Making best use of hygrometers

sandy700

I have a Switchbot temperature and humidity sensor and use the Switchbot app on my tablet, I also read the data to a spreadsheet using a raspberry pi when the sensor is in my greenhouse in the growing season.

That way a quick double click on a bat file on my computer and I have a spreadsheet without having to wait while the data is downloaded to my tablet then emailing it to myself.

Ectophile

I have a dumb hygrometer that was a present from my brother.

It sits on a shelf.  I look at it from time to time.  Provided it's in the green zone, I'm happy and don't do anything.  So far it's only ever been green.

Sometimes "smart" technology just makes things more complicated.

ChasingtheWelshdream

Relative humidity is a function of temperature. As the air heats up, it has capacity to hold more water. So for the same amount of water in the air, the humidity (RH%) will drop as the temperature rises.

The heating is on downstairs so the temperature in the bedroom is now around 16 degrees, but the humidity has gone up to 76%. (I shut the window at sunset)

It is raining outside but there isn’t any water ingress or damp patches. But the wall below the bay window has no insulation and develops mould.

What would this indicate to you? 

FreeBear

ChasingtheWelshdream said: It is raining outside but there isn’t any water ingress or damp patches. But the wall below the bay window has no insulation and develops mould.

What would this indicate to you? 

Assuming ground levels outside are below the DPC, I'd say that bit of wall is ripe for insulating. When you are ready to redecorate that room, stick some 65mm insulated plasterboard (50mm Celotex bonded to 12mm PB) on the entire external wall. Extend the window boards to suit, and give the walls a skim of plaster.

In the meantime, improving the air circulation in the bay would help. Do you have any furniture in that space ?

ChasingtheWelshdream

It is upstairs and furniture is pulled away from the wall and will definitely be insulated as soon as we can, it is damp to touch this morning.

One thing I wondered is whether floor length thermal curtains would help or hinder in the meantime, whether it would reduce airflow too much and trap moisture? 

Bendy_House

ChasingtheWelshdream said:

 (I shut the window at sunset)

What would this indicate to you? 

That would indicate that you shut the window at sunset. Which is very possibly when you should keep it open, at least on trickle, all night.

Most cond forms overnight.

Who uses that bedroom? And have you tried ventilating it overnight?

It would be very interesting to compare the readings of that room, vented and un.

Bendy_House

ChasingtheWelshdream said:

The heating is on downstairs so the temperature in the bedroom is now around 16 degrees, but the humidity has gone up to 76%. (I shut the window at sunset)

I would hazard, but it's only a guess, that what is happening with your bedroom is that it's being warmed to a fair degree - 16oC - by the heat from the living areas of the house below?

But, it's not only receiving warmth from there, but also all the moisture produced in that living area, which is being nicely held in that air by the warmer temps in the living area.

That ~20oC(?) air, with - I'm guessing - an RH in (pulls figure out of air) the high-60s (as FB says, warmer air can hold a LOT more water whilst STILL showing a LOWER RH) circulates up to your bedroom where it's cooled. The RH will soar as the air cools, cannot hold on to as much moisture, and approaches saturation point. Cond will likely follow, and INCREASE dramatically overnight as the bedroom temp falls further. 

Solutions: keep your bedroom at 20oC at all times..., or ventilate the moisture away.

ChasingtheWelshdream

That bedroom is ours and I forgot to say that I open the window wide when it is breezy outside but I usually leave a window on vent overnight anyway  (I like a cold bedroom). The TRV is set to 2 and rarely comes on, and the door generally closed during the day. It is north facing. 

There is a bay window with thin curtains (8 openers), a separate window (2 openers, no curtains) and a balcony door.

The window on vent usually has a little condensation on the bottom (this window has no curtains), but the bay window is always dripping whether one of those openings is left on vent or not. It seems excessive to leave all 8 openers of the bay on vent as that would be a lot of heat loss overnight compared to if we had trickle vents?

I have just moved the furniture further away and pulled some wallpaper off. It is saturated but the plaster seems dry so I am assuming that indicates surface condensation rather than external penetrating damp, which is reassuring?

Currently a sunny day, windows on opposite sides are wide open an RH is 70%, 15.9 degrees 

Bendy_House

I can see lots of experimenting about to happen

One will involve a double layer of duvet...

ChasingtheWelshdream

Double duvet is already deployed for hubby’s side of the bed. I like my feet out and fresh air 


In contrast, the other hygrometer in another south facing room was around 60-70% yesterday (also gets mould) in the dull damp day. Today it is sunny and has reached the dizzy heights of 21 and 45%. No way is it 21 degrees, so I guess it shouldn’t be in direct sunlight. I have moved it to the shade to see what happens.