Combi boiler and thermal store ?

[AbingdonBoy]

Hi All,

I am going to fitting a vacuum tube solar panel for water heating, an combine this with a solar store (using a plate heat exchanger to suppl mains hot water). i am also in the process of fitting a wood burnin stove with a back boiler, that i plan to link to the thermal store. With these two systems i should have hot water for a fair amount of th time, however, there are times when the solar panels are not working an the wood burning stove is not convient, and the hot water is going t need a top up. So i plan to run the 'hot' water through a Combi boile to 'assist' the hot water. The combi will also run the central heatin system.

My problem is that all of the major boiler manufacturers i have spoke to say that their systems will not work with a warm/hot input. Doe anyone know who does? I know that it is offered by one compan (Eco-Home?) but i have never heard of them.

Many thanks in advance for any help that you can give...

Regards,

AbingdonBoy

-- AbingdonBoy

[Christian McArdle]

I'd run the DHW straight off the heat bank. Use the gas boiler to heat that, rather than attempting to boost the tank output. Consider running the rads off the heatbank if the solar is going to provide significant heat. In spring/autumn, solar heating isn't such a bad idea. Obviously, in the depths of winter, the load will be too high and the solar energy too low to be practical.

Christian.

[John]

My neighbour has recently had a solar system installed which runs its heated mains pressure output through his Worcester Bosch CDi I have an invite to go round to see it but as yet have not done so. From what I hear so far it works just fine. The combi does not fire when the input is hot but cuts in if it is not. It then modulates to match the temperature-raising heat need. I can forsee a problem with a wood burner raising the input temperature "too high" which may need a thermostatic blending valve to keep the boiler mains input within acceptable levels

[Ed Sirett]

You may have meant Eco-Hometec. Andy Hall has a non-combi one of them and seems content with it.

However, probably, the best way to run things is to allow for the boiler to heat the store via another indirect coil. The controls can be set to keep the store up to the minimum temperature whilst the wood stove and solar will be allowed to take the store to the maximum allowed temperature. The CH can then be taken from the store as needed.

No doubt people with more knowledge of stores and banks than me will refine this scheme.

[Doctor Drivel]

Have a thermal store/heat bank, that has a coil for solar and one for the wood burner, or have them direct, and also heated by the boiler. Take the CH off the thermal store.

[Andy Hall]

They are simply a reseller for a number of German and Dutch manufacturers.

The boiler in question is the Micromat, made by MHG Heiztechnik (MBO of division of MAN the engine company).

It's a very well designed and made product, but not cheap.

There are a plethora of controls and monitoring in terms of weather compensation etc.

One of its big advantages is being able to modulate over a large range. For example, most models will drop down to 3-4kW and 40 degrees on the flow side.

It can be configured in a lot of different ways. For example, on the non-combi version, you can have completely separate behaviour for water heating vs. CH.

I use it to heat the HW in a fast recovery cylinder because it suits my purposes well - I am not using alternative sources of heat other than electricity as a backup.

There is an optional analogue sensor for the DHW, and this can be used to give precise control. I have it configured to heat the cylinder rapidly, and that's it. It doesn't overshoot on temperature. Equally, one could use it to maintain a certain store tempoerature.

With a boiler of this type, there is no point in using the thermal store to run the CH, unless there is another major heat source. Having the store in the middle effectively defeats the behaviour of the weather compensation.

Whether the combi version is suitable for heating the HW, prewarmed to almost the same temperature as for use, I am not sure. It's more typical to combine using the store.

[Doctor Drivel]

Matt, if you had a heat bank or thermal store you don't need a boiler like the MAN. The great thing about thermal stores is that cheap, simple non-modulating, and potentially more reliable boilers can be used.

[Aidan]

Ditto. Combi's are intended for flats & small houses, with all the components in one wall-mounted box. Fine for the installer, but a PITA to repair/service once the warranty has expired, compared to a plain system boiler.

[Doctor Drivel]

Nonsense.

[Andy Hall]

You had better discuss that with Matt.

As you have argued yourself on many occasions (e.g. in terms of condensing vs. non-condensing), there is not inherently a difference in complexity in the sense of a reliability factor between a simple boiler and a more complex one.

The issue with respect to reliability is design, component and build quality.

Use of a thermal store is a different matter entirely.

[David]

In article , Aidan writes

Having been subjected to daytime television yesterday... I did end up watching one of the build your own house type programs where they had reached the point of installing the heating system, they summed up the discussion by concluding that combi's are suitable for smaller houses but larger properties are better with stored hot water systems. I saw it on television so it must be true.

[PeTe33]

I have the Eco-Hometec EC36S (I think) It's actually made by MAN you know, the German company that makes Lorries and stuff.

The plumber that fitted it was extermely impressed with it's features and design etc.

It measures the temperature of the inlet water and adjusts heat input as required to bring water to Rqd. temp.

Also has outdoor temp sensor as standard which regulates C/H water based on outside temp.

Prolly twice the price of most boilers but very pleased with it so far.

HTH

[Doctor Drivel]

Matt, I am discussing it with Matt.

Properly designed condensing boilers are no more complex than non-condensing boiler - you obviously don't know this Matt.

Yes.

The less the better. Less = more reliable.

Yes.

Two out three Matt. Not bad.

When using a thermal store. Again... "Matt, if you had a heat bank or thermal store you don't need a boiler like the MAN. The great thing about thermal stores is that cheap, simple, non-modulating, and potentially more reliable boilers can be used."

[Doctor Drivel]

Bertie, you must believe everything you see on TV.

[PeTe33]

Nooo you are misguided. It only becomes genuinely true once you read it on the interweb!

[PeTe33]

The Combi works exactly the same way as your WRT sensing water temperature going in.

[David]

In article , Doctor Drivel writes

That's what I said John, do try to keep up

[Doctor Drivel]

Bertie, you need reassuring that all is right on the telly.

[Doctor Drivel]

Nonsense, only when in the Sun.