# Heat exchanger machine question



## otterolly

Hi guys

What is the general consensus on how long a heat exchanger machine should be left on ?

Do most people turn it on using a timer etc and turn it off after your first cup ? or do most people leave it on all day and turn off last thing in the evening ?

I don't know if leaving it on all day would cause any damage to the internals ? Electricity usage is not my major worry

Thanks


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## MediumRoastSteam

Some people leave the machine on all day, some people turn it off. I personally, turn it off as I have 2 coffees per day at the weekend. Comes on on a timer in the morning, have my coffee, turn it off, and then turn it on again 1 hour before. I think there was an entry in the BB manual for a Rocket Cellini which they recommend to turn the machine off instead of leaving it idle for over two hours for some reason which I no longer remember.


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## Dylan

Most prosumer HX machines are fine to be left on all day. I only turn mine off overnight. Turning it on and off uses more electricity as it takes more to heat up the boiler from cold than to keep it ticking over.


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## 4085

OP, is your question really in reference to the need for cooling flushes? If so, the water is still sitting there so you need to flush it out anyway


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## michaelmb45

Hi otterolly

My HX machine I use a timer to come on 30 min before I get up and it stays on for a few hours for the morning rush.

If I need it in the day I turn it back on using a wemo switch so it always has at least 30min warm up.


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## otterolly

Thanks guys

dfk41.... No just wondered if my appartamento would be fine left switched on all day or if I needed to switch it off after every coffee as I did not know if damage would occur if left on for any length of time


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## Mad Wally

Dylan said:


> Most prosumer HX machines are fine to be left on all day. I only turn mine off overnight. Turning it on and off uses more electricity as it takes more to heat up the boiler from cold than to keep it ticking over.


Sorry but that is not true. The efficiency of conversion from electricity to heat is 100% and heat losses are related directly to the temperature of the machine. A cold machine has no losses.


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## 4085

Mad Wally said:


> Sorry but that is not true. The efficiency of conversion from electricity to heat is 100% and heat losses are related directly to the temperature of the machine. A cold machine has no losses.


when heating from cold the element is working flat out. Once at temp, it cycles in and out. If you measure the amount of electricity used as many have done from start up, you may well find that taking into consideration from cold the machine has to come to working temp which might take 30 to 50 mins after pressure is reached, that there is very little difference, other than on paper


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## Dylan

Mad Wally said:


> Sorry but that is not true. The efficiency of conversion from electricity to heat is 100% and heat losses are related directly to the temperature of the machine. A cold machine has no losses.


It depends on the size of the machine and how often you have a cup of coffee. But yea, it's been measured by others and it is true given the right circumstances.


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## Mad Wally

Dylan said:


> It depends on the size of the machine and how often you have a cup of coffee. But yea, it's been measured by others and it is true given the right circumstances.





dfk41 said:


> when heating from cold the element is working flat out. Once at temp, it cycles in and out. If you measure the amount of electricity used as many have done from start up, you may well find that taking into consideration from cold the machine has to come to working temp which might take 30 to 50 mins after pressure is reached, that there is very little difference, other than on paper


Sorry, just too much ignorance. It is never true.

Simple: Electrical consumption = heat losses. Cold machine = no losses. Hot machine = losses.

Everything else is irrelevant including things as "heating element is on for long time" and "must heat up all the water in the boiler again"


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## Dylan

And what do you suppose is happening when you turn off the machine? Heat loss from a once heated up boiler maybe?


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## 4085

Mad Wally said:


> Sorry, just too much ignorance. It is never true.
> 
> Simple: Electrical consumption = heat losses. Cold machine = no losses. Hot machine = losses.
> 
> Everything else is irrelevant including things as "heating element is on for long time" and "must heat up all the water in the boiler again"


Disagree, many people including myself several times, but not recently, have measured this. you are theorising in a paper calculation. A machine left on for several hours will use little or no more juice than one which is constantly switched off.....try it if you do not believe me, which you obviously do not.....then come back and share your results


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## billt

dfk41 said:


> Disagree, many people including myself several times, but not recently, have measured this. you are theorising in a paper calculation. A machine left on for several hours will use little or no more juice than one which is constantly switched off.....try it if you do not believe me, which you obviously do not.....then come back and share your results


I can't believe this canard still has circulation.

Mad Wally is quite right, you will always use more energy if a machine is on all the time. Of course if you just switch it on and off several times during the day then the difference isn't going to be large, but it will still use less energy. And I have measured the consumption of one of my machines.

My machine isn't switched off during the day; the 20 minute or so delay isn't worth the energy saving.


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## Dylan

Having done some reading on this earlier today I'll have to humbly say that my previous comments are based on anecdotal evidence and in fact wrong.

Whilst it is true that heating a boiler from cold several times a day would use more energy that keeping it cycling on the pressurestat (again, anecdotal but I think this is right) a boiler doesn't cool down that fast, so when turning it on and off the subsequent re-heats dont have as much work to do. If you were to leave the boiler to fully cool there would be such a long period between cycles that firing it up again would have been more than equalled by keeping it on.

The difference in cost is pence however, so not worth it for many with a machine that takes 30-40 mins to heat up. There is also a cost question on what wears parts out quicker, but thats another issue.

Apologies for asserting incorrect facts. Shouldn't change the crux of the question for the OP, but best for information to be correct.


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## Mad Wally

I did the math using the following assumptions:

2 liter boiler

1400 watt heater

T ambient 20°C

T boiler 120°C

Heat loss 100 watt at 120°C and linear with temperature difference to ambient

Results:

On all the time

Three shots over the day one hour on / three hours off

Power consumption:

On 1.22 kWh

On/off 0.85 kWh

So a 30% saving.

Also i believe 100 watt standby loss for an HX machine is a conservative estimate however i have not measured this personally.

Details:

Heat-up time boiler from cold: 16.3 minutes (including heat losses)

Power for heat-up from cold: 0.249 kWh

Please feel free to comment


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