Thermal store vs Seperate Gas/Solar water and Gas/Wood boiler CH

[villain1985]

Hello

I have bought a house with 3 acres of forest and am trying to find a way to utilise this to maximal effect regards CH +/- HW. The house currently has a solar and Worcester 24Ri gas system going into a 2 coil hot water cylinder.

My question is would I be best with a thermal store and connecting all 3 inputs, solar, wood, gas?

My reservations about this from reading about thermal stores are:

1) I will only be able to use the wood boiler in an evening but the hot water will be needed in the morning, so will the water still be hot by morning or will the water in the store have cooled requiring the gas to be doing all the hot water heating anyway?
2) I've heard that you can only get 5-15mins of hot water from a thermal store before it runs out and needs reheating?
3) Thermal stores seem very expensive, and I'm struggling to find ones with an external plate heat exchanger.

These issues have made me consider whether I'd be better off instead keeping the current solar/gas system for hot water, but then installing a wood boiler linked to the CH in such a way that at night when the fires on it does all the heating, but then in the morning when we are asleep the gas will come on?

Has anyone heard of such a system as this?

Any thoughts greatly appreciated!

 

[Jimbob]

You can do what you want with enough money, but it's got to be worth it. Linking solid fuel to a system correctly is always going to be pricey, and to be honest, never normally works out when comparing to natural gas (mains gas).

But to answer some of your questions,

Yes thermal stores are terrible at holding heat, because of their high output coil for DHW spanning the entire store. You can get external heat exchanger ones but can't remember the brand...

I would personally forget it, 3 acres of forest isn't a lot to burn, best just use it for space heating. The cost of gas doesn't make it financially worth while at the moment.

I fit a lot of commercial biomass, and they're only really worth while when the rhi tariff is applied, fuel cost alone is similar. Could be a different story in 10 years though when gas hikes and technology cheapens

 

[Worcester]

Hello

I have bought a house with 3 acres of forest and am trying to find a way to utilise this to maximal effect regards CH +/- HW. The house currently has a solar and Worcester 24Ri gas system going into a 2 coil hot water cylinder.

My question is would I be best with a thermal store and connecting all 3 inputs, solar, wood, gas?

My reservations about this from reading about thermal stores are:

1) I will only be able to use the wood boiler in an evening but the hot water will be needed in the morning, so will the water still be hot by morning or will the water in the store have cooled requiring the gas to be doing all the hot water heating anyway?

Wood boilers need massive buffer tanks / thermal stores as they batch burn, minimum 50L / kW so for a 20kW log gassification boiler you'll need a 1000L buffer tank. The buffer tanks we install are well insulated and if no heat drawn from them will only lose 2°-3°K per day.

Log gassification boilers don't give out any heat to the room (well good ones don't )

2) I've heard that you can only get 5-15mins of hot water from a thermal store before it runs out and needs reheating?

B**x depends how big they are though if you've used all the buffer tank for heating, then you ain't got nothing left - see below

3) Thermal stores seem very expensive, and I'm struggling to find ones with an external plate heat exchanger.

Loads of them available from good installers.

These issues have made me consider whether I'd be better off instead keeping the current solar/gas system for hot water, but then installing a wood boiler linked to the CH in such a way that at night when the fires on it does all the heating, but then in the morning when we are asleep the gas will come on?

With only 3 acres of woodland (and you'll need to season the wood for the log gassification boiler) and being on mains gas, and looking to do it on the cheap, you'd be best off shoving in a couple or so multi fuel / log burners just for space heating and keep the gas and solar for your hot water.

Has anyone heard of such a system as this?

Any thoughts greatly appreciated!

Anything's possible see attached picture, DESIGNED and INSTALLED properly, you'd never run out of hot water, though it sounds like you've already decided it's out of your budget though:




IF you implemented the above AND metered the output from the log burner, it COULD be Domestic RHI compliant and you'd get paid for using the logs as heat.. and you MIGHT get all your capital expenditure back

 

[Ermintrude]

Fell the woodland and install 9000m2 of GsHP

 

[Roger Welton]

Fell the woodland and install 9000m2 of GsHP

And sell the timber at a fiver a bag, will be cost neutral.

 

[Centralheatking]

You dont state if you have a nat gas supply. if so its still cheaper than any
other option for heating and hot water. Logs and stuff are accerating in price
exponentially as demand is outstripping supply.

However if you do fell your forest you will permission I think cause its
too big - check Env Agency but can get a woodland improvement grant to re-plant.
I know this because I tryed to buy a forest last year near the M57 and went right thro it:tree:

Centralheatking

 

[happyflyer]

Too many options here usually means he will stay on gas heating, buy a shotgun and shoot pigeons in the woods, and Ermi's idea, the neighbours will go mad
and so will the local authority, Ermi wouldn't cut them down anyway, he's a tree huger. :wink_smile:

 

[Nostrum]

Thermal store is a simple concept. Heat in vs heat out.

To truly know how long the store will last you'll need to determine the volume, temperature of stored water, flow rate of DHW and temperature rise required.

In an ideal world you will want to be replenishing the store at a similar rate to it being used. As Worcester has said, a batch fired wood boiler isn't going to be able to do this, but a gas boiler may.

You could have both a cylinder and store (or a dual tank type arrangement maybe).

Lots of maths required to get it anywhere near practical, then you'll get an idea of price which may prove uneconomic.

 

[Worcester]

Oops

I'd made the assumption he was on LPG!!

If on natural gash then just keep it as it is and bung in the odd multifuel stove here and there, get f&f to do the same and charge them for the logs