On non-Inverter ACs, I only need to use the power input (e.g. 800W) to calculate my energy cost for a 12-hour usage. (800*12/1000 = 9.6kW-hr)

On Inverter ACs though, I know they don’t operate at 100% all the time, and most of the time the only information I get is their cooling capacity (e.g. 1hp ≈ 746W) and their EER (e.g. 12.2 kJ/hW).

How do I use these to get a rough estimate of the energy cost?

In: Engineering

ERR is Energy Efficiency Ratio. It is the ratio of electrical energy input to the thermal energy output. What might be confusing you is that thermal energy is often measured in BTU or kJ. 1kJ is 1Ws. But electrical energy is usually measured in kWh. So your 12.2 kJ/Wh is equivalent to 12,200s/h. Because there are 3600 seconds in an hour this is equivalent to 3.39 , no units as this is a ratio. This means that for every kWh of input into the air conditioner you may expect 3.39kWh of thermal output.

This does not give you enough information to calculate the energy usage of your AC system. It all depends on how much heat energy escapes the room it is installed in. If you already have an AC and know its EER you can measure how much energy it use and then multiply with the EER and you get how much energy you lose though your walls. You can then divide this by the EER of a new AC to calculate its energy usage. If you only have an electric heater its EER is 1, or 3.6kJ/Wh if you prefer.

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