Hot water

John Rumm wibbled on Tuesday 13 October 2009 05:20

Hi John

I got mine from Newark Copper

Came to 612 + VAT + 30 delivery though copper prices are volatile. I had 3 immersion bosses and loads of sensor pockets and tappings.

Mine is directly heated - I presume by "fast recovery" you want a coil?

They offer a choice of foam insulation depths too.

They were certainly very helpful to me and rang up to query when something looked like it wasn't going to work physically.

I had most dealings with Tom Sharpe.

Cheers

Tim

half a dozen tabs left in firefox with copper cylinder makers loaded up ready to read - that was the next one on the list ;-)

That sounds like it would be getting on for 300L - or is that the size including the foam etc? Oh, and I suppose you lose a bit for the solar coil.

OK ta.

Have you costed and selected sources for those bits yet? (ok, scratch that - I just looked at the spreadsheet you sent me!)

What connections are on that mixing valve BTW? They look threaded from the piccie...

Yup, I am going to use a sealed system primary (I want the space back occupied by the header tanks, plus there is not really enough head to make a vented system work well (that and I don't like vented systems at the best of times!).

That leaves the option of a coil, another PHE and pump, or a tank in tank type of arrangement. PHE is nice in that it gives rapid recovery, top down heating, and good condensing efficiency, but at the expense of another (albeit small) PHE and pump. However since its not going to be easy to arrange "on demand" heating of the store, the full boiler capacity recovery is less essential. A coile would probably be ok if its big enough to keep inside the boilers modulation range for most of the reheat.

How much did you go for? (I want some leakage to keep the airing cupboard warm)

Ta for that...

John Rumm wibbled on Tuesday 13 October 2009 17:56

I think it's nearer 250l - the dimensions are the size of the copper (no foam) but of course include the domed top and bottom, so you do lose out there. There are other standard sizes of cylinder - look at their solar page so you can probably select exactly what you want. The solar coil is

I went to visit DPS too. There stuff was nice, but they were fairly expensive as you found. And I decided I wanted more custom options on mine. I have:

Top, under dome + just above solar coil - boiler connections in direct 22mm compression (that's an option now, no need for 3/4" bosses).

About 1/3 and 2/3 height, 2 sets of 22mm - one for rads and one for UFH.

Solar coil is placed about 0 and 1/4 height.

Absolute top and bottom - expansion and feed/drain, dualling as DHW circuit.

6 dry sensor wells evenly spaced from top to bottom which one day I hope to shove some Dallas 1-wire temp sensors in and make the controller more intelligent - I can measure the stratification.

Doing the drawing was a bastard. Sketchup was just too painful with cylinders. So I went old-skool and used 2D CAD and contruction lines to draw top down and 4 side projections by hand. You could just as well do it on paper - Newark re-CAD it anyway.

I think Newark could make you the coil the way you want.

Ditto - so I went for 50mm. The can do 25mm or more than 50mm (though they say they hate doing really thick ones).

Cheers

The plus £600 for the Newark seen good value as the total price will be more than £1,500.

Take the hot for the shower direct from the plate "before" the blending valve. The mixer has its own temp control, so no need to run through another valve reducing flow/pressure.

Price up a SS cylinder from Advanced Appliances - custom made - before you go any further. They make them for Nu-Heat. No coil inside so cheaper. Then have a pressurised heat bank cylinder (no G3 required for a heat bank) and heat it directly with an Avantaplus system boiler. Have a Pressure discharge valve on the cylinder and leave the PDV on the boiler connected as well. Sp two ways out. Could have a high limit stat, set to 95C, as well. Simple and cheap and another level of protection.

In the return to the heat bank from the rads fit a Spirotech Magnaboost filter. It takes all solids and magnetite and a doddle to clean out - a DIY job with a bucket, just turning a tap.

I posted this for you on another thread.

One trick I did pick up from talking to them which I thought was quite cute was how they do their vent. They actually put an expansion vessel on it, but discharge the air side of it (I presume wither by removing the schrader valve or drilling the case). This means the store remains at atmospheric pressure, but you have an effective vapour barrier enclosing it. (probably looks better than sticking a rubber glove on the vent ;-)

A high as pos on the flat side. or right on top of the dome?

IIUC with the boiler I am considering it used a temperature sensor rather than a stat - so pockets for that would be handy. As you say, a few others to instrument the thing would be nice...

Wandering off at a side track, do you know of any good value data acquisition boards with to discrete and analogue inputs, and can run TCP/IP over ethernet?

Yup, I will draw it up a see what gives...

I am tempted to go that way as well - the price difference was not huge, and I can see a time that it will be running two showers at once plus incidental usage.

I am going to leave mine running under the control of the weather compensated output from the boiler. Split into a couple of zone with prog stat control for each (plus TRVs obviously).

Something that can shift at least 12kW most of the time would be good. That's well in the modulation range of the boiler.

I have visions someone with a bucket of foam and a bad attitude! ;-)

Can't see it being that much...

Say 700 for cylinder

I make that about £1,170, (or a bit more with scale inhibition) which seems quite attractive compared to the DPS quote.

Partly why I was thinking of using a 28mm valve. Since I will ultimatly probably have three showers, that would be lots of extra pipework for not much gain.

Just had a look at their web site. A comparable size off the shelf one to Tim's looks like coming in about the £845 mark.

Do you know if they have any manuals for their weather compensating controls hidden away on their web site?

stands (lacking programmable temperature control for two independent rad zones, plus it runs the rads from the store which I don't have any particular need to do).

It may be cheaper with a plain cylinder (no coil) with some custom tappings to your spec. That is not a bad price for a SS.

It is in the users instructions, which are downloadable.

I explained that to you in the last thread. It can have programmable temperature control for two independent red zones quite easily.

If you are having a DHW only heat bank, you may as well extend the size a little to create a CH buffer and run the CH from it. It is foolish not to.

You don't seem to understand what is going on. A modern condensing boiler will modulate down to around 6kW. This may be too large an output and result in boiler cycling. You seem to think your house will always require more than 6kW of heat. Once up to temperature it will require little to keep it warm on average.

Heat the bottom of the store (3-way valve activated by the Avantaplus dual-temp boiler to heat top DHW section and CH bottom) by the boiler using the internal weather compensation controls - no stat on the cylinder, all done in the boiler. The two CH circuits can come off the CH section and TRVs all around using a Smart pump for each zone. No wall stats are needed. The Smart pumps can inject into a CH circuit just 0.25kW if need be. A boiler directly on the CH circuit cannot do that. Anything below 6kW demand will entail the boiler cycles. The boiler will not cycle (or so infrequently) when reheating a large body of water. The store also gives "instant" heat up in the morning with the rads hot in a few minutes.

Having the boiler only heat the heat bank, means it is in the ideal hydraulic environment - full flow through the boiler at all times.

You have two things in your head:

1. The CH circuit must be pressurised
2. The CH circuit must be heated directly from the boiler.

You should reconsider these.

a) The whole system can be vented and no loss in performance at all - no cylidner coils. b) A pressurised heat bank can give 100% pressurisation using no cylidner coils. c) Having the heat bank heated directly by the boiler means the DHW section can be made smaller. The dual-temp boiler throws all its heat at the heat bank combining its energy with the cylinders.

The drawing I gave has two CH circuits directly off the cylinder. This ensures that both are independent of each other and one zone does not rob the other - easy to balance. The Smart pumps eliminate walls stats and by-passes and two Smart pumps means it is cheaper by not buying two zone valves and walls stats and less hassle in installing the stats. But you want timed temp reduction in the house, which as I have explained in the other thread is a doddle to do for you, and you can still have TRVs all around doing the prime temperature control of rooms - independently. Smart pumps use less electricity and reduce noise in the system.

They remove the shrader valve. They fit an anti-vacuum valve and vent with anti-evaporation protection. This could be a gravity (non-spring) check valve fitted vertically. If the pressures gets substantially above atmospheric then the check valve opens and allows out pressure. It take a bit of pressure to lift the valve from its seating. The anti-vacuum valve then steps in to allow air in if a vacuum occurs when cooling off. If the check valve fails and pressure builds up because, say check valve fails, the loose diaphragm will break.

Perhaps - I will drop em a spec and see. Not sure how much advantage having SS s going to be in reality - the water here is not particularly aggressive, and scale obviously won't be a problem in this application.

I was looking for a bit more detail - like how it controls two rad zones, what how interfacing with 240V controls is done etc.

(having said that, I don't think that the Remeha is quite mainstream enough anyway).

About the only benefit I can really see in this case) is that I could at a pinch dump some heat into the rads from the immersion heater in the event of a boiler failure.

These days it seems that CH run from the store is a good plan if:

Any others you can think of?

With this house as it stands, that is debatable alas. Given time and extra insulation it may improve. However its a bit of a moot point.

Indeed it could - not disagreeing with you.

You seem to be stuck in the stone age where boiler cycling is a major cause of inefficiency. With a modern light weigh HE, low water content, and pump overrun its almost a non issue. Any "spare" heat in the boiler gets dumped into the house anyway, plus there is not much of it. Weather compensation improves the situation further by reducing any overshoot should the main stat cease demand. So then it really only comes down to the couple of seconds of waste gas released at burner start.

So? As long as its warm enough when we are getting up, do we care how fast the rads heated up? In fact, ISTM that slower would be better since you will get less abrupt expansion noise from the rads and pipework.

The house design is much better suited to a sealed system. There is no loft as such and not really any usable ceiling void upstairs. There is only really one location one could have a F&E tank such that it would be above all the rads, and that is in the cupboard in our en suite where it currently is. Once I have had that and the main cistern away to create a shower, there will be nowhere ideal to put it. Even if I could find space for it, it would be at best about 12" above the top of the rads (its only 24" now). This means there is very little head which makes filling the system and clearing air locks etc a pain, and its very easy for the system as it stands to entrain air on startup.

All that is before we get onto the fact that I prefer sealed systems.

A charging coil will increase the reheat time a little (in fact it could double it compared to direct or PHE heating to about an hour from cold). However this will be done once early in the morning before the heating is on - so not really much to gain there. A second (smaller) PHE could fix that if it were a problem.

Sorry, you have lost me - combining energy with which cylinder? I am planning on one cylinder (i.e. the heat bank) and no other.

But you seem to forget that I *want* wall stats so that I can have different temperatures and times of operation over the course of the day.

Zone valves I already have two of, so would need one more. Stats I already have one of (not that it would be reused - but the wiring is there), and a second is not going to be difficult to arrange (I am getting to grips with the wiring routes through this house now!).

My zone valves use about 6W each. What does the pump use?

(not that the issue of waste heat from CH components is really that significant)

You could get a price on a presured version as well.

They have a doc with different setups to download.

What you think and how it is are two different things. As I have stated Remeha have bought out Baxi, so expect this boiler rebadged with a Baxi tag on it. The boiler has taken off like hot cakes and sells very well. It is highly specced and a dual-temp boiler and very reliable. I have already explained this to you.

You clearly do not understand CH buffering. Again I have already explianed the merits of it. No harmfull by-pass, boiler cycling elimianted etc. If you can't undetsand it there is not much I can do. It is best you take it that it just superior all around.

See above CH buffering.

It is not.

I am a pro not an amateur - please do not tell me how it works. In Gemany CH buffering it taking off big time. You have also got to take into account flow tnrough a small tubed spiral wound herat exchanger. TRVs will restrict flow and a by-pass is not always a good protector (which also reduces condening efficiency by sending hot water back to the return). A buffer will ensure that the return of the boiler will always be a low efficient temperature.

See above. sludge build up in modern heat exchanger connected directly to rads is now a major problem increasing inefficiencies as is gets baked on. The tubes become smaller and the baked on sludge acts as an insulator.

Expansion noise usually means poorly installed pipes. The instant heat is an added bonus and most people how have it love it.

Sealed or vented doesn't mean much. Consider a pressurised store.

That is new to me - a charging coil WILL NOT reheat the cylinder quicker. Heating a body of water direct is always quicker. Put an exchanger between and an inefficiency occurs. With the dual-temp boiler the DHW is at full belt (or what you set the boiler to) to reheat the cylinder. When it reverts to CH the weather compensator dictates the temperature of the lower CH section, which could be only 30-40C.

Yep one cylidner.

b) A pressurised heat bank can give 100% pressurisation using no cylinder coils. The boiler heat the cylinder directly the boiler and cylinder are pressurised to 1 bar cold. The cylinder is just another wide pipe in the system.

c) Having the heat bank heated directly by the boiler means the DHW section can be made smaller (that is self explanatory). The dual-temp boiler throws all its heat at the heat bank combining its energy with the cylinder's. (when reheating CH the boioer can be at full belt. Wheh the stiore is yup to temp, and DHW is being drawnn off in say the shower the bottom part will cool and the stat kicks in to call the boiler. The boioer dumps all its heat right at the top of the store where it is pumped out directly to the plate heat exchanger. I gave you this link to expain this.

I explained how that works in the other thread. You obviously didn't get it.

I assume you want a period of the day, when the house is unoccupied or partially unoccupied, and the temperature reduced. Easy. Have stat/programmer switching each Smart pump on each CH zone. Also have TRVs on "all" rads. Have the stat/programmer in a "representative" room in the zone. The room TRVs will be set to approx 21-22C by trial and error. Set the programmer as a "high limit" say 24-25C - the TRVs control each room and the programmer stays out of it. In the unoccupied time set it say to 18 or

Then you have a stat/programmer in each CH zone with timed temps and a master timer for the lot. The master timer can switch in the store to preheat the CH and switch out all CH zones.

They are prone to problems compares to pumps which give full flow when needed.

See above. The pump will use near nothing when just pumping 0.25 kW into the rad system.

Take on board what I say. You could have a great system cheaply using a dual-temp boiler, Smart pumps and CH off the store. A pressurised heat bank would be the best option as you have little space.

If you go down the route you going and having rads directly off the boiler, you would be better off buying an ATAG high flow combi (top quality) giving

Arduino?

and make it part of the primary circuit?

I have seen various fitters claiming faults on new units running as high as 50% as well.

If you do a search on them, you will also find few suppliers of new boilers and parts at the moment (compared to others). I accept that may change, but there is plenty of choice of established brands that are well catered for at the moment, so why the focus on this particular boiler?

I understand it, but I don't accept your argument that it offers any great advantages for my application. You start with a boiler that is >92% efficient, which already limits any improvement you can make in direct efficiency to explianed the merits of it. No harmfull by-pass, boiler cycling

Good, so stop trying.

I accept little you claim without hard numbers, alas you never provide them.

You claim to not be CORGI/Gas safe registers, so are clearly not a professional heating installer. So what are you a professional in exactly?

You seem to fail to understand closed loop control theory.

Why are you going to get sludge build up in a well maintained system? (if you use a nice sealed system you reduce the liklihood still further).

Short of pulling the house to bits to relay pipes etc, I don't have much control over that. Fortunately its not a big issue in this place.

I will take your word for it. Not something that I particularly care about though.

So I don't need to change my mind about using a sealed primary then? Thanks for that.

Erm, 1/10 for comprehension. Read it again slowly. I said a coil will

or in the rads you mean (which will hold more buffer water than the bottom of your store)...

So where did the "heat bank combining its energy with the cylinders." come from / mean?

Yup, I will see how it prices up.

A pressurised heat bank with immersion heater sounds suspiciously like an unvented cylinder in all but name, and presumably should be fitted with the same fail safe mechanisms though.

here you go again; the heat back *is* the cylinder

Yup, I have looked at these options. From a control point of view it seems easier to not tit about extending store capacity by recharging it on the fly unless one has to.

Perhaps. I must have been losing the will to live by then.

There are people here all day, so there is no time when it will be unheated as such. So daytime temperatures will usually be maintained above the night time setback temp.

The posher weather compensators appear to do all this and also act as one of the zone stats.

Near nothing? (not that I care about the 6W in the grand scheme of things!)

I knew it would not be long ;-)

Not enough flow rate... I know - install two of em.

Well the space occupied will be replacing that of the current cylinder in the airing cupboard.

Interesting ta...

Dave Liquorice wibbled on Wednesday 14 October 2009 23:02

That looks pretty cool and reasonably priced. AVR based too. You could use their programming environment or dump it and code in C, which works very nicely on the AVRs and gcc is the defacto compiler. Nicer to work with than PICs IMO.

You have an attitude - well you are from Essex. In the previous thread I knocked up a diagram for you and you never even wrote thanks, that's how bad you are. You are a waste of time. A know-it-all DIYer, who think he is cleverer than what he is.

You can't even grasp simple points, which is understandable as you are not a pro. But you counter with little more than know-it-all ignorance. If I go on I will be iterating three times, so I will cut it here. Just read back on what I wrote and do what I wrote. You even have a diagram.

BTW, YOU HAVE NOT fitted a 25/26 litre/min combi at all, you fitted an 11 l/min combi and not a good one at that.

What you are doing is not cheap and gives poor bang-for-buck. Be my guest, make a mess of it.

DPS claim the Pandora Heat Bank needs no overflow. This is nonsense. If the plate heat exchanger becomes holed the cylinder will fill with mains pressure water. This means something has to blow. That will be the weakest point, the rubber diaphragm open to atmosphere. Which means water spurting all over the place.

If /any/ mains-fed pipework or component becomes holed you'll have water spurting all over the place. Are PHEs especially liable to holing? Given the number of combis on my patch which I'd get called out to if such a thing happened (it hasn't) I think it must be improbable enough to discount. In other words I think DPS are at least as justified in discounting it as unvented cylinder manufacturers are in not calling for their products to be installed in blast-proof bunkers ;-)

Depends what its rating is. Minimum heat input seems to be about 1/3 of maximum on the Worcester-Bosch kebab[1] range, so for a 12kW unit you'd modulate down to a bit under 4kW.

Indeed, but is that a bad thing any more? I know it used to be back in the Jurassic era of unmodulating burners, cast-iron heat exchangers and open or unfanned balanced flues wafting stored heat away to the outside, but with a low water content fanned-draught modulating boiler how much of a penalty is there to the boiler running for, say, a minute and sitting there just circulating the system water for the next 10 or 20 minutes to achieve your example 0.25kW spring/autumn heating load? As I see it next to no heat is lost via the flue of the boiler casing when the boiler's not firing, and even in your heat-bank scenario you still need a pump to be running (albeit a possibly more efficient pump than fitted to yer average system boiler).

OK I'm a lost here: what is this 'dual-temp' boiler of which you speak? I mean, how is it different from, say, much of the Worcester-Bosch range where as far as I can see you can command the boiler to run at 75C for DHW overriding whatever flow temperature you have set for CH?[2]

Am I right in thinking these Remahas allow you to externally control the flow temperature via a weather compensation control? That is nice.[3]

..."next to no heat is lost via the flue OR the boiler casing"...