AC: Abbreviation for alternating current, a type of electric current in which the polarity is constantly reversing causing the electron flow to reverse.
AC or DC: Abbreviation for equipment capable of operating on alternating or direct current.
A-Coil: A heat exchanger consisting of two diagonal coils that are joined together in a manner that looks like the letter "A".
Air Conditioner: Any device that can change the temperature, humidity or general quality of the air.
Air Cleaner: Any device that removes undesirable particles from moving air.
Air Flow Volume: The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.
Air handler: An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and filter. Heaters for air handlers are sold as accessories. In some models heaters are factory installed. Allergen: Substance (such as dust mites, mold or mold spores) that can cause an allergic reaction.
B Biocide: Substance or chemical that kills organisms such as molds.
Building Information Modeling (BIM): A digital computer model of the physical and functional characteristics of a facility. Includes Load Calculation and Building Simulation Program. Model can be created prior to construction to predict the effects of energy conservation measures (ECM).
BTU: British thermal unit; the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The heat extracted from your home by an air conditioner is measured in BTUs.
BTUh:British thermal units per hour. 12,000 BTUh equals one ton of cooling.
Building Occupants: Describes people who spend extended time periods in the building. Clients and visitors are also occupants; they may have different tolerances and expectations from those who spend their entire workdays in the building, and they are likely to be more sensitive to odors.
Building Related Illness (BRI): Refers to illness brought on by exposure to the building air, where symptoms of diagnosable illnesses are identified (e.g., certain allergies or infections) and can be directly attributed to environmental agents in the air. Legionnaire’s disease and hypersensitivity pneumonitis are examples of BRI that can have serious, even life-threatening, consequences.
Building Simulation Program: Part of BIM analysis. Uses information from Load Calculation Program, along with Typical Meteorological Year (TMY) weather data, and utility and equipment data, to compute annual energy usage and utility cost of operation.
C Capacity: The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.
Celsius: The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C". To convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5 and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit).
CFM: Abbreviation for cubic feet per minute, a standard measurement of airflow. A typical system requires 400 cfm per ton of air conditioning.
Charge: To add refrigerant to a system. This is refrigerant contained in a sealed system or in the sensing bulb to a thermostatic expansion valve.
Coefficient of Performance (COP): A performance rating for any type of heat pump or air conditioner. Defined as the desired effect-namely, cooling or heating capacity-divided by the power consumed to provide that effect, where the desired effect and power consumed are in like units. COPc, the Coefficient of Performance in cooling, is the cooling capacity (in Btu/hr, for example) divided by the electrical power consumed, in the same units (Btu/hr in this example). Likewise, COPh, the Coefficient of Performance in heating, is the heating capacity divided by the electrical power consumed, expressed in like units. Note that COP is similar to Energy Efficiency Rating (EER), except that EER uses mixed units; that is, the cooling or heating capacity is in Btu/hr and the power consumed is in Watts. This is not a good idea, but it represents a simplification of the COP concept for non-technical individuals. See EER.
Note that COP typically decreases with temperature lift, and that an electric (resistance) heater will have a (constant) COPh of one, which means that one unit of electrical energy will produce one unit of heat or work.
Also note that COPh is theoretically one unit higher than COPc for the same lift; that is, COPh = COPc + 1 for the same lift.
Cooling Load Calculation: The amount of sensible heat and latent heat gain added to the structure, including the solar heat gain through the windows and infiltration through doors, windows, and leaks. Used to determine the size of the cooling system required.
Compressor: This is the heart of an air conditioning or heat pump system. It is part of the outdoor unit and pumps refrigerant in order to meet the cooling requirements of the system.
Condensate: Vapor that liquefies due to the lowering of its temperature to the saturation point.
Condenser coil: In an air conditioner, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. In a heat pump system, the coil absorbs heat from the outdoors.
Condenser fan: The fan that circulates air over the air-cooled condenser.
Contactor: A switch that can repeatedly cycle, making and breaking an electrical circuit. When sufficient current flows through the A-coil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.
DC:Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.
Damper: Found in ductwork, this movable plate opens and closes to control airflow. Dampers can be used to balance airflow in a duct system. They are also used in zoning to regulate airflow to certain rooms.
Defrost: To melt frost; as in from an air conditioner or heat pump coil.
Degree-day: A degree-day is a computation that gauges the amount of heating or cooling needed for a building. A degree-day is equal to 65 degrees Fahrenheit minus the mean outdoor temperature.
Dew Point Temperature: Temperature at which the air can no longer hold off of its water vapor. Condensates into liquid water. If the dew point is 75° the air feels thick and it is hard to breathe. 70° and above is oppressive.
Diffuser: A grille over an air supply duct having vanes to distribute the discharging air in a specific pattern or direction.
Drain pan: Also referred to as a condensate pan. This is a pan used to catch and collect condensate (in residential systems vapor is liquefied on the indoor coil, collected in the drain pan and removed through a drain line).
Dry Bulb Temperature: The temperature of the air measured with a dry thermocouple or thermometer with a dry bulb. The Dry-Bulb and Wet-Bulb temperatures can be used together to determine relative humidity.
Duct work:A pipe or conduit through which air is delivered. Ducts are typically made of metal, fiberboard or a flexible material. In a home comfort system, the size and application of ductwork is critical to performance and is as important as the equipment.
DX: Direct expansion; a system in which heat is transferred by the direct expansion of refrigerant.
ECM (Energy Conservation Measures): Recommendations resulting from an energy audit. Can include measures to improve the efficiency of lighting, HVAC equipment, utilities, and the building itself.
Energy Conservation:An effort to reduce the amount of energy needed to operate a device or process or even eliminate it. Methods include building maintenance, equipment replacement, addition of digital controls, and energy recovery.
Energy Efficiency: Calculated by dividing the work produced by the energy used within a process. The less energy consumed to produce the work, the greater the energy efficiency.
Energy Efficiency Ratio (EER): Similar to COP, EER is a measure of the relative performance of a heating or cooling appliance. Defined as the desired effect-namely, cooling or heating capacity-in Btu/hr, divided by power consumed, in Watts, to provide that effect. Note that the desired effect and power consumed are in specific and different units. EERc, the Energy Efficiency Ratio in cooling, is the cooling capacity, in Btu/hr, divided by the electrical power consumed, in Watts. Likewise, EERh, the Energy Efficiency Ratio in heating, is the heating capacity, in Btu/hr, divided by the electrical power consumed, in Watts.
While calculating a performance rating in mixed units is not proper engineering methodology, this simplification of the COP concept has been developed for non-technical individuals. The author believes this is very bad idea; however, it has become an industry standard, probably because it provides a larger number. The EER will always be larger than the COP for a system, because of the difference in units conversion, and can give the appearance of better performance. For example, an electric (resistance) heater will have a COPh of 1.0 and an EERh of 3.41.
To convert an EER to COP, simply multiply the EER value by 0.293 to obtain the equivalent COP value. Energy Management: A general term to cover the whole field of energy and its use. Can be divided into energy consumption, demand, efficiency, and conservation. Enthalpy: Total energy content
EPA: Environmental Protection Agency, Founded in 1970, the U.S. EPA leads the nation's environmental science, research, education and assessment efforts. The mission of the Environmental Protection Agency is to protect human health and the environment. The HVAC/R industry operates under EPA standards and regulations.
Exfiltration: A term used to describe uncontrolled air moving out of a building.
Expansion Valve: A refrigerant-metering valve with a pressure or temperature controlled orifice.
Evaporator coil: The other half of your air conditioning system located inside your home in the indoor unit. This is a tubing coil in which a volatile liquid evaporates and absorbs heat. This is where the refrigerant evaporates as it absorbs heat from the indoor air that passes over the coil.
Fahrenheit:The temperature scale on which water freezes at 32 degrees and boils at 212 degrees; designated by the letter F. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit number, multiply by 5 and divide by 9 (77 -32 equals 45, times 5 equals 225, divided by 9 equals 25 degrees Celsius).
Heat Exchanger: A device that moves heat energy from one fluid to another while maintaining a complete fluid separation. An area, box or coil where heat flows from the warmer to the colder fluid or surface.
Heat Gain: Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.
Heating Season Performance Factor (HSPF): Like the EER, this is a mixed units ratio. In this case, it is a ratio of estimated seasonal heating output, divided by estimated seasonal power consumption for an average U.S. climate. Similar to SEER, which is for cooling, it estimates the heating season performance by estimating the outdoor temperatures, and it takes into account the efficiency of the equipment for an entire heating season. The HSPF is more of a marketing tool than a useful engineering metric. By using a seasonally averaged outdoor temperature instead of the worst-case temperature, a higher performance “number” is obtained, which looks good on marketing literature.
Heat Load Calculation: An evaluation of sensible heat loss from a structure to the colder outside air as well as from infiltration through doors, windows, and leaks. Used to determine the size of the heating system required.
Heat Loss: The rate of heat transfer from a heated space to the outdoors.
Heat Pump: A mechanical-compression cycle refrigeration system that can be reversed to either heat or cool the controlled space.
Heat Transfer:The movement of heat energy from one point to another. The means for such movement are conduction, convection, and radiation.
HEPA (High-Efficiency Particulate Air): A HEPA filter is one that can remove at least 99.97% of airborne particles 0.3 micrometers (µm) in diameter. Particles of this size are the most difficult to filter and are thus considered the most penetrating particle size (MPPS). Particles that are larger or smaller are actually easier to filter out of the air.
Hertz:In alternating current (AC electricity), the number of cycles per second.
Humidifier:A machine that adds water vapor to the air to increase humidity.
Humidistat: A humidity-sensing control that cycles the humidifier on and off.
Humidity: The presence of water vapor in the air. Humidity Ratio: Also known as Specific Humidity, it is the ratio of the mass of water contained in a mass of dry air. For example, the pounds of water in a pound of dry air.
HVAC:Abbreviation for Heating, Ventilating and Air Conditioning
IAQ (Indoor Air Quality): Refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants. The quality of breathable air within a building.
Latent Heat:A type of heat, which when added to or taken from a substance, does not change the temperature of the substance. Instead, the heat energy enables the substance to change its state.
Leak Rate : The rate at which an appliance is losing refrigerant, measured between refrigerant charges or over 12 months, whichever is shorter. The leak rate is expressed in terms of the percentage of the appliance’s full charge that would be lost over a 12-month period if the current rate of loss were to continue over that period. The rate is calculated by using the following formula:
(Refrigerant added/Total Charge) x (365 days / year / D) x 100%
where D = the shorter of: # days since refrigerant last added or 365 days
Life Cycle Cost Analysis: A cost analysis that includes the total cost of installing, operating, and maintaining a device for the total life of the device.
Major Maintenance:Maintenance, service, or repair that involves removal of a vapor compression system compressor, condenser, evaporator, or auxiliary heat exchanger coil.
Media:The material in a filter that traps and holds the impurities.
MERV (Minimum Efficiency Reporting Value) Rating: A measurement designed by ASHRAE to rate the effectiveness of air filters. Represents the worst-case performance of a filter when dealing with particles in the range of 0.3 to 10 microns. The MERV rating is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass.
mVOC: Microbial volatile organic compound, a chemical made by a mold that may have a moldy or musty odor
Reclamation: To reprocess refrigerant to at least the purity specified in the ARI Standard 700, Specifications for Fluorocarbon Refrigerants, and to verify this purity using the analytical test procedures described in the Standard.
Recovery: To remove refrigerant in any condition from an appliance and to store it in an external container without necessarily testing or processing it in any way.
Recovery Efficiency: The percentage of refrigerant in an appliance that is recovered by a recycling or recovery unit.
Recycling: To extract refrigerant from an appliance and to clean refrigerant for reuse without meeting all of the requirements for reclamation. In general, recycled refrigerant is refrigerant that is cleaned using oil separation and single or multiple passes through devices such as replaceable-core filter driers, which reduce moisture, acidity, and particulate matter.
Refrigerant: A chemical that produces a refrigerating effect while expanding and vaporizing. Most residential air conditioning systems contain R-22 refrigerant. R-22 is regulated under the Montreal Protocol and in the United States by the Environmental Protection Agency. R-22 is scheduled to be in production until the year 2020. It's used in approximately 95 percent of air conditioning equipment manufactured in the U.S. today.
Relative Humidity: The ratio of weight of water in the air relative to the maximum weight of water that can be held in saturated air Renewable Energy: A repeatable source of energy, such as ethanol, a hydrocarbon fuel that can be produced through distillation of plants.
SEER: Like the EER, the SEER is a mixed units ratio. In this case, it is a ratio of estimated seasonal cooling output, divided by estimated seasonal power consumption for an average U.S. climate. Similar to HSPF, which is for heating, it estimates the cooling season performance by estimating the outdoor temperatures, and it takes into account the efficiency of the equipment for an entire cooling season. The SEER is more of a marketing tool than a useful engineering metric. By using a seasonally averaged outdoor temperature instead of the worst-case temperature, a higher performance “number” is obtained, which looks good on marketing literature. The minimum SEER rating for central air conditioning systems is 13 as of Jan. 23, 2006
Self-Contained System:A refrigerating system that can be moved without disconnecting any refrigerant lines; also know as a package unit.
Sensible Heat: That heat which, when added to or taken away from a substance, causes a rise or fall in temperature.
Sensor: Any device that reacts to a change in the conditions being measured, permitting the condition to be controlled.
Setpoint:The temperature or pressure at which a controller is set with the expectation that this will be a nominal value depending on the range of the controller.
Split System:The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler). Split systems must be matched for optimum efficiency.
T Thermostatic Expansion Valve: A refrigerant metering device that maintains a constant evaporator temperature by monitoring suction vapor superheat; also called a thermal expansion valve.
Thermostat: A thermostat consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.
Ton: A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.
Two-Stage Heating / Two-Stage Cooling: Two-stage heating and cooling is considered to be more efficient, because it operates at low speed most of the time. However, on days when more heating or air conditioning is required, it switches to the next stage for maximum comfort.
Watt: The unit of electrical power equal to the flow of one amp at a potential difference of one volt. Wet-Bulb Temperature: The temperature of the air measured with a wet thermocouple or thermometer with a wet bulb. The dry-bulb and wet-bulb temperatures can be used together to determine relative humidity.
Wet Bulb Thermometer: A thermometer whose bulb is covered with a piece of water-soaked cloth. The lowering of temperature that results from the evaporation of water around the bulb indicates the air's relative humidity.
Zoning System: A method of dividing a home into different comfort zones so each zone can be independently controlled depending on use and need; an air conditioning system capable of maintaining varying conditions for various rooms or zones.