Tumble dryers: energy efficiency

Sterlingtimes

Tumble dryers are rated according to an energy label.



They are rated according to energy consumption per year, i.e. kWh/year. This is given as a precise figure.

However, dryers with a lower energy ratings may have a good annual consumption figure and vice versa. Why is this?

My Hotpoint TVFM70B is a vented version, a B, 266 kWh/year.

The John Lewis JLTDH18 is a heat pump version, an A+ at 260 kWh/year. Not significantly better than my vented.

The Hotpoint TCM580BP condenser also a B rises to a dreadful 628 kWh/year.

An A+++ Grundig heat pump achieves 177 kWh per year.

Many heat pump dryers have very poor annual consumption figures.

edinburgher

211 kWh for our A++? heat pump Samsung, best we could find that wasn't £800 or so

Hate having a tumble dryer, but made a lot of sense with a baby.

zeupater

Hi

I seem to remember a previous discussion around this and have a feeling that the efficiency takes the load capacity & recycling of heat into account along with the control/monitoring functionality.

If it's a basic extractor it's dumping the humid warm air and domestic pre-heated air outside, condensing units recycle some of the energy and heat-pumps have an energy to heat multiplying factor through extraction of heat from the air and humidity water content on pump the evaporator side, which causes condensation (drying) and redelivering the energy as heat on the condenser side so some/most of the energy required is recycled, with any waste heat benefiting the domestic environment.

The monitoring/control can have a huge impact, some units will have a simple timed circuit, whilst others will continually sample/monitor the internal humidity and end the cycle when it is below a set threshold thus reducing the likelihood of wasting energy through unnecessarily long cycles.

Of course, efficiency labels will also assume optimal loading, so an appliance with triple the capacity using triple the energy should achieve a similar efficiency rating. If the consumer is dumb enough to buy (or, worse still, allow a sales-assistant on commission to sell them) a massive freezer, washing machine, dishwasher or tumble dryer (... etc) when a smaller unit would have been more appropriate, therefore underutilising the capacity and efficiency, then it's not really an efficiency-rating issue .. ..

HTH
Z

Cardew

This was discussed some time ago. IIRC the efficiency rating relates to how well a machine operates when filled to xx% of capacity(70%??) not how efficient it is at drying a given weight of different materials.

e.g. a machine with a small capacity might be more efficient(using the test criteria) than a large capacity machine. However the annual cost of running the larger capacity machine would be lower.

So a high efficiency, low capacity, machine could need to run 100 cycles to wash, say, 300kG of mixed washing, but a lower efficiency, higher capacity, machine wash the same load in, say 50 cycles.

Edit, posts crossed.

lstar337

zeupater wrote: »

Hi

I seem to remember a previous discussion around this and have a feeling that the efficiency takes the load capacity & recycling of heat into account along with the control/monitoring functionality.

If it's a basic extractor it's dumping the humid warm air and domestic pre-heated air outside, condensing units recycle some of the energy and heat-pumps have an energy to heat multiplying factor through extraction of heat from the air and humidity water content on pump the evaporator side, which causes condensation (drying) and redelivering the energy as heat on the condenser side so some/most of the energy required is recycled, with any waste heat benefiting the domestic environment.

The monitoring/control can have a huge impact, some units will have a simple timed circuit, whilst others will continually sample/monitor the internal humidity and end the cycle when it is below a set threshold thus reducing the likelihood of wasting energy through unnecessarily long cycles.

Of course, efficiency labels will also assume optimal loading, so an appliance with triple the capacity using triple the energy should achieve a similar efficiency rating. If the consumer is dumb enough to buy (or, worse still, allow a sales-assistant on commission to sell them) a massive freezer, washing machine, dishwasher or tumble dryer (... etc) when a smaller unit would have been more appropriate, therefore underutilising the capacity and efficiency, then it's not really an efficiency-rating issue .. ..

HTH
Z

I wonder how much energy is used manufacturing the energy efficiency labels?

Martyn1981

lstar337 wrote: »

I wonder how much energy is used manufacturing the energy efficiency labels?

That's a rather sticky issue!

Mart.

Sterlingtimes

Thank you all for your comments.

The weight capacities vary only slightly in the main, e.g. 7 or 8 kilograms. I would focus upon the annual price of energy consumed as a good proxy for comparison. Few heat pump dryers offer a significant improvement over the best vented dryers.

zeupater

Sterlingtimes wrote: »

Thank you all for your comments.

The weight capacities vary only slightly in the main, e.g. 7 or 8 kilograms. I would focus upon the annual price of energy consumed as a good proxy for comparison. Few heat pump dryers offer a significant improvement over the best vented dryers.

Hi

Main difference would simply be whether the heat recovery (/usage) from the more expensive technologies would actually be used ... for example, if the dryer was in an outbuilding (stables etc) or garage then it's lost anyway ....

HTH
Z

Ben84

Tumble dryers tend to be used most in winter, when household heating is needed. Vented ones will push air out the house which will get replaced with cold outside air, and you'll need more energy to replace the loss. They also release little heat in to the house, just a bit I suppose from the case getting warm. A heat pump dryer will go through various, more complex stages in moving heat around, but ultimately I assume it delivers the same amount of heating to the house as running an electric fire of the same wattage. So, for people who heat their house with electricity, using a condenser dryer during the winter should result in little or no change to their heating costs - assuming they don't leave the dryer on while they're out, which they really shouldn't anyway for safety. People who heat with gas will see some increase in their energy costs, but they are also getting the benefit of drying clothes.

Of course, waste heat has no benefit if you install the dryer somewhere you don't need any heating, or use it during the warm weather. Depends how you use them really, but dryers aren't necessarily the energy hog people think they are. We live in a relatively small, well insulated house and get much of our heating from waste heat. Mostly from the gas cooker, but also some from the condenser dryer. Our tumble drying happens to follow heating needs pretty well, because both depend on the weather.

Pincher

In the last few years, we just hang the washing out in the warmer month, so the tumble dryer only gets full use in winter. So, the difference in money is probably £10, £20 a year?

I have had washer/dryer as well, which are of course condensing.
Not had a heat pump one, but I see they are listed as condensing.
Let me just say, there is NO SUBSTITUTE for the dryness you can achieve with a proper vented dryer.

The only thing that comes close is a Miele washer/dryer I bought for a tenant.

In general, condensing sucks.

purple_hamster

My dryer (only used in the cold, dark months) takes such a long time. It can take 90 mins to dry a normal load of washing, longer for towels. Mine is a condenser. My friend has a vented one and it takes 30-45 mins to dry a load. I often wonder if they take into account drying time. Does mine really use less energy in over an hour than hers does in half that time?