Heat bank and wood burning boiler. Help and advice on spec please

[scruffders]

Hello all, :biggrin:

I am about to start restoring my house and would like to cut down on my usage of LPG. I plan to do this by fitting a Heat bank and a large wood burning boiler stove.
I very much need to tap the vast amnount of experience on this forum. Any information you van give will be gratfully received.


My property is a large 3 bed semi. The downstairs area is around 92 m2 (75% open plan) and will be heated by underfloor heating. The upstairs is around 72 m2 and will be heated by 5 rads.

I’m planning to have a 300 litre heat bank (thermal store) located in a bedroom. Next to the heat bank will be my LPG combi boiler from the kitchen which I plan to use as a secondary heat source. The main heat source will be a large wood burner with an integral back boiler, and this will be located in the kitchen 3mtrs below and 3 to 4mtrs to the side.

Some of the spec and planned features include:

1. I may get the Broseley evolution 26 stove as currently this is the only one with MCS accreditation (I think) and will enable me to get the RHI if it ever gets going!
2. The stove will be linked to the heat bank with 28mm? pipe and have a blending valve to ensure the returning water is not too cool.
3. I feel its better to have an open vented heat bank cylinder and I will connect the central heating side of my combi boiler to this by using a heat exchanger.
4. Even though these heat banks are supposed to heat quickly. If there is no hot water in it and I wish to take a shower say, I don’t want to wait till the boiler heats the top of the cylinder. So, I plan to link the DHW side of the combi to the hot water feed coming out of the cylinder using a 3 way valve and switch it over manually, so I can have a quick (and cheap) shower. I know I will, hopefully, not use this that much, but think it will be useful for the small cost of the 3 way valve.
5. I have a 4kw solar installation on my roof that I would like to make use of to heat the water in my proposed thermal store. I will use an “Immersun solar distribution box” to power two 3kw immersion heaters in my store. A lot cheaper and less maintenance than getting solar thermal panels.

There are a fair amount of other features but they are less important or I can’t remember them ATM. I also don’t want to make this post too long.

Questions I would like to ask are:

1. Is anyone aware of what the RHI will pay? And is it worth it?
2. A good quality stove that is cheaper than the 3k Broseley. If I don’t bother with the RHI.
3. My Idea of connecting the DHW off my combi (No4 above). Is it feasible?
4. Is it best to feed the hot water supply into the top or middle of the cylinder?
5. Can anybody suggest the best Heat Bank to get and why?
6. Is it better to pump everything with separate, isolated pumps, to aid a quick change if one packs in.
7. The feed/return for the boiler stove and the central heating (upstairs rads) feed directly off the Heat bank cyl, won’t it upset the stratification of the cyl? As I imagine they will be pumped with a fair pressure?
8. Do I put rust inhibitor in the heat bank/upstairs rads/boiler stove (as they are all linked).
9. Should I use a automated air supply duct to control my boiler stove automatically when the Heat bank gets up to temp?

I think that’s about it for now. My apologies for the length of this post. Any replies/comments/advice will be greatly appreciated.

I have also put a post in the “Looking for a plumber forum”. So, if anyone can recommend a competent heating engineer who can design and fit all of the above I will be very happy.

Many thanks

Mike

 

[Archmoco]

Scruffders,

did you ever get the Broseley stove? I've got one and also the RHI grant. I 'm struggling to get the 16kw for the water, but to be fair it it could be my operation of the stove or the charging in unit setup into the thermal store

 

[Worcester]

You could well be getting 16kW the question is for how long.... How big a buffer tank / thermal store have you got - ideally it should be at least 800 litres.

Are you using properly seasoned logs?

800 litres with a temperature drop of 20 degrees only gives you 18.6kWh of heat, so if you have a heat load requirement of 16kW, the thermal store will last for 1hr and 10 minutes...

or will heat up 320 litres of Hot water from cold to 60° ....

 

[Archmoco]

You could well be getting 16kW the question is for how long.... How big a buffer tank / thermal store have you got - ideally it should be at least 800 litres.

Are you using properly seasoned logs?

800 litres with a temperature drop of 20 degrees only gives you 18.6kWh of heat, so if you have a heat load requirement of 16kW, the thermal store will last for 1hr and 10 minutes...

or will heat up 320 litres of Hot water from cold to 60° ....

Worcester,

i've a 1000ltr Akvaterm Solar Plus with the stove connect via a Laddomat 21-60. I was only getting 2-3kw per hour but I was not burning well seasoned hardwood or enough of it. I've changed to Birch and Ash with a moisture content less than 5 %, and I'm burning the proper 5.5kg as noted in the manual, this had brought the kw up to around 8.

i was wondering what would happen if I reduced the Laddomat pump speed from 3 to 2?

regards
archmoco

 

[Ermintrude]

Set up an unvented in parallel to the store. A nice big lump being held at 85c will provide sufficient water! Sounds like your not burning right.

 

[Archmoco]

Removed double posting

 

[Worcester]

Doesn't the laddomat have an automatic thermostatic mixing valve built in to it? If so, the flow rate shouldn't make much difference , EXCEPT that too high a flow rate the the water doesn't have time to pick up the heat so just whizzes round and round...

I'm not familiar with your specific boiler/stove, so yes, it could make a difference - what advice were you given by the designer / installer?

Also sounds like it isn't burning right for some reason or other, either that or all the pipes aren't lagged and you're just throwing it all away before it has a chance to do anything useful

 

[Nostrum]

What's the problem with the hot water? Are you struggling to get the temperature up above a certain temp?

reducing pump speed may help increase flow temp which may be the problem here? Have you measured the flow temp from boiler?

 

[Nostrum]

Like buses..

 

[Archmoco]

I'll try pump speed 2 tomorrow. The pipes are under the screed buried in lagging and 150mm of kingspan so I shouldn't loose too much.

the designer is still looking at it.

it has transpired that my model stove was an early batch with only a 100mm exterior air connector, and now they come with 150mm as standard, so that might have an effect. I can get the 'new' bit for the stove but my duct is only 100mm.