For all those electrical tech savvy OzBargainers.
What is the easiest way I can estimate or even calculate the amount of energy my ducted AC is using.
Its cooling capacity is 14KW and heating capacity is 16KW. I understand different temperatures will have a different load. So say I set the thermostat at 25 degrees for cooling… how much energy or power does that consume?
The easiest way is to read the meter, run it for exactly one hour and read the meter again.
You'll need to make sure you do nothing else during that hour so the reading is accurate.
The fridge might come on during that hour so you might consider turning everything off before you start this experiment.
It's usually divide the capacity by 3…maybe 3.5 and could even be 4.
The easiest way is to read the meter, run it for exactly one hour and read the meter again.
Yeah pretty much this. If OP wants more readings I was gonna suggest finding where it plugged into the electrical system and just interposing a meter there too.
The larger systems might be hard-wired (or, even if they have a plug, they'll have a current draw larger than the typical portable household 10A meters can handle).
Could get a clamp meter onto the cable. The kind you'd use to measure a car's current draw.
yes it is hardwired in…
@mysterytal good idea to leave it running for an hour and observe the meters.. however I have those old analogue meters, they aren't the easiest things to decipher.
@elusive thought about that.. I will try this… just gotta get my hands on voltmeter
Could get a clamp meter onto the cable
You can't just clamp a meter over the whole cable - it will cancel out. You need to get access to just the active wire or just the neutral wire.
@pjetson: Good point. Hopefully they're separate (and long enough) at point where they're connected. Would also only show you instantaneous current (unless you go for the $$$ datalogging ones) so won't tell you much about an hour of usage.
@Archi: A standard volt/multimeter would be, best-case, useless, and worst-case actively dangerous. Don't do that. Your best bet is mysterytal's suggestion of reading the house meter.
Other things to note for the clamp meter:
Reading the house meter(s) is much easier.
Running the system for 1 hour may not give accurate readings.
If the system is an inverter like most these days it will increase/decrease frequency as required. If the temperature is close to set temperature it will run at a low frequency and draw less current. If the temperature is far from the set temperature it will run at a high frequency and draw more current. The outside temperature will also impact performance.
There generally isn't anything that can be done to reduce heating/cooling costs. If there was a way to reduce the energy consumption without effecting performance it would already be implemented.
Running heating at a lower temperature and cooling at a higher temperature is the best way to reduce your bill.
'I understand different temperatures will have a different load. so say I set the thermostat at 25 degrees for cooling… how much energy or power does that consume?'
Somewhere between 0 and the rated max input, i.e. 5kw.
Is it 25 degrees outside or 50? Is your home a sieve yet a west facing glasshouse?
Too many variables to accurately guess.
Another method, since you have the old analogue meters, is to use the spinning magnetic disk to obtain an instantaneous reading. The meter will have a figure stamped on it, mine from memory is 266 revolutions per Kwh.
For example, if it spins once every 15 seconds, thats 240 per hour or 240/266 Kwh.
Be aware that this is an instantaneous reading and does not take into account the cycling of the older a/c motors or the newer inverter models. If you want an overall figure, as others have pointed out, its best to take meters reading over several hours.
I use a raspberry pi for this. Produces a nice graph in a web page. It requires a current sensor placed around the active wire only. I have one on my hot water. Costs maybe 100 and gives quite accurate figures. I can put one together for you if you like.
Can also get it to sum up energy usage over a time range.
Ohh wow that's impressive..
Was it easy to install on a hardwired AC
@Archi: for my hot water service it was easy as there were individual wires behind a panel on the hot water. For other stuff you'd have to check. Either way an electrician should do it. You might need 2 current sensors, one for the internal and external unit. Depends if they are on the same unit.
Other option is to install a power meter in the switchboard. I'm reading data for my solar from one of these via rest API. I'll see if I can find a link.
You should look at the manufacturer's figures because it's not straightforward to calculate power draw from heating/cooling capacity for a heat pump.