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GLOSSARY ‘F’ to ‘H’
F.P.M.: A measure of air velocity in feet per minute. FACE VELOCITY: The velocity obtained by dividing the air quantity by the component face area. FAN, CENTRIFUGAL: A fan rotor or wheel within a scroll type housing and including driving mechanism supports for either belt drive or direct connection. FAN PERFORMANCE CURVE: Fan performance curve refers to the constant speed performance curve. This is a graphical presentation of static or total pressure and power input over a range of air volume flow rate at a stated inlet density and fan speed. It may include static and mechanical efficiency curves. The range of air volume flow rate which is covered generally extends from shutoff (zero air volume flow rate) to free delivery (zero fan static pressure). The pressure curves are generally referred to as the pressure-volume curves. FAN STATIC PRESSURE: The pressure added to the system by the fan. It equals the sum of pressure losses in the system minus the velocity pressure in the air at the fan inlet. FAN, TUBEAXIAL: A propeller or disc type wheel within a cylinder and including driving mechanism supports for either belt drive or direct connection. FAN, VANEAXIAL: A disc type wheel within a cylinder, a set of air guide vanes located either before or after the wheel and including driving mechanism supports for either belt drive or direct connection. FEDERAL REGISTER: Publication of U.S. government documents officially promulgated under the law, documents whose validity depends upon such publication. It is published on each day following a government working day. It is, in effect, the daily supplement to the Code of Federal Regulations, CFR. FEVER: An abnormal temperature of the body above 98.6oF (37oC). Exercise, anxiety, and dehydration may increase the temperature of healthy people. Infection, nerve disease, cancer, anemia, and many drugs may cause fever. No single theory explains why the temperature is increased. Fever increases metabolism 7% per oC, meaning more food needs to be eaten. Convulsions may occur in children whose fevers tend to rise quickly. Confusion is seen with high fevers in adults and in children. It may begin quickly or gradually. The period of highest fever is called the stadium or fastigium. It may last for a few days or up to 3 weeks. FILTER: A device to remove solid material from a fluid. FILTER EFFICIENCY: The efficiency of various filters can be established on the basis of entrapped particles; i.e., collection efficiency, or on the basis of particles passed through the filter, i.e., penetration efficiency. FILTER, HEPA: High-efficiency particulate air filter that is at least 99.97 percent efficient in removing thermally generated monodisperse dioctylphthalate smoke particles with a diameter of 0.3u. FLOW COEFFICIENT: A correction factor used for figuring volume flow rate of a fluid through an orifice. This factor includes the effects of contraction and turbulence loss (covered by the coefficient of discharge), plus the compressibility effect, and the effect of an upstream velocity other than zero. Since the latter two effects are negligible in many instances, the flow Coefficient is often equal to the coefficent of discharge. FLUID: Gas, vapor, or liquid. FREE AREA: The actual measured perpendicular area between the fins of a grille or register. FLYWHEEL EFFECT: In HVAC systems, to even out temperature variations in a building due to the temperature storage capabilities of the building's mass. FREQUENCY: The number of vibrations, waves, or cycles of any periodic phenomenon per second. In architectural acoustics, the interest lies in the audible frequency range of 20 to 20,000 cps Hertz (cycles per second). FREQUENCY SPECTRUM: Usually a visual representation of a complex sound or noise which has been resolved into frequency components. The detailed nature of a complex sound may be studied by obtaining its frequency spectrum. Frequency spectra are commonly obtained in octave bands, 1/3 octave bands, and various narrow bands. FRICTION: Friction is the resistance found at the duct and piping walls. Resistance creates a static pressure loss in systems. The primary purpose of a fan or pump is to produce a design volume of fluid at a pressure equal to the frictional resistance of the system and the other dynamic pressure losses of the components. FUMES: Airborne solid particles usually less than 1 micrometer (um) in size formed by condensation of vapors, sublimation, distillation, calcination, or chemical reaction. GAGE PRESSURE: Pressure measured with respect to atmospheric pressure. GAS: A state of matter in which substances exist in the form of nonaggregated molecules, and which, within acceptable limits of accuracy, satisfies the ideal gas laws: usually a highly superheated vapor. GAS CHROMATOGRAPHY: A gaseous detection technique which involves the separation of mixtures by passing them through a column that will enable the components to be held up for varying periods of time before they are detected and recorded. GERM: A microorganism; a microbe usually thought of as a pathogenic organism. GERMICIDE: An agent capable of killing germs. GRAINS OF MOISTURE: The unit of measurement of actual moisture contained in a sample of air. (7000 grains = one pound of water). GRAB SAMPLE: A sample which is taken within a very short time period. The sample is taken to determine the constituents at a specific time. GRAM (g): A metric unit of weight. One ounce equals 28.4 grams. GRAM-NEGATIVE BACTERIA: Bacteria that do not retain the crystal violet stain in their cells, when stained by the procedure described by Christian Gram, and thus appear pink or red when viewed under the light microscope. GRAM-POSITIVE BACTERIA: Bacteria that retain the crystal violet stain in their cells when stained by the procedure described by Christian Gram, and thus appear blue or purple when viewed under the light microscope. GRILLE: A louvered covering for an opening through which air passes. HALOGENATED HYDROCARBON: A chemical material that has carbon plus one or more of these elements: chlorine, fluorine, bromine, or iodine. HEAD, STATIC: The static pressure of fluid expressed in terms of the height of a column of the fluid, or of some manometric fluid, which it would support. HEAD, VELOCITY: In a flowing fluid, the height of the fluid or of some manometric fluid equivalent to its velocity pressure. HEAT: The form of energy that is transferred by virtue of a temperature difference. HEAT, LATENT: Change of enthalpy during a change of state, usually expressed in Btu per lb. With pure substances, latent heat is absorbed or rejected at constant pressure. HEAT, SENSIBLE: Heat which is associated with a change in temperature; specific heat exchange of temperature; in contrast to a heat interchange in which a change of state (latent heat) occurs. HEAT, SPECIFIC: The ratio of the quantity of heat required to raise the temperature of a given mass of any substance one degree to the quantity required to raise the temperature of an equal mass of a standard substance (usually water to 59oF) one degree. HEAT, TOTAL (ENTHALPY): The sum of sensible heat and latent heat between an arbitrary datum point and the temperature and state under consideration. HEAT EXCHANGER: A device specifically designed to transfer heat between two physically separated fluids. HEAT OF FUSION: Latent heat involved in changing between the solid and the liquid states. HEAT OF VAPORIZATION: Latent heat involved in the change between liquid and vapor states. HEAT PUMP: A refrigerating system employed to transfer heat into a space or substance. The condenser provides the heat while the evaporator is arranged to pick up heat from air, water, etc. By shifting the flow of air or other fluid, a heat pump system may also be used to cool the space. HEPA FILTER (HIGH EFFICIENCY PARTICULATE AIR FILTER): A disposable, extended medium, dry type filter with a particle removal efficiency of no less than 99.97 percent for 0.3u particles. HIGH LIMIT: The maximum desirable, or safe, temperature; an alarm given when this temperature is exceeded. HORSEPOWER: Unit of power in foot-pound-second system; work done at the rate of 550 ft-lb per sec, or 33,000 ft-lb per min. HOT DECK: The heating section of a multizone system; includes heating coil and duct. HOT GAS BYPASS: The piping and manual, but more often automatic, valve used to introduce compressor discharge gas directly into the evaporator. This type of arrangement will maintain compressor operation at light loads down to zero by falsely loading the evaporator and compressor. HUMIDIFIER: A device to add moisture to air. HUMIDIFIER LUNG: A type of allergic lung condition common among workers involved with refrigeration and air conditioning equipment. The allergy is to two kinds of fungus, Micropolyspora and Thermoactinomyces. Symptoms of the short-term form of the disease include chills, cough, fever, difficult breathing, loss of appetite, nausea, and vomiting. The long-term form of the disease is known by fatigue, cough, weight loss, and difficult breathing during exercise. Also called air conditioner lung. HUMIDISTAT: A regulatory device, actuated by changes in humidity, used for the automatic control of relative humidity. HUMIDITY: Water vapor within a given space. HUMIDITY, ABSOLUTE: The weight of water vapor per unit volume. HUMIDITY, PERCENTAGE: The ratio of the specific humidity of humid air to that of saturated air at the same temperature and pressure, usually expressed as a percentage (degree of saturation; saturation ratio). HUMIDITY RATIO: The ratio of the mass of the water vapor to the mass of dry air contained in the sample. HUMIDITY, RELATIVE: The ratio of the mol fraction of water vapor present in the air, to the mol fraction of water vapor present in saturated air at the same temperature and barometric pressure; approximately, it equals the ratio of the partial pressure or density of the water vapor in the air, to the saturation pressure or density, respectively, of water vapor at the same temperature. HUMIDITY, SPECIFIC: Weight of water vapor associated with 1 lb weight of dry air, also called humidity. HVAC: Heating, ventilation, and air conditioning. A system concerned with the temperature, humidity, cleanliness, and distribution of air. HYGROSCOPIC: Absorptive of moisture, readily absorbing and retaining moisture. HYPERSENSITIVITY: An altered state or activity in an individual following contact with certain kinds of substances (inanimate or animate). HYPERSENSITIVITY PNEUMONITIS: See Extrinsic Allergic Alveolitis.
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