Inverter Air Con: Beware Of High Standby Power

[DaveLee1688 1]

How to select an inverter air con that is really efficient

I recently found out that two air con condensers of my house each has standby power of 140VAR, and 25W. This is extremely surprising

for a 3/4 ticks energy labeled product.

What this means is that even when the air con is not turned on, there will be about 0.8 Amperes circulating in the wiring, which

eventually will end up as heat losses. 25W also means that about S$5 per month per condenser will be wasted for nothing per condenser.

How I realized this fact is when the utility bill showed significant power consumption end of last year when we went for vacation, even

with all applianced turned off. This was about 1 year after I changed 3 Pansonic non-inverter and 2 LG aircons (all one-to-one) to

2 Mitsubishi Starmex inverter aircons, one with 2 fan coils and another with 3. So, recently I bought an energy monitor (e2 from Efergy)

and a watt meter (eSocket, also from Efergy) that measures the power of appliances. With these, I discovered the culprits. I wrote to

NEA and they were very helpful and responsive, came to my house to confirm the measurements this morning.

Last week, I wrote to Mitsubishi, and they finally responded 2 days back to inform that the 140VAR is reactive power that is not being

charged by Singapore Power.

Nevertheless, the measurements show that the standby power consumption is significantly higher than other manufacturers, basing

on my researches and initial data that NEA has collected on this standby power. Based on what NEA staffs tell me this morning,

NEA is considering making declaration of standby power necessary for obtaining energy label (the ticks each product gets). Only

Australia has made standby power as part of their energy labeling process.

If you are planning to install an inverter air con, be aware that you cannot switch off the power to the aircon condenser easily, only

way is to go to the power distribution board. Doing so too frequently may be dangerous.

What are the alternatives:

a) Ask your aircon supplier for information on rated standby power, in terms of real-power and reactive power.

The real-power is the wattage that you are going to pay for.

A reasonable standby power for electronic controlled appliance should be way below 5W. For example, my Sharp microwave oven

consume just below 1W on standby.

The way to calculate how much you pay per month for standby power is : (Real-Standby-Power-Rating-in-Watts / 1000) x 24 x 30 x $0.26

$0.26 is the current amount you pay per kilowatt of power consumed.

The standby reactive power determine how much current gets circulating in the wire when the aircon is in standby. This has implications on

how thick the copper wire must be to prevent fire hazards. For example, two weeks ago, one of my condenser unit refused to start,

and the service man discovered after about an hour that the copper wire to the condenser is open circuited. Fortunately, my house

has a spare isolator (used to have 5 condensers, now 2), so, he just switched to alternate isolator to fix the problem. In my case,

not being aware of the high reactive current issue, the old copper wire for non-inverter condenser was used, probably causing it

to snapped during the hot June month when we turned on more frequent and for longer period.

b) Ask your aircon installer to install a separate switch for switching the power to the aircon condenser, something like the switch

for the water heater (hight current type). When you do not use the aircon, switch it off, just like the water heater. In fact, this

'was' the initial suggestion by Mitsubishi, but they quickly retracted this suggestion by sending another email within a minute.

So, the lesson I learned is that saving energy by switching to inverter aircon is not as simple as "buy brand X and reduce $Y",

there are some hidden $Z dollars around, and it is going to increase the diameter of copper wires for safety.

Hope this sharing will help Singaporean make some wise choices.

UPDATE: See Confirmation of findings and Further clarifications

Edited September 13, 2010 by mit3a28

[new_home_maker 0]

Wow ! Thank for this info.

I am getting Mit Starmex based on the 4 ticks and quiet operation.

Now I need to re-consider again THANKS to misleading standard from NEA !

Power consumption during standby mode is not something new ...

I only switch on on my air con at night and for the whole of day time 10am - 9pm -

the air con is wasting energy and $.

I checked with my air con supplier whom said that by switching off the aircon breaker

when not used will solve this problem (without damaging the air system). Is it true ?

If yes why did Mitsubish retracted this suggestion ?

Can Anyone suggest an alternative air con system with 4 ticks , quiet operation AND

low energy consumption during standby ? I need to re- consider my options.

Thanks in advance !

[DaveLee1688 1]

Wow ! Thank for this info.

I am getting Mit Starmex based on the 4 ticks and quiet operation.

Now I need to re-consider again THANKS to misleading standard from NEA !

Power consumption during standby mode is not something new ...

I only switch on on my air con at night and for the whole of day time 10am - 9pm -

the air con is wasting energy and $.

I checked with my air con supplier whom said that by switching off the aircon breaker

when not used will solve this problem (without damaging the air system). Is it true ?

If yes why did Mitsubish retracted this suggestion ?

Can Anyone suggest an alternative air con system with 4 ticks , quiet operation AND

low energy consumption during standby ? I need to re- consider my options.

Thanks in advance !

Well, the problem is not with NEA because all except one equivalent agency in the world

has made standby power declaration a mandatory requirement. However, NEA on

knowing about this issue has immediately taken action.

The problem is really with aircon manufacturers exploiting holes in the system.

However, let me also say that apart from the unusually high standby power of Starmex,

I am actually very happy about the performance in cooling and savings as compared

to the 1-to-1 non-inverter units I used to have. I am caught by surprise on this

high standby partly because of my high expectations on "3/4 ticks" systems,

expecting them not to waste unnecessary energies. However, I found that those

expectations are ahead of most of the world's energy labeling efforts, and hence

alerted NEA, and did the posting here so that others will not be similarly surprised.

On the issue of turning off the MCB/isolator when not in use, it will work, but carries with

it some dangers. I will not recommend it, and suspect why Mitsubishi retracted the

suggestion is from a safety point of view (the person who reply is a PR person, most

probably their technical people sounded the alert for the suggestion to be retracted

to avoid dragging Mitsubishi into legal problems if any electrocution happens as a

result). So, installing a separate switch, such as that for the heater, is safer because

those switches are designed to be operated by ordinary people and free from

leaking switching sparks to the user. Isolator and MCB are designed for technically

trained personnel. Not all switches are the same, chose one approved by SISIR

capable of switching 20 to 30 Amperes.

Having said the above, it is really not a good idea to begin with of having a switch

for purpose of cutting off standby power wastage. For new installations, I will suggest

to avoid choosing those brands which cannot assure you of low standby power.

For those like me who had already installed, we either collective urge Mitsubishi

to give us a solution or we help others to avoid getting trapped.

[buttwiser 0]

Is it only happening only to inverters or also affecting non-inverters?

[DaveLee1688 1]

Is it only happening only to inverters or also affecting non-inverters?

Based on preliminary findings by NEA staffs, I was told that it has something to do with the

design of Mitsubishi's Inverter, having a heater inside to separate some oils. Not sure

exactly what this means.

I did some research on Internet and retrieved some reports from agencies equivalent to

NEA that are responsible for Energy Label in other countries. Based on reports from Australia,

Hungary and Czechs, it appears that non-Inverter should not have this problem, but

depending on how the electronic controller is designed, the standby power will still

vary among products, but should certainly be below 5W.

Please also note also that if you have a private house and the copper wire path is quite

long, then, it is also safer to use thicker copper wires if you are using Inverter aircon

due to the low power factor.

One more point: Some might rush off to buy a power factor correction (PFC) device

in the market that claim to save energy. Please note that this is largely a scam,

it does nothing much to save your energy bill for low-tension household. I found

a report by NIST scientists (USA's equivalent of SISIR) dispelling the myths of

using PFC to save energy. The real benefit is that it will reduce the large

circulating reactive current in the copper wiring, thereby reducing the need for

large diameter opper wire. However, for this to be effective, the PFC must be

installed right next to the aircon condenser. Therefore, those small PFC device

from China on makeshift markets are not going to work, and in fact, may be

fire hazards if improperly used. So, be warend.

[buttwiser 0]

wow, thats certainly a large amt of research u did.

[DaveLee1688 1]

Well, I do research for a living ! I always believe in looking for facts.

It quite simple, just google with the keyword : +"energy label" +"standby power" and google will do the rest for you.

[new_home_maker 0]

Please also note also that if you have a private house and the copper wire path is quite

long, then, it is also safer to use thicker copper wires if you are using Inverter aircon

due to the low power factor.

Dear Mit3a28

1. Dun mind can you let us know what is the correct copper wire size for starmex inverter system 4

as recommended by Mitsubish?

2. Which brand in the market have lowest standby current ?

TIA

[donut88 1]

would the operating manual tell us abt the standby power? i need to read my Toshiba one....

[DaveLee1688 1]

What copper wire size?

Okay, I am not an expert in these wire stuffs, but google I can help a bit:

For wire gauge, see here Wire Gauge.

So, if you read the table, what you should really notice is that for the same wire gauge, the current

capacity is dependent on the insulation. For example, number 10 (the usual size for condenser) can

carry 30/35/40 Amperes, depending on whether the insulation is rated for 60C/75C/90C respectively.

The next larger capacity is number 8 (there is no metric size for number 9), which carries 40/50/55A

for the 3 temperatures.

So, it will be easier to ask your contractor for better insulation, 75C, than thicker wires because

copper wires are very expensive now.

If your cable run through the roof like mine, and the copper wire goes through twist and turns to get

to the compressor from the distribution board, you need to be a bit 'kiasu' because every twist and

turn may reduce the cross-section area of the wire. This is what probably happened in my case, resulting

in cable snap under high load.

Better get advice from a qualified electrician to have reliable second opinion.

Which one has lowest?

I really do not know which one has the lowest because none of them specify it clearly. Your best

bet is to ask the supplier. However, from hints I get, going for Daikin seems to be a good bet, but

again, I am not certain.

Edited July 25, 2010 by mit3a28

[DaveLee1688 1]

would the operating manual tell us abt the standby power? i need to read my Toshiba one....

Do not bet on this. You need to ask your supplier. Or try googling harder, or go to Toshiba

web site and submit an enquiry. The simplest way is this: Switch off all other circuit breakers

carefully on the distribution board, go to your utility meter, and read how much energy

it is eating up for a few minutes. You will get at least an idea in the order of magnitude on whether

it is 10's of watt-hour or just a few watt-hour. Note that the energy meter accumulate in kWh, so,

it may not be so easy to see the change if your aircon is good to the environment.

For my case, I spend few hundred dollars getting an energy monitor from Efergy to measure. It will

pay back in less than 6 months from savings from cutting off the standby power (for me, with 2 condensers,

it is S$10 per month). The Efergy eSocket cost S$55 at Sim Lim tower. Be warn that to really measure,

you need an electrician to help you. In my case, I am trained to mess with the distribution board

20 years ago during university course, but I do not suggest it to anyone who is not trained

to take a wiring apart. Also, for HDB, it will be against HDB rules to mess with the DB.

Have a nice weekend, do something than staring at your energy meters :-)

Edited July 25, 2010 by mit3a28

[neubie 2]

have you tried to use those clamp meters, eg like Kyoritsu http://www.kew-ltd.co.jp/en/products/clampmeters/index.html to tong one of the live or neutral (but not both together) wires to find out what is the actual current when on standby mode?

cos i believe the clamp meter is calibrated in RMS values, which is the actual heating effect, multiply the current by 230V and you shd get the correct power consumed by any device.

also, side track a bit, i read the starmex series of condenser units have this (switch) settings for HDB flats with and without current limitations. max operating current is 8.5A for MXY-3A28VA (system 3 with up to 14.6kW) for limited current applications and 12.65A for unlimited current applications...

now, we all know that the higher the current, the more energy the aircon consumes, so to save power, can installers simply configure the condenser to run at lower current and save power bills?

Edited July 25, 2010 by neubie

[wolflet 1]

have you tried to use those clamp meters, eg like Kyoritsu http://www.kew-ltd.co.jp/en/products/clampmeters/index.html to tong one of the live or neutral (but not both together) wires to find out what is the actual current when on standby mode?

cos i believe the clamp meter is calibrated in RMS values, which is the actual heating effect, multiply the current by 230V and you shd get the correct power consumed by any device.

also, side track a bit, i read the starmex series of condenser units have this (switch) settings for HDB flats with and without current limitations. max operating current is 8.5A for MXY-3A28VA (system 3 with up to 14.6kW) for limited current applications and 12.65A for unlimited current applications...

now, we all know that the higher the current, the more energy the aircon consumes, so to save power, can installers simply configure the condenser to run at lower current and save power bills?

losing out on cooling power with costs savings? not advisable if your system 3 is cooling 3 medium size bedrooms.

[neubie 2]

losing out on cooling power with costs savings? not advisable if your system 3 is cooling 3 medium size bedrooms.

nopez, the specs say the cooling capacity is the same, irrespective of application with or without current limitations...

[first 0]

"Which one has lowest?

I really do not know which one has the lowest because none of them specify it clearly. Your best

bet is to ask the supplier. However, from hints I get, going for Daikin seems to be a good bet, but

again, I am not certain."

I bought and installed DAIKIN Model 2MKS50ESG in May 2009. Previously using SANYO for more than 10 years. Very happy with SANYO. No problem for over 10 years... about 13 years to be exact.

After the change, my monthly kWh dropped by 150 on average.

No very sure about Power Consumption on standby. Did not check. And not a concern as overall kWh reduced. In fact I tend to switch on the DAIKIN for more hours than the old SANYO.

Never turn off aircon mains. Aircon main switch is always on. Only use remote control to switch off... i.e. Power is always supplied to both blower unit and condensing unit except compressor is not running. i.e. always on STANDBY.

Edited July 27, 2010 by first