Why are cold fill washing machines A+ rated?

kildarejohn · 14-03-2019 5:09pm #1

Most washing machines available today are cold fill only. This means they have to heat the water from c. 10 C (in winter) to 40 C using an electric immersion heater in an un-insulated steel drum. This uses at least 2kWhr for 60 litres.
A dual fill machine can use hot water heated at zero cost, with zero CO2 emission by your solar hot water panels.
Why are cold fill only machines even allowed, never mind rated as A++?

Gumbo · 14-03-2019 6:14pm

kildarejohn wrote: »

Most washing machines available today are cold fill only. This means they have to heat the water from c. 10 C (in winter) to 40 C using an electric immersion heater in an un-insulated steel drum. This uses at least 2kWhr for 60 litres.
A dual fill machine can use hot water heated at zero cost, with zero CO2 emission by your solar hot water panels.
Why are cold fill only machines even allowed, never mind rated as A++?

You are assuming people will have solar installed and then enough hot water to send to the WM.

kildarejohn · 14-03-2019 7:40pm

kceire wrote: »

You are assuming people will have solar installed and then enough hot water to send to the WM.

I mentioned solar in the OP as the best/cheapest form of form heating, but ANY form of central water heating (e.g. condensing boiler, solid fuel, heat pump, even night-rate immersion) would be more energy efficient/cheaper than heating water in the washing machine drum.

I believe that giving an A+ rating to a single fill machine is unjustified when dual fill machines are always more energy efficient, regardless of what form of domestic hot water system is in use.

KildareP · 14-03-2019 7:49pm

I'm not sure of how a hot fill machine would be more efficient?

Firstly, because of the extremely low volume of water most machines work with today, nowhere near 60 litres on the heating cycle, unless your hot water source is right next to the machine then most of the fill water will have been drawn off the cold water that was standing in the pipework so by the time the hot water got to the machine it has stopped calling for water. And then you have however many litres of hot water now standing in that same pipework, shedding it's heat.

Secondly, because hot fill machines in the past tended to only draw from the hot fill on a wash cycle in excess of 60C. Your average household wash only needs max. 40C in which case a hot fill machine would have only drawn off the cold fill anyway. I don't think any of the dual fill machines would "mix" the two inputs either, it would either draw hot, or cold, depending on the wash cycle temperature - but not both at the same time.

dclifford · 14-03-2019 7:55pm

The WM will heat enough water for the WM. Therefore, efficient
A hot water system will heat more water than needed by the WM. If the hot water system didn't let all of its energy go to use, then it has waste. So not fully efficient.

Calahonda52 · 14-03-2019 9:05pm

It is doable on a single input by:
1: fitting a secondary pump on a hot water loop from the tank so that always hot water at the intake.
2: use a Thermostatic mixing valve to blend the water to the required temp.
Downside is that rinsing will be in hot water also

kildarejohn · 14-03-2019 11:11pm

Posters KildareP and DClifford may be pedantically correct in terms of thermal efficiency of single fill being comparable to dual fill, but my point is about cost/CO2 emissions.
It may be more thermally "efficient" to use 1kWhr of high cost/high CO2 electricity compared to 1.2kWhr of cheap energy from solar/heat pump/solid fuel etc, but which is better?
People tend to exaggerate the importance of heat loss in the circulation pipework. In a typical semi-d the pipe run from the hot water cylinder to the kitchen is 10m of 12mm pipe and only holds c. 1.5 litre of water. So the "waste" heat in the circulation pipe is less than 10% of the heat going into the machine drum (and down the drain). Anyway the heat loss from the pipe is not real waste, as it goes to heat the house.
Calahonda's idea is interesting, but I would leave out the circulating pump, since as noted above, capacity of pipe is small anyway, hot water will reach the machine in half minute.

quentingargan · 15-03-2019 10:04am

My cold-fill washing machine uses about 620 watt-hours for a complete cycle. Before that, i had spent a lot extra on a dual-fill machine, only to discover (some already covered)

The machine automatically used both hot and cold for the first fill (I guess in case the water was hotter than my 40C setting)
The hot water was barely getting through the pipes when the machine finished its first fill

I now have a hose on my utility room tap. If I have heaps of solar hot water, I use this to fill through the detergent drawer from the hot tap. Otherwise, i let it do its thing late at night using off-peak power.

kildarejohn · 16-03-2019 7:16pm

quentingargan wrote: »

My cold-fill washing machine uses about 620 watt-hours for a complete cycle. Before that, i had spent a lot extra on a dual-fill machine, only to discover (some already covered)
The machine automatically used both hot and cold for the first fill (I guess in case the water was hotter than my 40C setting)

The hot water was barely getting through the pipes when the machine finished its first fill

I now have a hose on my utility room tap. If I have heaps of solar hot water, I use this to fill through the detergent drawer from the hot tap. Otherwise, i let it do its thing late at night using off-peak power.

Interesting post Quentin.
Your dual fill machine sounds like it was very poorly designed. It is amazing that a manufacturer would put in the hardware for dual fill (e.g. dual solenoid valves) and not put in an intelligent programme. This brings me back to Topic of post - why do authorities allow this? The only logical explanation as to why the manufacturers of Quentin's machine didn't bother with a sensible programme to manage hot/cold water input is because the authorities who define A+ rating didn't require them to.

Your current approach seems like good energy saving, but I don't think I or my spouse would be happy with the hose in the drawer approach!

quentingargan · 17-03-2019 2:25pm

kildarejohn wrote: »

Interesting post Quentin.
Your dual fill machine sounds like it was very poorly designed. It is amazing that a manufacturer would put in the hardware for dual fill (e.g. dual solenoid valves) and not put in an intelligent programme. This brings me back to Topic of post - why do authorities allow this? The only logical explanation as to why the manufacturers of Quentin's machine didn't bother with a sensible programme to manage hot/cold water input is because the authorities who define A+ rating didn't require them to.

Your current approach seems like good energy saving, but I don't think I or my spouse would be happy with the hose in the drawer approach!

A sensible programme would;

Run the hot tap until hot water arrived at the machine (bearing in mind that if there is no hot water, stop looking for it after X seconds
Measure the temperature (might be up to 60C) and mix the water to provide water no hotter than you have selected for the cycle
Even still, the drum and thermal mass of the machine and clothes will cool the water so it will then have to heat the water backup to your chosen temperature
A few people here might suggest that the first item would be wasting water.

Using my machine at night costs about 5c per wash. Feeding it with hot water would halve that. I don't see consumers paying for all the above.

Ubbquittious · 17-03-2019 2:56pm

quentingargan wrote: »

A sensible programme would;
Run the hot tap until hot water arrived at the machine (bearing in mind that if there is no hot water, stop looking for it after X seconds

Measure the temperature (might be up to 60C) and mix the water to provide water no hotter than you have selected for the cycle

Even still, the drum and thermal mass of the machine and clothes will cool the water so it will then have to heat the water backup to your chosen temperature

A few people here might suggest that the first item would be wasting water.

Using my machine at night costs about 5c per wash. Feeding it with hot water would halve that. I don't see consumers paying for all the above.

So only a few quid a year. Unless you are off the grid it isn't really worth making a song and a dance over it so.
I have a dish washer that throws up a random number of minutes to complete a cycle and I wonder if I fed it with warmer water would it reduce the time taken to complete.

I was thinking of a system where the washing machine could have a wireless sensor near the hot water tank and it could dump the initial cold water from the pipe and use only the warm water if there is warm water available. This would waste a few litres but would mean much less heating by the machine. Just depends on if you mind dumping a few extra litres

kildarejohn · 19-03-2019 12:15pm

Ubbquittious wrote: »

So only a few quid a year. Unless you are off the grid it isn't really worth making a song and a dance over it so.

Ubbiq. is right that its only a "few quid", how much will depend on all the issues raised in previous posts - it could be anything from €5 a year to €30 a year depending on your circumstances, whether you have very good solar water heating etc. So over the lifetime of a washing machine (6-10 years) a dual fill machine with intelligent programming could save you anything from €30 to €300. Personally, I would be happy to pay €100 more for such a machine - if it was available - but wouldn't be the right choice for everyone.

Why are cold fill washing machines A+ rated?

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