Are long 10mm pipes to kitchen sink OK?

[MJGas]

The fact is. you shouldnt put a secondary return on plastic pipe...

 

[JBPHS]

Putting a secondary recirc onto 10m of 10mm plastic fed from an unvented cylinder is bonkers mate.

Don't wanna be rude... but...

What would steel say Dan? Something about keyboards?



James.

 

[Dan Robinson]

Totally forgot about the secondary return on plastic pipe too

Shall go outside and flagellate myself .

What Steel gets up to with his keyboards is his own business

 

[ringi]

A secondary return is OK on plastic, provided the pump does not run for long at a time, and the loop is allowed to cold down for a lot of the day.

It is when the secondary return runs for most of the time, often at 65 or more that there are problems, the chlorine in the water eats the plastic and unlike a CH system keeps getting topped up as fresh water is introduced to the system.

(There was problems in the USA when plastic pipe were first used due to loops running 24hr a day with very hot water.)

 

[MJGas]

A secondary return is OK on plastic, provided the pump does not run for long at a time, and the loop is allowed to cold down for a lot of the day.

It is when the secondary return runs for most of the time, often at 65 or more that there are problems, the chlorine in the water eats the plastic and unlike a CH system keeps getting topped up as fresh water is introduced to the system.

(There was problems in the USA when plastic pipe were first used due to loops running 24hr a day with very hot water.)

Yeah try getting a plastic pipe manu to give you that in writing

 

[ringi]

This is what Speedfit says....

A continuously operated re-circulating system is a water-replenished circulating system which is maintained at a constant high temperature to provide a constant source of hot water.

Continuously operated re-circulating systems are used to distribute constant hot water to draw off points that may be distant from the source or hot water storage vessel.

Continuously operated re-circulating systems are very different from conventional hot water supply and central heating systems found in domestic properties, for which our products have been tested to, under either BS7291 Class S or WRAS approval standards, and for this reason Speedfit products must not be used on any continuously operated re-circulating systems as they are not approved under the current version of these standards.

The exception would be those systems which have been designed for domestic situations with intermittent temperature of less than a maximum of 65°C. This is in accordance with BS7291.

I think "Continuously" is the key word....

 

[Dan Robinson]

This is what Speedfit says....

A continuously operated re-circulating system is a water-replenished circulating system which is maintained at a constant high temperature to provide a constant source of hot water.

Continuously operated re-circulating systems are used to distribute constant hot water to draw off points that may be distant from the source or hot water storage vessel.

Continuously operated re-circulating systems are very different from conventional hot water supply and central heating systems found in domestic properties, for which our products have been tested to, under either BS7291 Class S or WRAS approval standards, and for this reason Speedfit products must not be used on any continuously operated re-circulating systems as they are not approved under the current version of these standards.

The exception would be those systems which have been designed for domestic situations with intermittent temperature of less than a maximum of 65°C. This is in accordance with BS7291.

I think "Continuously" is the key word....

hhhmmm - I wonder what manufacturer took a deeeeeeeeeppp sigh when I spoke to them recently about this very same subject .

 

[MJGas]

Yes and try getting a definition of the word continuously off them. Ring them up and see if they will give it you in writing. Of when you can use plastic piping with a secondary return.

 

[ringi]

I read it to mean that I can have a system with a push button that runs the pump for 10 minutes before a shower that is taken a few times a day. But not a system that tried to keep the water hot all the time.

So for my case, I would not risk it, as a PIR in the kitchen could have the pump running for a few hours.

I also question using plastic pipes where the hot water will be in use for many hours a day. E.g. showers in a swimming pool could be operating for over 12hr without the pipe being able to cool down even without any secondary return setup.

 

[MJGas]

You could always use mlcp

oh and what if the push button jammed on continuous

 

[Whitespirit66]

I think one or two places have started doing 10mm pipe in copper

Also, if 22mm holds too much water, I think 15mm pipe may possibly be available - in copper or plastic.

But don't quote me.


Jeez. And I thought my life was complicated!

 

[endecotp]

Do you know how to take account of the water loosing heat to the pipe?

Volume of copper in 1m of 10mm pipe with 1mm wall thickness = 2.8e-5 m3
Density of copper = 8.9 g/cm3 = 8.9e3 kg/m3
Specific heat capacity of copper = 0.39 J/gK = 390 J/kgK

So energy needed to heat 1m of pipe from 20C to 60C = 40 x 390 x 8.9e-3 x 2.8e-5 = 3.9e3 J

Heating 1l = 1kg of water by 40K requires 40 x 4181 = 1.7e5 J

So heating 1m of copper pipe takes the energy in 3.9e3 / 1.7e5 = 0.023 l of hot water.

Hmm. That sounds rather low to me! Anyone care to check?

 

[ringi]

endecotp,

Your calcs look correct, but it excludes heat lost from the copper pipe to the air round it. However I expect that is not important.

But from my practical experience hot water takes longer to arrive at a tap then is explained by all the maths so far on this thread.

 

[Agile]

I have my own interest in one aspect of this which the OP seems to be forgetting.

The flow rate to the kitchen tap through 10mm copper tube may not reach his 6 li/min depending on the supply pressure.

Does anyone have figures on the flow rate that will flow through 10 mm copper of say 10m length at different pressures?

Tony

 

[Dan Robinson]

Like I said in the cc. I am getting circa 7.5 litres a say 5 bar through 10 mm plastic.