Local WiFi devices can be operated by smartphones within the local WiFi network, using native apps, developed by the manufacturer of the air conditioning system. Such HVAC systems won’t be controllable once the smartphone is out of the range of the local WiFi network.
Such a concept can fit some of the home appliances, such as TV, Audio Video devices, etc. that require control only when we are around. There is no need to access them while we are away. However, when considering air conditioning systems, it is essential to have a remote access while we are not in the house (e.g. left the house and forgot to turn it off).
Another disadvantage of local WiFi networks are interruptions in the network connectivity. Once the phone set for WiFi, it can automatically switch to another WiFI network (without any notification), and the air conditioner is not accessible anymore.