Biomass Pellet Boiler - Thermal Store/Buffer Tank/Water tank question

RickMoney

Hi,

Looking at getting a pellet boiler installed on a house that is off mains. Currently no heating in house so it's a fresh install.

Intend for it to heat water as well as radiator central heating.

Originally, I thought to use an unvented water cylinder and the radiators connected directly.

Speaking with a supplier, they advise a thermal store to indirectly heat the water on demand and water for the radiators. These sound very expensive and I do not intend to install solar or other heating options.

Buffer tank - I'm trying to find out how these differ to thermal stores and water tanks. Can anyone advise how they operate?

Can anyone that has had a biomass installed please advise what they had installed and if they would do it different?

Thanks,

Rick

albyota

Depending on the heat demand, you could look at ETA PC Compact, no buffer required, just normal DHW cylinder and radiator circuit, operates on a standard S plan control.

AL

farmerboy

Just about to have a system similer to what you are looking for installed.

The original plan was for a thermal store and a MCZ/Trianco boiler at 25kw. We are looking to add solar at a later date so this is what was suggested.

Since then we have changed to having a OkoFen 25kw and this is being installed with an unvented cylinder, but still with the option of adding solar at a later date.

The reason for the change is a deal that the installer has got from OkoFen on the boiler for the next month, and the fact that it is easier to add on option at a later stage, plus the better reputation.

Price wise, for a total new system in a 4 bed old farm house with 11 rads, cylinder, manual fed boiler and controls were:
MCZ £13500
Trianco £14750
OkoFen £17400

RickMoney

Why is one boiler configuration with a thermal store and the other with a normal unvented cylinder?

farmerboy

Think its down to each boiler really. Was told a thermal store is needed to combat cycling as the boiler can't be just turned on and off like gas. The new system we are having is a 300l twin coil unvented cylinder, the old one had a 300l thermal store.

TBH not exactly sure, my installer is coming out on Friday to go through the final details. Will ask him

RickMoney

Thanks, I'd appreciate hearing their response. The area is pretty small that it needs to fit into so I'm looking at a smaller boiler - the MCZ Musa and will also need to crowbar in the water tank or whatever it needs too.

Robwiz

If the pellet boiler is required to modulate (burn at a low level) then the igniter does more work. As it's a consumable part it wears out, so if used more it will increase operating costs.

With a thermal store (TS), the boiler burns hard and at optimal efficiency until the TS set temperature is reached, so less cycling.

A TS gives the option of weather compensation controls, which blends the water in the TS with the return water to run the system at a lower flow temperature. The system reads outside temperature, and if it drops, anticipates a call for heat by increasing the flow temperature to match the higher heat loss due to the increased between inside and outside temperatures.

farmerboy

The reason for the change on my system is the way the boiler works.

The way I understood it is that the other systems quoted feed and ignite in a different way to the OkoFen meaning they cycle more as Robwiz has put above, so a thermal store is better.

RickMoney

Thats pretty much what the guy selling the MCZ said yesterday. The speed of getting the central heating up to temp will be longer than using a thermal store. I'll have to weigh up the costs as I expect they will cost a fortune.

Silent_Dancer

A buffer vessel is a smaller thermal store usually 50 to 100 litres. Do not install a biomass boiler without a store of some sort the bigger the better. With no thermal store the boiler will cycle more wasting fuel and reducing reliability.

captainhindsight_2

A biomass boiler, ideally needs a buffer tank.

By having a buffer tank it allows the boiler to burn at its most efficient for shorter periods of time meaning less fuel is used and less ash to clean up.

Burning wood cannot be controlled as easily as oil or gas, so trying to control it by feeding directly into the central heating system can be done but you won't get the same efficiencies or control of your heating as you would by having a buffer tank.

All a buffer tank is, is a big very well insulated tank full of hot water. The boiler keeps the water in the tank at a desired temperature (very hot), a coil goes through this store of hot water and heats up the water in the coil which is fed into your radiators and hot water cylinder.

So if you imagine, the boiler is heating up the water in the buffer tank and the buffer tank is heating up the water in the radiators..

It may sound a bit unnecessary, and you may ask why not just feed into the central heating system but as I said earlier it allows you to get the maximum amount of energy out of your fuel thus saving you money in the long run.