimated using the Dulong formula (Elliott and Yohe, 1981):

Q = 14,544C + 62,028[H - (O/8)]+ 4,050S

where C, H, O, and S are the mass fractions of carbon, hydrogen, oxygen, and sulfur, respectively, obtained from the ultimate analysis. Swelling, caking, and coking all refer to the property of certain bituminous coals, when slowly heated in an inert atmosphere to between 450 and 550 or 600 °F, to change in size, composition, and, notably, strength.

Under such conditions, the coal sample initially becomes soft and partially devolatilizes. With further heating, the sample takes on a fluid characteristic. During this fluid phase, further devolatilization causes the sample to swell. Still further heating results in the formation of a stable, porous, solid material with high strength.

There are several tests which have been developed based on this property to measure the degree and suitability of a coal for various processes. Some of the more popular are the free swelling index (ASTM Test Method D 720), the Gray-King assay test (initially developed and extensively used in Great Britain), and the Gieseler plastometer test (ASTM Test Method D 2639), as well as a whole host of dilatometric methods (Habermehl et al., 1981).

The results of these tests are often correlated with the ability of a coal to form a coke suitable for iron making. In the iron-making process, the high carbon content and high surface area of the coke are utilized to reduce iron oxide to elemental iron. The solid coke must also be strong enough to provide the structural matrix upon which the reactions take place.

Bituminous coals which have good coking properties are often referred to as metallurgical coals (Bituminous coals which do not have this property are, alternatively, referred to as steam coals because of their historically important use in raising steam for motive power or electricity generation.)

Ash fusibility is another important property of coals. This is a measure of the temperature range over which the mineral matter in the coal begins to soften and eventually to melt into a slag and to fuse together.

This phenomenon is important in combustion processes; it determines if and at what point the resultant ash becomes soft enough to stick to heat exchanger tubes and other boiler surfaces or at what temperature it becomes molten so that it flows (as slag), making removal as a liquid from the bottom of a combustor possible.

Reactivity of a coal is a very important property fundamental to all coal conversion processes (the most important of which are combustion, gasification, and liquefaction). In general, lower-rank coals are more reactive than higher-rank coals.

This is due to several different characteristics of coals, which vary with rank as well as with type. The most important characteristics are the surface area of the coal, its chemical composition, and the presence of certain minerals which can act as catalysts in the conversion reactions. The larger surface area present in lower-rank coals translates into a greater degree of penetration of gaseous reactant molecules into the interior of a coal particle.

Lower-rank coals have a less aromatic structure than higher-rank coals, which, along with contributing to larger surface area, also corresponds to a higher proportion of lower-energy, more-reactive chemical bonds. Lower-rank coals also tend to have higher proximate ash contents, and the associated mineral matter is more distributed — down to the atomic level.

Any catalytically active mineral matter is thus more highly dispersed, also. However, the reactivity of a coal also varies depending upon what conversion is being attempted. That is, the reactivity of a coal toward combustion (oxidation) is not the same as its reactivity toward liquefaction, and the order of reactivity established in a series of coals for one conversion process will not necessarily be the same as for another process.


A boiler, also referred to as a steam generator, is a major component in the plant cycle. It is a closed vessel that efficiently uses heat produced from the combustion of fuel to convert water to steam.

Efficiency is the most important characteristic of a boiler since it has a direct bearing on electricity production. Boilers are classified as either drum-type or once-through. Major components of boilers include an economizer, superheaters, reheaters, and spray attemperators.

The economizer is the section of the boiler tubes where feedwater is first introduced into the boiler and where flue gas is used to raise the temperature of the water.

Steam Drum (Drum Units Only).
The steam drum separates steam from the steam/water mixture and keeps the separated steam dry.

Superheaters are bundles of boiler tubing located in the ßow path of the hot gases that are created by the combustion of fuel in the boiler furnace. Heat is transferred from the combustion gases to the steam in the superheater tubes.

Superheaters are classified as primary and secondary. Steam passes first through the primary superheater (located in a relatively cool section of the boiler) after leaving the steam drum.

There the steam receives a fraction of its final superheat and then passes through the secondary superheater for the Reheaters.

Reheaters are bundles of boiler tubes that are exposed to the combustion gases in the same manner as superheaters.

Spray Attemperators.
Attemperators, also known as desuperheaters, are spray nozzles in the boiler tubes between the two superheaters.

These spray nozzles supply a fine mist of pure water into the flow path of the steam to prevent tube damage from overheating. Attemperators are provided for both the superheater and reheater.


The use of piping for plumbing, fire protection, and for the transport of hazardous materials may be subject to the provisions of a code and/or to those of local, state, federal, or other regulations.

All the major model plumbing codes which have become adopted, or referenced, by state and local jurisdictions permit and prescribe to a varying but fairly extensive degree the use of plastics piping for hot-cold water lines; water services; drain, waste, and vents (DWV); sewerage; and drainage.

Plastics piping is also covered by other codes, such as the following which are of interest to industrial users:

American National Standards Institute Codes

ANSI B31.3 Chemical Plant and Petroleum Refinery Piping

ANSI B31.8 Gas Transmission and Distribution Piping Systems

ANSI Z223.1 National Fuel Gas Code

Department of Transportation, Hazardous Materials Board, Office of Pipeline Safety Operations

Code of Federal Regulations (CFR),Title 49, Part 192,Transportation of Natural Gas and

Other Gas by Pipeline: Minimum Federal Safety Standards

Code of Federal Regulations (CFR), Title 49, Part 195, Transportation of Liquids by

Pipeline, Minimum Federal Safety Standards

The National Fire Protection Association (Quincy, Mass.) Model Codes

NFPA 30 Flammable and Combustible Liquids Code

NFPA 54 National Fuel Gas Code

NFPA 70 National Electrical Code*

NFPA 70A Electrical Code for One and Two Family Dwellings

NFPA 34 Outdoor Piping


Epoxy resins are strong and have good resistance to solvents, salts, caustics, and dilute acids. Epoxies are cross-linked by curing agents which become an integral part of the polymer and affect the thermal, chemical, and physical properties of the polymer.

For instance, the maximum service temperature of epoxy pressure pipe cured with anhydrides is 180°F (83°C), and it has little resistance to caustics; that cured with aromatic amines can be used at temperatures above 225°F (107°C), and it has good caustic resistance.

The major use of epoxy pipe is in oil fields, where its resistance to corrosion and paraffin buildup makes it preferable to steel pipe for crude-collection and saltwater-injection lines. Other uses are in the chemical process industry, in heating and air conditioning, in food processing, for gasoline and solvents, and in mining applications (including abrasive slurry transport, communications ducts, and power conduits).

Although typically not as strong as the epoxies, polyesters offer good resistance to mineral acids, bleaching solutions, and salts.The most commonly used polyester resins for pipe are isophthalic polyesters and bisphenol A fumarate polyesters.

Isophthalics have poorer resistance to caustics and oxidizers. Bisphenol A fumarates have improved resistance to these materials and are widely used in paper mills for bleach lines.

Isophthalic resin pipe is used in waste-treatment and power plants in services where corrosive conditions are not severe. Maximum operating-temperature limits for pressure pipe vary, depending upon the specific material, but are generally below 200°F (93°C).

Vinyl Esters.
These resins include chemical features of both epoxies and polyesters. Vinyl ester resins offer better chemical resistance, somewhat higher temperature limits, and better solvent resistance than ordinary polyesters but generally do not compare to epoxies in these properties.

Vinyl ester resins are preferred over polyesters because they are more chemical resistant than the isophthalics and less brittle than the bisphenol A fumarates.Typical services are in fertilizer plants (acid lines), chlorine plants (chlorine-saturated brine lines), and paper mills (caustic and black-liquor lines).

Furan resins offer very good chemical, solvent, and temperature resistance—up to about 300°F (150°C). Because they extend the limitations of the other resins, they are often selected for use in the processing industries in place of exotic metal piping.


Reinforced thermosetting resin pipe (RTRP) is a composite largely consisting of a reinforcement imbedded in, or surrounded by, cured thermosetting resin. Included in its composition may be granular or platelet fillers, thixotropic agents, pigments, or dyes.

The most frequently used reinforcement is fiberglass, in any one or a combination of the following forms: continuous filament, chopped fibers, and mats.While reinforcements such as asbestos or other mineral fibers are sometimes used, fiberglass-reinforced pipe (FRP) is by far the most popular.

One form of FRP, called reinforced plastic mortar pipe (RPMP), consists of a composite of layers of thermosetting resin–sand aggregate mixtures that are sandwiched by layers of resin-fiberglass reinforcements.

In another construction, the sand is replaced by glass microspheres.The high content of reinforcements in RTRP, which may run from 25 to 75 percent of the total pipe weight, and the specific design of the composite wall construction are the major determinants of the ultimate mechanical properties of the pipe.

The resin, although also influencing these properties somewhat, is the binder that holds the composite structure together, and it supplies the basic source of temperature and chemical resistance. Glass fibers, as well as many other reinforcements, do not have high resistance to chemical attack.

For enhanced chemical and/or abrasion resistance, RTRP construction may include a liner consisting of plastic (thermosetting or thermoplastic), ceramic, or other material. The outer surface of the pipe—especially that of the larger diameter sizes—may also be made “resin rich” to better resist weathering, handling, and spills.

Reinforced thermosetting resin pipe is available in a variety of resins, wall constructions, and liners with diameters ranging from 1 in (2.5 cm) to more than 16 ft (5 m). Stock and specially fabricated fittings are readily available.


Polyvinyl chloride (PVC) piping is made only from compounds containing no plasticizers and minimal quantities of other ingredients. To differentiate these materials from flexible, or plasticized PVCs (from which are made such items as upholstery, luggage, and laboratory tubing) they have been labeled rigid PVCs in the United States and unplasticized PVC (uPVC) in Europe.

Rigid PVCs used in piping range from Type I to Type III, as identified by an older classification system that is still much in use. In this system, the type designations are supplemented by grade designations (e.g., Grade 1 or 2) which further define the material’s properties.Type I materials, from which most pressure and nonpressure pipe is made, have been formulated to provide optimum strength as well as chemical and temperature resistance.

Type II materials are those formulated with modifiers that improve impact strength but that also somewhat reduce, depending on modifier type and quantity, the aforementioned properties of Type I materials. There is little call for Type II pipe, as the impact strength of the stronger Type I pipe is more than adequate for most uses.

Type III materials contain some inert fillers which tend to increase stiffness concomitant with some lowering of both tensile and impact strength and chemical resistance. Some nonpressure PVC piping, such as that used for conduit, sewerage, and drainage, is made from Type III PVCs.

The currently used classification system for rigid PVC materials for piping and other applications is described in ASTM D 1784,“Standard Specification for Rigid Polyvinyl Chloride and materials by numbered cells that designate value ranges for the following properties: impact resistance (toughness), tensile strength, modulus of elasticity (rigidity), deflection temperature (temperature resistance), and chemical resistance.

Because (as expanded in the discussion on properties) short-term properties of plastic materials are not a reliable predictor of long-term capabilities, those PVC materials that have been formulated for long-term pressure applications are also designated by their categorized maximum recommended hydrostatic design stress (RHDS) for water at 73.4°F (23°C) as determined from long-term pressure testing.

The most commonly used designation system for PVC pressure-piping materials is based on the above older designation system with two added digits that identify, in hundreds of pounds per square inch, the maximum recommended design stress.*

For example: PVC 1120 is a Type I, Grade 1 PVC (minimum cell class 12454-B) with a maximum recommended HDS of 2000 lb/in2 (13.8 MPa) for water at 73.4°F (23°C); PVC 2110 is a Type 2, Grade 1 PVC (minimum cell class 14333-D) with an RHDS of 1000 lb/in2 (6.9 MPa).

Most pressure-rated PVC pipe is made from PVC 1120 materials. The combination of good long-term strength with higher stiffness explains why PVC has become the principal plastic pipe material for both pressure and nonpressure applications.

Major uses include: water mains; water services; irrigation; drain, waste, and vent (DWV) pipes; sewerage and drainage; well casing; electric conduit; and power and communications.


Most thermoplastic pipes and fittings are made from materials containing no reinforcements, although fillers are occasionally used. Pipe is manufactured by the extrusion process, whereby molten material is continuously forced through a die that shapes the product.

After being formed by the die, the soft pipe is simultaneously sized and hardened by cooling it with water. Fittings and valves are usually produced by the injection-molding process, in which molten plastic is forced under pressure into a closed metal mold.

After cooling, the mold is opened and the finished part is removed. Some items, especially larger-sized fittings for which there is insufficient demand to justify construction of injection-molding tooling, are fabricated from pipe sections, or sheets, by utilizing thermal or solvent cementing fusion techniques.

To compensate for the lower strength, the fitting may either be made from a heavier wall stock or reinforced with a fiberglass-resin overwrap. The engineer designing a pressure-rated system should make sure that the pressure ratings of the selected fittings are adequate.

There is some thermoplastic pipe made of a cellular-core construction (for example, ASTM* F 628) in which the pipe wall consists of thin inner and outer solid skins sandwiching a high-density foam. The primary benefit of such construction is improved ring and longitudinal (beam) stiffness in relation to the material used.

Because the foam-wall structure results in some loss of strength, applications for cellular-core pipe are in nonpressure uses, such as for above- and below-ground drainage piping, which can take advantage of the more material-efficient ring and beam stiffness.

For buried nonpressure applications, a composite pipe (ASTM D 2680) is produced that consists of two concentric tubes that are integrally braced with a truss webbing. The resultant openings between the concentric tubes are filled with a lightweight concrete. This construction increases both the ring and the beam stiffness. Composite pipe is used only for nonpressure buried applications such as sewerage and drainage.

Several other processes for improving the radial (i.e., ring) stiffness of thermoplastic pipe for buried applications have in common the formation of some type of rib reinforcement.A well-established technique is forming corrugations in the pipe wall.

Corrugated polyethylene pipe (ASTM F 405) in sizes from 2 to 12 in (5 to 30 cm) is widely used for building foundations, land, highway, and agricultural drainage, and communications ducts. Ribbed pipe also is commercially made by the continuous spiral winding of the plastic over a mandrel of a specially shaped profile.

Adjacent layers of this profile are fused to each other to form a cylinder that is smooth on the inside and has ribbed reinforcements on the outside. The smooth inside diameter is preferable for many applications, such as sewerage, because it creates no flow disturbances. Pipes with ribbed construction are available in PVC and polyethylene (PE).

PE pipes, which are made with hollow ribs to minimize material usage, are available in sizes from 18 to 120 in (45 cm to 3 m) in diameter.  


Have you ever wondered why the passenger basket on a hot air balloon is suspended underneath and not simply strapped to the top of the balloon? After all, most hot air balloons are used for sightseeing and a basket on the top would give much better views.

Consider the balloon shown in the left-hand diagram of below:

The balloon floats because the hot air inside it is less dense than the cold air surrounding it, giving rise to a buoyancy force acting upwards through B. When this force equals the total weight of the balloon and basket, acting through the centre of gravity G, the balloon will float at a constant altitude.

As the wind changes and the occupants of the basket move around, the balloon will rock through a small angle θ. Since the centre of buoyancy is higher than the centre of gravity, any angular displacement produces a turning moment which acts to restore the balloon to an upright position. Such an arrangement is said to be in stable equilibrium.

Now look at the bizarre case in the right-hand diagram. The buoyancy force again equals the weight, but here any angular displacement causes a turning moment which makes the basket topple over. The reason for this is that the centre of buoyancy B is below G. The situation is known as unstable equilibrium.

Something very similar applies to ships, but there are cases where stable equilibrium can be achieved even where the centre of buoyancy is below the centre of gravity. This occurs because the shape of the displaced water alters as the ship rocks and so the centre of buoyancy moves sideways in the same direction as the ship is leaning.

Therefore the line of action of the buoyancy force also moves to the side of the ship which is further down in the water, and the buoyancy force tries to lift the ship back to the upright position. Whether or not the restoring moment is enough to make the ship stable depends on the position of the point where the line of action of the buoyancy force crosses the centreline of the ship, known as the metacentre, M .
The distance between G and M is known as the metacentric height.

If M is above G then the metacentric height is positive and the ship is in stable equilibrium. If G is above M then the metacentric height is negative and the ship is in unstable equilibrium. This is the situation which led to the sinking of King Henry VIII’s flagship, the Mary Rose, off Portsmouth.

This had sailed successfully for a number of years and was just stable as it cast off on its fateful last voyage, even though an unusually large shipment of weapons and soldiers had raised the centre of gravity to danger level.

Finally, when the soldiers crowded up onto deck for a last glimpse of land as the ship put out to sea, the centre of gravity rose so high that the first big wave they encountered away from the shelter of the harbour caused the ship to topple completely over.


A 20,000-kW turbogenerator is supplied with steam at 300 lb / in2 (abs) (2067.0
kPa) and a temperature of 650-F (343.3-C). The backpressure is 1 in (2.54 cm) Hg
absolute. At best efficiency, the steam rate is 10 lb (25.4 kg) per kWh. (a) What is
the combined thermal efficiency (CTE) of this unit? (b) What is the combined
engine efficiency (CEE)? (c) What is the ideal steam rate?

Calculation Procedure:
1. Determine the combined thermal efficiency
(a) Combined thermal efficiency, CTE = (3413/wr)(1/[h1 - h2]), where wr = combined steam rate, lb/kWh (kg/kWh); h1 = enthalpy of steam at throttle pressure and temperature, Btu/ lb (kJ / kg); h2 = enthalpy of steam at the turbine backpressure, Btu/ lb (kJ / kg). Using the steam tables and Mollier chart and substituting in this equation, CTE = (3413/10)(1/[1340.6 - 47.06]) = 0.2638, or 26.38 percent.

2. Find the combined engine efficiency
(b) Combined engine efficiency, CEE = (wi)/(we ) = (weight of steam used by ideal engine, lb /kWh (weight of steam used by actual engine, lb /kWh). The weights of steam used may also be expressed as Btu/ lb (kJ / kg). Thus, for the ideal engine, the value is 3413 Btu/ lb (7952.3 kJ/ kg). For the actual turbine, h1 – h2x is used, h2x is the enthalpy of the wet steam at exhaust conditions; h1 is as before.

Since the steam expands isentropically into the wet region below the dome of the T-S diagram, we must first determine the quality of the steam at point 2 either from a T-S diagram or Mollier chart or by calculation.

By calculation using the method of mixtures and the entropy at each point: S1 = S2 = 0.0914 – (x2 (1.9451). Then x2 = (1.6508 - 0.0914)/1.9451 = 0.80, or 80 percent quality. Substituting and summing, using steam-table values, h2x = 47.06 - 0.8(1047.8) = 885.3 Btu/ lb (2062.7 kJ/ kg).

(c) To find the CEE we first must obtain the ideal steam rate, wi = 3413/ (h1 - h2x ) = 3413/(1340.6 - 885.3) = 7.496 lb /kWh (3.4 kg/kWh).

Now, CEE = (7.496/10)(100) = 74.96 percent. This value is excellent for such a plant and is in a range being achieved today. Related Calculations. Use this approach to analyze the efficiency of any turbogenerator used in central-station, industrial, marine, and other plants.