Heat Banks Vs Heatrae sadia / OSO unvented system

[brookbond]

Been reading this forum sometime now but this is my first question and I haven't been able to see any one else asking it.

Question is about Heat Banks ( www.heatweb.com) vs OSO unvented type systems. Any got any comments or ever used the heat bank type of system - the claim is that they have less maintenance headaches than the OSO systems, they also says not building inspector required.

Obvious there are lots of posts about unvent systems but not seen anyone else talking heatbank so my guess they aren't liked or just too expensive when compare to the other options.

comment / thoughts - anyone actually got one

regard

chris ( brookbond)

 

[bripl]

try a search for boilermate they are similar also thermal stores as far as unvented i prefer to use the oso range as i have had no probs with them.if i remember correctly albion do a similar setup to the heatbank.

 

[simond]

Thats a good question and one that more people should ask. You would be surprised how many 'professionals' struggle with an answer.

The reason a heatbank is often described as superior to unvented is due to the amount of heat energy stored inside. This is because of the temperature of the stored water. In a conventional unvented cylinder it is inadvisable to heat the water to above 60 degrees centigrade, or else limescale deposition will be a problem.

The volume of water in a heatstore need not be greater than unvented but is typically kept at 82 degrees or thereabouts. Therefore the stored energy available within the unit is much larger, and in consequence there is a higher flow rate capability. Limescale in the stored water of a heatstore is not a problem for two reasons;

- the water is never replaced so there are a finite amount of deposits that can be produced
- you are supplied with some inhibitor to add to the water store

Heatstores are fundamentally safer than unvented, but have a different set of problems as time takes its toll so there is not much to choose between the two systems in terms of durability. The Pandora range you have been looking at are amongst the best of their type on the market.

The MOST important thing to check before installing any mains fed equipment is the water pressure and flow rate into the property. If you have less than 20 litres per minute you are wasting your money, you will have a Minorflo not a 'Megaflo'.

Flow rate specifications are often used by customers to justify purchasing a particular make of cylinder or heatstore. One well known brand of unvented cylinder makes a big deal out of claiming the highest flow rate.

Further info on low water pressure solutions for unvented can be found at www.hwch.co.uk

Simon Davies
HWCH Ltd

 

[brookbond]

thanks simon this was a very helpful reply.

out of interest in general term you say thermal stores " have a different set of problems " could you expand on this to help me understand

thanks

 

[ChrisR]

Corrosion in heat stores seems to still be an unpredictable and poor;y understood problem. You can't heat a heatstore with a boiler "condensing", because they're much too hot, so would lose efficiency if you had a C boiler. And you can get problems with recovery of temperature in the heatstore when a large heat-drain takes place - though I suspect this one is soluble with a little intelligence in use!

The Accumulators referred to in the detail of the link given above can help a lot with poor mains flow - I wish I inderstood why they're so darned expensive though!

 

[brookbond]

ok if condensing boilers are too hot - ( although
heatweb system to offer one as part of the package deal they do on a complete system) what comments would people have to the design I have been given as follows :-

combi alpha cb28x - doing hot water only to kitchen.
then control system to run hot water & central heating. Hot water to be either a thermal heat store ( hence my questions) or a unvents OSO type cylinder.

I am NOT doing any of the work ( apart the electrics as I'm a spark) but I do want to make sure the design from heating engineer is ok and therefore I am spending time reserching the design & options.

Alpha have no problems running unvent system off the CB28 ( already phoned they for a chat)

so should I be worried by Heat output from the CB28 ?

also just been studing the RMC product range and they do themaflow which is suppose to be design for combi boilers.

my worry is perhaps I really need to ask which bolier should I pick ?

 

[simond]

We would only advocate Vaillant, Worcester or Viessmann boilers. Or if you have a big house, a Kidd.

The condensing issue is not as big a problem as you might expect because it's the return temperature, not the flow, that you are interested in.

I would try and avoid condensing boilers anyway unless you are looking at one of the above makes, or are very handy with your soldering iron and spanners.

Simon
www.hwch.co.uk

 

[htgeng]

An unvented system subscribes to the K.I.S.S principle. The technology is widely understood by the industry and a nice flashy cylinder is likely to be a selling point for your house.

A heatstore is a niche product and sometimes requires lots of TLC by the owner to keep it up and running. This equates to nagging by the missus or tinkering by friends who think they know how to tweak it to run better.

Also lots of potentially maintenance hungry parts/labour. If the hot water pump stops, heat exchanger scales up or flow switch breaks you don't have hot water. In this respect I don't think they are much better than a combi boiler. At least with a combi boiler you have a good chance of getting someone local who will know how to fix it.

Also, not forgetting the previously mentioned lack of running efficiency with condensing boilers which our friend Mrs Beckett will soon be making everyone install by default.

Go for a megaflow or OSO. You know it makes sense.

 

[croydoncorgi]

The issue of condensing boilers and heatstores (and in fact ANY system which keeps the Return temperature above 56 degrees) is being widely ignored!

Even Simond has missed the point with his comment

The condensing issue is not as big a problem as you might expect because it's the return temperature, not the flow, that you are interested in.

.
Fact of the matter is that if the heatstore has been heating for more than (say) five minutes, ALL the water in it will be at roughly the same temperature due to internal convection currents. So once the heatstore temperature goes past 56 degrees, there's NO WAY the Return temperature at the boiler will be much less that that. So no condensing. And most heatstores are recommended to be operated at around 80 degrees to ensure half-decent hot water performance.

People (and possibly also Ministers of State!) are easily misled by plumes of steam coming out of condensing boiler flues. Just cos it's steaming does NOT necessarily mean that condensation is actually taking place INSIDE THE HEAT EXCHANGER.

 

[simond]

Whilst I concur that when the heatstore reaches temperature, the return flow will be higher than ideal, your opinion relies on the assumption that the heatstore gets back up to temperature in just five minutes.

If this assumption were correct, a Heatbank would offer an extremely economical proposition, whether fed by a condensing boiler or not.

I am not aware of any published research vis a vis the merits of running a high efficiency boiler into a Heatstore as opposed to an unvented cylinder. Until this has been done I am not qualified to advise a customer over their relative efficiency one way or the other. As a hot water supply system, though, they work very well and a large number of industrial sized installations use this principle.

Finally, a thought for Mr CroydonCorgi (he appears to be in our manor)!

SEDBUK measures the performance of a boiler when it is running. To the best of my knowledge it ignores pump over run, which almost all condensing boilers have to use because of their fragile little heat exchangers. Pump over-run takes a substantial amount of heat, runs for 3-5 minutes typically, and 'leaks' the heat to somewhere you won't notice it - typically a length of pipework (bypass) or through a hot water cylinder.

Firstly, who do you think pays for that heat? And if it has to be dissipated, is it better used in a heat store or an unvented cylinder? And how many times does a typical boiler turn on and off in an hour?

It is our view that the SEDBUK routine ignores 'standing losses' - and is therefore potentially misleading.

Those of you that have condensing boilers, when you hear the boiler turn off and the pump running, you are in 'energy wastage mode'. Did your installer explain that 'Pump over run' is a manufacturer term for 'energy being deliberately wasted'. What is the point in insulating your house if your boiler regularly throws heat away for 5 minutes?

NB: An Archie Kidd Boiler does not need pump over-run and is thus potentially more efficient than ANY of the others. Doesn't run in condensing mode all the time either. Not bad for a product which was designed in 1982.........and passed SEDBUK A in 2003. Don't believe everything you read about the new stuff, high efficiency boilers are not as modern an idea as the marketing people want you to think.

Simon
www.hwch.co.uk

 

[Water Systems]

I did search for fun....I can't believe the misinformation on this thread from so-called professionals.