Thermal Store Advice

[taliz]

I am wanting some advice on Thermal stores.

Our old combi boiler  has given up the ghost and I understand that this can be replaced with a system boiler in conjunction with a thermal store.  My house has no header tank and no space for one so I believe I need an unvented cylinder. 
I was looking at one of these,
http://www.advancedwater.co.uk/prod-480-088-2505.html
http://www.plumbnation.co.uk/site/gledhill-torrent-multifuelstore-sol-solar-sealed-system-open-vented-mains-pressure-thermal-store-cylinder/
 my house has one bath and two showers. Does any one have any comments on these, or suggest an alternative (that’s no more money).

I do plan on getting solar panels in the future.
I am getting a wood burning stove with a back boiler, will this hook up to the thermal store ok? I was under the impression that wood burners can only work with open vented systems.
Any comments?

[MarkB]

What do you want to do with your thermal store - DHW only, or also supply the heating system?

If you just want DHW, but want the heat source to come from either the gas boiler or the stove then a small thermal store might be OK, although I'd probably be inclined to go with a normal cylinder with the stove input going in via a coil instead (and a spare coil for solar later). All your space heating comes direct from the stove or boiler.

If you want to be able to capture heat from your stove to use later and take both DHW and heating from your store then you'll need a larger store than you are proposing - I would suggest a 1000l or more. These are big, heavy and expensive.

The power of the stove also has an impact on the size of the store - a larger stove really needs a larger store.

In either case, if you want to run two showers from a store then you either need relatively low flow rates, or a large heat exchanger (internal coil or external plate - I prefer the internal coil for several reasons). While a store might quote 30l/minute, you have to know the store and water draw-off temperatures to understand what this really means. If the store is at 90C then it's generally easy to get good flow rates, but you want to keep the store temperature as low as you can get away with to avoid standing losses, it gets harder to get good DHW temperatures and flow rates when the store is only at 50C.

If you're considering solar then a big store is only worthwhile if it can be effectively stratified, which is often expensive.

It used to be the case that you could only put stoves on a vented system. That is no longer the case if you have a stove with a quench coil fitted to protect against overheating.

With your budget, and suggestion of limited space, I would seriously question whether a small thermal store is the best solution. You may well be better off with a DHW cylinder instead. The only reason I can see would be to capture the back-boiler heat for use later, and for that you would need a bigger and more expensive store than you propose.

[taliz]

Thank you for your response.
We are refurbishing the house we plan to live in for at least the next 30 years so I would like to future proof it to some extent against rising fuel costs.
It will be insulated to the maximum amount our budget will allow.
My idea behind the the thermal store was to use a system boiler in conjunction with the wood burning stove to heat the house and store some of that energy to heat the DHW.
When the government unvail their plans for the green bank and RHI we would hopefully look at getting solar tubes at that point for DHW during the summer.
Ideally we would have waited until then for the whole instalation but our boiler is dead now..
The fact that I would need to buy a new combi now anyway, I was hoping that due to the length of time we plan on living here, a little extra in upgrading to something different will make savings over the longer term.
As renewable energy sources become more affordable and inscentivised they may be other ways of heating the store in the future.

Space is very limited and the tank's external diameter need to be less than 600mm ideally. We could go bigger but it would then have to get sited in the garage which is detached and a few meters away from the house, I expect this will cause it's own problems so not keen on this.

You talk of getting a standard tank and getting an extra coil fitted, how would the cost of this compare with a store??  Could this have the facility to add other heat sources in the future?

Whilst we do have two showers it would be unusual to use them both at once but you have got me concerned about the flow rate. I will need to do more research into this. I expect to have an emmersion heater built in for the odd times of high useage (guests staying etc..)

Or roof is pretty much bang on south so I am assuming with the correct tubes that keeping it hot in the summer shouldn't be a problem.

Thanks in advance for the input..

[dhaslam]

If you are using a wood stove for heating then the store needs to be large. Putting it in the garage isn't  too much of a problem if the pipe runs are reasonably short.   It is necessary to have the store well insulated anyway.   It should be possible  to use a dual coils  for  solar, in summer the top coil can be set as priority for DHW  and in winter the bottom coil to use at lower temperature  for preheating.   

The main thing is to have an efficient wood stove,  low emissions and high efficiency.