*Hot* washes and energy efficiency

[Martin Angove]

Dead washing machine, so quick question (the basket is already full of dirties)!

I know this has been done before but our uses are slightly different to the average:

The "energy efficiency" rating on washing machines relates (as I understand it) to the cotton cycle at 40C. This is, for all machines, a cold-fill-only wash.

Most (75%+) of our washes are at 60C or 90C because we use non-bio (sensitive skins), messy children (stains to lose) and have dirty nappies (three loads or so a week). In total we might do seven or eight (or more) loads of washing a week, though as the current machine is

4.5kg and we're now looking at 6kg or 7.5kg models this might change.

We have gas-heated stored water at about 60C, lagged pipework and the washing machine take-off is before both the bathroom and the kitchen (hence there is usually warm water close by).

50% or more of new machines are cold-fill only which I grant will make very very little practical difference to people who do the majority of washes at 40C or who have a run of cold pipework to empty or (obviously) who have combi boilers.

As I said though, 40C washes make up no more than 25% of our useage, so how much of a difference in both energy use (kWh) and time (waiting for the water to heat) is a cold-fill-only machine likely to make over a hot & cold machine?

And can anyone recommend a machine under £400? I've been told that Hotpoint and Hoover have the cheapest, most widely-available parts and are easiest to fix (that is one reason why the current Zanussi is considered "dead"). Is this true?

Hwyl!

M.

[John Laird]

If it's any help, the programme chart for my Bosch Maxx indicates that

*only* the "quick wash" option saves any time at all. However, the consumption rate chart indicates an extra 0.2-1.1kWh per load for cold-fill (a function of load size and desired washing temperature). For a 5kg load of cottons at 60C, the extra power usage is 0.55kWh.

These two charts aren't singing from the same hymn-sheet ! It's clear the cold-fill option must take longer.

HTH.

[Christian McArdle]

The washing machine energy rating is based on performance at 60C.

"The machine shall use less than or equal to 0,17 kWh of electrical energy per kg of washload measured according to EN60456:1999, using the same standard 60 °C cotton cycle as chosen for Commission Directive 95/12/EC (1)."

Modern machines really use very little water. It doesn't take much electricity to heat it up. Avoid US style machines that require a small lake to submerge the clothes in whilst the rotating "knife" agitates them.

Christian.

[Martin Angove]

Those are exactly the sort of figures I was looking for. 0.55kWh for a

5kg load probably equates to 5p of electricity or something which over a year (let's call it 350 loads if you read my previous post) is £17.50. Hardly a huge amount of money but:

1: H&C machines don't seem to cost any more than C only

2: This is 5kg at 60C and we do a fair number of 90C washes at the moment.

Maybe the machine just does 30 minutes of main wash whatever and if the water is cold, less of this will be at the rated temperature?

Hwyl!

M.

[Martin Angove]

Aah, right, that's changed in the last few years then. That would also explain some of the differences between ratings for H&C or C only machines - 0.3kWh seems to be common for otherwise similar machines. By pure guesswork I would reckon I could more than double that for a 90C wash if the H&C machine hot-fills only for the wash.

Yes. The fact is that even a cold-only machine is going to use less energy and less water than our dead machine. What grates is the "waste" (in a way) of water we already store hot, and the possible extra time it takes per cycle.

Hwyl!

M.

[Christian McArdle]

Don't see that 0.3kWh as total savings. Your stored energy system will be much less than 100% efficient at supplying it like the built in electric element manages. I would guess it would be considerably less than 50% efficient, as it will result in boiler firings, primary circuits getting hot, DHW supply lines getting hot Cold water run off at kitchen sink to get the lines primed with hot water all results in additional water usage, as well as power. As you are now probably in 40% overall efficiency territory for this small amount of water (efficiency would be higher if more water was required), versus 100% efficiency at 4 times the unit cost, you'll see that any cost improvement is marginal, and in some cases it may even be more costly to use hot fill than cold fill. In energy terms, the electricity would actually be more efficient than the cost figures indicate. Much more of the electricity cost is in distribution (not just energy losses during transmission), and the CO2 emmissions would probably certainly be higher from the gas CH solution than the (gas produced) electricity.

There will be no additional savings at all for 90C washes, as the DHW supply is likely to be around 55C, assuming it was entirely hot all the way to the washing machine tap (which it won't be), so both hot and cold fill will electrically heat the difference, using the same additional amount of electricity.

Christian.

[John Laird]

I think I'm paying about 5p/unit, so that would be about £10 extra. I'm amazed there are cold-water only washing machines around, but admit my current one is probably 5 years old. At 90C, the extra energy is

0.7/0.9/1.1kWh for 2/5/6kg loads. Do you *really* need to go to 90C though?

Good thinking, Batman. No reason at all why the drum isn't agitating the load with the soap at the same time as the water is heating.

[John Laird]

ICBW, but I think some machines won't "hot-fill only" as they tend to assume you will be using biological powder which I think activates at a low temperature and may not take to immediate contact with much hotter water.

[I used to have an old Servis which said it did this when the Bio option was used. My current machine has no Bio button. But from the fact that heating load starts to increases at 60C and they expect hot-water supply at 60-70C, that it must be mixing to a lower temperature.]

[Ed Sirett]

The trouble is that most machines nowadays use a such a small amount of water and only the smartest units use pure hot for anything except

90C washes.

The net effect of the hot fill is to simply heat the pipes/boiler/cylinder etc. No saving of energy but a cost saving to you (especially on the very hot washes is to have a dual tariff electric supply and do the washing at night.)

- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at

Gas fitting FAQ CH FAQ

[IMM]

Unless your cylinder is down the street, believe me lots of hot water comes though. My machine is only 3 years old.

[Martin Angove]

Yes, I see your point. However the picture isn't quite as bleak (for us) as you paint it:

The tank is heated in the morning for an hour or so and then holds sufficient hot water for our daytime needs until children's bath time. Washing up is dishwasher mainly - cold fill only ;-) This means that although there will be more water to heat in the evening, it is all done in one lump rather than in short bursts as the washing machine (or whatever) draws off. The pipework from tank to (almost) all outlets is lagged which means that standing water loses heat much less quickly than you'd imagine and water leaving the tank gets to the tap without losing much heat at all. Also, as I think I said before, the WM outlet is physically before the other hot outlets (ok, it is 3ft after the bath tap) so the chances of hot water being in the pipes is that much greater than might otherwise be the case.

Good point that I shouldn't see previously heated water as 100% efficient as yes, we do use gas and yes, it is an old boiler. Two things occur to me:

1: If we had solar hot water panels I'd be even more likely to want a H&C machine. 2: If we generated our own electricity and had enough capacity I'd probably go for cold fill only.

As to your point about any savings beyond 60C being completely non-existant I'm not so sure. Most H&C machines seem to mix-fill at 60C or below which means that the actual temperature of inlet water will be lower than 60 by some considerable margin. A H&C machine will still have a large heating job to do to get to 60. However at 90C (or 95 as in our old Zanussi) some machines hot fill only, therefore they have a higher starting temperature and have less of a job to do than C only machines.

To put it another way (and using completely out-of-thin-air figures)

Hot at 50C, cold at 10C, pressures and flow rates similar.

60C wash, cold fill, temperature raise required: 50C 60C wash, mix fill (30C), temperature raise required: 30C 90C wash, cold fill, temperature raise required: 80C 90C wash, hot fill, temperature raise required: 30C

Hwyl!

M.

[Martin Angove]

Ours is a really weird tarrif which we inherited when we bought the house (British Gas, so there's the additional complication of dual fuel discount): It is something like 14p per unit up to a certain level, then

6p per unit beyond that, plus VAT. We've only had two (I think) proper bills so far (we've had the house a year, but have only been living in it for 3 months or so) so the rate is a bit difficult to work out!

If you've seen some our nappies you'd be inclined to soak them in bleach, boil wash them with pre wash and then probably burn them afterwards :-) Usually though they soak overnight in Napisan then go through a normal 90/95C cycle. After this they look almost as clean as the day we bought them.

In fact, every reason for it to do just that if the element is anywhere near the bottom of the drum - some of the water closest to it, especially if trapped in clothes, may get much hotter than intended!

Hwyl!

M.

[N. Thornton]

I dont recommend either. Hoover is getting a bad rep now, and hotpoint, while better, is not particularly a good make. If you do want a hotpoint, there are lots of good clean 2 yo machines available for under 100.

Regards, NT

[Christian McArdle]

I suppose it is this that I'm not sure about. Every washing machine that I've installed has stated clearly that the DHW supply must be below 60C. I had always assumed that this meant that a 60C wash would be hot fill only. However, you seem to know more about the area that I do, so I don't dispute that they really do mix fill. I just think it odd that they would design it that way.

Christian.

[David H]

Just to throw a spanner in the works of your carefull calculations,

A few machines that I hae seen with an "A" rating have a drum that is very much smaller than the average, but still rated as a 9lb 4kg load.

This means that the drum is full with less nappies. therefore you will have to do two washes, where you only did one wash before. so this will double the price "per wash" therefore all your carefull calculations are out the machine with the dirty water:-(

Taking a sideways look; if two makes of washing machine take in say

5lts of water both have 2.5Kw heaters both machines will use the same amount of electricty to bring the water to the required temp.

So the only way to make one machine more efficent is to use less water, but as there is a minimum amount of water needed to wash a load of clothes the only way is to make the drum smaller, so there is less to wash, so less water so less electricty.

This could make it cheeper to run a "B" rated machine with a bigger drum.

sorry to upset your calculations, David

[Martin Angove]

Well, I don't really know a lot, but I have met a few machines in my travels and as far as I can tell they all mix-filled at 60C or below (the filling noise is different when cold is being used if the cold is at mains-ish pressure and the hot is gravity fed). No, I don't know why either. If temperature were a problem then surely the more modern machines could assess this and mix in enough cold to keep it within limits? As for the warning about the supply being 60C or lower the thing which entered my mind was whether this was purely down to construction materials - hot water in a PVC hose (for example) can cause all sorts of kinks and knots.

To add confusion to the matter, we took delivery of a new H&C fill machine yesterday (Monday), and it appears as though the hot valve is stuck, as even on the 95C wash it cold-filled! I even went so far as to make sure there was hot water within 6ft of the appliance and noted that after filling, the pipe was still cold towards the machine. And yes, I took the hose off the back of the machine and checked that water flowed through it :-)

Methinks a call to the service people is in order >:-/

Hwyl!

M.

[Martin Angove]

That's an interesting argument, but I don't quite follow. The "load" rating usually refers to dry cotton weight, so whether or not the drum is smaller, if I can physically get 4kg of nappies in, both machines will wash the same load, surely? (Leaving aside the fact that dirty nappies are never in fact dry!)

Hwyl!

M.

[N. Thornton]

The best way to do it is not to have a drum reservoir of water at all. Have a well peforated drum, and spray all run down water onto the clothes, so there is no water reservoir. It does however mean a pump to keep pumping dripoff up and onto the clothes. I'm surprised at how little this system is used, probably patented.

NT

[David H]

Yes I would agree with you, but, try this. When you have nothing better to do. Get the bathroom scales then all your clean nappies then all your clean towels then all your clean whatever, when you reach 4Kg put them all in the drum.

Then you will follow.

David.

[Buxnot]

Our hotpoint draws hot and cold on 40 degree, 50 degree and 60 degree washes, cold only on "quick wash", and hot only on 90 degree washes.

I've been sad enough to feel the feed hose get warm :)