How does a parted cold “tank in tank” dhw tank reheat?

[ringi]

As I understand it.

A “normal” dhw tank heats from a coil at the bottom, as cold water sinks to the bottom when 75% of the hot water has been used, there is still some hot water at the top. As the tank reheats, the remaining hot water at the top is not disturbed, so can be used while the tank reheats.

A “tank in tank” heats by the water in the outer tank being pumped var the boiler. The takes the coldest water from the bottom of the outer tank at say 10c, heats it to say 30c and puts it into the top of the outer tank. So would this not reduce the temperature of the remaining hot water at the top of the inner tank to 30c until part way through the heating process?

If so how can hot water be used while the tank is being reheated?

 

[45yearsagasman]

Don't have a clue what you're talking about. Never heard the term tank in tank.

 

[Terry lambert]

Tank in tank

instead of a coil with water from the boiler/heat source circulating through it to heat the water in the cylinder, it uses a cylinder inside the cylinder which gives a larger surface area and so more efficient heat transfer.

Water will naturally stratify and so the hottest water will always be at the top ( read stratification)

 

[ringi]

Tank in tank

Water will naturally stratify and so the hottest water will always be at the top ( read stratification)

I don’t believe this will happen while the water in the outside tank is being pump through the boiler, due to the flow rate of the water. At other times it will clearly be the case.

 

[ringi]

Don't have a clue what you're talking about. Never heard the term tank in tank.

They are not that common in the UK.

See http://www.acv.com/int-en/25_07/19/app.rvb

 

[jeff the gasman]

Think he's talking primatic cylinder!
Jeff

 

[St0rmer66]

It's just like having a bigger coil, it works no differently in terms of where the hot water will rise to etc.

 

[ringi]

Think he's talking primatic cylinder!
Jeff

I am not!

 

[Dan Robinson]

It's just like having a bigger coil, it works no differently in terms of where the hot water will rise to etc.

Until you try and drain the bugger.


Putting a 320 litre bad boy in in a couple of weeks. Hope the chlorine doesn't get to it .

 

[Gasguru]

As I understand it.

A “normal” dhw tank heats from a coil at the bottom, as cold water sinks to the bottom when 75% of the hot water has been used, there is still some hot water at the top. As the tank reheats, the remaining hot water at the top is not disturbed, so can be used while the tank reheats.

A “tank in tank” heats by the water in the outer tank being pumped var the boiler. The takes the coldest water from the bottom of the outer tank at say 10c, heats it to say 30c and puts it into the top of the outer tank. So would this not reduce the temperature of the remaining hot water at the top of the inner tank to 30c until part way through the heating process?

If so how can hot water be used while the tank is being reheated?

Agree with you, which is why tank in tanks are generally used with very high output boilers setup as a hot water priority system and are common on the continent. If you don't match the calorifier with the boiler to ensure a very rapid re-heat they won't perform properly.

 

[jeff the gasman]

Oooh pardon me if your OP sounded like you didn't know what you were talking about x

 

[ringi]

As I understand it.

A “normal” dhw tank heats from a coil at the bottom, as cold water sinks to the bottom when 75% of the hot water has been used, there is still some hot water at the top. As the tank reheats, the remaining hot water at the top is not disturbed, so can be used while the tank reheats.

A “tank in tank” heats by the water in the outer tank being pumped var the boiler. The takes the coldest water from the bottom of the outer tank at say 10c, heats it to say 30c and puts it into the top of the outer tank. So would this not reduce the temperature of the remaining hot water at the top of the inner tank to 30c until part way through the heating process?

If so how can hot water be used while the tank is being reheated?

Agree with you, which is why tank in tanks are generally used with very high output boilers setup as a hot water priority system and are common on the continent. If you don't match the calorifier with the boiler to ensure a very rapid re-heat they won't perform properly.

Thanks Gasguru,

Am glad I was not going mad, nothing in the acv docs seem to say you need a very high output boiler if you wish to be able to use hot water while the tank is recovering. (Unless you have the boiler running most of the time, so having the return too low to get much condensing.)

 

[Dan Robinson]

nothing in the acv docs seem to say you need a very high output boiler if you wish to be able to use hot water while the tank is recovering.

The tech specs should give a fairly hefty clue .

(Unless you have the boiler running most of the time, so having the return too low to get much condensing.)

Look at how it works again