Underfloor heating - Thermal store

[SmogLee]

My existing thermal store is leaking and I need a new one. Existing one is copper.

I have a mixture of old and new Nu-Heat underfloor heating. I don't know if you know the history with their red twin pipe, but it has no oxygen barrier and there have been problems.

Anyway, this means I need to keep the boiler feed water and the UFH circuits seperate. I also wish to maintain my Mains Pressure Hot water facility. looking forwards, I'd also like solar power connectivity.

This means I think i need a triple coil vented cylinder with integrated tank above.

The top coil will be for Domestic Hot water with the normal blending valve arrangement. We have a large 4 bedroom house with 2 showers and a bath. 2 young children so I'm thinking we need plenty of hot water going forwards. I think a 300 litre tank is appropriate????

I'll need a coil for the Under floor heating which needs to be at about 55 to 60 degrees leaving the tank.

The lowest coil is for future Solar.

I'll need two thermostats, an upper for DHW at 70 degrees? and a lower at 60 degrees I think.

The boiler feed and return pipes need to connect to the tank top and bottom I think, but I'm not sure due to future solar potential, does this mean that boiler feed pipe goes higher?

Where can I get such a tank??? Do I need a stainless one or copper?

What's all this finned coils business?

Any advice appreciated... especially as I'm losing a pint of water a day at the moment and I need to get a new tank soon.

I'm happy to drop the solar coil from the plan if necessary. But this would mean a twin coil solution, but I don't want the underfloor heating coil right at the bottom of the tank.

I appreciate I might need an external heat exchanger to sort this out.

Do you know if a stainless steel heat exchanger / coil is ok with Nu-heat pipe (no oxygen barrier), I know I have a bronze pump due to the ferrous issues.

HELP please
Thank you

Lee

 

[buffy27]

what type of boiler and what cold water supply have u .could u pressurise everything.do u understand how the coils work on an inderect system.u may b getting a bit mixed up.the heating mediums go through the coil in the cylinder and in doing this heats the domestic hot water.why would the underfloor have a coil in the cylinder.?.hopefully i can help.

 

[SmogLee]

It's a thermal store, so the boiler water is the mass of the water, not heated by a coil.

The underfloor has its own coil so that the water is seperate circuit.

Just for clarity, existing system is 2 coil.

Top coil is for mains pressure hot water with blending valve (< fairly normal arrangement)

Lower coil (which sits about middle, to lower part of tank) is for underfloor heating.

Boiler feed is at the bottom and boiler return is at the top of the tank.

 

[Deleted member 2053]

Normally you feed the underfloor directly off the thermal store - so if I understand you correctly you need to feed the underfloor through a coil in the store to prevent the ingress of air into the boiler system??? What sort of load is the underfloor? Normally a coil would be insufficient to drive UFH of any size and should you perhaps be rather thinking of a plate heat exchanger?

 

[SmogLee]

Normally you feed the underfloor directly off the thermal store - so if I understand you correctly you need to feed the underfloor through a coil in the store to prevent the ingress of air into the boiler system??? What sort of load is the underfloor? Normally a coil would be insufficient to drive UFH of any size and should you perhaps be rather thinking of a plate heat exchanger?

No idea of the load sorry.

Yes, you understand me correctly. However, it's not so much air, it's ferrous that needs to be avoided.. with air.

I think a plate heat exchanger is the way forwards, but this is mounted externally yes? How big?

And it is gravity fed on the Thermal store side yes? Obviously the underfloor heating circuit is pumped.

I have a very large 4 bed house. 5 zones.

 

[HTB]

Is it possible to dose the sealed part of the system with some form of inhibiter to prevent the oxygen/ferric reaction taking place thus preventing the "gassing off".

 

[Deleted member 2053]

well yes obviously you need to avoid air because of its corrosive effect.
If I were experimenting with this - and without previous experience that is what it would be - then I would use an external heat exchanger with a shunt pump. I would match the capacity if the exchanger as near as possible to the output of the boiler.

 

[SmogLee]

well yes obviously you need to avoid air because of its corrosive effect.
If I were experimenting with this - and without previous experience that is what it would be - then I would use an external heat exchanger with a shunt pump. I would match the capacity if the exchanger as near as possible to the output of the boiler.

Sounds good, Shunt pump? How does this work?

This was my concern with an external heat exchanger. How do I maintain flow through the heat exchanger (tank side)

 

[Deleted member 2053]

Basically a shunt pump pulls water from high in the thermal store and passes it through the heat exchanger, returning the cooler water to the store at the bottom. As this is for underfloor you will not need a flow switch to control the shunt pump - it can simply run when the underfloor pump is running. If you are buying a thermal store for hot water and underfloor then the position of the tappings for the underfloor should do fine.
Wasn't aware of this problem with early Nuheat pipe. Didn't stop the MD from being able to buy his Maserati though did it?

 

[SmogLee]

Basically a shunt pump pulls water from high in the thermal store and passes it through the heat exchanger, returning the cooler water to the store at the bottom. As this is for underfloor you will not need a flow switch to control the shunt pump - it can simply run when the underfloor pump is running. If you are buying a thermal store for hot water and underfloor then the position of the tappings for the underfloor should do fine.
Wasn't aware of this problem with early Nuheat pipe. Didn't stop the MD from being able to buy his Maserati though did it?

Thanks for that, could be a solution.

Nu-Heat were very lucky with that product. They managed to deflect a lot of legal issues.

Any idea what tank I should buy? Assuming the external heat exchanger solution.

 

[Deleted member 2053]

No I'm afraid my experience is limited to "Nuheat stuff was good and I have had problems with Gledhill". There were some recent postings on thermal stores with other contributors making recommendations so try a search on this site.

 

[SmogLee]

I searched for Thermal stores. Not a lot on here, except the funny thread about a bloke not recognising one. Actually, it looked like the same tank as mine. But no recommendations for a replacement.

 

[Deleted member 2053]

OK I'll see if I can dig something out. Might take me a few days - trying to sort out my self-assessment. Oh, the joys of being a tradesman!

 

[Plucky]

You need to get yourself one of these. Fitted several now and they are brilliant. Have a read up.

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