Replace vented set-up including pumps with unvented set-up?

[Alan Ambrose]

Apologies for yet another tank question. My objective is to get a more energy efficient set-up.

 

In my 5th floor flat there is a 30-year old vented set-up. It has two big custom made cube-like tanks (almost 1m cubed each) tight in a cupboard and two Stuart-Turner 3 bar twin pumps (hot and cold) for pressure - one for each bathroom. (Some time, way back, I had a second one installed so we could shower even when one pump failed.)

 

The upper vented cold tank is about 1m off the floor and there's a hot tank underneath, with thin-ish insulation and heated by two immersion heaters. (This was from a time when designers were scared of gas in flats and the flat has electricity only.) The incoming pressure is about 1.5 bar and I'm not sure whether or how often the mains pressure dips under that, but my upstairs neighbour has been having some trouble with mains pressure. I've applied a bit of extra insulation to the hot tank but it's not possible to get all around it and the temperature still falls off quite rapidly. (I've a Heatmiser system and can see the temperature fall-off quite easily and accurately.) I know the fall off is much faster than another more modern unvented set-up I have data on. There are some fancy taps and shower fittings here which need a minimum of 1.4 bar.

 

So the question is, how can I get a better insulated system without risking dodgy water pressure? The options seem to be:

 

(1) Replace with a more modern vented set-up with immersion heaters and keep the pumps.

(2) Replace with a more modern unvented set-up with immersion heaters, lose the pumps and take the risk on low water pressure.

(3) Go a bit off-piste and use something like a 12KW Heatrae Sadia electric boiler, lose the pumps and ditch all the tanks. Take the risk on low water pressure. I think a downstairs neighbour has something like that set-up.

 

Any thoughts?

 

Alan

 

[JohnMo]

To look after any dips in pressure you could install an accumulator and a check valve upstream.  The accumulator would be pressurised when the pressure is high and iron out the dips mostly. 50 or 60 L maybe big enough, other will chip in if I am talking rubbish.

 

12kW on demand heater, could be costly to run as it would use peak electrical, not off peak and still give a rubbish flow rate.

 

Other option for heating would be an exhaust air heat pump (EAHP) cylinder, a little bigger than an normal cylinder, with heat pump incorporated. 

 

Accumulator, EAHP, would gibe you a pressure stable unvented cylinder, with a cheap way of heating it

[Alan Ambrose]

OK thanks interesting. Heat pump isn't possible as although there's a small patio, it's nowhere near the cylinder and linking it up would involve ripping the flat apart.

 

I think I'll see if I can get a pressure data logger and then proceed down the well-insulated 'vented without pumps' or 'unvented cylinder with pumps' as required.

 

Alan

[JohnMo]

The heat pump I am referring to, is integrated in to the cylinder, not an outdoor unit

 

such as this https://www.heatershop.co.uk/dimplex-edl200uk?gclid=CjwKCAjw7p6aBhBiEiwA83fGuv1lhBgRkNTKXeOCKrMAh88nzCQ7629o7blDnXEtkFHPAkp4AdBQrRoCP5gQAvD_BwE

[Alan Ambrose]

Ah, that's interesting - I hadn't seen that product. A stretch to get the ducting to the outside but may be possible. I see max 20m of 160mm insulated straight ducting or less if it has bends. Claims 33 dBA. Has a separate immersion for backup.

 

Funnily enough, my downstairs neighbour contacted me to see if we 'had low water pressure' yesterday - I think he probably meant flow rate. But that leans towards keeping the pumps. Maybe there's some fancy cold water accumulator / pump which would guarantee pressure for the unvented Dimplex product.

 

I can't imagine who specified this set-up originally - this was the early 90s - 400L of cold plus 300L of hot plus 3-phase power ... in a 3-bed flat.

 

Alan

[JohnMo]

Maybe they had cold water storage to mitigate pressure fluctuations

[Nickfromwales]

7 hours ago, Alan Ambrose said:

Ah, that's interesting - I hadn't seen that product. A stretch to get the ducting to the outside but may be possible. I see max 20m of 160mm insulated straight ducting or less if it has bends. Claims 33 dBA. Has a separate immersion for backup.

 

Funnily enough, my downstairs neighbour contacted me to see if we 'had low water pressure' yesterday - I think he probably meant flow rate. But that leans towards keeping the pumps. Maybe there's some fancy cold water accumulator / pump which would guarantee pressure for the unvented Dimplex product.

 

I can't imagine who specified this set-up originally - this was the early 90s - 400L of cold plus 300L of hot plus 3-phase power ... in a 3-bed flat.

 

Alan

If this is a lifetime solution then I’d keep the 400L CWS, add a 100L ( 50L useful capacity ) cold mains accumulator, pumped off that as required only, and fit a Steibel Eltron 3 phase 27kW instantaneous water heater.

The Steibel is about the size of a shoe-box, just a bit longer, and is one of the most impressive bits of kit I’ve seen for a long time. I installed one for a client, in their annex / residence during their main build, and it is working very well indeed. Changes water temperature for duty too, so shower gets full wallop, basin tap gets a 1/3 and so on.

 

You may be able to clear out that airing cupboard space and just fit a 300L accumulator and go passive off the mains, but we’d need the statistical info from the data logging first to be brave enough to discount bulk storage.

 

You’d be at the mercy of electricity prices on demand, but the Steibel is nearly 100% efficient and you’d only ever heat the exact amount of water you used. The same single phase unit from the same supplier, I can piss faster than the hot water comes out of that btw. 

[Alan Ambrose]

>>> I can piss faster than the hot water comes out of that btw.

 

There will be some members on here, including me, that can't

 

Interesting thought, not crazy expensive ... and has the advantage of being fairly straightforward tech.

 

Alan

 

[Alan Ambrose]

I just noticed that one of my favourite youtubers, Marco Reps, replaced the Steibel 27kW instantaneous water heater in his house with a Kospel EPME 5.5-9kW one. For our German cousins, instantaneous water heater seem to be a standard thing. And because these devices are so simple, they seem to be very reasonably priced - about £500 & £300 respectively. I can't imagine that 'the Germans' would put up with anything dodgy. Anyone know why these are not more widely used in the UK?

 

Alan

[Alan Ambrose]

Answering my own question...

 

>>> Anyone know why these are not more widely used in the UK?

 

Duh, 27kW is ~110A - so only suitable for those few domestic premises with 3-phase installed. I understand 3-phase domestic is de rigeur ('streng'?) in Germany.

 

Alan

 

[Alan Ambrose]

p.s. I'm finding figures of 2.5 to 5 kWh for energy usage for 5-10 minute shower - which implies an instantaneous ~30kW heater would do the trick - if only using one shower at a time.

 

I guess that's why we need to store the stuff

 

Alan

[Nickfromwales]

On 31/10/2022 at 14:28, Alan Ambrose said:

p.s. I'm finding figures of 2.5 to 5 kWh for energy usage for 5-10 minute shower - which implies an instantaneous ~30kW heater would do the trick - if only using one shower at a time.

 

I guess that's why we need to store the stuff

 

Alan

The 27kW Stiebel is a very impressive unit. I’ve a 27kW gas combi, and there is very little in it. I’d be quite happy with that 3ph heater in my own home. 30kW instant is just too big, requiring a jump to 40a/ph. 32a/ph on the 27 is fine.