Dear anonymous,

a good source is: https://www.energy.gov/energysaver/room-air-conditioners

" A room air conditioner's efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity to the power input (in watts). The higher the EER rating, the more efficient the air conditioner. When buying a new room air conditioner, look for the ENERGY STAR label ( https://www.energystar.gov/products/heating_cooling/air_conditioning_room ). "

Product criteria: https://www.energystar.gov/products/heating_cooling/air_conditioning_room/key_product_criteria

Relevant for efficiency is proper design of the equipment (relevant for heat transfer is the surface area of the heat exchangers) and maintenance (keep evaporator and condenser clean

Dear anonymous:

If we talk about an AC system of gas-liquid refrigerant compression cycle :

Important parameters are the mass flow rate of the refrigerant, temperatures of the Heat and Cold sources (very important, since the COP is directly related to these magnitudes). As well as the Pressures & Temperatures at the entrance and exit of the compressor.

These are the most critical design parameters for a common vapor-compression cycle AC system.

Then, one would have to focus on specific design parameters for each of the components of the system, to enhance the performance of each individual system and impact the overall officiency of the system more. e.g. The shape and number of turns of the coil in the condenser and evaporator, the diameter of the pipe, select or control in a convenient way the operational parameters of the electric motor in the compressor, etc. etc.

Best Regards ! :)