Biomass for DHW & Heating with solar - lots of questions!!

[Fiddlers]

Hi Fiddlers,

Take a look at wood pellet or wood chip boilers, they will give you the low carbon result but with the automation of an oil or gas system, if you have local saw mills and tree surgeons, wood chip will be readily available at a very good price, you will need a fuel store, but you may get away with a "shed type" building which may not need planning permission, do not worry about a sealed system, as long as all the safety systems are in place it will make thing easier with the design of your heating system i.e. header tank feed and expansion pipes etc. you will also get away with a smaller buffer tank with a pellet or chip boiler due to the control of the boiler.

I know that you would like to to it your self, but I would recommend that you look for a Hetas registered installer as with all due respect by your own admission you do not know much about wood heating!
and this will ensure you comply with the building regs. for the future if you look to sell the house.

Terrier.

Hi, I did start out considering pellet and chip boilers but the initial costs (3x or more than a straight log boiler) put me off. Then I read about the issues of having to ensure the storage is completely dry to avoid rot and the fact that there doesn't seem to be a supplier within 30 miles led me to the current thinking of the log boiler. I guess if it all gets too much the boiler can always be substituted later for one with more convenience. As pointed out above, the store is the single most expensive part I'm considering - let alone the hassle of replacing it!
Good points on building regs. We're not planning to move for a very long time so will probably take the hit of getting it certified later if required - it'll probably change over time anyway
Regards,
James
Good point on building reg

[Fiddlers]

There really should be a 'useful theory docs' wiki page I could point you at, but you'll have to search the forum.
here are some useful threads:
http://www.navitron.org.uk/forum/index.php/topic,3411.html
http://www.navitron.org.uk/forum/index.php/topic,2281.html
http://www.navitron.org.uk/forum/index.php/topic,3857.html

Oooh, oooh, more to fill my little brain with  thanks!

[Fiddlers]

"Has anybody managed to install a 1500/2000 litre accumulator (probably Akvaterm) in a garage?"

I've got a 2,500L Akvaterm (and another 2,500L plain-Jane tank alongside it) in my garage.
...snip...

If you live anywhere near Suffolk let me know - you are welcome to come for a look-see and a chat.

Threads about installation of my systems are here:

60kW Log Batch Boiler and 5,000L Thermal Store Project Report
    
6 x 30 tube 58mm Panel Project Report

Blimey, nice response, thanks! There's a recurring theme of using a 2nd tank for DHW in the good Solar months which makes a lot of sense. Does anyone have such a system running? I'd like to see a piccy if possible of the setup...  sadly I'm nowhere near you (Southampton currently, soon to be North Dorset). I've read your full post on the install of the system. Very nice and an inspiration to many of us I'm sure!

[Fiddlers]

P.S. Consider retaining your existing boiler, or a modest replacement using the same fuel, as an additional heat source to your thermal stoe.  Useful to have an automated boiler when you go away ... or perhaps to keep the house warm if you break a leg and can't cart wood ...

Sadly the only thing we currently have for heating and DHW is a fairly ugly 80's Rayburn in the kitchen. Rigging that up to the boiler/store in the garage would be more effort than it's worth I suspect. We also need the space for a new leccy cooker
Thankfully we do have a log burner in one room, which will be easy given we'll have several tons of logs for the boiler!

Cheers,
James

[Brandon]

fiddlers, i am intrigued by your comment that a pellet boiler is 3x dearer than a log batch boiler.

With a pellet boiler there is no need for a thermal store, as it is an automated boiler just as a gas or oil boiler would be (I am not going to address in this post the merits of a thermal store as a means of CH buffering), but you could simply run a pellet boiler into an S-Plan heating system for example.

By the time you have added the auxiliary controls, pumps, valves (and the installation of them) you will find that a log boiler as a complete system will be at least as dear as a pellet boiler.

I am not trying to sway you in one direction or the other, but I am alarmed at the amount of people I meet who have installed systems that were not ideal for them (usually due to a lack of decent fuel supply, or over/under sized).

Most problems we encounter with "under-performing" systems are due to wet timber (about 70% less efficient, as the water has to be boiled off).

Farmers have long since solved keeping feed dry, and that is effectively pellets, just not wood.

[kristen]

"There's a recurring theme of using a 2nd tank for DHW in the good Solar months which makes a lot of sense. Does anyone have such a system running? I'd like to see a piccy if possible of the setup."

I think the general idea is that the Solar heats the DHW tank first, when that is hot the "dump" circuit (its a feature of a solar controller) switches a motorised valve (or a second pump) so heat goes to the larger store.  You then need a separate "dump" circuit if the larger store could ever reach maximum - that could just be a tank-stat that turns the central heating on!

"Sadly the only thing we currently have for heating and DHW is a fairly ugly 80's Rayburn in the kitchen. Rigging that up to the boiler/store in the garage would be more effort than it's worth I suspect. We also need the space for a new leccy cooker Smiley
Thankfully we do have a log burner in one room, which will be easy given we'll have several tons of logs for the boiler!"

I've got a pair 0f 9kW immersions on mine.  It will be blindingly expensive if I ever have to use them, but it would keep the house frost-free.  My old oil boiler broke down in the depths of Winter.  Took the "engineer" a week to fit us in. We have one open-fire, and one calor-gas mobile-stove thingie.  The house was COLD after a week. So I think the fact that a Thermal Store allows multiple heat sources means that folk should seriously considering having some sort of alternative. (Not to mention that a log boiler requires someone to be there to load it, and that can make going away "difficult")

[Fiddlers]

"I think the general idea is that the Solar heats the DHW tank first, when that is hot the "dump" circuit (its a feature of a solar controller) switches a motorised valve (or a second pump) so heat goes to the larger store.  You then need a separate "dump" circuit if the larger store could ever reach maximum - that could just be a tank-stat that turns the central heating on!"

Sounds simple enough for the heat supply. What I'm not so clear on is how I'd switch the DHW between the main accumulator and the small DHW tank. Or would I always draw DHW from the small tank and heat that from the accumulator when Solar isn't providing any heat?

"(Not to mention that a log boiler requires someone to be there to load it, and that can make going away "difficult")"

Good point. Not that I'll have any cash for going anyway for several years after I've purchased the house and sorted the heating 
Hmmmm. Maybe the Rayburn goes to the garage too as a backup heat source.

[dhaslam]

My solar panels heat a 250 litre cylinder, rather than the buffer tank.    The heat dump trnsfers heat to the 850 litre buffer tank and the latter can be cooled quickly by opening the insulation.    There is a separate difference controller  for transferring heat back to the DHW cylinder.  The buffer tank is heated by a stove and sonn by a heat pump as well.

[kristen]

"What I'm not so clear on is how I'd switch the DHW between the main accumulator and the small DHW tank. Or would I always draw DHW from the small tank and heat that from the accumulator when Solar isn't providing any heat?"

I would suggest that there is a pre-heat DHW coil in the buffer tank, and then a primary coil in the small DHW tank.  That way if there is any heat in the buffer that is used "first"

What I'm not sure about is what happens in the winter.  No solar, no heat in the small DHW tank ... (or on those days where there is not enough solar ...). Perhaps the boiler also heats the small DHW tank as a priority, and then the buffer tank?

As a refinement I suppose you could have a mechanical valve that passes the preheated water through the small DHW tank only if the small DHW tank is hotter than the top of Buffer.

Although, if the preheated water is already at, say, 60C there is no point passing it thought the small DHW tank at all. Might as well keep the small DHW "heat" for a cloudy day, instead.

You will need a thermostatic mixing valve blending cold into the DHW to reduce it to 60C (or whatever you set) before it enters the DHW circuit (or you need thermostatic vales at point-of-use, but allowing 90C water to enter the DHW circuit is going to cause huge thermal losses in the DHW pipework, so water entering at the lowest acceptable temperature** is preferably)

** which is basically the temperature at which the furthest most tap still provides hot water at an acceptable temperature, and possibly having considered any legionaries issues.

[Nuosmaa]

"you might like to clarify your '10C' standing losses. Standing losses really should be in kW rather than degreesC :-)"

Indeed. (I calculate that it is about 29kWh for my 2,500L store)"

That is an enormous loss from a tank with 100 mm polyurethane insulation. Urethane with lambda less than 0,028 and surface area of approximately 12 sqm simply calculating you should be in a fraction of that if the connections are properly insulated. I attached a thermal image of a similar tank of which you can clearly see where the heatloss is coming from. I would suspect heatflow on gravity to some pipes if your figure is with no heat consumption.

[lightfoot]

Welcome to the forum Nuosmaa - I hope we'll be hearing more from you.

[Nuosmaa]

Welcome to the forum Nuosmaa - I hope we'll be hearing more from you.

Thank you. You might be hearing more.

Continuing the previous: heatconductance is easy to calculate with insulation since the conductance will most likely be slower than the convection.
E (W)=    Lambda x A (sqm) x (tank C - ambient C)
                           insulation thickness (m)

To get that for a certain time or to get the Wh, just multiply the answer by the hours.

[lightfoot]

Welcome to the forum Nuosmaa - I hope we'll be hearing more from you.

Thank you. You might be hearing more.

Continuing the previous: heatconductance is easy to calculate with insulation since the conductance will most likely be slower than the convection.
E (W)=    Lambda x A (sqm) x (tank C - ambient C)
                           insulation thickness (mm)

To get that for a certain time or to get the Wh, just multiply the answer by the hours.

Hi Nuosmaa,

Unless I'm having a senior moment, I think you may of made a typo in your calculation - if the units for the K-value (Lambda) are W/mK etc, then the insulation thickness should be in m and not mm......

E (W)=    Lambda x A (sqm) x (tank C - ambient C)
                           insulation thickness (m)

[Nuosmaa]

Hi Nuosmaa,

Unless I'm having a senior moment, I think you may of made a typo in your calculation - if the units for the K-value (Lambda) are W/mK etc, then the insulation thickness should be in m and not mm......

E (W)=    Lambda x A (sqm) x (tank C - ambient C)
                           insulation thickness (m)

Thanks for the correction.

Yes, not a typo, but some shortcirquit as writing the units. So now corrected so the faulty formula won't be used.

[Fiddlers]

Hi all, long time since I've posted but I wanted to finish this thread off in the hope it's useful to others.

I've ordered a package through Eco Angus consisting of a 25KW log boiler (Orlan Super), 2000l Akvaterm (with 2 * DHW coils and 2 * spare hatches), Laddomat 21-60, mixing valves, safety cut off, etc. This will be installed in the garage with Uponor quattro underground piping to link up the house. I'm leaving the installers to supply the pipework, Uponor, chimney, lagging, etc. I'm planning to do the donkey work like prepping the garage & digging trenches.

Even with the good insulation on the Akvaterm I'm planning to box the tank in with walls packed with as much insulation as possible, with a door for inspection.

As for prices - going the Kotly route and shopping around for the Akvaterm would have been slightly cheaper (only by a few hundred quid overall) but Eco Angus came up with a pretty good package price and since I've not installed any of this before I'm happy to pay for local support, backup, parts supply, etc.

I'm planning on posting a sequence of install pictures along the lines of Kristens mega post, only for a slightly more humble system
Boiler & tank should be here in the next couple of weeks. Exciting times!

James