dehumidifier

Discussion in 'Motorhome Chat' started by laser101uk, Jan 17, 2014.

  1. laser101uk

    laser101uk Funster

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    Hi everyone,

    I have been looking at this dehumidifier on ebay

    http://www.ebay.co.uk/itm/310369744214?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

    My thoughts being that a blast with a dehumidifier now and again during the winter may help avoid potential damp spots building up while the van isn't being used as often.

    I wondered what other people thoughts and experiences were before I buy one? I have heard that the ones with the gel work well but I have never tried them.

    cheers Steve
     
  2. Tootles

    Tootles Funster

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    We keep one running all the time in our narrowboat. It has frost protection, and will last a week before having to be emptied in winter. Best thing ever.
    TIP: Keep watching ebay, and the local version as well. Ours cost £15.00, collected. :thumb:
     
  3. MikeandCarolyn

    MikeandCarolyn Read Only Funster

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    Ok,a dehumidifier removes moisture from the atmosphere,hence there will be water in it when in use.
    Think for a moment where that atmosphere in your van comes from-that's right,unless your van is hermetically sealed,it comes in from outside :BigGrin:

    When our van is not being used at all the humidity in the van is generally the same as it is outside.
    In winter I put a 600W oil filled heater in the van when it's not being used.
    This does 2 things,it keeps the temp in the van above freezing by a few Deg depending on how cold it is outside,it also keeps the humidity,generally, 15%-20% lower than the outside humidity.

    To think that a dehumidifier is keeping your van dry internally just because the tray is full of water on a regular basis could be a bit of an error-what you need to know is what the level of humidity is compared to outside.
    Well,that's my thoughts on the matter :Rofl1:

    Mike
     
    Last edited: Jan 17, 2014
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  4. mapa

    mapa Read Only Funster

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    We've had an electric one for years and it does a superb job, not a hint of damp in our MH. Empty it regularly though in damp weather as it soon fills up. We have a timer on ours and let it run about 6 hours a day. Cheaper to run than a heater as well.
     
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  5. Ed Excel

    Ed Excel Funster

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    It's a good idea to collect moisture from the air that enters your van, otherwise it will settle on another cold surface inside your Motorhome. Also, the more you can raise the internal temperature, the more moisture you will collect. Warmer air can carry more water. Have a look at the dehumidifier spec. It can collect 7ltrs of water per day, if you raise the room temperature to 20C. They don't say what it will collect at an ambient of 1C.
     
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  6. matamoros

    matamoros Funster

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    We have used electic compressor de humidifiers for years both for our house in Lancashire(damp!!) when we had a house. In the 5'er, it is persisting down now in Cabanas Portugal and the dehum is keeping the single glazed windows clear as a bell, wouldn't be without one.

    I have no experience of the dessicant variety but the only advantages that I can see are that they claim to be quiter but does this matter if you are not using the motorhome at the time. They also claim that it will work down to 1 deg but I would think not very efficiently and some form of heating would probably be necessary anyway.

    Contrary to the beliefs of some a dehum has no effect on the inflow of ambient external air and simply recirculates the air already in the van, obviously natural flow of air occurs through vents etc.

    The price of the one you are looking at seems high we have bought our last two for around €100 to €120 in France but have seen some on offer less than that.
     
  7. John Laidler

    John Laidler Funster

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  8. oldflemo

    oldflemo Funster

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    This might be a stupid question but what the heck I'm well known for them:-
    Is it sensible to run a small dehumidifier continuously during the winter powered off solar panels?
    I ask because I don't know if it damages the leisure batteries in extremely cold periods to be left in MH
    Thanks in anticipation
    Ian
     
  9. Ed Excel

    Ed Excel Funster

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    Not quite sure if I'm understanding your question correctly Ian. Are you concerned about damage to your leisure battery caused by cold weather, or, damage to your battery caused by dampness during cold weather?
     
  10. oldflemo

    oldflemo Funster

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    Damage to batteries was my concern during -say 10 conditions when condensation will be at its worst
    Ian
     
  11. Ed Excel

    Ed Excel Funster

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    I see. No, it's actually the opposite.

    Condensation gets worse with an increase in temperature not decrease. Water vapour rises, out of your van contents, as the temperature goes up due to, natural causes or you putting heat into the space and deposits itself on the coldest surface it can find, eg a single glazed window. Everyone knows how to get rid of it from their windscreen. Apply some warm air, which makes the water airborne again. If you don't collect it, or let it out through adequate ventilation, the cycle goes on and on!!
     
  12. oldflemo

    oldflemo Funster

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    I'm sorry can you clarify. Are you saying the batteries won't suffer in extremely low temperatures. ?
    I do understand condensation and the effects of interstitial condensation and when it occurs However I simply need to know if its ok to leave the batteries in winter in very low temperatures being charged by the solar panels and that charge used when required by a dehumidifier. I'm really sorry if I was not explicit in my original question
    Regards
    Ian
     
  13. Ed Excel

    Ed Excel Funster

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    Thanks for clarifying that Ian. I would suggest your leisure batteries will be ok, after all, vehicle starter batteries don't require special protection in the winter. You're doing the best thing keeping them charged. Although, if you're going to run something off your batteries they're not going to perform as well at low temperatures. I have a 12V dehumidifier which would drain my one leisure battery in less than a day at -10C.

    Hope this helps
    Ed
     
  14. Biged

    Biged Read Only Funster

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    Would not buy a desiccant dehumidifier, like it's been pointed out you can get a real one for less.

    With the real one you know exactly how much water has been removed....you have to empty its water container! and you don't have to dry out or replace the chemicals.

    The only down side to a real one is they can be heavy (its basically a small freezer on wheels)
    and they are as noisy as a fridge/freezer. We have had one for years and it gets lots of use all over the home in winter drying up condensation :thumb:

    Oh and you need a power supply.
     
  15. oldflemo

    oldflemo Funster

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    It does very much thank you.
    Clearly equally at -10 there would be no condensation. My intention was to fit a battery powered timer and as you correctly indicated only use the dehumidifier in the correct weather condensation producing conditions.
    Presently we use the simple cheap crystal dehumidifier in the caravan and over the winter we change the crystals twice and this simple system removes in excess of 5 litres every winter.
    Ian
     
  16. Zains Pops

    Zains Pops Funster

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    After many years in specialist air conditioning I have some experience of humidity control. The moisture in air is universal, if you have a machine which is trying to reduce the water content of air in a space it cannot be successful unless the space is hermetically sealed. A MH has ventilation built in and is therefore open to the ambient air conditions, a dehumidifier removing moisture within the MH will simply attract replacement moisture from the ambient. This water will show in the pump sump.
    Dehumidification in an unsealed space is the same as trying to pull a vacuum in a MH using a vacuum pump.....impossible.
    Now if the MH has a damp issue ie the water vapour pressure in the MH is above the surrounding condition then the dehumidifier will reduce the water vapour content in the space down to ambient, but the solution to that is to fix the damp!!
     
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  17. matamoros

    matamoros Funster

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    Not in my experience and I have used them in caravans, houses & static caravans to great effect, they do work!!

    Are you saying that dehumidifiers are sold under false pretenses and do not work??

    De humidifiers are not like air conditioning units in that they do not draw in ambient air( unless placed directly next to vent) and simply recirculate air that is already there. Ambient air will obviously enter the caravan etc through the very necessary vents in the normal recirculatory way.The dehum draws in a quantity of air in and expels more or less the same quantity of drier air into the same space, in a sealed space the process would work quicker, but a sealed space is not needed for them to be very effecive.
     
  18. Zains Pops

    Zains Pops Funster

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    Compressor units are exactly like AC units, they have a cooling coil which reduces the air temperature over the coil to below dew point thereby dropping the water vapour out of the air and into the tank.
    The chemical units simply draw the moisture into a desiccant gel which then needs to be dried usually by heating.
    Replacement water vapour will enter the space through the MH ventilation and therefore will add to the water seen in the tank. Water vapour behaves exactly the same as air pressure and will always move to replace any area of lower water vapour pressure.
     
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  19. John Laidler

    John Laidler Funster

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    I'm not sure it is as simple as that. Dry air is denser than moist air so if the vents are in the roof the dry air in the vehicle will tend to stay there.

    I learned this when I visited Sweden once to look at how their army kept vehicles for years in controlled humidity storage and heard how many Swedes have cabins by lakes which are locked up all winter. Many have dehumidifiers which are sited at the top of the building because that is where the moist air forms. Obviously not the same as a MH but worth noting.
     
  20. matamoros

    matamoros Funster

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    I am not a technical expert and will bow to your obvious greater knowledge on the mechanics of A/C units and de humidifiers but I did qualify my statement thus: [HI]in that they do not draw in ambient air[/HI] and[HI] Ambient air will obviously enter the caravan etc through the very necessary vents in the normal recirculatory way [/HI].

    Thinking about this since I am not sure that A/C units do either but assumed they did as mine has a very large lump stuck on the roof.

    Any statements I make are from observation and my admittedly limited knowledge of Physics, it is a long time since I was at school.

    I would be grateful if you could give, in not too technical terms, an explanation for the following observations.

    A/C units obviously work in reducing the temperature, and presumably the humidity,in a non sealed space. How so if ambient air is constantly replacing the cooled, dried air?

    Recently we suffered a heavy rainstorm, ambient temp was around 15deg C, internal temp in our single glazed 5'er was around 22 with a low wattage heater on and no condensation. Within 10 mins the windows had steamed up with condensation, we switched on the dehum and within 10/15 min all condensation had vanished, heavy rain continued with no further condensation.

    Our dehum has different settings in order to run continuously or to stop at various levels of humidity so obviously the manufacturers are expecting the unit to reduce the humidity in the enclosed, not sealed, space.

    We also have a single glazed static caravan in S. Brittany (damp!!) which is left unoccupied over the Winter and we leave dessicant crystals, non reusable, and reusable granules. We have no problems with damp or mould, bedding, cushions etc always smell fresh.

    The reusable crystals always have a recomendation for the volume that they will work in.

    My thinking on the above is that whatever method of de humidification is used the air is dried faster than damper ambient air enters the space thus resulting in a reduction in humidity.
     
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