Air Change

The amount of air required to completely replace the air in a room or building; not to be confused with re-circulated air.


Air Conditioner

Assembly of equipment for the simultaneous control of air temperature and relative humidity.


Air Cooled

Uses a fan to discharge heat from the condenser coil to the outdoors.


Air-Cooled System

A type of air conditioning system that uses freon as a refrigerant and air as a condensing medium. Typically, the air-cooled condenser is located outside and refrigerant lines are piped to it from the indoor unit.


Air Diffuser

Air distribution outlet or grille designed to direct airflow into desired patterns.


Air Flow

The distribution or movement of air.


Air Handler

The portion of the central air conditioning or heat pump system that moves heated or cooled air throughout a home’s ductwork. In some systems a furnace handles this function.


Auto Changeover

A control package that provides for automatic switching from a primary air conditioning system to a backup in the event of a failure of the primary system.


BTU (British Thermal Unit)

The standard of measurement used for measuring the amount of heat required to raise the temperature of one pound of water by one degree (Fahrenheit). BTUH – The number of BTUs in an hour.


Capacity

The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTU’s or KW. For cooling, it is usually given in tons or KW.


Central Air Conditioner System

System in which air is treated at a central location and carried to and from the rooms by one or more fans and a system of ducts.


Centrifugal Compressor

A type of compressor used in vapor compression refrigeration cycles where a rotating impeller is the device which compresses the refrigerant vapor. The vapor is drawn into the impeller axially, and is discharged radially after energy is added to the vapor within the impeller.


Charge

Amount of refrigerant in a system.


Chilled Water System

A type of air conditioning system that has no refrigerant in the unit itself. The refrigerant is contained in a chiller, which is located remotely. The chiller cools water, which is piped to the air conditioner to cool the space.


Comfort Air Conditioning

Comfort air conditioning systems are designed for the comfort of people, not the protection of computer-based electrical systems. Unlike people, computers generate dry (sensible) heat, but not humidity. Only about 60-70% of a comfort system’s total capacity is dedicated to the removal of sensible heat, while 30-40% is for dehumidification. With a large percentage of their total capacity devoted to the removal of moisture, comfort systems can lower room humidity far below acceptable standards. A larger comfort system is required to obtain the same sensible capacity as a precision cooling system.


Compressor

The pump that moves the refrigerant from the indoor evaporator to the outdoor condenser and back to the evaporator again. The compressor is often called “the heart of the system” because it circulates the refrigerant through the loop.


Condensation

The process by which a gas is changed into a liquid at constant temperature by heat removal. The moisture in the air turns into condensation fluid or water.


Condenser

A device that transfers unwanted heat out of a refrigeration system to a medium (either air, water, or a combination of air and water) that absorbs the heat and transfers it to a disposal point. There are three types of condensers: air-cooled condensers, water-cooled condensers, and evaporative condensers. The evaporative condenser uses a combination of air and water as its condensing medium. Most residential systems have an air-cooled condenser.


Condenser Coil

A series or network of tubes filled with refrigerant, normally located outside the home, that removes heat from the hot, gaseous refrigerant so that the refrigerant becomes liquid again.


Condensing Unit

Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil ignoring the reverse cycle operation, also the outdoor in a heat pump system.


COP (Coefficient of Performance)

This is a measure of the energy efficiency of a chiller.


Cooling Capacity

A measure of the ability of a unit to remove heat from an enclosed space. COP – Coefficient of Performance of a heat pump means the ratio of the rate of useful heat output delivered by the complete heat pump unit (exclusive of supplementary heating) to the corresponding rate of energy input, in consistent units and under operating conditions.


Cooling Load

Heat which flows into a space from outdoors and/or indoors.


Damper

Found in ductwork, this movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms.


Defrost Cycle

The process of removing ice or frost buildup from the outdoor coil during the heating season.


Dehumidification

The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.


Department of Energy (DOE)

A agency that sets industry efficiency standards and monitors the use of various energy sources.


Direct Expansion Systems

One of two types of basic cooling media (the other is chilled water). Direct expansion systems utilize freon for cooling and dehumidification. The three most common methods of heat rejection are air cooled, water cooled and glycol cooled.


Direct Ventilation

Pulls outside air for combustion and vents combustion gases directly outside.


Downflow

Refers to a type of precision air conditioning system that discharges air downward, directly beneath a raised floor, commonly found in computer rooms and modern office spaces.


Duct

A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.


Ductwork

Pipes or channels that carry air throughout a building.


Electronic Air Cleaner

An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.


Emergency Heat (Supplemental or Auxillary Heat)

The back-up heat built into a heat pump system.


Energy Efficiency Ratio (EER)

Means the ratio of the cooling capacity of the air conditioner in British Thermal Units per hour, to the total electrical input in watts under ARI-specified test conditions.


Enthalpy

Heat content or total heat, including both sensible and latent heat. The amount of heat contained in a refrigerant at any given temperature with reference to -40F.


Evaporator

Absorbs heat from the surrounding air or liquid and moves it outside the refrigerated area by means of a refrigerant. It is also known as a cooling coil, blower coil, chilling unit or indoor coil.


Evaporator Coil

A series or network of tubes filled with refrigerant located inside the home that take heat and moisture out of indoor air as liquid refrigerant evaporates.


Fahrenheit (Represented as degrees “F”)

The scale of temperature measurement most commonly used in the United States of America.


Filter

A device used to remove dust and other particles from air for the purposes of reducing the load on the respiratory system and to protect the HVAC equipment. Filters vary greatly in particle arrestance; the higher the MERV rating, the better the filter.


Four Way Valve

A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating.


Free Cooling System

Typically a water cooled or glycol cooled system with an additional coil that provides chilled water cooling when the outdoor ambient is cold thereby reducing or eliminating compressor operation. Provides efficient system operation in Nothern climates.


Free Delivery

There are no ducts and the unit may be installed in the field without ducts if needed.


Glycol-Cooled System

A type of air conditioning system that uses freon as a refrigerant and a water/glycol solution as a condensing medium. Typically, the glycol-cooled condenser is located inside the air conditioner with the rest of the refrigeration components. Water/glycol is piped to the unit from a drycooler or other suitable source. The glycol keeps the solution from freezing during winter operation.


Ground-Source

The ground or soil below the frost line is being used as the heat source or heat sink for a heat pump.


Ground Water-Source

Water from an underground well is being used as the heat source or heat sink for a heat pump.


Heat Exchanger

A device for the transfer of heat energy from the source to the conveying medium.


Heat Gain

The amount of heat gained, measured in BTU’s, from a space to be conditioned, at the local summer outdoor design temperature and a specified indoor design condition.


Heat Loss

The amount of heat lost, measured in BTU’s from a space to be conditioned, at the local winter outdoor design temperature and a specified indoor design condition.


Heat Pump

An air conditioner that contains a valve that allows it to alternate between heating and cooling.


Heat Source

A body of air or liquid from which heat is collected. With any heat pumps, the air outside the home is used as the heat source during the heating cycle.


Heating Capacity

The rate at which a specific device can add substantial heat to a substance, expressed in BTUh (British Thermal Units per hour).


Horizontal Furnace

A furnace that lies on its side, pulling in return air from one side and expelling warm air from the other.


HVAC

Heating, Ventilation, and Air Conditioning.


Humidification

The process of adding moisture to the air within a space.


Humidistat

A device designed to regulate humidity input by reacting to changes in the moisture content of the air.


Humidity

The amount of moisture in the air. Air conditioners remove moisture for added comfort.


Indoor Unit

This is usually located inside the house and contains the indoor coil, fan, motor, and filtering device, sometimes called the air handler.


Indoor Coil

Refrigerant containing portion of a fan coil unit similar to a car radiator, typically made of several rows of copper tubing with aluminum fins.


Infiltration

Air flow into a space usually through walls and leaks around doors and windows.


Insulation

Any material that slows down the transfer of heat.


Kilowatt (kW)

Equal to 1,000 watts. Kilowatt-hour (kWh) – A common unit of electrical consumption measured by the total energy created by one kilowatt in one hour. It is also used to measure heat gains, heat losses and the output or capacity of air conditioning systems in both heating and cooling modes.


Latent Cooling Capacity

An A/C system’s capability to remove moisture from the air.


Latent Heat

The heat energy needed to change the state of a substance (i.e.: from a liquid to a gas) but not it’s temperature.


LCD

An abbreviation for a screen type – Liquid Crystal Display.


Load Calculation

A mathematical design tool used to determine the heat gain and heat loss in a building so that properly sized air conditioning and heating equipment may be installed.


Microprocessor Controls

A control system that uses computer logic to operate and monitor an air conditioning system. Microprocessor controls are commonly used on modern precision air conditioning systems to maintain precise control of temperature and humidity and to monitor the units operation.


Outdoor Coil/Condensing Unit

The portion of a heat pump or central air conditioning system that is located outside the home and functions as a heat transfer point for collecting heat from and dispelling heat to the outside air.


Package System

A piece of air conditioning and heating equipment where all components are located in one cabinet. Used occasionally in residential applications, the package unit is installed either beside or on top of the home.


Packaged Unit

A self-contained heating and/or air conditioning system.


Refrigerant

A substance that produces a refrigerating effect while expanding or vaporizing.


Refrigerant Lines

Set of two copper lines connecting the outdoor unit and the indoor unit.


Register

Combination grille and damper assembly covering an air opening or end of an air duct.


Relative Humidity

The ratio of the amount of vapor contained in the air to the greatest amount the air could hold at that temperature. Normally expressed as a percentage.


Return Air

Air drawn into a heating unit after having been circulated from the heater’s output supply to a room.


Reversing Valve

A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating.


SEER (Seasonal Energy Efficiency Ratio)

A rating that denotes the efficiency of air conditioning equipment. It is the amount of cooling your equipment delivers for every dollar spent on electricity. It is the ratio of cooling delivered by a system, measured in BTUs, to the dollar cost of the electricity to run the system, as measured in watt-hours. This ratio is determined using specified federal test procedures. The higher the SEER, the more efficient the unit. The more efficient the unit, the lower the operating cost.


Sensible Cooling Capacity

An A/C system’s capability to remove heat from the air. (lower the temperature).


Sensible Heat

Heat energy that causes a rise or fall in the temperature of a gas, liquid or solid when added or removed from that material. Sensible heat changes the temperature by changing the speed at which the molecules move.


Setpoint

The temperature to which a thermostat is set for desired comfort level.


Split System

A central air conditioner consisting of two or more major components. The system usually consists of a compressor-containing unit and condenser, installed outside the building and a non-compressor – containing air handling unit installed within the building. This is the most common type of system installed in a home.


Supercooled Liquid

Liquid refrigerant cooled below its saturation point.


Subcooler

This is a section of some condensers in which the temperature of the condensed refrigerant liquid is reduced. This improves the energy efficiency of the chiller.


Subcooling

Creating a drop in temperature by removing sensible heat from a refrigerant liquid.


Superheated Vapor

Refrigerant vapor heated beyond its saturation point.


Superheating

Creating a rise in temperature by adding heat energy to a refrigeration vapor.


Supplementary Heat

The auxiliary or emergency heat, usually electrical resistance heat, provided at temperatures below a heat pump’s balance point.


Thermidistat

Highly sophisticated programmable thermostat that senses the outdoor temperature, indoor air temperature, and indoor relative humidity. A microprocessor communicates with the heating and cooling equipment to determine the most efficient way to achieve perfect comfort. When used with a variable speed blower motor, this cite can reduce humidity even when cooling isn’t necessary (as when the indoor temperature is 70 degrees but relative humidity is high, eg, when it’s raining).


Thermostat

A temperature control device, typically found on a wall inside that consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.


Upflow

A type of air conditioning system that discharges air into the conditioned space via a top-mounted discharge plenum or through an overhead duct system.


Vacuum Pump

A pump used to remove air and moisture from a refrigeration system at a pressure below atmospheric pressure.


Vapor Barrier

A moisture-impervious layer applied to the surfaces enclosing a humid space to prevent moisture travel to a point where it may condense due to lower temperature.


Vapor Seal

A vapor seal is an essential part of preventing moisture infiltration into or migration out of a critical space, such as a data processing center or other room that contains sensitive electronic instrumentation. Essentially, a vapor seal is a barrier that prevents air, moisture, and contaminants from migrating through tiny cracks or pores in the walls, floor, and ceiling into the critical space. Vapor barriers may be created using plastic film, vapor-retardant paint, vinyl wall coverings and vinyl floor systems, in combination with careful sealing of all openings (doors and windows) into the room.


Ventilation

The process of supplying or removing air, by natural or mechanical means, to or from any space. Such air may or may not have been conditioned.


Ventilator

A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.


Water Cooled System

A type of air conditioning system that uses freon as a refrigerant and water as a condensing medium. Typically, the water-cooled condenser is located inside the air conditioner with the rest of the refrigeration components. Water is piped to the unit from a cooling tower or other suitable source.


Water Source

Water is being used as the heat source or heat sink for a heat pump. Sources of underground water are wells and sources of surface water are lakes, large ponds, and rivers.


Watt

A unit of power that equals one joule per second. Named after James Watt.


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