Thermal store

[whatnow]

Thinking of putting a thermal store in with an aim of supplying heating and DHW for a four bedroom, two bathroom house. Store to be primarily heated by a back boiler on a wood burner, solar thermal with an existing oil fired boiler for back up.
Plumbing suppliers are a little uncertain on efficiency but currently thinking a 300 or maybe 400 ltr store. So does anyone have experience of a similar sized house/thermal store? What sized woodburner would it need, burning roughly how many hours a day? Is it going to be more than sufficient of supplying heat and water as there's little point in installing it then using the oil burner at all frequently.

 

[Kidds]

Can't see how a store of those sizes would work, I'd say you need a nought on the end.
I don't know much about thermal stores but I do know the ordinary hot water tank in my airing cupboard is 200 litres.

 

[Bloders]

i dont know the correct answer here, but to get an idea consider the following
1) Size of the existin oil boiler (30KW say)
2) How often it runs (contiuously, it would be 30KW. running 30 minutes in the hour, you could say 15KW)

3) Whats the working temp of a thermal store? Im guessing max 80, down to 65, so thats 15 deg c.
4) multiply 15 (from above) by the specific heat capacity of water (approx 4.187 Kj/KgK) This will give you a heat capacity per Kg (or litre) of water.

5) divide the demand by the capcity and you would have the answer of how much water would be needed if heated once per day to providide the heat
6) make another load of assumptions as to the size of your wood burner (in KW) and how long it would run.

This approach wont give a right answer, but it will give you a feel for whats going on.

 

[happycows]

Very similar here to your desired setup. Large four bed bungalow a dowling sumo 25kw woodburning stove linked to a 500l thermal store with oil rayburn pressure jet for backup. we need to light the fire for 3 hours to heat the house in the depths of winter. and get the store upto 70c 500l was the biggest i could fit in my airing cupboard. Central heating will heat house again in the morning for couple hours and do several showers(3 or4) and come on again for a hour before i come in to lunch at 1. By then still hot water in the top of the cylinder for washing hands ect but bottom will be 40c. light fire at 5 and off again.
summer time light twice a week to heat water for couple hours but can hardly live in the living room then.
I was told solar electric dumped direct to the heater elements in the cylinder was more profitable than solar thermal and my plan oneday.

 

[happycows]

 

[Bernt]

get someone in who knows what they are doing!!

 

[Bloders]

get someone in who knows what they are doing!!

that takes the fun out of it...

 

[whatnow]

Very similar here to your desired setup. Large four bed bungalow a dowling sumo 25kw woodburning stove linked to a 500l thermal store with oil rayburn pressure jet for backup. we need to light the fire for 3 hours to heat the house in the depths of winter. and get the store upto 70c 500l was the biggest i could fit in my airing cupboard. Central heating will heat house again in the morning for couple hours and do several showers(3 or4) and come on again for a hour before i come in to lunch at 1. By then still hot water in the top of the cylinder for washing hands ect but bottom will be 40c. light fire at 5 and off again.
summer time light twice a week to heat water for couple hours but can hardly live in the living room then.
I was told solar electric dumped direct to the heater elements in the cylinder was more profitable than solar thermal and my plan oneday.

Thanks Happycows, that's very helpful and interesting. Presumably you slumber the woodburner overnight but still need the Rayburn to come on in the morning? Do you time the central heating pump to allow the store to build up heat? Would you have put a larger volume store in if you could have fitted one?

 

[happycows]

No three hour burn and stop. you can't live for heat after that. The joy with this system is the whole house get nice and warm. not just swealtering by the fire and cold in the end bedrooms. Also once the whole house is warm it's much easier to keep it warm.
The rayburn comes on for half hour in the morning so I have a hot kettle and warms kitchen a bit so it's nice and warm as everyone gets up and just tops the stores heat a bit.
We usually flick central heating comes on as we light the fire. it's such a beast of a thing you can nearly see the thermal stores temperature needle move. There is a thermostat half way up the cylinder and if the central heating is demanding more heat in the bottom of the store it will automatically turn the rayburn on.
would I have gone bigger maybe....but I'm just thrilled with the system and being nice and warm for the cost of doing my own wood. Perhaps you could light the fire less often but it's nice having the fire going of a winters evening.
Our rayburn was a cheap secondhand one off ebay with a snugburner fitted. I'm sure a new one would be even more controllable and efficient. but our has used about 600 litres in nearly a year so not complaining.

 

[whatnow]

No three hour burn and stop. you can't live for heat after that. The joy with this system is the whole house get nice and warm. not just swealtering by the fire and cold in the end bedrooms. Also once the whole house is warm it's much easier to keep it warm.
The rayburn comes on for half hour in the morning so I have a hot kettle and warms kitchen a bit so it's nice and warm as everyone gets up and just tops the stores heat a bit.
We usually flick central heating comes on as we light the fire. it's such a beast of a thing you can nearly see the thermal stores temperature needle move. There is a thermostat half way up the cylinder and if the central heating is demanding more heat in the bottom of the store it will automatically turn the rayburn on.
would I have gone bigger maybe....but I'm just thrilled with the system and being nice and warm for the cost of doing my own wood. Perhaps you could light the fire less often but it's nice having the fire going of a winters evening.
Our rayburn was a cheap secondhand one off ebay with a snugburner fitted. I'm sure a new one would be even more controllable and efficient. but our has used about 600 litres in nearly a year so not complaining.

Do you think that your system could use the woodburner more and therefore not the rayburn if you had a smaller woodburner but ran it longer/overnight which you can't currently do as it's too hot in the room?

 

[happycows]

Yes the rayburn is a lifestyle and convenience thing and not essential. If we are going out for the evening and dont want to light the fire the rayburn will heat the house comfortably for us for less than £1 so when we come home its nice and warm and a hot kettle ready. Cakes always taste better out the rayburn too.
I belive it's better and more efficient to have a good fire burning well for a short time rather than ticking over for a long time.