Air-Conditioners

On a completely unrelated note (as usual), I suddenly realised that air-conditioners are more efficient in cooling a room down if the external weather condition is much cooler. This means that for places like sunny Singapore, the air-conditioner is actually working a lot harder to pump out the thermal energy from the room than say an air-conditioner in the middle of Alaska.

The principle of the air-conditioner is based on the heat pump, which in turn is based on the expansion and compression of the coolant fluid to transfer the thermal energy. A heat pump takes in thermal energy from one region and dumps it into another region. So, in the case of Singapore, the heat pump will take the excess thermal energy inside the room and dump it into the outside world. Except that when dumping the excess thermal energy, the Newton's law of cooling tells us that if the temperature gradient between the outside region and the coolant fluid is too low, the rate of transfer of the excess thermal energy will be lower. Now, taking that into consideration, it is clear that the heat pump is most efficient if the outside is cooler than the inside.

But if the outside is cooler than the inside, isn't it cheaper energy-wise to just open the bloody windows?

Also, I'm not a physicist. So don't lambast me when I use Newton's law of cooling as part of my explanation.