McMoria

Humidity and Health

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I'm trying to understand the effect of humidity in my living environment- a camper van.

My limited understanding is that the relative humidity in my camper van should be roughly between 40-80%.  And an ideal way to maintain lower humidity is apparently to increase the air flow by opening windows.  If the relative humidity outside is over 80% (which it is: 5 degrees C/ 83%) would this even help? And isn't it unhealthy simply being outside in this case?

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11 minutes ago, John Cuthber said:

If you warm cold air up the relative humidity falls.

Thank you for your reply and I understand the statement.  I suppose to clarify my question I'm looking for an idea of the correlation coefficient with regard to relative humidity and temperature where potential health concerns occur, be they respiratory, mould or bug related. For instance it could be 99% relative humidity but at -3 degrees C I'm not going to be worrying about mosquitoes.

Most information I can find relates only to high humidity/high temperature scenarios.

Edited by McMoria
clarification

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Ifit

On 2/4/2018 at 7:55 AM, McMoria said:

Thank you for your reply and I understand the statement.  I suppose to clarify my question I'm looking for an idea of the correlation coefficient with regard to relative humidity and temperature where potential health concerns occur, be they respiratory, mould or bug related. For instance it could be 99% relative humidity but at -3 degrees C I'm not going to be worrying about mosquitoes.

Most information I can find relates only to high humidity/high temperature scenarios.

If the partial pressure of water vapor in air approaches 100% (ie we approach 100% RH) water will drop out of the air. The easiest way to force this is by cooling. If it is -3 the water drops out as ice.  Snow or hoar frost or ice crystals etc. If it is above 0 it is dew, or rain, or mist, etc. The device used to work out air temperature/moisture vapor/condensation etc is the psychrometric chart. They are not hard to find on the net, and it is reasonably self evident how to use the thing.

As a note, if it is cold and humid, we tend to describe it as "clammy". Hot and humid as "muggy".

I'm not sure of the health issues you are looking for, and it's not an area I have any more info than the uninformed. Humidity and de-humidification is something I might be able to help with. Sometimes it's done with dessicant crystals, ie direct absorption, but the traditional method is to over cool the air well below dew point where the moisture condenses and drops out as condensation, dew if you prefer (so there is a lessor absolute quantity of water vapor in the air, even though it is 100% RH) then re-heat it. With less water vapor, the RH has reduced. It's pretty energy inefficient.

Oh, the effect of wind movement is a different thing again, but generally impacts perception rather than the actual "humidity". I can run through that if that is what you are looking for.

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On 03/02/2018 at 8:37 PM, McMoria said:

My limited understanding is that the relative humidity in my camper van should be roughly between 40-80%. 

80% seems high to me.

 

Here is my 'comfort zone' desktop humidity meter.

humid1.jpg.79484106257034884cf3b04a1cf4afa6.jpg

 

A camper van you say?

One thing to realise is that you don't need to raise the temperature very far to dramatically change the conditons for comfort or against mould.

a half to one and a half degress c is plenty.

That is ebcause the actual temp and humidity is not static but always fluctuating slightly.

As the temp drop some mositure condenses out and gives the mould spores a change to germinate and grow.

When the temp rises back the moisture re-evaporates, but the damage is done.

This is a self reinforcing cyclic process.

You can get very low wattage heaters to run all the time  in your enclosed space to maintaint the temp this much above ambient.

That will keep the mould away at reasonable cost.

 

Edited by studiot

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The effect of air flow:

If your campervan is indeed 80%RH, and outside is say, 40% - opening the windows will certainly help. But it is not because airflow is impacting humidity, is because you are replacing the humid air with drier air.

The human body moderates temperature by radiation and as it gets hotter by evaporation - sweat. If we have a hot humid environment, the air does not have much capacity to take up a lot of moisture. The boundary layer (for want of a better term)  close to the skin becomes saturated. In this case, air movement will help, because new air is dryer than the old boundary air (even if it is humid). So evaporation is more effective.

If it is a dry heat then air movement wont do anything - for practical purposes. If it is cool and humid it also wont pick up a lot of moisture because the max vapour pressure of moisture is low - even if it is cold and dry it doesnt have the capacity to pick up much moisture.

A heater will work if the source of the humidity is simply the internal air.

If you have an independent moisture source, say something got wet - the heater wont do much. Think about hiring a small dehumidifier. It's like a small air-conditioner but has a set point below the due point to extract moisture. They can be quite effective. Maybe run it for a week then return it.

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6 hours ago, druS said:

 If it is cool and humid it also wont pick up a lot of moisture because the max vapour pressure of moisture is low - even if it is cold and dry it doesnt have the capacity to pick up much moisture.

This is the critical aspect for me, Eg, the humidity inside is 80, and so is outside. But it's 2 degrees C or something. I'm figuring out if I have to worry about it with regard to respiratory issues (sounds like I don't as there just isn't enough moisture to worry about) and with regard to mould etc, which I am less confident about. 

 The cooling/reheating process you mention seems to be at odds with Studiot's comment on mould/spore generation and suggests simply warming but I may need further details from Studiot regarding that.

This was initially an issue because, the morning after the first sub-zero night I spent in the van, the polyester blanket over my duvet was soaked, the van was freezing, and the CO2/Fire alarm went off in some crazy error mode. The only difference was that I had shut all the windows. Now I leave them open a crack and don't seem to get it as bad.  I guess my own body's perspiration had condensed on the non-absorbing polyester and in the circuits of the alarm.

 

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20 minutes ago, McMoria said:

This is the critical aspect for me, Eg, the humidity inside is 80, and so is outside. But it's 2 degrees C or something. I'm figuring out if I have to worry about it with regard to respiratory issues (sounds like I don't as there just isn't enough moisture to worry about) and with regard to mould etc, which I am less confident about. 

 The cooling/reheating process you mention seems to be at odds with Studiot's comment on mould/spore generation and suggests simply warming but I may need further details from Studiot regarding that.

This was initially an issue because, the morning after the first sub-zero night I spent in the van, the polyester blanket over my duvet was soaked, the van was freezing, and the CO2/Fire alarm went off in some crazy error mode. The only difference was that I had shut all the windows. Now I leave them open a crack and don't seem to get it as bad.  I guess my own body's perspiration had condensed on the non-absorbing polyester and in the circuits of the alarm.

 

I used to go fishing at night in winter and I know it's  condensation from your breathing. You could do with a little extractor fan and a window open a little. At a minimum I think you want two points that are slightly open to allow air to move in  and out, preferably one at each end of the interior or even just one. each side

Edited by StringJunky

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38 minutes ago, McMoria said:

This is the critical aspect for me, Eg, the humidity inside is 80, and so is outside. But it's 2 degrees C or something. I'm figuring out if I have to worry about it with regard to respiratory issues (sounds like I don't as there just isn't enough moisture to worry about) and with regard to mould etc, which I am less confident about. 

 The cooling/reheating process you mention seems to be at odds with Studiot's comment on mould/spore generation and suggests simply warming but I may need further details from Studiot regarding that.

This was initially an issue because, the morning after the first sub-zero night I spent in the van, the polyester blanket over my duvet was soaked, the van was freezing, and the CO2/Fire alarm went off in some crazy error mode. The only difference was that I had shut all the windows. Now I leave them open a crack and don't seem to get it as bad.  I guess my own body's perspiration had condensed on the non-absorbing polyester and in the circuits of the alarm.

 

OK, Studiot, as usual is completely right, a bit of heat will go a long way in these circumstances.

At near freezing, I'd suggest opening the window will do naught. BUT, if there is a human inside breathing, you have a little humidifier in the system in these conditions. Mate I haven't experienced this much personally, one though a trip where I crossed the arctic circle in winter, and that same trip further south in very cold conditions.

Sleeping in a car north of the acrtic circle in winter my breath was easily creating enough humidity that I had freezing on the windows inside the car. Opening the windows solved the issue. OK down to  say -5 but if it's getting colder live with the frost.

Try a little heater, but at near freezing it doesnt need much breathing to create high humidity. Nor does it need a lot of heat to solve it.

Edited by druS
format clarification

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Yep, windows open help, and for me it's preferable anyway to have some air flow. My concern in the OP was just health effects of relative high humidity in low temperatures which it seems are minimal.

 

Cheers

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I don't think I disagree with anything dru said.

My comment was directed at minimal cost/effort solutions.

String Junky has exactly the right comment that you breathe out a considerable amount of moisture.

But more still comes out of the air as the temperature drops.
After standing in the drive for a while, my car often has condensation on the inside of the windows in the current weather

The absorbtion and retention process does not only apply to mould substance, it also applies to fabrics, such as covers.

In particular it applies to the fabric inner linings of vehicles.
The moisture builup in these can easily go stale.

All the problems are exacerbated by the confines of the space.

So yes a dehumidifier will help.

You can also get roof mounted ventilators/ extractors that are often fitted to commercial vehicles that will help a great deal and be better than cracking the windows open a tad.
Some of these extractors do not need power, which may be a bonus for you.

Boats often have wind powered extractors and small generators, most useful whne they are moored at night.

You haven't said if you are on a site with a mains electricity supply.

Anything you can do to keep the air moving will help and as I said just a small temperature lift will keep the internal air form a continual condensation cycle.

 

:)

 

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