Sharp Announces Sales of DC Powered Air Conditioner, Other Products To Follow

AmiMoJo writes: Sharp has announced that sales of DC powered air conditioners will begin by the end of the year. Most appliances use the standard AC electricity supply in homes, but as solar panels become more common switching to DC can save on conversion losses. Solar panels produce DC, which is then typically converted to AC before being fed into the house's wiring, and then converted back to DC again by appliances. Sharp has announced that it intends to produce a range of DC powered appliances for home use.

Comments

DC power?

[Joce640k]

Nikola Tesla is turning in his grave.

Re:DC power?

[K. S. Kyosuke]

Let's attach him to a DC generator, then. He can make himself useful once again. ;)

Re:DC power?

[MichaelSmith]

At 60Hz?

Single phase obviously.

Re:DC power?

[fuzzyfuzzyfungus]

Did he have anything against DC period, or just take the position that it wasn't so hot for transmission systems, especially since high efficiency DC-DC converters weren't exactly off the shelf items at the time?

Re:DC power?

[AmiMoJo]

That's it exactly. Back then things like frequency conversion and DC level switching had to be done mechanically. To change frequency you ran a motor that drove a gear that drove a generator at the new frequency, and did something similar for switching DC voltage levels.

Nowadays high voltage DC is used widely for transmission. Everything is solid state and highly efficient.

Re:DC power?

[Spazmania]

Basically, Sharp is eliminating the rectifier circuit from one of their existing products. Sharp currently sells it as an 'Inverter Air Conditioner".

Unlike most air conditioners, inverter air conditioners are always-on. The inverter varies the -frequency- of alternating current sine wave in order to change the cooling output of the air conditioner. It continuously outputs just enough cooling to maintain a steady temperature in the room.

To do this, the A/C converts the incoming wall power to DC and then back to variable frequency AC. Eliminating the initial AC to DC conversion here makes good sense.

Re:DC power?

[Mr D from 63]

High Voltage DC transmission makes sense in some applications. Its best as a single point to point solution over a fairly long distance, as line losses are minimized. High voltage DC switching and DC to AC conversion equipment is very expensive compared to AC, and typically has a shorter lifecycle, so you don't really want to have a lot of DC switchyards.

Re:DC power?

[Gryle]

Early Southern architecture had passive cooling systems, like double-hung windows, high ceilings, and constructing doorways and windows in such a way as to generate breezes as the air heated up during the day. The Spanish were particularly good at things like this.

Folks also had a different daily routine. They were up before the sun, worked until about lunch, had a big meal and a nap during the hottest part of the day, and then worked until late in the evening. The Spanish siesta is a good example of this, but the Italians have a similar concept. In modern days I see a lot of construction workers doing this too, particularly on road construction. The job site will be empty during the afternoon and work begins in the evening and lasts all night. (Some of this is to keep from interfering with day-to-day traffic patterns too.)

Re:Why not both?

[heypete]

AC has far lower transmission losses over long distances

Does it? I was always under the impression that AC was used for long-distance transmission because it could be easily stepped up to very high voltages with transformers while efficient DC-to-DC conversion was not possible until relatively recently. For the same power transmitted, resistive losses are lower at higher voltages as power lost to heat goes as I^2*R and lower currents could be used.

However, modern solid-state DC-to-DC converters are extremely efficient, can step DC voltages up to very high voltages and thus benefit from lower resistive losses in transmission. HVDC also benefits from not having to deal with inductive or capacitive losses in the cable.

In short, as far I know the key to minimizing losses in transmission lines is to use high voltages, not because of any inherent advantage of AC.

Re:DC power

[Megane]

The main advantage of AC is that you can use higher voltages safely, and higher voltages mean higher wattage with the same wires. And bigger wires are more expensive.

AC versus DC load breaking comparison with a knife switch

That was 220 volts, but 110 volts isn't much better on the DC side. There's a reason why DC-powered telecoms equipment uses 48 volts; much more than that and switches start arcing.

Ohmic loss is an issue when DC power is transmitted over power lines, but not so much when the DC is generated in the same building (solar panels, etc.).

Re:Why not both?

[aix tom]

Well, here you have 350 kV / 700 MW thyristor converter. It's easy to find, because it's pretty big. ;-)

http://new.abb.com/systems/hvd...
https://en.wikipedia.org/wiki/...

Re:Why not both?

[Spazmania]

High AC voltages have induction losses. They don't travel as well as low voltages.

BUT

The goal is to send lots of watts, not lots of amps or volts. Low amperages travel well. High amperages don't travel at all -- they lose most of their energy to heat. Simple transformers (which are basically just coils of wire) can swap amps for volts so that lots of watts can travel a long distance at low amperages.

Re:Why not both?

[Spazmania]

It's called an "inverter" air conditioner. It produces a variable-frequency AC sine wave from the DC voltage. The variable-frequency to the compressor changes the cooling output, so instead of turning the air conditioner on and off as the temperature wanders back and forth across the set point, it varies the frequency to keep the temperature steady.

http://www.acson-international...
https://en.wikipedia.org/wiki/...

It is brilliant.

Sharp already sells these air conditioners. They're just removing the DC rectifier circuit and running directly on DC instead of starting with 50hz or 60hz AC.

This is logical next step

[140Mandak262Jamuna]

People in USA and Europe with excellent grid connections are not aware of it. But in places like India with unreliable grid, people have been using backup electricity storage for quite some time. Typically truck lead-acid batteries are used to store enough energy to power a couple of ceiling fans, a few lamps and the TV, never forget the TV, for a few hours. They put up with power outages using these contraptions.

They use inverters to convert the DC to some square wave and approximate it to A/C using electronic gimmicks. Not a pure sine wave A/C, but close enough to run fans and the lamps. Energy conversion efficiency is not bad, the inverters do hot heat up too much. But they play havoc with the motors. So the Japanese A/C makers have been selling ruggadized air conditioners that can run on the inverter electricity.

The logical next step is to create A/C to run purely on DC. Probably it would use AC to DC converters to use grid electricity. Again this DC would be poor in quality compared to battery DC. So this Aircon also would need to be ruggadized.

All these calculations about when residential solar will become viable compared to coal or natural gas are completely different between G8 and rest of the world. Places like India will pay well over the current grid price for steady electricity supply. Not all of them. But the affluent population of India is about the size of Japan, some 120 million people. They have been making do with truck-battery-inverter contraptions, small gasoline generator sets etc. They would probably form the wave of early adopters who pay for the early fixed costs of solar panel factories.

Re:Why not both?

[OzPeter]

Wouldn't it be possible to have both in the same appliance?

Yeah, that AC/DC appliance would be really rocking, and a company that succeeds in doing it really would be a rising power. But I'd be worried about the low end manufactures doing dirty environmental deeds, dirt cheap as well as the build quality of the system overall. After all you don't want to be shaken all night long by your air conditioner - that would really lead you down a highway to hell.

Re:What Voltage?

[jenningsthecat]

Voltage doesn't kill; current kills and power burns. Higher voltage means lower current, and the same power.

Higher voltage only means lower MAXIMUM current, and then only if you assume constant power. However, it doesn't take much current to kill a person, and most real-world power sources can deliver enough current to kill under the right circumstances. (A mostly-dead flashlight battery can stop your heart if you bury electrodes deep enough in the right part of the body Also, think of Tasers - basically, low battery voltage raised to the point where it can stun or kill). Higher voltage usually makes death more likely, given the (approximately) constant resistance of a given current path through a body; I=E/R, so if E, (voltage) goes up, so does current. (Unless you're talking about static electricity from your clothing, or some other source which has high internal resistance/impedance and/or a small quantity of charge). And at still-higher prolonged voltages, the body's resistance can drop dramatically as parts of it start to boil and carbonize).

Your heart will fibrillate at 50mA AC or DC...

No. AC at a low enough frequency, (and at a surprisingly small current) will make the heart fibrillate; DC simply locks the heart muscle into a prolonged contraction. That's why defibrillators use DC - they temporarily 'freeze' the motion of the heart and give it chance to stop fibrillating and start beating normally.

Re:Why not both?

[Anonymous Coward]

Stop being a dick, he made an assumption that was incorrect, when proven otherwise he adjusted his stance.
If everyone who made assumptions acted like him most of the world problems would be solved.

Re:What Voltage?

[jenningsthecat]

DC can be problematic in that you can't always detect certain faults as there is not ground fault current, so there is inherently some greater chance of something like a bad connection overheating and causing damage, but that should not really be a concern if stuff is quality and installed correctly.

There's no connection between ground faults and bad connections that might cause overheating. But to the extent that DC systems might have lower voltage and therefore higher current, bad connections ARE more likely to overheat and cause fires. Also, there's no reason a properly installed DC system can't have Ground Fault Interrupters, although the ones currently used for AC won't work on DC. The ones designed for DC would be somewhat more complex, and probably bigger as well.

Another note: interrupting Direct Current without arcing can be difficult. AC has a zero crossing that extinguishes an arc across switch contacts, whereas the equivalent DC circuit may continue to arc across switch or relay contacts. Such switches and relays typically have heavier contacts and the contacts, when open, tend to have more space between them. The may also have permanent magnets nearby to act as 'blowouts' to extinguish any arc that develops.