Biomass boiler

[muttley9050]

Hey catweazel, think you misunderstood the system, the 3 1000l tanks are purely for dhw. Not sure why they fitted two expansions to each tank, just how it was designed. If you look at the first picture you can see a large grey 5000L tank for the space heating, this has its own 500L(i think) expansion(not shown in photo) if were burning logs the water from the large tank heats the 3 1000Ltanks via heat exchange. Twin coil: 1 for solar one for log burner. Space heating comes from tank underground into house and through heat exchanger in basement into rads. we too have no temp control at present(we will be fitting trvs when we get round to it, but the way we use boiler we wont be overheating. ITS all manually fed with logs. and we monitor heat manually, such a big old house(see pic) we would never get it roasting anyway.

Was never the objective. Comfortable was what we were after. Could of had bigger boiler,burn more wood etc, but didnt want too. Before this system we only had wood burners. System was more about getting corridors and landings commfortable too and not having our older residents carrying logs to the third floor to heat there rooms.

Web address to follow.

James

P.s. the only manual switching is between gas and log boiler for dhw.

Edited January 19, 2013 by muttley9050
Forgot something

[openspaceman]

Hey catweazel, think you misunderstood the system, the 3 1000l tanks are purely for dhw. Not sure why they fitted two expansions to each tank, just how it was designed. If you look at the first picture you can see a large grey 5000L tank for the space heating, this has its own 500L(i think) expansion(not shown in photo)

 

OK I assumed the expansion vessels were for both systems, I expect two 50l domestic ones were more available/cheaper than 100l. It doesn't matter how many expansion vessels you have, nor where they are in the system as long as the bladders are charged to the same pressure and they can cope with the 10% water volume expansion between cold and hot.

 

iITS all manually fed with logs. and we monitor heat manually, such a big old house(see pic)

Impressive, the old firm did something similar to a Buddhist monastery but that fired a gasifying cordwood boiler once per day. I worked well so I only made one familiarising visit and was never called out to it.

[skyhuck]

This year I'm moving my boiler, I want it in my yard, to save moving timber and allow me to heat our swimming pool with it through the summer, when its not heating the house.

 

This will involve adding about 60M of pipe, both ways, so 120M all together. My header tank is already two small, meaning I loose water when when heating from cold, the added water, due to extra pipping, will make things worse. I'm also thinking of adding an accumulator tank, adding even more volume.

 

I'm thinking of adding a heat exchanger to separate the boiler and house systems, to fix the problem.

 

Are there and pit falls to this?

 

Can anyone recommend which are best and how big does it need to be? the boiler is 150KW running 16 rads and DMHW.

[difflock]

Huck,

Treat owt I suggest with a little caution:001_huh:

(i) A 150kW boiler sounds huge?

(ii)what is your heat load?, and what size of pipe is needed to transfer this amount of hot water over 60m (since I was told 28mm was too small for my 40 kW, but its not:001_tt2:)

Distance is a killer in pipe sizing though I think the super smooth HeP2O Type pipe is not so bad, with fewer joints etc.

(ii) A rule of thumb for sizing accumulator tanks is 50litres per kW =4,500 litres = 4.5 tonne of water,( and I wish ours was larger than this rule of thumb calc determined. being 2200litre on a 40 kW boiler)

An unvented system is the only practical way btw (I think)

Otherwise a horrendous amount of "Fernox" type treatment needed.

Consider keeping your accumulator tank beside the house where the heat is needed,

2 reasons for this,

(i)the heat loss in the 60m of pipe is lost prior to storage.

(ii) Almost instant response when the rad circ pump is switched on, rather than the time lag associated with pumping 60m

gibber

mutter

and twitch

PS

there are some very good online "pipe sizing" calculation sites.

Edited January 19, 2013 by difflock

[farmer rod]

This year I'm moving my boiler, I want it in my yard, to save moving timber and allow me to heat our swimming pool with it through the summer, when its not heating the house.

 

This will involve adding about 60M of pipe, both ways, so 120M all together. My header tank is already two small, meaning I loose water when when heating from cold, the added water, due to extra pipping, will make things worse. I'm also thinking of adding an accumulator tank, adding even more volume.

 

I'm thinking of adding a heat exchanger to separate the boiler and house systems, to fix the problem.

 

Are there and pit falls to this?

 

Can anyone recommend which are best and how big does it need to be? the boiler is 150KW running 16 rads and DMHW.

 

 

Huck, the heat exchangers are are physically pretty small, but by the time you add the pipes, the take a bit of space. Sorry I dont know the make.

 

The district heating pipe does have a loss, regularly quoted as 25 watts per metre, 60m therefore is 1.5 kW (24/7) is 36kWh per day, at 3 pence is nearly £400 just to run the pipe. ( but no sweat if the logs are cheap)

[skyhuck]

Boiler is huge, but I burn mostly green timber so will be well under 150KW maximum it can achieve.

 

I'm using inch and half galvanised steel (inside diameter), I'm going to run it through a large plastic pipe and inject expanding form into the void for insulation.

 

Thinking of a vented system, possibly float oil of polystyrene on top of the heater tank to reduce oxygen intake into the water.

 

Just going to lag an old steel oil tank for the accumulator, don't really want it near the house.

 

Not to worried about heat loss, I'll just start drying my timber a bit and up my BTU out put

[openspaceman]

Huck,

Treat owt I suggest with a little caution:001_huh:

 

All seems sensible to me

 

i) A 150kW boiler sounds huge?

 

 

Bigger ones seem to be cheaper second hand and RHI may well put a lot on the market.

 

 

(ii) A rule of thumb for sizing accumulator tanks is 50litres per kW =4,500 litres = 4.5 tonne of water,( and I wish ours was larger than this rule of thumb calc determined. being 2200litre on a 40 kW boiler)

 

 

Mine's too small on that rule, mind the boiler holds 600 litres so the total is around 2600 with 150kW on dry woodchip , as Huck says wet wood derates it considerably, once you get to 40%mc I cannot get the flue temperature above 120C nor have a clear exhaust. I am getting some interesting drying patterns in the hopper though which surprise me. Along the lines of the monorator gasifier. In the past I believed one could ignore drying in the hopper but now...

 

An unvented system is the only practical way btw (I think)

 

I agree but in Huck's case the oil tank as an accumulator will not stand any pressure. He'll also need a fairly expensive pump for that volume and distance, prices start rocketing up once you get above a typical domestic15-50

[skyhuck]

Catweazel, what sort of heat exchanger would you recommend?

 

Or would I be better trying to use a very large header tank, possibly not in the house?

[openspaceman]

Catweazel, what sort of heat exchanger would you recommend?

 

Or would I be better trying to use a very large header tank, possibly not in the house?

 

Like Difflock you need to take my advice with some circumspection, I'm not so hot on the wet side as I dealt mostly with feed and burner issues (because the plumbing didn't often cause a problem).

 

When you say you lose water is that because the F&E tank overflows?

 

My thinking would be a pumped circuit in the house, drawing from a plate heat exchanger, the primary of which would be pumped from the boiler circuit. This keeps both circuits separate and you could go unvented in the house. It would also allow the primary circuit to be at a higher temperature than the house circuit.

 

Ball valves on the output of the boiler directing to either house circuit heat exchanger or swimming pool (but this may be an issue with DHW) on the grounds you will not need house heating and swimming pool heating.

 

To avoid a heat exchanger for the pool could you weight plastic pipe in a loop to the bottom of the pool? NB most domestic pex pipe is not suitable for chlorinated pool water. I think a general rule for 28mm pipe is 70W/m per deg K so to sink 50kW ( probably the maximum heat you can pump through 28mm) with pool at <20 and water at 75C you'll need about 150m of pipe. Else you will need a second plate heat exchanger which can cope with pool water and keep the pool pump running whilst the boiler is running.

 

I haven't got one out yet but used plate heat exchangers can be had from combi boilers.

 

Coils have too small a surface area to transfer these large amounts of heat.

[skyhuck]

Cat, yes I lose water from the house header-tank over flow.

 

Heat-exchangers for the pool seem pretty easy to come by, I have one already which I got of ebay, I'll probably get another.

 

There are large plate ones on ebay too.

 

I currently have the boiler about 10M from the house, plumbed straight in with no accumulator.

 

Its been used for 10 years, I have had issues with boiling the system on occasions.

 

At the moment the boiler is off through the summer and DHW is heated by immersion heater, my hope is that while heading the pool I can turn off all radiators and still heat the DHW, via the indirect coil in the immersion cylinder.

 

Thanks for your advice so far, its much appreciated