There is a geographical reason and a meteorological reason. First, the geographical reason - remember the position of the Sun in different seasons?

From the diagram above, it is obvious that in wintertime, the Sun stays to the south. This gives warmth to a south-facing apartment which lets sunshine in. On the other hand, in summertime, the Sun is nearly overhead in Hong Kong. Near Summer Solstice (June 21), the Sun will even be slightly north of us. A north-facing apartment tends to be warmer if sunshine gets in.

For further details about the position of the Sun in different seasons, please check the webpage at :-
https://www.hko.gov.hk/en/gts/astron2014/files/2014paths-sun.pdf

Second, the meteorological reason. In wintertime, a south-facing apartment with its back towards the north is less affected by the cold northeast monsoon, while in summertime it gets breezy under the southerly winds. This is also the reason for a windbreak north of a house in the countryside.

So, overall, for a south-facing apartment it tends to be warmer in winter, and breezy and not as hot in summer.

There is no clear-cut answer to this question. In terms of wind, it tends to get windier for an east-facing apartment because the prevailing wind in Hong Kong is from the east. For a west-facing apartment, it tends to be less breezy because westerly winds are normally light and relatively infrequent.

In terms of sunshine, the amount of sunshine (solar radiation to be exact) is basically the same for an east- and west-facing apartment. For an east-facing apartment, the warm weather starts earlier as the Sun rises from the east. The warmth received by the apartment's concrete is released after midday, as soon as its temperature is higher than the surroundings. The same occurs on a west-facing apartment, but the process starts at a later time, i.e. in the afternoon. The overall effect is that for an east-facing apartment, warm weather sets in earlier and ends earlier. For a west-facing apartment, it starts later and ends later, resulting in warmer nights.

In terms of the air temperature, the maximum temperature normally occurs at around 2 o'clock in the afternoon. At this time, it gets drier, i.e. the humidity becomes lower, because of higher temperatures. The combination of sunshine, higher temperatures and thus drier weather help disinfect the indoor environment. A west-facing apartment is therefore preferred if you do not like mouldy walls and clothes, which occur especially during springtime.

If you live in the Southern Hemisphere, e.g. in Australia or New Zealand, is it going to be the same?