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This graph is taken from the Stelrad Elite Catalogue. It's not the size of rad but the flow rate and, to a limited extent, the type of rad which determines the pressure drop across the rad.
but I never really understood the " Law of Communicating Vessels"
no, really don’t get that thing about the vessels. Didn’t know that central heating used impeller pumps either.
maybe you should quantify setting 3 and leave there
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Utter and complete bolleaux.
If that is in your book, it is referring to a pump moving a liquid to a higher level. In this case, the accelerator/pump is not transferring a fluid to a higher level, there is an equal volume flowing from high to low level and the two legs of the system are balanced.
You would have known that.
I've no idea what the restriction referred to is.
You had thought the pump head referred to the height of the building and now you are just making smoke to hide your embarrassment. It would have been an understandable and forgivable mistake, for a Year 1 NVQ trainee. I do not believe that you have any engineering qualifications. Do one. I'm sure that, in future, everyone will treat your discourses with the respect that you feel they deserve.
Having castigated Sanji for his bad workmanship, I think I should now come to his defence.
Danfoss have produced The Heating Book which goes into considerable detail about the design of District Heating Systems for towns and blocks of flats. Chapter Four has a section on the effects of gravity in high rise buildings which makes interesting reading as it tends to agree with Sanji's views.
In this chapter, the gravity effects of the risers of an 18 storey (54m) building are calculated as follows:
Flow Temp: 95oC - Density: 962.2 kg/m3
Return Temp: 70oC - Density: 977.8
Δρ = 15.6 kg/m3
Δp = 54 × 15.6 x 9.81
= 8.264 Pa = 8.3 kPa
This accounted for 30% of the pressure differential in the index circuit!
Although most of the book is not relevant, talking about power stations etc, some of it is very interesting and useful. I learnt all about valve authority and that the heat loss from a vertical uninsulated pipe is 20% less than from a horizontal one.
Having castigated Sanji for his bad workmanship, I think I should now come to his defence.
Danfoss have produced The Heating Book which goes into considerable detail about the design of District Heating Systems for towns and blocks of flats. Chapter Four has a section on the effects of gravity in high rise buildings which makes interesting reading as it tends to agree with Sanji's views.
In this chapter, the gravity effects of the risers of an 18 storey (54m) building are calculated as follows:
Flow Temp: 95oC - Density: 962.2 kg/m3
Return Temp: 70oC - Density: 977.8
Δρ = 15.6 kg/m3
Δp = 54 × 15.6 x 9.81
= 8.264 Pa = 8.3 kPa
This accounted for 30% of the pressure differential in the index circuit!
Although most of the book is not relevant, talking about power stations etc, some of it is very interesting and useful. I learnt all about valve authority and that the heat loss from a vertical uninsulated pipe is 20% less than from a horizontal one.
Errrrr, yeah, but the 95 degC flow is less dense than the 70 degC return, so that 8.3 kPa pressure difference is assisting the pump ( unless the boiler is on the upper floors). This is the opposite of what S-V has claimed.
See my post of Fri Dec 28, 2007 7:11 pm;
"The truth is the opposite; you will get (apparent) reduced head losses if you're pumping the flow upwards because of the gravity circulation effect; the hotter flow column is less dense than the descending return column."
In this case, the differential pressure due to 'gravity circulation' = (977.8- 962.2) x 9.81 x 54 Pa = 8.3 kPa.
That 8.3 kPa differential pressure is pushing the flow upwards.
Now S-V just needs to find a similar effect pushing the flow downwards with a pressure of approximately (8.3 + 19.4) kPa, enough to stop all circulation. In fact, it would have to be greater than that, since the pump head would increase as the flow rate decreased.
Any suggestions?
If you had an 2" pipe rising from the plant room straight up through the building to the loft/roof area, with legs off for each floor and dropping into one 21/2" or 2 x 2" return pipes it would work by gravity.
The biggest problem would be stopping the circulation and the pressure in the plant room.
The biggest problem would be stopping the circulation and the pressure in the plant room.
I learnt all about valve authority and that the heat loss from a vertical uninsulated pipe is 20% less than from a horizontal one.
Thats why I hold my soldering iron vertical when I want it to warm up quickly and horizontally when I want it to rest and keep itself cooler.
A vertical pipe keeps the upper parts warm with the convected heat from lower down.
Tony
To be picky, Onetap, in what circumstances might the flow be pumped downwards?Onetap said:
When the boiler is on the top floor!
I have forgotten where it was, perhaps a Birmingham tower block?
Tony
To be picky, Onetap, in what circumstances might the flow be pumped downwards?Onetap said:
When the boiler is on the top floor!
I have forgotten where it was, perhaps a Birmingham tower block?
Tony
Drayton Gadens, or didn't you see that one
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