Dehumidifier & heating over winter?

[dmmbruce]

Wet bilges

Whilst agreeing with most of the points in most of the posts, and being very interested in them, I feel that there has been insufficient stress on the water in the bilges.

If your boat is one where you vacuum the bilges out once a year, then ignore this.

I had severe condensation problems when I had VERY small leaks round some windows that let water into all sorts of wrong places. Eventually it would get to the bilges where it was obvious. In the meantime however it made the boat into a "warm water bath" (cold in winter). This trapped water contributed to the condensation that then streamed down the windows and made the whole problem worse.

Obviously I have now fixed the windows. This also exposed some other very small weeps. This was not enough. I had to trace and dry as much water as possible. This included drying the bilges thoroughly with dry cloths. Still not fixed. Finally put in an electric fan and left it blowing, on cold, with everything propped up and adequate venting.

After a few days, the boat was dry. No dehumidifyer needed. She is still dry having once achieved it.

Hope this helps
Mike

 

[lw395]

Dehumidifiers and timers

If you are paying a lot per unit for electricity, then maybe a good way of using a dehumidifier is to run it late afternoon. This is probably the warmest part of the day, when the air will contain most moisture. If you can extract most of this, then you should be able to get the boat to a stable dry state.
This approach is good if you are shutting the boat up with damp sails in, that you want to dry in the next few days.
OTOH, condensation occurs when the surfaces such as windows, deckheads are coldest, i.e early morning, so if you have a moisture source in the boat (such as a leak or a person breathing), this is the time when drying is needed. For this, you either need heat with your b+q dehumidifier, ventillation instead, or an absorbtion/dessicant dehumidier.

Humidistats afaik work on relative humidity, so will switch off in warm conditions when the air still holds enough moisture to cause condensation at night.

The point about keeping the bilge dry is absolutely right, when I had a rain leak which trickled through a cockpit locker into the aft bilge, I had problems with mold on the deckhead. Fixed the rain leak, fixed the problem, even on the mooring.

Where are all the eberbasto threads this year? beaucoup de hot air will dry your boat!

 

[johnpye]

If you are paying a lot per unit for electricity, then maybe a good way of using a dehumidifier is to run it late afternoon. This is probably the warmest part of the day, when the air will contain most moisture. If you can extract most of this, then you should be able to get the boat to a stable dry state.
This approach is good if you are shutting the boat up with damp sails in, that you want to dry in the next few days.
OTOH, condensation occurs when the surfaces such as windows, deckheads are coldest, i.e early morning, so if you have a moisture source in the boat (such as a leak or a person breathing), this is the time when drying is needed. For this, you either need heat with your b+q dehumidifier, ventillation instead, or an absorbtion/dessicant dehumidier.

Humidistats afaik work on relative humidity, so will switch off in warm conditions when the air still holds enough moisture to cause condensation at night.

The point about keeping the bilge dry is absolutely right, when I had a rain leak which trickled through a cockpit locker into the aft bilge, I had problems with mold on the deckhead. Fixed the rain leak, fixed the problem, even on the mooring.

Where are all the eberbasto threads this year? beaucoup de hot air will dry your boat!

Absolutely spot on!

 

[johnpye]

Theory and practice

So the device is defying the laws of physics - if it has been working there wont be 10 litres left in the air at 1deg! IF there is then it hasnt been working!
QED

I'm not sure this all helps from a practical point of view, but I must reply!

I don’t think the specification defies the laws of physics. If the machine has been switched off, there may still be moisture in the air! My point is that the dehumidifier is capable of working down to 1degree.

Consult the steam tables as used by HVCA for determining the size of air conditioning and dehumidifying plant
QED

I’m sure the tables provide a more detailed insight into condensation temperatures and hence the theoretical limits of performance for a refrigerant type of dehumidifier. No doubt the data would confirm the dramatic reduction in performance of this type below about 15 degrees.

The whole point of a desiccant dehumidifier is that it does not depend on condensation temperature, but uses adsorption, which is a different process. The rate of adsorption also varies with temperature and moisture content (though with a more complex relationship than condensation), but in the practical application within the dehumidifier, the machine remains capable of extracting moisture throughout its operating range, right down to an ambient temperature of 1 degree. The fact that you may have left it operating and therefore not need it to do so is unimportant.

What really matters is that a desiccant type can work efficiently in the temperature range experienced in unheated boats in the UK winter. Mould growth occurs down to about 5 or 10 degrees, and winter temperature seldom rises to 15 degrees, so it is in this range that the system needs to operate most effectively. This is something a desiccant system can do efficiently but a refrigerant system struggles to do.

 

[Matt341]

Thank you all for taking the time to reply.

I never really understood how dehumidifiers worked so this has been really helpful.

I only have one question left, mentioned above I should use a single line in through a vent and not plug the boats system in? I assume that this means to plug an adapter on the end that would allow me to plug something in? Is this safe as the only RCD protecting then will be the pontoon?

At the moment the shorepower system is simple with an inlet in the cockpit, through an rcd in the locker and then a double socket under the chart table, no charger etc. so will this have the same effect as running a lead into the boat? The last thing I want to find is that the boat has been glavanically eaten.

Advice on this would be great.

Many Thanks
Ian

 

[seamaster30]

I only have one question left, mentioned above I should use a single line in through a vent and not plug the boats system in? I assume that this means to plug an adapter on the end that would allow me to plug something in? Is this safe as the only RCD protecting then will be the pontoon?

At the moment the shorepower system is simple with an inlet in the cockpit, through an rcd in the locker and then a double socket under the chart table, no charger etc. so will this have the same effect as running a lead into the boat? The last thing I want to find is that the boat has been glavanically eaten.

Advice on this would be great.

Many Thanks
Ian

I would expect your system to be fine to use as is. - Unless there is any connection (say earthing) between the systems, you are correct that it would be no different to running in a separate lead.

 

[Matt341]

Thanks for the reply,

Had a good check of the system the other day, there is definitely no earth to the anode. It is basically just a straight wire through an RCD, I have checked it all and there are no breaks in the wire and it is tied back so it isn't rubbing on any rough edges.

It was installed in 2004 by a marine electrician so im guessing it is all wired correctly.

Will do regular checks on connections and wiring.

Thanks
Ian

 

[Vara]

Before anyone reads any more of my post, let me declare an interest that we sell desiccant dehumidifiers. Interpret my comments accordingly, but I hope the technical background that led to our product decision is a useful contribution.

I take it that you will be offering substantial discounts to forumites ordering from your website.

 

[Tex]

I have found this thread very interesting and informative and am tempted by JOHNPYE's device.
Question ...if i use this machine would i still be advised to have some form of frost protection heating ?

Vara also makes a good point John

 

[BAtoo]

FWIW; we use an ordinary B&Q dehumidifier draining through the sink with the boat shut up tight; seems to work OK; we run the drain through a cup to check water is coming through. Unit is set to run all the time and its humidity control is on about half-way. Boat seems drier than in the summer. If its really cold then a small greenhouse heater on a thermostat goes on too. Not sure what temperatures we reach - might put a logger in there this winter!

 

[earlybird]

FWIW; we use an ordinary B&Q dehumidifier draining through the sink with the boat shut up tight; seems to work OK; we run the drain through a cup to check water is coming through. Unit is set to run all the time and its humidity control is on about half_way

I use a B&Q de-humidifier in a similar way. I can't say that I'm over-impressed, although it does help a bit, I think. A difference is that I use it when the boat is on the hard-standing. Maybe the boat gets colder, esp at night, and this reduces its performance compared with being afloat. My de-humidifier is rated at about 200 watts IIRC, so I tell myself there is also a little bit of space-heating effect.
I quite like the look of the dessicant de-humidifiers, but I would be cautious about running costs. The specified 440/740 watt consumption would soon mean a tidy bill if it was running 24/7 at present leccy prices. Do they cycle on and off to reduce consumption?

 

[Highland laddie]

Before anyone reads any more of my post, let me declare an interest that we sell desiccant dehumidifiers. Interpret my comments accordingly, but I hope the technical background that led to our product decision is a useful contribution.

Practically all dehumidifiers sold in the UK are imported as domestic appliances. They are designed for household use, and can be expected work well within the home, drying laundry etc. The task of keeping an unused boat dry throughout the winter is a rather peculiar one, because the temperature in the boat will be lower than in a normal domestic environment. Unfortunately, the specification for dehumidifiers provided by importers is usually quoted (if at all) as an extraction rate at 30 degrees Celsius. Given that the normal temperature range during the autumn and winter is somewhere below zero up to a max of 10 or 15 degrees, this is not much help in evaluating their suitability for our application, and most resellers appear to choose models to suit particular price points without necessarily looking much further.

The £119 model mentioned is a refrigerant type, as are units available in retail stores. It works by drawing moist air over a refrigerated element, so water condenses on the element and drips away to the tank or drain. As the ambient temperature falls below about 15 degrees, the water on the cold element begins to freeze rather than condense. This particular model uses a hot gas defrosting system, so it is perfectly true to say that it is able to work at a lower temperature. I'd say it is ideal for a utility room where the temperature may drop to around ten degrees from time to time.

Some posts report success with cheap (refrigerant) dehumidifiers, and others have posted that it is necessary to have a heater as well as a dehumidifier to get the air warm enough to enable the dehumidifier to work. Both viewpoints are valid. With temperature in winter seldom rising to 15 degrees, any refrigerant dehumidifier in an unheated boat is working at the extreme lower limit of its possible range.

A desiccant dehumidifier works in a completely different way. The air is passed over a desiccant, which is recharged and continuously re-used. The desiccant is at ambient temperature (actually a bit warmer after recharging), and because it doesn’t have to cool the air to precipitate moisture, the process is significantly more energy-efficient, and practically all the energy consumed by the unit is converted into heat that warms the air while it is working. Even more importantly, there is little loss in efficiency throughout the operating range, including the crucial 1 to 15 degree range. (At zero, moisture freezes out of the air anyway). Our model’s extraction rate of ten litres per day is maintained over its entire working temperature range of 1 to 40 degrees.

We have more information on our website, including more detailed technical specifications.

Having said all the above, if you are using the boat regularly during the winter, then you will need some heating anyway, and you might find a refrigerant type is OK, even if less efficient.


If the bedding is staying on board all winter, I'd definitely run a pretty meaty dehumidifier.

PS, if the bilges are not dry, any dehumidifier will be an expensive way of emptying them

Thanks for the explanation regarding types of de-humidifiers. checked your website and wondered could you elaborate on power usesage

 

[jbweston]

Generally over winter the temperature during the night time is too low for the unit to work efficiently- thus there is no point in having it running over night hence use of the timer ... QED!

I agree completely. Also I don't want heater, charger and dehumidifier all running at the same time in order not to overload my supply.

 

[seamaster30]

I agree completely. Also I don't want heater, charger and dehumidifier all running at the same time in order not to overload my supply.

I must be lucky, my marina has a 15A supply and is unmetered.
I allow my automatic charger to regulate its self, the heaters to be controlled by their thermostats, and the dehumidifier to be controlled by it's humidistat.
That way I can be sure everything is running as it was designed.
At the end of the day, there is probably no solution that will suit every boat and every type of utility supply, so you have to make the best of what you have.
Would I use timers if I was on a metered supply? Probably not as I didn't in my old marina which was metered.
I figured the cost was insignificant compared to the musty smell and damage that can be caused by a damp environment.
If your boat doesn't smell damp, then whatever method you are using - it is correct one for your circumstances.

 

[johnpye]

Electricity usage

Thanks for the explanation regarding types of de-humidifiers. checked your website and wondered could you elaborate on power usesage

It certainly does cycle on and off, and only runs when called for by the humidistat, so you can control power usage by how high or low you set it. Some users also like to use a timer to limit usage, but this is not theoretically necessary.

The power rating tells you the maximum power it draws so you can make sure the supply can handle it. This is a pretty powerful machine, so it will only run for a short time each day once the humidity is under control.

 

[Gezzer]

I used to have one of the B&Q refrigerant types, it was Ok, it worked weel when it was above say 10 degrees, below that it was pretty useless, it did however keep the air circulating in the boat which is a good thing, to be at its best I had to combine it with some form of heating to keep the ambient temp up.

The other downside is that they are heavy old things, anyway last year I bit the bullet and went for one of the Dessicant types such as this

http://www.breathingspace.co.uk/more_info.php?department=8&product=125


It was I have to say a good buy, its very light, has a built in heater so if it does get cold it warms the air as well, remote drain, and it will re-start on its own after a power failure, many will not, so if you are wanting to put it on a timer its the way to go, the boat stays very dry inside all winter.

I am not connected to this company in any way, there are lots of outlets for X-dry type de-humidifiers I think

 

[Marsupial]

"I’m sure the tables provide a more detailed insight into condensation temperatures and hence the theoretical limits of performance for a refrigerant type of dehumidifier. No doubt the data would confirm the dramatic reduction in performance of this type below about 15 degrees."

No they dont, theyt simply explain how much water there is in the air at various temps. At low temps there is very little water in the air, so what ever you do be it absorbtion or refrigeration you wont catch much because there's not much there to catch.

As temp rises the air is able to take up more moisture so the meachines appear to be working better at higher temps simply because there is more water for them to catch.

I notice that absorbtion systems also use a heater to coax more water into the air where it can be dealt with; a sensible approach that is entirely inline with the physics of the problem.

I have no axe to grind either way but to say that a device is ineffective at low temps because there is no output is wrong unless you have some idea of how much water is in the air it is dealing with. By the time most refrig systems are running in 10degC the air is dry.

Anyway steam tables describe the ability of air to hold water, not the ability of machines to remove it. Not seen very often now are environmental engineers wandering around offices with a wet and dry thermometer trying to establish the relative humidity so they can consult the steam tables to determine how much extra water is in the air and hence the size of the plant/device needed to deal with it.

 

[enterprise]

I have for several years Run an X-Dry type dessicant machine (mine's actually called an amberdry).
As an early generation machine it does not restart if there is a power failure but this issue has been addressed in later machine's as i'm lead to believe.

I was somewhat sceptical at the start, the claims made seemed too good to be true but as we had bought it at a very special price (same as refrigerent type) we thought the best way was to try it & see.

Well 5 years later I can confirm we are still using it (winter layup only), what John says is very true, if our's broke tommorow we would buy another one the same to replace it.

The process develops heat as a byproduct, extraction, be it from Bilge, cusions, carpets & soft furnishings is better if the ambient temperature is as has already been quoted above zero, below which it would stay traped in all of the above making them cold & damp in the process.
If like us you occasionally use your boat during the winter then as soon as you intruduce heating, you immediatly have condensation, of course with a desiccant type the moisture has been removed already because the air temperature inside the boat is always at the optimal level for extraction & regulated by the humidistat, so it's not traped in the soft furnishings waiting for the ambient temperature to rise enough to allow the air to hold it.

Noise level is extremley low ( It can be on while aboard, even when sleeping), lightweight, & is less to run than a refrigerent type due to it only running when required.

I have posted on this subject probably every year for the last 5 years.
In the begining when I recomended the dessicant type I was made to feel as though I had unleashed an attack on anyone who dared to buy a refrigerent type, many who had bought a refrigerent dehumidifier felt it justified to explain the reason that thier choice was not to be questioned & tried in vain to point out that the refrigerent type was just as good, all I can say is go out & try the dessicant model.

Im glad to see that at least some are now willing to give the dessicant machines a try.

 

[johnpye]

Forumite discounts

I take it that you will be offering substantial discounts to forumites ordering from your website.

Price is pretty competitive on dehumidifiers.

List price for X-dry is £229.99. We've always kept our price below £200 and are matching the best we can find on the internet with more than £50 off list at present.

We've also just taken in stock of a smaller version of desiccant dehumidifier at £149.99 (list £170). Rated at 7 litres per day and 620W, it has all the key features. We think it should be well sufficient for a 45 ft boat.

Forumites could also try entering code PBO5 at checkout. It might work for the next few weeks...


Added link direct to dehumidifiers page: http://www.boatsheen.com/dehumidifiers.html

 

[Converging]

http://www.dehumidifiers-online.co.uk/premiair_dd122fw_mk3_dehumidif.html

I bought this one