High KW appliances and energy efficiency

Cardew

Buster_Danog wrote: »

Thanks for the replies guys. After starting this thread I realise the manufacturers tell you how much energy is actually used by the input value. So an air conditioner for example that has 2.6kw power might only be using 1kw of energy. You would therefore calculate costs and energy use based on the 1kw value. I guess that is the difference between the two is where the efficiency comes in.

We need to get the terminology of kW and kWh and efficiency correctly defined.


The rating of an appliance in kW has little relevance to the kWh it will use; and it is kWh that we pay for.


For instance a washing machine might have a heater rated at 2.5 kW and some washing cycles take 2 hours or more to complete. However it doesn't use 5kWh as the heater is only on for a very short period in that 2 hours and a typical consumption on a 2 hour cycle might be 0.6kWh - and that is mainly for the motor and pump.


Your analogy of air conditioning efficiency is misleading. Efficiency in that case, would be the ability of a unit to keep a room of a specified size, at a specified temperature, with a known outside temperature.


You quote an example of an a/c unit of '2.6kw power using 1kw
energy' as an example of efficiency.


A 2.6kW rated unit will use 2.6kW and over a certain period of time will use 1kWh. That period of time is determined by how long the A/C unit runs.


A 12kW unit will also use 1kWh over a certain period of time. Neither is a measure of efficiency; the 12kW a/c unit could be more or less efficient than the 2.6kW unit.