How much do combi boilers reduce flow - DHW alternatives
- Thread starter Buzzark
- Start date
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Thanks TonyAgile said:
I haven't missed the point, I'm well aware of this - I did actually mention this was going to be done. The open pipe flow test was done because if I use something which doesn't restrict flow e.g. some unvented's or thermal stores this is the flow I'll get. Flow on a restricted opening isn't going to flow any faster though, so it's a baseline figure "as is".
Unfortunately this voids the warranty though - at least with WB.Agile said:
Agile said:
Yes, as mentioned this has already been done about 2 years ago. It's in 25mm MDPE at the moment with this 15mm stocktap plonked in the middle - well done United Utilities, the previous owner was really honored to be able to pay around £2000 for a job well done - not! PS, thanks for not bothering to lag this pipe according to the regulations too.
Buzzark you are getting a lot wrong about pressure and flow!
2.3x is wrong. iirc it's about 3.2. But if you make one little bit of pipe bigger it won't make any difference at all.
If you're really only getting 14l/min from a good average pressure main , say 3 bar, you have a big resistance somewhere. It is NOT the bleedin stop cock, OK, inless it's faulty. Pressure drop across a 1/2" stop cock at 14l/min is about 1 metre, or about 0.3 metres for a 3/4".
2.3x is wrong. iirc it's about 3.2. But if you make one little bit of pipe bigger it won't make any difference at all.
If you're really only getting 14l/min from a good average pressure main , say 3 bar, you have a big resistance somewhere. It is NOT the bleedin stop cock, OK, inless it's faulty. Pressure drop across a 1/2" stop cock at 14l/min is about 1 metre, or about 0.3 metres for a 3/4".
Wrong - everything restricts the flow.
Chris this seems to be someone who thinks he knows more than the experts!
We try to help but whatever we say he thinks he knows more!
He has completely missed the fact that his shower needs a dynamic pressure of at least 0.5 bar to make the water exit the orifices at a reasonable velocity!
The thought that comes to my mind is that he thinks that anyone involved in plumbing is ALWAYS totally uneducated and would NEVER have a degree!
Its not clear why he has not already replaced the 1/2" stopcock ???
Tony
We try to help but whatever we say he thinks he knows more!
He has completely missed the fact that his shower needs a dynamic pressure of at least 0.5 bar to make the water exit the orifices at a reasonable velocity!
The thought that comes to my mind is that he thinks that anyone involved in plumbing is ALWAYS totally uneducated and would NEVER have a degree!
Its not clear why he has not already replaced the 1/2" stopcock ???
Tony
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Agile said:
Er, nope. Just trying to understand the logic - not trying to be offensive, sorry if it came out that way.
Not really, I realise I need dynamic pressure.
Actually, I know a couple of them with degrees, one with a masters... true, not all the ones I've met have been so educated but there's probably the same mix as any other profession. Fluid dynamics isn't exactly the easiest thing to get your head around.
It hasn't been a problem until now, I was quite happy with a tank fed, pumped shower but we're going to need the space. Like I said, that's booked in for next Friday.
Sorry if I've offended any of the experts. All I'm trying to say is that if you have a pipe with an internal cross section of 320mmsq like a 25mm MDPE pipe and restrict that opening with a 15mm stoptap which has a maximum cross section of 145mmsq (taken from 15mm copper tube) then for the same dynamic supply pressure there's a 2.3x difference in available flow. 1 bar dynamic pressure into a 145mmsq opening gives 13l/m flow, the same 1 bar dynamic pressure into a 320mmsq opening gives 30l/m.
I'm not talking about head loss in meters between 15mm and 22mm because each of those are rated against the pipe being the equivalent size as the stop tap, which isn't the case here.
After all, this is just how a tap works isn't it? Your tap has a maximum opening and it flows fully at that opening. You half close the tap by reducing the opening by a half and you get around half the flow - there's some difference according to the dynamic pressure but provided that remains reasonably constant or high enough at least, then this has less effect.
All I really wanted to know was;
If the flow/pressure/dynamic pressure isn't up to what we'd like it to be and we can't use a cold water storage tank and assuming we don't fit an accumulator...
What option gives the best performance for the water supply we feed it.
Obviously they all restrict flow to a degree, which make/model/type/option restricts the least.
Again, I do not wish to offend anyone by posing questions about the incoming supply - that will whatever it will be. Whether that's x or X doesn't really matter.
If the flow/pressure/dynamic pressure isn't up to what we'd like it to be and we can't use a cold water storage tank and assuming we don't fit an accumulator...
What option gives the best performance for the water supply we feed it.
Obviously they all restrict flow to a degree, which make/model/type/option restricts the least.
Again, I do not wish to offend anyone by posing questions about the incoming supply - that will whatever it will be. Whether that's x or X doesn't really matter.
One of my relatives had a saying - 'champagne ideas, beer money'.
If you want to raise your water flow either buy a faster combi ie: Vaillant 937, WB Highflo 440 or Viessmann 333, or an unvented, and bang an accumulator in front of them. This will cost money.
If you can't afford that, shower pump your gravity system and put up with the noise.
I like that - how true.simond said:
simond said:
Yes, an accumulator is probably above the beer money threshold.
We've currently got a nice reasonably powerful pumped shower set on a concrete isolation platform so no noise issues really there.
The problem we've got is that in order to get the best space in the loft, ideally the current cold water tank needs to go - if it came down to accumulator money, we'd probably be better compromising on losing that space.
I've got a loft planner coming in to see what our options are but where the tank is currently situated is really the best place for the stairs.
I suppose we could move it sideways and drop it down to just above a normal DHW cylinder, that might be an option.Life's always about compromises, or rather finding the best solution for your budget isn't it?
Just an update for what it's worth.
The plumber was tied up and got here too late to do the work yesterday.
So, I just bought the bits myself including a pressure gauge to take some readings.
Before the work:
14l/m at the bath tap (fastest flowing tap and close in height to the shower)
Static pressure 2.2 bar
Dynamic pressure 0.7 bar
After the work:
20l/m at the bath tap
Static pressure 2.2 bar
Dynamic pressure 1.3 bar
The work was done mid afternoon, on a Saturday.
I've just rechecked the static pressure and that's now at 2.6 bar @ 8.30pm so better than before.
So overall while the static pressure won't win any awards, it's not too bad.
14l/m to 20l/m makes a big difference visually when running a tap and you can feel it comes out with more force.
A 42% increase in flow and almost double the dynamic pressure is nothing to be sniffed at I suppose for about £18 and a couple of hours work.
I'm reasonably pleased at this point in that we should have enough to at least hit the break even point of matching the existing pumped shower while being able to clear space by removing the cold water feed tank.
We'll either be switching to a big storage combi, unvented or heatbank not quite decided yet. We don't have much pressure to work with so I've drawn up a table comparing all options/models and flow vs pressure. One to ponder on for now...
Another interesting find during the process was that the actual mains tap out on the street isn't a plastic one as expected. So even though UU put MDPE in, it seems they must have just done this within the boundry of the property so there might be a little more available in dynamic pressure if we could get that changed. I guess that would be a cost option though but it's worth asking?
Another option to give better dynamic pressure for showering might be to fit an accumulator as I guess we only need about 60 litres of water, probably less than that to suppliment the rate it comes in at. One for a seperate post I think.
The plumber was tied up and got here too late to do the work yesterday.
So, I just bought the bits myself including a pressure gauge to take some readings.
Before the work:
14l/m at the bath tap (fastest flowing tap and close in height to the shower)
Static pressure 2.2 bar
Dynamic pressure 0.7 bar
After the work:
20l/m at the bath tap
Static pressure 2.2 bar
Dynamic pressure 1.3 bar
The work was done mid afternoon, on a Saturday.
I've just rechecked the static pressure and that's now at 2.6 bar @ 8.30pm so better than before.
So overall while the static pressure won't win any awards, it's not too bad.
14l/m to 20l/m makes a big difference visually when running a tap and you can feel it comes out with more force.
A 42% increase in flow and almost double the dynamic pressure is nothing to be sniffed at I suppose for about £18 and a couple of hours work.
I'm reasonably pleased at this point in that we should have enough to at least hit the break even point of matching the existing pumped shower while being able to clear space by removing the cold water feed tank.
We'll either be switching to a big storage combi, unvented or heatbank not quite decided yet. We don't have much pressure to work with so I've drawn up a table comparing all options/models and flow vs pressure. One to ponder on for now...
Another interesting find during the process was that the actual mains tap out on the street isn't a plastic one as expected. So even though UU put MDPE in, it seems they must have just done this within the boundry of the property so there might be a little more available in dynamic pressure if we could get that changed. I guess that would be a cost option though but it's worth asking?
Another option to give better dynamic pressure for showering might be to fit an accumulator as I guess we only need about 60 litres of water, probably less than that to suppliment the rate it comes in at. One for a seperate post I think.
Ah yes, quite true - I just fitted the same sort of thing.
It looks pretty old and not "brassy" as such but it is dirty down there (about 3 ft) and I don't know how long it would take to change colour. I believe the work was done about 3 years ago but that's still a possibility.
It looks pretty old and not "brassy" as such but it is dirty down there (about 3 ft) and I don't know how long it would take to change colour. I believe the work was done about 3 years ago but that's still a possibility.
A
Amateur99
Buzzark, do you have a copy of that comparison table that you'd be willing to share?
And which solution did you end up going for? Would be very interested to hear about your experience, if you've got time.
Thanks!
I deleted the most complete one but have one from backup, unfortunately it doesn't paste well into here. It's nothing exciting either just details I was able to glean from the brochures etc to try and compare side by side and this is looking crap on the limited formatting of thise forum I'm afraid...
In the end I went with the Worcester Bosch Highflow 440. Even though the kit price was about the same between an unvented and the WB those who could quoted around £700-1000 more to fit the unvented. Weird, the unvented had all the pipes pretty much in place and was almost a straight swap.
The WB was also a better fit replacing the existing boiler and the company we chose had experience with them.
The install went really well and they did a really good job. The system was in good condition inside (very clean water, lots of inhibitor) but was cleaned overnight and flushed before the final completion.
Performance wise, it's very close to our 1.5Bar Salamander pump as a shower. The water pressure and available flow is holding it back a bit in terms of bath filling speed. I guess 40l/m of available flow would give us 20l/m of hot and again of cold. We've got 20l/m though and it will do that hot at around 62c or cold or half each.
Of course the temperature doesn't decrease like with the cylinder and pump it replaced. After a 10-12 minute shower it takes 4 minutes to finish re-heating the tank so I guess we're hardly draining much of the heat out of the thermal store.
As for operation, the instructions are a bit vague on how it functions as a hybrid/combi type system. Out of the box, it's a combi without a timer with DHW always there. Once the timer is on, it's more like a seperate system boiler and thermal store but in one box. It only keeps hot between the programmed hours and depletes the store in "Eco mode" when DHW demand is placed on it outside of these hours.
I guess you could have it always on for DHW if required.
Overall very pleased with the performance of the boiler and it would do more if we had the supply for it.
Still tweaking the new themostatic rad valves and system balancing etc to get the CH controlled to just how we want it and to try and keep the output low enough to make it condense as much as possible while on CH.
Hope that helps, just ask if there's something in particular I've not mentioned.
Sorry about the formatting of the table, had several goes and the forum just fights back!
- Solution. DHW flow. HW store size. Pressure required. Cost. Pro's. Con's. DHW backup?. Siting Wall or floor Sizes. Good/bad reviews?.
Boilers
Atmos 24/80 25l/m @ 60c 80 1.5 bar Large hw store Size No Floor Good quality, v good HW supply
WB Highflow combi 20l/m @ 65c 60L thermal store 1.5 bar 1530 Fits under counter, thermal store, 8-10 minute recharge, supposed to fill at least a bath probably more Reliability? No Under counter Floor 850h 600w 600d Poor reviews on reliability?
Potterton Powermax 30l/m @ 60c, or more 85 1 bar for 30l/m Best at limited pressure Size + poor reputation Yes Floor 1110h 550w 600d Poor reliability?
Vokera Linea combi 14l/m @ 35 rise 0 ? 753 Fits in cupboard without door Limited flow No In cupboard Wall 845h 453w 358d
Valliant EcoTec 937 15l/m @ 65c 15 0.75 bar Combi + better flow How long does better flow last? No In place of fridge Wall 720h 440w 600d ish
Ideal Istor 35l/m @ 65c 80 ? 1435 High flow Size No Floor 1550h 560w 600d Poor reliability?
Alpha CD50 18l/m @ 65c 52 ? 1075 High flow for size Big No In place of fridge Wall 900h 600w 450d + 200-250 above and below
WB 42CDi 17 @ 35 rise, 15 @ 42 rise 3.75 1.9 bar 1200 Fits in cupboard without door Flow No 760h 440w 360d
WB 37CDi 15 @ 35 rise, 13 @ 42 rise 3.75 1.6 bar 1022 Fits in cupboard without door Flow No 760h 440w 360d
U/V Cylinders
Valliant Unistor 20 in @2 bar, 17 out 125 658 16 REHEAT all parts inc 969h 554w
Keston Spa 125 23min heat 906h 550w top exit
Ariston Prima 125 658 18min REHEAT 20.5kw coil kit inc 995h 505w side exit
Range Tribune 23 out @ 1.3 bar static? 120 618 17min REHEAT 16.5kw all parts inc 906h 550w top exit
Oso 125 681 12kw 900h 580w top exit
Santon PremPlus 20 in @2 bar, 17 out 120 564 27min heat 12.5kw coil 906h 550w top exit
Glow Worm
Ariston Primo 210 Litre 210 750 Height 1475mm
Keston Spa 200 881 13min reheat 33kW 1165
Range Tribune 23 out @ 1.3 bar static? 210 708 22 reheat 18.9kW 1469
Vaillant UniSTOR 210 922 20.7 reheat 1499
Vaillant UniSTOR 180 787 16.5 reheat 1339
Range Tribune 180 681 21 reheat 18.9kW
In the end I went with the Worcester Bosch Highflow 440. Even though the kit price was about the same between an unvented and the WB those who could quoted around £700-1000 more to fit the unvented. Weird, the unvented had all the pipes pretty much in place and was almost a straight swap.
The WB was also a better fit replacing the existing boiler and the company we chose had experience with them.
The install went really well and they did a really good job. The system was in good condition inside (very clean water, lots of inhibitor) but was cleaned overnight and flushed before the final completion.
Performance wise, it's very close to our 1.5Bar Salamander pump as a shower. The water pressure and available flow is holding it back a bit in terms of bath filling speed. I guess 40l/m of available flow would give us 20l/m of hot and again of cold. We've got 20l/m though and it will do that hot at around 62c or cold or half each.
Of course the temperature doesn't decrease like with the cylinder and pump it replaced. After a 10-12 minute shower it takes 4 minutes to finish re-heating the tank so I guess we're hardly draining much of the heat out of the thermal store.
As for operation, the instructions are a bit vague on how it functions as a hybrid/combi type system. Out of the box, it's a combi without a timer with DHW always there. Once the timer is on, it's more like a seperate system boiler and thermal store but in one box. It only keeps hot between the programmed hours and depletes the store in "Eco mode" when DHW demand is placed on it outside of these hours.
I guess you could have it always on for DHW if required.
Overall very pleased with the performance of the boiler and it would do more if we had the supply for it.
Still tweaking the new themostatic rad valves and system balancing etc to get the CH controlled to just how we want it and to try and keep the output low enough to make it condense as much as possible while on CH.
Hope that helps, just ask if there's something in particular I've not mentioned.
Sorry about the formatting of the table, had several goes and the forum just fights back!
A
Amateur99
Buzzark, thank you so much for going to so much trouble to answer my questions - am really grateful.
Cheers!
Cheers!
No problem, although the "table" probably wasn't much use!
I personally found that getting useful information to make an informed decision quite a pain when going through the process. This is mainly down to the manufacturers, they could all try a lot harder.
I can't think of another industry quite as vague (from the manufacturers) in terms of detailed information about products. The manufacturers seem to think the installer will spend hours consulting with the customer, the installers of course don't have time to spend doing that and still don't have much much detailed info from the manufacturers either.
Take the example of setting up controls on the WB highflow for example. There's a boiler users guide, of course it only covers "the boiler" no controls. There's the controls guide which pretty much just covers plugging the device in and how to set some times...
Erm, rant over! It's an odd industry and one clearly not made at all easy for the installers.
Thankfully there are some very helpful folks on here, when they're not fighting over what's the best system to install! Even when they are, it's still useful information though.
I personally found that getting useful information to make an informed decision quite a pain when going through the process. This is mainly down to the manufacturers, they could all try a lot harder.
I can't think of another industry quite as vague (from the manufacturers) in terms of detailed information about products. The manufacturers seem to think the installer will spend hours consulting with the customer, the installers of course don't have time to spend doing that and still don't have much much detailed info from the manufacturers either.
Take the example of setting up controls on the WB highflow for example. There's a boiler users guide, of course it only covers "the boiler" no controls. There's the controls guide which pretty much just covers plugging the device in and how to set some times...
Erm, rant over! It's an odd industry and one clearly not made at all easy for the installers.
Thankfully there are some very helpful folks on here, when they're not fighting over what's the best system to install!
Even when they are, it's still useful information though.DIYnot Local
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