DC airconditioners: latest efficient models from Fujitsu

[astrayan]

I've just revisited the possibility of having air conditioning in a very well insulated room, due to a friend up the road, who is also interested in a commercial work environment. It gets disgustingly hot around here.

There are a few conditioners with modest power input, of around 420-540W, and an efficiency ratio of 4.3 -> 4.6.

If you want to investigate random brands, then you can check out the Australian Gov efficiency site: http://reg.energyrating.gov.au/compa...aginate_by=500

The best ones appear to be Daikin, LG, and Fujitsu. The Fujitsu has something tantalizing in its specs: a DC motor, with variable input, down to 250W. I don't know if this is just to run the fans, or whether the motor can go slow.

http://www.fujitsugeneral.com.au/product/213/asta07jec-cooling-only/

Compressor Type
DC Rotary

Input, Range (Watts)
250-1270

That's all it says; no voltage or anything useful. Knowing our luck, this will be a DC compressor like on the Danfoss fridges, which have a 2 phase input. I'm just wondering if it's worth investigating whether these motors could be driven directly off panels, or whether it would be a complete waste of time. The good thing about directly driving it from panels, would be that the panel output would regulate the speed of the compressor. A bugbear of AC solar aircon, is that just when you turn it on, a cloud turns up, which means you end up drawing from your batteries, during a time when you are trying to charge them. You then need a circuit to shut off the aircon during small clouds.

Do any of you know anything about what's in these air conditioners?

[Sunking]

I can answer some of your questions as I have experience with the Fujitsu split units.

I think what is confusing you is the compressor is DC, however the input power is AC which you can pick up on the specs as it requires 2 (1 for the compressor unit outside, and 1 for the fan inside) single phase at 50 Hz @ 240 volts AC operating on 10 amp circuits. The unit has a built in rectifier to convert AC to DC power. The reason they do this is because it is easier, less expensive, and more efficient to control a variable speed compressor motor with DC verse AC. The compressor motor is a BLDC motor, and is driven with a 3-phase variable frequency driver (VFD) inverter.

So to answer your question you cannot run the unit in question directly from a solar panel. Secondly note the cooling capacity of the unit in question is a maximum of 10,200 BTU's which is less than 1-ton which means a small room. I have no idea if that is enough cooling capacity to meet your needs. Based on total power needed to run both compressor and fan requires up to 3000 watts to generate up to 10.200 BTU's which is decent but not great.

[astrayan]

Thanks for that. So, it will have to be run off an inverter, because even with large amounts of R&D, the DC motor probably uses 315V peak, (240VAC rectified).

I have tried to run an old Sanyo aircon on an inverter, and generator, but the input spec was 740W, and that tended to go up, as the solar voltage fell, and the inverter inefficiency kicked in. The power was all over the place.

I know that to run an aircon, you would need a dedicated solar panel set, an MPPT (of some kind), and an inverter. To run a 420W unit, you would need maybe 600W of panels, and the 40A MPPT would have to be tricked or programmed into outputting 14.5V (or better). There would have to be a module that detected loss of sun, that shut everything down.

I know the 2.2kw aircon is small, but the definition of "room" will be changed. Most standard rooms have thermal mass, windows and thermal leakage. Here, the room will have no appreciable windows, perhaps 0.7mm steel or canvass walls, and 20cm of insulation. (I would try to avoid having 2.4tons of plasterboard cladding.) The room/shed will contain (say) 100m3 of air, which has a mass of 120kg, or the same thermal mass as 30kg of water. (This would require 120,000 joules per C to cool, or 60 seconds per degree) Cooling steel cladding may take 20 minutes.

With paranoid design, it should be possible to cool an entire 6x9m shed with a single small aircon.

[Naptown]

With air conditioning most of the battle is dehumidification unless you happen to be in the Sahara.
It takes almost 1000 Btu's to condense one pound of water from the air.
There are companies that are now starting to produce solar dehumidifiers
This in conjunction with a/c may prove to be a viable alternative solution.

[Sunking]

I know that to run an aircon, you would need a dedicated solar panel set, an MPPT (of some kind), and an inverter. .

Plus some huge batteries.

Lennox and another manufacture claim to have Solar powered air conditioners but they are not. They are regular heat pumps and they hire a solar contractor to install a grid tied system on your home.

[SunEagle]

Plus some huge batteries.

Lennox and another manufacture claim to have Solar powered air conditioners but they are not. They are regular heat pumps and they hire a solar contractor to install a grid tied system on your home.

I have seen those commercials down here in Florida. It didn't make any sense to me that solar could run a house AC unit. Now it makes sense they are selling a PV system along with the AC unit.

Almost like them "Steak" companies that sell you all types of steak for low prices. What they are really selling is the freezer to keep that meat in.

[astrayan]

With air conditioning most of the battle is dehumidification unless you happen to be in the Sahara.
It takes almost 1000 Btu's to condense one pound of water from the air.
There are companies that are now starting to produce solar dehumidifiers
This in conjunction with a/c may prove to be a viable alternative solution.

Do you know how solar dehumidifiers work? I thought of heating calcium chloride, and then passing air through it later, but it's a bit corrosive and messy.

I got a note back from the Fujitsu man, and he said that the low power figures, (sometimes 250W), are when the unit is more or less idling, with the compressor on low power.

I wonder how much efficiency would be gained by rigging up 240V of solar panels. It may be a who cares thing, because solar panels are so cheap, you can just buy another 20% to cover the loss.

[Naptown]

The dehumidifiers work with a desiccant wheel
Inside air is run across half the wheel and greatly heated air is run from outside in a separate compartment to dry it again
I would imagine there would be some heating of the indoor air from the hot desiccant coming back in
I have only seen pictures of these so I have no practical experience with how well they work.

You are on the right track with the mini split and perhaps some ballasted PV and a legal grid tie to offset cost
Ballasted so no holes in roof and you can take it with you if you move

[russ]

Search Energy Recovery Ventilation ERV

[Naptown]

Search Energy Recovery Ventilation ERV

different animal from the dehumidifer

[russ]

different animal from the dehumidifer

Many incorporate a humidifier - mine for example. I have one Rich.

[Naptown]

Hrv's I always reccomend for indoor pool applications particularly for winter operation.
I went to a community indoor pool a couple of years ago and during the winter they were using a 10 ton a/c unit and propane reheat for dehumidification year round.
Talk about wasting their money. The developer of the community put it in knowing they would turn it over to the HOA in a year or two. They didn't care how much it cost to operate.
I proposed doing liquid pool covers on both the pool and hot tub to reduce evaporative losses and dehumidification demands on the heated pool and installing HRV's to reduce dehumidification costs further.
It was a retirement community and I don't think the board understood anything. They got all upset about the pool cover as soon as they read chemical into the equation.
Actually it is nothing more than about 80% isopropyl alcohol and some fatty acids similar to lanolin and things found in cosmetics.
Never went anywhere

[astrayan]

From time to time, I have wondered why you can make an aircon that works the same way as a gas fridge.

http://home.howstuffworks.com/refrigerator5.htm

I have no idea of the efficiency of a gas fridge, but it sounds like you would need about 5kw of sun, to have a decent effect.

[inetdog]

From time to time, I have wondered why you can make an aircon that works the same way as a gas fridge.

http://home.howstuffworks.com/refrigerator5.htm

I have no idea of the efficiency of a gas fridge, but it sounds like you would need about 5kw of sun, to have a decent effect.

You can do this, and the concept actually makes economic sense in some cases. But an even better economic return comes from using solar heating to regenerate a desiccant, and using the desiccant to supplement a conventional air conditioning system. This works best in hot humid climates. (Remove the moisture from the inside air first to make it easier for the A/C to cool it.) If you do this, you forgo any advantage from using evaporator coil condensate to cool the condenser coil, but in a very humid climate that would not be a major factor anyway.

[astrayan]

My maths tells me that the latent heat of evaporation of water is 2.2 MJ per kg. A kg, being what most aircons are supposed to condense in an hour. Since the output is typically 2.5kW, then this amounts to 900 seconds of power per hour - or 25% of the aircon output is devoted to water condensation.

Adding water into the back end of a conventional aircon is doable, using a mister, or just a drip, to make sure the hot condenser is well-supplied with coolant. However, it can result in corrosion of the copper-aluminium junctions.

The conventional aircon, with no mister, or any solar turbo, is the most general el-cheapo case, so is the most commonly designed, and the cheapest. There are cases where "Solar" Air Conditioners have added heat from a panel, for magic effect, but even if the physics of this makes sense, manufacturers are behind the times, and don't start with an efficient compressor. (The mass-produced Daikin models use a reluctance motor, which can now be driven properly, by little computers. They claim 20% more efficiency, due to high torque, which is highly plausible.)

The Koolsola air conditioner sales pitch attempts to describe a process, by which their solar panel helps, but fails, dismally.

http://www.lhsps.com.au/koolsola-air-conditioning/how-does-it-work

In order to make their product perform better, they claim that a conventional efficiency is EER 2.38

http://www.lhsps.com.au/koolsola-air-conditioning/statistics

The LG K09 models reach EER 5.4, probably when they are going slowly, and outputting only 300W. At this level, you could air condition a coffin, very well.

http://www.lg.com/au/residential-air-conditioners/lg-K09AWN-11

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Here's an analysis of using ammonia as a coolant in a standard-concept air conditioner, getting COP up to 6.

http://www.airah.org.au/imis15_prod/Content_Files/Divisionmeetingpresentations/QLD/PPQLD_24-02-2010SJ.pdf

The efficiency of ammonia is attributed to better refrigerant properties, which makes me wonder when there will be a push back to it, despite toxicity problems.

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This article deals with whether Ammonia Absorption air conditioners are practical.

http://www.treehugger.com/sustainable-product-design/more-efficient-solar-powered-air-conditioner-developed-australia.html

http://eprints.qut.edu.au/49358/1/Paolo_Corrada_Solar_2011_article_final_reviewed_v2.pdf

They are possible, but electrical solar panels are getting cheap.