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Author Topic: Twin thermal Store or single larger tank?  (Read 2880 times)
Jamesmac
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« on: September 26, 2014, 12:05:37 PM »

I'm in the process of arranging for a new Log Gasification boiler to be installed in my house, it is going to be a 36kw Windhager and needs a 2000ltr thermal store.

The contractor who I'm likely to go with has recommended I have 2 x 1000ltr tanks installed rather than paying the premium for the Akvaterm 2000ltr oval tank as the system is being installed in an existing property that is currently heated with oil.... There is plenty of room for the new boiler and either option of tanks (i.e. single oval or twin in series).

My question is: - Is there any down side to having the twin tanks or will they operate pretty much the same and as efficiently as the single larger tank? I have my doubts but have no real experience in these things and have found next to no answers online on this matter... I'd be very interested on hearing peoples opinions on the matter on here!

Thanks

James
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stannn
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« Reply #1 on: September 26, 2014, 12:28:28 PM »

Welcome Jamesmac
Assuming that the store insulation is the same thickness for both sizes of tank, the downside is that the surface area of 2 off 1000L tanks is much greater than that of one 2000L tank. So, 2 tanks will lose heat to the room faster than one tank (all other things being equal).
Stan
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dhaslam
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« Reply #2 on: September 26, 2014, 12:58:25 PM »

Tanks of that size  are quite difficult to handle.  My tank , nominally 1000 litres, weighs  183 kilos and the double sized one weighs 386 kilos.    The  bigger one wouldn't fit through normal door openings.
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Jamesmac
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« Reply #3 on: September 26, 2014, 01:11:26 PM »

Stannn... thanks for your very quick response!!

The installer insists there's no difference between either setup, I have no reason to not believe him but can't help thinking the larger body of water would offer better performance in retaining heat... I guess the larger area of external tank surface from two tanks will be a factor over a single larger tank! If that's the only issue than I may not need to worry too much then!!

dhaslam... the Akvatherm tank is oval and is only 810mm wide so it will fit through the door but it does weigh in about 450kg (I think) so would be a hassle to get in!!! My installer insists that he almost always installs twin tanks in systems in existing buildings and has never had any problems with them working.... I just wasn't sure if it he was just opting for the easier option for himself!! In fairness, it'll be much easier to get the two single tanks in the room and I can just make sure the connecting pipes are well insulated to prevent any heat loss though the pipework!
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oliver90owner
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« Reply #4 on: September 26, 2014, 01:27:36 PM »

Oval versus what?  Cuboid or cylindrical?  Flat surfaces could be stood close together and insulated between tanks.  Flat surfaces are easier, if adding further insulation.  Cylindrical tanks are the norm for minimum suface area, and other reasons, for copper, but not so necessary for a thermal store, I would think?
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Jamesmac
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« Reply #5 on: September 26, 2014, 01:31:38 PM »

I'm guessing (and fairly certain) that it's twin cylindrical tanks he's offering!
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biff
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« Reply #6 on: September 26, 2014, 01:49:20 PM »

It it were my decision,
                        I would tend to go for the twin tanks. Even though the bigger body of water would retain the heat longer (maybe). You could combat that and go the extra mile by surrounding the lot with freezer panels. With the twin tanks you have more alternatives and can adjust better between summer running costs and winter running costs. One of the twin tanks would get up to temp much quicker than the big tank. There is bound to be a bit more pipework and at that bore,would be more expensive to install. So costs wise,I doubt that if he would gain anything by trying to push the twin tanks on you.
          It,s an interesting dilemma.
                                    Biff
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oliver90owner
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« Reply #7 on: September 26, 2014, 01:55:07 PM »

In addition to Biff, if you have two tanks, and either can be isolated, you would not be totally stuffed if there was a fault in one tank....
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knighty
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« Reply #8 on: September 26, 2014, 02:39:39 PM »

2 tanks will have higher heat loss (but if they're inside the house, heat will be lost into your house, so not really 'lost' at all)

but with 2 tanks, you should have better stratification... because you can have 1 tank of hot and one cold

with one big tank, the top of it can be hot and the bottom cold... but heat will be conducted down the metal sides of the tank, and there's a limit to the stratification of the water in the tank ?


better stratification should mean you don;t have to fire up the boiler as much in the summer :-)
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Jamesmac
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« Reply #9 on: September 26, 2014, 03:16:14 PM »

Sounds like I'm worried about nothing and in addition, the two tanks may have some positives over a single tank!!! Think I'll go with the proposed system!!

Thanks for all you thoughts and comments!! They're very much appreciated  Grin
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Tinbum
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« Reply #10 on: September 26, 2014, 03:37:59 PM »

As a slight aside- I priced up a 1500l tank and a 2000l tank and was pleased I did- the 2000l was only 50 more than the 1500l!!
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Jamesmac
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« Reply #11 on: September 26, 2014, 03:45:52 PM »

As a slight aside- I priced up a 1500l tank and a 2000l tank and was pleased I did- the 2000l was only 50 more than the 1500l!!

Yea, I noticed that too!! The 2000ltr is about 200ltrs bigger than I need for a 36kw boiler but still not too much more that it causes a problem getting up to temperature for being oversized...
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Nickel2
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« Reply #12 on: September 26, 2014, 06:45:25 PM »

As a matter of interest, how much floor-strengthening is needed to support 2450 kg / 2.4 tons?
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Jamesmac
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« Reply #13 on: September 27, 2014, 10:53:02 PM »

I'm going on the basis of none due to it already being a concrete slab, but at worst a steel plate could be used to spread the load!! It won't be such a problem with two tanks either... Twice as many feet to share the loads!!
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