Cold water accumulator/potable water expansion vessel

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I have a mains pressure system with Gledhill Torrent thermal store. I have good pressure and flow (static 5 bar; dynamic 1 bar 25 l/min) to enable a good shower, but I have recently installed an en-suite, so now have two showers. Shower flow rate drops if two showers are operating, washing machine is running, or kitchen tap is turned on.

I had originally thought about upgrading supply pipe (currently 1960s black alkathene) but then discovered accumulators. I have done some research on the internet, from which I gather that the cheapest accumulators are made by the likes of Altecnic (Ultra Pro), but are advertised as expansion vessels because of patent issues.

The only place I could put an accumulator is in my loft (chalet bungalow) which would necessitate a horizontal cylinder: a further reason for preferring Altecnic over more expensive brands, which seem to be all vertical. The largest accumulator I could manouvre into the loft space would be 80-100 litres, so I was thinking of starting with one, seeing how it goes, and if necessary installing a second, and possibly third, in series. Even three in series (240/300 litres) would be about half the cost of what I have been quoted for upgrading my supply pipe.

I have spoken to the plumber who installed my Gledhill Torrent, but he has never fitted an accumulator.

I would appreciate comments on this proposal.
 
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Try running the showers cold and see how the flowrate performs when other taps are opened.
 
100 litre accumulator would offer very little improvement. Not worth the bother, the boost would not last very long.

There are FIFO issues with horizontal units too.

NB: If it is cheap you want, there are cheaper accumulators than Altecnics', you haven't been looking long enough. But they are nowhere near as good as the Global Water Solutions GC range.
 
I had thought that 100 litres would give me the bare minimum of what I need, which is in the morning when two people are having a shower at the same time with a 5 minute overlap. At 7/8 litres/minute per shower (eco shower heads), that is a total of 70/80 litres. Before and after this overlap period, mains pressure/flow would be adequate. But to allow for possibly longer overlap and use of other outlets, such as washing machine, kitchen taps, at the same time, I had thought it would be worth going to 200 litres.
 
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Thats probably because you imagine that a 100 li vessel will give you a supply enhancement of 100 litres!

There are a lot of factors involved and with a 5 Bar static pressure thats a help.

However, with your usage the vessel will mostly be depleted whilst you take the first shower.

An upgraded supply pipe is obviously the best thing to do.

Congratulations on understanding that its the dynamic pressure thats relevant! Many plumbers dont even know that.

Tony
 
Expansion Vessels are goverened by an acceptance factor based on the initial pre-charge and the standing pressure, Vessels have an acceptance factor of between 50 - 85% so a 100 Ltr Vessel will only store between 50-85 Litres of water, the rest is compressed air in the diaphragm, so in reality a 100 Litre vessel is not very big in water volume terms ;)
 
In his case a 100 li vessel will give about 80li of output but during the first shower the majority of stored water will run out as the pipe pressure reduces from 5 Bar to only 1 Bar.

So that is not the answer!

Tony
 
NOTE: See comment by Steve32 later in this thread about the correct way to connect an Altecnic accumulator.

Hi Winty,

I’m not a plumber. However, we have an Altecnic 300 liter expansion vessel installed in our house, which, yes, serves us as an an accumulator. When I first considered installing an accumulator 3-4 years ago this forum was a great help, so here is me giving something back – the perspective of an accumulator owner :) Hopefully there will be people out there benefiting from this post.

First of all, our accumulator does not feed all the cold water taps in the house. It feeds the combi boiler (to maintain best possible warm water supply everywhere in the house). In addition, it feeds cold water to the bath and two showers (one above the bath and one in a separate en-suite).

Cold water in the rest of the house does not come from the accumulator. This has the benefit that if someone fill the kettle, waters the garden, flushes a toilet and so on this does not affect the cold water supply to the showers/bath. Yes, if someone uses hot water, say in the kitchen, the shower does get affected, but not very much (on average less than when the combi was supplied directly by the mains).

Again, the above and the remaining post is a user perspective – not a plumber.

Occasionally, maybe once every three month maybe (?) the accumulator will run empty. It usually happens when there is a lot of water use in the house generally, combined with someone taking a long shower and then the next person showering may suddenly be left with a sudden drop of in the shower performance. Immediate solution is to turn off the shower, wait for 3 minutes (not pleasant of course) and then turn on the shower again and use the one minute or so of normal shower performance to at least rinse off. The size of the accumulator is key here... see further down... my 300 liter doesn’t really accumulate 300 liters.

More generally, the showers have performed very well indeed over the 3 years we have had the accumulator. Overall, I am completely sold on the concept. However....

With the Altecnic expansion vessel (we have a normal vertical one) the mains water enters at the bottom of the vessel, and exits at the top. I think this means that if the vessels should fail (e.g. rubber bladder ruptures) then we are left with no supply to the combi, and no cold water to the bath and showers. I am not 100% sure because it may be that the water is able to flow through the vessel even if the bladder has ruptured – however, I suspect not. This means that if i were to install this anew i would ask my plumber to put in a ‘bypass’ so that in the case the vessel fails it can be bypassed by the turn of a knob of some kind.

Recently, and the reason why I again find myself on this forum and looking around for info on accumulators, is that we have had black residue appearing in the bath when filling it and coming out ogf the showers. I had my plumber on the line, and after briefly discussing the problem we suspect the source is the Altecnic expansion vessel – perhaps the rubber bladder beginning to show signs of age? It seems a quite short life span – 3 years, but then again the Altecnic has a replaceable bladder and there can be only one reason for why the bladder is replaceable – it wears out over time.

I am now faced with a decision... what to do. The cheapest replacement bladder I have found – but probably didn’t search hard enough is about £300+, which is almost the price of a new Altecnic vessel. I suspect if I tried harder I could find it for about 100-150 pounds, but I have been exploring a different option.

I have pretty much decided to replace the Altecnic vessel with an accumulator from either GAH (Coldstream) or CWC (Mainsboost). Originally (3 years ago) I wanted the Coldstream one, but it was expensive and hard to get. It is still expensive but finances have improved and hopefully have time to wait for delivery this time. This switch has the following benefits for me (the user perspective).

1. I will go for a larger model. Either the Coldstream 500 or the Mainsboost 450. As far as I can tell these are exactly the same, similarly priced (around or just above £1000), but with the patent for its use as accumulator recently passing from GAH to CWC, making the Mainsboost accumulator slightly more ‘legitimate’ (but as a user I don’t think I am breaking any rules/laws either way). The Coldstream seems to have more detailed/professional documentation.

2. With the slightly larger vessel we are less likely to experience the occasional shower failure.

3. The Coldstream and Mainsboost accumulators only have a single pipe going into it. This is unlike the Altecnic with separate inlet and outlet. If there is a failure with the vessel it can be more easily isolated (and it doesn’t require additional plumbing of a bypass – see above).

Drawback ??? Coldstream and Mainsboost bladder is not replaceable... will I have to replace this new accumulator every X years?? Bladder is not good word for these vessels because it is more like a diaphragm. The Altecnic is more like an actual bladder. Pictures are available on the net...

Some last bits –technical so any professionals out there: Please forgive and correct!!

Winty, I think a 100 liter vessel will frustrate rather than please. Again, our 300 liter Altecnic only feeds the showers and combi, but still we get occasional shower failure – yes, not often, but still. A 100 vessel will at best offer about 65 liter of water, maybe less (see discussion of pressure differentials further down). With accumulators bigger is indeed better. Yes, I understand you have particular challenges with the siting of the vessel (in the loft). I am not sure what Simond meant when he said “There are FIFO issues with horizontal units...”. maybe ‘first in first out’ ? With a hot water tank this would be a big problem... but with a cold water accumulator??? I imagine a horizontal solution may result in buildup of some stagnant water on the bottom side of the bladder?? Note the Altecnic bladder is sort of like a doughnut shaped thingy.... not sure if this is different in the horizontal units. If they are designed for horizontal use maybe there has been some adjustment to the design?

The performance of an accumulator is all about the pressure difference between the incoming mains and the precharge pressure of the vessel (the pressure of the vessel when empty). I only explain the following in my own words because I never saw an full explanation of this elsewhere. Again, any pros out there may choose to correct me. As I understand it, the difference in pressure should be between 1 and 1.5 bar (may vary across different expansion vessels and manufacturers so check documentation!!). In our case, the incoming mains pressure is static normal around 3 or 3.5. Dynamic pressure will be different of course, but as I understand it the accumulator design means that the accumulator benefits from the highest possible level of dynamic pressure across time, and this will be similar to the static pressure (when no water is used by us or neighbours and no water company issues). 3 – 3.5 mains means that the precharge pressure of the vessel needs to be about 2 bar. The 1- 1.5 bar difference allows the mains water to force itself into the accumulator and inflate it to the recommended capacity (around 50-60 % of the gross capacity ??). If, for instance, the incoming mains is 2 bar and the accumulator vessel precharge pressure is 2 bar then no mains water will be able to force itself into the vessel and the accumulator will not accumulate anything. Of course, the solution is to reduce the precharge pressure of the vessel to compensate for a lower pressure mains. Conversely, if the pressure difference between the mains and the precharge of the vessel is more than the recommended 1.5 bar then the main pressure will cause the accumulator bladder to expand more than what is recommended. I believe the Mainsboost and Coldstream accumulators recommend installing a pressure reducing valve between the mains and the vessel to avoid the latter situation.

In the above considerations, the flow-rate of the incoming main is less important. It is the pressure that inflates the accumulator – flow-rate does nothing. I think flow rate from accumulator to shower will be affected by pipe-run and size of pipes. One of our showers has better performance because it is has significantly shorter and less complex pipe-runs from accumulator and combi.

All in all, while needing some careful planning, and having possible lifespan issues, I think accumulators are a great solution!!!

Juup
Manchester
 
Thank you everyone for their comments, and to Juup in particular for a very detailed account of their experience. I am now thinking about a larger Mainsboost/Coldstream, but finding somewhere to put it is the main problem. I have converted the former semi-integral garage into living accommodation (and have a new detached garage some distance from the house) so am short on internal space, apart from the low loft (chalet bungalow) which is why I was originally interested in a horizontal accumulator. I spoke to someone at GAH who said I could install the accumulator outside, provided it was enclosed. I could site it next to the outside wall of the house and build a small wooden lean-to around it.

I realise that upgrading the mains supply pipe is another possible solution. However, I am concerned that pressure and flow may drop in the future, as a result of water shortages (if this summer is anything to go by) and possible new housing developments in this area. A Mainsboost accumulator would be future-proof, as a Mainsboost Charger could be added later, if necessary.

Winty
 
Hi Winty,

Putting it outside sounds interesting. Note, though, that you will have to prevent it from freezing. Last winter was awfully cold!! If there is a longer cold spell you're in trouble, no? A wooden lean-to might not be sufficient... maybe if it is well insulated and some kind of limited heat source for the coldest winter weeks??? Maybe a simple bathroom fan extracting air (and heat) from the house into the lean-to? Or maybe dig a hole and build the insulated lean-to over the hole, thereby benefiting from the ambient heat from the ground in winter? Or maybe in the detached garage?

We put it in the corner of a utility room and built a custom enclose around it. The result looks a bit like a squarish chimney breast, and hence inconspicuous.

Juup
 
Hi Juup

The GAH website has a FAQ on installing the Coldstream outside:

Q.Can the accumulators be installed outside, in a open garage or shed?

A.Yes, the C2 range is ideal and designed with this in mind, remember no power supply, or drainage requirements so they can go almost anywhere, basements garages etc. The pipe size can also be run in plastic from the accumulator to the house in the correct size.

Since this is specifically mentioned as a possibility, I'm sure GAH or TrentClyde can give further information on the level of insulation required.

Winty
 
Both the Mainsboost and the Coldstream are the same product, but you get more fittings with the TWS unit. Both are licenced in the UK by S Elsey.

Size is everything with accumulators. When the bag goes you will not get a leak but the accumulator will weigh nearly twice as much - bear this in mind when you position it in your loft!

We've fitted 100s of GC450s (with either GAH or TWS on the side), over the last 6 years, not a single diaphragm has failed to my knowledge.

I can think of only a handful of smaller units we've done, the cost/benefit analysis does not really work with the smaller sizes. With GC450 you can normally expect to get around 225 litres out.

There was a lot of negative comments some years back when I first started promoting the use of accumulators on this forum, its nice to see some good feedback.
 
Yes, seems a reasonably assumption... they should be able to advise on this. Good luck taking this forward.

I just this afternoon ordered a Coldstream 500 from here:

http://www.plumbclick.co.uk/gb/home

The path to find the vessels is:

Home > Heating > Hot Water Cylinders & Accessories > Potable Water Pressure Accumulators

The price: 763 pounds (including VAT) and less than 10 pounds for delivery. This is a good 300 pounds less than elsewhere, so I half expect to receive a phone call soon to tell me the price quoted online was wrong, or at the very least that the delivery cost is significantly higher.

The only place I have seen Mainsboost ones is:

http://www.heatingmerchant.com/Cold_water_boosting

Juup
 
Thanks Simond for the added (and otherwise hard to come by) detail.

Perhaps the most interesting part of my story (left out earlier) was the time I spent 3 years back trying to convince my cautious plumber that the accumulator principle would work for us. He had never done one before. He is now booked to install the larger Coldstream once it arrives.

Juup
 
i have installed both altecnic and dualstream (gah) accumulators and find both to be reliable i will say the gah is better finished.

juup wrote
With the Altecnic expansion vessel (we have a normal vertical one) the mains water enters at the bottom of the vessel, and exits at the top

every altecnic i have installed or seen installed only has one connection at the bottom the top fitting is supplied to allow a pressure gauge or prv to be fitted or blanked off you may have a model that i have not seen but i would advise you check this.
this may be why you have black residue in the taps and bath

the pre charge of accumulators supplied is usually between 3-4 bar the pressure should be checked and adjusted accordingly on installation and periodically the charge should be 1.5bar below incoming mains pressure min pressure 0.5 bar.
 

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