This glossary is intended to explain some of the techical and industry jargon surrounding heating, ventilation and air conditioning in plain English. It should help you to understand the technical specifications and capabilities of different air conditioning units, humidifiers, heaters, fans and dehumidifiers, and help to identify the most suitable solution for your climate control problem.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

A/C
Abbreviation for Air Conditioning or Air Conditioner.

Air Change
The amount of air needed in order to completely replace the air in a structure.

Air Cleaner
An appliance designed to remove contaminants from air. Also known as an air purifier.

Air Con
Short form of air conditioning or air conditioner.

Air Conditioner
A system for regulating the temperature and humidity of air within a structure.

Air Conditioning
A general term for systems which regulate temperature and humidity.

Air Purifier
An appliance designed to remove contaminants from air. Also known as an air cleaner.

Air To Air
A type of refrigerative air conditioning in which the moisture condensed from cooled air is re-evaporated and vended outside through as hose with the warm air. Unlike a monoblock air conditioner it can run continuously.

Ambient Temperature
The surrounding temperature of the atmosphere or environment.

B

BTU
British Thermal Unit. A unit defined as the amount of energy required to increase the temperature of one pound of water by one degree Fahrenheit. Now more commonly used in the US.

C

Chiller

An air conditioning system which circulates cooled water to the conditioned space. An evaporator that cools the water in such a system.

Chloroflurocarbons (CFC)
A substance used as a refrigerant. No longer used due to adverse environmental impact.

Compressor
A device for compressing gases such as air.

Condensation
The process of converting from a gas to a liquid.

Condenser
A system which removes heat and moisture from air. Condensers may be air-cooled, water cooled or evaporative.

Conditioned Space

The area being cooled or heated by an air conditioning system.

Controller
A panel that controls an air conditioning unit.

Cooling Capacity
The ability of an air conditioner to cool an area of a given size. Typically measured in Kilowatts (KW).

CPA
Construction Plant-Hire Association. An industry trade body of which CAS Hire is a member.

D

Dalton's Law

The total pressure in a vessel equals the sum of the vapour pressures of the individual gases in the vessel.

Dehumidifier
A device intended to reduce the moisture content (humidity) of air. A dehumidifier is effectively a type of air conditioner which passes air over a condenser to remove moisture, and then warms the air back up to room temperature.

Dessication

The process of removal of moisture from a substance.

E

Energy Efficiency Ratio (EER)

The ratio given by dividing the cooling capacity of an air conditioning system (in BTU/hour) by Watts of electricity used.

Evaporation
The process of converting from a liquid to a gaseous state.

Evaporative Air Cooler
An air conditioner which works by evaporating water and releasing it into the air. Heat is absorbed as the water evaporates (latent heat of vaporisation). Works best in areas of low humidity, but does not need an outside vent, unlike a refrigerative air conditioning system.

Evaporator Temperature
The temperature of refrigerant boiling in an evaporator.

F

Filter
A device to remove particulate matter from air.

H

Heat Exchanger
A device which allows heat to be transferred from one medium to another.

Heating Capacity
The rate at which a device can add heat to a substance, measured in BTUh (British Thermal Units per hour) or Kilowatts (kW).

HEPA Filter
High Efficiency Particulate Air Filter. A type of air filter which can typically remove airborne particulate contaminants as small as 0.3 micrometers in diameter.

Hose Air Conditioner
A type of refrigerative air conditioning which needs to be vented to the outside via an air duct. May be monoblock or air-to-air in type.

Humidifier
A device designed to add moisture to air.

Humidity
The amount of water vapour or moisture in the air. Air can hold higher amounts of water vapour when warmer. Expressed as a percentage of the amount of moisture air could hold at a given temperature. Comfortable humidity levels are typically 30-70% rh (relative humidity).

HVAC
Heating, Ventilation and Air Conditioning.

HVCA
Heating and Ventilation Contractors' Association. An industry trade body of which CAS Hire is a member.

Hydrofluorocarbons (HFC)
A coolant gas used as a replacement for chlorofluorocarbons (CFCs).

I

IEEE
Institute of Electrical and Electronics Engineers. An international industry professional body.

Insulation
A material that slows down the transfer of heat from one place to another.

J

Joule (J)
Unit of energy or work equivalent to one watt per second, 0.238 Calories, or 9.484 X 10-4 British Thermal Unit (BTU).

K

Kilowatt (kW)
A unit of power used in heating and cooling. Equal to 1,000 Watts (W).

Kilowatt Hour (kWh)
A unit of energy consumption equal to 3.6 megajoules. Equal to the energy produced by 1000 Watts of power in 1 hour. Typically used as the measurement of energy consumption in electricity bills.

L

Latent Cooling Capacity
The ability of an air conditioner to remove moisture from air.

Latent Heat
The amount of heat energy needed to change the state of a substance at a constant temperature (e.g. latent heat of vaporisation).

M

Mobile Air Conditioner
A portable air conditioning unit fitted with wheels or castors for easy mobility.

Monoblock Air Conditioner
A type of refrigerative air conditioning unit which collects the water condensed from the cooled air in a tray and stops operating when the tray is full.

N

Natural Ventilation
Air flow provided by natural means such as open windows or doors.

O

Outdoor Air Supply
Air brought into a space from outdoors which has not previously circulated through an air conditioning system.

P

Packaged Unit
A self contained air conditioner or heater.

Particulates
Fine particles of solid matter such as dust or smoke found in air. Can be removed with an air filter.

Portable Air Conditioner
A mobile air conditioning unit fitted with wheels or castors. Useful for short-term use during hot weather.

Power
The rate at which work is done. Measured in Watts (W)

Psychrometer

A device for measuring relative humidity.

R

Refrigerant
A substance which provides a cooling effect, typically while it evaporates.

Refrigerative Air Conditioner
A type of air conditioning which uses air to exchange heat. Typically also dehunidifies air as it cools it. Portable refrigerative air conditioners are either split or hose.

Relative Humidity
The amount of water vapour suspended in the air. Expressed as a percentage of the maximum amount which air can hold at that specific temperature.

Remote System
A cooling system where the condenser is far from the evaporator.

Return Air
Air that is returned to a heating or cooling system from a heated or cooled area.

S

Saturated Air
Air which is at 100% relative humidity. i.e. air which contains the maximum possible amount of water vapour for its temperature and pressure.

Saturated Gas
A gas which is in equilibrium with its liquid state, where the rate of condensation equals the rate of evaporation.

Space Heater
A type of heater used to heat a single room. Often refers to a portable heater.

Specific Humidity
The weight of water vapour per unit weight of dry air.

Split Air Conditioning
An air conditioning system consisting of two units connected by a flexible pipe. An internal evaporator is placed inside the room to be cooled, while the external condenser is placed out side, for example on a windowsill or balcony.

Swamp Air Conditioner
A nickname for an evaporative air cooler.

T

Temperature
The measure of intensity of heat. Measured in degrees Fahrenheit or Celsius/Centigrade.

Therm
A unit of heat equal to 100,000 BTU (British Thermal Units)

Thermostat
A temperature sensitive switch.

Ton
A unit of air cooling capacity equal to 12,000 BTU per hour. Equal to melting 1 ton of ice in 24 hours.

V

Ventilation
The process of moving air into and out of a structure. May be by natural means (such as open windows) or mechanical means (such as air conditioning).

W

Watt (W)

Unit of Electrical power equal to 1 Joule per second.

Z

Zeotropic Refrigerant

A type of refrigerant consisting of several components with different volatilities. Its saturation temperatures and composition change during evaporation and condensing even at constant temperature.

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