Glossary of Terms used in HVAC

Air Conditioning


The term air conditioning refers to the cooling and dehumidification of indoor air for thermal comfort. In a broader sense, the term can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air. An air conditioner (AC or A/C in North American English, aircon in British and Australian English) is an appliance, system, or mechanism designed to stabilise the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), typically using a refrigeration cycle but sometimes using evaporation, most commonly for comfort cooling in buildings and motor vehicles.

Airflow

The distribution or movement of air.

Air Handler/Coil Blower

The indoor part of an air conditioner or heat pump that moves cooled or heated air throughout the ductwork of your home. An air handler is usually a furnace or a blower coil.


American Society of Heating, Refrigerating, and Air-Conditioning Engineers

 

ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) is an organization devoted to the advancement of indoor-environment-control technology in the heating, ventilation, and air conditioning (HVAC) industry. ASHRAE was founded in 1894 to serve as a source of technical standards and guidelines. Since that time, it has grown into an international society that offers educational information, courses, seminars, career guidance, and publications. The organization also promotes a code of ethics for HVAC professionals and provides for liaison with the general public. It is based out of the town of Washington D.C.

Bioaerosols

Microscopic living organisms suspended in the air that grow and multiply in warm, humid places.

Btu

A British thermal unit is a unit of heat energy. One Btu is the amount of heat required to raise one pound of water by one degree Fahrenheit. The higher the Btu rating, the greater the heating capacity of the system.

Carbon Monoxide

An odorless, colorless, tasteless, poisonous and flammable gas that is produced when carbon burns with insufficient air.

Central Air Conditioning System

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

CFM

Stands for Cubic Feet per Minute. This measurement indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being moved through the ductwork by the system.

Compressor

The part of the outdoor air conditioner or heat pump that compresses and pumps refrigerant to meet household cooling requirements.

Condenser Coil

The outdoor portion of an air conditioner or heat pump that either releases or collects heat, depending on the time of the year.

Damper

A movable plate, located in the ductwork, that regulates airflow. Dampers are used to direct air to the areas that need it most. Typically used in a zoning application.

Ductwork

The method by which air is channeled from the furnace or the blower coil throughout your home.

Electronic Air Cleaner

An electronic device that filters out large particles and bioaerosols in indoor air.

ENERGY STAR®

An EPA (Environmental Protection Agency) designation attached to HVAC products that meet or exceed EPA guidelines for high-efficiency performance above the standard government minimums.


Energy use

 

It should be noted that in a thermodynamically closed system, any energy input into the system that is being maintained at a set temperature (which is a standard mode of operation for modern air conditioners) requires that the energy removal rate from the air conditioner increase. This increase has the effect that for each unit of energy input into the system (say to power a light bulb in the closed system) requires the air conditioner to remove that energy. In order to do that the air conditioner must increase its consumption by the inverse of its efficiency times the input unit of energy. As an example presume that inside the closed system a 100 watt light bulb is activated, and the air conditioner has an efficiency of 200%. The air conditioner's energy consumption will increase by 50 watts to compensate for this, thus making the 100 W light bulb utilise a total of 150 W of energy.

 

Note that it is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%, see Coefficient of performance.

EPA

The Environmental Protection Agency develops and enforces federal environmental regulations. The EPA oversees the nationwide Energy Star® program.

Evaporator Coil

The part of the air conditioner or heat pump that is located inside the air handler or attached to the furnace. Its primary function is to absorb the heat from the air in your house.

Heat pump

 

Heat pump is a term for a type of air conditioner in which the refrigeration cycle is able to be reversed, producing heat instead of cold in the indoor environment. Using an air conditioner in this way to produce heat is significantly more efficient than electric resistance heating. Some home-owners elect to have a heat pump system installed, which is actually simply a central air conditioner with heat pump functionality (the refrigeration cycle is reversed in the winter). When the heat pump is enabled, the indoor evaporator coil switches roles and becomes the condensor coil, producing heat. The outdoor condensor unit also switches roles to serve as the evaporator, and produces cold air (colder than the ambient outdoor air).

 

Heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 40-55°F (4-13°C), because heat pumps become inefficient in more extreme cold. This is due to the problem of the outdoor unit's coil forming ice, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil back to being the condensor coil so that it can heat up and de-ice. A heat pump system therefore will have a form of electric resistance heating in the indoor air path that is activated only in this mode in order to compensate for the temporary air conditioning, which would otherwise generate undesirable cold air in the winter. The icing problem becomes much more prevalent with lower outdoor temperatures, so heat pumps are commonly installed in tandem with a more conventional form of heating, such as a natural gas or oil furnace, which is used instead of the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during the milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.

 

Some more expensive window air conditioning units have the heat pump function. However, a window unit that has a "heat" selection is not necessarily a heat pump because some units use electric resistance heat when heating is desired. A unit that has true heat pump functionality will be indicated in its literature by the term "heat pump".

 

Horizontal Flow

When an air handler or furnace is positioned on its side and circulates air in one end and out the other. Ideal for attic or crawl space installations.

Humidifier

An indoor air quality device that introduces moisture to heated air as it passes from the furnace into the ductwork for distribution throughout the home.

Humidistat

An automatic device used to maintain humidity at a fixed or adjustable set point.

MERV Rating

The MERV (Minimum Efficiency Reporting Value) rating of a filter describes the size of the holes in the filter that allow air to pass through. The higher the MERV rating, the smaller the holes in the filter, the higher the efficiency.

Micron

A unit of measure equal to one millionth of a meter, or one thousandth of a millimeter.

Odors/Chemicals

Air contaminants in the form of gases.

Particles

Any substances measuring less than 100 microns in diameter. The EPA has found that small particles (less than 2.5 microns) are responsible for the health effects of greatest concern.


Portable air conditioners

 

A portable air conditioner or portable A/C is an air conditioner on wheels that can be easily transported inside a home or office. They are currently available with capacities of about 6,000 to 60,000 BTU/h (1,800 to 18,000 watts output) and with and without electric resistance heaters. Portable true air conditioners come in two forms, split and hose. Evaporative coolers, sometimes called conditioners, are also portable.

 

Air-cooled portable air conditioners are compressor-based refrigerant system that use air to exchange heat, in the same way as a car or typical household air conditioner. With this type of system the air is dehumidified as it is cooled. They collect water condensed from the cooled air, and produce hot air which must be vented outside of the cooled area (they transfer heat from the air in the cooled area to air which must be vented).

 

A split system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit.

 

Hose systems, which can be Air-to-Air and Monoblock, are vented to the outside via air ducts. The "monoblock" version collects the water in a bucket or tray and stops when full. The Air-to-Air version re-evaporates the water and discharges it through the ducted hose, and can run continuously.

 

A single-duct unit draws air out of the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms, thus reducing efficiency. Modern units run on approximately 1 to 3 ratio i.e., to produce 3 kW of cooling this will use 1 kW of electricity. A dual-duct unit draws air from outside to cool its condenser instead of from inside the room, and thus is more efficient than most single-duct units.

 

As a rule of thumb, 400 square feet (37 m²) can be cooled per 12,000 BTU/h (3.5 kW or one ton of air conditioning) by a refrigerative air conditioner. However, other factors will affect the total heat load.

 

Evaporative air coolers, sometimes called air conditioners, do not have a compressor or condenser. Instead liquid water is evaporated, releasing the vapour into the cooled area. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation, cooling the air—humans and other animals use the same mechanism to cool themselves by sweating. Disadvantages are that unless ambient humidity is low (dry climate) cooling is limited and the cooled air is very humid and can feel clammy. They have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable; and they are cheaper to install and use much less energy than refrigerative air conditioners.

Programmable Thermostat

A thermostat with the ability to record different temperature/time settings for your heating and/or cooling equipment.

R410A Refrigerant

A chlorine-free refrigerant that meets the EPA's newest, most stringent environmental guidelines.

Refrigerant

A chemical that produces a cooling effect while expanding or vaporizing. Most residential air conditioning units contain the standard R-22 refrigerant, or Freon.

Refrigerant Lines

Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.

Scroll Compressor

A specially designed compressor that works in a circular motion, as opposed to up-and-down piston action.

SEER

The cooling performance of air conditioners and heat pumps is rated using the SEER (Seasonal Energy Efficiency Ratio) system, which ranges from 13.00 to 20.00 for new systems. The higher the SEER, the better the efficiency, the greater your energy savings.

Package Unit

A heating and cooling system contained in one outdoor unit.

Split System

An HVAC system in which some components are located inside the structure of the house and some are located outside. Split systems should be matched for optimal efficiency.

Thermostat

Usually found on an inside wall, this device operates as a control to regulate your heating and cooling equipment, allowing you to adjust your home comfort at the touch of a switch.

Ton

Unit of measurement for determining cooling capacity. One ton equals 12,000 Btuh.

Two-Stage Operation

Provides two levels of heating or cooling output for greater temperature control, energy efficiency and improved indoor air quality.

Variable Speed Motor

A motor that automatically adjusts the flow of warm or cool air for ultimate comfort.

Zoning

A method of partitioning a home into independently controlled comfort zones for enhanced comfort and efficiency.

 
 
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