3kw for 15mm pipe?

[mutley racers]

Hi guys, i have just been thinking. In a book i have it says that 15mm copper tube can carry 3kw.

So i am thinking that a indirect cylinder only needs 3kw to get the out put. Is it possible to pipe up the flow and return for the hot water in 15mm pipe?

Am interested to hear what you all have to say.

Regards

Lee

 

[Toddyplumb]

Are you thinking of a 3KW immersion heater ?
What is the diameter of the primary coil ? And what is its rating ? Bet its more than 3KW

 

[mrlennie]

On another note most standard indirect cylinders take an age to heat up so you'd want max flow.

 

[quality]

Hi guys, i have just been thinking. In a book i have it says that 15mm copper tube can carry 3kw
Lee

3Kw of what gas or water or heat transfered

 

[mutley racers]

The diameter of the coil seems really small. About 12mm i think.

Am not sure what the kilowatt rating is for the vessel though.

I just know that when you size a boiler for an indirect system you normally add 3kw for the cylinder.

Thanks for your replies

Regards

Lee

i would imagine, heat transferred

 

[quality]

It takes 4.18 Kj to raise 1 Kg of water 1 degrees centigrade - 1 Kw is 3600 kj do the math
I think that's it but it is late
cheers

 

[tamz]

The heat carrying capacity of 15mm copper is around 10kw depending on length, flow rate and temperature drop.

As Quality said you can work it out with the formula

litres x deltaT x specific heat capacity of water/seconds in an hour
eg 200 x 50 x 4.186/3600 = 11.63kw assuming starting from cold.
So it would take 11.63kw of energy to raise the temp of 200 litres of water by 50 deg.

By transposing the formula you could work out how long it would take to heat 200 litres with 10kw
200 x 50 x 4.186/10=4186 seconds (nearly 70 minutes)
Compare that to a coil connected to 22mm where the heat carrying capacity is around 22kw.
200 x 50 x 4.186/22=1903 seconds (about 32 minutes)

Transposed again
seconds x kw/deltaT x 4.186 = litres
eg 1903 x 22/50 x 4.186 = 41866/209.3 = 200 litres

Play around with the numbers and see what you get (you can change everything except the 4.186)

This all depends on what size boiler, what type system, flow rates, coil capacity etc.
Few cylinder manufactures actually state the reheat times using the coil as there are so many variables, rather they quote the coil surface area.
If you have a 15kw boiler on an S plan the flow of water would be shared with the rads and the cylinder return would most likely have a balancing valve fitted so in reality 15mm would do for the hot water.
A 24kw boiler with a divertor valve system (which would allow the full capacity to go to the cylinder) would be better with 22mm primaries.
It is all horses for courses.
Work it out to your (the customers) requirements and fit it to suit.

Enough brain work. I'm off to bed

 

[ferret]

Hi mutley basically yes you can and it will work but it will take longer to heat up , but why would you want to??? I have seen whole installs on 15mm after the boiler primaries and they work , just a pig to balance

 

[Toddyplumb]

If you do go the 15mm route make sure you rig up some sort of air seperator just before the coil inlet or you will trap air in the top of the coil !
As Tamz said the manufacturers state coil areas as each size of cylinder has to be able to heat up in less than 25 mins (I think )

 

[doitmyself]

Hi guys, i have just been thinking. In a book i have it says that 15mm copper tube can carry 3kw.

The figures you see quoted are related to using the pipe to feed radiators. The flow rate (litres/minute) through a radiator is proportional to the wattage of the radiator (1kw = 1.44l/min, 2 KW = 2.88 l/min). The speed (metres/min) at which the water has to flow through a pipe is inversely proportional to the cross-section area of the pipe - the smaller the pipe the greater the speed to achieve the same flow rate. So 10kW through a 15mm pipe has a speed of 1.5m/sec; but through a 22mm pipe it will be only 0.68m/sec.

If the speed is too low (below about 0.3m/sec) there is a danger that sludge will collect in horizontal runs. If it is too high, above 1.5m/sec, the sound of the water flowing though the pipe can be heard. Pipes are therefore sized (or should be) to give a flow rate between the two limits. The higher the speed of the water, the greater the friction in the pipe, so the head will be greater, which means a more powerful pump.

So i am thinking that a indirect cylinder only needs 3kw to get the out put.

I assume you get the 3kW from the allowance added central heating requirement to give the boiler size required. This allowance is added so there is some spare capacity to reheat the cylinder while the central heating is on. When the CH is off, the full output of the boiler can be used to reheat the cylinder.

15mm pipe might be able to deliver the heat to a HW cylinder, but the speed will be too high, so it will be audible. Range cylinders warm-up times assume a flow rate of 15 litre/min or 0.25 litres/sec. With a 15mm pipe this gives a speed of 1.73m/sec, which is well above the high limit for noise.

 

[mutley racers]

Wow, thank you guys. This is amzing stuff you are telling me.

Now where did you learn all this stuff? I have never learnt anything like this at college.

Are there books or something that gives you all this info?

I am interested to know and learn.

Cheers guys

 

[quality]

Wow, thank you guys. This is amzing stuff you are telling me.

Now where did you learn all this stuff? I have never learnt anything like this at college.

Are there books or something that gives you all this info?

I am interested to know and learn.

Cheers guys

Are you first year at college or ?

 

[tamz]

Wow, thank you guys. This is amzing stuff you are telling me.

Now where did you learn all this stuff? I have never learnt anything like this at college.

Are there books or something that gives you all this info?

I am interested to know and learn.

Cheers guys

Learned it all in collage. Covered in 2nd or 3rd year?? and more in depth in 4th year. But that was in the 70's. We used to have 1 1/2 hours a day for maths. Even taught how to do 3 dimensional trigonometry.
I did another year after that as well for technician grade (that no one would pay the rate for). Then a Scotec in building services (equivilent to HNC).

And who says plumbers are thick