Heat map
Concise method of visualising demand profile data at (say) 30 minute intervals, in which demand levels are colour-coded on a grid with each vertical stripe representing one day, running midnight to midnight from top to bottom. Read more and see example

Heat recovery
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HEM
High efficiency motor: electric motor designed to reduce losses and maximise mechanical power output for a given electrical power input

HVAC
Heating, ventilating, and air-conditioning.

HAWT
Horizontal-axis Wind Turbine

Heat pump
Refrigeration equipment usually to provide heat by cooling outside air, body of water, or ground

HF
High frequency. In energy management usually referring to the frequency of power supplied to fluorescent discharge lamps by electronic as opposed to inductive choke control gear.

Heat map display