Air Conditioner Standby using 300W

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Re: Air Conditioner Standby using 300W

Postby djg » Wed Jun 26, 2013 11:08 am

I have done a bit of research into this lately.

Yes, a number of the larger ducted systems will use up to 350W sump heater. It is typically in models that also get sold overseas and the unit is expected to start up in colder conditions than we typically get in most of Aus. It also seems that when sitting cold the refrigerant and the oil in the compressor can mix, which is what causes damage to the compressor at startup.

Yes, turn the unit off at the breaker when not using it for extended periods.

Be very careful as to when you turn it back on vs use the system. Your manual should note a time between initial power connection and using the system - mine states 24hrs. Sure, these are very conservative, but as your warranty can be voided be careful. The reason for such a long time is not just the temperature of the compressor fluids - it allows time for the refrigerant to be separated from the oil over a period of time after reaching a good temperature.

Different compressors / oil / refrigerant combinations require different amounts of warmup before use, so don't take somebody else's figure and use it - research your own manual / model.

Unfortunately I've been unable to find any quantitative data as to what temperatures / times / etc, are really needed in normal operation, so I don't know how much I can bend the 24hrs stated in my manual or what level to set a thermostat at, etc.

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Re: Air Conditioner Standby using 300W

Postby hypereng » Wed Jun 26, 2013 12:11 pm

Air-conditioner standby power is a combination of the relatively low electronic load and the sump heater load.

The sump heater load is significantly dominate.
Why is a sump heater needed?
The sump heater, as it states, heats the sump of the compressor.
In doing so it ensures that the refrigerant, which is both gas and liquid in various parts of the system, will not collect in the sump of the compressor.

Why is this a problem - liquid refrigerant dissolved or undissolved (depends on the oil/refrigerate combination )
is not a lubricant and so could result in accelerated mechanical wear within the bearings and/or the compressor itself. Additionally the total volume of liquids within the sump can increase in some conditions until the liquids are sucked into the intake of the compressor. Liquids, oil or liquid refrigerants are totally incompressible, so this is quite likely to lead to a failure to start.. The bad thing about that is that many compressors are too dumb to understand this and may fail due to the excessive locked rotor currents ( about 5 times the full load current ),good thing about this is that if the motor can survive this condition the internal heat generated by these high currents will boil away the excessive refrigerant accumulation and return the system to normal.
Many model rely purely on the sump heaters ( crankcase heaters ) to prevent this problem. Basically this is a cheap and nasty solution and is in considerant of both the environment and the end users power costs.

There are several options:
1. Disconnect the sump heater and run the risk of a compressor failure - BTW when the motor burns out, the evaporated wire insulation contaminates the entire system, so the cost of the repair is far greater than just the cost of a new compressor.
2. ensure that the compressor is never the coolest component in the system - usually not viable.
3. Activate the sump heater for just 1 hour prior to each start up after any period longer than say 4 hours of inactivity - definitely saves total power usage, but requires a solution to this logical problem.
4. Prevent the compressor from destroying itself if refrigerant does accumulate.
I suggest that there is a product that can protect the compressor but its primary function is to reduce the motor starting inrush current. As a free feature of this product, the compressor is protected from destruction if the sump is flooded with liquid refrigerant. There are other protective features, such as low voltage shutdown - another well known cause of destroyed motors. However the primary function of this product is to reduce the initial startup inrush surge. All single phase compressors above 2Hp are technically illegal to connect to a domestic supply. Adding this device resolves this legal issues and as an additional benefit protects the compressor from most failure modes - including liquid refrigerant - so it is now possible to safety disconnect the energy sapping sump heater.
If the compressor sump is flooded, the softstarter will shut the compressor down safely , however the energy added to the motor will ensure that the refrigerant, if it has collected, will be evaporated, if not at the very first attempt, but some after. This process is automatic.

For your general Interest, the company that developed this product has offered the air-conditioning industry a version of their product, that at no additional cost would provide crankcase heating that is performed intelligently, resulting in a significant energy saving - but that energy saving is not relevant to their marketing. These savings are achieved by recognizing that there is no need to heat up a hot compressor, which is exactly what they still do. If the compressor is in normal use and therefor, remains hot, there can be no refrigerant condensation, yet, even to this day, at ever shut down the sump heater is switched on, even though there is no technical need to do so.

for more information.
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Re: Air Conditioner Standby using 300W

Postby Bthree » Wed Jun 26, 2013 1:38 pm

The mystery is solved, thank you hypereng for the explaination, makes sense.

Been trying to find this out for ages, all but given up on a solution.
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Re: Air Conditioner Standby using 300W

Postby jsull » Thu Jul 11, 2013 9:23 pm

I have had a reply from Mitsubishi about the power consumption (see below). I don't know anything about reactive current. I assume if it is not measured as part of an electricity bill it wouldn't show up on my EMPower monitor as consumption?

I thank you for your enquiry about the non-operating power (standby) consumption of your PUHZ-RP140VKA2-A and offer the following explanation.

The model you have mentioned will draw an average of 65 watts whilst in a non-operating (standby) mode, this power is required to retain memory, time clock functions, a small current draw through the noise filter circuit in order to meet EMC (Electro Magnetic Compatibility) requirements plus there is current applied via the compressor winding to maintain compressor oil temperature.

Please see the compressor energising method below:

Most of the current passing through this circuit is reactive current. Reactive power is not measured as part of a consumer’s electricity bill;

The true non-operating (standby) power that consumers pay for in their electricity bill is an average of 65watts on the model PUHZ-RP140VKA2-A, 73watts for 3 phase models.

Mitsubishi Electric models sold in Australia are tested to AS/NZS 3823.1 to comply with the Minimum Energy Performance Standard (MEPS) AS/NZS3823.2; this standard requires the inclusion of standby power to determine the systems Annualised Energy Efficiency Ratio (AEER). From 1/4/2011 a minimum AEER was mandated for air conditioners <65kw output capacity.

More information about the relevant Standards and MEPS can be found at

The non-operating power is an integral element of the AEER calculation and therefore the appliance registration process. Non-complying units cannot be sold in Australia.
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Re: Air Conditioner Standby using 300W

Postby FarmerJohn » Fri Jul 12, 2013 10:03 am

Most of the current passing through this circuit is reactive current. Reactive power is not measured as part of a consumer’s electricity bill;

Huh ? Imagine my reaction at being billed :)
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Re: Air Conditioner Standby using 300W

Postby Smurf1976 » Fri Jul 12, 2013 8:41 pm

Residential electricity meters record KWh, not KVAh, and as such you do not pay for reactive power.

The one thing I am not certain of however is whether a net meter used with solar can be "confused" in a situation where true power (KW) is flowing in one direction whilst apparent power (KVA) is flowing in the opposite direction. Eg your household load is 900W (true power) but 1100 KVA (apparent power) whilst the inverter is producing 1000W. In that situation there is an export of 100W true power, but an import of 100VA and I'm not sure how the meter actually would see this.
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Re: Air Conditioner Standby using 300W

Postby lantern » Fri Oct 25, 2013 8:28 am

Asked my installer, when he installed last year, what is the standby current, he shrugged his shoulders and said "Why would you want to know that".
Anyhow had a sparky round a couple of weeks ago and I asked him to measure it.
48W. now that's about $30 per bill, a work mate of mine also measured his and his figure was 78W.
They are both new Panasonic units, can't get any info from Panasonic.
Needless to say both units are now turned off.
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Re: Air Conditioner Standby using 300W

Postby munrre » Fri Oct 25, 2013 10:07 am

I tell everyone who will listen.

Funny you never hear Big Energy advising their customers about this disgusting waste of energy.
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Re: Air Conditioner Standby using 300W

Postby jimbo » Fri Oct 25, 2013 10:20 am

How do they keep their rating with such high standby usage??
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Re: Air Conditioner Standby using 300W

Postby davidg » Sun Nov 03, 2013 9:43 pm

jimbo wrote:How do they keep their rating with such high standby usage??

There is a heater so to speak that keeps the lubrication oil in them warm enough for instant start-up. Mainly required for colder climates, fortunately the heater does not run all the time it's temperature controlled. If the unit is a larger one like ours it needs a couple hours with power on not running before being used, not really an issue I reckon, to save those extra bucks.
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