Difference between revisions of "Clothes dryer"
(→Energy Use: maths)
Revision as of 20:43, 8 December 2010
The Clothes line and Tumble dryer are the well known clothes drying options. Here a 3rd option is presented with advantages over tumble drying. This closet dryer consists of a dehumidifier in a large wardrobe, walk-in wardrobe or utility room.
How it works
Clothes are taken out of the washing machine and put away in the wardrobe. And that's it, the end user need do nothing else.
Putting damp clothes in the wardrobe sets the dehumidifier running. The dehumidifier fans the air round, warms the space slightly, creates a dry climate and removes the moisture. The dehumidifier switches off when the clothes are dry.
Utility room version
Clothes are dried in the utility room by the dried air. There is generally space for many washing loads. There is then no need for a tumble dryer in the kitchen.
Advantages & Disadvantages
Advantages compared to tumble dryer:
- Takes up less space
- Takes up no kitchen space
- One less operation per load, since the clothes all go from washer to wardrobe, not via the dryer.
- Less dryer noise.
- Much less energy consumption than any type of tumble dryer
- Much lower run cost
- Much less wear on clothes
- Produces deionised water suitable for steam ironing, steam cleaning, batteries, etc
- Can dry pillows
- Heavier clothes such as winter coats can take many hours to fully dry. However this is rarely a disadvantage in reality. You would have to be not so well disorganised for this to be a problem.
- If a wardrobe is used as both dryer and final destination, you'll likely need a bigger one, as all washing will now go into it.
Instead of a large wardrobe, its also an option to put the dehumidifier in a utility room and dry there. This doesn't eliminate the extra clothes moving step, but it fits better with having multiple destinations for the dried clothes, as is popular.
Adding a fan in the room or closet greatly speeds up drying times. A ceiling fan is the most effective.
A non humidistatic dehumidifier may be used, and simply switched off when clothes are dry. Non-humidistatic machines are cheaper to buy. A one-shot timer is also a good option with these machines, these switch off after a preset time.
Where fastest possible drying is needed, a big fan is added with a wire rack next to it, and clothes are put on the rack for speed drying. A ceiling fan can be used for this, with a horizontal rack below it.
Normally all clothes are hanging.
Socks can be put in a plastic matrix on one side if this is preferred to a multi-bar hanger. Drawer dividers are used to create this matrix of miniature cubbyholes.
For items to be stacked, such as bedding, these can't be stacked when wet, but can be once dry. They can be put in the wardrobe on slatted or wire shelves to dry, or one can use extra large bedding hangers. If you don't find a supplier, these hangers can be made from 4mm fencing wire.
Some ventilation is recommended, clothes need at least some fresh air to dry fresh. Ventilation does not noticeably affect drying times.
Whole pillows of all types may be dried with this system. Laundering whole pillows much improves bedding freshness, and thus enables feather pillows to last decades.
Pillows need forced airflow during drying to dry the centre of the fill sufficiently quickly.
Pillows must be totally dried right to the core. If not, they will not finish drying on their own afterwards due to lack of interior airflow, and only a little damp is needed for mould to establish itself. Mould causes a stink, ending the usable life of a pillow. Drying at the core is slower than the outer layers due to slower airflow, and the pillow can feel bone dry outside but still be wet inside. With 2 days of fan drying I've not had one go bad yet - this is probably more than needed.
There is also a time limit for drying, beyond which mould will begin to grow. Pillows can't be left lying around a day or 2 before being dried.
Pillows need to be placed either very close to the air outlet on the dehumidifier or very close to the separate fan to achieve sufficient air flow and drying speed. They need much longer dry times than clothes. If in any doubt, leave them drying for longer.
The dehumidifier should ideally be humidistatic, and preferably have a continuous drain connection. Higher power machines are not recommended.
Approx figures per 5kg load:
- 0.15kWh - closet dryer, or £48 per decade
- 2.1kWh - heat pump tumble dryer, £650 per decade
- 4kWh - new condenser tumble dryer, £1124 per decade
- ? - non-condenser tumble dryer
Thus the closet dryer uses about 1/17th the energy of one of the most efficient tumble dryers, and 1/26th the energy of a typical condenser dryer.
A 200w dehumidifier running 25% of the time equals 50w average. Run for an 9 hour overnight drying cycle that's 0.45kWh, and that will dry a few tumble loads in one go, so about 0.15kWh per 5kg load. If you're only drying one load the energy consumption per load is similar, the machine running less of the time.
New condensor tumble dryers consume in the region of 4kWh per 5kg load.
Non-condenser venting dryers use a fair bit more energy per cycle.
The John Lewis heat pump tumble dryer claims 2.1kWh per 5kg cycle.
At 12p per kW,
- 0.15kWh = 1.8p x5/week = 9p x52 weeks = £4.86 x10yrs = £48
- 2.1kWh = 25.2p x5/week = £1.26 x52 weeks = £65.52 x10yrs = £650
- 4kWh = 48p x5/week = £2.40 x52 weeks = £124.80 x10yrs = £1124
Closet dryers cost less than tumblers in 3 areas:
- Purchase cost
- Run cost
- Less clothes wear
- Tumble Dryer over £200
- Humidistatic dehumidifier + ceiling fan £170
- Non-humidistatic dehumidifier: £100+
- Used dehumidifier £25-60
New tumble dryers cost over £200 for a cheap one, rising to over £500 for a Miele.
Dehumidifiers cost £100+ for non humidistatic models, and £150+ for humidistatic.
Ceiling fans cost anything from under £20 upwards.
- £2,500 per 20 yrs - Tumble dryer
- £80 per 20 yrs - Dehumidifier
Here we assume costs of 10p per kWh for electricity, and 6x 5kg loads dried per week. Drying more (or use of a non-condensiing dryer) will increase the savings from a dehumidifier.
A dehumidifier may use 0.15kWh per 5kg load, at a cost of 1.5p per load. This is £3:90 per annum or £78 per 20 year product life.
A condensing tumble dryer using 5kWh per 4kg load costs 40p a load, £125 per year, and £2,500 in electricity per 20 year product life.
Thus buying a dehumidifer saves in the region of £2,400 in electricity during its life. This is a payback of around 100% pa ROI.
Clothes wear cost
The other cost that's hard to quantify is the wear on clothes caused by tumble dryers. The amount of lint tumblers produce suggests that they are a major cause of clothing wear. But in the absence of any hard figures we are left guessing how much difference they make to clothing life, and what this costs in money and energy.
Perhaps more idea could be obtained by
- measuring the lint removed from clothes per time period by a tumble dryer,
- weighing some clothes new and when worn out to find out how much weight loss makes them worn out.
All one can say without the figures is that if you ever throw clothes out due to wear, they would have lasted longer, and quite likely a lot longer, with a non-tumble method of drying, and that loss of clothing costs money and requires energy to replace.
How much this wear costs each family is unknown.
Don't the clothes dry stiff and rough?
No. Drying over a heat source causes this, but the closet dryer uses dry air rather than heat, and the problem doesn't occur.
Why does it use less energy than a tumble dryer?
The main use for energy in a tumble dryer is heat. A dehumidifier produces very little heat. Instead of heat the dehumidifier uses dried air to increase the rate of water evaporation from clothing.
The other use of energy in a tumbler is to turn the drum. Most tumble dryers have no drum bearings, and turn stiffly. This can take 100-200w. There is no such energy use with the dehumidifier.
Adding a separate fan increases power consumption with a dehumidifier setup, but it also reduces drying times, resulting in similar energy consumption.
But I thought condensing tumble dryers just recirculate the heat, so very little is used?
Not exactly. Nearly all condensing dryers use cold water to condense the water vapour in the air path. This removes heat as well as water vapour. There is a desire to remove as much water as possible, but as little heat as possible, so a compromise is inevitable. This means that some of the heat is removed each time the air goes round. Consequently power consumption is lower than open circuit machines, but still not low.
There are also refrigeration cycle tumble driers available now, using the same technology as a dehumidifier to dry the closed air loop. But...
- They're very expensive to buy
- These are still using power to rotate the clothes
- They are still heating the air
- They have most of the downsides of other tumble dryers.
Don't dry clothes get damp when you put wet ones in with them?
When I put wet clothes in, I leave a 1" - 2" gap from the dry clothes so no damp transfer occurs. The air is dry during the drying process because the dehumidifier can remove damp much faster than the clothes evaporate it.
I have tried pushing wet clothes up against dry ones, and the amount of damp transmitted is very small, such that the now dampened cloth dries out quickly even without the dehumidifier running. Presumably the constant flow of dry air evaporates any absorbed damp at the same time as damp is being transferred.
How much noise does a dehumidifier make?
Inevitably it depends on the model, but noise is not generally a problem with the lower power (200w) units. One of mine makes a little more noise than a fridge, since it is a refrigeration circuit plus a quiet low power fan. With the door closed it is not audible, with door open it is. The older one is quieter, and I have sometimes walked next to it in a quiet room without noticing it was running.
This doesn't mean there are no noisy models out there, but they are designed for use amid daily living, and are much quieter than tumble dryers. An advantage of buying a used machine is you can check for yourself its quiet.
Larger dehumidifiers such as used to dry out new buildings are another matter, and aren't so well suited to this use.
What about used dehumidifiers?
They are few and far between. If buying used, you may have to scan the papers and wait months to find one.
They are also not the simplest to check. Refrigeration systems can fail while looking and sounding normal, so like most used items there is an element of risk there.
Used machines may lack a piped drain facility, or may come without the connector for it. This only matters if you plan to plumb it in so you never need to empty it.
Used machines often could do with a cleanout of the collection tank. Some also have an air filter that will want cleaning.
One thing you must always do
A dehumidifier should be left standing for 24hrs the right way up before use. This is because it may be tipped over during transport, or by the person or shop you bought it from. Tipping causes compressor lubricant to leave the compressor, and it takes time for this to drain back in. Running a dehumidifier that has just been tipped can kill it.
What about clothes wear?
Wear shows most on collars, sleeve ends, the bottom edges of trousers, and as bobbling on jumpers. And a lot of clothes get thrown out due to these.
Repeated bending, bumping into things and rubbing all cause wear. Static electricity is also known to be a significant cause of wear, especially for woollens. Tumble dryers do a fair amount of all of these, and the result shows in all the lint that the machine collects, which is material stripped off the clothes. The closet dryer does none of this, as the clothes don't move during drying.
Is it really safe to have clothes waving about above a heat source?
Clothes don't move during drying. High power dehumidifiers that would blow clothes around are not recommended. The airflow is less than a breeze, it is not noticeable.
Low power dehumidifiers such as 200w machines don't produce significant warmth, and nothing in them runs hot enough to ignite anything. Even if the fan vent is 3/4 blocked there is no cause of fire.
Both compressor and fan must be protected by an overheat cutout to avoid signficant legal liability for the manufacturer, and to ensure the product runs reliably. Thus all domestic dehumidifiers have these features built in.
Clothes are porous, and even wrapping a blanket around a dehumidifier will not stop the airflow. It will reduce it, but not stop it.
Despite all this, multiple layers of safety are always a good thing, as in the real world things do go wrong now & then. It is therefore recommended to be totally safe that clothes are not hung over the dehumidifier.
What if I don't want the whole family's clothes in one wardrobe?
One incarnation is a dryer and wardrobe in one, but it can just be used as a dryer if preferred, with dry clothes being moved to personal wardrobes elsewhere.
Can I use desiccant instead?
No, desiccants don't have anywhere near the rate of water absorption needed.
How come leaving the door ajar makes little difference?
First there is no significant heat build up in the drying cupboard, so an open door doesn't change the drying temperature noticeably.
Secondly, the rate at which even a basic dehumidifier removes water vapour from the air is greater than the rate at which water vapour diffuses from a room interior into the cupboard, so low RH is maintained either way. This is because even a basic dehumidifier can usually remove much more water vapour than is present in typical room air.
The difference it makes is that a limited amount of water vapour is removed from the room air when the door is left ajar.
Why aren't these systems on sale?
At present the method is more or less unheard of. Given its many advantages:
- cost advantages,
- the current worries about energy,
- space savings,
- and the elimination of clothes wear during drying
I expect it might become a popular system in time.
There is also nothing much to sell, as its just a dehumidifier in a big wardrobe. Wardrobe manufacturers could make a concealed dehumidifier compartment with vents and tubes for air circulation, but this will only happen once there is market demand.
There is also the widely held belief today that clothes must be tumbled to be soft, due to experience with non-tumbling electric dryers and radiators. Consequently few people are looking to purchase non-tumbling drying systems.
I run a laundry, can I use this system?
Yes, and you can say goodbye to most of your dryer running/fuel costs. But there are caveats.
- Drying cycle can take longer than tumble dryers if your fan power is low. OTOH you can dry a large amount of loads at once.
- A relatively high power dehumidifier is needed for a roomful of clothing.
- When sizing your dehumidifier, bear in mind that dehumidifier ratings are normally given at 30C, and extraction rate is much lower at 20C.
- No powerful wiring or plumbing is needed to run the dehumidifier, just plug it into a mains socket.
- A ceiling fan is needed to get good airflow all round a packed room. A large powerful one is wanted to minimise drying times.
- High power dehumidifiers in a fanned room need a guard over them to keep fallen clothes off. The guard should be fine enough to be effective against all clothing items. EML (expanded metal lath) would be effective.
- Items to be dried should be hung up, either on rods or hangers, which takes longer than bundling into a tumble dryer. A quicker alternative for some types of item might be layered wire racks, but this would inevitably cause a good deal of creasing.
- If you need even faster drying, a room heated to 30C gives optimum drying speed, and uses less fuel than tumble drying.
- If you use a mix of tumble dryers and a drying room, you could arrange the air to move from drying room into the tumber then back to the drying room. Heat lost from the tumble dryers then warms the room, and the dryers are fed with dried air.
- How well the washers remove residual water from clothing has a big effect on drying time. This depends of course on drum diameter, spin speed and spin time.
Some personal experiences of this system:
1. I find a 400W compressor based dehumidifier will dry a load of washing this way in 60 minutes after a 1400RPM spin. Towels and thick denims may require longer.
2. I use a 200w dehumidifier in a walk-in room, and a 1000rpm washer. Clothes dry overnight. I tend to leave the door ajar so the clothes get fresh air, and this has no noticeable impact on drying times.
3. Unlike a tumble dryer, I get no lint from drying clothes. The drying room needs cleaning less often than other rooms. This means things that would wear down in a tumbler last better.
4. I was surprised by how low the condensate conductivity is. The water is actually purer than shop bought deionised water, so is good for all deionised water uses.
5. When drying pillows I hang them right under the ceiling fan, leaving it on full all night. They're mostly dried out by morning. I then re-hang them the other way up, and after work they're finished.
Dehumidifiers are protected by overtemperature cutouts on both compressor and fan, but it is still best not to permit clothes to cover the machine while in use. For large wardrobe spaces, the machine can be placed with no clothes above it. For furniture sized wardrobes, a shelf or rack over the dehumidifier can keep clothes off.
A high power machine in a small space is not recommended, as the warmth it produces may exceed the machine's ambient temperature ratings.
What if I'm not sure?
You can talk to us at news:uk.d-i-y. Or you could try it and see. If you like it, you should save around 20x what you paid for it in electricity alone, so even as a blind gamble its a pretty good one.