Halide refrigerants
Family of refrigerants containing halogen chemicals.
Halide torch
Type of torch used to safely detect halogen refrigerant leaks in system.
Halogens
Substance containing; fluorine, chlorine, bromine, or iodine.
Head
Pressure, usually expressed in feet of water, inches of mercury, or millimeters of mercury.
Head, Static
Pressure of Quid 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
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 operates electrical circuit if high-side pressure becomes too high.
Head Pressure Safety Controls
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.
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 that acts on substances to raise their temperature; energy associated with random motion of molecules.
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 surface. (Evaporators and condensers are heat exchangers.)
Heat Gains
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
Loss of warm air, resulting in a lower 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 Btuh per pound (335 kJ/kg).
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 Transfer
Movement of heat from one body or substance to another. Radiation, conduction, convection, or a combination of these three methods may transfer heat.
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 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 cave motor sealed within same casing which contains compressor.
Hermetic Unit
Refrigeration 6ystem which has a compressor driven by a motor contained in compressor dome or housing.
Hertz (Hz)
Correct terminology for cycles per second.
Hg. (mercury)
Heavy silver-white metallic element, only metal that is liquid at ordinary room temperature.
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 bonnet on a furnace is too hot. Also called a safety stat.
High-pressure Cut-Out
Electrical control switch, operated by the high-side pressure, that automatically opens electrical circuit if pressure is too high.
High, Side
The parts of a refrigerating system subject to the condenser pressure.
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-Surface Ignition System
Furnace ignition system in which a silicon carbide element is heated in order t light the main burner. No pilot light is needed.
Hot Water Heating System
System in which water is circulated 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.
Humidifier
Device used to add to the humidity.
Humidistat
Electrical control that is operated by change in the humidity.
Humidity
Moisture: Dampness of air.
Hunting
The cycling above and below the set point.
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 CPCs.
Hydrofluorocarbons (HFCs)
A type of refrigerant that will not damage the ozone layer.
Hydrogen
A light gas that makes up a small part of atmosphere. It is present in most fuels.
Hydrometer
Floating instrument used to measure 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 moisture in the air.
Hygroscopic
Ability of a substance to absorb and release moisture and change physical dimensions as its moisture content changes.