Do portable air conditioners work?

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Do portable air conditioners work?

Postby Quokka2 » Fri Mar 01, 2013 12:38 pm

I promised myself years ago never to buy one of these, but with with two small upstairs rooms uninhabitable for most of our WA summer and difficult (read expensive) to cool by conventional means, we were tempted by the offer of a "large room" unit at under $600. The sticker on the appliance said 4.7kW out for 1.57kW in, implying a respectable Energy Efficiency Ratio of 2.99, so we decided to give it a try. The unit is single vent reverse-cycle refrigerated, a type which seems to dominate the market these days.

I installed it by the book, with the outside exhaust duct half extended and fed through a hole I had made in the wall, as the supplied window kit didn't suit our wind-out windows. I turned it on for the first time in the late afternoon with the inside and outside temps both about 31C. Pretty soon, it was gushing cool air, but was very slow to make any difference to the room temperature, although the compressor was hammering away all the time (quite noisily for a "silent" model). Armed only with a hand-held Skymate anemometer/thermometer and a plug-through electricity meter, I decided to find out why.

Output of the appliance can be measured by the amount of heating of the room air discharged from the 125mm exhaust duct. The highest air speed I could measure from the this duct was 10.5m/sec, so it would be generous to assume that the appliance was moving about 100L/sec of air out of the room. A series of measurements under different ambient conditions during the evening and the following day indicated the difference between the room air temperature and the outside exhaust was usually around 23C, but varied from 21C to 27C. A difference of 24C at 100L/sec airflow represents an output of 2800W.

The inputs to this process are the electricity consumed, which I measured, and the heat extracted from the room, which I determined by difference (as the airflow from the front is well diffused and I couldn't estimate it with the equipment I had). The heat extracted from the room is actually the sum of the "coolth" blown out of the front of the unit (at a refreshing 12C or so) and the heat radiated back into the room from the plastic exhaust duct at the back (duh!). For most of the time the appliance was only pulling 960W from the mains (the highest reading was 1100W when the temperature difference was 27C).

At 1000W, the typical cooling output (heat extracted from the room) is thereby 1800W, with a maximum just over 2000W. This is unlikely to match the heat infiltration into even a reasonably well-insulated room on a hot day.

The errors involved in this admittedly rudimentary evaluation are insufficient to change the conclusions, which include a couple of game-stoppers:

Problem 1: Excess Ventilation
The 100L/sec of hot air blown out of the exhaust duct has to be replaced, so that much outside air is being sucked into the house somewhere. This would change the air in a reasonable-sized living room every 10 minutes, which is getting close to evaporative air-con territory and negating the benefit of all that insulation that Juliar squandered our taxes on.

Problem 2: Poor Efficiency
By my measurements at least, the implied EER of 2.99 (4700/1570) is actually closer to 1.80 (1800/1000). A lower exhaust airflow or higher wattage consumption would worsen this figure drastically, as it does for all practical purposes anyway when the inflow of replacement air is taken into account. If the outside temperature is 15C higher than the inside temperature, then even if the house could be perfectly insulated, the heat transfer into the house caused by this appliance becomes equal to the 1800 watts of apparent benefit, and the nett effect of operating this unit is NIL (apart from increasing your electricity bill). :(

I appreciate there are reasons (renting comes to mind) why people can't install a decent split system, however a portable air-con would appear to be an appliance of last resort if a window air-con can't be installed temporarily. There appears to be no benefit to owning a portable air-con unless:

    You can find one with dual ducts, so that it doesn't pull all that hot air into your house (I haven't);
    Your house is poorly insulated (an evaporative air-con may work better and would be cheaper);
    You only want to cool the house down faster after it has become cool outside (a fan in the window may work better and would be cheaper);
    You only want to sit in front of it (sitting in front of an open fridge may work better and would be cheaper).
We took ours back to the shop without bothering to test its performance under reverse cycle; all the issues mentioned would still apply.

These appliances would appear to be a waste of both money and resources; if this thread results in a few tempted by end-of-summer sale prices to buy a split system instead, I won't have done the environment or the retailers any disservice :)

If there is a demand for these things, there must be a need for a new generation of window air-conditioners, designed to fit a sliding window and to operate efficiently on a 10A circuit using modern inverter technology. How about it Fujitsu and Panasonic?
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Re: Do portable air conditioners work?

Postby Tracker » Fri Mar 01, 2013 2:49 pm

..
From the working units that I have found on junk heaps, I suspect that others have found the same issues..

I too, think the greatest issue is the exhaust air...
As you say, it has to suck that air from somewhere, and the cooling power is likely just enough to cope with that extra load...

The GE Skinny is a great machine.. It was designed to sit in the tracks of a slide window..
I have two of them and have actually carved out between the studs and fitted them in the Master BR and the brides craft room...

The benefit is that they suck and blow from the outside.. Hence they dont have the portable unit's problems..

http://www.ebay.com.au/itm/LG-Gold-Window-Air-Conditioner-/251234366289?pt=AU_AirConditioners&hash=item3a7ebc3351&_uhb=1#ht_852wt_934.
this might be as close as you get these days... Just noticed it on EBAY when searching for "SKINNY"
..
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Re: Do portable air conditioners work?

Postby Clemo » Fri Mar 01, 2013 3:05 pm

Quokka2 wrote:Do portable air conditioners work?


No.
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Re: Do portable air conditioners work?

Postby Tracker » Fri Mar 01, 2013 3:16 pm

.
Thanks, CLEMO...

I will be VERY surprised if anyone finds they DO work..
I have two here, amongst my junk..
They both blow the COLD air, but a room NEVER cools..
I am confident that it's because of that issue of sucking hot air into the room to replace the exhausted air..
..
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Re: Do portable air conditioners work?

Postby Gordon-Loomberah » Fri Mar 01, 2013 4:44 pm

We were given one a few years ago, and you really do have to stand in front of it to get any cooling effect. Quokka's observations of COP are interesting, but the supposed COP on the Dimplex here is really just garbage!
The claim of 850W input and 3500W cooling is surely a joke! It starts off using around 850W, but as the temperature outside rises, it jumps up to about 1600W. The air that is meant to be cooling the room is best described as "relatively cool", not much below 20C, and we decided that standing in front of the fan running on high speed feels much cooler. 40W vs 1600W!

It is going to the tip, at least the plastic body parts, we dont want to inflict this abomination on anyone that will be using coal-fired electricity to run it, but I might salvage the fan out of it first... and I may investigate the feasibility of using the refrigeration part of it for water cooling duty, to keep the trout cool when I have the aquaponics up and running.
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Re: Do portable air conditioners work?

Postby Tracker » Fri Mar 01, 2013 6:34 pm

Gordon-Loomberah wrote:... and I may investigate the feasibility of using the refrigeration part of it for water cooling duty, to keep the trout cool when I have the aquaponics up and running.

and that might be about the best use...
I have thought of using one of mine the form the basis of a KEG cooler.. for a Coke-Syrup canister..
Home-brew beer naturally.. ;)
...
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Re: Do portable air conditioners work?

Postby Quokka2 » Fri Mar 01, 2013 11:18 pm

Tracker wrote:..The GE Skinny is a great machine.. .


I guess I had something like that in mind; there is an LG one as well but I suspect both are discontinued, and after the hottest Summer on record, not too many for sale in the West right now. If it fitted between 450mm-spaced studs, that would be a bonus.

By the way, thanks everyone for the response - this is a message that really needs to get out there... I found some reviews of these things on a retailer's web site and everyone seemed to like them - would I be too cynical if I thought less favourable reviews had been deleted? My favourite was from someone who said "...'just like sitting in front of the fridge". Couldn't agree more :lol:
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Re: Do portable air conditioners work?

Postby offgridQLD » Sun Mar 03, 2013 12:25 am

Yes its a good point with the portable units they really are a terrible design.

You cant go past the Mitsubishi range of inverter split systems. The SRK20ZJX-S puts out 2 kw cooling & 2.5kw heating from just 350w in.It's very quiet just 20db inside on silent mode and 40db outside at 1m from the compressor unit .Along with bacterial resistant plastic on the internal fan to stop that funky mold that AC systems attract. They are a quality unit so you do pay a premium for it but i think its worth it for something you are going to install and use for 20 years or more.

Most of our house is very open plan with very height ceilings so Air conditioning is out of the question (living off grid) Though we have a little computer/office/2nd tv room that's about 4mx4m. Just a small room with a sofa and a desk. Its on the south side of our house. We plan to install a Mitsubishi E SRK20ZJX-S in that room. Most of the time we don't need AC it as we get great evening and daytime breezes up in the hills.Though there is the odd day that's hot and the wind doesn't play nice. A day like that it would be nice to have that small room as the escape oasis that's Air conditioned.

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Re: Do portable air conditioners work?

Postby Privatteer » Sun Mar 03, 2013 1:54 am

Delonghi Spec 77L/sec. Air output 65deg with outside temp 32deg. 50dB.
Have not measured the power usage but spec says 1200w max with 4.400 kW cooling capacity.

Don't use it often and when I do I usually add some water so it can use its evaporative mode as well.
While its nowhere as good as a split it still keeps a 6x6m room at 20deg on the really bad days ie 40deg which is when I use it.
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Re: Do portable air conditioners work?

Postby Tracker » Sun Mar 03, 2013 10:21 am

Privatteer wrote:Delonghi Spec 77L/sec. Air output 65deg with outside temp 32deg. 50dB.
Have not measured the power usage but spec says 1200w max with 4.400 kW cooling capacity. ....

So here is one that seems to actually work..

So, the general feeling is that most feel good if you stand in front of them :cry: , but some machines might actually COOL an appropriate room.. :!:

Interesting..
...
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