We bought a 1.5bar shower pump to use with a mixer shower. Our plumber has said that our cylinder is too small - it is 94 litres- and we need to get a bigger one (or give up and install an electric shower). If a
1.5 bar pump draws around 12 litres a minute isn't this enough for a shower each for two people? Do we really need to go to the expense and effort of changing our cylinder?Any advice or comments will be very much appreciated.
Thanks, Emma and Andy (Leeds)
It really depends on what you want to achieve.
If it's a sensation of needle jets on the skin, then fitting a smaller shower head or one with finer jets will help.
10-12 lpm is typical for these.If you want a decent pressure and volume then 15-20lpm is more reasonable and what you would get with a typical adjustable pattern shower head.
If you have a 94 litre cylinder with water heated to 60 degrees and you mix it with cold mains water to produce shower temperature water you can calculate the volume you would get and thus how long the shower will run using
Vc[Tf-Tc] = Vh[Th-Tf]
where
Vc = cold volume Vh = hot volume Tf = mixed water temperature Th = hot temperature Tc = cold temperature
At this time of year, mains cold temperature averages around 8 degrees so
Vc ( 40 - 8 ) = 94 ( 60 - 40 )
32 x Vc = 1880Vc = 58.75
Thus you will get around 150 litres of shower temperature before the water runs out.
The shower will run for 10-15 mins depending on flow rate.
In practice, the performance isn't quite as bad as that because the boiler will start reheating the cylinder as soon as it begins to cool. However, if the cylinder is a relatively old one, the heating rate won't be very high since heat is not transferred from the boiler that quickly.
If you want to make a big difference, then you need to increase the cylinder size and make it a fast recovery type.
Otherwise showers will need to short or intimate.
Thanks very much for your helpful reply. It is much appreciated - when one is struggling to understand these things that lie outside one's normal competance!
Best E and A
Store the water hotter, which mean effectively increasing the cylinder size. You can store the water at 60 to 80C depending on what suits you. You must fit a thermopstaic blending valve (TMV) on the hot water outlet of the cylinder dropping the temperature down to 45C to 55C at the taps. You can us the 60C to 80C water directly to the shower mixer if thermostatic. Cost? £30 to 50 depending on quality of blending valve.
Lag the pipes in the airing cupboard.
Did he comment on the cystern tank? That supplies the cold for the shower and refils the cylinder so needs to be a decent size. If thats OK I'd say with the thermostat turned up as DrDrivel says and extra laggining on the cylinder and pipes and having the boiler heating the water at the time you take showers then 94 litres will be good.
Except that we don't know how quickly the boiler can heat the cylinder
- it may be one with a small coil, or gravity heated, or not using a diverter valve. Any of these will result in slow reheat rate to the point that the addition from the boiler may not make a lot of difference.
Extra lagging on the cylinder and pipes won't affect the performance or capacity - only the heat losses in the steady state.
You can use the 60C to 80C water directly to the shower mixer i
thermostatic. Cost? £30 to 50 depending on quality of blending valve.
Lag the pipes in the airing cupboard.
Do you mean that water above 65 degrees will be going through th shower pump? If this is the case then this could cause cavitation o the pump. The water supplied to these pumps needs to be under 6 degrees. Correct me if I wrong??
-- Fatboise
Turning up the cylinder temperature may be a real hazard if young children are around. You are talking of 80C coming out of a hot tap, with skin removing properties. I'd either do as Andy says and settle for short showers or fit a decent size cylinder as the experienced plumber advocates.
Regards Capitol
Depends on the pump. See instructions. If the temp is belwo 65C then take the shower through the TMV.
Which is silly, a lot of mess and expensive when £30 to £50 for a TMV can solve the lot.
The principle is interesting, but if one thinks it through, increasing the temperature to 80 degrees provides the equivalent of about 120 litres of 60 degree water and only in the steady state. This may well still not be enough. I didn't find it so, having had a 120 litre cylinder and wanting to run successive showers and/or baths. I increased mine to 200 litres.
Furthermore, the contribution from the boiler, when the heat is transferred via a standard cylinder coil, will not be anything like as great when heating the water in the 80 degree range as it is up to 60 degrees simply because the cylinder temperature approaches the primary water temperature.
In practice, once cold water is entering the cylinder, this won't matter too much while the shower is running (what heat there is will be added), but recovery time up to 80 degrees is a lot longer than to
60 degrees because less heat is transferred at higher temperatures, with consequent cycling or modulating of the boiler.
You could always install the pump and try it. If the cylinder is too small it will go cold when the water is exhausted. If this is too quick for you then you could try one of the other suggested solutions.
Matt, it works.
You never tried a TMV, as you had never heard of opne.
In practice it works, and is cheap and gives virtually constant DHW temps.
A modulating boiler can supply a constant 80C, whether full on burner or at the lowest.
The cheapest and first attack is a TMV. Even after fitting that, if the cylinder is too small then the TMV is a very welcome addition to a new cylinder giving constant DHW temps.
ACV sell a tank-in-tank cylinder which is set to 65C minimum (the cylinder stat cannot go below this temp) to conform to EU anti-legionella regs. They provide a TMV to drop the DHW temp. TMVs are becoming the norm and may be standard soon.
I didn't say that it wouldn't "work", only that it may well not be adequate.
Don't be silly. It wouldn't have done the job in terms of providing enough water. You can't get a quart out of a pint pot.
Until the hot water runs out.
The point is that if it is a standard cyinder (and remember your point was that the cylinder would not need to be changed), then the coil surface area is limited and results in low heat transfer as compared with a fat recovery type.
The boiler will modulate or cycle because the return temperature approaches the flow temperature and the average heat transfer will be limited by the coil surface area and the difference in temperature between primary and secondary water.
With a standard cylinder, and attempting to heat to 80 degrees, this will happen a great deal sooner than with either a fast recovery cylinder or a direct heat bank. Therefore the issue of recovery time to 80 degrees becomes a real issue.
I am not disagreeing that an 80 degree cylinder plus a thermostatic blending valve will do *something* - I am suggesting that it probably won't do enough to make a worthwhile difference in this case.
Therefore, I think that the pragmatic solution would be
- Install the shower pump - that will be needed anyway.
- Try out how long the shower runs and whether recovery time is good enough.
- Check also that cold water storage is enough.
If all of the above passes, then there is nothing more to do
If not, then decide whether adding 20% or so to flow rate or run time meets the requirements.
If it does, then perhaps the blending valve approach is worth considering.
If it doesn't, then upgrade the cylinder. This avoids spending money on a blending valve that might not give the desired increase in usable hot water volume
It only cost a few quid to fit and no scalding water either. If nor good enough then spend a fortune on upgrading the cylinder. If upgrading the cylinder then a heat bank should be considered and go all mains pressure and no silly pumps. A plumber will always say a new cylinder as he wants to rip the customer off.
You had never heard of one until the likes of me told you.
Which it will with any cylinder.
I know that, and your statement was pointless.
Again, I know that, and your statement was pointless.
Again, I know that, and your statement was pointless. The issue is not fast recovery. It is to store more energy at a higher temperature, blending down via TMV.
You are guessing. A poor guess too.
I may be worth looking at the age and state of the cylinder and assessing. If dodgy, then look at a mains pressure heat bank if the mains flow and pressure is god enough. If the cylinder needs upgrading "and" a top quality pump, then the little extra, if there is any extra, is worth it to go thermal store or heat bank mains pressure, a much superior solution and no screaming power shower pumps.
About £50 plus fitting.....
Apart from the one to feed the heat exchanger, but we'll leave that aside.
He may also want to provide a solution that will work and for which he won't get called back.
Actually I had, but either way it doesn't alter what can and can't be achieved.
Obviously. The issue is when.
I'm glad to hear that you were aware of the limitations.
I just wanted to be sure. Often your schemes defy physics.
If you are trying to have a series of showers based on a possibly inadequate supply of hot water, recovery is very important.
It will take considerably longer than direct proportion for the cylinder to be reheated to 80 degrees than it does to 60 degrees.
We are both guessing. You don't know what the desired flow rate and desired run time for the shower is. Without that data, it is all conjecture.
Two points.
- Good quality shower pumps do not scream.
- Mains pressure water systems require an adequate pressure and flow of mains water.
I have seen them cheaper.
A Thermal store has none. A heat bank has a stadrad CH pumps. Quiet and reliable. Not a screaming power shower effort.
He should give the customer the options and take it from there. Here we have three. TMV, big conventional cylinder or heat bank.
Matt, you never.
Depends on the customers needs.
No, you are. I am objectively giving options on known information.
So, £300 and an extra large cylinder. May as well go mains pressure thermal store/heat bank.
Gosh. You don't say.
Whatever. Fitting cost will be >> materials.
Which is why I suggested leaving it aside.
Yes, and they are not equivalent.
The heatbank and larger cylinder have the potential to deliver as much water as the customer wants within reason. The TMV is limited to whatever the cylinder can provide.
Quite. If you read the original post, having at least two showers was a requirement.
So you're telepathic now? You know the flow rate of the shower and how long the users would like to stand under it?
Somebody has to since you usually gloss over that point.
Matt, power shower pumps should left back in the merchants.
You got it. If a cylinder is required I would go thermal store/heat bank as the pump to do two showers, or two pumps, wopuld be an expensive item(s). Albion Mainsflows are cheap enough and require no water pressure pumps.
Depends on the flow rate of each, not everyone wants a 30 litres/min rush. If high flows are called for and the maisn are uop to it. Then a thermal store/heat bank is the way to go.
No. Just more experienced at these matters than you.
It is stating the obvious.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.