Bard AI:

According to the Energy Star program, increasing your air conditioner temperature by 1 degree Celsius can save you up to 3% on your energy bill. So, if your average monthly energy bill is $100, you could save up to $3 per month by setting your air conditioner 1 degree higher.

That said, it's important to find a temperature that is comfortable for you and your family. If you're too hot, you're likely to turn the air conditioner down anyway, which will offset your savings.

Running your air conditioner at 24 degrees Celsius is a good start, but you may be able to save even more by setting it to 25 degrees Celsius or higher. If you can tolerate it, try setting your air conditioner to 26 degrees Celsius or higher. You may be surprised at how comfortable you are.

Here are some tips for saving energy when using your air conditioner:

Set the thermostat to the highest comfortable temperature.
Use ceiling fans to circulate the air.
Close the curtains and blinds during the day to keep the sun out.
Insulate your home to keep the heat out in the summer and the cold out in the winter.
Schedule your air conditioner to turn off when you're not home.
By following these tips, you can save energy and money on your air conditioning bill.

This one Tuya (paired with the Tuya 20A Wifi switches), also connected to home assistant.

Would it be very expensive to have smart home system? wiring and electrical works will be more than double the cost?

Most of smart home devices are battery powered and wireless, no need wiring.
Cost can be from few hundreds to few thousands depending on the number of devices

For me personally, I spend about RM 45 - RM 60 per switch (Some Wifi,.some ZigBee). Some plug points also changed to ZigBee capable ones (about that range).

Small sensors like door sensors, motion sensors all between 20+-100+

Smart capable lights are pretty affordable, yeelight bulbs or Ikea ZigBee capable bulbs are sub RM100. But some can be up to 300-400 also. Depends on needs and use case.

If you plan to use something like home assistant, a small server running 24/7 is needed. A raspberry pi (the recommended route) or a mini PC will do. Brands like sonoff also have their own hub, but many would be against going with a specific brand of applicances for everything. Expect to spend RM 200-500 depending on wants and needs.

Overall will definitely spend double or triple compared to standard dumb equipment.