Category Archives: dehumidifier

dehumidifier 3: hot-plate hiccough

Yesterday, I was hoping to continue work on my dehumidifier project; using a desiccant wheel to adsorb water onto silica gel balls on one side of a machine, and hot air to evaporate water from the balls (regenerate them) on the other side.

The hot-plate arrived for the machine. I tested it, using an old 12V adaptor for power supply. It works well – heats up very quickly. I don’t know what its limits are, but I feel that 105°C is well within its capabilities.

But instead of then working on the machine itself, I spent a few hours making space on my son’s laptop and then installing the Unity development platform. I’ve been trying to get him away from Scratch and onto something more practical, because Scratch is nice, but it’s a dead end.

You won’t find people designing grown-up programs in Scratch, because it simply doesn’t have the capabilities. Database access, complex graphics, file manipulation.

But Unity does, because it binds naturally to some languages that you can then use elsewhere. In this case, C#. But, beggars can’t be choosers!

I bought him a book on how to start coding in C# by creating a game in Unity. With the book, you build a side-scroller game. I really hope he likes it. More than that, I hope the book is not obsolete already!

On the desiccant wheel project, I realised there is a really bad problem – in order to regenerate, the silica gel balls must be baked at more than 100°C in order to let the water evaporate.

PLA (the plastic I print in at the moment) melts at 180°C, but its glass-transition temperate (its Tg) is between 65°C and 70°C. That means that if I have a section of my machine which is around 105°C, then the plastic there may warp.

While this is a real problem, I don’t think it’s insurmountable. The first thing I will do is to just try it as if it will all just work out fine. You never know! And if it turns out there is a problem, I will come up with a solution. That’s what I do.

The biggest warping problem will be the grill on the inner-facing part of the desiccant wheel (green in the image), which keeps the silica gel ball bags from falling out. If that warps, then it will quickly jam the wheel from turning. A redesign of the wheel is major. It would involve changing how the wheel is turned, and probably changing the orientation of the entire machine.

The way I have it at the moment, the wheel rotates on-edge, with two big circles with small air-holes in them, to allow air into the silica gel balls contained inside. If I was to change the orientation so the wheel is held flat with the green grill facing upwards, then the grill would not be needed at all, and the hot air could be blown directly onto the bags themselves.

This is a major change to the design, though, because I would then need to change how to wheel is balanced (currently two ball-bearings on the edge) and how the wheel is rotated in the first place (currently a gearbox held against the grill).

A possible solution is to move the gearbox underneath the flat wheel. Hmm… Yeah, I think that’s actually a good solution. I have a plan now.

dehumidifier 2: Rolling the drum

I tried setting this up so that the drum could be rolled from an elastic band or cog against the edge of the drum, but it turned out there was a simpler way – the little air-holes in the drum are an equal distance apart, so I designed and printed a gearbox that could turn the drum using those holes.

It sacrifices a little bit of surface area for the cold side of the drum, but I don’t think it will make a huge difference.

I made a few 1mm errors in the gear box prototypes, but when I corrected them, it worked as soon as I applied power to the motor. The motor I’m using in this case is one of the standard yellow geared motors (like this).

I’m still waiting for the heating element to arrive, but have a few fans I can use to get started on the airflow. I don’t even know what size the heating element I ordered is, so can’t design that side yet, but I can design the cold side while I wait. I’ll get started on that tonight.

The 3D printer I’m using is an Anet A8, and I have to say that it’s a dream to work with compared to my old Makibox 3D printer. I was amazed when I printed out the drum and enclosure for this project and they fit perfectly. With the Makibox, the circles would have been flattened and I’d have to sand away any bits that rub, but this one is just perfect.

Even the gearbox would have been impossible to print on the Makibox. The Anet A8 is so good that when some of my students were asking me for a bill of materials to make a 3D printer, I told them that even though it would be possible to spend €120 or so and make a 3D printer from scratch, they’re better off spending $150 and buying one of these ones instead.

dehumidifier 1: Dehumidifier project

I recently finished building the frame of a shed, and covered it with temporary cladding (MDF and plastic) to protect it during the winter until I have more time and money next year to continue with it.

There is a small lake starting to grow in the shed. I don’t think it’s coming up from underneath the soil, and the door end of the shed is covered in plastic to stop rain coming in, so I think the lake is forming from condensation. The air in the shed is basically dumping water on the inner walls of the shed and that water is then rolling down and converging in a large pool.

Because the shed was being built to house a lab, I had planned on building a dehumidifier at some point anyway (I like to build things, even if it might be easy to buy them), but this is encouraging me to get on with it now and build it early.

So over the last week, I bought a half-kilogram (500g) of desiccant crystals, which just arrived, and I’ve started designing the machine.

I’m using the idea of a “desiccant wheel” – a constantly turning wheel where most of it is adsorbing water, and the final part is being dried of its water and regenerated, with the water being blown out as damp air, and either collected in a jar, or dumped outside (what I’ll be doing).

I designed a small wheel last night and started it printing. It’s 60mm in radius (12cm diameter), so really small for this purpose, but as this is my first time making a dehumidifier, I want to make something small and test it, before making a bigger one.

You can see from the image that the wheel is segmented into six parts. The idea is that the wheel will revolve about once an hour, with each segment getting about ten minutes of that hour with hot air being blown through it while cold air is blowing through the rest.

Heat encourages desiccant crystals to dry, with the collected water evaporating and making the hot air damp. That hot air will be blown into a tube that leads outside the shed. Eventually, I may use the water for an indoor gardening setup, but for now, I’ll just get rid of it.

The 5 remaining segments will have cold air blowing through them, with the dampness in that air being adsorbed onto the surface of the crystals, getting those crystals ready for their next ten minute session in the hot air drying part.

I’m waiting now for the heating element to arrive so I can design the fan section and the electronics to keep the temperature constant.

When the hardware is finished, I’ll then need to start testing it with different temperatures, different fan speeds, different wheel speeds, to see how to get the most moisture out as quickly as possible.

I’ll put my design up on Thingiverse as soon as I’m finished and have a working system, and may even start selling prints if this works out.

I’m thinking that I may have two versions – one which is tuned so you just turn it on and it gets to work, and another which is smart enough to measure relative humidity and work towards a specified value.