I would be grateful for someone to confirm or otherwise my thinking on the
required size for an expansion vessel.

I am refurbishing a large old mill. Heating and ho****er will be via heat
pump (22kW). I need an expansion vessel for the sealed heating circuit
Capacities in litres a
CH Manifold 1 73
CH Manifold 2 82
CH Manifold 3 98
CH Manifold 4 105
Other Pipes 15
Jacket for unvented tank 450

I have drawn on tables from rwc.co.uk and a formula from
http://zusters.flamcogroup.com/pdf/pdf/3.pdf
and my thinking is that a 24 litre vessel should do it.
Any other offers with reasons?
Regards
Bruce

On Feb 26, 9:35*am, "BruceB" wrote:
I would be grateful for someone to confirm or otherwise my thinking on the
required size for an expansion vessel.

I am refurbishing a large old mill. *Heating and ho****er will be via heat
pump (22kW). I need an expansion vessel for the sealed heating circuit
Capacities in litres a
CH Manifold 1 * * * 73
CH Manifold 2 * * * 82
CH Manifold 3 * * * 98
CH Manifold 4 * * *105
Other Pipes * * * * * * *15
Jacket for unvented tank *450

I have drawn on tables from rwc.co.uk and a formula fromhttp://zusters.flamcogroup.com/pdf/pdf/3.pdf
*and my thinking is that a 24 litre vessel should do it.
Any other offers with reasons?
Regards
Bruce


Do you really have roughly 1000 litres of water? IIRC the expansion
is about 4% in volume if you go from cold to boiling. that suggests
40 litres of expansion so you'd need a vessl much larger than that.


Robert

"RobertL" wrote in message
...
On Feb 26, 9:35 am, "

Do you really have roughly 1000 litres of water? IIRC the expansion
is about 4% in volume if you go from cold to boiling. that suggests
40 litres of expansion so you'd need a vessl much larger than that.



It seems a lot, but the figures are correct. However the operating
temperatures are much lower than boiling, say 45 for the water circulating
in the building and 60 for the hw tank. I think that ambient to those
temperatures is all the expansion vessel needs to allow for, as any higer
temperatures are a failure mode and the relief valves can do their job?

BruceB wrote:

Jacket for unvented tank 450

What exactly does this mean? Is that actually the water content on the
primary side of the heating circuit, or the DHW content of the tank?

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
et...
BruceB wrote:

Jacket for unvented tank 450

What exactly does this mean? Is that actually the water content on the
primary side of the heating circuit, or the DHW content of the tank?

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

NIBE VPAS 300/450
volume of primary circuit 450
volume of DHW 300

I am coming to the conclusion I have undersized it and might need a second
expansion vessel!

On Sat, 28 Feb 2009 16:51:58 +0000, BruceB wrote:

"John Rumm" wrote in message
et...
BruceB wrote:

Jacket for unvented tank 450

What exactly does this mean? Is that actually the water content on the
primary side of the heating circuit, or the DHW content of the tank?

--
Cheers,

John.

/================================================== ===============\ |
Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------| |
John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

NIBE VPAS 300/450
volume of primary circuit 450
volume of DHW 300

I am coming to the conclusion I have undersized it and might need a
second expansion vessel!

I would strongly recommend against sealed primaries over 200 litres.
Install as a small pressurized primary and use a big water-water heat
exchanger.

If you really have 450 litres of sealed primary then about 45l of
expansion vessels should do it.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html