Damp, mould and the threat to health

[XFool]

Yes but my borderline O level physics pass comes in here, doesn't the condensing water give off its latent heat, in addition to the electrical energy put in by the compressor.

I forgot about that.

Perhaps we then need to go into how the moisture got into the air in the first place...

I won't hold my breath.

[ReformedCharacter]

I can see that overall such a unit must add some heat to a room (inefficiencies: heat from motor, work done by fan on air. More heating than cooling? etc.), but as a dehumidifier is fundamentally a heat pump (like fridge mechanism) working in a closed space, essentially it's just moving the heat around in a room rather than heating it.

Depends on the dehumidifier surely? AFAIK there are two main types, refrigerant and desiccant. Living now in an old house with a number of unused rooms (children left home), we have one refrigerant and a number of desiccants, the latter run for a couple of hours in the winter in unused rooms by timer. AIUI refrigerant dehumidifiers are less efficient at low temperatures unlike desiccants.

How do desiccant dehumidifiers work in a domestic environment? Can they last through the winter and be 'reversed' during summer or do the desiccants need to be physically replaced.

Desiccant dehumidifiers work by using a large desiccant wheel to adsorb moisture from the process air stream. As the process air is dried, the moisture content of the wheel rises. To remove this moisture the wheel is in constant rotation and a second air stream is heated and passed through the wheel. This heated air steam picks up the moisture from the wheel, in turn drying the wheel so it is reactivated and able to continue to dry the process air.

Passing the warm moist air through a condenser causes the water to drip into a collection tank, no removal of the desiccant required.

https://www.toyotomi.eu/product-category/dehumidifying/dessiccant-type-dehumidifier/

I find ours work well and the power consumption is fairly low.

https://www.amazon.co.uk/EcoAir-DD122-Simple-Desiccant-Dehumidifier/dp/B00474K8SY/ref=sr_1_19?c=ts&keywords=Dehumidifiers&qid=1669221864&s=kitchen-appliances&sr=1-19&ts_id=3593780031

RC

[XFool]

Desiccant dehumidifiers work by using a large desiccant wheel to adsorb moisture from the process air stream. As the process air is dried, the moisture content of the wheel rises. To remove this moisture the wheel is in constant rotation and a second air stream is heated and passed through the wheel. This heated air steam picks up the moisture from the wheel, in turn drying the wheel so it is reactivated and able to continue to dry the process air.

Passing the warm moist air through a condenser causes the water to drip into a collection tank, no removal of the desiccant required.

https://www.toyotomi.eu/product-category/dehumidifying/dessiccant-type-dehumidifier/

"In fact the dehumidifier consist of a desiccant rotor, a heating device and a condenser (heat exchanger element)
If you look at the picture shown you will quickly understand the principle:"

Not by me I'm afraid.

"Humidity absorbed by the rotor" ?
"Humid Air in" "Cooling the condenser" ?
"Water in the rotor dried out by heat" ?

[Dod101]

I am bemused. I occasionally open windows in my house even in winter for the purpose of removing otherwise stale air but I have three bathrooms in my house, two of which have a shower and the other a bath (which I never use) The bathroom that is used most is fairly big but I never open the window. There is an extractor fan which works automatically when the lights are switched on and runs for a few minutes afterwards. I have never had mould in any of the bathrooms.

I am genuinely puzzled by mould which I have always associated with a high humidity and heat. When I lived in Hong Kong which has said high humidity and heat for 7/8 months of the year, before air conditioning was universal, all flats had a so called 'hot room', although 'dry room' would be a better description. It had no windows and a free standing dehumidifier which had to be emptied of water very regularly and kept running 24 hours a day. Anything subject to mould was kept there, all leather items from shoes to handbags, many clothes, and of course many foodstuffs.

I have never had any issue with mould in this country but it must surely be caused by a lack of ventilation, drying clothes in a small enclosed space and/or water leaking on to ceilings and so on. For it to be as bad as it was for this family it should obviously have been investigated because something was wrong. As a threat to health it must have been bad, as it surely was from photos in the newspaper. The landlord should certainly have been actively investigating this, from self interest if nothing else because it must have been damaging his property.

Dod

[ReformedCharacter]

"In fact the dehumidifier consist of a desiccant rotor, a heating device and a condenser (heat exchanger element)
If you look at the picture shown you will quickly understand the principle:"

Not by me I'm afraid.

"Humidity absorbed by the rotor" ?
"Humid Air in" "Cooling the condenser" ?
"Water in the rotor dried out by heat" ?

Source: https://uk.trotec.com/products-services/machinery-homecomfort/dehumidification/practical-knowledge-concerning-dehumidifiers/overview-of-dehumidification-methods/desiccant-dehumidifiers/

RC

[XFool]

...Gotcha! Thanks.

So, effectively, the desiccant is in or on the Desiccant Wheel and the incoming moist air passes over it and dried, then drawn though and out by the fan. There is a separate stream of circulating air (source not shown in above) that dries the desiccant out as it passes by and carries this moisture to the condenser - which is cooled by the incoming moist air that is being dried - and then passed on to the heater before re-entering the Desiccant Wheel drying area.

A bit puzzling to see both the hot and 'cool' air apparently passing through the condenser at the same time. (Still not too sure about that...)
Also occurs to me that such a device would work best if the incoming air was not very warm/hot.

[Dod101]

I have not the slightest idea how that diagram helps anyone to understand how a dehumidifier works but in any case it is irrelevant to the subject of the thread.

A dehumidifier almost by definition works best with incoming hot humid air. I do not understand how air could be humid enough in the UK climate to make dehumidification worthwhile.

Dod

[XFool]

...(God forbid we are allowed to understand things on TLF!)

[James]

How do desiccant dehumidifiers work in a domestic environment? Can they last through the winter and be 'reversed' during summer or do the desiccants need to be physically replaced.

I lived for a bit in Hong Kong where the problem was humidity rather than cold and damp. We had desicant dehumidifiers in the wardrobes to prevent clothes getting damp. They were filled with hydrophilic pellets that turned to a gel before getting thrown out. Didn't look particularly reuseable.

[88V8]

A dehumidifier almost by definition works best with incoming hot humid air. I do not understand how air could be humid enough in the UK climate to make dehumidification worthwhile.

Ours pull about half a gallon a day, each, so they do make a difference.

We have two identical refrigerant dehumidifers, one in the sitting room where the temp is typically in the low/mid 60s, and one in the cellar where the main source of heat is a storage rad and the dehumidifier itself, so it is no warmer.

Our mould room is upstairs and perhaps perversely we do not have a dehumidifier in there, but we do have two fans on timers and I open the window twice daily while the fans are running.

It gets mouldy because the walls are thin - wattle & daub - and the thatch roof gets saturated at the eaves which creates a cold bridge. Probably not a problem when the cottage was new and there were two inglenoook fires likely lit 24/7/365 as they would have drawn a lot of air through and in any case there would have been no glass in the window openings.

I think the damp roof/cold bridge is the main cause as the kitchen immediately below and of the same wattle construction has no mould at all.

I have the impression that the dehumidifiers are quite local in their effect; there is no door between the cellar/kitchen/sitting room but the unit in the cellar fills up much faster.

There must be millions of spores swirling around me as I write, looking for somewhere to alight. Just as well I can't see them.

V8

[XFool]

Um...

A bit puzzling to see both the hot and 'cool' air apparently passing through the condenser at the same time. (Still not too sure about that...)

Ahem! I feel bound to point out that the original diagram posted and the second diagram posted seem to contradict each other. (One shows air passing into and out of the "condenser" - which seems to me to contradict the alleged mode of operation! The other, both streams passing past the condenser, which seems...puzzling.)

No wonder I am having difficulty understanding.

[mc2fool]

I do not understand how air could be humid enough in the UK climate to make dehumidification worthwhile.

Well, ok, while it's not the kind of hit-you-with-a-sledgehammer hot-humidity of HK or Florida in summer, the UK has quite a damp climate. Go to https://www.bbc.co.uk/weather and pick somewhere, or stick in your postcode, and then click on an individual time slot and it'll very likely show 70-80-90% humidity.

Whether it's "worthwhile" having a dehumidifier is, I guess, a matter of choice (I've never had one), although much of the discussion has been about artificial humidity, from cooking, showering, etc, rather than from the climate.

[Dod101]

A dehumidifier almost by definition works best with incoming hot humid air. I do not understand how air could be humid enough in the UK climate to make dehumidification worthwhile.

Ours pull about half a gallon a day, each, so they do make a difference.

We have two identical refrigerant dehumidifers, one in the sitting room where the temp is typically in the low/mid 60s, and one in the cellar where the main source of heat is a storage rad and the dehumidifier itself, so it is no warmer.

Our mould room is upstairs and perhaps perversely we do not have a dehumidifier in there, but we do have two fans on timers and I open the window twice daily while the fans are running.

It gets mouldy because the walls are thin - wattle & daub - and the thatch roof gets saturated at the eaves which creates a cold bridge. Probably not a problem when the cottage was new and there were two inglenoook fires likely lit 24/7/365 as they would have drawn a lot of air through and in any case there would have been no glass in the window openings.

I think the damp roof/cold bridge is the main cause as the kitchen immediately below and of the same wattle construction has no mould at all.

I have the impression that the dehumidifiers are quite local in their effect; there is no door between the cellar/kitchen/sitting room but the unit in the cellar fills up much faster.

There must be millions of spores swirling around me as I write, looking for somewhere to alight. Just as well I can't see them.

V8

Yours is clearly a special case but we are I assume discussing the normal current building style.

Dod

[servodude]

A dehumidifier almost by definition works best with incoming hot humid air. I do not understand how air could be humid enough in the UK climate to make dehumidification worthwhile.

Ours pull about half a gallon a day, each, so they do make a difference.

We have two identical refrigerant dehumidifers, one in the sitting room where the temp is typically in the low/mid 60s, and one in the cellar where the main source of heat is a storage rad and the dehumidifier itself, so it is no warmer.

Our mould room is upstairs and perhaps perversely we do not have a dehumidifier in there, but we do have two fans on timers and I open the window twice daily while the fans are running.

It gets mouldy because the walls are thin - wattle & daub - and the thatch roof gets saturated at the eaves which creates a cold bridge. Probably not a problem when the cottage was new and there were two inglenoook fires likely lit 24/7/365 as they would have drawn a lot of air through and in any case there would have been no glass in the window openings.

I think the damp roof/cold bridge is the main cause as the kitchen immediately below and of the same wattle construction has no mould at all.

I have the impression that the dehumidifiers are quite local in their effect; there is no door between the cellar/kitchen/sitting room but the unit in the cellar fills up much faster.

There must be millions of spores swirling around me as I write, looking for somewhere to alight. Just as well I can't see them.

V8

Yours is clearly a special case but we are I assume discussing the normal current building style.

Dod

We got our dehumidifier living in a post-war block-of-four "villa" in Edinburgh.
It had since been fitted with really effective uPVC double glazing and had the chimney blocked.
Indoor temp was probably 18-20 deg in winter with the heating on and our two weans under 4 running about.

The dehumidifier (a "portable" Delonghi from Lewis's) was bought when we realised that hanging washing inside in the "sun" at the patio doors was causing the wallpaper to start peeling off. It worked brilliantly to stop the problem and make the place a lot more habitable (high humidity being a big player in what makes a place feel "stuffy")

The UK is surprisingly humid - it's part of what makes dressing properly in winter so tricky. I find it much easier to be comfortable in the colder drier Scandinavian climate where you are less likely to perspire under outdoor clothing.

-sd

[Dod101]

I conclude that I have the space and air circulation for it never to have been a problem. I have in fact been drying a duvet cover and sheet in my utility room . They will dry in about 12/18 hours but I have never had any mould or suggestion of mould. I think to get mould the other ingredient, apart from relatively high humidity, is cold walls and ceiling for moisture to condense. All very interesting I must say.

Dod

[Nimrod103]

I conclude that I have the space and air circulation for it never to have been a problem. I have in fact been drying a duvet cover and sheet in my utility room . They will dry in about 12/18 hours but I have never had any mould or suggestion of mould. I think to get mould the other ingredient, apart from relatively high humidity, is cold walls and ceiling for moisture to condense. All very interesting I must say.

Dod

I think it is the humidity issue more than anything. Like Dod I live in a biggish house with plenty of air circulation, but still haven't turned the heating on (the ambient room temp is 13 deg C at present). We do laundry about 3 times a week, and hang the clothes up in the utility room where they dry in about 2-3 days. We have no mould problem generally. Mould comes from condensation, so keeping the humidity in the house down is vital. But at 12-13 deg the air can't carry much water.

You have to be careful of particular danger spots - our unused front bedroom is a risk and I will be keeping an eye on the outside walls during the depths of winter.

My friend who swears by his dehumidifier, keeps it in his converted loft, where he runs his model railway. Being at the top of the house, and largely unventilated, that is where the warm humid air rises to, so of course he collects a lot of condensed water.

[88V8]

We got our dehumidifier living in a post-war block-of-four "villa" in Edinburgh..... make the place a lot more habitable (high humidity being a big player in what makes a place feel "stuffy")
The UK is surprisingly humid ...

As I may have mentioned before, it's pretty damp in our C17 cottage, around 70%RH by the autumn, and it's very noticeable how much warmer it feels just by bringing the RH down.
The woodburners have a great effect, despite having lit up for less than a week the RH is already down to c60% and by the end of winter it will be around 45% and the cottage will feel much cosier despite no uplift in the actual temperature.

V8

[AsleepInYorkshire]

Another young man's health appears to be suffering because of poor ventilation

Quite a harrowing and deeply saddening video in my opinion. Unbelievable that this is happening in the UK. Watching this video did leave me feeling awash with negativity.

AiY(D)

[AsleepInYorkshire]

This may be of interest to some Fools.

It's a link to an investigative reporters Twitter page.

He seems to have the bit between his teeth regarding the subject of mould in Housing Association homes.

https://twitter.com/DanielHewittITV

Thank you

Take care

AiY(D)

[TahiPanasDua]

I found reading the above posts fascinating and while frequently accurate there are some of the usual misconceptions about how it is formed and cured.

Working as an architect in Scotland decades ago I was from time to time invited to inspect "damp" in households. In the age of paraffin heaters, such visits were much more frequent. The problem was always mould as a result of condensation. The word "damp" is frequently used but is too general a word and is best avoided as it can refer to wetness from a number of differing sources including external water penetration, rising damp, etc.

Condensation is formed where warm moist air meets cold surfaces.

Condensation is usually easy to spot as it generally occurs, or is worse, on the coldest walls in the house, particularly those north-facing. It is often most evident in rooms with poor or no ventilation. Within such rooms it is generally worse in those parts of the room with the poorest air circulation such as in the warmer upper corners or in semi-enclosed recesses as evident even in the fleeting TV shots of the dead child's house.

Condensation attracts mould which relishes warm moist surfaces. That it is mould and not water penetration is evident from its location and initial spotty clumping.

The enemy of condensation and subsequent mould is ventilation. This is the ultimate cure.

Sorry if you knew all that already!

TP2.