Electricity consumption monitors.

[Sam Vimes]

What an interesting turn these threads take

Just back to the issue of keeping a tank powered to maintiain 70degC or having it on demand. As the Prof says there are too many variables to be able to have a definitive answer to this that fits all users. But here's something to consider.

Water at 70degC is, as the saying goes, "To hot to handle". You can spend all that energy heating the water to 70degC then go and add cold water at the point of use to make it usable for washing as an example.

There are at least two reasons that I can think of for having the tank stat set to 70degC.

1. To kill of Legionaires bacteria - although a temperature above 55degC would do this.

2. It makes the tank act as a thermal store. In other words if you have say an 150 litre tank of water at 70degC then by adding water at 10degC to this you'd get approx. 300 litres of water at 40degC. I say approx. because tanks dont have a uniform temperature throughout.

So, it could be possible on the days that the demand for hot water is low to have the stat set to something like 45degC. Then on the days when you need a lot of hot water - a couple of baths perhaps - it could be raised to 70degC in advance.

Other possibilities for savings also exist. Having a small volume localised hot water heater near the point of use for example. So instead of heating the full 150 litre tank to then run 5 or so litres of water into the kitchen sink, you could just have a small water heater in the kitchen area which you switch on when needed. Instantaneous hot water heatersare also a possibility but I've been disspointed with these in the past unless you get something powerful like an electric shower unit, which creates certain installation problems.

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Saying that certain devices are not economical to use has no meaning unless you state what you are comparing it too. Also we have to consider the convenience factor. I could go down to the local burn and bang my clothes on a rock which would cost very little but the idea is not that attractive so I don't mind paying for a machine to do it.

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Before trading in your working washing machine or whatever, do your homework. How much will you actually save by getting a better rated machine and how long will it take to recover the cost of the new machine.

 

[Jcloughie]

1. To kill of Legionaires bacteria - although a temperature above 55degC would do this.

That surprised me because I think that Alde heating provide hot water at 55 but there is a hotter anti bacterial, mode which should be run every so often to clear bacteria. The wording from IOSH say that it will incubate up to 50 and only begin to die off in excess of that.

John

 

[Ern]

That surprised me because I think that Alde heating provide hot water at 55 but there is a hotter anti bacterial, mode which should be run every so often to clear bacteria. The wording from IOSH say that it will incubate up to 50 and only begin to die off in excess of that.

John

I think our Alde water is heated to about 70 for anti-bacterial purpose. If the caravan has not been used and the heating therefore off for a couple of weeks, the initial water temperature comes up to 70 ish.

 

[Buckman]

With air source heating, the water is heated up between hours of 12 and 3am. Once water reaches optimum temperature the thermostat shuts down the machine only to switch it back on if the temperature of the water drops below 55C or whatever it has been set at.
According to the monitor this morning optimum temperature was reached at 12.30am. Hot water will not be heated up again until 12am tonight unless we over ride the setting for one hour. In that hour we will not have heating only hot water heating.

 

[ProfJohnL]

...Water at 70degC is, as the saying goes, "To hot to handle". You can spend all that energy heating the water to 70degC then go and add cold water at the point of use to make it usable for washing as an example.

There are at least two reasons that I can think of for having the tank stat set to 70degC.

1. To kill of Legionaires bacteria - although a temperature above 55degC would do this.

2. It makes the tank act as a thermal store. In other words if you have say an 150 litre tank of water at 70degC then by adding water at 10degC to this you'd get approx. 300 litres of water at 40degC. I say approx. because tanks dont have a uniform temperature throughout.

So, it could be possible on the days that the demand for hot water is low to have the stat set to something like 45degC. Then on the days when you need a lot of hot water - a couple of baths perhaps - it could be raised to 70degC in advance.

Other possibilities for savings also exist. Having a small volume localised hot water heater near the point of use for example. So instead of heating the full 150 litre tank to then run 5 or so litres of water into the kitchen sink, you could just have a small water heater in the kitchen area which you switch on when needed. Instantaneous hot water heatersare also a possibility but I've been disspointed with these in the past unless you get something powerful like an electric shower unit, which creates certain installation problems.

******

Saying that certain devices are not economical to use has no meaning unless you state what you are comparing it too. Also we have to consider the convenience factor. I could go down to the local burn and bang my clothes on a rock which would cost very little but the idea is not that attractive so I don't mind paying for a machine to do it...

In terms of caravan water heating, there are regulations that determine the maximum water temperature the heating device is allowed to produce and from memory it is 70C. It was this relatively high permitted temperature that actually made storage water heating practical for caravans for exactly because of the way you can dilute the hot water with cold to produce a larger quantity of warm water, enough to shower with, exactly the reason Sam has pointed out.
To shower without such a high storage temperature, you would need a much bigger hot, sorry warm tank, which would increase the weight and size of the heater, something the caravan manufacturers and users would not tolerate well.

Because of the restricted power available to a caravan(16Amp or less ) it would be impractical to consider electric showeres, as you need at least 6kW or more(approx 24A) to raise the temperature of the volume of water needed enough to be comfortable or practical.

Whilst the bottled gas supply in a caravan can probably supply that sort of gas rate, designing a safe, regulation compliant, practical, instantaneous gas water heater suitable for a touring caravan has not yet happened.

 

[Sam Vimes]

That surprised me because I think that Alde heating provide hot water at 55 but there is a hotter anti bacterial, mode which should be run every so often to clear bacteria. The wording from IOSH say that it will incubate up to 50 and only begin to die off in excess of that.

John

The figure I gave of 55degC came from the information on our Hot Water Solar panel if my memory serves me correctly. Other information seems to indicate that the bacteria is dormat below 20degC, active between 20-45 and then starts to die off at various rates from 50degC upwards. I think the bacteria die almost instantanously at 70degC so perhaps this is why that figure is chosen for thermostats.

It appears to me that its a bit more complicated than that though since hot water tanks may be at 70degC but this is usually the top of the tank and there may be a 20/30 deg temperature drop towards the bottom. Of course running off hot water introduces colder water at the bottom.

I also wonder if the Cholrine added to the supply also has some affect on the bacteria. We have a whole house water filter that removes chlorine and we are advised to flush the pipes with something like a Milton solution once a year when we change the filters