Originally Posted by
coolcoil
The biggest reason for the difference is units of measure. For cooling, USA values are in EER (Btu/W), while Europe uses COP (W/W). To convert from a COP value to an EER value, multiply by 3.412. Do that and you will see that the values are similar. For heating, both the USA and Europe use COP, so there is no conversion needed.
The European and USA test points are somewhat different, so you if you tested the same unit to the different procedures you would get slightly different results. European test points reflect the generally colder temperatures in Europe, while the Indian ISEER tests at higher points and gives more weight to the higher temperatures than in the USA or Europe.