High pressure hot tanks

[aberdeeneuan]

Morning all,

We're in the process of sorting out a new boiler and hot tank for the house. The boiler is all agreed, but we want to fit a high pressure hot system to the house as well, looking at an OSO system. Now, the plumber has made noises about the mains pressure and that he may need to pump it into the system, but I didn;t think you could do that now?

Having heard some of the stories on here about pumps I'm keen to avoid that route, so what's the guideline? And how can I actually check the mains pressure? The taps are all ancient and knackered and all give varying pressure as a result.

[rovermorris999]

There's a bit about this in my thread on ground source heat pumps. One contributer said I needed 3 bar pressure for it to work properly, another said the flow rate was more important than the pressure. I'm on the end of the line in a rural area and the pressure varies a lot so I'll stick to a vented system. I would think if you look at suppliers of pressurised cylinders they'll give the pressure and flow rate ranges within which they'll work.

[Hereward]

You need decent flow (ideally >10 litres per minute) of incoming cold water. Time how long it takes to fill a 1-litre jug at all your cold taps and work it out.

[V10Mike]

You need pressure AND flow. We had a mains hot water system installed, but although we have 1.5 to 2 bar mains pressure (which is enough) the flow was insufficient. In this case the answer was a pressurized cold water storage tank. I would be surprised if your mains supply didn't have sufficient pressure -if you have a big enough cold tank you don't need it all day -ours builds up pressure at night, when neighborhood demand drops off.

[aberdeeneuan]

That's an interesting option, fed it from a cold tank - I'd rather do that than pump it!

Anyone else done it that way?

[gtr-gaz]

aberdeeneuan said:

That's an interesting option, fed it from a cold tank - I'd rather do that than pump it!

Anyone else done it that way?

Not yet but, about to use this system http://www.gah.co.uk/heating/dualstream/why-choose...

[V10Mike]

gtr-gaz said:

aberdeeneuan said:

That's an interesting option, fed it from a cold tank - I'd rather do that than pump it!

Anyone else done it that way?

Not yet but, about to use this system http://www.gah.co.uk/heating/dualstream/why-choose...

That's the one we've got -our mains flow was low so we ended up with two 300 litre cold water accumulators, but this supplies four bathrooms. Not cheap but worth it, and you get mains pressure everywhere, easy temperature regulation in your showers, because the pressure is balanced between hot and cold, and potable water from every cold tap as it's a sealed system.

[Ricky_M]

With regards to tsting your mains water pressure.

http://www.machinemart.co.uk/shop/product/details/...

[Arthur Jackson]

Hereward said:

You need decent flow (ideally >10 litres per minute) of incoming cold water. Time how long it takes to fill a 1-litre jug at all your cold taps and work it out.

10 litres a minute is nowhere near enough for an unvented cylinder. Make it 25 and you'd be nearer.

[Arthur Jackson]

aberdeeneuan said:

.....looking at an OSO system.

If OSO still use the air bubble in their cylinders I would look elsewhere. Particularly if your water comes from underground reservoirs. I would go with a cylinder with an external pressure vessel, probably the Ariston Primo, which (I think) is what GAH use onthe Dualstream.

[aberdeeneuan]

Arthur Jackson said:

aberdeeneuan said:

.....looking at an OSO system.

If OSO still use the air bubble in their cylinders I would look elsewhere. Particularly if your water comes from underground reservoirs.

what's the issue with the air bubble? I guess air in a high pressure tank isn't that clever.

[Arthur Jackson]

OSO used to use a system whereby the expansion is taken up by trapping air inside the tank. This is fine until the water absorbs the air. I've seen this happen inside 4 months and it then has to be reinstated.

[aberdeeneuan]

Ah, that would be a bit of a nightmare. It's the new Super S series, but I can't work out if it's got the air bubble or not.

Is it an issue if it's pumped?

[Tuna]

Another alternative is a thermal store, which is what we've got.

The tank is vented, so no pressurised system to maintain. Hot water is at mains pressure and the flow rates are good. The tank can also be used to combine a range of heat sources, so you can add solar, a wood stove or ground source heat pump to keep bills down.