United CoolAir Glossary
Halide refrigerants
Family of refrigerants containing halogen chemicals.
Halide torch
Type of torch used to safely detect halogen refrigerant leaks in system.
Halogens
Substances containing fluorine, chlorine, bromine, or iodine.
HCFC
See Hydrochlorofluorocarbon
Head
Pressure, usually expressed in feet of water, inches of mercury, or millimeters of mercury.
Head friction
Head required to overcome friction of the interior surface of a conductor and between fluid particles in motion.
Head pressure
Pressure that exists in condensing side of refrigerating system.
Head pressure control
Pressure-operated control that opens electrical circuit if high-side pressure becomes too high.
Head pressure safety cutout
Motor protection device wired in series with motor; will shut off the motor when excessive head pressures occur.
Head velocity
Height of fluid equivalent to its velocity pressure in flowing fluid.
Head, static
Pressure of fluid expressed in terms of height of column of the fluid, such as water or mercury.
Head, total static
Static head from the surface of the supply source to the free discharge surface.
Header
Length of pipe or vessel, to which two or more pipe lines are joined, that carries fluid from a common source to various points of use.
Heat
Form of energy.
Heat absorber
The low-pressure side of a refrigeration system. The evaporator absorbs heat.
Heat anticipators
A thermostatic anticipator.
Heat dissipater
The high-pressure side of a refrigeration system. The condenser dissipates heat.
Heat energy
Kinetic energy of molecules in motion.
Heat exchanger
Device used to transfer heat from a warm or hot surface to a cold or cooler medium. (Evaporators and condensers are heat exchangers.)
Heat gain
Heat added to a space being cooled.
Heat input method
Method of sizing motor in which the required energy from the motor is the amount of heat added to the vapor in the compressor.
Heat insulators
Poor conductors of heat.
Heat lag
The time it takes for heat to travel through a substance heated on one side.
Heat leakage
Flow of heat through a substance.
Heat leakage load
Total amount of heat that leaks from a structure.
Heat load
Amount of heat removed during a period of 24 hours.
Heat loss
Amount of heat lost, measured as BTUH, from a conditioned space, at a specified outdoor temperature and specified indoor temperature.
Heat of compression
Additional temperature produced by increased pressure.
Heat of fusion
Heat released from a substance to change it from a liquid state to a solid state. The heat of fusion of ice is 144 Btu per pound (335 kJ/kg).
Heat of Vaporization
Latent heat involved in the change between liquid and vapor states.
Heat pipe
High efficiency gas furnace that uses vertical liquid filled pipes. The pipes are heated by a burner at their base, and the liquid boils and vaporizes within the pipe. The furnace blower circulates air over the pipes for heating.
Heat pump
Compression cycle system used to supply heat to a temperature-controlled space. The same system can also remove heat from the same space.
Heat recovery system
Produces and stores hot water by transferring heat from condenser to cooler water.
Heat sink
Relatively cold surface capable of absorbing heat.
Heat Source
A body of air or liquid from which heat is collected.
Heat transfer
Movement of heat from one body or substance to another. Heat may be transferred by radia¬tion, conduction, convection, or a combination of these three methods.
Heat transfer coefficient
(U-value) A measure of the amount of heat that a material or combination of materials will allow through.
Heat transfer module
Primary system of heat transfer in a glycol water solution forced-air furnace. The heat transfer module contains the ignitor, burner, and primary solution circulating coil.
Heat transfer rate (Q)
The amount of heat transfer through a given material per unit time.
Heating coil
Heat transfer device consisting of a coil of piping, that releases heat.
Heating control
Device that controls temperature of a heat transfer unit.
Heating Seasonal Performance Factor (HSPF)
Measures the heating efficiency of a heat pump.
Heating value
Amount of heat that may be obtained by burning a fuel. The heating value is usually expressed in Btu per lb., Btu per gal., or kJ /kg.
Hermetic compressor
Compressor that has the driving motor sealed inside the compressor housing. The motor operates in an atmosphere of the refrigerant.
Hermetic motor
Compressor drive motor sealed within same casing which contains compressor.
Hermetic unit
Refrigeration system which has a compres¬sor driven by a motor contained in compressor dome or housing.
Hertz (Hz)
Correct terminology for cycles per second.
HFC
See Hydrfluorocarbon.
Hg. (mercury)
Heavy silver-white metallic element; only metal that is liquid at ordinary room temperature.
High side
The parts of a refrigerating system subject to the condenser pressure.
High-efficiency gas furnace
Furnace that uses recycling of combustion gases or pulse combustion to obtain operating efficiencies from 85% to 95%.
High-limit control
Control that stops the flow of gas when the discharge air temperature on a furnace is too hot. Also called a safety stat.
High-pressure cutout
Electrical control switch, operated by the high-side pressure, that automatically opens electrical circuit if pressure is too high.
High-side float
Refrigerant control mechanism that controls the level of the liquid refrigerant in the high pressure side of mechanism.
Horizontal furnace
A furnace in which air blows horizontally through the heat exchanger.
Horsepower
Unit of power equal to 33,000 ft.-lb. of work per minute. One electrical horsepower equals 746 W.
Hot gas
High temperature gas taken from the compressor used to defrost the evaporator.
Hot gas bypass
Piping system in refrigerating unit that moves hot refrigerant gas from condenser into low pressure side.
Hot gas defrost
Defrosting system in which hot refrigerant gas from the high side is directed through the evaporator for short period of time at predetermined intervals in order to remove frost.
Hot junction
The part of thermoelectric circuit that releases heat.
Hot water heating system
System in which water is circu¬lated through heating coils.
Hot wire
1-Resistance wire in an electrical relay which expands when heated and contracts when cooled. 2-Electrical lead which has a voltage difference between it and the ground.
Hot-surface ignition system
Furnace ignition system in which a silicon carbide element is heated in order to light the main burner. No pilot light is needed.
Humidifier
Device used to add moisture to the air.
Humidistat
Electrical control that is operated by changing humidity.
Humidity
Moisture or water vapor mixed with other gases in the atmosphere.
Humidity Ratio
See Specific Humidity.
Hunting
The cycling above and below the set point.
HVAC
Heating, Ventilating, Air Conditioning HVAC/R: Heating, Ventilating, Air Conditioning & Refrigeration
Hydraulics
Having to do with the mechanical properties of water and other liquids in motion.
Hydrocarbons
Organic compounds containing only hydrogen and carbon atoms in various combinations.
Hydrochlorofluorocarbons (HCFCs)
Type of refrigerant that is damaging to the ozone layer, but to a lesser degree than CFCs.
Hydrofluorocarbons (HFCs)
A type of refrigerant that will not damage the ozone layer.
Hydrogen
A light gas that makes up a small part of the atmosphere. It is present in most fuels.
Hydrometer
Floating instrument used to measure the specific gravity of a liquid.
Hydronic
Heating system that circulates a heated fluid, usually water, through baseboard coils by means of a circulating pump controlled by a thermostat.
Hygrometer
Instrument used to measure amount of moisture in the air.
Hygroscopic
Ability of a substance to absorb and release moisture and change physical dimensions as it’s moisture content changes.