I have come to crunch time on my renovation project. After 5 years of building I now have to decide which thermal store to install.

Upto this point I have designed for a DPS / Specflue Excel thermal store.

I have a 13kw boiler stove (not installed yet but pipework in )
I have 2kw Solar Photvlotaic
I have planned for Solar thermal.
I have 120 sqm of underfloor heating.
I do have mains gas available.


However the most recent qoute I have had from DPS/ specflue has come to about £7000!!!!!

This is for the cylinder alone with various technologies to facilitate the above inputs. This does not include solar panels or pump stations etc
I am sure I could de-spec this a little to bring it down 10-15% or so but even so.

My hope was to be as self sustainable as possible.

I am a plumber (of sorts) so installation of most of the above will be /has been cost free.

However at those prices it has become just too unrealistic.

My feeling is that alot of what the DPS excel thermal store offers and infact most of the cost is the technology for the input from the wood burner back boiler.

If I was to chose an alternative such as an unvented cylinder with solar coil only I could save a fortune on the installtion cost.

I am begining to think that any financial (dirty word I know) benefit I hope to achieve from burning wood over using gas is significantly outweighed by the installation fixed cost of the DPS thermal store system.

Plus there is the added convenience of using gas itself.

I do have a supply of wood for free (though quite a few miles away)

Can anybody help me here!! i have had the DPS excel system in mind the whole build, infact my heart has been set that way for years.

What are the alternatives? I have to be realistic with cost yet want to be self sustainable. I am in an urban environment (small rural town in Essex).

My ideal solution would be DPS Excel heatbank with Solar thermal input, wood burning stove boiler input, and ideally a gas combi boiler back up that allows for instantaneous hot water for convenience (DPS have an externall heat exchanger for combis- yet more money !!!)

PLEASE HELP!

Many thanks all.
Tim

Hi,

Have a look through many threads – search for accumulator / buffer / store etc etc.

I don’t really get involved with thermal store system design these days so any info I have is out of date. With the rapid expansion of wood stoves / boilers recently there is a lot more info out there and numerous suppliers to compare against each other. It’s not so much the dark art it used to be.

I expect the high price comes from a) being DPS or the new co what ever they are called and b) if it’s the sealed / pressurised version then is fabricated in s/s.

Sealed or unsealed, the norm elsewhere in Europe is mild steel so £1k ish would cover a decent size say 1000 lit basic vessel insulated inc some internal coils etc but with no kit hanging off it. For the UK in copper 400-500 lit is about a big as it goes. In m/s smallest available is 400-500 lit.

If you have UFH you will be shifting a fair volume of water around does this mean you stove will always be lit? Do you work at home for example? I’m sure you went through all of this with DPS and there is an element of system design within the DPS price.

So you can pretty much design and build yourself around a generic vessel. Obviously that’s a bit of an under-statement.

You require a vessel/tank/buffer store call it what you will – you can’t make this yourself. A loading valve+pump to charge it with hot water e.g. a Laddomatt or similar (name not description) so you need to buy that. This is all primary side. After that you can pretty much design what you want to use that store of heat. You then either pump this hot water to a plate exchanger for DHW; alternatively store has various styles of coils/vessels internally for prep of DHW. New plate exchangers can be pricey, but not if taken from old combi boilers.
Some off takes to feed heating loops plus some pumps / valves
There are lots of tanks/vessels with a multitude of off takes and sensor point with or with out solar or DHW. Some are more expensive than others, there will always be a bit of a premium on some, just they way they are marketed.


What DPS offer is a “system fit” i.e. its all fabricated so just hook it up and that costs £££, just look at the price difference between a bare UV cylinder and one with controls/pump/diverter(y plan) etc already fitted (e.g. heatrae sadia megaflo).

With help here a system can be specified, a good heating engineer will do the rest. But beware it can get a bit Heath Robinson with valves and pumps and exchangers all over the place which can be half the attraction (must be a bloke thing).

That said there is a valid argument that if on mains gas then the simplest and cheapest option is to go with bog standard gas system and spend the money/effort elsewhere.

Cheers Mike up North

Hi again,

Have a look at accumulatortanks dot co dot uk for info on the Akvaterm stores (very attractive as vessels go), these for example are now available via “stoves on line” type outlets so readily available.

For cheap supply have a look at thermal-store dot co or buffer-tank dot co. I’ve no connection to these and these do seem to be a straight forward sales front - the use of English suggests their origins and only a mobile phone number is questionable.

However, that said they show just about every combination of shape / size / coil with dimensions etc and internal views and show prices. Cannot vouch for quality or steel spec or anything else – just have a look. Should keep you going for a while.

This to many (particularly in Europe) is pretty regular kit and the heating engineer would select one of these pretty much as you’d expect a plumber to select a shower valve and get on with it. So it doesn’t need to mega expensive. Particularly as there are other options – the straight gas option is probably seen by many now as the greenest (if as they say –“if you must have a heating system”). You don’t want to spend a fortune on something you later find yourself defending.

The point about if you need it relates to doing everything you can to reduce the heat load in the first place, then and only then consider heat supply. Obviously you need hot water. But as you reduce the heat load it gets harder and harder to justify and make big complex installations at a large financial cost. Which is where the straight forward out the box gas option wins over.

Cheers, Mike up North

Tim, I had a quick glance at the DPS store's you mentioned. I have no knowlege of their quality etc but at first glance two small things stand out 1. why is the insulation so thin, or did I read that wrong. I think German DIN standards demand 100mm minimum. 2. the solar input, (coil) is quite low in the tank. The upshot of this is that in Summer when you're not using your CH, unless you have a very large Solar array the collector is having to work very hard to heat the mass of water above the coil. This water is then feeding your PHx and allowing for losses, and to get decent DHW you will need to be pushing about 60°C water into the primary side of the PHx. Is your intended Solar array capable of that?
Balancing so many different functions, flows and returns, into one vessel is never going to be easy, especially when that vesssel is having to cope with such varying seasonal demands. Then trying to give the whole thing a degree of automation is a job and a half. As Steamy Tea said you need to crunch the numbers, look at your lifestyle demands, CH demands, heat inputs into the store, and how and when they will be used. For instance in the middle of Summer you don't want to be "having " to light a fire, just to get a bath. The Sun, ( Ha! ), should provide that, maybe with a little occasional nudge from your Solar PV, if you get it right.

P.S. Glad to hear you're getting things sorted Matt.

Posted By: mattwpriceI don't want to seem to be advertising so i am a little reticent about putting the make of my store on here. My tank and system is German though,

I don't regard that as advertising unless you sell them - just a recommendation and I would be interested as well.

I went for a Newark 300 litre thermal store because it was the largest size we could accommodate in the space available. It has not been a great success as the heat capacity is simply insufficient, meaning that whilst our wood pellet boiler isn’t exactly cycling non-stop we are a long way from the desirable “long burn and then off” situation. So yes, I would endorse getting the largest thermal store that is practicable.

The solar coil is at the very bottom of the store and hence unless we get a full blue sky day (I think we had one of those back in 2010?) we get a lot of warm water rather than hot. We are now considering a separate 180 - 200 litre solar cylinder just for DHW purposes and when that is satisfied, then diverting excess hot solar water into the thermal store.

Posted By: owlmanThis water is then feeding your PHx and allowing for losses, and to get decent DHW you will need to be pushing about 60°C water into the primary side of the PHx.

in defence of the PHx system we have 475 DPS PHx and as long as the store temp of anything over 40 then water is perfectly hot. This is because the store is pumping hot store water through the PHx so its a v.efficient exchange, although there is technically an electricity fuel hit.

The 30 tube array seems to have no trouble lifting the tank from say 25-45 in a decent Spring / modest summer day and far more on a good day. Seem to observe tnak keping pace throgh the day with the collector temp till about 50deg then the collector seems to outstrip the tank. Best days tank can get up to 60/70 with thermal. However that's just monitoring it prior to occupancy (ie very little draw off during the day).

On the flip side would agree with the insulation as it can drop from 45 to 37ish over night but additional insulation is an option (see thread on same).

Slightly off topic, as the tubes seem to have no trouble getting the tank somewhere between 35-40 even on a crap day and a cool tank (as seen during the winter/early spring), I'm going to add in a inline electric heater to lift the water we need up that last 5 degrees rather than having to lift the whole store with immersions during intermediate days (ie cloudy but quite warm winter, ealry spring/late autumn days.

Specflue however seem to have pretty much doubled the DPS prices. I had a quote from DPS for around 1800, then they had their financial problems and a year or so later Specflue DPS quoted nearly £4k I haggled them down closer to £3k, so could well imagine them having a go at selling a system like mine for £4.5k... (+ VAT).

Any one else do Phx?

J

Could be!

J

Hi, sorry for the delay in replying. I have a solarbayer store with two solar coils and 'sls' system which is essentially a bean can with lots of tubes coming out of it. One sits at the top and the bottom of the tank and minimises 'churn' of outtake and intake water serving the plate heat exchanger and hopefully maintaining the stratification. It has 100mm detatchable insulation. I bought (imported) through my company and so got a decentish discount. I also purchased their solar controller and pump station and fresh water station ( plate heat exchanger and pump and controller) for the mains pressure hot water. if you have a company I am sure you could get similar discounts. Please give me a shout if you need anything more. I should point out that this isn't a recommendation, merely what I have got and am currently installing. I went from 300 to 1000 litres due to the (on consideration) very reasonable advice received by the kind posters on here who I am sure no far more about this than I. I am confident my system will work and provide more than enough hot water during summer and add to the heating requirements during the shoulder months. I'm on my iPhone on a train back from London so I must apologise for not going into great detail and also the likely typing mistakes. I will fill in more detail on request though

<blockquote><cite>Posted By: owlman</cite>Posted By: Jeff B............... We are now considering a separate 180 - 200 litre solar cylinder just for DHW purposes.

That's the approach I used Jeff, it works well.</blockquote>

Owlman - thanks for your response. Did you have the same problem as us i.e. thermal store too small for space heating purposes and too large for DHW? Do you have a plate heat exchanger in conjunction with your solar cylinder (for mains pressure DHW) or do you just have a coil in the cylinder?

Finally, any potential snags that I should be looking out for?

Posted By: Jeff B............ Did you have the same problem as us i.e. thermal store too small for space heating purposes and too large for DHW? Do you have a plate heat exchanger in conjunction with your solar cylinder (for mains pressure DHW) or do you just have a coil in the cylinder?

In a nutshell .....yes. My accumulator is 2000l which I considered was the minimum for CH purposes without standing over the log-gas boiler 24/7 stuffing wood in it. I wanted it to last a day or so in the harshest winter months providing both CH, and DHW via my PHx. The clue to making this work is, essentially threefold, first insulate and reduce demand. Second efficient controls and, third correct positioning of flows and returns out and back to the tank, in order to keep good stratification in the tank, and fully utilise the advantage of the two ton plus of hot water. There may be other reasons that come to mind and if I think of them I'll let you know.
The downside of this large scale industrial approach to heating and DHW is that if you try and heat this two ton monster to a degree hot enough to feed both the CH and DHW with a solar array you may need upwards of 20M2 of collectors. So everthing starts to get out of hand. As a result I opted for a Summer/Winter approach. With my boiler and accumulator providing heat and DHW mid Autumn to mid Spring and then when the boiler is shut down for Summer I throw a switch and work on my solar array for the rest of the year just for DHW. Because my cold mains water is routed via the pressurised 180l SS solar cylinder all year I do get some solar gain even in the winter months as the incoming mains is pre-heated before it enters the PHx, often to about 30°C meaning it doesn't have to work so hard and consequently doesn't deplete the store so much. This solution means that the potable water supply in the 180l cylinder is constantly refreshed, instead of stagnating all winter. I'm generally satisfied with the set up and I've tried to some extent to futureproof the layout. I'm still improving insulation.

Finally, any potential snags that I should be looking out for?

Loads. but I'll try and answer them, BTW I'm not a heating engineer, there are other on here who are much more adept at calculations etc.. I do however, have an eye for detail, the cabinetmakers affliction called perfection and a broad understanding of how the jigsaw fits together, plus years of experience of remodelling others houses to a degree I can't afford.
Mike

Hi,
You will find in many standard from the book designs that the thermal store is just that – a store and instead of as we expect DHW from internal coil/external plateX, that the heat is piped to a conventional un-vented cylinder (probably DHW will include solar anyway, probably would have an elec immersion as well). This way with high solar gain store depletion is minimised to a top up function. Obviously in countries where there is a more constant colder temp and high solar conditions such as Alps and so forth this works better. So having a 2000+ lit thermal store and a 200 lit DHW cylinder is not unusual. In fact it comes back to the point I made in another thread about trying to shoe horn many functions into one box. Price wise a store with internal coils/tank in tank/plateX wouldn’t be much different to buying a plain store (i.e. a tank) and a separate off the shelf DHW cylinder. The –plumbing to the DHW is pretty much as per normal as the cylinder receives heat from the store instead of a boiler.

Cheers, Mike up North

Apologies Jeff my mind was drifting a bit. My "loads " comment refered to setting up a dedicated large scale accumulator etc., not to your particular case of installing a small summer only tank in tandem with your main store. This I think will work fine in principle, and is not so expensive if you do the work yourself.

ST I can't think of a reason why it would't work,