Thermal Store Size Confusion

[mitchino]

I'm trying to cut our enormous oil bill and heat our house in a more sustainable way. We currently use a Worcester Bosch Heatslave 26/32 Oil Combi providing hot water and heat to 12 radiators. I now want to introduce alternative heating sources into the mix. The plan therefore is to fit a vented thermal store system.

I would estimate we need around 10-12KW heating plus hot water.

Initially I'm looking at connecting a Clearview 650 with boiler (either the 27,000btu or 40,000btu unit). We have a free wood supply from our neighbours sawmill and our 6 acres of woodland. I would also at this stage be looking at connecting a conventional (condensing?) oil boiler to provide back-up. Eventually I intend to add solar, and ultimately an immersion run from a micro hydro system (producing around a constant 1KW).

What I'm finding most confusing is information regarding thermal store sizing. There seem to be two camps regarding this, one saying I need a smallish store of 250-350Litres, and another recommending a monster 1500Litre store.

What size of store do I really need?

 

[Terrywookfit]

You will certainly cut your oil bill but it would appear that you have money to spare !!
With the system that you propose it is unlikely that you will ever recover the installation costs!!
A condensing oil boiler will NOT be much more efficient than your existing one!!
As for your solar plan etc !!
Well if you must do your bit to try and save the planet , then its your choice (and money)!
The woodburner and thermal store makes sense!!
As for size of store !
Do you have some where suitable to keep 1.5 tons of stored water???
I think the smaller one would be perfectly adequate !!

 

[mitchino]

I don't have money to burn actually, but when your oil bill is around £2000 a year, then something has to be done! The solar system and the micro hydro are possible options for the future, the woodburner and thermal store are the main items I want to get moving on. I'd love to keep the Worcester Bosch combi and attach it to the thermal store, but as far as I understand it can only handle a cold input and so it won't work. I'm glad to hear I'll be fine with a smaller thermal store, but I still don't understand why!?

 

[Terrywookfit]

What do you mean by cold input??

What dont you understand ??

 

[Balenza]

Terrrywoofit wrote

What do you mean by cold input??

I think he means pre heating to the combi supplied cold water.

 

[Balenza]

Grant UK have just launched this -

http://www.grantuk.com/pdf/grantcombisol.pdf
I don't think their is any reason why it wouldn't work with solid fuel.

 

[mitchino]

Terry Woofit wrote:
What do you mean by cold input??
What dont you understand ??

I mean that most combi's inlet valves can't handle warm water, therefore couldn't work with a thermal store, though I was wondering if I could ignore the hot water circuit of the combi, and connect it via its central heating circuit - surely that can take a warm feed?

What I still don't understand is why some people (mainly on another forum) are recommending 2000Litre Thermal stores.

Just to clarify what I'm trying to achieve:

The system I had envisaged works along the following lines: There is a thermal store which provides hot water via a heat exchanger heating mains water. The central heating is driven by a pump and uses the water in the thermal store. The operation of the pump would be controlled by a timer and thermostat. The woodburner would be the primary source of heat, backed up by the oil boiler which would kick in if the thermal store temperature dropped below a certain point. So if I was driving the central heating hard and having a shower or bath, both primary heat sources would be working, but crucially, the woodburner would reduce the amount of work the boiler has to do, and therefore I'd use less oil over the year.

Eventually I'd add the other inputs - solar and immersion, which would reduce further the need for the boiler to kick in.

[/quote]

 

[Biggles..]

Take a look at heatweb.com(DPS) i've just pre ordered one for a job. Service so far is excellent and their designers certainly know their stuff and are happy to help.

The one i've ordered will run underfloor and space heating, hot water, solid fuel boiler and gas boiler inlets. 45litres/min dhw. they sized it at 300 litres for a 4 bathroom property, plus kitchen utility etc.

 

[simond]

The Clearview stove is a nice piece of kit - I have one - but the use of a woodburner for heating water may cause you maintenance issues on the flue and stove itself.

If you have the stove as a part of your lounge you may be disappointed by the significantly high tar deposits all over the 'clearview' glass.

I have found the tech support from Clearview less than helpful in this respect with a couple of customers who are doing what you describe. Both have now had the heat exchanger removed.

I would put in a more efficient boiler, and just use the stove for additional space heating in the downstairs. Add a Honeywell Hometronic radiator system and use the heat more wisely.

Solar is never going to pay back in your lifetime.

PS: My Clearview is fine, but I don't have a water jacket so the internal temperatures allow more complete combustion.

 

[mitchino]

I've heard that the worst of the tar is caused by heating up the initial body of water in the boiler before it has started circulating. You can reduce tar by making sure you get a very hot fire going as quickly as possible when you light the stove by burning smaller bits of very dry wood. Also I've been told that a 'jacket' type of boiler is worse for tar than a 'baffle' version. One reason I'm keen on a clearview is that they can run very hot and are very efficient, so hopefully might be less tarry than other stoves.