Posted By: PASBThank you, Bowman, for distilling the arguments: I think you've come closest to answering my biggest question, namely that there DOES seem to be a good case for 'going heat-store' if you've got the space (which I have) for higher tank volumes.

DPS made the GXV, which went under a kitchen top. The idea was to combine the energy of the boiler and cylinder. Works a treat. People here have the impression that stores have to be huge to be cost effective or only suitable for multiple heat sources. That is clearly wrong.

The Worcester-Bosch Highflow 440 and 550 have integral heat banks and perform brilliantly in a boiler/heat bank combi package the size of a standard washing machine for under worktop use. They can be packaged very tightly. And no G3.

Where are the billy goats Gruff when you need them?

Heat loss from a large store will be less than from a small store for equal joules of energy stored all other things being equal.

I don't think anyone is suggesting that stores have to be "huge", and I can't see anyone suggesting that they are only suitable for multiple sources. I do think that extremely polarized opinions tend to only be valid in a very few circustances, especially when supported by irrelevent information and meaningless phrases.

Q. My only heat source is a wood boiler kicking out 12.5kW, I have a steady heating load of 3kW, and I'd like to keep 5kWh for DHW, how big a store and at what tempreture do I need if I only want to run one batch of wood in the morning and one in the evening, assuming zero losses?

"particularly important" != required

Posted by Water Systems 7 hours ago

"You made that up. Selectrive amnesia again. Re-read the thread."

Final evidence that Water Systems is a well known troll on the UK DIY newsgroup. He goes by various names, John Burns Curtis, IMM (DIMM), Doctor Drivel, etc.

He claims to be a heating engineer, but has never produced any evidence when asked. His favourite hobby horse used to be combi boilers as the answer to all heating problems. Every now and again he pops up on other groups, like this one and participates in threads like this, generating lots of heat but very little light.

The quote above is absolutely typical of his style; when he calls someone a plant pot the proof will be absolute.

PASB, Bowman, Jerseyman...and Yeoman of olde England, hear ye... :))

OK, ok, it's Sunday evening and the Six Nations is on, and England won (Pyrrhic victory anyone?) so I'm happy-ish...

Interesting debate - but also a re-hash - 3rd time and counting - of Tom's attempts to justify his (uncertified?...his silence on this subject is deafening) notifiable and certifiable (!) installation of WB-Unvented, so we aren't covering much new ground here as far as merits go, especially as the two technologies aren't directly comparable - see posts above - so this was always going to be a specious debate started by a man with no leg to stand on.

First things first:

ralphd - you come across as reasoned, but even if you ARE an approved UDHW installer, please be cautious in telling people they don't need to get their unvented cylinder serviced annually - aka your bull comment - as most mfrs recommend this. I quote from the BS-approved UDHW systems training manual, under the heading of maintenance, p40:

"...the installer is responsible for the safe INSTALLATION of the unit. He/she must also make his customer aware that periodic checks of the equipment are ESSENTIAL FOR SAFETY... some manufacturers recommend a MAXIMUM of 12 months. Experience of local water conditions may indicate that MORE FREQUENT inspection is desirable." ( caps mine)

Water systems, your absence from the diplomatic Corps will not be mourned. Heh heh! :) Yet you talk a dialect of sense in common trade language readily recognisable by fellow professionals.

I understand your irritation, but don't expect your obvious experience in this field to be recognised by all present. I'm still a newbie here, but recognised quickly that leading a horse to water on these forums is not going to make him drink. There are definite agendas present rather than a search for 'truth' per se - an example is Tom's justification-of-purchase - which it appears no amount of logic or experience will shift. Selective blindness seems to be an 'in' thing to some here. Unfortunately, that confuses other genuine people who are looking for answers, which is the only reason I persist in posting. Under the present format I don't expect to convince many - it's like trying to find truth in Westminster...

Also it is clear that the trade, due to their own career-path and hence experience, are divided, so what chance does the layman have? I admit to being a Thermal Store fan, having fitted my first Swedish models in 1983. I am also an unvented installer and have been for several years...because there are times when it fits the bill...or Ben.

And I don't know in a multiple-post, multi-skill-level forum like this IF one can ever put forward a cogent argument as some bod or other who has the internet and can do quasi-research then believes he has the knowledge to tackle someone who has walked the walk for half a working life. And they will attempt to win the argument rather than find the best solution.

But I'll try: In a snapshot. Two definitions:

UNVENTED: A useful way to have high-pressure HOT WATER when heated by a 'controlled' appliance - ie immersion with manual re-set overheat stat, oil or gas boiler or heat-pump. Building control, along with HETAS, the official WB/SF body, do not recommend direct gravity connection to a WB/SF stove. In this they are backed up by most UK stove mfrs plus at least two major unvented mfrs - OSO and Range (the ones I spoke to in order to be sure of my facts in another, previous thread). Their reticence should give most competent thinkers/DIYers pause for thought and a big 'WHY don't they??'

Advantages are ease of siting and high performance. Disadvantages are service costs, limitations of application inherently higher risk and more damage if things do go pear-shaped, the way all the best disasters tend to occur.

THERMAL STORE: A way of storing HOT WATER and/or HEATING (this alone makes any direct comparison void), or HOT WATER alone, or HEATING alone.

Advantages: Allows storage of heat for these purposes, from uncontrolled appliances or controlled appliances. Can work on gravity/combined gravity/pump if so designed. Can be connected to virtually any appliance known to the ingenuity of man, and if designed with a little forethought, can be connected to any future appliance too (Stirling engine anyone....?) so your investment is 'future-proofed' in that you can plug n play with other technologies.

Disadvantages: If combined for heating/DHW, or DHW alone the need to keep the store at a persistently high temperature - not very 'eco' and reliant on an automatic (read oil or gas) input.

My personal preference is a smaller DHW cylinder at high temps, coupled to a larger TS which allows decay and therefore useful heat input to the building even at lower temps - think underfloor at 35-40 C - something we are going to see more of as the 'automatic' fuels dwindle.

Economy vs comfort...it's a whole new debate.

Regards

Crusoe

ralphd

It's wrong? Really? I didn't know that or I should never have quoted it. No, no, I just double checked with the manual , and it's current, and it really does say that, as do the manufacturers quoted above whom I checked with. Maybe if as a software developer you feel strongly that it's wrong you should take it up with them.

Please state your source for stating they are wrong - this is clearly not your own opinion as a software developer, right?

The US - Buffalo area at least, where I have in-laws, vented tanks with WB installations are used - though I can't say how commonly.

As far as safety goes - European tanks are recognised as having more protection than US tanks, but it sort-of speaks for itself that if one has to have special training to install these tanks - and I do - then risk is deemed by those in the know - mfrs and approval bodies - not to mention experienced installers - as greater than vented.

There are regular, if infrequent (to date) cases of UDHW tank explosions from the US. The latest was a 2008 incident in Phoenix, detailed on ABC15.com/news 'The water heater ended up on a sidewalk about two blocks away, across from a school... Fire spokesperson Victor Rangel said homeowners need to keep up with the maintenance of water heaters'.

Most trained or trainee plumbers have seen pictures of the devastation caused by this kind of event...often the side of a house taken out...but you think maintenance unnecessary?

Regards

Crusoe

Posted By: crusoeinstallation of WB-Unvented, so we aren't covering much new ground here as far as merits go, especially as the two technologies aren't directly comparable - see posts above - so this was always going to be a specious debate started by a man with no leg to stand on.

It is amazing how many think they are comparable. I can understand an amateur thinking that but "plumbers" do as well.

Water systems, your absence from the diplomatic Corps will not be mourned. Heh heh! :) Yet you talk a dialect of sense in common trade language readily recognisable by fellow professionals.

In the circumstances I consider myself highly diplomatic. Yes. those who understand thermal system would connect. Getting people to understand CH buffering and the importance of no cycling is difficult.

I understand your irritation, but don't expect your obvious experience in this field to be recognised by all present.

I found that out.

Unfortunately, that confuses other genuine people who are looking for answers, which is the only reason I persist in posting.

The same here. The old wives tales have to be dispelled.

Also it is clear that the trade, due to their own career-path and hence experience, are divided, so what chance does the layman have? I admit to being a Thermal Store fan, having fitted my first Swedish models in 1983. I am also an unvented installer and have been for several years...because there are times when it fits the bill...or Ben.

The trade only fit what they are familiar with, not the best solution or best cost effective solution. I have seen flats with large unvented cylinders and system boilers, making the airing cupboard (or what is left of it) look like a school boiler house. A simple high flow combi was clearly the answer, but old wives tales take over. Many tell me they know what they are doing as they have been doing it for 20 years. It is 1 years experience repeated 20 times, learning nothing new.

And I don't know in a multiple-post, multi-skill-level forum like this IF one can ever put forward a cogent argument as some bod or other who has the internet and can do quasi-research then believes he has the knowledge to tackle someone who has walked the walk for half a working life. And they will attempt to win the argument rather than find the best solution.

Yes, this Nigel (Ivan is it?) is like that. The counter arguments are so ridiculous. Anyone with brains would welcome experienced and knowledgeable people and use them. But many know-it-alls know all the answers.

Advantages are ease of siting and high performance. Disadvantages are service costs, limitations of application inherently higher risk and more damage if things do go pear-shaped, the way all the best disasters tend to occur.

Advantages are ease of siting and high performance. That is not an unvented advantage over a DHW only heat bank (the equivalent), as they both gives this.

I honestly cannot think of where an unvented cylinder has an advantage over a heat bank, and where one would be more beneficial. Please tell me of a situation where that would be the case - I can't think of one?

I thought an unvented would be good as a solar preheat to a combi. However Alpha do the AlphaSmart, which is a thermal store combi preheat and flow enhancer, which works wonderfully and gives high flows and never runs out of DHW and gives electric backup too.

THERMAL STORE: A way of storing HOT WATER and/or HEATING (this alone makes any direct comparison void), or HOT WATER alone, or HEATING alone.

Disadvantages: If combined for heating/DHW, or DHW alone the need to keep the store at a persistently high temperature - not very 'eco' and reliant on an automatic (read oil or gas) input.

This disadvantage is not relevant to a heat bank using a plate heat X. They can operate at 5C below tap temperature the plates are so efficient, as many on this thread have testified. 5C is neither here nor there in a highly insulated cylinder. A storage cylinder (unvented or not) needs water stored at 65C to eliminate legionella, then blended down to 50-55C at the taps. Many heat banks can operate at 65C.

A well designed heat bank can heat just the upper DHW section in summer. When CH is off the bottom CH section does not get heated.

My personal preference is a smaller DHW cylinder at high temps, coupled to a larger TS which allows decay and therefore useful heat input to the building even at lower temps - think underfloor at 35-40 C - something we are going to see more of as the 'automatic' fuels dwindle.

Or eliminate the cylinder and have the TS pre-heat the combi inlet, as does the AlphaSmart. Then a cylinder is eliminated.

A well designed TS can have the upper section high grade heat, heated by controlled fossil fuel (elec, gas, oil) . An appropriate baffle is all that is needed, then no extra cylinder. As Andy noted, he took his heat bank up to ceiling height as all the space up there is usually wasted. Elson design square TS's to fit high up in cupboards. Square or rectangular stores are the way forwards, as they save so much space.

Economy vs comfort...it's a whole new debate.

Usually if comfort is aimed at, and successfully implemented, the economy follows.

One question whilst we're on stores which I've never found the answer to...

Say you have a low grade heat input - say winter solar or heat pump feeding in water at 35 degrees to the bottom of the tank, will the top of the store get up to 60 odd degrees or are you limited to what your flow temperature of the source is giving you?

My guess would be you're no limited it will get hotter at the top, but it depends on the height of the tank, as once the bottom hits the example 35 degrees, you wont be able to add any more from your low grade source.

I better explain what I mean a bit better.

From a cold start - the bottom of the tank will be at cold water supply temp - say 10 degrees. So the heatpump/solar supplying 35 degree water can provide a 25 degree uplift. Now that heat will stratify - but how fast and will the bottom of the tank remain at say 20 degrees for a fair while allowing the 35 degree source to still provide a 15 degree uplift. Over time an even with stratification effects the bottom of the tank will reach 35 degrees, and therefore not take anymore heat. At this point will the top of the tank be 35 degrees? I suspect not, but will it be 40, 50, 60, 70 or 80 degrees?

Just to keep in on topic - will this effect be any better with unvented vs a heat store. I'd have thought heatstore are designed to work like this and have noted several have baffles to try and prevent "stirring", where as an unvented cylinder is designed to store hot water.

PS is there a good book on explaining hydro-thermodynamics and sizing heat stores?

If you start with a tank of water at a uniform temperature of say 35C and allow it to stand/settle/stratify the top will never get hotter than 35C but the bottom might get colder.

Hot water tank explosions are rare, but they do occur:
http://www.masterplumbers.com/plumbnews/2001/dec/avon.asp
http://seattlepi.nwsource.com/local/33094_boom28.shtml
http://www2.canada.com/edmonton/edmontonjournal/news/story.html?id=02acabcc-e7c4-43e4-8fe0-5c298527e2d5

Paul in Montreal

Posted By: ralphd
Thanks for the reference.
Now I will agree that is something that can and has happened.

The next question is whether or not it is relevant; i.e. are they so rare that it is nothing to be concerned about?

-Ralph

One is enough. Do you want to see bodies before you believe it?

Posted By: Water Systems

Posted By: ralphd
Thanks for the reference.
Now I will agree that is something that can and has happened.

The next question is whether or not it is relevant; i.e. are they so rare that it is nothing to be concerned about?

-Ralph

One is enough. Do you want to see bodies before you believe it?

Your question includes a false statement. I said I do believe it can happen (actually belief has little to do with it, I am convinced based on credible and quantitative evidence).

One is not enough. For example meteorites have crashed through roofs and injured people.
neo.jpl.nasa.gov/news/news139.html
www.spacedaily.com/news/meteor-04c.html
en.wikinews.org/wiki/Meteorite_falls_through_roof_of_house_in_New_Jersey

If you really believe that one is enough (rather than just being argumentative) you will support standards to build more meteor-resistant roofs.

-Ralph

Posted By: Paul in Montreal

Posted By: Water SystemsOne is enough. Do you want to see bodies before you believe it?

Nothing we do in society has a zero risk. Might as well ban gas heating since there's always at least one house per year that explodes due to a leak. Note that at least one of the tank explosions was because the safety valve had been circumvented somehow. Also don't forget that many people in the UK get scalded every year because of having hot water stored at 60C due to an irrational fear of legionella - which would be pretty much eliminated with mains-pressure hot water tanks. But that's a whole other argument.

Paul in Montreal.

Potable water stored in a cylinder, vented or unvented, carries the same legionella risk.

A risk where you have little alternative and has to minimised and lived with - we have no alternative to gas, oil and elec'. But these are far less risk to say to open coals fires, which had many people burnt to death by clothes catching fire (an aunt of mine, way, way before I was born, was killed as a child when her dress caught fire - quite common at the time). There is an economic alternative to the risks of an unvented cylinder, as with an open coal fire - a vented heat bank. That is whole point - there is no need for unvented cylinders.

Having water stored at over 60C (good thing) and coming out of the taps at that temp is foolish. A blending valve should be used to drop the tap temperatures.

Two wrongs do not make a right. Where the risk can be eliminated completely you eliminate it.