Standby power consumption. Ducted and Split A/C

Ducted A/C power consumption.

We have an older ducted air conditioner system.

Dakin RZP125 Super Inverter.

While I realize Choice don’t test ducted systems, a literature review would be interesting if only to compile information on efficiency scores etc.

My issue is that since I’ve installed a PowerPal to monitor power consumption on our heating circuit I’ve realized how much power is consumed in the various operating modes.

Power Off at switchboard 0 W

Power with A/C off 60 W

Power with A/C on but thermostat off 440 W

Maximum Power with compressor running 2100 W - 5600 W

The only power usage figure I’ve ever seen for a A/C unit is its maximum power. I’ve never seen figures for the standby power, or power consumed when on, but temperature has been reached and hence the compressor is off.

The Power with A/C off is the same in winter and summer and hence isn’t related to anti frost protection.

These power usage figure really are rather disgusting, but I’ve been unable to find if more recent units are any more power efficient.

What is the situation with split units? Again, I’ve never seen any mention of standby power consumption.


Welcome to the Choice Community Greg.

Air conditioners don’t really need any frost protection, the refrigerant’s melting point is way below any temperature that might be encountered in Australia.

They do however have crankcase heaters, so that the unit is ready to go immediately when you turn it on, amongst other reasons.

Some info here:


Before looking at more recent units, your high power usage may be a symptom of older and lower standards of installation, or unwanted leakage. How your home is constructed, insulated and orientated will also influence the heating/cooling load, hence power consumed.

A newer inverter to replace what you are saying is also an inverter is likely to make only a small difference to the power consumed. The power draw when the thermostat is off is mostly the circulating fan in operation. Dirty ducts, filters, directing vanes, and grills all create extra loadings on the fan.

For refrigerant air conditioners the efficiency is not quoted as a percentage. The effectiveness is expressed as a COP. There is a COP for cooling and a different and slightly higher COP for heating. The higher the COP the more energy efficient a refrigerant air con will be. You will need to find the COP for your existing unit to compare with any replacement.

There is a discussion of split systems in the following that may be of further interest.


Inverters have a minimum and maximum range, the compressor while running the AC is never truly off. What it does is it moves towards it’s minimum output to maintain the temp setting. In your case this looks like around 2kW.

Old style AC used to stop the compressor and then restart it when the temp was too far away from the set point. This required a large amount of energy to start the compressor (very large amounts in fact) and Inverters avoid this after initial starting and so are much more energy friendly. The Inverter compressor if the unit is running to control temperatures, does not stop, it continues to run between it’s minimum and maximum values based on how close the temperature is to the set point. Turning the temperature control off and just leaving the circulating fan running will be the least amount of energy used except for when all units are turned off.

What can make a big difference is that you need to size the AC for the room/rooms it is cooling/heating. Too large a unit and the minimum may still be too high for the required output and it will work rather inefficiently. Too small and it will always run too hard and most inverters can over run (up to 150%) for short periods (30 mins or so) to quickly heat or cool the room/area then return to normal running. That is taking into account after an over run they under run at about 80% capacity for a similar period. If too small a capacity this means they are almost always in this cycle.

The circulating fan/fans also never stop while the unit is running and may pull around the 400 watts that was also noted, 60 watts would be standby power so the AC is ready to start on command.

As already noted by @mark_m, ensuring the filters are clean is also important as restrictive flow will mean the fans work harder to draw and circulate the air so use more power.

From what I can find on this model it’s running range is between 6 kW cooling minimum to 14.5 kW and heating is 6 kW to 16.2 kW and the scroll fans pull 55+55 watts (dual scroll fans). But it also shows is there are internal units and they also have power requirements of about 90 watts each and the outside unit Crankcase heater is 30 watts. This unit inverter uses up to 17 frequency steps (including the over run ones) to fine control the heating and cooling.


Thank you for your comments.

My main comment is really about the level of power consumption when the A/C is neither heating or cooling and the fact that this appears to be totally undocumented for all units I have investigated.

The unit is in its 20th year and has been almost faultless during that time, but sooner or latter it will need replacing.

As the unit is generally left on 24/7 over winter the always on power consumption becomes an issue.

In winter we also have a problem with the outside unit frosting which isn’t surprising when the air temperature is often below 5 deg and the humidity approaching 100%. The defrost works OK but this makes it inefficient.

What technology would avoid this in regions where the heat exchanger may get ice on it in winter?

Leaving it on 24/7 so the house stays warmer. It doesn’t then have to work as hard first thing in the morning.
The optimum solution is a ground source heat pump, but as demand is very low the prices are correspondingly high in Australia.

I’m a little uncertain, if I may ask.

Are you able to clarify details of the indoor unit/s installed with your RZP125 outdoor unit? The standard Aussie install per Daikin for this model is one or two ceiling mounted cassettes? Code FHYCPxxxxx.

In that instance it is not a ducted system, but a high capacity single or dual head split system.

A ducted air conditioning system has interconnected ducting through the house. One system of ducts to deliver hot or cold air and a second for the return air.

As at @grahroll explained there are a number of electrical loads that contribute to the electrical power consumed when the outdoor unit goes off load. The Air Conditioner does not shutdown unless one turns it off. The cycling and other loads @grahroll has commented on in respect of your unit.

In respect of the electrical load differences between the system you have now and a replacement. It may be best to discuss that with Daikin or the specialists you prefer to deal with. Every home has different thermal loads and losses. As home owners we have varying comfort levels, and our climates vary immensely across the country.

A thorough response is really about designing, IE matching the size and type of system selected (multiple systems), to meet the property and personal needs. It’s likely a replacement system will deliver the same comfort for less power usage. But only if it is appropriate to your needs and correctly sized.

In respect of comparing the power consumed with the outdoor unit off load. For a system sized correctly, the power required to deliver the cooling or heating will be many times greater than the power consumed when the unit is off load. It may be better to base any decisions on the COP of newer units compared to your 20yo unit, and not place too much emphasis on the off load usage.


The outdoor unit is a RZP125DV1
The indoor unit is a FDYP125DFV1
It is a ducted system



As suggested previously when the outdoor unit goes to off load, IE system mode is in heat or cool but the out door unit is not heating or cooling.

The following data sheet shows the indoor unit has a 500W output power motor for the fan. Input power will be considerably greater at full load. This will continue to run as it is needed to circulate the air. You will likely have an in duct temperature sensor as part of the indoor unit, or optionally a room installed remote. The 400W power recorded to power this fan and other electrical loads is not unexpected.

One does needs to look at the whole of the system and how it’s designed - configured.

I could not bring up the indoor ducted unit from Daikin’s Aussie web site. Assume the UK data sheet is the same base spec.


Thanks Mark

The fan is 1 x 490

The real question is are the newer units smarter with their power consumption?

I will try to attach a power consumption graph for the 24 Aug which is reasonably representative.

You can see the baseline power consumption at about 400 + W for the largest portion of the day.

There is also a standard hot water system on the same circuit with a 2400 W element that is on between 7:00 and 9:00 AM.

The unit was off between about 2:00 and 3:30 pm.

The indoor fan unit sounds as if its multi speed, but the off-load power consumption is still 400 W which is a lot over a period of time.

I suspect the unit is about the correct size to get everything up to temperature in the mornings.

We also normally supplement the heating with a wood fired heater in the evenings.


The inverter is stepping as they do ie it is moving between the various levels of power operation. The morning operation appears more smooth than the afternoon but still has significant movement in the range. If you use supplementary heating this may be why such variation occurs. Even at the lowest level I see some small steps in power usage. Are you having a regular service done on the unit? If not it may be worth getting the unit checked to see if it is still within correct parameters.

As I noted in my previous post this unit has 17 steps it can cycle through. I think that 400 watts wouldn’t be unusual even today for circulating fans, base rate of inverter running, crankcase heating, and outside scroll fans running.

These steps should normally mean the rate of change should be smoother except when first starting up.


A ducted system as you have shown in the recoding requires a powerful circulating fan. It needs to overcome the duct resistance as well as provide energy to move the air mass.

Whether a newer designed replacement is any smarter?
The best ones to ask are the agents or tech support for each brand. Note that for your system it is the in line duct head unit (indoor unit) that provides the circulating fan. The outdoor unit is independent. The fan power required to move the air in the ducted system is a function of the duct design.

A newer designed head unit may have a higher efficiency fan and motor. It may have a greater range of speeds, or the option to turn the fan off and use a remote room temperature sensor. All good questions for the professional suppliers.

The current Daikin equivalent systems offer a 3 speed fan. I’ve not the time today to look further as to how these units are controlled. Daikin could better answer.

This tech sheet also provides details of the COP for the newer Daikin options in heating and cooling modes. These can be compared with your existing system specifications. Or to a replacement system from other brands.

Re the strategy of leaving the air con on all the time, your graphs suggests it would be better to turn it off at night and after the morning peak. It is not contributing any heating or cooling for half the day.

It may suit to take or send a copy of the power graph to assist in any discussions with prospective suppliers. Larger scale commercial systems have independent management systems that can control every aspect of ventilation. These include timed settings and ventilation shutdown. Our modern split systems have built in user programable timers for time of day operation. They also have provision for remote monitoring and control.


When focus (and the original question) is on power consumption it is common that one criteria gets overlooked - comfort. The difference in comfort, be it temperature or just gently moving air 24x7 is not quantifiable without being the occupant and being there :wink:

Many who are able to pay the bill be it from the grid or a PV are more than happy to ‘pay’ the trade-off.

@greg-g should have a considered think about what his household’s enjoyment factor is from the ducted system and keep those features or functions front and centre while investigating newer systems.


Thank you all for your inputs.

Comfort is the reason we leave it on overnight although I would like the option of setting a minimum temperature lower than 16 deg.

Our daily consumption varies between 40 – 50 Kw/day which is what we use in our large 70 year old house for the A/C and hot water. There is also a solar hot water system that doesn’t perform that well.

To some extent the COP is useful for comparing systems, and the spec sheets will give a good idea of maximum power consumptions, but I can’t find anyway to ascertain what the power consumption is likely to be when in standby, or operating with the compressor off as all the motors are VSD controlled.

Our 9Kw Solar PV system doesn’t help with the heating bills as in Tasi we have separate metering for tariffs 31 and 41. We could go to a TOU tariff but it’s of no benefit to us as the majority of the power goes to heating in winter or in the evenings when solar generation is minimal. Batteries are not financially viable at this stage.

My original comments still stand regarding documentation especially with the more common split systems. All the data gives is COP and maximum power consumption. There is no comment that I’ve ever seen on power consumption in the various standby modes. Most people can’t measure the standby power as the devices are hardwired.

When looking at brands I would think that Dakin and MHI would be the top choice. Comfort, Convenience and reliability are the main criteria. Any comments are welcome


I am glad that we don’t have power bills like that.

Greg - in the interest of embracing new, and apparrently notably more efficient technology, I attempted to get a ground source heat pump system for the air con for the new house I built on an ordinary suburban block in Sydney (block size 900 sq meters). I even visited their showroom and listened to their informmation. They never followed up, even after a secong attempt to engage their services. They seemed uniterested, or more likely, unable to actually quote and install a system for me.
If you do an online search it seems these systems are very popular in the US yet nobody here in Australia seems able to deliver them - very disappointing, because it seems to be a really good idea for home aircoditioning and even home hot water.

1 Like

I have a 22 year old ducted Daikin FDY90 system and decided to look into a replacement unit. The power usage didn’t initially bother me but then the main motor seized. It seemed a good idea to book a Daikin technician figuring it was worth the service charge to ask him about a replacement. He told me a new unit would require replacing all the ducting as well as the unit despite the fact that the old ducting was sound (something to do with the warranty, perhaps?). This seemed a dreadful waste so I settled on replacing the motor and fan blades plus the PCBs. The two things unobtainable were the relays. The always helpful technician looked up the technical sheet and drew a diagram on how an electrician could put in a bypass switch that would still allow the unit to be used, but without high speed. I made the interesting discovery that the new motor and blades even on the low speed heated the house during last Winter just as quickly.


I too have been told that replacing our ducted air con would require new ducting. It seems to be a thing. We haven’t needed to yet although our current one is 15 years old.
I don’t know about energy consumption but I live in Qld and we used to have enormous bills, large house, pool etc until we put in solar a few years ago. Fortunately we had 3 phase power so could put a lot on the roof. It was $28,000 worth of solar and we paid $21,000 of that from our pockets, as the government contributed $7,000. It paid for itself completely in 3 years even though it was long after the days of good tariffs for selling your excess power. Our bills are tiny. It was a cold and grey winter here in SE Queensland and we often had the air con set to 20 all night with half the house zoned off. Our bill was $18 for the quarter.


Great stuff.