Is it worth getting a vent for a tumble dryer?

[dishman]

Condensor dryers do have their own filters. Although you also have to clean the condensor element of all the fluff every month or so. I used to wash mine using the shower.

Washer/Dryers are usually awful, both in performance and energy consumption. They should be a last resort/compromise for the smallest of spaces.

I do however find a lot of the filters on modern machines badly designed. They usually slot into the door frame (below the door), however after you have removed the filter, there is a gap, and there is always fluff stuck at the bottom of the gap which is very hard to remove.

 

[SimonH2]

1) The majority of the heat is still latent within the waste water that ...

Actually, I think you'll find that the bulk of the heat energy is recovered by the condensation of the water vapour. Whilst the water will still be warm, it's a small proportion of the heat that was originally put in.

My parents bought a condenser some years ago and it's turned out very well. My mum pulls it out and points it through the door from the kitchen to hallway - so it circulates warm air round the ground floor of the house. Emptying the container isn't really much of a chore when you consider how much work goes into doing the washing !

 

[Hugh Jaleak]

I have a White Knight, still going strong after 15 years! It is an electric version though, not sure about gas and clothes, doesn't seem a good combination!

 

[dishman]

1) The majority of the heat is still latent within the waste water that ...

Actually, I think you'll find that the bulk of the heat energy is recovered by the condensation of the water vapour. Whilst the water will still be warm, it's a small proportion of the heat that was originally put in.

My parents bought a condenser some years ago and it's turned out very well. My mum pulls it out and points it through the door from the kitchen to hallway - so it circulates warm air round the ground floor of the house. Emptying the container isn't really much of a chore when you consider how much work goes into doing the washing !

While some heat is indeed expelled into the room, I would still assert that a large amount/majority is contained with the waste water. In condensers I have emptied mid cycle, the water has been very very hot. I also find that (regardless of the claims that the moisure is fully sealed in the machine) ambient humidity rises with the use of a condenser dryer. This may not good in winter and could cause slight damp issues elsewhere in the house. Althought the solution is far far better then drying clothes on radiators etc which can be a huge contributor to damp in winter.

Furthermore, the condenser on a condenser dryer requires a temperature differential. The condenser is air cooled, so for water to condense efficiently the ambient temperature that is sucked in and blown across the condensor needs to be a lot cooler than the hot air in the machine.

As the air temperature of the room the dryer is in rises, the less of a temperature differential there is and the less efficient the machine will become.

This is why vented dryers are in my opinion and from all the literature I have read, more efficient than condensors.

Condensers with Heat Pumps are a different story. They are the most efficient electric form of tumble drying. They extract the heat from the water and reuse it to dry the clothes.

Hugh Jaleak - Domestic gas dryers are not thet common in the UK - just because of tradition I guess. However, you will find that all Commercial dryers (in laundrettes and hotels etc.) are gas powered.

They are also very common in the US and a bit more common in Europe.

 

[SimonH2]

While some heat is indeed expelled into the room, I would still assert that a large amount/majority is contained with the waste water. In condensers I have emptied mid cycle, the water has been very very hot.

Have you compared the values ?
Latent heat of evaporation is 2,270 kJ/kg
Specific Heat Capacity is around 4.2 kJ/kgK
See http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html

So each kg of water gives out 2270 kJ as it condenses. It'll give out a little more through cooling, but say it ends up 50˚C above ambient, then there's still only around 210 kJ retained as waste heat in the hot condensate - ie only about 1/10 of the heat recovered from condensing it.

So it's recovering something in the order of 90% of the heat that you would prefer to shove outside trying to heat the garden.

I also find that (regardless of the claims that the moisure is fully sealed in the machine) ambient humidity rises with the use of a condenser dryer. This may not good in winter and could cause slight damp issues elsewhere in the house. Althought the solution is far far better then drying clothes on radiators etc which can be a huge contributor to damp in winter.

Agreed, it doesn't get all the water out. My mother likes the humidifier aspect as the house is otherwise quite dry.

Furthermore, the condenser on a condenser dryer requires a temperature differential. The condenser is air cooled, so for water to condense efficiently the ambient temperature that is sucked in and blown across the condensor needs to be a lot cooler than the hot air in the machine.

As the air temperature of the room the dryer is in rises, the less of a temperature differential there is and the less efficient the machine will become.

This is why vented dryers are in my opinion and from all the literature I have read, more efficient than condensors.

You need to differentiate between drying efficiency (how fast it dries clothes) and thermal efficiency (how much energy it requires to do it).
You are right that a condenser model is probably slower at drying for a given drum temperature, but it's going to use a LOT less energy. As above, there is a lot of energy recovered from the condensate - and this is energy you don't have to put in.

 

[jeds]

Just an empirical look at energy ratings tells me that for the same drum capacity, condenser driers are generally one rating better than vented. Most 8 or 9kg vented machines are cat C whereas condensors are cat B. (that's most - not all!) Heat pump machines will be the way to go in future but at the moment they don't return enough saving to make up the difference in price.