Experience tells me that your damp, humid underfloor storage area could be damp and humid, possibly for days at a time, when we have foggy or wet weather.

Might need expert advice about this.

The temperature of the air inside and outside also matters. Warm air can have a lower relative humidity than colder air while at the same time holding more water. so any control system may (will?) need to factor the temperature difference in as well as the relative humidity.

A friend had a similar problem and during a spell of warm dry weather he ventilated his cold damp basement and found it getting wetter! this counter-intuitive effect is apparently because the warm outside air, which seems dry, can often contain more water as vapour than the same air can contain when it is ducted into a cold basement, so the surplus water condenses out.

Rod

Edited By Rod Renshaw on 09/10/2020 09:53:08

I would try a dehumidifier with a central heating condensate pump to get rid of the collected moisture. Changing the air might move some water vapour out but will also bring some water vapour in. Two steps forward one step back.

Martin C

All good stuff, especially the comments about dew point.

1/2hp seems far more than you need, work out the capacity needed from changes per hour, 3 or 4 will do, more is for cooking or puddles of groundwater etc.

I have bought one of these for fume extraction, I still need to get it installed pulling through filters so I won't over reccommend it until it proves itself. Its worth noting that the biggest is only 120W. There is a size calculator on the page to the right.

link

Head over the parapet time because I'm terrible at maths!

How long would it take a ½ HP motor to empty a 3 x 4 x 2.5 metre cellar assuming a lift of 3 metres at standard temperature and pressure?

This is my answer in SMath Studio. I tried to use Units with odd results (what's a m³s) but believe the numbers are right:

Three seconds assumes the fan is 100% efficient, runs at full speed instantly and that that the outlet isn't constricted. 15 seconds might be more reasonable in the real world.

Replacing the air in the cellar quickly is an advantage. The purpose is to remove moisture, so faster the better; a 35W fan would take ten times longer, more if the cellar is wetting the air continually.

On the other hand, 35W fans are quiet. A big fan firing up in the cellar at 4am might wake the neighbours!

Happy to be told the calculation is wrong, and what I did wrong with the units!

Enthusiastic supporters of the Imperial System are invited to do the calculation in feet, pounds and seconds. One cubic inch of air weighs 0.00075oz. Extra points for answers in gallons.

Dave

Surely it’s far easier and less programming to connect arduino to router and not use raspberry pi.

Maurice

It's certainly an alternative, not necessarily easier. Arduino Boards don't come with Ethernet or Wifi, but a shield like this or this could be plugged in and programmed. It's the 'and programmed' part that's the challenge. I accept someone versed in Arduino's Ethernet library who knew nothing about Linux might well find it easier to buy a shield, program it and cut out the Raspberry. Particularly effective approach if the interaction is very simple.

RaspberryPi being a real computer means it supports Serial USB, Ethernet and Wifi at full throttle – all the tools and hardware are available. As such it makes a good bridge between the outside world and a microcontroller that only understands Serial I/O. Basically, the Raspberry does all the hard network stuff like DDNS and there's no significant limit to the size or complexity of the programs it can host.

As an example, I'm using a Raspberry as a Bridge to my Arduino clock at the moment. A short script writes whatever the Arduino is sending via USB to a file (which could grow to 5 or 6 Gb). As the raspberry links automatically to my home network, I can log in and view the growing file at any time. I can copy it to another computer without interrupting the capture, stop and start the capture, process the file on the raspberry, check how big it is and anything else file related. Apart from the script all the software is standard functionality. I don't have to program anything, but could if I wanted. Unlike the Arduino, which is tiny, the Raspberry isn't going to run out of puff.

Dave

**LINK**

Phuket weather.

Regards, Bear..

Edited By Grizzly bear on 10/10/2020 13:16:08

…"Measuring temperature is important for calculating the relative humdity. However, theoretically I need the absolute humdity level to decide whether to start pumping air. And the temperature inside and out will be approx the same and only varies from 25 degC on a cool night to 35 degC on a hot day. So basic humidity is all I need."…

If you need a humidity sensor device, then I can confirm that is what I am using in the form of a Sonoff TH10 (plus the sensor).

The eWeLink app allows me to select temperature or humidity. I have it set to switch on my bathroom fan when humidity reaches 75%. and off when below this figure.

It's been working quite reliably for over a year now and still functions without a network connection once it has been programmed.

Martin.

When as an apprentice at Vickers Weybridge, the high speed wind tunnel (Mach 6 !!) needed dry air. Fresh air was slowly passed over trays of silica gel and stored in an old barage baloon. When the tunnel ran, it consumed the dry air from the barage baloon – very quickly. Usual run time of the tunnel was about 6 seconds and it was just about possible to do 2 runs per day. Each run allowed the model to be moved 2 or 3 times (Quickly) and a schleron photo taken of the airstream passing over the model. I digress,

Dry the air before entering the basement ?

Dave, the incoming air does work against atmospheric pressure, which is in balance, so the outgoing air floats in the in-coming. Its more like moving a counter-weighted lift than moving the load on its own.

Its really a viscous flow problem, not a potential energy one. It would be interesting to know if your answer is anywhere near correct, it could make a good rule of thumb.

Great point Speedy Builder 5. The problem of moisture-laden air entering cold properties is a common one in historic monuments and can cause mould. The solution of drying incoming air (Air conditioning) is getting popular where budgets allow.

Glad you're sorted out Colin. I'm still in disarray due to Roger's comments. Yesterday I proved conclusively to myself that Roger is wrong, only to realise my counter-argument was fallacious. Too many things making my brain hurt at the moment!

Dave