HVAC Glossary

Alternative HVAC Solutions would like to offer the following HVAC Glossary as a helpful tool for you, our customer, to help with the various terms and technical definitions for the heating, cooling and indoor air quality industry.

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Saturation Temperature -  Also referred to as the boiling point or the condensing temperature. This is the temperature at which a refrigerant will change state from a liquid to a vapor or visa versa.
SEER -  (Seasonal Energy Efficiency Ratio) An efficiency measurement that is similar to Miles Per Gallon for cars. The higher this number, the more energy efficient they system is. The amount of cooling your equipment delivers per every dollar spent on electricity. The higher the number the lower the operating cost (not more cooling.) SEER applies to air conditioners and heat pumps. In the past, a unit with a SEER of 8.00 was considered standard efficiency, and a unit with a 10.00 SEER was considered high efficiency. After January 1, 1992 , the minimum SEER required by the DOE is 10.00 and 15.00+ SEER is considered high efficiency. EER & SEER can not be compared equally. Air source equipment is rated by SEER and geothermal equipment is rated by EER. New units have SEER ratings from 10 to 17 BTUs per watt. The total cooling of a central unitary air conditioner or unitary heat pump in Btu's during its normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period. The Seasonal Energy Efficiency Ratio is a standard method of rating air conditioners based on three tests. All three tests are run at 80 degrees Fahrenheit inside and 82 degrees Fahrenheit outside. The first test is run with humid indoor conditions, the second with dry indoor conditions, and the third with dry conditions cycling the air conditioner on for 6 minutes and off for 24 minutes. The published SEER may not represent the actual seasonal energy efficiency of an air conditioner in your climate. The total cooling output of a central air conditioning unit in Btus during its normal usage period for cooling divided by the total electrical energy input in watt-hours during the same period, as deteRebholtz Mechanicalned using specified federal test procedures. [Title 20, Section 2-1602(c)(11)].
Sensible Cooling Load -  The heat gain of the home due to conduction, solar radiation, infiltration, appliances, people, and pets. Burning a light bulb, for example, adds only sensible load to the house. This sensible load raises the dry-bulb temperature.
Sensible Heat -  Heat, that when added or removed, causes a change in temperature but not in state. Heat that results in a temperature change.
Sensitization -  Repeated or single exposure to an allergen that results in the exposed individual becoming hypersensitive to the allergen.
Setback -  A reduction of climate control energy demand in HVAC controls when a building is unoccupied.
Setpoint -  The temperature to which a thermostat is set to result in a desired heated space temperature.
Short-Circuiting -  Situation that occurs when the supply air flows to return or exhaust grilles before entering the breathing zone (area of a room where people are). To avoid short-circuiting, the supply air must be delivered at a temperature and velocity that results in mixing throughout the space.
Sick building -  A building in which the indoor air quality is considered to be unacceptable to a substantial majority of occupants.
Sick Building Syndrome -  (SBS) A phenomenon in which building occupants experience a variety of health and/or comfort effects linked to time spent in a particular building, but where no specific illness or causative agent can be identified. Symptoms in sufferers often include headaches, eye irritation, and respiratory irritation. Term that refers to a set of symptoms that affect some number of building occupants during the time they spend in the building and diminish or go away altogether during periods when they leave the building. (Contrast with Building Related Illness.)
Single Package -  A year 'round heating and air conditioning system that has all the components completely encased in one unit outside the home.
Sizing -  Refers to the procedure a heating contractor goes through to determine how large a furnace (measured in btuh) is needed to heat a house efficiently. Too small a furnace won't deliver enough heating; too large a furnace increases energy costs and can have an adverse effect on comfort. Sizing depends on the square-footage of the home, the amount of ceiling and wall insulation, the window area, use of storm doors, storm windows, and more.
Smoke stick -  A diagnostic tool used to observe air flow. Usually it consists of a chemical in a squeezable container. When squeezed it emits smoke which visibly follows air flow currents.
Sound Attenuators -  Components which are inserted into the air distribution system and designed to reduce airborne noise which is propagated along the ducts.
Sound Rating Number -  (SRN) Sound is measured in bels (a bel equals 10 decibels). The SRN of a unit is based on ARI test, performed at ARI standard rating conditions. Average sound rating range from 7.0 to 8.0 decibels. The lower the SRN rating, the quieter the unit.
Sound Ratings -  Although sound does not affect the efficiency of a unit, it will certainly affect your comfort. If your unit has a low sound level, you will hardly notice it is operating. But if it has a higher sound level, it may mean your good night's sleep is disturbed every time it runs!
Source Control -  A preventive strategy for reducing airborne contaminant levels through removal of the material or activity generating the pollutants.
Sources -  Sources of indoor air pollutants. Indoor air pollutants can originate within the building or be drawn in from outdoors. Common sources include people, fixtures and furnishings, photocopiers, plants, food, etc.
Specific Heat -  In English units, the quantity of heat, in Btu, needed to raise the temperature of one pound of material one degree Fahrenheit.
Split System -  Refrigeration or air conditioning installation, which places condensing unit outside or away from evaporator. These unit are connected together by a supply and return refrigerant lines. Also applicable to heat pump installations. A combination heat pump or air conditioner with indoor components such as a furnace or blower coil. To maximize effectiveness, Split Systems should be matched.
Spore -  Molds reproduce by means of spores. Spores are microscopic; they vary in shape and size (2-100 micrometers). Spores may travel in several ways--they may be passively moved (by a breeze or waterdrop), mechanically disturbed (by a person or animal passing by), or actively discharged by the mold (usually under moist conditions or high humidity).
Spread -  (LS) (for a supply air device) Maximum distance between two vertical planes tangent to a specified envelope and perpendicular to a plane through the core center. The spread are generally referred to the envelope corresponding to 0.25 m/s for zero supply temperature differential (i.e., under isothermal conditions).
SRN -  (Sound Rating Number) Sound is measured in bels (a bel equals 10 decibels). The SRN of a unit is based on ARI test, performed at ARI standard rating conditions. Average sound rating range from 7.0 to 8.0 decibels. The lower the SRN rating, the quieter the unit.
Stack effect -  A condition resulting from the rise of heated air, which creates positive pressure near the top of the building and negative pressure toward the bottom. Stack effect pressures have been known to overpower mechanical ventilation systems, disrupting proper circulation and contributing to the infiltration and stagnation of pollutants.
Standard Industrial Classification -  (SIC) A set of codes developed by the Office of Management and Budget, which categorizes business into groups with similar economic activities.
Static Pressure -  Condition that exists when an equal amount of air is supplied to and exhausted from a space. At static pressure, equilibrium has been reached.
Statistical Significance -  The probability that and degree to which the results of an experimental study describe an actual relationship between two factors beyond that which might be expected by pure coincidence.
Straight Cool -  This is an air conditioner that uses different forms of heating such as Natural Gas, LP Gas, Electric Resistance heat and oil.
Stratosphere -  Part of the atmosphere, the gases that encircle the Earth. The stratosphere is a layer of the atmosphere 9-31 miles above the Earth. Ozone in the stratosphere filters out harmful sun rays, including a type of sunlight called ultraviolet B, which has been linked to health and environmental damage.
Subcooled Liquid -  Liquid refrigerant which is cooled below its saturation temperature.
Superheated Vapor -  Refrigerant vapor which is heated above its saturation temperature. If a refrigerant is superheated, there is no liquid present.
Supplementary Heat -  (Emergency Heat) The auxiliary or emergency heat provided at temperatures below a heat pump's balance point. It is usually electrical resistance heat.
Supply -  The ductwork that carries air from the air handler to the rooms in the house.
Supply Air -  The air flow entering the treated space.
Swamp Cooler -  See Evaporative Cooler.
Switchover Valve -  A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating. Also called a reversing valve or four-way valve.
System -  A combination of equipment and/or controls, accessories, interconnecting means and elements by which energy is transformed to perform a specific function, such as climate control, service water heating, or lighting.
Systems Control -  The control of indoor air pollutants through the use of mechanical means such as ventilation control or air cleaning.