10 mm Pipe lagging and radiator fitting - local supplier

[Lusi83]

So now I'm confused...
I've only just insulated under the floor boards (200mm mineral wool netted up) - so it how long the pipes have been there isn't relevant and there is quite a big space under there (on a slope - approx 4ft at highest part) - almost an upside down attic.

If I had 8mm pipes in a well insulated attic shouldn't I insulate them?


If I used 15mm insulation wouldn't I have to mess around with taping it up or something ...and a lot of the pipes are at the lowest point so I'll be crawling on my stomach...

I know the thinner bore stuff is expensive - but it will be my only expense (apart from time and staples) - so I feel it would be worth it..

(The insulation and netting was (very kindly????) left in my attic by fitters who used the wrong stuff (no ventilation) - so the whole lot had to come down - only did this job to try and get rid of some....)

 

[D_Hailsham]

Suppose the insulation was totally perfect, or VERY good indeed like a vacuum flask? Then that would not be true!

Agreed, provided the thermal conductivity of the insulation was 0.

Now another senario for you to consider! Get a fan and blow cold air at the pipe, OK? So it will cool quicker?

You will increase the heat loss due to convection.

Well if you agree with that then encase the 10 mm pipe inside a tube of say 20 mm so the tube prevents draughts reaching the pipe! Surely that will lose less heat than the pipe in the open?

Are you talking about a tube made of insulation material or just what?

Assuming it is an insulated tube, there will be a temperature drop across the insulation. The surface temperature of the tube may not be the same as the ambient temperature, so there will be less heat lost per unit area. But the surface area has increased; so the heat loss will increase.

The text book you seem to have read must have been talking about a not very good insulation.

The type of insulation was not even mentioned. It is pure physics.

That green quote you have copied, why should that supposition be any different with a 100 mm tube compared with a 10 mm tube if it were true?

It's true of any size pipe. But there is a get out There is also a critical insulation thickness. To quote from Thermal Engineering By R.K. Rajput:
The addition of insulation always increases the conductive thermal resistance. But when the total thermal resistance is made of conductive thermal resistance and convective thermal resistance, the addition of insulation in some cases may reduce the convective thermal resistance due to increase in surface area, as in the case of a cylinder and a sphere, and the total thermal resistance may actually decrease resulting in increased heat flow. It may be shown that the thermal resistance actually decreases and then increases in some cases.

The thickness up to which heat flow increases and after which heat flow decreases is termed as critical thickness. in case of cylinders and spheres it is called critical radius.

So, provided the insulation is thicker than the critical radius, you are OK.

 

[bengasman]

Oh no. I have just found this on the net:

For a circular pipe with length very large compared to outer diameter, it may be assumed that the heat flows only in radial directions. If a layer of insulation is installed around the circular pipe to reduce the amount of heat transfer, then it is assumed that the heat transfer will be decreased by adding more insulation. By adding the insulation around the pipe the outside surface area is increased, which will increase the heat transfer.

So may be the authors got it right after all.

No wonder you never managed to a install boiler, you keep hunting until you find something that is either outdated, or impractical, or just complete nonsense.
This marvel of engineering info does not even specify any size, but states it as a general fact.
The deduction is: do NOT insulate pipes, you dumb children, the increased surface will actually loose more heat than a pipe without insulation.

This is the typical problem of an engineer trying to explain things to desk jockeys; the lack of hands on experience makes it impossible for them to understand the real working of things.

 

[D_Hailsham]

outdated, or impractical, or just complete nonsense.

It's none of those things. There are numerous current text books and scientific papers about this topic. For an example, read my last post.

It may not be too important when insulating central heating pipes, but it is critical when it comes to insulating electric cables, where the insulation must be thick enough for electrical safety but not too thick that the cable overheats.

This marvel of engineering info does not even specify any size, but states it as a general fact.

It is a general fact. The specifics will depend on the situation. In any case it is nothing to do with engineering, it's just physics.

The deduction is: do NOT insulate pipes, you dumb children, the increased surface will actually loose more heat than a pipe without insulation.

Someone could only come to that conclusion if they either failed to read what was written or did not understand it.

 

[bengasman]

Like I mentioned before, if you had actually installed boilers, you would realise what a load of nonsense you have produced here.

 

[AnimalGlu]

So now I'm confused...

So am I.

I just thought I'd do a quick search to see if I needed a thicker wall of insulation for 10mm microbore pipe (than for 22mm pipe) and the next thing I know I've wasted an hour looking through physics and air conditioning forums.

Ideally I'd like to replace the microbore pipe that is currently spiralling through my crawlspace for a distance of approx 6m but I have decided that I don't want to try fitting this pipe (15 or 22mm) whilst lying on my back in the cold.

For this reason, I think I'll try adding insulation as I figure the cold draught under the house will have less effect on an insulated pipe.

Plus at some point my boiler frost stat will kick in anyway so if I can increase the time it takes the pipe to cool, then I'm better off. http://www.leaningpinesoftware.com/hot_water_pipes_pipe_cooling.shtml

Although on second thoughts...

 

[kevplumb]

Let's put it this way, Knauf, who are probably the largest manufacturer of pipe insulation, do not make anything smaller than 15mm.

http://www.pipelagging.com/domestic....html?osCsid=a3f73672460c910236483eace8182a72


armaflex do

 

[AnimalGlu]

Let's put it this way, Knauf, who are probably the largest manufacturer of pipe insulation, do not make anything smaller than 15mm.

http://www.pipelagging.com/domestic....html?osCsid=a3f73672460c910236483eace8182a72


armaflex do

I was thinking of buying this:-
http://www.pipelagging.com/10mm-pipe-insulation-slit-tubolit-tl1013dg-13mm-wall-p-718.html

As it might be easier to fit around the current roller-coaster like installation.

 

[kevplumb]

sounds like a plan