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

 

[johnnymc]

Hi Worcester. Thanks for the post, Fair comment, which is one of the reasons i prefer to plumb it myself, there are a number of different ways to approach the system, all of which would work, there is no hard and fast rule, Any plumber i might choose would be a lucky dip, and would have his own way to do things,
In the heel of the hunt, I haven't started yet so i will always have the option to contract a plumber if i believe i am so far out of my depth,
I would prefer a consultant rather than a plumber, but everybody wants to install their own systems, I have been looking for a " heating system designer" on the net, but no body posts this up as an optional service.
I was planning to put a heat dump radiator off the stove in my kitchen, as its fairly easy to get to with the larger pipe size it will require.
the Ecocat looks interesting, I was moving towards a unit like the Gledhill Torrent green heat, although ive seen some comments to stay away from this unit on the forum,
My stanley Oil stove is also a cooker and we run it to heat the kitchen, like an Aga. but im thinking with a heat sink from the wood stove in the kitchen, it might be an expensive way to cook during the winter,
Im hunting around here in ireland to try and find something similar to avoid having to ship from the UK. The stove supplier is in the UK so will ship that for sure. the strange thing is that often i can find things and ship from the UK for less than i can buy them here!! only time will tell.
I appreciate your support.

 

[Worcester]

@Howsie, I understand where you are coming from, his request though was simple and it deserves and answer, even though he is not a professional.

From the contributions so far, I almost concur with what you said earlier "Anybody can make it work, but not many people make it work properly or legally."

The actual answer from our experience of installing and fixing systems, I would actually also challenge that "Anybody can make it work" - they can't.

Thermal stores are a complex area and 98% of people working in the heating sector don't know how to size them, design them to work with multiple heat sources or how to install them properly. - Buying one off the shelf from your local plumbase / plumbcentre isn't the correct solution in 99% of multi-fuel renewable energy environments.

You should have heard the 'interesting' discussions we've had with the design engineers at the likes of Gledhill and Worcester about the assumptions they've had to make about the average (non MCS) installers design and installation capabilities.

By giving johnnymc unfettered honest advice he can then at least ask a professional what they would recommend, and see if their reasoning ties up with the advice from here, elsewise he's just going to get a load of bulls**t from a bunch of people that talk good and don't know what they are talking about.

Remember the 'Pay it forward' philosophy - this is a place for advice rather than just saying "you ain't a pro so I'm not going to tell you" educate him properly with free advice and then if he still chooses to do it himself, he's only got himself to blame. - Otherwise he'll do it anyway and get it all wrong....

 

[Worcester]

p.s. you can get unvented thermal stores .......

 

[Gray0689]

p.s. you can get unvented thermal stores .......

Can you give me a link to one as I've never seen one
How can it be legal in uk to have it unvented

 

[Gray0689]

Hi Worcester. Thanks for the post, Fair comment, which is one of the reasons i prefer to plumb it myself, there are a number of different ways to approach the system, all of which would work, there is no hard and fast rule, Any plumber i might choose would be a lucky dip, and would have his own way to do things,
In the heel of the hunt, I haven't started yet so i will always have the option to contract a plumber if i believe i am so far out of my depth,
I would prefer a consultant rather than a plumber, but everybody wants to install their own systems, I have been looking for a " heating system designer" on the net, but no body posts this up as an optional service.
I was planning to put a heat dump radiator off the stove in my kitchen, as its fairly easy to get to with the larger pipe size it will require.
the Ecocat looks interesting, I was moving towards a unit like the Gledhill Torrent green heat, although ive seen some comments to stay away from this unit on the forum,
My stanley Oil stove is also a cooker and we run it to heat the kitchen, like an Aga. but im thinking with a heat sink from the wood stove in the kitchen, it might be an expensive way to cook during the winter,
Im hunting around here in ireland to try and find something similar to avoid having to ship from the UK. The stove supplier is in the UK so will ship that for sure. the strange thing is that often i can find things and ship from the UK for less than i can buy them here!! only time will tell.
I appreciate your support.

If your fro Ireland try copper industries there from toome
They do maxipods thermal stores
And boru stoves are Irish and very good

 

[johnnymc]

Hi Dancinplumba,
Im not pumping off mains, i have a gravity system, with low head and long runs to taps,
I am running two 3 bar pumps, one hot, one cold, Im about to put in a blending valve to the hot to reduce the amount of hot water draw off, and scalding issues.
the pumps are 3bar at 1 inch, im feeding them in and out with 3/4 so the flow is reduced somewhat, but the pressure is very good in the shower. Ive put restrictor valves on the sink feed to reduce splashing!!

 

[Gray0689]

Hi Dancinplumba,
Im not pumping off mains, i have a gravity system, with low head and long runs to taps,
I am running two 3 bar pumps, one hot, one cold, Im about to put in a blending valve to the hot to reduce the amount of hot water draw off, and scalding issues.
the pumps are 3bar at 1 inch, im feeding them in and out with 3/4 so the flow is reduced somewhat, but the pressure is very good in the shower. Ive put restrictor valves on the sink feed to reduce splashing!!

Why 2 pumps a single hole house pump would of done

 

[johnnymc]

Hi Gray0689, Ive seen many vented stores,
My understanding is that they have to be for wood stoves etc unless you use indirect coils form a vented system,
I cant post links for some strange reason, but here are a couple ive been looking at
Heat bank at heat web.com, The Gledhill torrent mentioned before are vented.
Ive been looking at the Copper industries Solar pod, with three coils.
Boru stoves are good, but the only stove ive found inset with 24kw to water 10kw to room is the Aquatherm, and have only found it in the UK at Stoves online. Looks like a pretty good stove, and have seen a couple of pretty good reviews.

 

[Gray0689]

Hi Gray0689, Ive seen many vented stores,
My understanding is that they have to be for wood stoves etc unless you use indirect coils form a vented system,
I cant post links for some strange reason, but here are a couple ive been looking at
Heat bank at heat web.com, The Gledhill torrent mentioned before are vented.
Ive been looking at the Copper industries Solar pod, with three coils.
Boru stoves are good, but the only stove ive found inset with 24kw to water 10kw to room is the Aquatherm, and have only found it in the UK at Stoves online. Looks like a pretty good stove, and have seen a couple of pretty good reviews.

I've never seen an unvented thermal store
They HAVE to be vented imho

 

[johnnymc]

I was advised that a dual pump had a higher fail rate because of the dual impeller.
I have a fit for purpose hot water pump, and a standard cold water pump to me it made sense, a bit pricey for sure,
I couldnt pump into my copper cylinder for obvious reasons so it was either single pump two impeller or two pumps.
they are good quality pumps ans so far very reliable. ( 6months)

 

[SimonG]

An unvented thermal store, never seen one, never heard of one and can't see the need for one.

 

[Gray0689]

I was advised that a dual pump had a higher fail rate because of the dual impeller.
I have a fit for purpose hot water pump, and a standard cold water pump to me it made sense, a bit pricey for sure,
I couldnt pump into my copper cylinder for obvious reasons so it was either single pump two impeller or two pumps.
they are good quality pumps ans so far very reliable. ( 6months)

Good Stuart turner would of been better option IMO
But if it works for you then it's not wrong

 

[johnnymc]

sorry, just realised you were talking about unvented,
I have found them more prevelant than vented

 

[Gray0689]

An unvented thermal store, never seen one, never heard of one and can't see the need for one.

Lol glad someone agrees with me lol

 

[SimonG]

To me it's either unvented or it's a thermal store. Just can't see what you would get combining the two.

 

[Worcester]

Standard practice in the renewables sector to use unvented stores with multiple heat sources.

:: AKVA SOLAR - see about 3/4 of the way down using solar and biomass.

99.9% of the thermal stores we install are unvented, and the G3 regs don't apply to thermal stores....

PROPERLY designed with correctly sized thermal stores and properly sized heat supplies (back up boiler if primary heat source is a back boiler wood burning stove..) you'll never have the fight over heating or hot water, thanks to stratification, baffling, flow and return positioning and the correct use of direct and indirect approaches, sometimes with external plate heat exchangers. That way you never have a shortage of hot water or heat. It's also why we never (and you shouldn't) simply walk in to pb or pc and buy an x00 litre thermal store.

You don't need hot water tank at all this way..

 

[Gray0689]

Standard practice in the renewables sector to use unvented stores with multiple heat sources.

:: AKVA SOLAR - see about 3/4 of the way down using solar and biomass.

99.9% of the thermal stores we install are unvented, and the G3 regs don't apply to thermal stores....

PROPERLY designed with correctly sized thermal stores and properly sized heat supplies (back up boiler if primary heat source is a back boiler wood burning stove..) you'll never have the fight over heating or hot water, thanks to stratification, baffling, flow and return positioning and the correct use of direct and indirect approaches, sometimes with external plate heat exchangers. That way you never have a shortage of hot water or heat. It's also why we never (and you shouldn't) simply walk in to pb or pc and buy an x00 litre thermal store.

You don't need hot water tank at all this way..

How does a unvented thermal store pass building regs?

 

[Gray0689]

How does a unvented thermal store pass building regs?

Thanks for link Worcester I'll have a look

 

[Howsie]

Hi Worcester. Thanks for the post, Fair comment, which is one of the reasons i prefer to plumb it myself, there are a number of different ways to approach the system, all of which would work, there is no hard and fast rule, Any plumber i might choose would be a lucky dip, and would have his own way to do things,
In the heel of the hunt, I haven't started yet so i will always have the option to contract a plumber if i believe i am so far out of my depth,
I would prefer a consultant rather than a plumber, but everybody wants to install their own systems, I have been looking for a " heating system designer" on the net, but no body posts this up as an optional service.
I was planning to put a heat dump radiator off the stove in my kitchen, as its fairly easy to get to with the larger pipe size it will require.
the Ecocat looks interesting, I was moving towards a unit like the Gledhill Torrent green heat, although ive seen some comments to stay away from this unit on the forum,
My stanley Oil stove is also a cooker and we run it to heat the kitchen, like an Aga. but im thinking with a heat sink from the wood stove in the kitchen, it might be an expensive way to cook during the winter,
Im hunting around here in ireland to try and find something similar to avoid having to ship from the UK. The stove supplier is in the UK so will ship that for sure. the strange thing is that often i can find things and ship from the UK for less than i can buy them here!! only time will tell.
I appreciate your support.

What's the difference between a consultant and a plumber? I know the answer but I don't think you do.

 

[Ermintrude]

Advised him to hire a designer! M&E consultants are everywhere. Probably charge 5k. Including commissioning.

Designers design , fitters fit. Have a go Henry's .....

Points are valid but think bloke is over spec and under engineered.

Seems like wants to wash and bathe whole of Ireland in one go and heat the water from two candles and a energy from a wind toy.

Don't think a thermal dump is going to be required, as soon as demand is satisfied switch over the the steam turbines and let the 6mW rip.

http://www.carbontrust.com/media/129472/ctc810-insights-into-biomass-heat-installations.pdf