Glossary – H

Harmonic Frequency: This frequency is a multiple of the fundamental frequency of the power source. Harmonic frequencies of 60Hz would be 120, 180, 240, and so on. Harmonic frequencies can cause problems with motor operation and power distribution systems.


Heat Flow: When two objects of different temperature are brought together, energy will always be transferred from the hotter to the cooler object. The objects will exchange thermal energy, until thermal equilibrium is reached, i.e. until their temperatures are equal.


Heat Transfer: The transmission of thermal energy from a location of higher temperature to a location of lower temperature. This can occur by conduction, convection or radiation.


Hertz (Hz): Unit of measure of frequency in cycles per second. Alternating current power in the United States is usually 60 Hz.


Horsepower (HP): A unit that is used to measure the power of engines and motors. One unit of horsepower is equal to the power needed to lift 550 pounds one foot in one second. This unit has been widely replaced by the watt in scientific usage; one horsepower is equal to 745.7 watts.


Hull Survey: An examination of the structural components of a vessel such as the sides, deck, and cabin. It excludes electrical or mechanical systems, and rigging.


Humidity: The amount of water vapor present in the air. Water vapor is the gaseous state of water and is invisible to the human eye. See Relative Humidity.


HVAC: Heating, ventilation, and air conditioning is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality.