P1:  Measuring point for compressor acceptance test. Pressure at the compressor inlet flange.

P2:  Measuring point for compressor acceptance test. Pressure at the compressor outlet flange.

P3:  Measuring point for compressor acceptance test. Pressure before an orifice or nozzle, downstream of compressor discharge.

P4:  Measuring point for compressor acceptance test. Distribution pressure (headers).

P5:  Measuring point for compressor acceptance test. Pressure at the point of use.

PA – Pascal: A unit of measurement of air pressure. One column inch of water equals 247 pascals. Atmospheric pressure (29.92 inches of mercury) is equivalent to 102,000 PA.

Package Power:  The total power absorbed by a compressor, including the power absorbed by all pumps, fans, coolers and the like.

Package Unit:  A term to describe an air conditioner system where all the components are contained within one unit.

Packaged Air Conditioner: An air conditioner that contains the compressor, evaporator, and condenser in a single cabinet.

PAH: Polycyclic Aromatic Hydrocarbons. Natural products from the incomplete combustion of carbon compounds - forest fires, volcanic eruptions and decomposing organic matter are all natural sources of PAH. Certain industrial processes are man made sources.

Palm Coupling:  A compressed air coupling commonly used on European rail and road vehicles to connect one vehicle to the next.

Particle Density:  An important parameter in establishing an entrained particle’s potential to impinge on control surfaces and cause erosion.

Particulate(s); Particulate Matter (PM-10): A criteria air pollutant. Particulate matter includes dust, soot and other tiny bits of solid materials that are released into and move around in the air. Particulates are produced by many sources, including burning of diesel fuels by trucks and buses, incineration of garbage, mixing and application of fertilizers and pesticides, road construction, industrial processes such as steel making, mining operations, agricultural burning (field and slash burning), and operation of fireplaces and woodstoves. Particulate pollution can cause eye, nose and throat irritation and other health problems.

Particulate Matter:   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 Type Filter:  A device designed to remove solids, such as dirt, scale, rust and other contaminants from the air system.

Parts per Million (ppm): A measure of concentration, or how much substance is in a given sample.

Parts Per Billion (ppb)/Parts Per Million (ppm): Units commonly used to express contamination ratios, as in establishing the maximum permissible amount of a contaminant in Passive solar energy: Solar energy collected by non active systems e.g. windows, atria etc..

Pascal: Unit of pressure. House air tightness tests are typically conducted with a pressure difference of 50 Pascals between the inside and outside. 50 Pascals is equal to 5.008 mm (0.2 in) of water at 12.9oC.

Passive Solar Energy: Solar energy collected by non active systems e.g. windows, atria etc.

Pathogen:  Any agent, especially a microorganism (e.g. viruses or bacteria), able to cause disease.

Paving Breaker:  A hand held pneumatic tool. Designed for light demolition work, digging, making holes etc.

Payback Period: The number of years that an investment in energy conservation will take to repay its cost through energy savings.

PCBs:   Polychlorinated biphenyls.

pCi/l:   Pico Curies per liter; a measure of radon concentration.

PDP:  Pressure dew point temperature (°C).

Peak Levels: A level of airborne pollutants that is much higher than average. They can occur over a short period of minutes or hours in response to sudden releases, or they can occur due to a longer term build-up over several days.

Peak Load Plant: A plant usually housing old, low-efficiency steam units, gas turbines, diesels, or pumped storage hydroelectric equipment normally used during the peak-load periods.

Peak Stream Flow:  The maximum expected flow of surface water at a waste management facility from a tributary watershed for a given recurrence interval.

Peaking Capacity: Capacity of generating equipment normally reserved for operation during the hours of highest daily, weekly, or seasonal loads. Some generating equipment may be operated at certain times as peaking capacity and at other times to serve loads on an around-the-clock basis.

Pedestal Type Centrifugal Compressor:  A single inlet compressor with the impeller or impellers mounted on a shaft supported by two bearings in a pedestal, with the driver coupled to the compressor shaft.

PEFR: Peak expiratory flow rate. A measure of lung function and the fastest rate at which air moves through the airways during a forced expiration.

PELs:  Permissible Exposure Limits (standards set by the Occupational, Safety and Health Administration - OSHA).

Pellet: Fuel made from dried ground wood or other biomass waste (such as corn) compressed into 25mm x 6mm (1” x ¼”) cylinders.

Percent of Possible Sunshine: The actual number of hours of sunshine expressed as a percentage for the month (or other period of time).

Percent Radiation Received: The monthly mean Global Radiation of a horizontal plane, expressed as a percentage of the monthly mean radiation on a horizontal plane outside the atmosphere.

Perched Groundwater:  Unconfined groundwater separated from the underlying main body of groundwater by unsaturated rock or other strata.  Water that accumulates beneath the earth’s surface but above the primary water-bearing zone (aquifer) is termed perched groundwater.  Typically, perched groundwater collects above laterally discontinuous, less permeable deposits (e.g. clay lenses) contained in an otherwise permeable deposit.

Perception:   Awareness of the effects of stimuli.

Percolation:  The flow or filtering of water or other liquids through subsurface rock or soil layers, usually continuing to groundwater.

Perennial Stream:  Water bodies, or segments thereof, that contain flow throughout the year.

Perfect Intercooling:  Is obtained when the gas is cooled to first stage inlet temperature following each stage of compression.

Performance Curve:  A plot of expected operating characteristics (e.g., discharge pressure versus inlet capacity, shaft horsepower versus inlet capacity).

Perlite: A heat-expanded mineral used for insulation.

Perm: A measurement of how much water vapor a material will let pass through it per unit of time.

Permeance: Water vapour permeance is the rate of water vapour diffusion through a sheet of any thickness of material (or assembly between parallel surfaces). It is the water vapour flow to the differences of the vapour pressures on the opposite surfaces. Permeance is measured in perms (m2.K/W).

Permeability: Water vapour permeability is a property of a substance which permits passage of water vapour. When permeability varies with psychrometric conditions, the 'spot' or 'specific permeability' defines the property at a specific condition.

Permit: A document that resembles a license, required by the Clean Air Act for big (major) sources of air pollution, such as power plants, chemical factories and, in some cases, smaller polluters.

Permit Fees: Fees paid by businesses required to have a permit. Permit fees are like the fees drivers pay to register their cars. The money from permit fees will help pay for state air pollution control activities.

Permit to Operate (P/O): An operational permit issued yearly by an air district to sources that meet specified regulations.

Peroxyacytal Nitrate: A group of compounds formed from the photochemical reactions of nitrogen and organic compounds. PANs are components of smog and known to cause eye irritation.

Persistence:   Length of time a compound remains in the environment once introduced.

Personal Watercraft (PWC): Watercraft that do not have outboard, inboard, or stern drive engines. This encompasses the watercraft typically referred to as Jet Skis, Waverunners, etc.

Pest:   Any form of animal, plant, or terrestrial life that is injurious to health or the environment.

Pesticide:  (a) Chemical used to kill destructive insects or other small animals. (b) A general term for insecticides, herbicides and fungicides. Insecticides kill or prevent the growth of insects. Herbicides control or destroy plants. Fungicides control or destroy fungi. Some pesticides can accumulate in the food chain and contaminate the environment.

Petroleum: A mixture of hydrocarbons existing in the liquid state found in natural underground reservoirs often associated with gas.  Petroleum includes fuel oil No. 2, No. 4, No. 5, No. 6; topped crude; kerosene; and jet fuel.

pH: A scale from 0 to 15 for measuring alkalinity or salinity.

Phase-change materials: Materials with a phase change point close to the desired room temperature which can be used either to reduce temperature fluctuations within a room or to store energy in the phase change process (usually melting) and re-releasing it to the system when its temperature falls below the transition point. Phase change materials may be surface mounted as in phase change tiles or storage based as in latent heat stores for active solar systems (see latent heat).

Phosphate:  Phosphates are formed from elemental phosphorus.  They exist in three forms: Orthophosphate, metaphosphate (or polyphosphate), and organically bound phosphate.

Phosphorus (P):  An element.  It is an essential nutrient for plants and animals.

Photochemical Oxidants or Smog:  Air pollutants formed by the action of sunlight on oxides of nitrogen and hydrocarbons.

Photochemical Reaction: A term referring to chemical reactions brought about by the light energy of the sun. The reaction of nitrogen oxides with hydrocarbons in the presence of sunlight to form ozone is an example of a photochemical reaction.

Photolysis: Chemical decomposition induced by light or other energy.

Photosynthesis:  The biological synthesis of chemical compounds in the presence of light.

Physical Adsorption: The assimilation of gas, vapor, or dissolved matter by the surface of another substance resulting from the electrostatic interaction between molecules of gas or vapor and a surface.

Physical Environment (thermal environment): The environment in a room or building defined by its the environmental variables.

Phytotoxic:   Something that harms plants.

PicoCurie(pCi): A unit for measuring radioactivity, often expressed as picoCuries per liter (pCi/L) of air.

PICs:   Products of incomplete combustion. All particles and gases that are emitted from an object at the time it is burning.

Piezometer:  A non-pumping well, generally of small diameter, which is used to measure the elevation of the water table or potentiometric surface.  A piezometer generally has a short well screen through which water can enter.

Pilot (Payment in Lieu of Taxes): Lease payments collected by the Battery Park City authority from developers building, and condominium owners living, on the 92-acres known as Battery Park City. These funds are assessed by the City of New York Department of Finance. The tax rate is set by the New York City Council. Excess Pilot revenue is given to the City of New York annually.

Pinion:  The smaller of two mating or meshing gears; can be either the driving or the driven gear.

Piston Displacement:  Net volume actually displaced by the compressor piston at rated machine speed, generally expressed in cubic feet per minute (usually CFM). For multistage compressors, the piston displacement of the first stage only is commonly stated as that of the entire machine.

PIU:   Perimeter induction unit.

Planktonic Organism:  Phytoplankton, zooplankton, and the larvae and eggs of worms, mollusks, and arthropods, and the eggs and larval forms of fishes.

Plant: A facility at which are located prime movers, electric generators, and auxiliary equipment for converting mechanical, chemical, and/or nuclear energy into electric energy. A plant may contain more than one type of prime mover.

Plant Use: The electric energy used in the operation of a plant. Included in this definition is the energy required for pumping at pumped storage plants.

Plant-Use Electricity: The electric energy used in the operation of a plant. This energy total is subtracted from the gross energy production of the plant; for reporting purposes the plant energy production is then reported as a net figure. The energy required for pumping at pumped storage plants is, by definition, subtracted, and the energy production for these plants is then reported as a net figure.

Plaster: A plastic mixture of sand, lime, and Portland cement spread over wood or metal lath to form the interior surfaces of walls and ceilings.

Plate: A piece of lumber installed horizontally to which the vertical studs in a wall frame are attached.

Pleated Filter:  A filter element whose medium consists of a series of uniform folds and has the geometric form of a cylinder, cone, disc, plate  . . . Synonymous with “convoluted” and “corrugated.”

Plenum: The piece of ductwork, usually found above the heat exchanger of a hot air furnace, that connects the air handler to the main supply duct.

Plug Flow:   A flow regime where the flow is predominately in one direction and contaminants are swept along with the flow.

Plumb: Absolutely vertical at a right angle to the earth's surface.

Plume:  A body of contaminated groundwater flowing from a specific source.  The movement of the [contaminated] groundwater is influenced by such factors as local groundwater flow patterns, the character of the aquifer in which the [contaminated] groundwater is contained, and the density [and other physical and chemical properties] of the contaminants. 

Plywood: Laminated wood sheeting with layers cross-grained to each other.

PM: Preventive Maintenance.

PM10/PM2.5: PM10 is measure of particles in the atmosphere with a diameter of less than 10 or equal to a nominal 10 micrometers. PM2.5 is a measure of smaller particles in the air.

PM2.5: Includes tiny particles with an aerodynamic diameter less than or equal to a nominal 2.5 microns. This fraction of particulate matter penetrates
most deeply into the lungs. 

PM10 (Particulate Matter): A criteria air pollutant consisting of small particles with an aerodynamic diameter less than or equal to a nominal 10 microns (about 1/7 the diameter of a single human hair). Their small size allows them to make their way to the air sacs deep within the lungs where they may be deposited and result in adverse health effects . PM10 also causes visibility reduction.

Pneumatic:  Of, relating to, or using air. Moved by air pressure. Filled with compressed air.

Pneumatics:  Engineering science pertaining to gaseous pressure and flow.

Pneumatic Tools:  Tools that operate by air pressure.

PNEUROP Oxidation Test (POT):  Is a standardized method to determine the carbon  formation characteristics of compressor lubricants.

Point of Use:  A single outlet or limited number of outlets in a building used to connect tools or equipment to the air system.

Point Source: A stationary location or fixed facility from which pollutants are discharged; any single identifiable source of pollution; e.g. a pipe, ditch, ship, ore pit, factory smokestack.

Pollen:  Pronunciation (pol′ĕn).  Microspores of seed plants carried by wind or insects before fertilization; important in the etiology of hay fever and other allergies.   [L. fine dust, fine flour].

Pollutant:  Dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal and agricultural waste discharged into water.

Pollutant Pathways: Avenues for distribution of pollutants in a building. HVAC systems are the primary pathways in most buildings; however all building components interact to affect how air movement distributes pollutants. Also - a term used in the IAQ Tools for Schools: IAQ Coordinator's Guide.

Pollution:  (a) An alteration of the quality of state waters by waste to a degree that unreasonably affects their beneficial uses or facilities that serve their beneficial uses, (b) Pollution may include contamination.

Polycyclic Aromatic Hydrocarbons (PAHs): Organic compounds which include only carbon and hydrogen with a fused ring structure containing at least two benzene (six-sided) rings. PAHs may also contain additional fused rings that are not six-sided. The combustion of organic substances is a common source of atmospheric PAHs.

Polyethylene: Polymer plastic used for vapor barriers, air barriers, and foam backer rod.

Polyisocyanurate: A plastic foam insulation sold in sheets, similar in composition to polyurethane.

Polymer: Natural or synthetic chemical compounds composed of up to millions of repeated linked units, each of a relatively light and simple molecule.

Polystyrene Insulation: A rigid plastic foam insulation, usually white or blue in color.

Polyurethane: A versatile plastic foam insulation, usually yellow in color.

Pollutant Release and Transfer Register (PRTR): A Mexican program, created in 2001, requiring mandatory reporting by industrial facilities of potentially hazardous polluted materials emitted or passed into the environment from various media. Similar to the Toxic Release Inventory (TRI) in U.S. and the National Pollutant Release Inventory (NPRI) in Canada.

Pore:  A small channel or opening in a filter medium which allows passage of gas.

Porter Cologne Water Quality Control Act:  Enacted by California Legislature in 1970, it contains a complete framework for the regulation of waste discharges to both surface and ground waters of the State. It further provides for the adoption of water quality control plans and the implementation of these plans by adopting waste discharge requirements for each discharge of waste that could impact the waters of the state.

Positive Crankcase Ventilation (PCV): An emission control system for a reciprocating internal combustion engine that involves recirculating gases that blow by the piston rings during combustion from the crankcase back into the intake manifold so they can be more completely burned.

Positive Displacement Compressors:  Compressors in which successive volumes of air or gas are confined within a closed space, and compressed. They may be either reciprocating or rotating. (Trap air and then squeeze it to the desired pressure).

Positive Pressure: Condition that exists when more air is supplied to a space than is exhausted, so the air pressure within that space is greater than that in surrounding areas. Under this condition, if an opening exists, air will flow from the positively pressurized space into surrounding areas.

Posting:  The placement of a sign or signs at an area of a public beach that informs the public of contamination of recreational water and the risk of possible illness, and advises against swimming and/or water contact. The placement of signs may be temporary, as a result of monitoring that indicates a single microbiological indicator standard is exceeded (e.g., or more permanent, where monitoring indicates regular or sporadic contamination (e.g., a storm drain, or a water body with poor water circulation), or where sources of contamination are identifiable and can be explained (e.g., storm drain water, or residential wild or domestic animal populations).

Potable Water: Water that is safe for drinking.

Potential Energy:  Energy in a stored or packaged form, like fuel oil, coal, wood, etc.

Pounds per Square Inch:  PSI – Pounds per square inch.

Pour Point:  Is the temperature at which oil begins to flow under prescribed conditions.

Power: The rate at which energy is transferred. Electrical energy is usually measured in watts. Also used for a measurement of capacity.

Power Generation: A process of converting thermal, mechanical, chemical or nuclear energy into electric energy.

Power Theoretical:  The mechanical power required to compress polytropically and to deliver, through the specified range of pressures, the gas delivered by the compressor.

Power Wheel:  A built in mechanical device to recover a portion of the power consumed by a constant speed centrifugal compressor when operating at reduced capacity or reduced pressure rise, or both.

PPB:  A measurement. Parts per billion.
 
PPM:  A measurement. Parts per million.

Precipitator:  Pollution control device that collects particles from an air stream.

Precursor: In photochemistry, a compound antecedent to a pollutant. For example, volatile organic compounds (VOCs) and nitrogen oxides react in sunlight to form ozone or other photochemical oxidants. As such, VOCs and oxides of nitrogen are precursors.

PPB:   Parts per billion.

PPD - Predicted Percentage Dissatisfied: The percentage of subject population who will be dissatisfied (uncomfortable) in a given environment as predicted by a theoretical index (generally that of Fanger). See PMV.

PPM:   Parts per million.

Pre Open Warn:  An audible or visual discharge at a pressure slightly lower than the set pressure on a valve. Warns the operator that the valve is about to open.

Precipitator: Pollution control device that collects particles from an air stream. (See Electrostatic Precipitator.)

Precool:  Pre-cooling of intake air for compressors and blowers.

Precooler:  A heat exchanger located immediately preceding an ejector to condense and remove a portion of the vapor in the mixture and thus reduce the total lb/hr to be handled.

Preference Vote: The response by a subject as to their preference at the time of asking; this may be a preference for a warmer or cooler environment, or for a particular response on a comfort scale.

Preheating: In air conditioning: to heat the air before other processes.

Prescribed Burning: The planned application of fire to vegetation to achieve any specific objective on lands selected in advance of that application. In California, prescribed burning is governed under the Agricultural Burning Guidelines.

Pressed Wood Products: A group of materials used in building and furniture construction that are made from wood veneers, particles, or fibers bonded together with an adhesive under heat and pressure

Pressure: The normal force exerted by a homogeneous liquid or gas, per unit of area, on the wall of the container .

Pressure Absolute:  The total pressure measured from absolute zero ( i.e., from an absolute vacuum).

Pressure Back:  The pressure encountered on the return side of a system.

Pressure Cracking:  The pressure at which a pressure operated valve begins to pass a gas.

Pressure Critical:  Is the saturation pressure at the critical temperature.

Pressure Dew Point:  Is the temperature at which moisture begins to condense in a compressed air system.

Pressure Diagnostics: The practice of measuring pressures and flows in buildings to control air leakage, and also to ensure adequate heating and cooling air flows and ventilation.

Pressure difference: The difference in pressure of the volume of air enclosed by the building envelope and the air surrounding the envelope.

Pressure Discharge:  Is the total gas pressure (static plus velocity) at the discharge port of the compressor. Velocity pressure is considered only with dynamic compressors.

Pressure drop: The loss of force applied over a filtering surface due to restriction of airflow.

Pressure Gauge:  A device that indicates pressure differential above or below atmospheric pressure.

Pressure Inlet:  Is the total pressure (static plus velocity) at the inlet flange of the compressor.

Pressure Pan: A device used to block a duct register while measuring the static pressure behind it.

Pressure, Gauge:  The amount by which the total absolute pressure exceeds the ambient atmospheric pressure.

Pressure Pot:  In spray painting applications, a sealed paint cup with a paint gun which puts a measured amount of air pressure into it. This then forces the paint to the gun for atomization.

Pressure Range:  Difference between minimum and maximum pressures for an air compressor. Also called cut in-cut out or load-no load pressure range.

Pressure Rated:  The qualified operating pressure which is recommended for a component or a system by the manufacturer.

Pressure Regulating Valve:  A valve which enables pressure to be reduced, or kept constant at a desired level.

Pressure Relief Device:  A device actuated by inlet static pressure and designed to open during an emergency or abnormal condition to prevent a rise of internal pressure in excess of a specified value.

Pressure Rise:  The difference between the discharge pressure and the intake pressure.

Pressure Static:  The pressure measured in a flowing stream (liquid or gas) in such a manner that no effect on the measurement is produced by the velocity of the stream.

Pressure System:  The pressure which overcomes the total resistances in a system. It includes all losses as well as useful work.

Pressure Total:  The pressure that would be produced by stopping a moving stream of liquid or gas.

Pressure Velocity:  The total pressure minus the static pressure in an air or gas stream.

Pressure, Static: In flowing air, the total pressure minus velocity pressure. The portion of the pressure that pushes equally in all directions.

Pressure, Total: In flowing air, the sum of the static pressure and the velocity pressure.

Pressure, Velocity:   In flowing air, the pressure due to the velocity and density of the air.

Pressuretrol: A control that turns a steam boiler's burner on and off as steam pressure changes.

Pretreatment:  Removal of toxic or hazardous substances from wastewater before it is discharged into a wastewater collection, treatment and disposal system.

Prevention of Significant Deterioration (PSD): EPA program in which state and/or federal permits are required in order to restrict emissions from new or modified sources in places where air quality already meets or exceeds primary and secondary ambient air quality standards.

Preventive Maintenance: Regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, material, and systems failure by ensuring that parts, materials and systems are in good working order.

Primary Particles: Particles that are directly emitted from combustion and fugitive dust sources. (Compare with Secondary Particle.)

Primary Standard:  A pollution limit based on health effects. Primary standards are set for criteria air pollutants.

Primary Treatment:  A treatment process, utilizing a sedimentation tank, wherein a portion of the suspended matter is removed from the wastewater, but little or no colloidal or dissolved matter.  Primary treatment generally removes from 50 to 75 percent of the suspended matter and 20 to 40 percent of the BOD from the wastewater.

Prime Mover: The engine, turbine, water wheel, or similar machine that drives an electric generator; or, for reporting purposes, a device that converts energy to electricity directly (e.g., photovoltaic solar and fuel cells).

Prime Window: The main window installed on the outside wall consisting of fixed or moveable lights that slide on permanently fixed tracks (not to be confused with a storm window).

Priority Pollutant:  Those pollutants listed by the Administrator of the USEPA in Section 307 (a) of the Clean Water Act.

Probit Analysis: A statistical analysis whereby the proportion of people casting different comfort votes at a particular temperature can be estimated for a population from the results from a sample.

Process:  Occurs whenever the system undergoes either a change in state or an energy transfer at a steady stare.

Profile Angle (vertical shadow angle): The angle between the direction of the sun resolved in a vertical plane perpendicular to the face of the solar aperture, on the normal of the solar aperture. This angle is used to predict the effect of shading devices in sectional drawings.

ProgrammableThermostat:  A type of thermostat that allows the user to program into the devices’ memory a pre-set schedule of times (when certain temperatures occur) to turn on HVAC equipment.

Prohibition:  An order or law forbidding something to be done.

Propane:  A hydrocarbon gas, C3H8, occurring in crude oil, natural gas, and refinery cracking gas. It is used as a fuel, a solvent, and a refrigerant. Propane liquefies under pressure and is the major component of liquefied petroleum gas (LPG).

Priority List: The list or ranking of installation measures developed by a program to produce the most cost effective energy savings results based on a savings to investment ratio calculation.

Program Income: Income earned by the grantee from grant-supported activities, including but not limited to, income from service fees, sale of commodities, usage or rental fees, and royalties on patents and copyrights.

Propellant: A gas with a high vapor pressure used to force formulations out of aerosol spray cans. Among the gases used are butanes, propanes and nitrogen.

Proposition 65: Safe Drinking and Toxic Enforcement Act of 1986, also known as Proposition 65. This Act is codified in California Health and Safety Code section 25249.5, et seq. No person in the course of doing business shall knowingly discharge or release a chemical known to the state to cause cancer or reproductive toxicity into water or into land where such chemical passes or probably will pass into any source of drinking water, without first giving clear and reasonable warning to such individual.

PSI:  Pounds per square inch.

PSIA:  Pounds per square inch, absolute.

PSID:  Pounds per square inch, differential.

PSIG:  Pounds per square inch, gauge. Pressure indicated by a pressure gauge.

PSL (Polystyrene Latex Spheres):  Uniformly sized latex particles used as a challenge agent in some filter tests when suspended in an aerosol.

Pseudo Critical Pressure:  The saturation pressure at the critical temperature. It is the highest vapor pressure that the liquid can exert.

Psycogenic Illness: This syndrome has been defined as a group of symptoms that develop in an individual (or a group of individuals in the same indoor environment) who are under some type of physical or emotional stress. This does not mean that individuals have a psychiatric disorder or that they are imagining symptoms.

Psychological Factors:   Psychological, organizational, and personal stressors that could produce symptoms similar to poor indoor air quality.

Psychrometry:  Has to do with the properties of air-water vapor mixtures in the atmosphere.

Psychosocial Factors: Psychological, organizational, and personal stressors that could produce symptoms similar to those caused by poor indoor air quality.

Psychrometrics: The study of the relationship between air, water vapor, and heat.

Psychophysics: The branch of psychology dealing with the relationship between our sensations and the stimuli from the physical world.

Psychometry: The study of the interactions between temperature and water vapour in air. Includes relative humidities, wet and dry bulb temperatures, enthalpy, and so on.

PTFE:  Polytetrafluorethylene.

Public Workshop: A workshop held by a public agency for the purpose of informing the public and obtaining its input on the development of a regulatory action or control measure by that agency.

Publicly Owned Treatment Work (POTW):  A wastewater treatment plant owned by a state or municipality. The term also may include devices and systems used in the storage, treatment, recycling and reclamation of municipal sewage or industrial wastes of a liquid nature.

Pulmonary Function Test (PFT):  Assessment of the respiratory system that provides information about ventilation, airflow, lung volumes and capacity, and the diffusion of gas incorporating spirometry, peak flow meters, and the body plethysmograph.

Pulsation Damper:  A small receiver fitted on the inlet or discharge of a reciprocating compressor. The device is designed to remove the resonance from the compressor thereby reducing noise.

Pump Test:  A field test by which a well is pumped for a period of time and data are collected for use in assessing characteristics of subsurface water-bearing zones, or aquifers.

Pumped Storage Hydroelectric Plant: A plant that usually generates electric energy during peak-load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available to do so. When additional generating capacity is needed, the water can be released from the reservoir through a conduit to turbine generators located in a power plant at a lower level.

Pumping:  Is the reversal of flow within a dynamic compressor that takes place when the capacity being handled is reduced to a point where insufficient pressure is being generated to maintain flow. Also known as surge.

Purge Air:  The portion of dry, full line pressure, compressed air taken from the drying side tower of a dual tower desiccant dryer system. Expanded to a very low pressure and passed across the wet desiccant to strip the moisture in the desiccant of the regenerating tower. In the case of an external blower type dryer, the purge air is atmospheric air compressed by a blower and heated by an external heater to strip moisture off a wet desiccant bed.

Purifier: A purifier is a device that cleans the air of viruses and microscopic organisms as well as dust and allergens. Purifiers are especially useful for people who suffer from allergies and wish to live an allergy-free lifestyle.

Purlins: Framing members that sit on top of rafters, perpendicular to them, designed to spread support to roofing materials.

PV – Photovoltaic: A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semi-conductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multi-crystalline, or amorphous forms.

PV (Photovoltaic) Panels: Uses semiconductor material to efficiently and directly convert sunlight into electricity. Power is produced when sunlight strikes the semiconductor material which creates an electric current.

PVC:  Polyvinyl chloride; a type of plastic.

Pyrophoric: A substance that will ignite spontaneously in air at a temperature of 1300 F (54.40 C) or below.