UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old September 16th 03, 11:13 AM
Julia Mann
 
Posts: n/a
Default Megaflow Query

I need some urgent advice please!

I live in a flat and am about to have a new indirect hot water tank
installed. The guy who is doing it has also fitted new taps for me
throughout the flat, but the pressure of the hot water is awful. The
single tap on the bath is fine but the mixers in the bathroom, kitchen
and bedrooms have just a dribble of water.

I was then advised to have a megaflow fitted which would increase the
flow. I am waiting for a price for this but have also heard that some
taps are only suitable for high pressure systems, which may be the
cause of my worries, and just fitting new taps could solve it, and
save me a load of money! Also, what can I expect the megaflow unit to
cost?

Any advice asap would be most appreciated!

  #2   Report Post  
Old September 16th 03, 11:22 AM
IMM
 
Posts: n/a
Default Megaflow Query


"Julia Mann" wrote in message
om...
I need some urgent advice please!

I live in a flat and am about to have a new indirect hot water tank
installed. The guy who is doing it has also fitted new taps for me
throughout the flat, but the pressure of the hot water is awful. The
single tap on the bath is fine but the mixers in the bathroom, kitchen
and bedrooms have just a dribble of water.

I was then advised to have a megaflow fitted which would increase the
flow. I am waiting for a price for this but have also heard that some
taps are only suitable for high pressure systems, which may be the
cause of my worries, and just fitting new taps could solve it, and
save me a load of money! Also, what can I expect the megaflow unit to
cost?

Any advice asap would be most appreciated!


Firstly, what system do you have now? Secondly, Megaflos work from cold
water mains
pressure, so what is your mains pressure and flow rate like?

Thirdly, avoid the Megaflo, assuming you are replacing your existing system,
and get a heat bank, which are far better.
http://www.range-cylinders.co.uk (go to thermal storage)
http://www.heatweb.com






---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003


  #3   Report Post  
Old September 16th 03, 11:23 AM
Christian McArdle
 
Posts: n/a
Default Megaflow Query

and just fitting new taps could solve it, and save me a load
of money! Also, what can I expect the megaflow unit to cost?


The Megaflo will cost about 600 quid plus whatever mark up the guy thinks he
can get away with plus fitting (prob over 1000 quid in total). Although you
may get slightly better flow just replacing the taps, the Megaflo is a
seriously nice hot water system with fantastic performance. Compared to
gravity hot water systems and combi boilers, it is on a completely different
planet.

On the other hand, if you have a flat, you might just prefer a combi boiler,
as it means you don't need a cylinder at all. Pretty slow on the bath, but
good for showers.

Provided you have good mains pressure and flow, expect an unvented cylinder
to be able to fill a bath in under 2 minutes. Showers will never be the same
again.

Soon, you'll get a post from IMM advising you to get a heat bank instead.
These have certain advantages and disadvantages compared to an unvented
cylinder. They require the boiler to heat at a higher temperature, which is
less efficient and they have lower flow rates. However, they are simpler to
install and don't require the complicated safety systems that unvented
cylinders need. (There are plenty more issues on both sides of that one).

Christian.


  #5   Report Post  
Old September 16th 03, 12:13 PM
dmc
 
Posts: n/a
Default Megaflow Query

In article ,
Christian McArdle wrote:

Soon, you'll get a post from IMM advising you to get a heat bank instead.


He beat you by a couple of minutes this time :-)

Darren



  #6   Report Post  
Old September 16th 03, 02:37 PM
IMM
 
Posts: n/a
Default Megaflow Query


"Christian McArdle" wrote in message
. net...

Soon, you'll get a post from IMM advising you
to get a heat bank instead.


Already posted.

These have certain advantages and disadvantages
compared to an unvented cylinder.


Advantages far outweigh disadvantage. Look...

Advantages of Heat-Banks

- Instant high pressure hot water - When the store has reached temperature
water is delivered instantly at the taps.

- High mains water pressures at up to 10 bar, compared to 3.5 bar with
unvenetd cylinders.

- Very high water flow-rate - The high-end heat-banks have a flow-rate up to
45 litres/min.

- Long efficient boiler burn - Reduces boiler on-off cycling increasing
efficiency, although inefficient boiler cycling is no longer a major problem
with boilers with forced flues.

- Maintains optimum boiler temperature range using ablending valve the
flow/return of the boiler can be kept to opimum mainatinaing greater
effciencies. The boiler operates at optimum performance.

- Combines the output of the stored water and the boiler see the DPS GXV

- Cylinder may be smaller for a similar performance - smaler cylinders than
unvented cylinders.

- Cylinder at low pressure - Unlike an unvented cylinder it does not store
water at high pressures.

- Fast cylinder recovery rate - When the boiler is connected directly to the
heat-bank, and not via an indirect coil, the recovery rate is rapid.
Although in some cases a boiler may heat the heat-bank via an indirect coil,
reducing the recovery rate.

- Legionella bacteria eliminated - The Legionella bacteria cannot survive in
the high temperature sealed conditions of a heat-bank.

- No scale build-up in heat-bank Containing primary and not secondary
fresh water,
there is no scale build-up inside the heat-bank.

- Cold water storage eliminated - No need for cold water storage tanks.

- Solar heating storage - Water heated via solar panels may be stored in the
heat-bank via a solar coil.

- Easy maintenance - If an external plate heat exchanger requires cleaning
or replacing it is a matter of draining down the heat-bank, or closing
isolating vales, and unscrewing the plate heat-exchanger. In some rare
instances plate heat-exchangers are fitted directly inside the heat-bank
preventing on-site maintenance.

- Easy to improve hot water flowrates By simply adding additional plate
heat-exchangers in parallel, hot water flow rates may be improved. Retrofit
additions are possible if extra bathrooms or showers are installed. This is
impossible with unvented cylinders.

- Stored water vessel need not be cylindrical As no internal coil is used
for hot water heat transfer the stored water vessel may be any shape, as
opposed to a thermal store which has to be cylindrical for maximum
efficiency. This has advantages where space is limited.

Disadvantages of Heat-Banks

- The store needs be near fully temperature to supply baths - Before any hot
water is drawn off, the store must be up to temperature. Many later
versions use a blending valve on the return to the boiler to ensure only up
to temperature water is pumped into the store by the boiler. This prevents
agitation of the stored water, and aiding heat stratification within the
store giving useful water at the top of the store within a shot time. The
water is heated only in one pass through the boiler.

- May not take full advantage of a condensing boiler - Maintaining the
stored water at 75C to 80C results in a generally high boiler return
temperature. This will not take full advantage of a condensing boiler,
which increases in efficiency with lower return temperatures. With the
superior heat stratification of taller cylinders this problem will be
reduced. Condensing boilers with a high operational flow and return
temperature differential are best suited to thermal stores and heat banks.
Overall efficiency with condensing boilers is still very good.

- Lower water temperatures with fast flow-rates - As with Combi boilers,
fast flow-rates through the plate heat-exchanger results in lower water
temperatures. This is not so pronounced with heat-banks as with
thermal-stores. This also applies to unvented cylinders and combi's. With
a heat bank, extra plate heat-exchangers can be fitted to increase flow
rates.

They require the boiler to heat at a
higher temperature,


See above.

they have lower flow rates.


No so. They can operate up to 10 bar pressure. Unveneed cylinders can only
operate up a typical 3.5 bar.

However, they are simpler to
install and don't require the complicated
safety systems that unvented
cylinders need. (There are plenty more issues
on both sides of that one).


Advantages mainly to heat banks by miles.


---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003


  #7   Report Post  
Old September 16th 03, 02:41 PM
Christian McArdle
 
Posts: n/a
Default Megaflow Query

Mains flow at the kitchen cold tap is ~20 litres/min - the hot tap is
the same[2].


Heatrae Sadia recommend an absolute minimum 20lpm flow from your mains for
the Megaflo. This is definitely on the low side of what you should be using.
You are certainly limited by the maximum flow from the mains, rather than
the system inside your house. As a very rough guide for the maximum flow
rates for hot water you should expect for mains pressure systems:

Combi boiler (non-storage): 10 lpm
Heat bank: 40 lpm
Unvented cylinder: 75lpm

Obviously, these will vary a lot between manufacturer and boiler power etc.
However, none of these systems can provide more flow than your mains supply.
If you only have 20lpm from the mains and it is not practical to upgrade the
supply, then a combi might be more appropriate than an unvented cylinder
(being cheaper and smaller).

well but the shower flow rate is only around 9l/min.


Shower hoses and heads are notorious for slowing down the water. In
particular, if they are designed for combi boilers, they will do their best
to reduce the flow below 10 lpm for more reliable operation. It is possible
to get wider bore hoses and bigger holes in the shower head if your system
can provide a greater flow. If the shower head was designed for an electric
shower, it would have an even slower rate.

Christian.


  #8   Report Post  
Old September 16th 03, 03:04 PM
Christian McArdle
 
Posts: n/a
Default Megaflow Query

Whilst I agree with many of the advantages, I'd say not everything is
entirely true.

- High mains water pressures at up to 10 bar, compared to 3.5 bar with
unvenetd cylinders.


DPS seem to want a pressure reducing valve if static pressure is above 6
bar.

- Very high water flow-rate - The high-end heat-banks have a flow-rate up

to
45 litres/min.


Whilst very good, unvented cylinders will supply more. (i.e. Megaflo claims
72 lpm)

- Cold water storage eliminated - No need for cold water storage tanks.


A header or expansion tank is needed for the vented heat bank store. This is
frequently combined with the store itself in a combination cylinder, but
this requires additional head room.

- Lower water temperatures with fast flow-rates - As with Combi boilers,
fast flow-rates through the plate heat-exchanger results in lower water
temperatures. (...) This also applies to unvented cylinders (...)


Could you explain how increased flow rates decrease water temperature with
an unvented cylinder? The limit on flow rate with an unvented cylinder is
how much water you can shove through the thing, presuming a good design on
the water inlet that doesn't unduly disturb stratification. Obviously, if
you draw at 75lpm, a 150l cylinder will be cold well within 2 minutes (but
then you've already filled close to 2 baths by then).

No so. They can operate up to 10 bar pressure. Unveneed cylinders can only
operate up a typical 3.5 bar.


Again, the only heat bank I've got details for (DPS Pandora) claims 6 bar.
However, the pressure reduction isn't as bad as it seems. Obviously, as
water is drawn off, the pressure falls massively. So even if your static
pressure is 6 bar, drawing 75lpm will cause the pressure to collapse below 3
bar, meaning the pressure reducing valve is fully open, and only providing a
restriction in line with the reduced bore of its opening, probably
equivalent to a 90 degree elbow or a few metres of pipe.

Christian.


  #10   Report Post  
Old September 16th 03, 03:52 PM
Christian McArdle
 
Posts: n/a
Default Megaflow Query

What's the reply likely to be if I call Severn Trent and ask them to
turn the flow up?


20 lpm will almost certainly be within what they consider to be their
contractual obligations. It is on the poor side of normal, but not as bad as
some get. Your only hope is that the problem is between the street and your
cylinder. Compare with other nearby houses to see if they are any better.
Make sure the stop cock is fully open. Make sure they piped the main run to
the cylinder in 22mm and your main supply to the stop cock in 25mm MDPE.

My fear would be, however, that the entire district suffers from low
pressure, as a new house will have a new water supply anyway.

Christian.





Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
General Combi-boiler heating query Peter Watson UK diy 5 September 3rd 03 04:06 PM
F&G Concept 2000 Consumer Unit Live Busbar Query Andy Taylor UK diy 1 September 3rd 03 01:52 PM
ariston boiler query IMM UK diy 2 August 28th 03 12:14 AM
Garage door opener query Andrew McKay UK diy 3 July 29th 03 03:11 PM
LPG cooker - gas supply query drlurch UK diy 2 July 14th 03 11:58 AM


All times are GMT +1. The time now is 02:35 PM.

Powered by vBulletin® Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright 2004-2020 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"

 

Copyright © 2017