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Glossary of Terms

Terminology Description
Absolute Pressure The sum of the gauge and the atmospheric pressure. For instance, if the steam gauge on the boiler shows 50 pounds the absolute pressure of the steam is 64.7 pounds.
Actuator, Linear An electric or pnematic device that sets a valve, damper or linkage a straight line motion.
Actuator, Rotary An electric or pnematic device that sets a valve, damper or linkage a circular motion.
Actuator, Differential An electric or pnematic device that creates differential motion between two shafts.
Analog Input / Output A continuous or numerical value signal. Typically, provided in 4-20mA or 1-5 Vdc signals.
Annunciator A device that shows the source of events. Annunciators typically provide the date and time of plant alarms and events.
Assured Low Fire Cutoff Modulates the boiler to Low Fire before shutting the boiler down.
Atmospheric Pressure The pressure due to the weight of the atmosphere. It is expressed in pounds per sq. in. or inches of mercury column. One inch of mercury is equivalent to .49 lbs. per sq. in. atmospheric pressure at sea level is 14.7 lbs. per sq. in. or 30 in. mercury column.
Automatic Atomizer Post Purge This term refers to a Burner Management System (Flame Safeguard System) feature that enables the oil atomizer's oil tube to be purged with atomizing medium as part of a normal automatic shutdown. The shutdown sequence requires starting the igniter to ensure all unburned fuel is combusted. This feature requires an automated atomizing media valve and atomizer arrangement. This feature leaves the gun clean and ready for the next start request.
Blockware The PCC-III uses a "Blockware" configuration language. Functions (AIN, PID, LOALM, F(x).) are simply copied into a configuration, and then the control signals are "wired" from block to block.
Boiler Control System See Combustion Control
Boiler Efficiency The efficiency of a burner-boiler combination is simply the amount of useful energy leaving the system expressed as a percentage of the chemical energy in the fuel entering the system. Two methods:
  • Input/Output - difficult to obtain fuel flow, steam flow and steam quality measurements with degree of accuracy required. With 80% efficiency a 5% change can have a major impact
  • Efficiency "By Losses" method - Boiler/burner assumed to be a black box
Consider all energies leaving the system. Boiler efficiency ordinarily means the combined efficiency of boiler, furnace and burners and is arrived at by determining the ratio between the heat actually absorbed by the water and the total heat of the fuel released in the boiler furnace.
British Thermal Unit (BTU): The quantity of heat necessary to raise one lb. of water one degree Fahrenheit.
Burner Management System Or Flame Safeguard System, is a Control System that is dedicated to boiler safety, operator assistance in the starting and stopping of fuel preparation and burning equipment, and the prevention of mis-operation of and damage to fuel preparation and fuel burning equipment.
Building Automation System General term used to describe a system that is used to monitor and control individual room temperatures, lighting and/or security. These systems may include boiler room monitoring over a communication interface.
Calorific Or Heat Value The total heat, in BTU generated per lb. of liquid or solid fuel, or per cu. ft. of gas at the standard temperature of 60 degrees Fahrenheit and pressure of 30 in. mercury. Fuels containing hydrogen have two heat values, the gross (higher heating value), and net (lower heating value). The gross heat value is the heat produced by complete combustion when the water vapor formed is condensed and gives up its latent heat. The net heat value is the heat produced when the water formed by combustion escapes without being condensed.
Carbon Dioxide (CO 2 ) Carbon Dioxide is the product of complete combustion of Carbon and Oxygen.
Carbon Monoxide (CO) Produced from any source that burns fuel.. .causes chest pain in heart patients, headaches, reduced mental alertness.
Characterizer Curve, F(x) Function block that generates a block output based on a user generated Output vs. Input profile (i.e., y=f(x)).
Combustion Combustion, in its most basic sense, is the process whereby the hydrogen and carbon in fuels is combined with oxygen from the air to release heat. The chemical union of the combustible material with oxygen, with the resultant generation of light and heat. In the combustion of fuel, each particle of fuel, previously heated to kindling temperature, is brought into contact with the proper amount of oxygen causing the fuel to oxidize as completely as possible.
Combustion Air Composition By Volume
  • 20.95% Oxygen, O 2
  • 79.05% Nitrogen, N 2
By Weight
  • 23.14% Oxygen
  • 76.86% Nitrogen
Can be up to 9% H 2 O by volume in Summer Traces of Argon and CO 2
Combustion, Complete The complete oxidation of the fuel, regardless of whether it is accomplished with an excess amount of oxygen or air, or just the theoretical amount required for perfect combustion.
Combustion Control 1.       Maintain proper fuel to air ratio at all times 2.       Too little air causes unburned fuel losses 3.       Too much air causes excessive stack losses 4.       Improper fuel air ratio can be DANGEROUS 5.       Always keep fuel to air ratio SAFE 6.       Interface with burner management for: 1.       Purge 2.       Low fire light off 3.       Modulate fuel and air when safe to do so
Combustion Control, Jackshaft (single point positioning) Air control dampers and fuel flow metering valves are mechanically linked. One actuator simultaneously moves both fuel and air in order to maintain the desired system temperature or pressure. It is assumed that a given position will always provide a particular fuel flow and air flow.
Combustion Control, Parallel Positioning The fuel control valves are positioned by one actuator while the air control damper is positioned by a second actuator. For every particular firing rate, there is one and only one position for the fuel valves and a corresponding position for the air damper. For digital controllers, the fuel-air ratio is varied by creating a digital curve of fuel position vs. air position.
Combustion Control, Fully Metered Both the fuel flow and the air flow are accurately measured. For every particular firing rate, there is one and only one setpoint value for fuel flow, and there is only one corresponding setpoint for air flow. Generally, the air flow setpoint is generated as a characterized function of the fuel flow rate. Cross Limiting prevents the measured fuel flow from exceeding the value corresponding to the measured air flow. Separate closed loop controllers are used for both fuel and air flow control.
Combustion, Perfect The complete oxidation of the fuel, with the exact theoretical (stoichiometric) amount of oxygen (air) required.
Combustion Rate Or Heat Release The number of BTU per hour released per cu. ft. of combustion space or furnace volume.
  • RS-485
  • RS-232
Drum Level Control See Feedwater Control
Fine Particulate Matter (PM 2.5 ) Produced from any source that burns ash containing fuels. Also formed from reaction of other pollutants (acid rain, NO X , SO X , organics).. causes: i ncreased respiratory disease, lung damage, cancer, and premature death; reduced visibility; surface soiling.
Flame Safeguard System See Burner Management System
Flue Gas Monitoring, Safety High stack temperature switch indicates rising stack temperature. High stack temperature can be an indicator of low water level, excessive tube fouling or short circuiting. High stack oxygen switch indicates poor combustion conditions.
Heat Capacity The ability of a body to absorb heat. Heat capacity is measured by the number of BTU that may be stored in a unit volume of a substance at a specific temperature. It is a function of the substance's weight, specific heat, and temperature difference.
Heat, Latent 1.       The heat required to change the physical state of a substance without changing its temperature. 2.       Latent heat of water vapor in stack 3.       Fixed amount depending on hydrogen in fuel 4.       About 5% of fuel input for fuel oil 5.       About 9% of fuel input for natural gas 6.       Assumes a non-condensing boiler (typical)
Heat, Sensible Sensible Heat is defined as the heat energy stored in a substance as a result of an increase in its temperature.
  • Sensible heat of stack gasses
  • Typically around 10% of fuel input
  • Increased mass flow and stack temperature increase the loss
Heat, Specific The quantity of heat for any substance (expressed in BTU) required to raise a unit of weight or volume of that substance one degree F. at a given temperature. For example, the specific heat of water is 1.0. meaning that 1 BTU is required to raise the temperature of 1 lb. of water 1 degree F. This term "Heat, Specific" is most important to anyone using heat generating equipment, for knowing the specific heat of a substance to be heated, knowing the temperature to which the substance must be raised and knowing approximately the thermal efficiency of the heating equipment, you can calculate the amount of fuel consumption for the operation. This, of course, is important in selecting the proper sized burner for the job.
Heat, Temperature: Heat is a form of energy. Temperature indicates a result of heat energy, namely, the intensity, or the pressure of heat on a particular substance. For example, take two different substances, such as fuel oil and water. Suppose each is at a temperature of 60° F. Now, if the temperature of each is raised to 100° F. , each has undergone a rise of 40° but the amount of heat in each is vastly different. Illustration: for water (100° - 60°) x 1 (specific heat of water) = 40 BTU per lb. = the amount of heat in the water above 60° F. for oil (100° - 60°) x .5 (specific heat of oil) = 20 BTU per lb. = the amount of heat in the oil above 60° F.
Heat Transfer The term employed in describing qualitatively or quantitatively, the transfer of heat from a relatively hot substance to a cooler substance. The actual transfer of heat from one substance to another, such as from flame to work being heated, is accomplished by radiation, conduction or convection. Any one or a combination of these means may accomplish the transfer of heat.
  • CONDUCTION: the flow of heat from one part of a body to another part of the same body, or from one body to another in physical contact with it without displacement of the particles of the body. For example: the passage of heat along an iron bar one end of which is held in a fire.
  • CONVECTION: the process of beating a substance by the motion of warmer fluids or gases, in contact with the substance. Thus water tubes in a boiler may be heated by means of the hot products of combustion sweeping over them. The surfaces of the boiler tubes are thus heated by convection, then conduct the beat through the metal of the tubes to the inner surface in contact with the water where the heat is transferred by a combination of conduction and convection to the water.
  • RADIATION: the transfer of heat between bodies separated from each other by an appreciable distance. Radiation of beat takes place between bodies of different temperatures at all distances apart and follows the laws for the radiation of light. The heat rays proceed in straight lines and the intensity of the rays radiated from any one source varied inversely as the square of their distances from the source.
Lead Boiler The lead boiler is the first boiler to start and the last boiler to stop.
Lead / Lag Sequence Selection
  • AUTOMATIC ROTATION- "Automatic Rotation" changes the boiler selected as the "lead" based on time.
  • CUSTOM SELECTION- Using "Custom Selection" the operator can select any boiler lead / lag sequence desired. The sequence can be set 1,2,3,4 or 2,3,1,4 or 4,1,3,2 etc. . Useful for Plants with un-equal size boilers.
  • MANUAL SELECTION- Under "Manual Selection" the operator selects an individual boiler to start or stop.
Lead / Lag Modulation Burner lights at low fire and can drive to any firing rate between low and high fire.
  • SERIES MODULATION- The lead boiler is modulated according to load and the lag boilers are base loaded at a pre-determined value for peak efficiency.
  • UNISON (PARALLEL) MODULATION- All boilers fire at the same firing rate. This mode is required for most hot water boilers in order to achieve the Supply Header Setpoint Temperature. Assuming that the water gpm is proportioned among the boilers, unequal firing rates would cause unequal boiler outlet temperatures, and would result in a "blended" water Supply temperature.
  • BASE LOAD AUTO-SHIFT - Also called "Helper Mode". The objective is to minimize cycling boilers on and off due to short term load swings while maintaining peak Boiler Base Load Efficiency whenever possible. When the load increases and lead boiler modulates up to high fire, the lag boilers will automatically increase their Base Load firing rate to "Help" maintain setpoint without starting up another Lag boiler. When the load decreases, the Lag boilers will resume firing at the Normal Base Load for peak Plant Efficiency. If the load increase is long term, another lag boiler will be started. The control logic works similarly as the plant load drives the lead boiler to minimum load.
Lag Boiler The lag boiler is the next boiler to start and first to stop.
Low Fire Shutdown Boilers are brought to minimum fire position prior to shutting off.
National Fire Protection Association (NFPA) NFPA is dedicated to protecting people and their property from the devastating effects of fire. In some way, virtually every building, process, service, design, and installation in society today is affected by codes and standards developed through NFPA's true consensus system. Through NFPA's National Fire Codes®, as well as its education and community outreach programs, NFPA is a worldwide advisor on fire safety and protection. Boiler firing systems in the USA follow the guidelines of the NFPA's 85 (previously 8501 & 8502) code.
Nitrogen Dioxide (NO 2 ) Produced from any source that burns fuel.. causes lung irritation and damage and reacts in the atmosphere to form ozone and acid rain.
NRTL UL is an example of a product safety organization known generically as a Nationally Recognized Testing Laboratory (NRTL). NRTLs provide independent evaluation, testing, and certification of the safety of electrical products. The term NRTL and the requirements for recognition are established by the Occupational Safety and Health Act (OSHA) 29 CFR1910, which requires that all electrical equipment used in employee workplaces be NRTL-approved where such approval is available.
Optical Isolation "opto-isolated"
Outdoor Reset For heating plants, the hot water setpoint can be adjusted based on the outside temperature. This is called "Outdoor Reset".
Oxygen Trim A sensor measures flue gas oxygen and a closed loop controller compares the actual oxygen level to the desired oxygen level. The air (or fuel) flow is trimmed by the controller until the oxygen level is corrected. The desired oxygen level for each firing rate must be entered into a characterized setpoint curve generator. For dual fuel burners, independent curves must be entered. The control strategy must include variable gain (ratio trimming) and setpoint lead/lag logic to prevent control oscillation. Oxygen Trim maintains the lowest possible burner excess air level from low to high fire. Burners that don't have Oxygen Trim must run with Extra Excess Air to allow safe operation during variations in weather, fuel, and linkage. Extra fuel is burned to heat the Extra Excess Air and it leaves the stack as lost energy. Oxygen Trim minimizes Excess air and saves fuel.
Ozone (O 3 ) Formed when reactive organic gases (ROG) and nitrogen oxides react in the presence of sunlight. ROG sources include any source that burns fuel; solvents; petroleum processing and storage; and pesticides.. causes breathing difficulties, lung tissue damage, vegetation damage, damage to rubber and some plastics
"Pulser AI" The PWC has Pulse inputs, 0.6 ppm - 4000 Hz, 0-15 Vdc. These inputs allow PWC to receive inputs from pulse output devices that are low cost flow meter and KW meter options. Typically, existing meters can be retro-fitted with pulsers.
PID Control "Proportional + Integral + Derivative" Control algorithms continuously change the output signal until the setpoint equals the process (or desired) variable. Most Accurate Control Logic available.
PWC Plant Wide Controller
SCADA Supervisory Control And Data Acquisition; also referred to as a remote control and monitoring system.
Setback The hot water setpoint can be changed depending on the time of day, day of week or week of year. Reducing the heater temperature (or "Setback") during unoccupied times saves energy.
  • Single Pole, Single Throw, Single Pole, Double Throw
  • Relay, control switch or sensor contact configuration
Steam, Saturated Saturated steam is water vapor at the temperature of the boiling point corresponding to pressure.
Steam, Wet either saturated or superheated steam which contains moisture.
Steam, Dry either saturated or superheated steam containing no moisture.
Steam, Superheated steam heated to a temperature above that corresponding to its pressure.
Therm A unit originally adopted by many gas companies for measuring and billing the gas to customers. One therm is equivalent to 100,000 BTU.
Thermal Expansion Is the temporary increase in volume or linear dimensions of materials when heated. The material returns to its original dimensions when cooled. This is not to be confused with permanent volume changes or growth which many materials undergo when heated.
Thermal Shock is the strain produced in a material due to sudden changes in temperature.
Thermal Spalling the result of thermal shock, is defined as a fracture of the refractory material and occurs as the breaking off of pieces from the hot surfaces of the refractory.
UL-508 UL-508 is the Industrial Control Equipment Standard. UL-508 is an assembly standard, i.e. in addition to requiring that all components be approved, the standard addresses enclosure construction, wiring methods, overcurrent protection, and other aspects of how the components are applied and assembled in a control panel.
Variable Frequency Drives
  • PWM
  • Adjustable Frequency Drive (AFD)
  • Adjustable SPEED Drives (ASD)
  • VARIABLE Frequency Drives (VFD)
  • Inverters
  • Frequency Converters
  • Drives
  • Different names for the same thing.
Variable Speed Fan
  • Dampers substantially increase Fan Hp and Fan kW Consumption.
  • Dampers are Evil!
  • Inlet Vortex Dampers waste less Hp than any type of inlet and outlet Blade Dampers.
  • Variable Speed Fans Control air flow with minimum fan shaft Hp.
  • Variable Speed Fans have been field proven in thousands of HVAC air handler applications.
Vortex Dampers Vortex dampers or Inlet control vanes give an initial spin (or vortex) to air entering a centrifugal fan. By adjusting angle of vanes the degree of spin and volumetric output are regulated.