Air Conditioner Standby using 300W

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Air Conditioner Standby using 300W

Postby jsull » Sat Jun 22, 2013 10:11 pm

We have a Mitsubishi Electric ducted air conditioner, model PUHZ-RP140VKA2 which was installed in March. After getting our solar sytem installed and using the online monitoring we noticed that it uses almost 300W constantly while in standby. We had the installer out and he verified this but said he didn't know what it should use. I have had absolutely no luck with getting anyone at Mitsubishi Electric to tell me what the standby usage sholud be. They said they didn't know and referred me to the energyrating.gov.au site. I can't find the information there. The installer now says that all major units of all brands use 250-300W in standby. It sounds incredible that a unit could use about 7kW/h per day while not operating. I know crankcase heaters use power but this seems excessive. I would appreciate any advice on what this unit should be using in standby or where/how I can get that information.
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Re: Air Conditioner Standby using 300W

Postby Privatteer » Sat Jun 22, 2013 11:22 pm

According to the model you linked to its actually a heat pump combined unit. I would assume there is a pump somewhere exchanging refrigerant/water with your HWS to heat the water.
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Re: Air Conditioner Standby using 300W

Postby Bthree » Sun Jun 23, 2013 10:07 am

I have a Carrier ducted unit about 6 Kv.
It has a compressor sump heater to keep the oil and refrigerant viscose primarily helpful in winter.
The element uses around 65watts when the compressor is NOT running.
I asked my installer a couple of times about the effect if the heater was removed, Loss of warranty, my AC is now out of warranty so I asked the question again, .. Possible lockup of the compressor resulting in burnout and destruction, the bill around $4000
He sited a case of a factory that switched the power off to the whole facility overnight and on again in the morning, the result was many compressor failures until the practice was stopped.

I have considered installing a switch to disconnect the heater in summer but chickened out, also thought about placing a button thermo switch on the compressor but could not find one around the 10-15 degree mark so gave up.

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Re: Air Conditioner Standby using 300W

Postby KPrawn68 » Sun Jun 23, 2013 11:12 am

I'm a bit vague here, so when you unit comes out the box new, why doesn't it seize first time its started?
Sounds like con to me.
I'd be complaining to Consumer affairs about misleading ( albeit missing important info about standby power)
7kWh a day that's almost half a households daily use
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Re: Air Conditioner Standby using 300W

Postby Gordon-Loomberah » Sun Jun 23, 2013 11:24 am

It's almost a whole day's use here much of the time! If you aren't using it, it cant passibly need to be heating all the time, it is just wasteful, of energy and money. There certainly is no heater running while it is sitting in a warehouse or on a ship for months on end before installation...
Much more sensible would be to have the heater on for an hour or so before you want to heat or cool with it. Sure it takes a bit of planning, but is more environmentally sound, and easier on the wallet.
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Re: Air Conditioner Standby using 300W

Postby jimbo » Sun Jun 23, 2013 12:37 pm

My Mitsubishi Heavy Industries split system uses only 2w on standby so i'm guessing it doesn't use a sump heater. Like Gordon stated, turn it off at the mains and just switch it on half hour b4 start up. 300w sounds a bit excessive, are you sure it's 24/7?
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Re: Air Conditioner Standby using 300W

Postby Bthree » Sun Jun 23, 2013 12:58 pm

300 watts sounds more like the whole house base load usage
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Re: Air Conditioner Standby using 300W

Postby davidg » Sun Jun 23, 2013 4:04 pm

Bthree wrote:the result was many compressor failures until the practice was stopped.
Yes, cold and oil that is too viscous, likely be as a result of the compressor running stone cold oil and trying to run flat out straight away, thats one of the reasons why the heater is in the sump.

How about something like this Digital Thermostat, when the temp is high enough only then will the compressor be allowed to run, to cover the higher currents use an SSR to suit, a bit of a mod in the A/C unit and that should make it pretty bullet proof to turning it off completely and protecting it from compressor destruction if too cold in the sump.
Last edited by davidg on Sun Jun 23, 2013 4:42 pm, edited 1 time in total.
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Re: Air Conditioner Standby using 300W

Postby Privatteer » Sun Jun 23, 2013 4:17 pm

Bthree wrote:He sited a case of a factory that switched the power off to the whole facility overnight and on again in the morning, the result was many compressor failures until the practice was stopped.


I tried to avoid aircons but I remember quite a few off them having a jumper to disable the heater on standby. They had warning about delayed startup if selected to defrost in very cold environments.
For most of Australia I would think temps are above freezing enough to do without the heater.

@300w I still think his heatpump is running a exchanger with the HWS to shed heat and it should stop eventually.
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Re: Air Conditioner Standby using 300W

Postby Smurf1976 » Sun Jun 23, 2013 7:22 pm

I can't avoid noticing that many such systems have no such heater at all which raises questions about the overall design of those that supposedly need them.
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