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When current is injected into a Peltier device/thermo-electric cooler, it heats up, when the current is reversed, it cools down. Why does it takes less time to heat up than to cool down?

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    $\begingroup$ What is your evidence for the asymetrical heating / cooling? $\endgroup$
    – Solar Mike
    Jun 12 '17 at 8:07
  • $\begingroup$ What temperatures? $\endgroup$
    – JMac
    Jun 12 '17 at 10:33
  • $\begingroup$ This question comes perilously close to the "hot water freezes faster than cold" flame war. However, as restated by Olin L., the functionality seems clear. $\endgroup$ Jun 12 '17 at 14:25
  • $\begingroup$ @Solar Mike. experiment $\endgroup$
    – Frank
    Jun 12 '17 at 17:11
  • $\begingroup$ @ JMac. Between 5 and 45oC $\endgroup$
    – Frank
    Jun 12 '17 at 17:11
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Peltier devices are quite inefficient. A simple first-order approximation for a Peltier is a perfect heat pump in series with a resistor. The heat pump moves heat symmetrically proportional to the current, but the resistor always makes heat proportional to the square of the current.

The unavoidable heater in a Peltier device makes it overall better at making heat than cold.

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