Just bought a new washing machine (Hoover HNL 7146) to replace my
12-year old model. To my surprise (I should have checked the spec more carefully), it has only a cold water inlet. Guide book says this is more 'energy efficient'. How can that typically be true? We have a high volume of hot water remaining in airing cupboard tank after a couple of showers and a bit of dish-washing each morning. Effectively just cooling down throughout the day...
Newer machines use less water so in many houses they would be filling with the cold dead leg of the hot water anyway. I believe there is also an issue with Bio powders.
Easier to control the temperature as well - just a thermostat and heater. No external influence such as the availability of hot water and its temp.
Terry Pinnell typed
The hot water has to run through pipes, where it often spends much time cooling. There is probably enough cold water in my hot pipes to fill the machine. After the machine has filled, the really hot water just chills in the pipes. Really hot water could damage some fabrics.
There is also a move to cooler washes, 30/40 degC rather than 40/50/60degC.
The hot water is even more often too hot, which, anyway, requires more complex controls to part fill with hot and then switch to cold, which, as well as increasing the complexity/cost of the machine, increases the total solenoid water valve cycles leading to lower reliability. The issue of stored hot water is also becoming smaller here as more people use combi's/tanks are so well lagged the hot water doesn't need to be "used up" over a day.
Having said all that it's really just to make them cheaper so they can sell against the competition, I suspect!
For homes that use gas to heat water there may be increased cost using electricity to heat the wash water. Only sixpence on everybody's bill perhaps, but as Tesco say, 'every little helps'.
That's not to gainsay the points made about the leg of cold water in the pipes, too hot water, simpler controls, greater reliability, cheaper unit production cost etc
Roger R
On Mon, 29 Jan 2007 09:09:46 +0000 someone who may be Terry Pinnell wrote this:-
That is the spin manufacturers put on it, but really what they are doing is saving themselves money, not just by removing a few bits and pieces but also by having one machine for the whole of Europe.
They often claim that heating water by electricity in a large cylinder and transporting it by pipe is not as efficient as heating water in the machine. This ignores the fact that in the UK water is often not heated by electricity in the cylinder.
Provided the source of hot water is near the machine and the pipes are properly insulated they are lying when they say not using centrally heated water is more energy efficient. If the source of water is a long way away and the pipes are not insulated then there may be something in what they say. The typical UK house is between these two extremes, the source of hot water is not too far away, but the pipes are uninsulated.
This remains true despite lower wash temperatures and lower water consumption of modern machines. It is especially true where water is heated centrally by environmentally friendly means, like solar heating.
On Mon, 29 Jan 2007 11:09:18 -0000 someone who may be "Roger R" wrote this:-
That rather depends on the design. A long run of uninsulated pipe to a remote utility room means that a lot of cold will be drawn before any hot arrives and a lot of hot water will then cool down and the heat wasted. On the other hand drawing off from a short insulated run means little cold will be drawn off first and the unused hot water may be used at other fittings before it cools.
Alternatively ; a cold-fill only machine can heat it's water using the 'environmentally friendly means' of off-peak electricity from base-load nuclear power stations! Ones probability of demanding energy from a gas-turbine plant is so much less at 0h-dark-hundred! Much less Carbon Dioxide - even Tony says so! Think how many pennies less each wash takes using off-peak electricity!
On Mon, 29 Jan 2007 11:59:35 GMT someone who may be "Brian Sharrock" wrote this:-
Ha ha.
However, the failure of such large power stations tends to cause lots of problems, as the current "crisis" in Scotland shows
It probably reduces the cost to the same as using hot and cold fill:-)
Thanks for all the informative replies, much appreciated.
Here, the water is centrally heated by gas, which is cheaper than electric heating. And the utility room is almost directly below the hot water tank, so the pipe run is fairly short. Even at the kitchen sink, which is further away, the water runs hot in only about 5-10 seconds. So I suspect that, with the arguable exception of the reliability issue, this will prove a more expensive machine than the last.
BTW, I had assumed that my previous Hoover would not simply run the 'hot' water intake for a set time (or set volume), but would first wait for its temperature to rise? Is that in fact not the case, as some of the replies imply?
However it could be done the most cheaply is how it will be done.
So it'll probably be a simple timer, ignoring the pressure, flow rate, temperature, whatever...
I suppose it's too much to hope for that the cold-fill-only washing machines would incorporate a heat-exchanger, to preheat the incoming cold with the heat from any used water being flushed?
Pete
I think there is a float valve actually.
Some yonks ago; I had to replace the dish-washer ~ I know it's not what you asked ~ but there's a heat-exchanger dish-washer 'out there'. IIRC, the heated water is held in a pipe matrix while cold water inlet contra-flows and extract the heat I was enthusiastic ... then I noted the price!
I know there's an air-operated 'full-ness' switch. Ignoring the pressure, flow rate, temperature, time etc, a plastic bottle connected to the base of the drum, is connected via a tiny tube to the pressure switch mounted _above_ the drum ~ to obviate water leaks~ which ~ via the 'controller' ~ switches 'closed' the water inlet valves. Some switches detect multiple levels [Economy, half-full, Full].
It doesn't matter too much how long the valve is open - nor how much stuff is to be washed , whether it's absorbent towels or non-absorbent plastic; the sensor senses 'height of water in the drum' = pressure. {sometimes the bottle's mouth gets gunged-up with detergent residue]
There is another angle to take into account here. You can get better washing results from cold fill than hot in some circumstances (even where ultimately you are using a "hot" wash). Some protein stains etc are more easily removed with a period soakink in cold water first. Contact with hot water would tend to "set" the stain.
Not quite sure what you mean by "wait for its temperature to rise" - it would not know the temperature until after it had filled with it...
IF having filled to the required level the temperature was still too low, then it would indeed enter a heating cycle and wait until the water reached the target temp before proceeding with the next wash stage.
On Mon, 29 Jan 2007 17:13:43 GMT someone who may be "Brian Sharrock" wrote this:-
That's how it has worked in the few such machines I have looked inside.
It is one of the reasons for ensuring that the hot enters the machines at least as fast as the cold, by ensuring both are at the same pressure. Personally I prefer low pressure, almost no noise and no noticeable water hammer to damage the pipes.
temperature to rise" - it
There is another angle to take into account here. You can get better washing results from cold fill than hot in some circumstances (even where ultimately you are using a "hot" wash). Some protein stains etc are more easily removed with a period soakink in cold water first. Contact with hot water would tend to "set" the stain
This is the real reason for recent washing machines not having a hot fill. The thermal shock of hot water hitting many food and oil stains hardens them and reduces the effectiveness of the powder. Further the enzymes in biological powders begin to be killed off once the temperature starts to exceed the mid 30's C. In fact hot fill machines are/were a peculiarly British feature. I encountered this for the first time as long a go as 1976 when we went to live in Germany. None of the appartments we looked at had provision for hot water fill.
And of course it now no longer makes any sense to produce washing machines just for the British market.
The point that others have raised concerning the length of pipe runs is very real. You'd be surprised at how little water modern machines require for the wash phase. Gone are the bad old days of the Hotpoint top loader which had tubs as large as paddling pools and a thirst to match.
Graham
On mine it, supposedly, detects the drop in pressure when you start to mix the water and cloths so it can guess at how much it is washing. It then does economy washes if there isn't much. I have no idea if it works.
Mine takes in so little water it wouldn't have time to run hot. So you'd have to heat it with electricity anyway. Also makes sure the water is at the correct temperature.
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