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GLOSSARY ‘O’ to ‘R’
OCCUPIED ZONE: The region within an occupied space between planes 3 and 72 inches (75 and 1800 mm) above the floor and more than 2 feet (600 mm) from the walls or fixed air conditioning equipment (see ASHRAE Standard 55-1981). OCTAVE BAND (O.B.): A range of frequency where the highest frequency of the band is double the lowest frequency of the band. The band is usually specified by the center frequency. ODOR: A quality of gases, vapors, or particles which stimulates the olfactory organs; typically unpleasant or objectionable. OLF: (From "olfactory") A perceived air quality term which attempts to quantify a given pollution load. One person creates 1 olf of bioeffluents. If there are 10 cubic meters of floor space per person, then people create 0.1 olf per mē (olf/mē). Other sources are compared and quantified by olfs. For example, if 40% of the people smoke, this adds 0.2 olf/mē to the load. OMNIVORE: Animal that obtains its nutrients from both plants and animals. OPERATIVE TEMPERATURE (to): The uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual non-uniform environment. Operative temperature is numerically the average, weighted by respective heat transfer coefficients (hc and hr), of the air (ta) and mean radiant temperatures (tr). to = (hcta + hrtr)/hc+hr) At air speeds of 80 fpm (0.4 m/s) or less and tr less than 120 F,(50oC) operative temperature is approximately the simple average of the air and mean radiant temperatures and equal to the adjusted dry bulb temperature. OPTIMUM OPERATIVE TEMPERATURE: Temperature that satisfies the greatest possible number of people at a given clothing and activity level. OUTLET, CEILING: A round, square, rectangular, or linear air diffuser located in the ceiling, which provides a horizontal distribution pattern of primary and secondary air over the occupied zone and induces low velocity secondary air motion through the occupied zone. OUTLET, SLOTTED: A long, narrow air distribution outlet, comprised of deflecting members, located in the ceiling sidewall, or sill, with an aspect ratio greater than 10, designed to distribute supply air in varying directions and planes, and arranged to promote mixing of primary air and secondary room air. OUTLET, VANED: A register or grille equipped with vertical and/or horizontal adjustable vanes. OUTLET VELOCITY: The average velocity of air emerging from the outlet measured in the plane of the outlet. OUTPUT: Capacity, duty, performance, net refrigeration produced by system. OUTSIDE AIR OPENING: Any opening used as an entry for air from outdoors. PARTICULATE: A state of matter in which solid or liquid substances exist in the form of aggregated molecules or particles. Airborne particulate matter is typically in the size range of 0.01 to 100 micrometers. PARTICULATE MATTER: A suspension of fine solid or liquid particles in air, such as dust, fog, fume, mist, smoke, or sprays. Particulate matter suspended in air is commonly known as an aerosol. PATHOGEN: Any microorganism capable of causing disease. PATHOGENIC: Having the ability to produce or cause a disease. pH: Means used to express the degree of acidity or alkalinity of a solution with neutrality indicated as seven. PERMISSABLE EXPOSURE LIMIT (PEL): An exposure limit is published and enforced by OSHA as legal standard. PHENOLIC RESINS: A class of resins produced as the condensation product of phenol or substituted phenol and formaldehyde or other aldehydes. PICKUP: The temperature increase across a coil. PITOT TUBE: A device consisting of two concentric tubes, one serving to measure the total or impact pressure existing in the airstream, the other to measure the static pressure only. PLANE RADIANT TEMPERATURE: The uniform temperature of an enclosure in which the incident radiant flux on one side of a small plane element is the same as in the existing environment. PNEUMONIA: A swelling of the lungs, commonly caused by breathed-in bacteria (Diplococcus pneumoniae). Parts of the lungs become plugged with a fiberlike fluid. Pneumonia may also be caused by virus rickettsiae, and fungi. Symptoms of pneumonia are severe chills, a high fever (which may reach 105oF), headache, cough, and chronic pain. An involved lower lobe of the right lung may cause a pain that is like appendicitis. Red blood cells leaking into the air sacs of the lungs causes a rust-colored sputum that may be a sure sign of pneumococcal infection. The disease continues, sputum may become thicker and have pus. The patient may have painful attacks of coughing. Breathing often becomes painful, shallow, and rapid. The pulse rate goes up, often over 120 beats a minute. Other signs may be heavy sweating and bluish skin. Stomach and bowel disorders and an outbreak of shingles (herpes simplex) on the face may also occur. Children with pneumonia may have seizures. The affected area of a lobe becomes filled with fluids and firm. A distinct breathing sound is heard by the physician. X-ray films are taken of the lungs. Laboratory tests of sputum and blood help in finding the cause. POINT OF OPERATION: Used to designate the single set fan performance values which correspond to the point of intersection of the system curve and the fan pressure-volume curve. POTABLE WATER: Water that is safe for human consumption. POWER (P): Expressed in watts (W) or kilowatts (kW), and is equal to: in DC circuit, P = EI and P = I2R in AC circuit, P = EI X Power factor PREHEAT: A coil used to raise the outside air temperature above freezing, generally to 35oF.; the process of raising the temperature. PRESSURE: The normal force exerted by a homogeneous liquid or gas, per unit of area, on the wall of its container. PRESSURE, ABSOLUTE: Pressure referred to that of a perfect vacuum. It is the sum of gauge pressure and atmospheric pressure. PRESSURE, ATMOSPHERIC: It is the pressure indicated by a barometer. Standard atmosphere is the pressure equivalent of 14.697 psi or 29.921 in. of mercury at 32F. PRESSURE DROP: Pressure loss in fluid pressure, as from one end of a duct to the other, due to friction, dynamic losses, and changes in velocity pressure. PRESSURE, GAUGE: Pressure above atmospheric. PRESSURE LOSS: The term used in the register industry to indicate how much total pressure is required to move air through a register. PRESSURE, SATURATION: The saturation pressure for a pure substance for any given temperature is that pressure at which vapor and liquid, or vapor and solid, can coexist in stable equilibrium. PRESSURE, STATIC (SP): The normal force per unit area that would be exerted by a moving fluid on a small body immersed in it if the body were carried along with the fluid. Practically, it is the normal force per unit are at a small hole in a wall of the duct through which the fluid flows (piezometer) or on the surface of a stationary tube at a point where the disturbances, created by inserting the tube, cancel. It is supposed that the thermodynamic properties of a moving fluid depend on static pressure in exactly the same manner as those of the same fluid at rest depend upon its uniform hydrostatic pressure. PRESSURE, TOTAL (TP): In the theory of the flow of fluids, the sum of the static pressure and the velocity pressure at the point of measurement. Also called dynamic pressure. PRESSURE, VAPOR: The pressure exerted by a vapor. If a vapor is kept in confinement over its liquid so that the vapor can accumulate above the liquid, the temperature being held constant, the vapor pressure approaches a fixed limit called the maximum, or saturated, vapor pressure, dependent only on the temperature and the liquid. PRESSURE, VELOCITY (VP): In moving fluid, the pressure capable of causing an equivalent velocity, if applied to move the same fluid through an orifice such that all pressure energy expended is converted into kinetic energy. PRIMARY AIR: The initial airstream discharged by an air outlet (the air being supplied by a fan or supply duct) prior to any entrainment of the ambient air. PSYCHROMETER: An instrument for ascertaining the humidity or hygrometric state of the atmosphere. PSYCHROMETRIC CHART: A graphical representation of the thermodynamic properties of moist air. PSYCHROPHILE: An organism that grows optimally within the temperature range of 32oF to 68oF (0oC to 20oC). PURE CULTURE: A culture of microorganisms in which all cells are of a single type. RADIANT TEMPERATURE ASYMMETRY: The difference between the plane radiant temperature of the two opposite sides of a small plane element. RADIATION, THERMAL: The transmission of heat through space by wave motion; the passage of heat from one object to another without warming the space between. RADIUS OF DIFFUSION: The horizontal distance in feet from the diffuser to a point where the terminal velocity of 50 feet per minute occurs. RASH: A skin swelling. Kinds of rashes are butterfly rash, diaper rash, drug rash, heat rash. RECIPROCATING: In refrigeration, a type of compressor which compresses refrigerant vapor by moving a piston up and down in a cylinder. REFRIGERANT: The fluid used for heat transfer in a refrigerating system, which absorbs heat at a low temperature and a low pressure of the fluid and rejects heat at a higher temperature and a higher pressure of fluid, usually involving changes of state of the fluid. REGISTER: A grille which is equipped with a damper or control valve, and which directs air in a non-spreading jet. REHEAT: a coil placed after the cooling coil, used to raise the air temperature; the process of raising the cooled air temperature. Used mainly with DX coil dehumidification. RELATIVE HUMIDITY: The ratio of the quanity of water vapor present in the air compared to the quanity of water vapor present in saturated air at the same temperature and barometric pressure. RESET: A process of automatically adjusting the control point of a given controller to compensate for changes in outdoor temperature. The hot deck control point is normally reset upward as the outdoor temperature drops. The cold deck control point is normally reset downward as the outdoor temperature increases. RESPIRABLE PARTICLES: Those particles in air which penetrate into and are deposited in the nonciliated portion of the lung. RESPIRABLE SIZE PARTICULATES: Particulates in the size range that permits them to penetrate deep into the lungs upon inhalation. RETURN: Any opening through which air is removed from a conditioned space. RETURN AIR: Air returned from conditioned or refrigerated space. REVERBERATION: The persistence of sound in an enclosed space after the sound source has stopped. In a reverberation room, it is characterized by the decay or dying away the sound. REVERBERATION TIME: The reverberation time of an enclosed space is the number of seconds required, or that would be required were the decay rate to remain constant, for the sound pressure level to decrease by 60 decibels. RISER SHAFT: A vertical shaft designed to house electric cables, piping and ductwork. ROOM CRITERIA CURVES (RC CURVES): Curves similar to NC curves that represent a close approximation to a well balanced, bland-sounding spectrum. ROOM DRY BULB: The actual temperature of the conditioned room or space as measured with an accurate thermometer. ROOM VELOCITY: The residual air velocity level in the occupied zone of the conditioned space (e.g. 65, 50, 35 fpm). ROTAMETER: A flow meter, consisting of a precision-bored, tapered, transparent tube with a solid float inside. Used for calibrating instruments.
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