Cheaper to leave immersion on all the time?

Nono Toure

I have a power shower which I use over the electric shower, electric shower is crap. I used to turn on the heat to get the power shower heated up, but seeing as it's summer I don't have the heating on.

I used to then turn the immersion on (bath) for an hour or so to get water for the shower, but someone told me it's cheaper to leave the immersion on (sink) 24/7 as it only tops up the hot water every so often and the water will already be fairly warm so it doesn't have much heating to do.

Is it cheaper/cheap to leave the immersion on (sink) 24/7 as opposed to only putting it on daily for 1 hour (bath) ?

Thanks

2011

It is best to only heat the amount of water that you require (so far as is possible). So leaving the immersion on all of the time would be very inefficient and costly.

Heating water electrically is far more expensive than heating it with oil or gas. If I were you I would install a zone valve on your heating system allowing the radiators to be turned off during eh summer so that the water can be heated using the boiler. This is a far cheaper solution.

Bruthal

Also, just leaving it on sink the whole time will only have enough water heated for an extremely short shower.

If an immersion cylinder had 100 percent insulation/thermal isolation, then leaving the immersion on full time would work fine. But they don't.

As said, it would be a lot better to use the central heating to do it. With radiator zone(s) off via motorized valve for summer.

crossmolinalad

Bruthal wrote: »

Also, just leaving it on sink the whole time will only have enough water heated for an extremely short shower.

If an immersion cylinder had 100 percent insulation/thermal isolation, then leaving the immersion on full time would work fine. But they don't.

As said, it would be a lot better to use the central heating to do it. With radiator zone(s) off via motorized valve for summer.

We bought a immersion heater in the Netherlands called a daalderop vitroc 120 litre electric boiler
It works on our storage heater meter heats up at nighttime and allday hot water 65 degrees
When u tough the boiler/waterheater on the outside its stone cold and using about a 3 euros a week heating
Works perfect using it with 5 people and hot water never ends

jennyhayes123

We moved house this year, we had intended to use our electric shower in summer but I don't like not having hot water in taps so I decided to leave immersion on all time. We have a meter. We have gone from using €20 credit a week to €25 so very reasonable and well worth it. Don't turn on and off as you have to heat from cold every time.
There are 6 of us in house

Nono Toure

jennyhayes123 wrote: »

We moved house this year, we had intended to use our electric shower in summer but I don't like not having hot water in taps so I decided to leave immersion on all time. We have a meter. We have gone from using €20 credit a week to €25 so very reasonable and well worth it. Don't turn on and off as you have to heat from cold every time.
There are 6 of us in house

Hi,

25 credit, does that mean your esb bills are gone from 20 euro per week to just 25euro per week? If so, that's not bad at all. Is the immersion heating on bath or sink?

2011

jennyhayes123 wrote: »

We moved house this year, we had intended to use our electric shower in summer but I don't like not having hot water in taps so I decided to leave immersion on all time. We have a meter. We have gone from using €20 credit a week to €25 so very reasonable and well worth it. Don't turn on and off as you have to heat from cold every time.
There are 6 of us in house

On the basis that a unit of electricity costs about €0.20 then €3.00 will buy you about 15 units of electricity.
A unit of electricity = 1 kW for one hour.
A watt = 1 joule per second.
Therefore 15 units of electricity = 15 x 1000 x 3600 = 54,000,000 or 54 x 10^6 Joules.

Tap water is about 7 DegC. 50 DegC would be a nice minimum temperature form a hot tap. That is a temperature increase of 43 DegC.

Using this formula (and assuming no losses) we can work out how much water the 15 units of electricity would heat:
E = m × c × dT

Where:
E is the energy transferred in joules, J = 5.4 x 10^6
c is the specific heat capacity in J / kg / °C = 4200
dT is the change in temperature in °C = 43
m is the mass of the water in kg = Unknown

Therefore:

54 x 10^6 = m x 4200 x 43

m = 54 x 10^6 / (4200 x 43) = 30

So m = 300 kg of water which is equal to 300 litres of water

Therefore if we ignore all losses for €3.00 you will have 300 litres of water per week, so a weekly allowance of 50 litres of hot water per occupant.
I can't really see how the "hot water never ends"

Nono Toure

2011 wrote: »

On the basis that a unit of electricity costs about €0.20 then €3.00 will buy you about 15 units of electricity.
A unit of electricity = 1 kW for one hour.
A watt = 1 joule per second.
Therefore 15 units of electricity = 15 x 1000 x 360 = 5,400,000 or 5.4 x 10^6 Joules.

Tap water is about 7 DegC. 50 DegC would be a nice minimum temperature form a hot tap. That is a temperature increase of 43 DegC.

Using this formula (and assuming no losses) we can work out how much water the 15 units of electricity would heat:
E = m × c × 𝝙t

Where:
E is the energy transferred in joules, J = 5.4 x 10^6
c is the specific heat capacity in J / kg / °C = 4200
𝝙t change in temperature in °C = 43
m is the mass of the water in kg = Unknown

Therefore:

5.4 x 10^6 = m x 4200 x 43

m = 5.4 x 10^6 / (4200 x 43) = 30

So m = 30 kg of water which is equal to 30 litres of water

Therefore if we ignore all losses for €3.00 you will have 30 litres of water per week, so a weekly allowance of 5 litres of hot water per occupant.
I can't really see how the "hot water never ends"

:o:D

2011

jennyhayes123 wrote: »

Don't turn on and off as you have to heat from cold every time.

This is not cost effective because:

1) There is a cost associated with keeping the water hot. This is because insulation is not perfect. In simple terms this means that every hour that the hot water is not used will cost money to maintain the temperature.

2) It is very expensive to heat water electrically.


Did you ever hear the expression "Run like you have left the immersion on" ??

:D:D:D:D

TheChizler

2011 wrote: »

jennyhayes123 wrote: »

We moved house this year, we had intended to use our electric shower in summer but I don't like not having hot water in taps so I decided to leave immersion on all time. We have a meter. We have gone from using 20 credit a week to 25 so very reasonable and well worth it. Don't turn on and off as you have to heat from cold every time.
There are 6 of us in house

On the basis that a unit of electricity costs about 0.20 then 3.00 will buy you about 15 units of electricity.
A unit of electricity = 1 kW for one hour.
A watt = 1 joule per second.
Therefore 15 units of electricity = 15 x 1000 x 360 = 5,400,000 or 5.4 x 10^6 Joules.

Tap water is about 7 DegC. 50 DegC would be a nice minimum temperature form a hot tap. That is a temperature increase of 43 DegC.

Using this formula (and assuming no losses) we can work out how much water the 15 units of electricity would heat:
E = m c t

Where:
E is the energy transferred in joules, J = 5.4 x 10^6
c is the specific heat capacity in J / kg / C = 4200
t change in temperature in C = 43
m is the mass of the water in kg = Unknown

Therefore:

5.4 x 10^6 = m x 4200 x 43

m = 5.4 x 10^6 / (4200 x 43) = 30

So m = 30 kg of water which is equal to 30 litres of water

Therefore if we ignore all losses for 3.00 you will have 30 litres of water per week, so a weekly allowance of 5 litres of hot water per occupant.
I can't really see how the "hot water never ends"

3600 seconds in an hour!

300 L isn't huge either though.

2011

TheChizler wrote: »

3600 seconds in an hour!

300 L isn't huge either though.

I stand corrected! :mad::mad:
Secondary school physics lets me down again!

So 50 litres of hot water per occupant per week :eek:
Slightly less unhygienic

Joe1919

I did a test once on a green insulated copper cylinder 18 X 30 inches to calculate the 'standby' electrical consumption of the immersion in the 'sink' position at 60 c.
The electrical consumption was a little under 3kw/hr over a 24 hour period, so we are probably talking about 60 cent/day to keep the immersion kept on at sink only with no water used.
I reckon this could be reduced a small bit by possibly wrapping green insulation with tinfoil and fitting an additional lagging jacket over. Also take note that pipe work close to cylinder was not insulated so there may be loss there. There is also probably loss due to heat in top of cylinder being radiated down to colder water at bottom but I dont think this can be easily prevented.

2011

Joe1919 wrote: »

I did a test once on a green insulated copper cylinder 18 X 30 inches to calculate the 'standby' electrical consumption of the immersion in the 'sink' position at 60 c.
The electrical consumption was a little under 3kw/hr over a 24 hour period, so we are probably talking about 60 cent/day to keep the immersion kept on at sink only with no water used.
I reckon this could be reduced a small bit by possibly wrapping green insulation with tinfoil and fitting an additional lagging jacket over. Also take note that pipe work close to cylinder was not insulated so there may be loss there. There is also probably loss due to heat in top of cylinder being radiated down to colder water at bottom but I dont think this can be easily prevented.

You do realise that the "sink" element only heats a small portion of water that is at the top of the tank?
It would be enough to fill a "sink", not enough for a shower or bath.

Besides my points that illustrate why this is a costly solution in post #9 still stand.

Sleeper12

2011 wrote:

So 50 litres of hot water per occupant per week Slightly less unhygienic

I use that much everyday just having a shower.:)

Nono Toure

2011 wrote: »

You do realise that the "sink" element only heats a small portion of water that is at the top of the tank?
It would be enough to fill a "sink", not enough for a shower or bath.

When mine is on sink I can get a 10 min shower out of it at high pressure.

Sarn

The 'sink' part also gives me plenty for a power shower. I guess it depends on how long a shower you like.

PopTarts

Sink part also works for me.

I'd have enough for 10-15 min shower and a sink full for a shave, face wash etc.

Sleeper12

Nono Toure wrote:

When mine is on sink I can get a 10 min shower out of it at high pressure.

It depends on what you are calling high pressure. My shower would use a full cylinder of hot water in 10mins.

EDIT: I'm just thinking its possible some posters have their immersion wired backwards SINK actually heating bath & BATH only heating sink element.
Its possible that their thermostat is faulty or set too high
Its either that or the story of the loaves & fishes comes to mind

Bruthal

Nono Toure wrote: »

When mine is on sink I can get a 10 min shower out of it at high pressure.

Pressure...... volume. The relationship between them is usually confused.

Have a near cold shower and you might get an hour long shower.

Joe1919

By the way, on the test I mentioned, the water output temperature and quantity was measured. The 'sink' position gave an output of 12 litres at about 57c before the temperature started to drop. An additional 6-8 litres of warmish (about 50 reducing to 40c) water was measured before the water went cold. The 'bath' position was not measured.

Its not recommended to turn down immersion temperature much below 60 c as bacteria can multiply, especially at 40c. I think some type of time switch has the potential to save on standby costs, but if the person showers early in the morning, the switch would need to be set to come on an hour (or two) beforehand to 'boost' water temp etc.

There are different hot water cylinders and different immersion heater lengths out there.
It is possible to do a rough calculation of the 'stanby' loss (what it costs just to keep the hot water there on standby without use) in your hot water system. For example, if you go away regularly for weekends etc., simply take the esb meter readings when you go and when you come back, and compare the usage over the fixed period with the water ON in one case and the water OFF in the other, and the difference should be your water usage. (This should allow for other standby appliances like fridge, alarms etc by comparing like with like etc)

Bruthal

Sarn wrote: »

The 'sink' part also gives me plenty for a power shower. I guess it depends on how long a shower you like.

Either a very short one, or a cold one.

2011

Joe1919 wrote: »

I did a test once on a green insulated copper cylinder 18 X 30 inches to calculate the 'standby' electrical consumption of the immersion in the 'sink' position at 60 c.
The electrical consumption was a little under 3kw/hr over a 24 hour period, so we are probably talking about 60 cent/day to keep the immersion kept on at sink only with no water used.

Nice one.
So that is €219 per annum.

By the way, on the test I mentioned, the water output temperature and quantity was measured. The 'sink' position gave an output of 12 litres at about 57c before the temperature started to drop.

So that is €219 to just to keep 12 liters of water at the set point for a year:eek::eek:
What a waste of money :mad:

I wonder what benefit people think they are getting for this money?

Clearly heat is being lost from the water because the immersion is required to maintain the set point. This heat escapes into the surrounding air.
Whereas if the immersion was only on when required less heat would be lost to the surroundings, resulting in more cost savings. This is why immersion timers were invented.

As has been pointed out earlier an immersion on all of the time would only make sense if it were possible to have perfect insulation, which of course is not an option.

jennyhayes123

Nono Toure wrote:

25 credit, does that mean your esb bills are gone from 20 euro per week to just 25euro per week? If so, that's not bad at all. Is the immersion heating on bath or sink?

Yes. I was topping up by €20 whilst oil was heating water. Now I top up by €25. I have it on bath all time. Our cylinder is bigger than standard cylinder