I need to replace an air conditioner and would like to make sure that the new one is sized correctly. One obvious way is to do a detailed load calculation. It seems like an even better, or equally good, way to do a load calculation is to measure the AC run time percentage during the hottest times of day during the hottest days of the year (I'm in central Florida so I am not too concerned with heat). For example, if I have a four ton system that is only running 50% of the time during the hottest time of day on the hottest days of the year, then it would seem reasonable to conclude that a 2 or 2.5 ton unit would probably suffice and be the closest match for the variables that exist in this particular house.
The challenge then is how to determine the run time percentage. I came across this device and also this device and was wondering if either of them would measure that run time based on data from the wires going to and from the thermostat. From calling the company that makes the product I understand that they only work on DC circuits. I am not knowledgeable on thermostat wiring.
So what do you think? Would this work to log and graph run time or is there a better or easier way? Also, what do you think about the idea of monitoring run time percentage on the hottest days of the year to determine your true load needs?
Thanks for your thoughts.