1 October

Russell and Dave About air con and efficiency, which we didn’t get time to finish. The units themselves aren’t breaking any rules of thermodynamics by outputting far more energy than what they consume, because they don’t actually produce any heat or cold. They just shift existing heat around (they extract it from the surrounding air, and pump it, thus they’re heat pumps). Heating efficiency in an air con unit is measured as the COP (Coefficient of Performance), ratio of heat output to electrical power input. Cooling efficiency is measured as EER (Energy Efficiency Ratio), the ratio of cooling output by the device to the electrical power used by the device. For modern air con units both EER and COS are at least 5, you get 5kw of heat or cooling for every 1kw of power input to the device. So that’s a minimum 500% efficiency. The magic comes because that 1kw of electric input is used just to shift 5Kw of existing heat around between the inside and outside air of the house - the unit doesn’t have to generate the heat or cold.