Any experience with unvented cylinders and/or mains booster sets?

ch_152

Hello,

I've recently moved into a flat which has a rather shonky plumbing arrangement:

• Downstairs cold tap run off incoming mains (pressure is low. ~7 L/min).
• Downstairs hot tap run from a vented tank with immersion heater (located upstairs in utility cupboard), with an additional pump to increase flow rate (noisy!)
• Upstairs taps and shower over bath from the cold water storage tank (also upstairs) and hot water tank, using the pump for reasonable pressure
• Upstairs electric shower run off mains, also at terrible pressure

I've been looking at options to upgrade the system and have been told that replacing the current vented hot water tank with an unvented one will increase the hot water pressure throughout (hopefully removing the need for the pump which is in the spare bedroom utility cupboard and heinously loud).

I could then also install (or may need to install regardless as the mains pressure might be too low for the vented cylinder) a mains booster set such that the shower could be run off the normal hot/cold water - removing the electric shower (which doesn't fit very well with my Economy 7 tariff).

Slightly worried that the mains booster set will be just as bad as the little pump that's currently installed, but at least that would be located downstairs (i.e not in somebody's bedroom).


Any experience, or alternative recommendations?


Cheers


Chris

knightstyle

First find out why the mains pressure is low, faulty stop !!!!!! for example. What is the pressure like in the other flats?
Yes a sealed system with a mains booster pump will help if the mains pressure is low.

BUFF

ch_152 said:

Hello,

I've recently moved into a flat which has a rather shonky plumbing arrangement:

• Downstairs cold tap run off incoming mains (pressure is low. ~7 L/min).

Flow (L/min) is not pressure (bars)
Do you know what the pressure is? 

GDB2222

If the mains flow is low, then the unvented cylinder will have an equally low flow. It’s a terrible idea unless the mains flow issue is solved first.


We have an unvented cylinder and it is great.

ch_152

Thanks for the replies. I haven't yet made friends with any of the neighbours so don't know about the pressure in other areas of the development - but is worth an ask.

@BUFF good point. How does one find out the pressure?

GDB2222 said:

If the mains flow is low, then the unvented cylinder will have an equally low flow. It’s a terrible idea unless the mains flow issue is solved first.


We have an unvented cylinder and it is great.

Okay, that makes sense. So the mains booster is a bit of a pre-requisite by the sounds of it. Thanks for the feedback on the unvented cylinder.

MikeJXE

I'm not a plumber but I do like to know how things work 

Can you explain if the incoming water is slow (low pressure) how can a pump push it out any faster ? (High pressure) it don't make any sense to me 

ThisIsWeird

Hi CH.

As said above, the first thing to do is to find out whether there's a fault or other issue causing your cold mains to be so poor, or whether that's 'it' - 7lpm is your lot. What storey is your flat on? And are there any above you?

Most Water Boards are obliged to provide a minimum flow rate of 9lpm, but this is at ground level, so this can and will drop off as you go 'up'.

(On that note, pressure and flow are quite different, although usually connected/associated to some degree. For instance, the minimum 9lpm mains 'flow' delivered at a decent ~2+bar pressure should be able to maintain most of that flow a few levels up, whereas a 9lpm flow delivered by a poor ~1bar pressure would soon have the flow dropping off noticeably on each floor. 'Flow' is easy to measure - you've just done it. I presume you opened a cold kitchen tap full on, and ran it for, say, 6 seconds. Then multiplied the measured amount of water given out by 10? Pressure requires a pressure gauge, but you can tell a lot by just how 'splashy' the flow is, and how easy to stop with your thumb. Any judgement on this?)

Ok, if the incoming flow is 'it', then you need to look at doing something internal, within your own flat. A very simple and lowish ~£350-ish cost method is to fit a mains booster bump like a 'Salamander' to your incoming pipe, and this will instantly give you 12lpm, which is the maximum you are allowed to boost the mains by. That would be a significant improvement over the current '7', and your electric shower should now work at pretty much its intended rate with this - which is still pretty poor as leccy showers are the worst. From what you describe, tho', apart from an improved electric shower and a faster-running cold kitchen tap, the Salamander would do nothing to boost the hot & cold supplies inside your flat, because they're being delivered by 'gravity' (the vented tanks), although currently boosted by other, unpleasantly-noisy, pumps. Awful setup.

Q - where is your CWS located?

There are a few solutions. But first find out if the cold mains is as good as you can get. If it can be improved by running a new mains supply pipe, or fixing a dodgy stopcock, then that is clearly the 'solution'. (Tho' it won't help Solutions:

1) Fit a mains Salamander to boost your 'incoming' to 12lpm. Quick and simple and pretty cheap. This will sort your electric shower, cold kitchen tap, but nothing else. Then you'd need to replace your internal 'booster' pumps with types which are much quieter in operation (I know someone who had Grundfos pumps fitted to each supply from their tanks, which were based on the well-known CH circulation pumps. These were actually really superb in operation, providing a gentle ~0.75b boost at a decent flow rate, and the really good thing about them was that they weren't noisy or excessively gushy - it was quite a 'natural' delivery, but both pumps soon burned out as they hadn't been installed properly ).

2) Fit a Salamander and swap your vented hot cylinder to an unvented type, and lose the CWS (cold water tank). This would be a marginal improvement over what you currently have, but bear in mind the incoming 12lpm would be shared between the H and C, so 12lpm would be your 'lot'. Ie, adequate, but not 'good'. It would have other advantages, tho' - you'd lose the CWS, and the noisy pumps. £350 for the Sala, and ~£1k+ for the unvented, and a fair bit of plumbing cost. For just about 'adequate'.

3) Now the serious stuff Properly boost the internal system by adding a mains booster with accumulator. These will have a built-in 12lpm mains pump, but will use this to charge up a storage accumulator (of various sizes), which will then deliver this stored, pressurised water at pretty much whatever rate you want. These 'work'. Wow, do they work! Smaller models will fit inside a 600mm kitchen base unit. Larger models will require a bit more room, tho' still smaller than a hot tank. Ok, that's half the job - it still won't help your internal 'vented' system, so that has to change too. So your options are (a) to fit the accumulator and replace your vented hot with an unvented cylinder, losing the CWS and internal booster pumps, or (b) to fit the accumulator and use it to drive a combi boiler, so you'd lose the CWS, the hot cylinder (none required) and current pumps.

So, '3' is the full solution, and I know that it works as my bro had one fitted in his 6th-floor flat. He now has water flow and pressure that will knock you over in the shower. In fact it was sooo powerful, he had to have a Pressure Reducing Valve fitted to the outlet of the accumulator to reduce the pressure to 1 bar, since his shower was designed for the previous 'vented' system. Even at 'only' 1 bar, the flow is astonishing at full rate - you simply could not ask for more. Cost? Option (a) would be ~£1-1.5k for the accumulator, and similar for the unvented cylinder, plus all the required plumbing. (b) would be ditto for the accumulator, and ~£3k for the combi, and plumbing. These are obviously rough ballparks. Option (a) would need more room, as you'd require space for the accumulator, a hot cylinder, and the boiler. (b) requires space for the accumulator and the new combi - all the tanks, hot and cold, would go. My bro has option (b), and luckily has the accumulator on the building's roof inside a purpose-made shed.

A word on mains booster accumulators. There are two essential types; one - typically the Grundfos - has a tank which is filled by the existing mains flow, and it then boosts the output. This is what my bro has. This means the pump fires up every time a tap is turned on, and it can be noticeable (although not for my bro as it's on the roof...). I personally don't like this design, because I hate pumps coming on every time you turn a tap (although it works quite 'naturally' in practice), but also because he had friends visiting recently who managed to empty the Grundfos through having looong showers in succession. He now had a mains Salamander also fitted, in order to boost the supply to the accumulator, so it is kept topped up at the 12lpm rate and shouldn't ever empty again! The other accumulator type is as made by Challis, and is the type I actually wanted him to get, but the plumber he found 'only fitted Grundfos, mate'. The Challis has a pressurised tank (the Grundfos is just effectively a vented CWS), so the mains booster pump fitted to it (essentially a 'Salamander' type) fills the accum, and pressurises it to around 3bar. When you then open a hot or cold tap, you are getting whatever flow you want - up to say 30lpm quite easily - delivered at 3bar! That is WOW! Obviously, if you open all your taps, you'll empty the tank pretty quickly, but they are large enough to not do so easily, and drawing 30lpm is just off-the-scale anyway. But it can do it. My understanding of the Challis is that the pump only fires up to refill the tank when needed, so drawing off some water - washing your hands and stuff - won't always have it firing up. But, it will mean that the pump will keep going after taps have been shut as it refills and repressurises the accum. Being only a 12lpm pump, it ain't as noisy as the Grundfos's powerful outputting pump.

I contacted Challis, and actually spoke to Mr C himself. It was what I wanted to get, but my bro really struggled to find anyone in London who knew about these mains accumulators (that was ~10 years ago), and the only one he found would only do the Grund. But, it really really is the 'answer', but could be noisy inside a flat. If you are ground-floor, is there any chance of fitting it outside? Garage? Shed? Purpose-built?

ThisIsWeird

MikeJXE said:

I'm not a plumber but I do like to know how things work 

Can you explain if the incoming water is slow (low pressure) how can a pump push it out any faster ? (High pressure) it don't make any sense to me 

The relationship between pressure and flow can be confusing.

Flow is just that - the amount of water being delivered in litres per minute. This same quantity can be delivered under high pressure, or low, or anything in between. If it's delivered at a high pressure, the flow can be sent up multiple house storeys without the flow dropping off much. If the pressure is low, the flow rate will drop off more obviously with each floor height.

In practice, in your home, if you have a very good flow coming out your kitchen cold tap, then almost certainly it'll be delivered by a correspondingly high pressure too. And vice versa - a very poor flow will likely have a low pressure behind it. That's because, when allowing for everything else - pipe size, etc. - if you increase the pressure, the flow will also increase by a corresponding amount. 

But not always.

Imagine your cold mains stopcock is fully open, and is delivering a whopping 30lpm at 3 bar - nice. If you turn the stopcock down, what will happen? The flow will drop off, ultimately until you have only a trickle coming through. What's happened to the pressure? The 'static' pressure is still 3 bar You can prove this to yourself by placing your thumb over the end of the tap spout when it's at this trickle - the water pressure will still reach the 3 bar under your thumb, and will still push your thumb off. Not as dramatically - quickly - as with the fast-running tap, but it'll still do it. Ditto, a 3 bar mains pressure, with the flow turned down to a trickle using the stopcock, will still reach up multiple storeys of height. Not as quickly, but it will get there. But a low pressure will just not get the flow up 'there', whether turned on fast or slow.

'Vented' domestic water systems rely purely on gravity to supply the taps - the CWS is usually just 1 to 3 metres above the bath height, for example. The water pressure will be very low - a fraction of one bar. Does this mean the flow is poor too? No, it can gush out the taps with abandon. The only practical differences are, you need to use larger pipes to deliver this low-pressure flow (which is why such bath taps have 22mm pipes), and you can stop this gush very easily with your thumb.

Another example of high-flow with low-pressure - place a barrel of water on a stand, and punch a large hole in its bottom - stand under it. You will get gallons of water per minute landing on your head, but at only 0.03 bar pressure (est...)

An example of an unexpected relationship is a pressure-washer - most of us have used these. You pull the trigger, and the water sprays out very powerfully. It also looks as though a lot of water is coming out, yes? Try this next time - aim it into a bucket, and pull the trigger for 10 seconds. Now just empty the garden hose directly into the bucket also for 10 seconds. The latter won't be nearly as dramatic, but - guess what - there will almost certainly be less water in your bucket when delivered by the pressure washer. Less water, but it's being delivered at a whopping 10 bar or more.

A sometimes good analogy is with electricity (these don't always work); 'pressure' is the voltage. This is what drives the electricity along a wire. It is its 'force'. It's what will push the electricity through your body, and along thousands of miles of cable. The actual 'flow' is current. As with water, for any given size of pipe (or wire), if you double the pressure (voltage) you will get a corresponding doubling of flow (current).

The Salamander mains booster pump 'sucks' the extra water out of the street mains. 'Sucks' sucks as a scientific word - it shouldn't be used - but you know what I mean :-)

They are regulated to not draw more than 12 lpm. It can deliver this meagre 12lpm at a very healthy pressure, tho', a bit like a pressure washer. It's restricted to 12lpm because much more than this could run the risk of depriving your neighbours :-)

ch_152

ThisIsWeird said:

Hi CH.

...

Thanks so much for this response, and for the explanation of pressure vs flow below it - very useful.

So a few bits to add:

I'm on the second and top floors of a 3 floor development. Built early 70's. 

By CWS do you mean cold water store? If so, it's in the top of the utility cupboard on the top floor. 

The pump the vented cylinder and cold water stores currently run through is actually a salamander pump (photo at the end of this message). The pressure when this runs to the upstairs taps is fine. Nothing great, but fine. But it often takes a couple of seconds to kick in, and is also loud!

I think the system the plumber was proposing to me was either 2 or 3. But 3 was what I was thinking would need to be the case (having a "buffer vessel" of sorts (accumulator as you call it) on the mains water). Thanks for the notes on the accumulators though. I'm not often likely to run into the case where it would run out (e.g numerous showers). 

I'm also currently in the situation where a pump runs whenever anyone uses the taps, so that doesn't bother me toooo much.


Thanks again.

ThisIsWeird

ch_152 said:

I'm on the second and top floors of a 3 floor development. Built early 70's. 

By CWS do you mean cold water store? If so, it's in the top of the utility cupboard on the top floor. 

The pump the vented cylinder and cold water stores currently run through is actually a salamander pump (photo at the end of this message). The pressure when this runs to the upstairs taps is fine. Nothing great, but fine. But it often takes a couple of seconds to kick in, and is also loud!

I think the system the plumber was proposing to me was either 2 or 3. But 3 was what I was thinking would need to be the case (having a "buffer vessel" of sorts (accumulator as you call it) on the mains water). Thanks for the notes on the accumulators though. I'm not often likely to run into the case where it would run out (e.g numerous showers). 

I'm also currently in the situation where a pump runs whenever anyone uses the taps, so that doesn't bother me toooo much.

Yes, the CWS is the cold water storage tank, and it's the height of this that provides the hot and cold flows to everything in your flat apart from the cold kitchen sink, which comes direct from the mains. If the CWS can be raised, then that's the best solution. You don't happen to have an accessible flat roof, do you?!

'Salamander' is a make, just like Grundfos and Stuart-Turner - the three big makes. I doubt there's much to choose between them, but a lot comes down to how well they are installed - mounted on vibe-free pads, etc. They will always be a bit noisy, tho'.

Solution '2' - changing to an unvented cylinder and adding a Salamander (or similar) booster pump to the mains - will always be limited to the max 12lpm flow permitted by the Water Boards. That 12lpm will be shared between the H&C. I would suggest that this would be 'just about' acceptable, but it won't be 'good'. It'll be a fair bit of money, so you'd need to know you'd be happy with just this level of improvement.

'3' is the ultimate solution, and will give you everything you could possibly want. You will need to find room for the unit, of course, and also a swap to an unvented hot cylinder. If you don't think your water demand will be that high, then you can almost certainly fit in a smaller booster-accum, and a small unvented cylinder too - perhaps they'll both fit in the same cupboard? Worth some research. When full, they will provide all you could possibly want. Even when 'empty' - if you manage to drain the accumulator - it will still keep providing the 12lpm from the mains, just like solution 2.

First, tho', is to find out if the flow can be improved passively, eg by fitting a new supply pipe, or locating a fault in the current one if that's the case. Also worth having your mains tested properly for flow and pressure - remember, these are different. If you find, for example, that your pitiful 7lpm flow can not be improved, but it's actually being delivered at a healthy, say, 2bar or above - then that would be great news because you could fit a passive accumulator, one that doesn't even need a pump! Challis make pump-free versions that rely on being 'charged up' by the existing water pressure. They have a compressible membrane inside the tank, with sealed air on one side. The mains supply fills the water side at whatever rate it can, and compresses this air bubble. The water will therefore be stored at the mains pressure, and can then be released to the flat at whatever flow rate you want.

https://www.challisshowers.com/about-the-company (and others by Grudnfos, S-T, etc)

ch_152

ThisIsWeird said:

..

Again, thanks very much for the detail here. Yeah I had looked at raising the CWS, unfortunately there's no real opportunity to do so (it's not far off touching the ceiling and don't have access to the roof as it's a leasehold flat).

I think I'm starting to understand this though. If my incoming water is at high enough pressure, it's able to fill the accumulator tank without needing to be pumped in. If my incoming water pressure is not good, it won't be able to fill the accumulator so requires a pump beforehand. I assume all the pipework after the accumulator likely needs to be replaced so that it can accommodate the higher volume of water coming out of the accumulator?


The Challis manual has some useful schematics in too (including with unvented cylinders)
 (https://www.dropbox.com/s/3auydj6x3m3qeki/131018%20Challis%20CMS%20Booster%20Manual%20A4%20Prf2%20copy-compressed.pdf?dl=0)


In terms of locations, I think I'd keep the unvented cylinder in the cupboard upstairs where the current vented cylinder and CWS live. There's decent spot down in the meter cupboard (where the cold water enters the property) to fit an accumulator too - although would it be considered terribly unwise to locate a cylinder of pressurised water in the cupboard where the incoming electricity is?!

Guess I also need to look into what kind of capacities of both the unvented cylinder and the accumulator I would need to see where they fit best...


But you're right, a bit more investigation to do first into the flow rate and pressure. Will get someone to check the pipework and the stopcock etc.



Here's a stupid question. If everyone installed mains booster pumps which "suck" water at a greater rate from the supply to the building or development, surely that would cause issues somewhere upstream?!