Humidity monitoring

The setup:
I have automated heating. It has humidity sensors, although currently I ignore them. It will soon be cheaper to burn chip pan fat to heat your home then run the heating. Thus I need to squeeze the heating systems coffers a little more.

For purposes of discussion humidity and relative humidity will be used interchangeably and if I need to refer to absolute humidity I shall be specific.

Also for points of discussion I’m assuming a range of 30-70% indoor humidity as acceptable. Anything within that range has “no action” from the humidity monitor system.

The core code is literally an integer comparison per zone on a given min/max range for RH.

What to do about it if they are above/below? First request/demand Humidification or Dehumidification for that zone.

… and what can we do about those requests/demands? I don’t have (de)humidifiers in every room!

Here is the plan. It occurred to me that I am part of the automation system and while, ideally it would replace all steps in a process, there is nothing saying it can’t automate part of the process.

My Realtime grafana dash board is basically my chrome homepage. It already shows automated heating demands/control states. I can simply put a section for other “requests/demands” from the automation system which suggest that “I” should do something. Something like open a window, air a room out, buy a dehumidifier, eliminate sources of moisture etc.

However, there “are” things the system “can” do without my help.

RH is basically relative because how much water can be held within the air (in grams per cubic meter) has an upper limit based (mostly) on temperature. I say mostly as the atmosphere is not an ideal gas in an ideal volume. Pressure and other elements play a small part, usually this value is published as the dew point and/or can be rearranged out of “cloud base”.

The important point is… in a confined space the amount of moisture in the air is FIXED unless it is either vented or condenses on surfaces. The temperature however (and air pressure) varies.

At it’s worst case you have steam not extracted by the kitchen extractor pumping 100s of ml of water into the air downstairs and a cupboard in an unused room upstairs receiving that warm moist air as it rises. It’s warm, so the RH is only 70%. However, without venting when the temperature falls 5*C overnight, the RH can come very close to 100% and condensation form, literally dew! In the morning when the temp rises again the humidity drops to 68%. The other 2% will slowly evaporate into the air again until it’s 70% again. This creates a lovely environment for fungus and bacteria, there own little wet/dry season.

So we can control the temperature. If at any stage through the night a zone reaches 70% humidity, the system will raise a demand for dehumidification. The heating system can pick that up and check if that particular zone is within parameters to accept heating. If it is, heat it.

Raising the temp will immediately lower the RH. It’s a temporary fix of course and an expensive one. So the dehumidification demands should become a highlighted dashboard item.

Last year I closed a room off for 2 months. Windows and doors closed. Opened it in February to find mould on the walls, window frames and sill (the later eaten into the wood). Luckily the room was due painting and was lined with vinyl washable paper, so a quick spray with bleach, dry and paint over, 5 coats!

Any other thoughts, experiences?

By, they way, I also know I could just put a threshold alarm on the humidity entity in HA, just prefer to keep HA a “remote” only. It’s handy on the phone. Still have to get it to work on the watch though.

I’ll add my own critique.

Weather compensation might be wise, by looking at outside temp AND the forecasted minimum temps and dewpoint and maybe forecasting the humidity through each night and warning about it / taking action ahead of time.

Have a look at this. It may help you a little to automate some things, if u use it wisely… :wink:

It’s a pretty crude reading even after compensation. I turn my dehumidifiers on if the chance is > 70% but only if the outdoor temp is less than 10°C. It has pretty much stopped condensation on my windows.

Interesting. I see you offset the indoor temp based on the outdoor temp to try and work out the temperature of the interface (windows/walls). If I understand correctly.

If my room is at 20C has a humidity of 66% and the outdoor temp is 12C, it could be predicted the temperature of the window glass could be the halfway point at 16*C. Offsetting the RH to that temperature is a basic calculation and may report the relative humidity at that interface point is more like 71%H.

At the moment my issue is my house seems to have a lot of humidity. This is sort of expected as it’s end of summer. I’m showing 60+% in all rooms and with the windows shut that’s hitting over 72% at times. 74% was the highest. Simply because the heating has not been on for months and months and I’ve not had the windows open enough.

Luckily I caught this before the temps plummet. I can now air the house with all the windows open while it’s still over 16*C outside during the day.

When the heating kicks in as the temps come down the RH will fall. At the end of winter last year I was noticing the opposite problem, in that rooms that used a lot of heating had low humidity, 24% was the lowest recorded, not good for health, static or fire hazards!

Having a heated fish tank with an unsealed lid that loses a litre a week or more won’t help. Not running the kitchen extractor at full tilt when cooking is also a probably cause.

Anyway, as a first step I colour coded my humidty gauges on the dash board, to get a feel for the data. I might add your calculated “effective interface RH” as a second set of gauges to see how that plays out too.

Right now, if I implemented my original idea of using heating to temporarily offset the RH below 70%, I would be running quite a lot of heating as soon as the windows close at night.

Look how effective opening a few windows was at 10am! Outdoor humidity dropping rapidly probably helped though tehe.

Worryingly high humidity in my attic, which is meant to be a cold space! I do NOT want mould on the roof timbers! In fairness it experiences HUGE temperature fluctuations. When the sun is out beating on the concrete roof it can get to 37C in there. Then a few hours later when the sun sets it drops to 15*C in a matter of hours.

Come to think. My last place was a modern built apartment. I had a humidity and pressure thing on the wall. I never seen it go higher than 50% and that was after cooking. Mostly it sat pinned at 41%.

Now I live in a much older, 1960s house that has many issues in terms of needing modernized. So I’m surprised to see humidity swinging all over the place.

Might need to up the priority on doing some modernisation, sealing and insulating.