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