Climate Control (Energy at Home)

Moving heat from where it is abundant to where it is needed, instead of creating it from scratch.

Moving heat instead of creating it

For most of the history of home heating, heating a home meant burning something — wood, coal, gas — or passing electric current through a resistor, converting chemical or electrical energy directly into heat. That heat generated from scratch can never exceed, in the best case, one hundred percent of the energy invested: it is a physical limit imposed by conservation of energy. The most efficient modern climate control, however, does not generate heat from scratch: it moves it from one place to another using a compression-and-expansion cycle of a refrigerant, extracting heat from a cold source — outdoor air, the ground, a water well — and delivering it to the warm source that needs heating, or the reverse in cooling mode. Because it is not creating energy but relocating it, it can deliver considerably more useful heat than the electricity it consumes to run that process.

The same physical principle, two opposite uses

Refrigerators, freezers, air conditioners and heat pumps all share exactly the same basic thermodynamic cycle; the difference lies in which of the two heat sources — the one being cooled or the one being heated — is the one actually worth exploiting in each specific application. An air conditioner extracts heat from inside a home and expels it outdoors, cooling the interior as the useful effect. A reversible heat pump can do exactly the opposite in winter — extract heat from outdoors, however cold it seems, and deliver it indoors — and work as an air conditioner in summer by reversing the direction of the cycle. Understanding this equivalence helps evaluate any climate-control equipment's efficiency claims with sound judgment, and distinguish between what physics allows and what a specific manufacturer has actually managed to build.