How the machines and gadgets around us work.
What it is and why it matters — intuition first, little or no math.
Air conditioners and heat pumps don’t make heat or cold. They move heat from one place to another, using a special liquid that soaks up heat when it evaporates and gives it back when it condenses.
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A refrigerant is the special fluid inside fridges, air conditioners and heat pumps. It boils at very low temperatures, so it can soak up heat even from cold air and carry it somewhere else.
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How to calculate it, with formulas and worked examples.
The coefficient of performance (COP) tells how much heat a heat pump delivers for each unit of electricity it uses. A COP of 3.5 means 3.5 kilowatt-hours of heat from just 1 kilowatt-hour of electricity.
Numbers & formulasUnder the hood