In occupied buildings, carbon dioxide, human odors and other contaminants such as volatile organic compounds (VOC) or odors and particles from machinery and the process function need to be continuously removed or unhealthy conditions will result.

Ventilation is the process of supplying “fresh” outside air to occupied buildings in the proper amount to offset the contaminants produced by people and equipment.

In many instances, local building codes, association guidelines, or government or company protocols stipulate the amount of ventilation required for buildings and work environments. Ventilation systems have been around for a long time.

In 1490, Leonardo da Vinci designed a water driven fan to ventilate a suite of rooms. In 1660, a gravity exhaust ventilating system was used in the British House of Parliament. Then, almost two hundred years later, in 1836, the supply air and exhaust air ventilation system in the British House of Parliament used fans driven by steam engines.

Today, ventilation guidelines are approximately 15 to 25 cfm (cubic feet per minute) of air volume per person of outside air (OA) for non-smoking areas, 50 cfm for smoking areas. Ventilation air may also be required as additional or “make-up” air (MUA) for kitchen exhausts, fume hood exhaust systems, and restroom and other exhaust systems.

Maintaining room or conditioned space pressurization (typically +0.03 to +0.05 inches of water gage) in commercial and institutional buildings is part of proper ventilation.


The figure above shows 20% of the total supply air is ventilation outside air (OA) and 80% is return air (RA). The outside air is brought (or forced) into the mixed air plenum by the action of the supply air fan. The outside air coming through the outside damper is mixed with the return air from the conditioned space.

The return air dampers control the amount of return air. If the room pressure is too high, the exhaust air (EA) dampers open to let some of the return air escape to the outside, which relieves some of the pressure in the conditioned space. Exhaust air dampers are also called relief air dampers.


Calculate gpm of water flow if the heating coil load is 243,810 Btuh and TD is 20°F (200°F EWT - 180°F LWT). Btuh = gpm × 500 × TD

Btuh = Btu per hour
gpm = volume of water flow, gallons per minute
500 = constant
60 min/hr × 8.33 lb/gal × 1 Btu/lb/°F
TD = temperature difference of the water entering (EWT) and leaving (LWT) the coil. ΔT may be used substituted for TD.

gpm = Btuh ÷ (500 × TD)
gpm = 243,810 ÷ (500 × 20)

24.4 gpm of water flows through the heating coil.
Now calculate the air TD across the heating coil if:

198,450 Btuh is the Sensible Room Heating Load.

The math is: 198,450 = 5250 cfm × 1.08 × 35 TD (105-70)
243,810 Btuh is the Sensible Coil Heating Load.

The difference of 45,360 Btuh (243,810–198,450) is the additional heat required for the outside air.
The math is: 45,360 = 1050 cfm × 1.08 × 40 TD (70-30)
LAT - leaving air temperature (coil). (Also called SAT, supply air temperature) (105°F)
EAT - entering air temperature (coil), (also called RAT, room air temperature) (70°F)
OAT - outside air temperature (30°F)

TD = Btuh ÷ (1.08 × cfm)
TD = 243,810 ÷ (1.08 × 5250)
43°F TD (62 EAT + 43 TD = 105 LAT)
243,810 Btuh is the Sensible Coil Heating Load.
The math is: 243,810 = 5250 cfm × 1.08 × 43 TD (105-62)
The mixed air temperature (MAT also called EAT) was calculated
using this equation:
MAT = (%OA × OAT) + (%RA × RAT)

MAT = mixed air temperature

OAT = outside air temperature
RAT = return air temperature, also called room air temperature

MAT = (20% × 30°F) + (80% × 70°F)
MAT = (6) + (56)

MAT = 62 °F


For a better understanding of boiler construction and operation, let’s examine a four-pass, internally fired, fire tube, natural gas-fired, forced-draft, marine, wet-back boiler. The boiler consists of a cylindrical steel shell which is called the pressure vessel.

It is covered with several inches of insulation to reduce heat loss. The insulation is then covered with an outer metal jacket to prevent damage to the insulation. Some of the other components are a burner, a forced-draft fan and various controls.

When the boiler is started it will go through a purge cycle in which the draft fan at the front of the boiler will force air through the combustion chamber and out the stack at the front of the boiler. This purges any combustibles that might be in combustion chamber.

An electrical signal from control circuit will open the pilot valve allowing natural gas to flow to the burner pilot light. A flame detector will verify that the pilot is lit and gas will then be supplied to the main burner.

The draft fan forces air into the combustion chamber and combustion takes place. The hot combustion gases flow down the chamber and into the tubes for the second pass back to the front of the boiler.

As the gases pass through the tubes they are giving up heat into the water. The gases enter into the front chamber of the boiler, called the header, and make another loop to the back of the boiler for the third pass.

The fourth pass brings the hot gases back to the front of the boiler and out the stack. The temperature in the combustion chamber is several thousand degrees while the temperature of the gases exiting the stack should be about 320 degrees (or 150 degrees above the medium temperature).


A fire tube boiler, as the name suggests, has the hot flue gases from the combustion chamber, the chamber in which combustion takes place, passing through tubes and out the boiler stack. These tubes are surrounded by water.

The heat from the hot gases transfers through the walls of the tubes and heats the water. Fire tube boilers may be further classified as externally fired, meaning that the fire is entirely external to the boiler or they may be classified as internally fired, in which case, the fire is enclosed entirely within the steel shell of the boiler.

Two other classifications of fire tube boilers are wet-back or dryback. This refers to the compartment at the end of the combustion chamber.

This compartment is used as an insulating plenum so that the heat from the combustion chamber, which can be several thousand degrees, does not reach the boiler’s steel jacket. If the compartment is filled with water it is known as a wet-back boiler and conversely, if the compartment contains only air is called a dry-back boiler.

Still another grouping of fire tube boilers is by appearance or usage. The two common types used today in HVAC heating systems are the marine or Scotch marine boiler and the firebox boiler. The marine boiler was originally used on steam ships and is long and cylindrical is shape.

The firebox boiler has a rectangular shape, almost to the point of being square. A Scotch marine fire tube boiler has the flame in the furnace and the combustion gases inside the tubes. The furnace and tubes are within a larger vessel, which contains the water and steam.

Fire tube boilers are also identified by the number of passes that the flue gases take through the tubes. Boilers are classified as two-, three- or four-pass. The combustion chamber is considered the first pass.

Therefore, a two-pass boiler would have one-pass down the combustion chamber looping around and the second pass coming back to the front of the boiler and out the stack. A three-pass boiler would have an additional row of tubes for the gas to pass through going to the back of the boiler and out the stack.

A fourpass boiler would have yet another additional row of tubes for the gas to pass through going to the front of the boiler and out the stack. An easy way to recognize a two-, three- or four-pass boiler is by the location of the stack. A two- or four-pass boiler will have the stack at the front, while a three-pass boiler will have the stack at the back.

Fire tube boilers are available for low and high pressure steam, or hot water applications. The size range is from 15 to 1500 boiler horsepower (a boiler horsepower is 33,475 Btuh). HVAC fire tube boilers are typically used for low pressure applications.


Hot water heating systems (Figure below) transport heat by circulating heated water to a designated area. Heat is released from the water as it flows through the heating unit (coil, terminal).

After heat is released, the water returns to the boiler to be reheated and recirculated. Low temperature hot water boilers are ≤ 250°F. High temperature hot water boilers are >250°F.

Hot water heating systems produce heat more consistently than steam heating systems. The water in a hot water heating system remains in the lines at all times.

The water in the heating unit lines heats and cools slowly, resulting in an even rate of heat production. When pressure is lost in the steam heating system, steam leaves the heating units resulting in a more rapid loss of heat than in a hot water heating system.

In addition, the steam heating system has a longer recovery time in producing heat after the boiler is shut down.

Boilers are used in both hot water heating systems and steam heating systems. The hot water heating systems most often encountered in HVAC work will be low temperature systems with boiler water temperatures generally in the range of 170-200 degrees Fahrenheit.

Most of the steam heating systems will use low pressure steam, operating at 15 psig (30 psia, and 250°F). There are a great many types and classifications of boilers. Boilers can be classified by size, construction, appearance, original usage, and fuel used.

Fossil-fuel boilers will be either natural gas-fired, liquid petroleum (LP) gas-fired, or oil-fired. Some boilers are set up so that the operating fuel can be switched to natural gas, LP gas or oil, depending on the fuel price and availability.

The construction of boilers remains basically the same whether they’re water boilers or steam boilers. However, water or steam boilers are divided by their internal construction into fire tube or water tube boilers.


Steam traps are installed in locations where condensate is formed and collects, such as all low points, below heat exchangers and coils, at risers and expansion loops, at intervals along horizontal pipe runs, ahead of valves, at ends of mains, before pumps, etc. The purpose of a steam trap is to separate the steam (vapor) side of the heating system from the condensate (water) side.

A steam trap collects condensate and allows the trapped condensate to be drained from the system, while still limiting the escape of steam. The condensate may be returned to the boiler by a gravity return system, a mechanical return system using a vacuum pump (closed system), or condensate pump (open system).

Condensate must be trapped and then drained immediately from the system. If it isn’t, the operating efficiency of the system is reduced because the heat transfer rate is slowed. In addition, the build up of condensate can cause physical damage to the system from “water hammer.”

Water hammer can occur in a steam distribution system when the condensate is allowed to accumulate on the bottom of horizontal pipes and is pushed along by the velocity of the steam passing over it. As the velocity increases, the condensate can form into a non-compressible slug of water.

 If this slug of water is suddenly stopped by a pipe fitting, bend, or valve the result is a shock wave which can, and often does, cause damage to the system (such as blowing strainers and valves apart).

Steam traps also allow air to escape. This prevents the build up of air in the system which reduces the heat transfer efficiency of the system and may cause air binding in the heat exchanger.

In a steam heating system, water enters a heat conversion unit (a heat exchanger, the boiler, etc.) and is changed into steam. When the water is boiled, some air in the water is also released into the steam and is moved along with the steam to the heat exchanger.

As the heat is released at the heat exchangers (and through pipe radiation losses), the steam is changed into condensate water. Some of the air in the piping system is absorbed back into the water. However, much of the air collects in the heat exchanger and must be vented.

Steam traps are classified as thermostatic, mechanical or thermodynamic. Thermostatic traps sense the temperature difference between the steam and the condensate using an expanding bellows or bimetal strip to operate a valve mechanism.

Mechanical traps use a float to determine the condensate level in the trap and then operate a discharge valve to release the accumulated condensate. Some thermodynamic traps use a disc which closes to the high velocity steam and opens to the low velocity condensate. Other types will use an orifice which flashes the hot condensate into steam as the condensate passes through the orifice.


Dehumidification occurs when air passing through a chilled water coil, a refrigerant coil or a chemical dehumidifier releases moisture and is dehumidified. The air leaves the dehumidifier at condition point A (70°FDB and 10%RH).

In this example, the dry bulb temperature remains constant while the wet bulb temperature, dew point temperature, relative humidity and specific humidity decrease. In a typical commercial and industrial cooling coil HVAC system, using either a chilled water coil or a refrigerant coil, the psychrometric process is both cooling and dehumidification simultaneously (see below). When using a chemical dehumidifier, the process is heating and dehumidifying.

Heating and Humidification
Both heating and humidification occurs when air passes through a warm water spray or steam. The air absorbs moisture and is humidified and heated simultaneously. The air leaves the spray at 80°FDB and 50%RH (condition C). The dry bulb temperature, wet bulb temperature, dew point temperature, relative humidity and specific humidity increase.

Cooling and Humidification
When air passes through cold water, either a spray or a wetted pad, it absorbs moisture and is humidified and cooled simultaneously. This is “evaporative cooling” and is effective in dry (arid) areas with low relative humidity. The air leaves the spray at 80°FDB, 70°FWB and 61%RH (B). The wet bulb temperature remains constant while the dry bulb temperature decreases. The dew point temperature, relative humidity and specific humidity increase.

Heating and Dehumidification
When air passes through a chemical dehumidifier the psychrometric process is heating and dehumidifying following along a constant wet bulb line. The air leaves the dehumidifier at condition point D (80°FDB, 60°FWB and 30%RH). The wet bulb temperature remains constant while the dry bulb temperature increases. The dew point temperature, relative humidity and specific humidity decrease.

Cooling and Dehumidification
Air is dehumidified and cooled simultaneously by passing it through sprays of cold water or over a cold surface such as an energized refrigerant coil or chilled water coil. The most common type of HVAC cooling is “mechanical cooling” using a cold surface.


Sensible Heating
Sensible heating is heat added to the air, which causes the air temperature to increase. Sensible heat is measured using a standard thermometer.

A horizontal line on the psych chart represents any heating process such as a typical residential or commercial office heating process that adds sensible heat only.

Air enters the heating coil at 50°FDB and 40°FWB (condition point A) and leaves the heating coil at 100°FDB and 62.5°FWB (condition point B). As the air is heated, the dry bulb and wet bulb temperatures increase but the dew point temperature and the moisture content (specific humidity) remain constant.

The relative humidity also changes from 40% to less than 10%. This change in relative humidity is because as the air gets warmer, the air can hold more moisture (per pound of air), but because the amount of moisture is the same, about 22 grains, the relative humidity goes down.

Sensible Cooling
Opposite of sensible heating only would be sensible cooling only. This is not common but is used in some applications. Chemical dehumidification is one example. Sensible cooling is heat removed from the air, which causes the air temperature to decrease as sensed by a thermometer.

A horizontal line on the psych chart also represents any cooling process that removes sensible heat only. Air enters the cooling coil at 100°FDB and 62.5°FWB (B) and leaves the cooling coil at 50°FDB and 40°FWB (A).

As the air is cooled (heat removed), the dry bulb and wet bulb temperatures decrease but the dew point temperature (27°FDP) and the moisture content (22 grains) remain constant. The relative humidity also changes from approximately 8% to 40%.

This change in relative humidity is because as the air gets cooler, the air’s ability to hold moisture (per pound of air) lessens, but because the amount of moisture is the same, the relative humidity goes up.


H is for Heating
• Types of Boilers
— Steam
— Water
• Boiler Pressures
— Low
— High
• Boiler Fuels
— Natural Gas
— Oil
— Coal
— Electricity
• Boiler Configurations
— Fire Tube
— Water Tube

• Furnace Fuels
— Natural Gas
— Oil
— Coal
— LPG (Liquid Petroleum Gas)
— Electricity

Heating Coils
• Types of Heating Coils
— Steam
— Water
— Electrical

V is for Ventilation for each of the following:
1) Approximately 20 cfm (cubic feet per minute) of air volume per person of outside air (OA) for ventilation for non-smoking areas.

2) Make-up air (MUA) for exhaust systems such as:
— Kitchen hoods
— Fume hoods
— Toilets

3) Room (conditioned space) pressurization — +0.03 to +0.05 inches of water gage for commercial buildings

AC is for Air Conditioning
For most of us, air conditioning means comfort cooling with either chilled water systems or refrigerant systems. Both of these systems include cooling coils to remove heat from the air.

• Chilled Water Systems
— Vapor-compression system
— Absorption system

• Refrigeration (DX) Systems
— Vapor-compression system

• Cooling Coils
— Water coil
— Refrigerant (DX) coil

Cooling and heating coils are heat transfer devices or heat exchangers. They come in a variety of types and sizes and are designed for various fluid combinations: water, refrigerant or steam. Water coils are used for heating, cooling or dehumidifying air and are most often made of copper headers and tubes with aluminum or copper fins and galvanized steel frames.

AC (Air Conditioning) also means conditioning the air in the following ways:
• Temperature (tempering the air) Cooling (removing heat)

Heating (adding heat)
• Humidity control
— Dehumidifying (removing moisture)
— Humidifying (adding moisture)
• Volume of airflow
— cfm (cubic feet per minute)
• Velocity (speed) of airflow
— fpm (feet per minute)
• Cleaning
— Filtering
• Pattern of airflow
— Direction
• horizontal
• vertical


The specific heat of a substance is the heat energy required to raise the temperature of unit mass of the substance by one degree. In terms of the quantities involved, the specific heat of a substance is the heat energy required to raise the temperature of l kg of the material by 1°C (or K, since they have the same interval on the temperature scale).

The units of specific heat are therefore J/kgK.

Different substances have different specific heats, for instance copper is 390 J/kgK and cast iron is 500 J/kgK. In practice this means that if you wish to increase the temperature of a lump of iron it would require more heat energy to do it than if it was a lump of copper of the same mass.

Alternatively, you could say the iron ‘soaks up’ more heat energy for a given rise in temperature. Remember that heat energy is measured in joules or kilojoules (1000 joules).

The only difference between the kelvin and the centigrade temperature scales is where they start from. Kelvin starts at –273 (absolute zero) and centigrade starts at 0. A degree change is the same for each.

The equation for calculating heat energy required to heat a solid is therefore the mass to be heated multiplied by the specific heat of the substance, c, available in tables, multiplied by the number of degrees rise in temperature, T.

Q = m.c. T
Putting in the units,
kJ = kg × kJ/ kg.K × K

Note that on the right-hand side, the kg and K terms cancel to leave kJ. It is useful to do a units check on all formulas you use.


1. The boiler in a canteen contains 6 kg of water at 20°C. How
much heat energy is required to raise the temperature of the
water to 100°C? Specific heat of water = 4190 J/kgK.
Q = m.c. T
Q = 6 × 4190 × (100 – 20)
Q = 2 011 200 J = 2011.2 kJ

2. How many kilograms of copper can be raised from 15°C to
60°C by the absorption of 80 kJ of heat energy? Specific heat
of copper = 390 kJ/kgK.
Q = m.c. T
80 000 = m × 390 × (60 – 15)
m =
80 000
390 × 45
= 4.56 kg


A cast-iron radiator is a heat-emitting unit that transmits a portion of its heat by radiation and the remainder by convection. An exposed radiator (or freestanding radiator) transmits approximately half of its heat by radiation, the exact amount depending on the size and number of the sections.

The balance of the emission is by conduction to the air in contact with the heating surface, and the resulting circulation of the air warms by convection.

To size a column-type or tube-type cast-iron radiator, first measure its height in inches and then count the number of sections and the number of tubes or columns in each section (see Figure 2-3). The sections are the divisions or separations of a cast-iron radiator as seen when standing directly in front of it.

When you look at the radiator from its narrow end, you can see that each section consists of one or more vertical columns or pipes.

These vertical columns or pipes (they are called columns in the traditional cast-iron radiators) are 21⁄2 inches wide. In newer radiators, they are called tubes and are only 11⁄2 inches wide.

Find the square-foot EDR (equivalent direct radiation) of one section of the radiator. Multiply that figure by the number of sections in the radiator module to arrive at the square-foot EDR rating of that radiator.

Multiply the square-foot EDR rating by 240 Btu per hour to obtain the heating capacity of that radiator in a steam heating system or by 170 Btu per hour for its heating capacity in a hot-water heating system.


A hydronic hot-water heating system circulates hot water to every room through baseboard panels. “Hydronic” is another term for forced hot-water heating. The hot water gives off its heat energy by utilizing fins attached to the tubing or channel carrying the hot water.

Baseboard panels mounted around the outer perimeter of the home provide a curtain of warmth that surrounds those inside. Radiant heat rays warm the room surfaces. Rising currents of convected warm air block out drafts and cold. Walls stay warm and cold spots are eliminated.

A boiler provides water between 120 and 210 degrees F. The water is pumped through the piping in the baseboard. Today’s boilers are very efficient and very small in size. Most units are the size of an automatic washing machine; some are as small as suitcases and can be hung on the wall, depending on the size of the home being heated.

Circulating Pump
Booster pumps are used to circulate hot water through the pipes. These pumps are designed to handle a
wide range of pumping capacities. They will vary in size from small booster pumps with a 5-gallon-perminute
capacity to those capable of handling thousands of gallons per minute.

Piping Arrangements
There are two different piping arrangements utilized by the hydronic hot-water system: the series loop
and the one-pipe system, which is utilized in zoning. The zone-controlled system has two circulators that are
attached to a single boiler, and separate thermostats are used to control the zones. There are, of course,
other methods, but these two are among the most commonly used in home heating. The plumbing requirements
are minimal, usually employing copper tubing with soldered joints.

One-pipe systems may be operated on either forced or gravity circulation. Care must be taken to design and install the system with the characteristic temperature drop found in the heat-emitting units farthest from the boiler in mind.

The design of gravity circulation and one-pipe systems must be planned very carefully to allow for heat load and losses in the system. The advantage of the one-pipe system lies in its ability to allow one or two of the heat-emitting units to be shut off without interfering with the flow of hot water to the other units.

This is not the case in the series-loop system, where the units are connected in series and form a part of the supply line. The piping varies so that one allows the cutoff and the other does not. It is obvious that the series-loop system is less expensive to install because it has a very simple piping arrangement.

Hot Water for Other Purposes
It is possible to use the boiler of a hydronic heating system to supply heat for such purposes as snow melting, a swimming pool, domestic hot water for household use, and other purposes. Separate circuits are created for each of these purposes, which are controlled by their own thermostats.

Each is designed to tap into the main heating circuit from which it receives its supply of hot water. Hot water for household use, for instance, can be obtained by means of a heat exchanger or special coil inserted into the boiler.

Note that the supply water does not come in contact with water being heated by the boiler for the baseboard units and other purposes.

One of the disadvantages of the hydronic system is its slow recovery time. If an outside door is opened during cold weather for any period of time, it takes a considerable length of time for the room to once again come up to a comfortable temperature.

There is also noise made by the piping heating up and expanding and popping; it becomes rather annoying at night when you are in a quiet room and not too sleepy. The main advantage, however, is its economical operation. The type of fuel used determines the expense. The boilers can be electrically heated, heated with natural gas, or heated with oil.


Hot-water heating systems transmit only sensible heat to radiators, as distinguished from steam systems that work principally by the latent heat of evaporation. The result is that the radiator temperature of a steam system is relatively high compared to that of a hot-water system. In a hot-water system, latent heat is not given off to a great degree, so more heating surface is required.

Advantages of hot-water heating include:
1. Temperatures may widely vary, so it is more flexible than low-pressure (above atmospheric) steam systems.

2. The radiators will remain warm for a considerable time after the heat-generating fire has gone out; thus the system is a reservoir for storing heat.

Disadvantages include:
1. There is a danger of freezing when not in use.
2. More or larger heating surfaces (radiators) are required than with steam systems.

There are actually two types of hot-water systems, depending on how heated water flows: thermal and forced circulation.

The word “thermal” refers to systems that depend on the difference in the weight of water per unit of volume at different temperatures to form the motive force that results in circulation. This type is rightfully called a gravity hot-water system.

The difference in the density or weight of hot and cold water causes natural circulation throughout the system. This circulation is necessary in order for the water to carry the heat from the boiler to the radiators.

In the forced-circulation type of hot-water system a pump is used to force the water through the piping.
Thus, the flow is entirely independent of the difference in water temperature.

Gravity hot-water systems are used mainly in small buildings such as homes and small business places.

Advantages of this type of system include:
1. Ease of operation.
2. Low installation costs.
3. Low maintenance costs.

Disadvantages include:
1. Possible water damage in case of leaks.
2. Rapid temperature changes result in a slow response from the system.
3. Properly balancing the flow of water to radiators is sometimes difficult.
4. Nonattendance when the heat-generating unit fails may result in a freeze-up.
5. Flow depends on gravity, and as a result larger pipe sizes are required for good operation.

Forced-hot-water heating systems require a pump that forces the water through the piping system. Limitations of flow, dependent on water-temperature differences, do not exist in this type of system. It may be of either the one- or two-pipe variety.

In two-pipe systems, either direct or reversed returns and up-feed or down-feed mains may be used. The path of the water from the boiler into and through the radiator and back again to the boiler is almost the same length for each of the radiators in the system.

It is common to use one-pipe forced-circulation systems for small and medium-sized buildings when hot water is used as the heating medium.

Advantages of forced circulation include:
1. There is rapid response to temperature changes.
2. Smaller pipe sizes may be installed.
3. Room temperatures can be automatically controlled if either the burner or the flow of water is thermostatically controlled.
4. There is less danger of water freeze and damage.

Disadvantages include:
1. All high points must be vented.

Radiant-panel heating is the method of heating a room by raising the temperature of one or more of its interior surfaces (floor, walls, or ceiling) instead of heating the air.

One of the most common methods of achieving radiant heating is by the installation of specially constructed pipe coils or lengths of tubing in the floor, walls, or ceiling.

These coils generally consist of smallbore wrought-iron, steel, brass, or copper pipe, usually with an inside diameter of 3/8 to 1 inch. Every consideration should be given to complete building insulation when radiant panel heating is used.

Air venting is necessary to the proper control of any panel hot-water heating system. Collection of air in either the circuit pipe or pipe coils results in a shortage of heat.

Because of the continuous slope of the coil connections, it may be sufficient to install automatic vents at the top of the return riser only, omitting such vents on the supply riser.


The first step is to develop a consistent plan of control for heat-using equipment throughout the facility. Decide whether to control heating operation at the plant, at the end-use equipment, or in some combination of these two.

Each approach has advantages and disadvantages:

• minimizing steam consumption by turning off the end-use equipment. You can install shutdown controls on each item of end-use equipment. From an overall efficiency standpoint, this method is good because each piece of end-use equipment can shut down in accordance with its individual heating requirements.

The major disadvantage of this method is the expense and maintenance of having separate controls at each item of end-use equipment. The boiler senses the disappearance of heating load when the end-use equipment shuts off.

Boiler output falls as the end-use equipment shuts down, and no separate boiler plant controls may be required. However, this method does not eliminate the energy consumed to keep the boiler system warmed up, to replace distribution system losses, and to operate boiler plant auxiliary equipment.  To avoid these losses, you need additional controls to shut down the boiler plant itself.

• minimizing steam consumption by shutting down the boiler plant. At the other extreme, you may shut down the boiler system, which will shut down all the equipment served by the system. This method is much less expensive than installing individual shutdown controls on the end-use equipment.

This method wastes some energy unless all enduse equipment operates on the same schedule. For example, if the boiler plant serves radiators, operating a boiler to provide heat to one room keeps every radiator in the facility working.

Another disadvantage of this method is that it does not stop the energy consumption of non-heating components of end-use equipment, such as the fans in fan-coil units.

• minimizing steam consumption when end-use equipment operates on a variety of schedules. In situations where some end-use equipment operates on a shorter schedule than the boiler plant, you can provide separate shutdown controls just for the equipment that operates on shorter schedules.

For example, you might install such controls for the administrative spaces in a hotel, while the guest rooms have heating available continuously or seasonally.

• minimizing steam consumption using different control criteria. You can use different methods of shutdown for the boiler plant and the end-use equipment. For example, you might shut down enduse equipment with timeclocks and shut down the boiler plant with an outside air temperature sensor.

There may be many ways to distribute shutdown control of heating within a facility. Your objective is to make the boiler plant respond efficiently to the range of conditions that may occur, including the operating schedule of heating equipment, outside temperature, etc., and to satisfy the constraints of cost, reliability, and maintenance requirements.


Many of the refrigeration appliances used in the home are “frost-free.” The frost-free appliance could more accurately be termed “automatic defrost.” The brain of the frost-free appliance is the defrost timer.

The job of this timer is to disconnect the compressor circuit and connect a resistive heating element located near the evaporator at regular time intervals. The defrost heater is thermostatically controlled and is used to melt any frost formation on the evaporator.

The defrost heater is permitted to operate for some length of time before the timer disconnects it from the circuit and permits the compressor to operate again.


The defrost timer is operated by a single-phase synchronous motor like those used to operate electric wall clocks, Figure 28–1. The contacts are operated by a cam that is gear driven by the clock motor. A schematic drawing of the timer is shown in Figure 28–2.

Notice that terminal 1 is connected to the common of a single-pole double-throw switch. Terminals 2 and 4 are connected to stationary contacts of the switch. In the normal operating mode, the switch makes connection between contacts 1 and 4.

When the defrost cycle is activated, the contact will change position and make connection between terminals 1 and 2. Terminal 3 is connected to one lead of the motor. The other motor lead is brought outside the case.

This permits the timer to be connected in one of two ways, which are:
1. The continuous run timer.
2. The cumulative compressor run timer.

It should be noted that the schematic drawing can be a little misleading. In the schematic shown, the timer contact can only make connection between terminals 1 and 4, or terminals 1 and 2. In actual practice, a common problem with this timer is that the movable contact becomes stuck between terminals 4 and 2. This causes the compressor and defrost heater to operate at the same time.

The schematic for the continuous run timer is shown in Figure 28–3. Notice in this circuit that the pigtail lead of the motor has been connected to terminal 1, and that terminal 1 is connected directly to the power source.

Terminal 3 is connected directly to the neutral. This places the timer motor directly across the power source, which permits the motor to operate on a continuous basis. Figure 28–4 shows the operation of the timer in the compressor run cycle.

Notice there is a current path through the timer motor and a path through the timer contact to the thermostat. This permits power to be applied to the compressor and evaporator motor when the thermostat closes.

Figure 28–5 shows the operation of the circuit when the timer changes the contact and activates the defrost cycle. Notice there is still a complete circuit through the timer motor. When the timer contact changes position, the circuit to the thermostat is open and the circuit to the defrost heater is closed.

The heater can now melt any frost accumulation on the evaporator. At the end of the defrost cycle, the timer contact returns to its normal position and permits the compressor to be operated by the thermostat.

The cumulative compressor run timer circuit gets its name from the fact that the timer motor is permitted to operate only when the compressor is in operation and the thermostat is closed. The schematic for this circuit is shown in Figure 28–6. Notice that the pigtail lead of the clock motor has been connected to terminal 2 instead of terminal 1. Figure 28–7 shows the current path during compressor operation.

The timer contact is making connection between terminals 1 and 4. This permits power to be applied to the thermostat. When the thermostat contact closes, current is permitted to fl ow through the compressor motor, the evaporator fan motor, and the defrost timer motor. In this circuit, the timer motor is connected in series with the defrost heater.

The operation of the timer motor is not affected, however, because the impedance of the timer motor is much greater than the resistance of the heater. For this reason almost all the voltage of this circuit is dropped across the timer motor.

The impedance of the timer motor also limits the current fl ow through the defrost heater to such an extent that it does not become warm. Figure 28–8 shows the current path through the circuit when the defrost cycle has been activated.

Notice in this circuit that the defrost heater is connected directly to the power line. This permits the heater to operate at full power and melt any frost accumulation on the evaporator. There is also a current path through the timer motor and run winding of the compressor motor.

In this circuit, the timer motor is connected in series with the run winding of the compressor. As before, the impedance of the timer motor is much greater than the impedance of the run winding of the compressor.

This permits almost all the voltage in this circuit to be applied across the timer motor. At the end of the defrost cycle, the timer contact returns to its normal position and the compressor is permitted to operate.


Btuh = cfm × 1.08 × TD


Btuh = Btu per hour (sensible heat) also written Btuhs
cfm = volume of airflow, cubic feet per minute
1.08 = constant:
60 min/hr × 0.075 lb/cf (density of air) × 0.24 Btu/lb°F (specific heat of air)
TD = dry bulb temperature difference of the air entering and leaving a coil EAT – LAT or LAT – EAT (Entering Air Temperature and Leaving Air Temperature).

TD (temperature difference) is often written as delta T or ΔT. In applications where cfm to the conditioned space needs to be calculated, the TD is the difference between the supply air temperature dry bulb and the room temperature dry bulb.

To find volume: cfm = Btuh ÷ (1.08 × TD)
To find temperature difference: TD = Btuh ÷ (1.08 × cfm)

Btuh = cfm × 4.5 × Δh

Btuh = Btu per hour (total heat) also written Btuht
cfm = volume of airflow, cubic feet per minute
4.5 = constant: 60 min/hr × 0.075 lb/cf
Δh = Btu/lb change in total heat content (enthalpy) of the air

The total heat content of the air is determined from a wet bulb and dry bulb temperature, and a psychrometric chart. For example, the air temperature leaving a typical commercial cooling coil might be 55°Fdb and 54°Fwb.

Plotting these temperatures on a psychrometric chart gives an enthalpy (total heat content) of the air at 22.627 Btu/lb.

To find volume: cfm = Btuh ÷ (4.5 × Δh)
To find enthalpy difference: Δh = Btuh ÷ (4.5 × cfm)

Btuh = gpm × 500 × TD

Btuh = Btu per hour
gpm = volume of water flow, gallons per minute
500 = constant:
60 min/hr × 8.33 lb/gal (weight of water) × 1 Btu/lb°F (specific heat of water).
TD = temperature difference of the water entering and leaving a coil EWT – LWT or LWT – EWT (Entering Water Temperature and Leaving Water Temperature).

TD can also be expressed as ΔT.

To find volume: gpm = Btuh ÷ (500 × TD)
To find temperature difference: TD = Btuh ÷ (500 × gpm)

The boiling point or boiling temperature of water can be changed by changing the pressure on the water. In the case of water in a heating system if the pressure is to be changed, the water must be in a boiler and then the water can be boiled at a temperature of 212°F or 250°F or any other temperature.

The only requirement is that the pressure in the boiler is changed to the one corresponding to the desired boiling point. If the pressure is 14.7 psia the boiling temperature is 212°F. A common low pressure HVAC steam heating system, for instance, operates at 15 pounds per square inch gage pressure (psig), which is an absolute pressure of 30 psia and a temperature of 250°F.

Sea Level Barometric Pressure is 14.7 pounds per square inch absolute (psia)
Sea Level Barometric Pressure is 0 pounds per square inch gage (psig) psia = psig + 14.7 pounds per square inch absolute = pounds per square inch gage + 14.7

As a hint for calculations psia can stand for “psi add 14.7” to gage pressure.

Sea Level Barometric Pressure is 29.92 inches of mercury (“Hg)

Sometimes sea level barometric pressure, for estimation purposes only, is rounded off to 15 psia and 30 inches of mercury.

1 psi equals 2.04” Hg (sometimes, for estimation purposes only, rounded to
1 psi = 2” Hg)
1” Hg equals 0.49 psi (sometimes, for estimation purposes only, rounded to
1” Hg = 0.5 psi)


Sensible Heat
People, lights, motors, heating equipment and outdoor air are examples of substances that give off sensible heat. A seated person in an office, for instance, gives off approximately 225 Btuh of sensible heat into the conditioned space.

Enthalpy units of sensible heat are in Btu/lb°F. The change in the sensible heat level as measured with an ordinary thermometer is sensible temperature.

Sensible temperature is measured in degrees Fahrenheit (°F) and it is indicated as dry bulb (db) temperature. Sensible temperatures are written °Fdb. For example, 55°Fdb.

Latent Heat
The definition of latent or hidden heat is: heat that is known to be added to or removed from a substance but no temperature change is recorded.” The heat released by boiling water is an example of latent heat.

Once water is brought to the boiling point, adding more heat only makes it boil faster; it does not raise the temperature of the water. The level of latent heat is measured in degrees Fahrenheit (°F) and it is indicated as dew point (dp) temperature (for example, 60°Fdp).

Enthalpy is in Btu/lb°F. People, water equipment, and outdoor air are examples of substances that give off latent heat. A seated person in an office gives off approximately 225 Btuh of latent heat into the conditioned space.

Total Heat
Total heat is the sum of sensible heat and latent heat. It is measured in degrees Fahrenheit (°F) and it is indicated as wet bulb (wb) temperature. For example, 54°Fwb. Total heat level is measured with an ordinary thermometer; however, the thermometer tip is covered with a sock made from a water-absorbing material.

The sock is wetted with distilled water and the thermometer is placed in the air stream in the air handling unit or duct. As air moves across the wet sock, some of the water is evaporated.

Evaporation cools the remaining water in the sock and cools the thermometer. The decrease in the temperature of the wet bulb thermometer is called “wet bulb depression.” For room wet bulb temperature the wet bulb thermometer is typically in an instrument such as a sling- or power-psychrometer along with a dry bulb thermometer.

Enthalpy is in Btu/lb°F. A seated person gives off approximately 450 Btuh of total heat (225 Btuh sensible heat plus 225 Btuh latent heat).


The three types of heat transfer are conduction, convection and radiation.

Conduction heat transfer is heat energy traveling from one molecule to another. A heat exchanger in an HVAC system or home furnace uses conduction to transfer heat.

Your hand touching a cold wall is an example of heat transfer by conduction from your hand to the wall. However, heat does not conduct at the same rate in all materials. For example, all HVAC copper conducts at a different rate than iron or aluminum, etc.

Heat transfer by convection is when some substance that is readily movable such as air, water, steam, or refrigerant moves heat from one location to another. Compare the words “convection” (the action of conveying) and “convey” (to take or carry from one place to another).

An HVAC system uses convection in the form of air, water, steam and refrigerants in ducts and piping to convey heat energy to various parts of the system. When air is heated, it rises; this is heat transfer by “natural” convection.

“Forced” convection is when a fan or pump is used to convey heat in fluids such as air and water. For example, many large buildings have a central heating plant where water is heated and pumped throughout the building to the final heated space. Fans then move heated air into the conditioned space.

Heat transferred by radiation travels through space without heating the space. Radiation or radiant heat does not transfer the actual temperature value. The first solid object that the heat rays encounter absorbs the radiant heat.

A portable electric space heater that glows red-hot is an example of heat transfer by radiation. As the electric heater coil glows red-hot it radiates heat into the room. The space heater does not heat the air (the space)—instead it heats the solid objects that come into contact with the heat rays.

Any heater that glows has the same effect. However, radiant heat diminishes by the square of the distance traveled; therefore, space heaters must be placed accordingly. Another good example of radiant heat is the sun; the sun heats the earth, but not the air around the earth.

The sun is also a good example of diminishing heat. The earth does not experience the total heat of the sun because the sun is some 93 million miles from the earth.


An HVAC system is designed to provide conditioned air to the occupied space, also called the “conditioned” space, to maintain the desired level of comfort. To begin to explain how an HVAC system works let’s set some design conditions.

First, we will need to determine the ventilation requirements. We know that in the respiratory process the contaminate carbon dioxide is exhaled.

In buildings with a large number of people, carbon dioxide and other contaminants such as smoke from cigarettes and odors from machinery must be continuously removed or unhealthy conditions will result.

The process of supplying “fresh” air (now most often called outside air) to buildings in the proper amount to offset the contaminants produced by people and equipment is known as “ventilation.”

Not only does the outside air that is introduced into the conditioned space offset the contaminants in the air but because of its larger ion content, outside air has a “fresh air” smell in contrast to the “stale” or “dead air” smell noticed in overcrowded rooms that do not have proper ventilation.

In many instances, local building codes stipulate the amount of ventilation required for buildings and work environments. Let’s say that an HVAC system supplies air to a suite in an office complex and the code requirement is for 20 cubic feet per minute (abbreviated cfm) of outside air for each building occupant.

If the suite is designed for 10 people then the total outside air requirement for the people in the suite is 200 cfm. An additional amount of outside ventilation air may be required if there are exhaust hoods such as laboratory fume hoods, kitchen hoods, and spray hoods or there are other areas where the air needs to be exhausted or vented to the outside such as bathrooms and restrooms.

This ventilation air is called make-up air. If more air is brought into a room (conditioned space) than is taken out of a room the room becomes positively pressurized. If more air is taken out of a room than is brought into a room the room becomes negatively pressurized.

These air pressures, whether positive or negative are measured in inches of water gage (in wg) or inches of water column (in wc).

Commercial office buildings are typically positively pressurized to about 0.03 inches of water pressure. This is done to keep outside air from “infiltrating” into the conditioned space through openings in or around doorways, windows, etc.

Other areas that need positive pressurization are hospital operating rooms and clean rooms. Examples of negative rooms are commercial kitchens, hospital intensive care units (ICU) and fume hood laboratories.


The objectives of HVAC systems are to provide an acceptable level of occupancy comfort and process function, to maintain good indoor air quality (IAQ), and to keep system costs and energy requirements to a minimum.

Commercial heating, ventilating, and air conditioning (HVAC) systems provide the people working inside buildings with “conditioned air” so that they will have a comfortable and safe work environment.

People respond to their work environment in many ways and many factors affect their health, attitude and productivity. “Air quality” and the “condition of the air” are two very important factors.

By “conditioned air” and “good air quality,” we mean that air should be clean and odor-free and the temperature, humidity, and movement of the air will be within certain acceptable comfort ranges.

ASHRAE, the American Society of Heating, Refrigerating and Air Conditioning Engineers, has established standards which outline indoor comfort conditions that are thermally acceptable to 80% or more of a commercial building’s occupants.

Generally, these comfort conditions, sometimes called the “comfort zone,” are between 68°F and 75°F for winter and 73°F to 78°F during the summer. Both these ranges are for room air at approximately 50% relative humidity and moving at a slow speed (velocity) of 30 feet per minute or less.

An HVAC system is simply a group of components working together to move heat to where it is wanted (the conditioned space), or remove heat from where it is not wanted (the conditioned space), and put it where it is unobjectionable (the outside air).

The components in a typical roof-mounted package HVAC system below are:

1. An indoor fan (blower) to circulate the supply and return air.

2. Supply air ductwork in which the air flows from the fan to the room.

3. Air devices such as supply air outlets and return air inlets.

4. Return air ductwork in which the air flows back from the room to the mixed air chamber (plenum).

5. A mixed air chamber to receive the return air and mix it with outside air.

6. An outside air device such as a louver, opening or duct to allow for the entrance of outside air into the mixed air plenum.

7. A filter section to remove dirt and dust particles from the air.

8. Heat exchangers such as a refrigerant evaporator and condenser coil for cooling, and a furnace for heating.

9. A compressor to compress the refrigerant vapor and pump the refrigerant around the refrigeration system.

10. An outdoor fan (blower) to circulate outside air across the condenser coil.

11. Controls to start, stop or regulate the flow of air, refrigerant, and electricity.


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Iron-base alloys containing at least 12 percent chromium are called stainless steels. The most important characteristic of these steels is their resistance to many, but not all, corrosive conditions.

The four types available are the ferritic chromium steels, the austenitic chromium-nickel steels, and the martensitic and precipitation-hardenable stainless steels.

The ferritic chromium steels have a chromium content ranging from 12 to 27 percent.

Their corrosion resistance is a function of the chromium content, so that alloys containing less than 12 percent still exhibit some corrosion resistance, although they may rust. The quench-hardenability of these steels is a function of both the chromium and the carbon content.

The very high carbon steels have good quench hardenability up to about 18 percent chromium, while in the lower carbon ranges it ceases at about 13 percent. If a little nickel is added, these steels retain some degree of hardenability up to 20 percent chromium.

If the chromium content exceeds 18 percent, they become difficult to weld, and at the very high chromium levels the hardness becomes so great that very careful attention must be paid to the service conditions. Since chromium is expensive, the designer will choose the lowest chromium content consistent with the corrosive conditions.

The chromium-nickel stainless steels retain the austenitic structure at room temperature; hence, they are not amenable to heat treatment. The strength of these steels can be greatly improved by cold working.

They are not magnetic unless cold-worked. Their work hardenability properties also cause them to be difficult to machine.

All the chromium-nickel steels may be welded. They have greater corrosion-resistant properties than the plain chromium steels. When more chromium is added for greater corrosion resistance, more nickel must also be added if the austenitic properties are to be retained.


In many operations, radiation is the dominant heat transfer mode. The heated material's geometry may be simple (such as a sheet) or complex and/or discontinuous. It may be stationary (batch-processed) or moving.

Radiant heating can be supplied directly via combustion or indirectly with electric or gas-heated elements. In general, the treated material and the surrounding gaseous environment are both radiatively participating. If the material is semitransparent to thermal radiation, it may be cold (negligible volumetric emission) or may be at a high enough temperature so that significant volumetric emission occurs.

Processing with inert gases to prevent surface oxidation or combustion is common, so convection and conduction can occur in conjunction with radiative transfer, and these modes are coupled to the radiative exchange through heat transfer interactions at various solid surfaces. For other processes (such as chemical vapor deposition), specific gases are introduced at selected locations so that, even though the heat transfer may be radiatively dominated, understanding the advective transport of important chemical species is of equal or primary concern.

A review of technologies in which heating is induced primarily by radiation is available. Material temperatures induced by radiation heat transfer depend upon:

1. The spectral-directional absorption, reflection, and transmission characteristics of the load
2. The spectral-directional emission characteristics of the radiation source (or sink)
3. The spectral radiation characteristics of the medium separating the source and load
4. The geometrical configuration of the load relative to the source
5. The thermophysical properties of the load
6. Associated convection and/or conduction heat transfer processes

Items 1-4 determine the degree to which the radiation source and material load are thermally coupled and can be addressed with the heat transfer analysis. Items 5 and 6 may be quantified with an analysis, which takes into account the multimode heat transfer effects discussed elsewhere in this handbook.

Because of the nonlinear nature of radiative heat transfer, few correlations exist that can be applied to relevant materials processing situations.


Mass production adopted in the earlier part of the 20th century was based on the principles of interchangeable parts, specialized machines, and division of labor. The focus was primarily on improving productivity through process innovation.

The primary objective was to reduce cost and thus cause an increase in demand. Most large companies ignored niche markets and customer desires, leaving them to the small companies. This manufacturing management paradigm started to loosen its grip on most consumer industries around the 1960s and 1970s in response to developing global competition pressures.

A paradigm shift toward customization was full blown by the late 1980s in several industries, naturally, at different levels. The objective was set as ‘‘variety and customization through flexibility and quick responsiveness.’’

The key features of today’s marketplace are (1) fragmented demand (the niches are the market) (2) low cost and high quality (customers are demanding high-quality products, not in direct relation to the cost of the product), (3) short product development cycles, and (4) short product cycles.

The result is less demand for a specific product but increased demand for the overall product family of the company, whose strategy is to develop, produce, market, and deliver affordable goods with enough variety and customization that almost everyone purchases their own desired product.

The primary (fundamental) prerequisite to achieving mass customization can be noted as having customizable products with modularized components. Examples of customizable (reconfigurable) products include Braun’s flex-control electric razor, which is self-adjusting to the user’s facial profile, Reebok’s Pump shoes that can be (air) pumped for better fit (similar to customizable ‘‘removable’’ casts for foot fractures), and finally Dell’s personal computers, customized by the buyer and assembled specifically for them.

In this context, standardization for customization is a competitive tool for companies marketing several related products, such as Black & Decker’s line of power tools, which use a common set of standardized subassemblies (clusters, modules, etc.).

The primary steps for the design of a mass customizable product are
1. Identifying customer needs: This stage is similar to any product (concept) design stage with the exception of identifying potential personal differences in requirements for a common overall functional requirement for the product.

2. Develop concepts: Concepts (alternatives) should be developed and compared with a special emphasis for allowing modularity in final engineering design. (QFD and Pugh’s methods should be utilized.)

3. Modularization of chosen concept: The chosen design concept should be evaluated and iteratively modified with the objective of modularization (i.e., mass customization) and fit within the larger family of products, with which the proposed design will share modules.


The U.S.A. has always been the leader in product innovation but not very adept at converting basic R&D into viable commercial products. An exception is software design and marketing, where the U.S.A. maintains three quarters of the world’s software market with an excellent information network.

The 1980s and early 1990s were typified in U.S.A. by significant downsizing, where companies tried to achieve lean manufacturing machines capable of producing products of superior quality (as good as Japanese).

Reengineering became a key word for change in the way managers thought about their manufacturing processes, though the results were far from revolutionary. Often external consultants were brought in to propose management strategies that were not followed up after their departure.

The late 1990s, however, saw a dramatic shift in U.S. productivity, building on innovation in the philosophy of product design. This combined with the economic (mostly financial) problems that came about in Japan resulted in an unprecedented manufacturing boom in the U.S.A. Hewlett- Packard (HP) was a typical U.S. company capturing a large share of the world’s color ink-jet printers and scanners.

HP went from no printer manufacturing in 1984 to nearly $8 billion in sales in the mid-1990s. A primary factor in this success was HP’s strategic flexibility.

It is important, however, to note that although the U.S.A. currently has a quarter of the world gross domestic product (GDP), the European Economic Community (EEC) is now the world’s largest market, with the U.S.A. in second place. U.S. manufacturing companies are partially responsible for this drop, primarily because of their short-term vision and concentration on domestic markets.

Despite the economic good times, most still continue to emphasize the objective of quarterly profits by maximizing the utilization of their current capacity (technological and workforce). The following selective objectives are representative of the current (not-so-competitive) state of the U.S. manufacturing industry:

Customer responsiveness: Deliver what is ordered, in contrast to working with customers to provide solutions that fit their current product’s lifecycle requirements and furthermore anticipate their future requirements.

Manufacturing process responsiveness: Dependence on hard tooling, fixed capacity and processes that lag product needs, in contrast to having a reconfigurable and scalable manufacturing plant that implements cost effective processes that lead product needs and can react to rapidly changing customer requirements.

One must not confuse automated machines with truly autonomous systems that have closed-loop processing capability for self-diagnosis and error recovery. Variable capacity must be seen as a strategic weapon to be used for competitiveness and not something to be simply solved by outsourcing or leasing equipment based on the latest received orders.

Human resource responsiveness: Encouragement of company loyalty in exchange for lifetime employment promise, in contrast to hiring of ‘‘knowledge individuals’’ who plan their own careers and expect to be supported in their continuing education efforts.

The current U.S. workforce is in a high state of flux, where a company’s equity is constantly evaluated by the knowledge and skills of its employees as opposed to only by the value of their capital. In the future, companies will be forced invest not only in capacity and technology but also in training that will increase the value of their employees, without a fear of possible greater turnover.

Global market responsiveness: Dependence on local companies run by locals but that are led by business strategies developed in the U.S.A., in contrast to operating globally (including distributed R&D efforts) and aiming to achieve high world market share.  Globalization requires understanding of local markets and cultures for rapid responsiveness with no particular loyalty to any domestic politics.


A butterfly valve is a quarter-turn valve that controls flow by means of a circular disk pivoting on its central axis.

● For fully open or fully closed service
● For throttling service
● For frequent operation
● Where positive shutoff is required for gases or liquids
● Where minimum amount of fluid trapped in line is allowed
● For low pressure drop across valve

● General service, cryogenic service, high-temperature service, liquids, gases, slurries, liquids with suspended solids

● Compact, lightweight, low-cost
● Low maintenance
● Minimum number of moving parts
● No pockets
● High capacity
● Straight-through flow
● Self-cleaning

● High torque for actuation
● Limited pressure-drop capability
● Prone to cavitation

● Construction: wafer, lug wafer, flanged, screwed, fully lined
● Style: single offset, double offset, triple offset

● Body: bronze, iron, ductile iron, carbon steel, low-alloy steel, stainless steel, Monel, nickel alloys, PVC plastic, plastic/elastomer lined
● Disk: all metals, elastomer coatings such as TFE, Kynar, Buna-N, neoprene, Hypalon
● Seat: elastomeric, plastic, nickel plated, stellite, tungsten carbide, ceramic

Special Installation and Maintenance Instructions
● May be operated by lever, handwheel, or chainwheel.
● Allow sufficient space for operation of handle if lever-operated.
● Valves should remain in closed position during all handling and installation operations.

Ordering Specifications
● Type of construction
● Style
● Type of seat
● Body material
● Disk material
● Seat material
● Type of actuation
● Operating pressure
● Operating temperature


A ball valve is a quarter-turn valve in which a drilled ball rotates between seats, allowing straight-through flow in the open position and shutting off flow when the ball is rotated 90° and blocks the flow passage.

● For on-off, nonthrottling service
● Throttling service with special trim
● Where quick opening is required
● Where minimum resistance to flow is needed

● General service, high temperatures, cryogenic service, slurries

● Low cost
● High capacity
● Bidirectional shutoff
● Straight-through pattern
● Low leakage
● Self-cleaning
● Low maintenance
● No lubrication requirement
● Compact
● Tight sealing with low torque
● Good throttling characteristics with special trim

● Poor throttling characteristics with standard ball designs
● Susceptible to seal wear with soft seats
● Prone to cavitation with standard ball designs

● Construction: top entry, split body, end entry, or welded
● Style: floating ball, trunnion mounted, rising stem, or throttling
● Ports: three-way, venturi, full ported, reduced port, or venturi

● Body: bronze, iron, ductile iron, aluminum, carbon steel, low-alloy steel, stainless steel, Monel, nickel alloys, titanium, tantalum, zirconium, polypropylene, PVC plastics
● Seat: elastomeric, plastic, nickel plated, stellite, tungsten carbide, or ceramic

Special Installation and Maintenance Instructions
● Allow sufficient space for operation of handle.

Ordering Specifications
● Operating temperature
● Operating pressure
● Type of construction
● Style

● Type of port in ball
● Body material
● Seat material
● Type of actuation


A globe valve is a multiturn valve in which closure is achieved by means of a disk or plug that seals or stops the fluid on a seat generally parallel to the line flow.

● For throttling service or flow regulation
● For frequent operations
● For positive shutoff of gases or air
● Where some resistance to flow is acceptable

● General service, liquids, vapors, gases, corrosives, slurries

● Efficient throttling with minimum wire drawing or disk or seat erosion
● Short disk travel and fewer turns to operate, saving time and wear on stem and bonnet
● Accurate flow control
● Available in multiports

● High pressure drop
● Relatively high cost

● Standard, Y pattern, angle, three-way

● Body: bronze, all iron, cast iron, forged steel, Monel, cast steel, stainless steel, plastics
● Trim: various

Special Installation and Maintenance Instructions
● Install so pressure is under disk, except in high-temperature steam service.
● Lubricate on strict schedule.
● Flush foreign matter off seat by opening valve slightly.
● Correct packing leaks immediately by tightening the packing nut.

Ordering Specifications
● Type of end connection
● Type of disk
● Type of seat
● Type of stem assembly
● Type of bonnet assembly
● Pressure rating
● Temperature rating


A plug valve is a quarter-turn valve that controls flow by means of a cylindrical or tapered plug with a hole through the center, which can be positioned from open to closed by a 90° turn.

● For fully open or fully closed service
● For frequent operation
● For low pressure drop across the valve
● For minimum resistance to flow
● For minimum amount of fluid trapped in line

● General service, blow-down service, liquids, gases, steam,
corrosives, abrasive media, slurries

● High capacity
● Low cost
● Tight shutoff
● Quick operation

● High torque for actuation
● Seat wear
● Cavitation at low pressure drop

● Lubricated, nonlubricated, multiport

● Bronze, iron, ductile iron, carbon steel, low-alloy steel, stainless steel, Monel, nickel alloys,
PVC plastic, plastic-lined

Special Installation and Maintenance Instructions
● Allow space for operation of handle on wrench-operated valves.
● For lubricated plug valves, lubricate before putting into service.
● For lubricated plug valves, lubricate on regular schedule.

Ordering Specifications
● Body material
● Plug material
● Temperature rating
● Pressure rating
● Port arrangement, if multiport valve
● Lubricant, if lubricated valve


A gate valve is a multiturn valve in which the port is closed by a flat-faced vertical disk that slides at right angles over the seat.

● For fully open or fully closed, nonthrottling service
● For infrequent operation
● For minimum resistance to flow
● For minimum amounts of fluid trapped in line

● General service, oil, gas, air, slurries, heavy liquids, steam,
noncondensing gases and liquids, corrosive liquids

● High capacity
● Tight shutoff
● Low cost
● Simple design and operation
● Little resistance to flow

● Poor flow control
● High operating force
● Cavitates at low pressure drop
● Must be kept in fully open or fully closed position
● Throttling position will erode seat and disk
● Body cavity pressure lock on certain designs

● Gate: solid wedge, flexible wedge, split wedge, double disk, slab, expanding slab, through
● Stem: standard, packing, outside screw and yoke

● Body: bronze, iron, ductile iron, carbon steel, low-alloy steel, stainless steel, Monel, nickel
alloys, PVC plastic
● Trim: various

Special Installation and Maintenance Instructions
● Lubricate on regular schedule.
● Correct packing leaks immediately.
● Always cool system when closing down a hot line and checking closed valves.
● Never force valves closed with wrench or pry.
● Open valves slowly to prevent hydraulic shock in line.
● Close valves slowly to help flush trapped sediment and dirt.

Ordering Specifications
● Type of end connections
● Type of wedge or gate
● Type of seat
● Type of stem assembly
● Type of bonnet assembly
● Type of stem packing
● Pressure rating: operating and design
● Temperature rating: operating and design


With every method of welding, safety is of paramount consideration, but each type has precautions that apply to that type of equipment in particular. In all forms of electric welding, including arc welding, high-amperage electrical current is the primary hazard.

All of your cables, plugs and leads should be inspected regularly for any signs of defects. Even dirt or paint overspray on connections can cause arcing and poor welds. Water, of course, is a good conductor of electricity, and therefore should be avoided in the work area.

Your clothing, equipment and especially the floor must be kept dry to avoid the possibility of electrical shock. Rubber-soled shoes are recommended, but athletic shoes (non-leather) are not. Most experts will tell you not to wear metal jewelry such as watchbands, rings, bracelets, necklaces or belt buckles when welding.

If electric welder power comes into contact with metal articles you are wearing, they can become instantly hot to the point of melting, or can cause electric shock. Of the electric welding methods, arc welding requires the most protection of your face and body during welding.

The intensity of the arc produces strong UV and infrared radiation. Any skin exposed during the welding process can become burned, in severity ranging from mild sunburn to serious burns, with the symptoms not appearing until eight hours after the exposure.

Leave the top button unbuttoned on your shift and you'll have a nasty V-shaped burn on your neck after only a short while arc-welding. Likewise, wear fire-resistant, long-sleeved shirts, and keep your sleeves rolled down at all times. Keep these shirts just for welding, and tear off the pockets if they have any, or keep them empty and buttoned.

An experienced weldor friend of ours was recently burned painfully when welding overhead with just a shop shirt on — a hot bead of spatter went right into his shirt pocket and burned into his chest. Without the pockets, there's a chance the bead will roll off onto the floor rather than stay in one spot on your shirt. For this same reason, your pants should be kept uncuffed, and never tucked into your boots.

If you are going to be doing arc-welding often, we'd recommend you invest in some leather safety clothing, like jackets, vests or pull-on sleeves that go over your regular shirt. Arc-welding is prone to more spattering than other types of welding, and these leather weldor's clothes are highly resistant to arc spatter.

Probably your most sensitive and fragile body parts exposed to welding dangers are your eyes. Even the tiniest bit of spatter in an unprotected eye can have truly long-lasting negative effects. Always wear a full coverage safety helmet when welding, preferably with a leather flap at the bottom- front that protects your neck area.

Especially when welding overhead, like underneath a vehicle, wear a cloth cap backwards ( bill to back) to cover your hair and the back of your neck. Your helmet should be equipped with the proper safety lens for the type of welding you are doing, or your eyes could receive overexposure of UV and infrared rays in a very short time.

Never observe anyone else doing arc-welding unless you are wearing proper eye protection, and make sure that when you are welding that there is no one observing you who could be hurt by watching, particularly children. Watching too much arc will not show immediate effects, but later the affected eyes will be sore, and with a sensation almost like having lots of sand in your eyes.

If you do not yet have your own welder, but want to watch someone else work, get your own helmet to observe through. If you do have a welder, you may want to keep a spare helmet around in case someone wants to observe your welding prowess.

Your eyes can be permanently damaged by overexposure to arc rays, but they must also be protected when working around most shop equipment, such as grinders, mills, drills and sanders, all equipment that may be involved in your welding project. Keep several pair of good safety glasses around your shop, the kind that have protection all the way around the sides.

After arc-welding, you will also want to wear these safety glasses when chipping slag from your welds. The little fragments that break off are like glass. Always keep a very complete first-aid kit accessible in your work area in case of accidents.

A particular hazard with arc welding is the presence of fumes. When the electrode is consumed, the flux is vaporized, creating the shielding gasses that protect the weld from contamination during formation. Depending on the metal being welded, other gasses may be released as the metal is melted.

Most welding gasses are colorless, odorless, tasteless and inert, but this is not to imply that they are harmless. Any of the common welding gasses can displace oxygen, an  when you are breathing in air that contains less than 18% oxygen, you may experience dizziness, or even lose consciousness.

For this reason, arc welding, or any welding process, should be performed only where there is adequate ventilation. In the case of arc welding, there is less chance of the shielding gasses being blown away and causing a bad weld, so if you find yourself welding in one spot too long, or in a confined area, you can use a household fan somewhere in your work area to maintain air circulation.


The engine installation should be designed with maintenance requirements in mind. Serviceable components such as filters, fittings, and connections should be readily accessible to the engine operator. Routine engine maintenance will not be neglected if the operator has easy access to the engine.

Sufficient service space must be present on all sides of the engine to allow for removal of even the largest engine components. An overhead crane should be incorporated into the engine-room design to assist the mechanic-operator in removing heavy assemblies. Air-line connections will be necessary for air power tools, as will scaffolding for servicing the engine.

In engine-generator installations sufficient airflow must be provided into the engine room for ventilation and combustion air. It is also good practice to calculate the amount of heat transferred to the room air (i.e., engine and generator radiator heat, plus any other heat sources) to determine the temperature rise of the engine-room air.

In many cases it is necessary to increase the engine-room airflow to maintain reasonable operating temperatures.

The following are general rule of thumb values that assume the only radiating heat source in the engine room is the engine-generator set. For greater accuracy, an independent engineering study should be made covering the following points:

Cubic feet per minute of air required to limit air room temperature rise to 18°F (10°C), over normal ambient = 45 × kilowatt rating
Cubic feet per minute of combustion air required = 3.5 × kilowatt rating for diesel engines
Cubic feet per minute of combustion air required = 2.4 × kilowatt rating for gas engines

The total air requirement equals the sum of the cubic feet per minute of combustion air plus the cubic feet per minute required to limit the room temperature rise.

Other ventilation considerations are filters for sandy or dusty areas and louvered openings at both inlet and outlet air openings. The louvers can be motor-operated and temperaturecontrolled.

Cooling System
Potential problems with the engine cooling system can be avoided if the following considerations are incorporated into the design and installation of the cooling system. Excessive fittings, elbows, and connectors in the system piping will impede coolant flow. Use of fittings should be kept to a minimum.

An expansion-tank balance line should be incorporated into the cooling system, running to the suction side of the water pump.This balance line will maintain a net positive suction at the inlet of the pump and reduce the possibility of air locks and cavitational erosion.

All filters, fill points, and bleed cocks should be installed in an easy-to-reach location. Place the radiator away from a wall or any other obstruction that causes air recirculation or restricts airflow.These obstructions would also include any dirt source, vehicle travel path, air-conditioning units, or exhaust stacks and chimneys.

Remember that the radiator must bein a location where it can be cleaned and serviced. In installations where gaseous or LP fuels are used, keep all floor drains and service trenches out of the engine enclosure. LP and some constituents of natural gas can be heavier than air and will quickly flow into such low spots, creating a fire hazard.

Exhaust System
Plan the exhaust system so that the gases are expelled to a safe outside area, consistent with all local building and environmental codes. Do not discharge gases near windows, ventilation shafts, or air inlets.The exhaust outlet must be designed to keep out water, dust, and dirt. To avoid metal stress and turbocharger damage, support the exhaust system independently, keeping the weight of the piping off the engine.

Roller-type supports and flexible exhaust connections should be used to absorb thermal expansion. (If overhead cranes and hoists are used in the engine room, the exhaust-system piping may have to be supported from below.)

A condensate trap and drain should be designed into the exhaust system.The drain should be in an easy-to-reach location.

If the exhaust systems of more than one engine are to be connected to a common exhaust, the engine manufacturer should be consulted beforehand. Exhaust-system backflow (common in such connections) could result in an engine that is not running. Exhaust-system backpressure should be checked periodically. The backpressure must fall within the limits established by the engine manufacturer.

Air Induction
As with other engine systems, accessibility is the key to air-induction system maintenance.The filter element should be positioned so that it can be easily removed and replaced. The filter should always be positioned at the entrance to the air induction system; when combustion air is ducted in from outside the engine room, the filter should be at the opening to the piping.

All systems should be equipped with a restriction indicator to show excess pressure drop due to filter-element plugging.

Always locate the air inlet away from concentrations of dirt, exhaust stacks, fuel tanks, tank vents, and stockpiles of chemicals and industrial wastes. Try to duct air to the engine from a cool, dry, dirt-free area.The ambient temperature at the air inlet location should ideally be 60 to 90°F (15 to 32°C).

Run all air ducts away from engine exhaust pipes, heating lines, or other hot areas.Remember to allow clearance for overhead lifts and cranes when air ducts run through the engine room.

Air ducts should be thoroughly sealed to avoid drawing dirty air in behind the filter. The ducting must be checked periodically for leaks.

Air-system ducting should be seamless, welded-seam, or PVC piping. Flanged fittings with gaskets, not threaded connections, should be used between pipe sections to avoid restrictions in the system.

The best ducting system is as short and straight as possible, using long-radius bends and low-restriction fittings. Never allow air-duct restriction to exceed 2 in (50.8 mm) of water column. Air-ducting systems must be leak-free under vacuum conditions.

Engine Alignment
The alignment of the engine mount and the alignment between the engine and the driven equipment is critical to long engine life. Alignment should be checked periodically according to the manufacturer’s recommendations.
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