indirect cylinders versus thermal store efficiency query

[johnnymc]

Hi, New to the forum, experienced DIYer, looking for some advise.
I am currently exploring upgrading our back boiler unit to an Aquatherm 34KW log stove and am unsure about which type of cylinder would be best for our situation.
The cylinder now is vented and gravity fed with two coils, one for oil, one for back boiler, we intend to add solar hot water to the system when we win the lottery! so need to factor this in to the new tank to be sourced.
I have 2 X 3bar pumps on the domestic water system to pump hot and cold water through the house as we have very little head.
there is not much Space available for the new cylinder. only about 60 to 70cm dia by max 180cm high so only suitable for between 350 and 450 ltr tank, would like to avoid a buffer tank.
I am of a mind to get a 350-450ltr gravity fed cylinder with solar coil and 2 other coils for oil and wood stove and draw the Hot water off and run the heating off the system as we currently do,thus avoiding the heat exchangers for DHW and central heating
I am concerned that the DHW heat exchangers would have trouble coping with 3bar feed pushing 45 to 70 Ltr of water per min depending on demand,( according to pump Manufacturer)
Can a thermal store be used with gravity fed ?
can the DJW coils cope with such a demand?
I am also unsure, given the relative small size of the tank that the extra cost of a thermal store would really be value for money, as with such a small store, we will still need to run wood or oil to be able to heat the house, given we are a household of 5 people, i am also assuming that in the summer months solar would be able to manage the requirement of hot water with a smaller cylinder using immersion as backup, .?
I appreciate your comments, suggestions.

I have also some questions about laddomat valves and zoning the system, but will wait till the tank issue is resolved but i am wondering is better to post those questions here, or in the central heating section ?
thanks

 

[Howsie]

Welcome to the forum.

IMHO this is not a project for a DIY'er, no matter how experienced. I suggest contact a suitably qualified plumber to talk though your options and you have a huge number of variables in this equation, all of which require a calculator and good working knowledge.

 

[johnnymc]

Hi Howsie, thanks for the welcome.
to an extent i agree, A little knowledge can be a dangerous thing, but i will install my own system.
I have already renovated my house, built my extension and installed my stanley stove, all a huge learning curve not without difficulty, but i am no Newbie!
I will engage a professional chimney engineer to line my flue modify my hearth and physically install the unit to the chimney so as it will be safe, but i will do the plumbing and wiring of the controls, everything will be open vented and have pressure valves, hence the question about tanks.
I understand enough to make something that works, I want to understand better to be able to finesse the system to be as efficient as possible for my situation, and hope to gain good advise from the experienced members on this forum,
I have read many of the posts held here, its a great resource, I hope to get some good suggestions and opinions as i proceed with planning my project.

 

[Howsie]

Anybody can make it work, but not many people make it work properly or legally. I've been to loads of self installed UFH and solar systems, they work but are not installed right or safely. They don't save the customer money because they are not sized correctly. Yada, yada, yada. We've have two solar thermal installs to repair this week because they weren't done properly by people who were not qualified to install them.

Good luck with your project.

 

[johnnymc]

thanks for you candor,
i look forward to other advise from the group

 

[Howsie]

My pleasure. I'm sure others will be along shortly.

 

[Ermintrude]

Not sure what info u have but sizing seems a tad cockeyed! Get a pro in, he can design it and specify correctly. 45 to 75 lpm? What??? U running 4" ??
I wouldn't think that a domestic cylinder would deliver that! To lift 45lpm @ 35c rise is some thing like 100kw. For ur thermal store to sustain anything more than a few seconds ur going to need 1000s of litres.

 

[Gray0689]

Hi Howsie, thanks for the welcome.
to an extent i agree, A little knowledge can be a dangerous thing, but i will install my own system.
I have already renovated my house, built my extension and installed my stanley stove, all a huge learning curve not without difficulty, but i am no Newbie!
I will engage a professional chimney engineer to line my flue modify my hearth and physically install the unit to the chimney so as it will be safe, but i will do the plumbing and wiring of the controls, everything will be open vented and have pressure valves, hence the question about tanks.
I understand enough to make something that works, I want to understand better to be able to finesse the system to be as efficient as possible for my situation, and hope to gain good advise from the experienced members on this forum,
I have read many of the posts held here, its a great resource, I hope to get some good suggestions and opinions as i proceed with planning my project.

Welcome mate
And I totally agree with howsie
You shouldn't be doing it yourself if you need to ask them question

 

[lame plumber]

I tend to side with Howsie on this one.

 

[Howsie]

You need one of these

 

[Worcester]

Guys, I think Johhny M needs a proper reply, not just 'go speak to the professionals' - reason - 90% of the plumbers aren't qualified to answer his question. So independent discussion here about the merits of sizing his thermal store vs and Indirect cylinder is a valid point.

We are highly active in the renewables area and regularly install thermal stores and we know that actually his question is the most important and also the most difficult one of all to answer - too many 'rules' of thumb are applied by most people - net effect they systems don't work together.

Bottom line: he has 4 potential heat sources (oil, solid, sun and leccy) and two uses heating and DHW.

Because of the uncontrollable nature of the solid fuel heat source, we would recommend a thermal store, and maybe even a heat dump if necessary, that way when he wants the heat at a time it isn't generated he's got it (after all that's what a store is for..)

Note: You don't need an unvented certificate to install an unvented thermal store..

3 bar sounds a bit excessive for your water as I believe the regs only allow you to boost to 12 Litres per minute... so lets not go there

Your oil boiler and back boiler could then both be direct to the thermal store (as we do with biomass boilers), the solar would be indirect and the DHW indirect via either an internal coil or (easier) an external plate heat exchanger, the central heating would also be direct of the thermal store. - Alternatively if you wish to seperate the systems any one of those heat inputs / outputs could be done through a coil or heat exchanger.

A thermal store will not be cheap - you might want to have a look at this one - it is specifically designed for multi fuel systems as well as maximising the solar benefit :
Chelmer Heating - Ecocat Thermal Store Cylinder - How it Works or google search Chelmer Heating ecocat thermal store

Tell Brent I told you to call him

Any one else care to contribute or correct my advise

 

[dancinplumba]

Nothing wrong with 3 bar, and its only pumping direct off mains that is limited to 12lts/min, without suppliers permission

 

[Ermintrude]

800l SLME ACV store? Only manage 800l in ten mins at a 45c rise?

Works on various heat inputs. If really greedy fit two in parallel with relevant controls?

 

[Howsie]

Jonny M wants to undertake something that is clearly beyond him and I'm not about to help him make more of a bodge of it.

 

[Gray0689]

Guys, I think Johhny M needs a proper reply, not just 'go speak to the professionals' - reason - 90% of the plumbers aren't qualified to answer his question. So independent discussion here about the merits of sizing his thermal store vs and Indirect cylinder is a valid point.

We are highly active in the renewables area and regularly install thermal stores and we know that actually his question is the most important and also the most difficult one of all to answer - too many 'rules' of thumb are applied by most people - net effect they systems don't work together.

Bottom line: he has 4 potential heat sources (oil, solid, sun and leccy) and two uses heating and DHW.

Because of the uncontrollable nature of the solid fuel heat source, we would recommend a thermal store, and maybe even a heat dump if necessary, that way when he wants the heat at a time it isn't generated he's got it (after all that's what a store is for..)

Note: You don't need an unvented certificate to install an unvented thermal store..

3 bar sounds a bit excessive for your water as I believe the regs only allow you to boost to 12 Litres per minute... so lets not go there

Your oil boiler and back boiler could then both be direct to the thermal store (as we do with biomass boilers), the solar would be indirect and the DHW indirect via either an internal coil or (easier) an external plate heat exchanger, the central heating would also be direct of the thermal store. - Alternatively if you wish to seperate the systems any one of those heat inputs / outputs could be done through a coil or heat exchanger.

A thermal store will not be cheap - you might want to have a look at this one - it is specifically designed for multi fuel systems as well as maximising the solar benefit :
Chelmer Heating - Ecocat Thermal Store Cylinder - How it Works or google search Chelmer Heating ecocat thermal store

Tell Brent I told you to call him

Any one else care to contribute or correct my advise

There is no maybe there will have to be a heat dump no matter what
Thermal stores are ok but if you got 5 people with a high hot water demand
It can be a bit tricky when you want everything going at once ie heating on and ho****er being used at once you can quickly starve the ho****er demand with heating on from what you have said I'd personally be thinking you would be better with a buffer tank

And ps Worcester a thermal store is not unvented
mains pressure hot water and vented on store