Mega Flo vs Thermal store

[indus]

Hi there

At the moment I have an indirect thermal store type set up with a gas boiler. The thermal store is in the loft it looks like this

It was fitted about 5 years ago and its made by this company and I think this is their current version

http://www.albionwaterheaters.com/product-combination-cylinders.html

On the whole I'm happy with it, I do have an issue when it comes to maintenance as most jobbing plumbers don't seem to understand it and say something like.......'never seen that before mate, you should have got a mega flo'

I do find though that if I'm running one shower and then run another at the same time the water temp drops.

Now my loft conversion has just started and if I were to make a change now is the time to do it. So the questions are

1) Is there any benefit to me changing over to a Mega Flo?

2) Should I keep the current system but perhaps upgrade the thermal store. I've been reading about modern ones with ?heat plate exchangers or something which are meant to be better.

(At present there are three shower rooms and one bath in the house once the loft conversion is done there will be four showers. There will be about 25 rads)

 

[Youllneverguess]

You need to find yourself some better plumbers.

 

[indus]

You need to find yourself some better plumbers.

Not a very useful post is it? But then I'm sure you probably knew that

What do you see in the plumbing that makes it below your standards?

 

[Youllneverguess]

I was referring to your jobbing plumbers who can't figure out how a thermal store works! smart ass.

 

[SimonH2]

I was referring to your jobbing plumbers who can't figure out how a thermal store works!

That does, anecdotally, seem to one of the biggest problems with them.

I'm curious though - is your heating plumbed through this, or is it plumed as something like a "Y plan" ? reason I ask is that there's a bypass valve in the plumbing and if done (what I'd call) "right" then there is zero requirement for anything like that - and it does look like it has a modulating pump in the circuit. The answer to that question does have an impact on what I'd suggest. Also, no mention of solar panels or wood burning stoves, so I assume nothing like that ?

If this is just providing hot water, then it matters not what you use ! An unvented cylinder (which seems second only to a combi in the "I'd rip it out and replace it with X" stakes) would provide mains pressure hot water, and have less tendency for the outlet temp to droop. The downside is that you then have a pressurised cylinder of hot water - installation is notifiable and you can only use a complete package, both on safety grounds.

You may want to look into the specs of the cylinder you have installed. It is correct that the DHW coil has a finite capacity, and it may be that it's under-specced for what you need. To a certain extent you can mitigate that by turning up the stat - at the expense of higher standing losses.

A heat bank doesn't automatically have a higher capacity - but it's easier to make a high capacity PHE than a high capacity DHW coil for a thermal store.

It may be apparent from some of my other posts that I'm in favour of thermal stores. If you use them for the heating as well as DHW then you can avoid the need to run the boiler at low power for long periods to run the heating, and avoid the problems of trying to match low flow rates appropriate to a fully TRV heating system with the need for a minimum flow rate through the boiler.

 

[indus]

Thanks Simon

1) No solar panels or wood burning stoves

2) It provides hot water and central heating

If my current thermal store is under specced how do I decide on a better specced one? Would it be one with a larger capacity or the ones I see advertised that have two internal coils rather than one?

If you use a heat bank does that mean that the internal coil is no longer used, or can the two be used together?

Thanks for your input

 

[SimonH2]

1) No solar panels or wood burning stoves

2) It provides hot water and central heating

OK. I have a feeling it's been plumbed wrongly.
On your second picture, the pump on the right that has a large box going a quarter way round the body - is that a modulating pump feeding the CH ? If so then the bypass isn't needed and really shouldn't be there as the pump will modulate when the TRVs close.
And is the input from the boiler direct (ie the water in the store goes round the boiler) or indirect (there's a coil separating them) ?

If my current thermal store is under specced how do I decide on a better specced one? Would it be one with a larger capacity or the ones I see advertised that have two internal coils rather than one?

If you use a heat bank does that mean that the internal coil is no longer used, or can the two be used together?

Good questions - not sure of the answers !
I don't see why you couldn't pre-heat the DHW with a PHE and then put it through the existing coil. The biggest issue would then be getting the water out and back into the store as it's not got the tappings there. While not ideal, I guess you'd have to tee into the boiler and/or heating tappings.

As for specs, there are two key figures for a thermal store or heat bank - volume and DHW power. Volume isn't really relevant to you since you only have the gas boiler and so heat storage isn't the main consideration - you only need enough storage to supply the peak demands (eg running a bath) without exceeding the capability of the boiler to reheat it. Your issue is DHW heating capacity.
Having two coils isn't inherently higher capacity than a single coil - ie two small coils might do the same as one large one. However, as the coils get higher in capacity they get bulkier and harder to make, hence the tendency to fit two coils as the capacity gets larger.


Lastly, am I right in assuming the thermostat in the bottom of the cylinder is controlling the boiler ? What temperature is it set at ? Is there anything controlling the boiler output temperature, or is it just set at some high flow rate and just adding a relatively constant delta-T to the water going through it ?

 

[indus]

Hi Simon, I'm going to do my best to try and answer the questions but please keep in mind I'm a layman!

1)On your second picture, the pump on the right that has a large box going a quarter way round the body - is that a modulating pump feeding the CH

Yes, its a pump that supplies the central heating


2)And is the input from the boiler direct (ie the water in the store goes round the boiler) or indirect (there's a coil separating them) ?

To the best of my knowledge the boiler communicates with the main body of the TS directly. Then when you need hot water cold mains water goes through a coil that is inside the TS and so becomes heated up, hence coming out at the taps hot.
The hot water in the main body of the tank afaik is what supplies the CH.

Though as far as I was aware the set up of my system was termed 'indirect', so I'm a little confused there.


3)astly, am I right in assuming the thermostat in the bottom of the cylinder is controlling the boiler ? What temperature is it set at ? Is there anything controlling the boiler output temperature, or is it just set at some high flow rate and just adding a relatively constant delta-T to the water going through it ?


Good question, I'll try and answer it. I think from what the plumber who fitted it told me it does control the boiler output (that plumber has now retired and emigrated!)

If I explain the wiring that might shed some light on things?

If you see that white box on the closest left hand corner it is marked honeywell. It has the following wires

a) One going to each of the two pumps

b)One going to that other smaller box that is actually tapped into the TS

c)Four or five wires that go down through the floor and connect to a honeywell control unit that is attached to the boiler downstairs

I can't see what the thermostat is set to as there is nothing externally on the honeywell box next to the boiler telling you the setting. I'm fairly sure however that I remember the plumber saying that the temp should be set to 80 degrees.


Thanks again for your help

 

[Norcon]

You could try dps heat web (Thermal Integration Ltd) who build pre fabricated boards for retrofitting to boost existing thermal stores.
Four showers needs a hefty mains supply whether it be unvented or a heat bank conversion.
Indicate your requirements to them and price it up.

 

[indus]

You could try dps heat web (Thermal Integration Ltd) who build pre fabricated boards for retrofitting to boost existing thermal stores.
Four showers needs a hefty mains supply whether it be unvented or a heat bank conversion.
Indicate your requirements to them and price it up.

Thanks Norcon

Could you explain how these 'pre fabricated boards' boost the existing thermal stores?

Thanks again

 

[Norcon]

Through a plate heat exchanger connected across the boiler f&r tappings close to the store.
You could use the existing coil for the kitchen/basin hot water supply and the plate for the high flows. (ie - Bath fill and showers)

 

[indus]

I really need to make a decision soon whether I want to change my thermal store system to a Megaflo.

My loft conversion is coming on in leaps and bounds and now would be the time to get this done.

Basically the issue is that if I try and run a two outlets at the same time ie a shower and a tap, or two showers there is quite a significant drop in both pressure and temp. if I turn one off then everything thing seems fine.

Once the loft extension is done I'll have one bath and three shower rooms and so it would be nice to be able to run two at the same time.

Would a Mega flo improve this matter?

Thanks

 

[Agile]

I am surprised that no one has commented on the pump on the left !

Its mounted at the wrong angle. Any competent plumber would know that.

A few years ago I sent a trainee ( with an MSc ) to a customer where their plumber was present.

The trainee pointed out to the plumber that he had installed the pump wrongly, ( just like yours ).

The plumber replied that he had fitted hundreds like that.

The trainee, quick as a flash, replied "you have fitted hundreds wrongly then".

The reality is that the standard of competence of so many plumbers is abysmally low!

Tony

 

[Biggles..]

Why is the left pump wrong.

 

[Dan Robinson]

Leccy box on the bottom...