One of the key issues in a campervan is removing water. Water being in lots of places that it shouldn’t be. No matter how well you insulate your van, there will be always be condensation surfaces. The vans themselves will always have little corners here and there that are poorly ventilated (mould hates ventilation). Many things in a van add water.. c.900ml/day water is perspired/exhaled on average per person. So at peak occupancy over 8 hours, 2 people and one smallish collie will be adding well over a pint of water to a pretty small box. Add to that wet clothes, washing up, cooking (for which ventilation is pretty important…)..
In general, the answer to this is more ventilation and massively overpowered heaters to compensate for the heat loss. This offends my sense of efficiency.
Enter, the heat exchanger!! Theoretically, an air heat exchanger should perform a dual function in this use case. Remove water filled warm air from van, use it to heat incoming fresh drier air, save energy and fight mould. All this thing.
I found a chap had been working on a similar idea for a home made exchanger for a chilly flat. Someone else has done a lot of the work?? Get in.
Whilst his design seems a good start for my needs, there are definitely some things that I want to add. As this is going in the van, I need some wifi capability if I want to log the data nicely, so I’m using a Wemos Mini Pro as the base board for the project. This is a fantastic wee ESP8266 board that does wifi, talks arduino, and is basically made of pixie dust and wizardry.
Firstly, I’ll have to make adapters for the air inputs, because I printed the parts before realising I have 100mm air intakes with 54mm on the exchanger. no big deal, but won’t be as lovely.
Secondly, I want to track humidity as well as temperature. For this purpose I purchased some DHT11 sensors.. and then promptly discovered that they are a bit rubbish, only do 1 degree granularity and apparently break in about two years of use max (I broke one already). I’ve ordered some BME280 sensors to swap in.
Third, I want to drive the fans automatically based on the sensor readings, and for this I’m using TIP120 Darlington Transistors to drive the 12v fans from the 3.3/5v board..
Fourth, I want some feedback. A related requirement is that I want some dimmer lighting for chilling with – the lighting I have currently is very efficient and bright and not terribly relaxing. So, I’m adding a small string of RGB LEDs to the board.
Pop on a couple of switches and we’re getting pretty maxed out on the IO. No matter, I think we’re done!
Lastly.. it’s not quite MaD sCiEnCe looking enough, is it? I think we can do better. I think we can.
Assembling the main body of the heat exchanger was .. a little frustrating. After a few incidents – the last of which resulted in me staring into space and counting to a billion – I worked out a moderately efficient method using a bit of pole (and glueing the pox ridden ends on the tube. Most of a hackspace evening went on this, up to a gritted teeth finish at midnight when everyone was packing up around me..
Almost ready to install, v1 code pretty much done, I’ll update this post once it’s in the van..