Auxiliary Heater v Dehumidifier

[Jabberwocky]

Air from outside a vehicle will be dry.

I don't think that is correct.
Air outside your Cali will always have some moisture in it. Its called humidity.

Moisture in the Air = Humidity​

Water is present as a liquid and as a gas in the atmosphere. The amount of water vapour in the air is called humidity. The amount of water vapour the air can hold depends on the temperature of the air. Warm air can hold more water vapor, while cold air cannot hold as much.

 

[soulstyledevon]

I don't think that is correct.
Air outside your Cali will always have some moisture in it. Its called humidity.

Moisture in the Air = Humidity​

Water is present as a liquid and as a gas in the atmosphere. The amount of water vapour in the air is called humidity. The amount of water vapour the air can hold depends on the temperature of the air. Warm air can hold more water vapor, while cold air cannot hold as much.

Possibly in the Brazilian Rain Forrest. But not here in Blighty or anywhere in Europe for that matter.
Air will always be drier outside...

 

[Jabberwocky]

For what its worth the Humidity forecast in London today is 91% (17:00 hrs) my home is 62% and in the Cali is 70%.

 

[soulstyledevon]

For what its worth the Humidity forecast in London today is 91% (17:00 hrs) my home is 62% and in the Cali is 70%.

Your home is 62% because of the moisture within it.
Go and take a reading of the moisture content outside and come back to me...


Infact.
Go and open some windows in the house for about 45mins.
I guarantee the moisture level in your house drops by some margin.

 

[soulstyledevon]

Here is a typical example.
Yesterday it was raining. Opened my windows shortly after getting up. Just a couple of inches between the main bedrooms and closed at lunchtime before going out.
You can see the moisture levels drop and rise with this.

That’s because drier air from outside is replacing the moist air within. The levels have risen through the night as we breath.
People complain about damp within houses. It’s because houses are now so air tight, they don’t get the chance to breath.

 

[andyinluton]

Your home is 62% because of the moisture within it.
Go and take a reading of the moisture content outside and come back to me...


Infact.
Go and open some windows in the house for about 45mins.
I guarantee the moisture level in your house drops by some margin.

If outside is 91% opening all the windows means inside will increase to 91% once the temperatures equalise.

You’ve used a poor example to try & prove the point - of course having a couple of people producing moisture inside a house will increase its relative humidity.

An unheated empty house will have the same RH as outside given the amount of ventilation required by building regs.

If you had a Parcel of air at 99% RH outside at say 10 degrees and were able to bring it into a heated house at 20degrees the RH would drop drastically as the amount of water the air can hold is a function of its temperature.

This is why condensation forms, warm air meets a cold surface & the amount of water it can hold drops so it deposits the water on the cold surface.

 

[soulstyledevon]

If outside is 91% opening all the windows means inside will increase to 91% once the temperatures equalise.

Not how I understand it.
The air is heated and this expands. Which changes the measuring of the relative humidity...
My house was built in 1928 and apparently suffered from damp issues.

What I found was the house wasn’t being aired properly. Since moving in, we open the windows almost daily and added extraction in bathrooms and kitchen.
62% humidity would be on the higher side of humidity within a home.
As you can see from the graph above my daily average is 48%. This would be considered spot on. Note, this is in a bedroom with on-suite bathroom and past issue of damp...???

 

[andyinluton]

You said air will always be drier outside.

That’s what I’m disagreeing with.

If you leave your windows open all day the air inside will match the air outside - unless your heating the whole area as well as your house. If you had measured the RH outside as well I would expect it to be at 48% if the temperature was the same as inside.

If you are producing water vapour in a house - boiling a kettle, using a shower, breathing etc of course the moisture content will go up.

Anytime it’s warmer outside than indoors there’s a good chance the air inside could be drier than outside.

A m3 of air at 5 degrees celcius at 100% relative humidity contains the same amount of water as a m3 at 20 degrees at 53%

 

[AlisonF]

So going back to @Lesley Dale ’s question... I use my dehumidifier in the van and in the house. I always make sure the heating is on so as to maximise the moisture in the air so the dehumidifier has something to work with.
Occasionally I have condensation on some windows at home. Leaving the dehumidifier on does not help with that if the heating is not on.
I think you will also find the same with dehumidifier bags. I’ve tried those as well, and if temperature is low, they do not help as absorb vapour not condensation.

 

[Jabberwocky]

Your home is 62% because of the moisture within it.
Go and take a reading of the moisture content outside and come back to me...


Infact.
Go and open some windows in the house for about 45mins.
I guarantee the moisture level in your house drops by some margin.

87% outside.

 

[Andy]

My van has sat on my drive a lot in the past year. Discovered it actually felt damp inside. Had dehumidifier running in it for 36 hours, pulled out around 2 litres of water so far !!
Dehumidifiers are brilliant things.

 

[2into1]

My van has sat on my drive a lot in the past year. Discovered it actually felt damp inside. Had dehumidifier running in it for 36 hours, pulled out around 2 litres of water so far !!
Dehumidifiers are brilliant things.

I'd the interested in the maths of what humidity level would have been required in the space of a Cali to hold 2L of water.
On the upside, the weather around your village will have been dryer than forecast...
I'd try closing all the dash vents.

 

[andyinluton]

Max water capacity per M3 of air at various temperatures is as below.


degrees celcius grammes per m3
-5 3.37
0 4.89
5 6.82
10 9.39
15 12.8
20 17.3
30 30.4

To get 2000 grammes out you've probably got a combination of the following:
Standing water - ie condensation
A bloody big van - at a guess a cali is only something like 14m3
External air entering the van

 

[Andy]

I'd the interested in the maths of what humidity level would have been required in the space of a Cali to hold 2L of water.
On the upside, the weather around your village will have been dryer than forecast...
I'd try closing all the dash vents.

Good idea, had not thought of that.