A Driving Instructor's Blog


The Chillmax AirI wrote this in the very hot summer of 2019, but each year around spring time adverts start appearing involving these ‘revolutionary no-install air conditioners’.

Be aware that these devices do not work to anything like the levels claimed. The original article follows.

Early in July 2019, I saw the Chillmax Air advertised on TV in one of those shouty ads. 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 that in order to cool a large space effectively you’re going to need something with a big fan and a special refrigerant. In practical terms, that means a fairly bulky device with a motor-driven compressor, a closed radiator for the refrigerant to pass through, a 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’. In some cases, you also need to collect or drain the condensed water that comes out of the air as it cools. A typical proper air conditioner for a small or medium-sized room will be about the size of bedside cabinet. The Chillmax Air is not much bigger than six CD cases glued into a cube.

If you’ve used a normal desk fan you will know that you only feel cooler if you’re sweating a bit. That’s because the fan evaporates your sweat as it pushes air over it, and that evaporation is accompanied by a small cooling effect – it’s called ‘evaporative cooling’. If you’re not sweating, you don’t feel the effect. 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, because it’s what determines whether the Chillmax is any good).

As an aside, many liquids exhibit the evaporative cooling effect. In the case of diethyl ether (the stuff they used to use as an anaesthetic), if you force it to evaporate very quickly you can even freeze water (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, partly due to the massive headache the fumes gave me), it doesn’t have much practical application these days. Early refrigerators used it, which was spectacularly dangerous.

The Chillmax Air uses the evaporative cooling effect of water, and this is much less than with ether – similar to sweat, in fact. 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 ads, 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 was.

When I first 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 a 5″ computer fan, so it can’t beat a proper desk fan for air flow. The air did seem a little cooler compared with what my desk fan was blowing at me, but it also felt ‘softer’ – that’s very important, and I’ll explain 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 (the red line is where I moved it).

Chillmax - temperature log in hot and sticky conditionsThe ambient temperature where I ran the test was about 29ºC. The Chillmax brought this down by about 4ºC.

So, the Chillmax definitely cools the air that passes through it. Let’s work on the assumption that it would be able to get the same 4ºC drop no matter what the ambient temperature was. If your room is 38ºC, pulling it down to 34ºC still means it’s bloody hot. And also note that since the Chillmax is physically so small, the cooling is very localised – it won’t cool a room down, and you have to have it less than a metre from your face to feel anything.

Now, some people might be thinking that a 4ºC is better than nothing at all. And they’d be right if it was just a matter of temperature. But there’s more to it than that. I mentioned that the exhaust from the Chillmax felt ‘softer’. I knew what it was, but my data logger shows it in numbers.

These are is the data for relative humidity recorded at the same time as the temperature measurement, above (the red line is where I moved the logger). The humidity went up dramatically – a jump of about 30%RH.

Chillmax - RH log in hot and sticky conditionsAs I’ve already explained, the Chillmax works by evaporating water on fibrous panels by forcing air across them. That water has got to go somewhere, and in this case it comes out as vapour in the cooled air. In the right light, you can actually see it – it’s essentially fog. And just like when it’s foggy outside, and everywhere gets damp, this vapour can condense on surfaces. My data logger collected some and began to drip during the test, and I have since discovered that it also condenses on the front grille and can drip periodically, so you’d need to be careful what you had underneath it if you placed it on a shelf. The fan is quite powerful enough to project the drips forward slightly when they drop.

The ambient humidity in the room where I did the test was about 44%RH. The Chillmax sent that up to over 70%RH.

It’s this elevation of the humidity of the cooled air which really brings into question whether the Chillmax is worth the investment. You’re probably aware that you can have a hot summer day in the high 20s where it is pleasant and comfortable, but a cooler and overcast day might be horribly sticky – or muggy. 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. Once you reach the maximum, any extra vapour condenses out as a liquid – misted up windows, dampness, even drips and pools of moisture on window sills or under lamp posts. Cold air can only hold a small amount of moisture before condensation occurs, but hot air can carry much more (think ‘sauna’). Although ‘humidity’ technically refers to the amount of water in the air, the figure most people are referring to when they say it is relative humidity. This is the amount of moisture in the air expressed as a percentage of the maximum amount it could hold at that temperature, hence the units %RH. It’s a very complicated subject, but the important factor for us here is that when it is warm or hot, higher relative humidity is uncomfortable. Indeed, you may have seen weather forecasts where they give the actual temperature and the ‘feels like’ equivalent – that’s a reference to the ‘Heat Index’, which takes into account the effect of the %RH. Here’s a graphical chart for that.

Heat Index - graphical representationAs an example, if the air temperature is 30ºC and 50%RH, it will feel like 31ºC, but if the humidity goes up to 80%RH, then it will feel like 38ºC – even though the thermometer still tells you it’s 30ºC.

Another example. If the air temperature is 35ºC, at 50%RH it will feel like 41ºC, but send the humidity up to 80%RH and it’ll feel like 57ºC – even though the thermometer still reads 35ºC.

The calculation for this is complex (you should see how long my Excel formula for it is). It is non-linear, and the increase in ‘feels like’ is greater at higher temperatures. It also contains an element of opinion/perception, which is why there’s no point using numbers above about 60ºC. But the ‘Heat Index’ is what forecasters use. Incidentally, the official health designations for the colours are: yellow – caution; amber – extreme caution; orange – danger; and red – extreme danger. Vulnerable people need to take these into consideration before going out in hot weather.

However, this is where the problems come in for the Chillmax and similar devices. If it’s 35ºC and 40%RH, it’ll feel like 37ºC. Cool the air to 31ºC but send the humidity up to 80%RH, and it’ll feel like 41ºC. So it’s actually hotter in terms of comfort. Do the same comparison when the surrounding temperature is 38ºC, and the ‘feels like’ goes from 43ºC to over 50ºC!

At lower temperatures the Chillmax will produce a slight net cooling effect. But if the air temperature is above about 30ºC (and 50%RH) – which isn’t excessively hot or humid to start with – it’ll actually make you feel warmer. And if it is already humid outside, you’ll feel hotter still.

Proper air conditioners remove water from the air they cool. This removal of moisture is why the air from proper air conditioners feels crisp, as opposed to the ‘softness’ of moist air. 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 officially replace the fibre inserts in the radiator, 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 likely on the lowest of the three fan speeds, since on top speed it runs out in less than three hours.  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 isn’t just the temperature that needs to come down.

Does it really work?

It does cool the air by a few degrees, so in that sense it works. However, it also sends the humidity up, and in most cases that actually makes you feel hotter and more uncomfortable. In that sense, it doesn’t work.

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. Only this evaporation results in the cooling effect observed.

Will it cool more if I put the filter in the freezer?

It might – while you’re blowing air over ice. But once they defrost, which will happen in a few minutes in the temperatures you’ll likely be experiencing, then no. You’ll also have more condensate to deal with from the melted ice pouring out of the front grille.

You may see reviews on Amazon claiming that freezing the filters (or using ice cubes in the water tank) does give cooler air. Trust me – apart from what I just said about blowing air over ice, it doesn’t. Science is involved, and evaporative cooling doesn’t work like that.

Can I use it to cool my PC?

Someone found this article on the search term “jml chillmax air for pc cooling”. No. Blowing damp air into your PC would be dangerous, potentially expensive, and would only gain you 4ºC at best.

Can you get larger versions?

You can certainly get larger evaporative coolers, though not the Chillmax specifically. 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. Be careful if you read any of the reviews – people may have noticed cooling in already cooler conditions, but trust me – if it’s very warm and humid, you will not notice any effect.

People say it works

Be careful when you read those one-line reviews. If you test it when it’s only 20ºC outside – as many of these people have – then yes, it blows noticeably cooler air at you. But science is involved, and at temperatures above about 28-30ºC you’ll actually feel hotter. The fact that it increases humidity is the key factor. Remember that the reason you even found this article was probably because it’s over 30ºC outside – the more above that it is, then the more hits I get.

So, does the Chillmax work?

It cools the inlet air by several degrees. But it sends the humidity of that air up considerably, and this cancels out the benefits of the cooling effect when it is very hot. The ‘Heat Index’ is the key detail, as explained above.

Only the air being directed at you is cooler. Once that slightly cooler air has passed through warmer air, it’ll be close to ambient again. The device cannot cool down a room. It’s far too small for that.

Humidity can carry much further, though. So in a small room, you could easily increase the ‘ambient’ RH without any cooling at all, and that will make it feel even hotter. If it is already hot, the amount of water vapour the air can hold before reaching 100% RH will be substantial. The increased humidity of the outlet air does produce localised condensation, so you have to be careful to keep it away from electrical sockets where it might drip on them. The unit also contains a significant volume of water when full, so you don’t want to knock it over.


DoogleBooks LCD drawing and writing padEver since I became an instructor I’ve managed to get through a lot of notebooks. Anyone who does this job will know that you have to sketch a lot of things when you’re explaining stuff to pupils.

I started off buying notepads, but realised that was quite expensive – especially if you wanted the larger sizes. Then I turned to making my own, by ring-binding punched copier paper and using that. I discovered that normal two- or four-hole punching was no good, because the sheets could easily get torn with all the handling and jolting they get in the car, so I turned to spiral binding. That served me well for many years – but I was starting to feel my conscience nagging me over the amount of paper I was getting through.

A few years ago now, I tried using my laptop. It’s a Surface Book Pro with a detachable screen so it can be used as a tablet. With a simple sketching app, it was fine – but there was still the hassle of getting it out, booting up, then detaching the screen, then reattaching it and powering down when I’d finished. There’s no way I wanted my Surface loose in the car while it was moving and quite frankly – in some of the places you have to cover – waving a two and a half grand laptop around is not the smartest thing you can do.

Then I had one of my thoughts. It occurred to me that there must be something out there that could just be used as a drawing board, but which didn’t involve dirty rags covered in black marker from the dry-wipe boards some people use. That was when I came across LCD drawing pads. At the time I first tried them, they were usually 6 inch or 9 inch screens. I found a 10 inch one and it worked great. I still have it, in fact. But a couple of years ago, while still looking for something better, I came across DoogleBooks.

The main attraction at the time was its size – it’s a 12 inch screen, so about the size of a piece of A4 paper. It also boasted an erase function (you can erase parts of your diagram with an eraser on the stylus) and a bright screen – my original cheap import was quite faint, though still perfectly usable. It comes with a padded protective case and a separate eraser, a lanyard for the stylus, and some spare tips, and a few bits and pieces for kids rather than adults (and which I never did figure out what they were for).

It is powered by – believe it or not – a standard watch battery, which lasts ages (I’m still on the original after nearly two years). That’s because the device is not illuminated in any way, so doesn’t draw much power.

You ‘turn it on’ with a very small switch on the back, though this is a ‘lock’ function rather than a power button as far as I can tell. The stylus clips neatly into the frame (come to think of it, it was because the clip on the cheap one I bought snapped which got me looking again) and has a nice long lanyard so you don’t lose it.

Once powered/unlocked you just write or draw whatever you want. The width of the stroke is governed by pressure and angle of the stylus nib, so you can get thin lines or thicker ones as needed. If you want to start again, you just press the button on the left in the picture above with the trash can symbol twice, and the screen is cleared. The double-press is a safety feature so you don’t erase by mistake – see the next bit for why.

If you make a minor mistake, you can erase just part of whatever you’ve drawn or written. Press the other button until the red LED comes on, then use either the small rubber eraser on the other end of the stylus, or the larger rectangular one which is supplied – just like you would with pencil on paper. Once you’ve erased whatever you want, press that button again until the LED goes out and you’re back in drawing mode. Due to the proximity of the buttons, you can see why complete erase needs two presses. This selective erase does work, but be aware it does leave slight smudges behind – again, like you’d get with a pencil on paper.

It is not a computer. Anything you write or draw exists only on the screen for as long as it’s there. You cannot transfer it to a computer, since it is not a digital image – it is exactly the same as a pen or pencil drawing. If you write ‘CAT’, that’s just some shapes and lines – the tablet doesn’t know what you’ve written. If you erase something by mistake, it’s gone forever – there’s no undo feature. If you want to save anything, you can take a picture – pupils often take a shot of things I draw so they can look at them later, just like they used to when I drew on paper.

The device I used previously had a much fainter screen, and this meant that on evening lessons it could be difficult to see what you’d drawn. As I explained earlier, there are no backlights on these things, and they are literally the same as pen and paper – you can’t see drawings made using those in the dark, either. However, DoogleBooks has a much brighter screen contrast and you can see your drawings clearly with the interior light on. The photo above was taken at dusk with no lighting, and that’s the contrast you get.

It’s been one of the best things I’ve bought in a long while. I actually have a spare in reserve, which came about because the original Amazon order never arrived, and the owner of the British company which sells them sent out a replacement. Several weeks later, the other one arrived – God knows where it had been – and when I offered to return it the owner said to keep it as a gesture of goodwill!

They now do several different models, mainly aimed at kids, with different screen colours. And whereas the only frame colour available when I bought mine was cyan (which is actually my least favourite colour in the whole world), they now do them in a range of colours. Just be careful to choose the ‘’partial erasure’ one unless you want to save a couple of quid and lose a bit of functionality.

It’s infinitely better than using a dry wipe board. There’s no mess, and it is ready to use the instant you take it out of its case. Unlike dry wipe systems, when you erase, you erase – no ink getting stuck in scratches, which always happens with dry wipe markers. And the stylus lasts oodles longer than a marker pen. And there’s no thick pads of drawings to dispose of when you’ve filled up a notepad.


AUSDOM AW615Until I saw this article on the BBC, I had no idea there was a webcam shortage. But apparently, the lockdown has meant these, too, have been panic-bought into oblivion, and they are difficult to get hold of.

During the lockdown, I’ve been having a nightly Skype session with my mate who lives in Leeds. Initially, we were just doing voice, but he upgraded his laptop and we were then able to do video calls. However, although my Surface Pro laptop has a camera, I prefer to use my desktop.

Over the years I’ve had several webcams, but since I didn’t typically use them much they inevitably ended up being put in a box somewhere and forgotten about. They were always oddly-shaped things, too. All curves and funny angles – and far, far bigger than they needed to be. This time around, I started looking for a simply bullet-style camera that could sit on the top edge of one of my monitors without it wanting to break into a song and dance routine and flash pretty lights at me for no apparent reason if I was on Facebook or something. I also wanted HD.

One of my preferred brands is Logitech. However, their HD cameras have all the usual angles and curves, with the added ‘benefit’ of being the size of an iPhone thanks to whatever fancy additional features Logitech is trying to sell to nutjobs who post on Instagram and Tik Tok every five minutes. I just wanted a camera – I have a separate microphone, anyway.

After more searching I came across a camera that looked like exactly what I was after on Amazon. The AUSDOM AW615.

It’s full HD, does 16:9 widescreen, and it does have a microphone (it’s also manual focus and wide-angle). For me, the most important detail was it’s shape and size – the camera itself is a short cylinder, and it has a bendy clip and bracket so you can put it in different positions on different monitors or surfaces. At that time, the price was around £70 (at the time of writing it is on offer at £50), but what I did then was take a look on AliExpress. It was obviously (to me, anyway) a Chinese device, and it was carried by many sellers on AliExpress. if I bought direct it turned out the price was $33 (about £25). So that’s where I bought it from. Incidentally, if you check out any of the models above, they’re cheaper if you buy directly from China – but it’s up to you.

It took about three weeks to arrive, but lead times are always a little longer from China anyway.

It doesn’t need any software – you just plug it in and Windows does what it needs to do to recognise it. As with any webcam, you really need to connect it directly to a USB 2.0 port on your computer, and not through any daisy-chain of hubs. If you do that, you’re likely to get problems, especially with a HD image at 30fps, which is this camera’s spec.

It works like a charm. Nice sharp picture, and you can do all the things with it that Skype lets you – blur background, add image, and so on. My boom microphone is better for sound, but the microphone on it works perfectly well. Definitely worth considering if you’re after a webcam.


ReadlyA couple of years ago I was having a clear out and I was amazed at the number of magazines I’d collected over the years. They were mainly my Classic Rock mags, and part of my decision to have a clear out was that I’d been getting more and more disillusioned with that particular publication.

At the time, I was on an annual subscription, but Planet Rock had just launched its own magazine and that did exactly what it said on the tin – it covered rock music. Classic Rock acquired a new editor, and she made it clear in her introductory piece what she was planning. Subsequently, any rock music they covered had to include at least half female acts – meaning it became obscure and far from ‘classic’, at best – and they also decided that (as just one example) Depeche Mode somehow ticked both the ‘classic’ and ‘rock’ boxes at the same time (actually, they decided twice in the space of just a couple of months with that one example). Then they did their ‘best 100 female artists of all time’ issue, and necessarily had to include non-rock genres to fill it out. That was it from me, and I cancelled my sub.

Before any feminists start frothing at the mouth over this, I go to see lots of female artists and bands with female members. I actually seek them out if I hear them on Planet Rock and like the sound. Like Samantha Fish, Haim, Paramore, Evanescence, Courtney Love, Joanne Shaw Taylor, The Lounge Kittens… I just don’t need any feminist magazine editors trying to filter out the men for me. And if you don’t like the fact that I don’t like that fact, click the back button and go somewhere else.

Planet Rock mag suits me fine, but when the lockdown came along, it also came with a lot of extra time for reading and finding tips on how to do stuff I wouldn’t have otherwise had time for. And going out to buy magazines wasn’t an option – even if it would have been of benefit with the ‘current’ issue on sale (you usually need a series of them).

A few years ago, as a result of my quest to find some authentic German food recipes, I came across a subscription service called Readly. It carries – and this is no exaggeration – thousands of UK titles. They’re all the ones you see on the newsstands (and many you don’t), from TV Times, OK!, Hello!, through all the photography and amateur DIY magazines, through to music and musicians (including Classic Rock). They cover specialist computer and technology subjects, gaming, weddings, cycling, fishing, horse riding, pets… everything (but no X-rated adult stuff). Including back issues, too, which multiplies the content by at least ten. And as I already implied, they have similar numbers of publications from Europe, Asia, and America. They’ve also recently started including newspapers, though it’s only The Independent and Evening Standard right now.

My normal Readly subscription is less than £8 a month, but they offer a two months for free trial. Even so, at £8 a month, that’s the newsstand cost of just three magazines! If you were after foreign magazines, you’d probably pay more than that for a single issue once shipping was included.

You can get the Readly app with the offer through Amazon (it’s free), and you can read on your phone, tablet, or computer. You can also read offline by downloading the content.

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