The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.
What's the collected wisdom about heat stores versus unvented DHW
systems these days?

On 23/03/17 03:32, wrote:
The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.
What's the collected wisdom about heat stores versus unvented DHW
systems these days?
AFAIAC heatbanks are **** and if you actually want hot water that works
you need a tankful of it.

And electric pumps are **** and if you want a decent flow rate you need
mains pressure. Of course that means you also need a water softener.

--
A lie can travel halfway around the world while the truth is putting on
its shoes.

On 23/03/2017 03:32, wrote:

The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.

What's the collected wisdom about heat stores versus unvented DHW
systems these days?

I needed to make the choice about 4 years ago, and was initially looking
at doing a DIY heatbank with a high power PHE[1] for the hot water takeoff.

In the end I went the unvented route since it produces lower overall
system complexity, and could deliver adequate water with a smaller store
size. The cost worked out slightly cheaper for the unvented.

I ended up going for a 210L Vaillant cylinder rather than a megaflow
though. So far this has been fine. Not had any issues with the PRV,
although I did have a problem with the overtemp/pressure valve letting
by - this seemed to be a result of water hammer causing it to open very
briefly when a tap is shut off abruptly, and the hard water scale
eventually forming in the valve preventing it reseating completely. I
needed to remove it, descale it, and polish the surface flat again where
it had been pitted by the scale.

[1] Similar to http://wiki.diyfaq.org.uk/index.php/DIY_Heat_Bank
but with a 100kW+ PHE

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 23/03/2017 11:35, John Rumm wrote:
On 23/03/2017 03:32, wrote:

The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.

What's the collected wisdom about heat stores versus unvented DHW
systems these days?

I needed to make the choice about 4 years ago, and was initially looking
at doing a DIY heatbank with a high power PHE[1] for the hot water takeoff.

In the end I went the unvented route since it produces lower overall
system complexity, and could deliver adequate water with a smaller store
size. The cost worked out slightly cheaper for the unvented.

I ended up going for a 210L Vaillant cylinder rather than a megaflow
though. So far this has been fine. Not had any issues with the PRV,
although I did have a problem with the overtemp/pressure valve letting
by - this seemed to be a result of water hammer causing it to open very
briefly when a tap is shut off abruptly, and the hard water scale
eventually forming in the valve preventing it reseating completely. I
needed to remove it, descale it, and polish the surface flat again where
it had been pitted by the scale.

[1] Similar to http://wiki.diyfaq.org.uk/index.php/DIY_Heat_Bank
but with a 100kW+ PHE


I suspect I'll be making the same decision. If I had some low grade heat
sources a heat bank might be worthwile (I think) but with just an
oil-fired boiler I can feel a pull towards a straightforward unvented
cylinder. There's loads of space next to the boiler so I might go a tad
larger, to a 250L.
Why did you opt for Vaillant rather than Megaflow?

(PS It's interesting to re-read what I wrote in the early hours during a
sleepless night - maybe it's good that I didn't try to do anything more
demanding or dangerous ;-)

On 23/03/2017 09:16, The Natural Philosopher wrote:
On 23/03/17 03:32, wrote:
The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.
What's the collected wisdom about heat stores versus unvented DHW
systems these days?
AFAIAC heatbanks are **** and if you actually want hot water that works
you need a tankful of it.

And electric pumps are **** and if you want a decent flow rate you need
mains pressure. Of course that means you also need a water softener.


Hmm, I always regretted not fitting a softener in this house when I was
doing all the work so thanks for reminding. A softener will be on the
shopping list.

On 23/03/2017 12:41, wrote:
On 23/03/2017 11:35, John Rumm wrote:
On 23/03/2017 03:32, wrote:

The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.

What's the collected wisdom about heat stores versus unvented DHW
systems these days?

I needed to make the choice about 4 years ago, and was initially looking
at doing a DIY heatbank with a high power PHE[1] for the hot water
takeoff.

In the end I went the unvented route since it produces lower overall
system complexity, and could deliver adequate water with a smaller store
size. The cost worked out slightly cheaper for the unvented.

I ended up going for a 210L Vaillant cylinder rather than a megaflow
though. So far this has been fine. Not had any issues with the PRV,
although I did have a problem with the overtemp/pressure valve letting
by - this seemed to be a result of water hammer causing it to open very
briefly when a tap is shut off abruptly, and the hard water scale
eventually forming in the valve preventing it reseating completely. I
needed to remove it, descale it, and polish the surface flat again where
it had been pitted by the scale.

[1] Similar to http://wiki.diyfaq.org.uk/index.php/DIY_Heat_Bank
but with a 100kW+ PHE


I suspect I'll be making the same decision. If I had some low grade heat
sources a heat bank might be worthwile (I think) but with just an
oil-fired boiler I can feel a pull towards a straightforward unvented
cylinder. There's loads of space next to the boiler so I might go a tad
larger, to a 250L.

Why did you opt for Vaillant rather than Megaflow?

Combination of reasons really.

Since I was doing a complicated install conversion from a conventional
gravity system with one zone and conventional cylinder to a sealed
system system boiler, with split temperature operation, weather
compensation, and two independent thermostatically controlled heating
zones, there was a thought that keeping it all Vaillant may simplify
integration, and make resolving system problems simpler.

Some of their literature is not very good on the "bigger picture" system
integration aspects of their stuff. So for example, it was not clear if
the cylinder would also interface to the ebus system used by the stats
and wiring centre etc. With hindsight - the answer is no - it just uses
a NTC thermocouple and a normal 2 port valve for control. (which also
meant I needed to run an extra cable back to the boiler which I had not
realised I would need!)

Also it looked nicely made, and the price was ok.

Lastly I was not as keen on the internal air bubble approach used by the
megaflow for expansion space. The Vaillant uses a standard external
expansion vessel.


(PS It's interesting to re-read what I wrote in the early hours during a
sleepless night - maybe it's good that I didn't try to do anything more
demanding or dangerous ;-)

There was a moment it looked like you were suggesting a bacon butty ;-)



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 3/23/2017 9:16 AM, The Natural Philosopher wrote:
On 23/03/17 03:32, wrote:
The questions keep coming. When I sorted out my present house, about ten
years ago, I very nearly went for a heat bacn but the lead time wsa too
long so ended-up with 210L Megaflow - it's been great but the pressure
reducer and safety valves are a minor pain.
What's the collected wisdom about heat stores versus unvented DHW
systems these days?
AFAIAC heatbanks are **** and if you actually want hot water that works
you need a tankful of it.

And electric pumps are ****

Stuart Turners are OK

On Thu, 23 Mar 2017 09:16:02 +0000, The Natural Philosopher wrote:

AFAIAC heatbanks are **** and if you actually want hot water that works
you need a tankful of it.

Thermal store here does fine for DHW and that only take heat from the
top half of the store.

And electric pumps are **** and if you want a decent flow rate you need
mains pressure.

DHW is mains pressure, just passes through a coil in the store with a
thermostaic mixer valve on the output to limit the temperature at the
taps. The store sits at about 80 C.

Of course that means you also need a water softener.

Only if you have **** water. haven't neede to descale the kettle
since they switched the source from an adit on the hill side a mile
away to Burnhope a good number of years ago.

--
Cheers
Dave.