Accurate hygrometer / humidity meter for the workshop

For those feeling more adventurous I designed an Arduino based Dewpoint Monitor for the workshop that displays the various parameters and if the dewpoint comes within a defined limit, it enables a power outlet to turn on heaters. The trigger point is defined in the Arduino code. More efficient than just leaving a heater on.

I ran some 'proper' PCBs for our club members and have 5 or so left for first takers via PM or via my blog. If there is more demand than I might consider running some more boards. There is a download PDF write up on my blog via the link below

Dewpoint monitor

Alan, I can see how it does make much better sense to focus on dewpoint than humidity, and in my case if I achieve 10deg C min temperature in my workshop with oil filled radiator , then if on the odd occasion that the Dew Point rises above the workshop/machinery temp a dehumidifier can be triggered to only run then, I can see how my electricity bill could be kept to a minimum. How accurate is the PCB sensor? I have PM'd you. Adam

Hi Adam

I will follow up on the PM.

The DHT22 is the more expensive version which has better specifications. Its temperature measuring range is from -40 to +125 degrees Celsius with +-0.5 degrees accuracy, while the DHT11 temperature range is from 0 to 50 degrees Celsius with +-2 degrees accuracy. Also the DHT22 sensor has better humidity measuring range, from 0 to 100% with 2-5% accuracy, while the DHT11 humidity range is from 20 to 80% with 5% accuracy.

The DHT22 is more tolerant of a long cable length for remote monitoring.

Alan

Edited By Alan Wood 4 on 01/01/2022 15:12:41

The better specified sensor helps but positioning is important too. For example, a sensor in sunlight will read high temperature and that mucks up the humidity reading as well. The sensor can lose calibration and have to be reset, whilst long exposure to strong sunlight can permanently damage it. Also ironic that a device used to calculate the dew point, dies when it gets condensation on it!

Some sort of shield helps, plus putting the sensor in a guarded position - somewhere away from natural and artificial heat, and definitely dry!

Dave

I bought a cheap combined hygrometer/thermometer off Amazon, with 24hr and all time max/min functions. I later bought a 200W dehumidifier which has a built in hygrometer (so you can set a target humidity.

Positioned about six feet apart and at different heights, they both read consistently within 1% of each other which suggests that they are probably plenty accurate enough.

Interestingly, I found an old 'analogue' hygromneter, the kind that has a coated metal coil. I always assumed that these were pretty hit and miss, but it follows the digital ones within a few percent, always reading higher so if I adjusted it it would probably be surprisingly accurate.

On dehumidifiers, I spent a lot of time searching online and found this one which has vastly more features than other cheap ones (odour filter, hygrometer, programmable humistat, two-speed fan, supplied tube/drain port as well as built in receptacle) , and yet appears to be about the cheapest out there.

www.appliancesdirect.co.uk/p/cd10l/electriq-cd10l-dehumidifier

It can easily fills the tank overnight (useful source of 'distilled water' although I haven't timed it and now use it with a drain. It's actual energy use seems to average much less than 200 watts and it got the humidity down from over 80% to my target of around 75% in about a week.

I should say my workshop is well insulated and sealed, and although it's about 22 square metres the dehumidifier seems to work well.

Neil

Edited By Neil Wyatt on 01/01/2022 17:23:17

My dehmidifier has a setting that claims to do the job of a tumble drier at a fraction of the cost.

Neil thanks that ElectricQ looks good value. I might follow you in on that one. A friend who is somewhat of a weather tracking hobbyist with all the kit, tipped me this afternoon that very local outdoor weather info covering DewPoint can be found on wow.metoffice.gov.uk which shows on a map your nearest independent private weather stations and their readings. Falling Dewpoint readings, and narrowing of gap between Temp and Dewpoint outdoors, could be a useful alert forewarning for indoors action with dehumidifiers. Likewise, when outdoors DewPoint rises above your targeted workshop temperature (in my case 10deg C minimum) alert for immediate action. Incidentally his view is that if you want reliable hygrometers go to the expert weather equipment makers like Netatmo.

Edited By Adam Harris on 01/01/2022 18:56:22

Rising DewPoint readings...