Under floor heating & AKVANTTI 1400 litre Acumulator tank advice.

[SteveH]

 It's interesting how projects change as they evolve

 We have had to ditch our idea of home brewed low-grade storage tanks & move to a commercial accumulator, a more conventional approach, but almost certainly more reliable.

Original post here:

 I'd better give everyone a little more information before asking for your input & opinions:

The house is constructed from a reinforced concrete skeleton with infill cavity block walls, these may also be insulated & the whole structure will have a 50mm exterior surface insulation. The building has a very large thermal mass & the projected U-value is 0.35 - 0.40, not well insulated in comparison to northern Europe, but suitable for the climate of Crete.

Climate info at the bottom of the page on this link
 
 The heated floor area of the house will be approx 130 - 150m². The system is to be wet heated low temperature water @ 40°C, the store temperature can be above this & circulated heating water can be fed to the heating circuits via a thermal mixing valve. The construction is plastic pipe in 100mm cast concrete slab above 50mm insulation. This mass should stabilise internal temperatures.

 Current Solar water heating specification is for 3 x 30 tube 47mm ET collectors facing south & connected in series, feeding into a 320 litre thermal store for domestic hot water with a AKVANTTI 1400 litre accumulator in parallel.  Both these tanks are going in the basement. The DHW tank gets first call on solar output & when up to temperature the excess goes into the accumulator for use by the under floor heating. This should be easy enough with a motorised 2-position valve on the solar return pipe.

 There is a wood burning stove specified with a boiler for supplemental heat supply (8 kw/hour max) to top up in case of solar deficit & in colder weather conditions. Both DHW heat stores & accumulator will be heated from this sources via a separate circuit of pipe work pump & indirect coils. Again DHW gets first call on resources.

 I've had a chat with Mike at Navitron & he has pointed out a potential problem.

If you have space then having two cylinders sounds like a sensible idea. One thing to bare in mind is that if you are running a wood burner into this cylinder it will need to be vented and I would imagine the standard in Crete would be to have unvented cylinders. This has caused problems for our customers in the past so it would be worth double checking that the underfloor heating system is compatible with a vented tank.

 I  know there are a few people that post on this Forum who have taken a similar approach with AKVANTTI Accumulator Tanks in other EU countries. I'm very intersted in your input here.

OK... Question time.

 I suspect my UFH is designed for an unvented system & with both tanks in the basement & a flat roof with no roof void, installing a header tank up their would be quite a pain. I'm just wondering if I could turn the AKVANTTI Accumulator Tank into an indirect heat store by using a mains pressure DHW coil for the UFH. The peak demand from the majority of the UFH is quite low as it is designed to be low temperature & high thermal mass designed to maintain a steady temperature?

 If the DHW coil is not up to the Job, is there another indirect system using an external heat exchanger that would be suitable?

 Any free software out there so I can get a schismatic together so this post makes more sense?  (I have to get this system approved so the property can be signed off & I will need a local installer to do this, even if I do the work myself)

 Please ask me questions & give me your opinion's...

 Steve...

 
 


 

 

 

[SteveH]

 Have I upset everybody or is the question too hard...

 Does anybody think I can use the domestic hot water coil (45 litre/min) to feed the UFH?



 I think I'll have to ask for a special tank to be made...

 Take a AKVANTTI 1400 litre & add an indirect heating coil to the standard heating feed & return.




AKVANTTI 1400 EK, CONNECTIONS FROM TOP: 
1. Entry from boiler NS 50
2. Return to boiler NS 50
3. Exit to heating circuit NS 32
4. Return from heating circuit NS 32
5. Domestic hot water coil 45 l/min NS 20, 2pcs
6. Air Bleeder NS 25



AKVANTTI 1400 EK, PIPE CONNECTIONS FROM SIDE:
7. Drain coupling NS 25
8. Electrical Resistor Unit NS 50, 3pcs
9. Thermostat Unit / Thermometer  NS 20

 Then see if the company can add the solar heating coil from there AKVAir Solar range of tanks.

 Then, hopfully, use the domestic hot water coil to feed the UFH...

[dhaslam]

I think you should re consider connecting the wood burner to the system.   A small wood burner would be fairly ineffective in heating  a buffer tank of that size.  If you used a  small non-boiler model it would heat the house quickly  on cold evenings.   I understand that in Crete it is very rare to have more than a few days without sun and it should be possible to size the system to store enough heat on solar only  in winter and have a very large heat dump or shading of the panels in summer.   

[SteveH]

 Good points.

 The inclusion of a boiler was mainly as a backup to the solar for the separate 320 litre DHW heat store... This does have an indirect heating coil to help maintain stratification.

 Thinking about it (What I should have done before )There is no need for a separate indirect coil in the buffer tank as the top of the buffer tank is higher than the boiler on the stove...

 I think i was a little confused... I was thinking because the DHW heat store had an indirect coil the whole of the stove boiler system had to be an indirect system.

 If I connect the fire boiler to the buffer tank the open feed side will allow expansion into the buffer tank along the unused feed pipe when the DHW heat store coil is receiving the fire boilers output.

 For the sake of a motorised valve & a couple of lengths of pipe a connection to the buffer tank seemed sensible as a dump for the fire boiler.

 I'm also waiting to find out about an absorption cooler that will take summer overproduction of solar & chill the UFH (I suppose it will become under floor cooling).

 With the panels mounted to optimise winter sun at 60° the Navitron calculator gives me a pretty flat 3 kWh/m² (2.9 - 3.6) Average Daily Insolation through the year.

 

[wookey]

You asked about software for drawing schematics. This has just been posted: http://www.navitron.org.uk/forum/index.php/topic,7539.0.html which is  set of solar symbols for the Dia drawing tool, which is Free software available for both Linux and Windows.

[SteveH]

You asked about software for drawing schematics. This has just been posted: http://www.navitron.org.uk/forum/index.php/topic,7539.0.html which is  set of solar symbols for the Dia drawing tool, which is Free software available for both Linux and Windows.

 Thanks wookey,

 If you look at the topic I got there before you.... still not able to load Scotts SolarShapesLibrary...

[dhaslam]

So the stove is also in the basement like the  two cylinders.  This does make it a lot easier.    Also a stove is more suitable for just topping up the temperature for DHW.     It is a pity that the option to have additional storage didn't work out,     

[SteveH]

 I didn't explain that well... the build is on a slopping site so the basement is underground, but the lounge is on the same level but above ground...

 Not given-up on additional storage yet...

[SteveH]

 I've struggled to produce a schematic for the solar & heating system I would like to use in our new build in Crete. Could you look over it & see if it makes sense?

Here is a quick view:-




  Have I "c0cked it -up'...?

[Brandon]

slightly puzzled as to why you are not putting the wood burner direct into the thermal store... then the 3 port diverter (er1) on the return...

(Tired, and possibly a bit dulled...)

[SteveH]

(Tired, and possibly a bit dulled...)

 Me too... tomorrow

[Poolguy]

Steve
The DHW coil if its an LK35 has enough guts to get a good change for your UFH but why do you want to do that. You will be pulling the highest grade heat out of the Accumulator (or have I miss understood you.)

I have the Akvantti 2400lt and my heating circuit for UFH will come off about 1/3 way up the tank so that I can heat the top to get DHW and Gard stratification by dumping lowergrade 25-35° into the UFH circuit to provide what is essentially an extension to the thermal storage (albeit concrete). That approach is designed to keep the bottom of the tank where the solar coil is around 20° to ensure that there is maximum harvest even on dull days. these days when the system is not on you will see on my charts www.poolguyenergy.com that the bottom and top of the Accumulator follow each other very closely - not very clever.

Your design is essentially the same as mine with live and dead water tanks, solar in series, and a third heat source. But I do not understand the thinking behind the UFH, seems to me that your taking water that is (should be) too hot, so you will loose a lot through losses arising from a large differential. As your Akvantti doesn't have a baffle plate to prevent circulation you will find that the bottom and top will quick equalize in temperature(ref charts again). That means the bottom of the tank will be too hot to absorb all the heat out of the solar coil before it goes back to the roof. So the idea of a UFH is as as much about stratification for you as it is about distribution of heat.

I'm working with the Akvaterm boys to change the tank design to fix the problem and it can be done but its a non standard tank, so if you've already bought one then you'll have to do it the hard way (like mine). But if not then I can show you other schematics that will make sense of what you are trying to do.

Andrew

[SteveH]

slightly puzzled as to why you are not putting the wood burner direct into the thermal store... then the 3 port diverter (er1) on the return...

 My thinking is that a standard 3 port motorised valve is fine for CH systems & would be in this position in a gas or oil burning system. Would need a more expensive valve on the return. Just being a "Cheap skate"....

The DHW coil if its an LK35 has enough guts to get a good change for your UFH but why do you want to do that. You will be pulling the highest grade heat out of the Accumulator (or have I miss understood you.)

I have the Akvantti 2400lt and my heating circuit for UFH will come off about 1/3 way up the tank so that I can heat the top to get DHW and Gard stratification by dumping lowergrade 25-35° into the UFH circuit to provide what is essentially an extension to the thermal storage (albeit concrete).

That approach is designed to keep the bottom of the tank where the solar coil is around 20° to ensure that there is maximum harvest even on dull days. these days when the system is not on you will see on my charts www.poolguyenergy.com that the bottom and top of the Accumulator follow each other very closely - not very clever.

Your design is essentially the same as mine with live and dead water tanks, solar in series, and a third heat source. But I do not understand the thinking behind the UFH, seems to me that your taking water that is (should be) too hot, so you will loose a lot through losses arising from a large differential. As your Akvantti doesn't have a baffle plate to prevent circulation you will find that the bottom and top will quick equalize in temperature(ref charts again). That means the bottom of the tank will be too hot to absorb all the heat out of the solar coil before it goes back to the roof. So the idea of a UFH is as as much about stratification for you as it is about distribution of heat.

I'm working with the Akvaterm boys to change the tank design to fix the problem and it can be done but its a non standard tank, so if you've already bought one then you'll have to do it the hard way (like mine). But if not then I can show you other schematics that will make sense of what you are trying to do.

 The feed into the heating system (On heating scheme drawing not shown here) is via a TMV set for 30°C. This means I can run the accumulator at anything from 25° up to 75° + if I need to store more heat energy. In essence it is a heat dump for the solar & anything left over from using the wood stove to heat the DHW heat store. As with your UFH I'm also using the floor mass as a major additional heat energy store. I've been told "Hot Water is very important" (SWMBO) hence the dedicated heat store for DHW that gets first call on solar & stove boiler output.


 I planned not to worry too much about stratification in the AKVANTTI. I'm not getting my DHW from the accumulator & I was under the impression that the wood stove, being an unregulated heat source, had to be on an open vented curcit & it was easier (& cheaper) just to use the standard open connections into the accumulate. ( I've now found out this stove can be used on a closed pressurised system) I know this is going to stuff the stratification but as long as I can keep the Accumulator above 30°C I don't see too much trouble with this...

 If you look at the inputs from the Stove & Solar they are unlikely to be running in tandem even during winter, solar when the sun shines & stove in the evening & dull days possibly, then over night everything in the accumulator gets chance to settle down, so the solar input period should start with a stable if mixed tank.

 I've not ordered yet but I have asked Navitron to enquire about a special tank with an indirect coil to supply the DHW, rather than use the domestic hot water coil.

 Always happy to learn from others experience Andrew, so I would like to see your schismatics.

 Steve


Andrew