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The Chillmax AirEarly in July, I saw this thing advertised on TV. Then, the same evening, I was shopping in Asda and saw it on display. I am an idiot for things like this, and bought it on impulse so I could test whether it worked or not.

As a chemist, I know full well that if you want to cool a large space down effectively you’re going to need something that uses a special refrigerant. From a practical perspective – where people are going to be in that space, and you need to cool for long periods – that’s going to mean some sort of motor-driven compressor, a closed radiator filled with the refrigerant, a big fan to suck air in and blow it across the radiator, and a wide exhaust pipe through the wall or window to get rid of the “removed heat”. Oh, and probably some sort of collection bucket for the condensed water it takes out, because proper air conditioners dehumidify the air they cool.

The Chillmax Air is much simpler. Anyone who has used a normal fan will know that you only feel “cooler” if you’re sweating. That’s because the fan evaporates your sweat, and that evaporation is accompanied by a small cooling effect – it’s called “evaporative cooling”. Conversely, if the surrounding air is very humid, then no matter how powerful your fan is, you will feel little or no cooling because sweat can only evaporate if the air has capacity to hold additional moisture (I’ll explain that a bit more later).  This same evaporative cooling effect can even be used to freeze water – albeit in very small amounts (and if you’re lucky) – when you force diethyl ether (the stuff they used to use as an anaesthetic) to evaporate quickly. The evaporative cooling effect of different liquids varies greatly, and ether will cool down to a very low temperature if you do it properly. However, ether is both highly flammable and toxic, so apart from demonstrating it in the school lab (where I remember it from, along with the massive headache it gave me), it doesn’t have much practical application these days (though early refrigerators used it, which was spectacularly dangerous).

The Chillmax Air uses the evaporative cooling effect of water. The unit consists of a reservoir at the top, which you fill with normal tap water, and this drips down on to a radiator unit which has ten sideways-stacked fibre panels in it through which a fan blows air. The water evaporates from the fibre panels, and the evaporatively cooled air comes out through the front grille. According to the marketing spiel on the TV ad, you’d be forgiven for thinking you’re going to get frostbite if you sit too close. I knew this wasn’t going to happen – but I wanted to know just how effective the Chillmax Air was.

When I set it up and turned it on, the first thing I noticed was that the fan is quite powerful, so you get a good flow of air directed at you – but note that that it’s only about 5″ in diameter, so it can’t beat a proper desk fan for air flow. The next thing I noticed was that the air did seem a little cooler compared with what my desk fan was blowing at me. It also felt different in another way, which I’ll also come to later. But the big question was how much cooler was the exhaust air?

I fired up my trusty data logger and left it in front of my desk fan for 30 minutes for the control data. Then I moved it and suspended it in front of the Chillmax for the same period of time. This is what it recorded (red line is the switch over point).Chillmax Air - temperature recording

The ambient temperature where I ran the test was about 26ºC (it rose by about half a degree because I had entered the room, turned on the TV and my PC, and so on). The Chillmax brought this down by about 2.5ºC (the blip at the end is where it had just run out of water and was starting to warm up again, and I estimate that it might have dropped another degree at most).

So, the Chillmax definitely cools the air that passes through it, albeit by a small amount. Let’s work on the assumption that it would be able to get the same 2.5-3.5ºC drop no matter what the ambient temperature was. It’s for you to decide if that’s worth the investment, but be aware that if the ambient temperature is 38ºC, pulling it down to 35ºC still means it’s damned hot.

But there’s a little more to it than that. I mentioned that the exhaust from the Chillmax felt different to what my fan was throwing at me, and not just cooler. If I was going to try and put a word to it, I’d say it felt softer. I already knew what it was, but my data logger shows it in numbers.

This is the data for relative humidity recorded at the same time as the temperature measurement, above (red line is the switch over).Chillmax Air - relative humidity recording

As I’ve already explained, the Chillmax works by evaporating water on fibrous panels by forcing air across them. So where does the water go once it has evaporated? Quite simply, it comes out as a vapour in the cooled air. Well, most of it does. Some of it actually condensed on to my data logger and began to drip during my test. I have since discovered that it also condenses on the front grille and can drip periodically, so you need to be careful if you put it on a shelf with, say, your laptop underneath. This is especially true if you’ve set the grille (which is adjustable) to aim slightly downwards, which you probably would do if it was above eye level. And the fan is quite powerful enough to project the drips forward when they drop.

The ambient humidity in the room where I did the test was about 43%RH. The Chillmax sent that up to nearly 58%RH. The drop at the end is where the water ran out, and it is likely that it would have settled around 60%RH. And that was why the air coming out of it feels softer – it’s more humid than the air being sucked in. When you turn the Chillmax on, you can actually see the vapour in the right light – it’s basically fog.

It’s this raised humidity of the cooled air which really brings into question whether the Chillmax is worth the investment. Most people will know that you can have a hot summer day in the high 20s where it is comfortable and pleasant, and another – perhaps slightly cooler – one which is really sticky and sweaty. That’s because of the humidity, or water vapour in the air.

The amount of water vapour that air can hold varies with the temperature. At very low temperatures, air might only be able to hold a few milligrammes of water per kg, but at higher temperatures this can go up to nearly 100g per kg of air. People generally refer to this as “the humidity”, but the important measurement – and the one people are probably referring to without realising it – is the relative humidity (RH). This is the amount of water in the air expressed as a percentage of the maximum amount it could hold. When the RH hits 100% (more or less the dew point, though there’s a bit more to it than that) at any temperature, then any additional water will condense out immediately. It’s why your car windscreen fogs up in winter as soon as you get inside, because the air is already close to 100%RH and your breath and perspiration immediately causes the dew point to be exceeded. But even below the dew point, you can still get some condensation if there are nuclei which promote it (such as data loggers and the grille on the front of the Chillmax). But the most important detail in all this is that at higher temperatures, high RH is uncomfortable.

The real issue with evaporative cooling comes with changes of temperature when it is already humid. If it is 30ºC outside and 90%RH, dropping the temperature by 3ºC will send the RH up automatically – possibly hitting the dew point there and then. But if you are adding another 500g of water (which is how much the Chillmax holds when you fill it up), and as my data logger showed, you’re pushing the RH up by at least another 10%. On a hot and sticky day, and with the air unable to hold any more moisture, you’re likely to notice dampness when using the Chillmax (I noticed it even in this test). And as I have already mentioned, when the RH is high evaporative cooling from your sweat is less effective, so you would actually feel more uncomfortable even though the air is a few degrees cooler.

Proper air conditioners remove water from the air they cool – so much so that the best ones have humidifiers in them to stop the cooled air from being too dry. In my car, for example, if I have the A/C on the lowest temperature setting my lips start to feel sore because they’re losing moisture, and other people say that it dries their hair out. Proper A/C units use a special refrigerant the same as you get in fridges and freezers, and they cool the inlet air so much that the RH goes beyond the dew point and most of the water condenses out – that’s why you get a pool of water under your car if you stop with the air conditioning turned on in humid weather (or have problems with them icing up if they’re badly drained). It’s also why it is nice and comfy inside an air-conditioned car (apart from your lips) when it’s hot and sweaty outside, even if you have your A/C set at a normal temperature rather than deep-freeze mode most people use. Dry air feels crisp, whereas moist air feels… well, softer. Almost like a sauna if it’s hot enough. The Chillmax does the opposite of normal A/Cs, and adds moisture.

Aesthetically speaking, the Chillmax is a cube – more or less – about 15cm along each side. There are two buttons on the top rear, one which changes the fan speed to one of three settings (or off), with a blue LED for each, and another button that turns the night light on or off. There’s a flap on the top front through which you add the water. The radiator system is a plastic-framed insert which you access by pulling the front grille out. It slots in and out easily. You can’t replace the fibre inserts in the radiator (well, I think you could if you could get hold of them), but you can buy the whole radiator assembly from JML for £15. My only major gripe is the power cable. The jack plug that goes into the Chillmax is quite stubby and doesn’t go into the socket very far, so it is easy to dislodge it. However, the cable itself is quite long, and the  mains plug is a moulded UK type.

JML claims the Chillmax can run for up to 10 hours per fill, but this is undoubtedly on the lowest of the three fan speeds. At top speed, it runs out in less than three hours. To be fair to it, you do still get a noticeable cooling effect on the lowest speed, and since the water lasts longer then, less of it will be getting pumped into the air at any one time, and that might offset what I said about humidity very slightly – but it’s still being pumped out.  JML sells the humidification as a positive without relating it to the comfort relationship between temperature and RH, but note what I said above. If you want to cool down in humid weather, it probably isn’t just the temperature that needs to come down, certainly not a mere 3ºC drop, and definitely not if that means pushing high humidity even higher.

Update #1: I have now tested it in what I considered to be hot and sticky conditions – the kind of weather that means you’re sweating even when sitting still.

Here’s the temperature log (red line again shows the switch over between desk fan and Chillmax.Chillmax - temperature log in hot and sticky conditions

The Chillmax still achieved a similar temperature drop to the initial test. However, the air did not actually feel any cooler blowing on my face. If anything, it was more uncomfortable, though this is a subjective comment. The graph for Relative Humidity below explains why.

Chillmax - RH log in hot and sticky conditionsThe ambient RH was similar to last time, but the Chillmax sent it up to about 70% (a larger jump than in the first test). This is why there was no noticeable improvement in comfort – the small temperature drop was cancelled out by making the air much more humid (i.e. sticky).

You might find the Chillmax useful. It’s quite a smart little device – it’s not a Rolls Royce build, but it’s not badly made for what it is – and not that noisy (but you can hear the fan on the top speed). It certainly cools the air. A little, at any rate. Unfortunately, the increase in humidity that goes along with that cooling definitely seems to cancel it out out at higher temperatures.

Update #2: I tried it in the latest heatwave (33ºC outside on 23 July) and you can’t feel any cooling effect at all.

Update #3: Right! That’s it! That “latest heatwave” maxed at 38°C indoors on 25 July, and even now – 1am on 26 July – it’s 36°C at 50%RH and I feel The Devil biting my ass. The last thing I want is to send the RH up to 90% using the Chillmax to get the temperature down to only 33°C. God knows how I’m going to sleep tonight. So I have a proper air conditioner arriving tomorrow – watch out for a review of that.

Does it really work?

Well, it does cool the air by a few degrees, but it also sends the humidity up. So if it is already humid and sticky, the cooling effect is completely cancelled out by the extra stickiness. You might get away with that if your windows are open and there’s a through-draught in your house (or personal space), but if it’s also very hot you may not see any benefit at all.

It definitely doesn’t do what you might think it does from those TV ads. It would be fine if it just cooled, but the fact that it also humidifies is the main problem you’re likely to experience.

From my own use of it, I would say that it is a better humidifier than it is a cooler – especially when it is very hot, which is the last thing you want.

Will it cool more if I use ice water?

No. Evaporative coolers are not influenced significantly by the temperature of the water used in them. The temperature of the air that comes out depends on the temperature (and humidity) of the air going in, and the science of evaporation.

Can I use it to cool my PC?

Someone found this article on the search term “jml chillmax air for pc cooling”. If they mean what I think they mean, no, there is absolutely no way you want to be blowing damp air into your PC.

They might have meant powering it from a PC. The mains adapter is rated 5.0V at 1.8A, so assuming the Chillmax does draw 1.8A (and it probably doesn’t, as this is the maximum rating of the adapter) then your PC couldn’t supply that current from a USB port. USB ports are rated at 0.5A or 0.9A depending on the type. Dedicated charging USB ports can handle up to 1.5A, and although that’s a close call (the fan in the Chillmax looks like a computer fan), personally I wouldn’t risk trying to power it from a PC.

Can you get larger versions?

You can certainly get larger evaporative coolers. The working principle is that the larger the surface area of water, and the greater the airflow over that water, then the greater will be the possible drop in temperature at the front end. However, cooling effectiveness is influenced greatly by the RH of the air going in.

If the air is very dry, then a large evaporative cooler might be able to drop inlet air at 30ºC down by as much as 10ºC. However, if the inlet air is very humid, the temperature drop could be as little as 1ºC. In the UK, the realistic temperature drop you could expect on a non-humid day for a large cooler would be around 5-6ºC, but on a sticky day you’d only get about a 3ºC drop.

Suppliers of these devices say that they need good ventilation or extraction, and I would imagine that’s so the humid air can escape. If you’re evaporating more water to get better cooling on larger devices, you’re also producing a lot more water vapour.

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