Need help setting up thermal store

Dear Group,
Following advice from the archives of this group we've had a thermal store installed to service our house with it's gleaming new extension. The store is a 350 litre Gledhill Torrent RE Solar in the loft, and a Ferolli 25OV boiler installed in the loft too. There is a "hot water" / "heating" programmable timer that operate the two zone valves, (as per the Gledhill wiring diagram), and a Heatmiser programmable room stat in the lounge. There are 50 evacuated solar tubes installed on the roof for the solar side of things, along with their associated pump, controller etc.
The system is built pretty much as per page 4 of the Gledhill manual; http://www.gledhill.net/pdfmanuals/Building%20Products/TorrentRE-Iss3.pdf (but with no underfloor heating circuit).
What I'm looking for is advice from those who've been there on how to set up timers, bypass valves etc, so as to best utilise the system.
I think I'm fairly clear on what needs to happen in the summer; My idea is to set the "hot water" to come on before sunrise for half an hour or so, to ensure that the store is adequately charged for morning ablutions, and then hope that the sun fully charges the store throughout the day.
The quandry is what to do in the current, wintery climate? The system is currently wired as per page 9 of the above manual, with the store thermostat set to 75C, and it seems to me that the problem with this setup is that the boiler only fires, (and hence the store only heats), when the room stat calls for heat. This means that once the room temperature has been satisfied then the store may be left only partially charged, thus potentially compromising the ability to provide hot-enough DHW. (and IIUC also doesn't help prevent the boiler cycling that thermal stores are supposed to help with). Is the answer to have the store permanently charged, and just use the room stat to operate the heating zone valve? i.e either set the "hot water" timer to be on whenever the heating timer is on, or alternatively wire the "heating timer" to operate the pump/cylinder stat, and have the programmable room stat merely switch the heating zone valve? Obviously I also still want to extract as much of the suns meagre solar offerings as possible, and so the ideal for this is to have as cool a store as possible... hmmm.
Previous posters have written of the advantages of being able to rapidly dump heat from the store into the radiators, and hence quickly heat the home. This is one area that is currently slightly disappointing. If you look at the photograph on page 7 of the manual you can see that the cylinder thermostat is roughly in line with the entering (boiler flow), hot water. However, the water that is pumped *from* the store around the heating system comes from, I would guess, 40-50cm below this stat, and is therefore considerably cooler. Is this right / normal, and how does it fit in with the rapid-heat-up scenario?
Finally, can anyone offer any advice as to how to set up the automatic bypass valve. What kind of figure does it need to be set to, (IIRC the range is 0.05 to 0.5 bar). Are there any tips or 'usual' settings for this?
Any advice from the several subscribers who have similar systems on how best to optimise my system is very much appreciated.
Many thanks, Mike H
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On Sat, 6 Dec 2008 13:34:31 -0800 (PST) someone who may be pepper
A lot of questions. When I have had time to digest it I will try and reply.
--
David Hansen, Edinburgh
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One thing I must ask, is why you say the room 'stat must satisfy the heating but might leave the heat store partially charged? The central heating should not interfere with the DHW side of things at all. You should set the DHW to the temperature you want it, then leave it alone. It should not be connected to a room 'stat or any other thermostat other than the ones which control the heat store itself.
The programmable 'stat in your room is for the central heating, and nothing else other than the central heating.
So why should the room 'stat have any effect on your heat store and DHW system? Although you have correctly identified the mistake at the end of the paragraph on this matter.
The heat store should actually heat quite evenly across its full length and breadth, so the thermostat on the store is placed in a more central position than on a normal small hot water cylinder. Because the store should be pretty constantly charged all the time, it can then be used to dump heat back into the central heating side to give a rapid sort of boost before the actual heating has got up to temperature. That's why the store should be set and forgotten. It's why this type of storage and heating system is used, all be it on a larger scale, in most commercial developments now.
Setting the automatic by-pass valve. It is easier to set the by-pass valve if you can disconnect the zone valves from the power, but leave the rest of the system running as normal.
First, open the zone valves manual and set the system running. The by-pass valve should be closed to allow normal operation. Now close both zone valves and the by-pass valve should open to allow circulation through it. If it doesn't, then adjust it. If it opens while in normal operation, it is to sensitive and also needs adjusted. That's the easy way to set the by-pass valve.
Have a play around with it all, it can't bite. And have fun with it.
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Hey Hey Hey !!! :-) That should say open the zone valves "manually" not manual. I nearly had you opening the instruction book for the zone valves. LOL
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On Sat, 6 Dec 2008 13:34:31 -0800 (PST) someone who may be pepper

The first thing I noticed is that is that the S-Plan wiring diagram does not appear to entirely correspond with the plumbing in Diagram 1. For example it appears that Diagram 1 shows a heating system where the temperature of the rooms is controlled entirely by thermostatic valves, unless the two valves underneath the bypass valve in the diagram are motorised and it is intended that only one will be open at any time, in which case the bypass valve is redundant [1]. Given that I could well be missing something, here are my thoughts.

You might also like to try not having the boiler on at all in summer. Enough heat should remain in the store to provide enough hot water for washing in the morning if it is properly sized and installed. If on rare occasions it isn't, give the boiler 30 minutes or so.

I think the control system shown in that diagram is over-complicated though I will leave this for the moment and come back to it later.
Following the diagram through it seems to me that if either the heating or domestic hot water motorised valve is open (which depends only on their own thermostat) then there will be a signal to fire the boiler, via contact 10 in the wiring centre, provided it is not intercepted by the boiler hold-off thermostat. Thus the store thermostat should bring the boiler on as necessary, which is easy to test by turning down the heating thermostat and turning up the store thermostat. If it doesn't then the wiring is not to the diagram.

See below.

Presumably from the connection marked "28mm compression connection boiler return (open vented)", which does seem a little low to me.

I'm not sure it does anything, but I would set it to 0.5 bar just to keep it from opening unless necessary. All the other components should withstand at least 1 bar.
My impression of the plumbing and particularly the wiring is that these were drawn up by someone with decades of experience in "conventional" heating systems who then modified their standard arrangements to allow for the new-fangled thermal store, instead of starting with an open mind from first principles. As a result they have ended up with something over-complicated. No-doubt an interesting challenge to them, but it is not elegant.
This isn't a disaster, but I am going to suggest some modifications which I think will produce a better system. I'll leave aside the question of whether you can make them yourself or will need to get an installer back.
Plumbing
I would separate out the boiler and heating pipework, providing them each with a pump and doing away with the motorised valves [2] and bypass valve. The store should be the neutral point, so pumping would be out of the store, on the return from the store to the boiler and on the flow from the store to the heating. Assuming all the connections shown on page 7 are present, but some are blanked off, I would connect things as follows:
Flow from boiler - 28mm compression connection alternative energy flow (open vented)
Return to boiler - 28mm compression connection boiler return (open vented)
Flow to heating - 28mm compression connection boiler flow (open vented)
Return from heating - 28mm compression connection alternative energy return (open vented)
This simplifies the plumbing. The connections are not ideal, but seem to be the best that can be done with the store as it is.
I put the heating return lowest down to make the most of solar. There is an argument to put the boiler return, from store to boiler, lowest down to maximise the amount of condensing the boiler does. It can be argued either way and on another day might I have gone for that.
Controls
The wiring diagram talks about the DeltaSol BS, but there are four models of this controller and I would install this setup with either the BS3 or the BS4 controller. Both of these can control a boiler, as well as solar.
Assuming the plumbing has been modified as I suggested and a BS3 or BS4 is used the two port valves, store thermostat and boiler hold-off thermostat are all exterminated. Instead the solar controller keeps an eye on the store temperatures via its own sensors. The solar controller tells the boiler when to fire and the boiler controls its own pump, which just pumps water round the boiler circuit as necessary. The solar controller can be told things like when the boiler should be available, what temperature to warm the store up to when there is solar output, what temperature to warm the store up to when there is no solar output and so on. It is all explained in the "mounting instructions" on <http://www.resol.de/en/english.shtml . In essence the solar controller controls heat input to the store.
Heat output is controlled by the heating controller. If I was starting from scratch this would be a single channel controller, but in this case I would just use the heating side of the existing controller. This controls the heating pump via the room thermostat (or thermostats if more than one zone, see [2]).
When heating starts hot water will be taken out of the store. This will reduce store temperature and eventually the solar controller will bring the boiler on for some time to re-charge the store, then it will be off for some time. With the right settings, which will be a matter of fiddling, the store temperatures will be such that hot water is still always available. My guess is that as long as the store temperature is above 50C there will be enough hot water for anything but a large bath. This will give the long boiler burns you want.
If the solar controller is a BS1 or BS2 then I would make use of the existing equipment to do much the same thing. The HW side of the existing ST6400 controller operates the boiler, via the thermal store and boiler hold-off thermostats. The heating side of the controller operates the heating pump via the room thermostat. I am assuming that the ST6400 provides fully independent times for heating and hot water. Certainly in winter the store should be active all day, so that whenever heating depletes the store that will bring on the boiler.
As solar is location dependent there are no sets of foolproof numbers to plug in to get ideal performance. It is necessary to understand and learn to get the best out of it.
[1] I see that there is a feed direct to the pump if one or both of the motorised valves is open, but in this case the bypass is still redundant.
[2] Or possibly re-using the motorised valves. They could be used to provide two zones of heating, each controlled by a local thermostat. Where these zones are depends on the house and pipework. East/west or top/ground floor are possible, depending on orientation of the house and room arrangements. By buying more valves and thermostats more zones can be created.
--
David Hansen, Edinburgh
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On Sun, 07 Dec 2008 17:00:31 +0000 someone who may be David Hansen

And obviously whether the time clock has enabled the valve or not.

Obviously domestic hot water draw-off will also decrease the store temperature and may eventually bring the boiler on. However, this effect will be much less than that of the heating.
--
David Hansen, Edinburgh
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Many thanks Big Wallop and David Hansen, Much excellent advice to digest there, and I will respond in due course. I don't think I will be changing any pipework in the immediate future, (too much other 'stuff' going on), but I think I understand the immediate change I need to make is to keep the store charged permanently during the day (during the winter). For the immediate effect I can just set the "hot water" to be on all day, and I'll wind the bypass all the way up to 0.5!
David, I need to investigate exactly which solar controller I have. It is certainly a Resol DeltaSol BS, but I'll have to check which model when I'm back home - the options presented by models 3 or 4 sound interesting.
I now notice that I don't have the "boiler hold off pipe thermostat" which is shown attached to the solar pipework in the Gledhill circuit diagram - I'm not sure what this actually does, and whether I need such a thing. - any clues?.
Finally, a quick question regarding my boiler. It is a Ferrolli Optimax 25 OV, which the manual claims the heating temperature "can be varied from a minimum of 30 C to a maximum of 90 C". Mine only winds up to 80 C, so does anyone know if there is an installer menu, (press this whilst holding that whilst picking your nose type of thing), that lets me wind the beast all the way up to the metaphorical "11"?
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On Sun, 7 Dec 2008 13:23:57 -0800 (PST) someone who may be pepper

I presume the printed instructions and box say which model it is. If not there is presumably a "diagnostic" screen on the controller which shows model number, firmware and so on. Perhaps there is a label, cunningly fitted to the back so you can't see it when the controller is fastened to the wall. A triumph of ideas on visual appearance over usefulness.

Solar heats the store relatively slowly. If there is solar available then it makes sense to hold off the boiler to give solar a chance to warm the store up.
Solar controllers which also control boilers can usually be set up with two set temperatures for boiler heating. One is when solar is not active, the other is when solar is active and this in effect sets a minimum floor to store temperature.
I would only fit a separate thermostat to do this if the solar controller will not control a boiler and you would prefer not to replace it with one which does.
--
David Hansen, Edinburgh
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David,
It looks like I have the 68.03 model of the DeltaSol BS. This model has two relay outputs, one of which can be used for controlling "after- heating", (according to the Resol litterature). I am not clear on exactly how they invisiage this being implemented, or to which of the four possible sensors the "AH O" and "AH F" settings relate. I am also not clear on when exactly the second relay is energised... is it when AH O is exceeded or when the temperature falls below AH O etc etc? I have emailed Resol with the same question, but if you happen to already know the answer then your help is once again appreciated. Mike
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On Tue, 9 Dec 2008 16:28:20 -0800 (PST) someone who may be pepper

Then you are in luck. It will hold off the boiler if thermal heating is available.
I can't remember the manual (and you can read it just as well as I can), but my recollection is that this can be used for two functions, either controlling a boiler or controlling a heat dump circuit, depending on the programming. It might even be possible to control two stores, with one being charged first, but that may be beyond it.

I don't know the answer. My guess is that it depends on whether it is programmed as a boiler or a heat dump. If you connect a light bulb to the output of the second relay then you can play until you work out how it works.
When you are happy, connect it to the boiler and rationalise the wiring.
As you are sticking with the same hydraulic arrangements you will need to work out how to energise the pump when the following requirements are met:
1) the thermal store is being recharged. Either the motorised valve direct to the boiler must be open, or the motorised valve round the heating circuit must be open (called from the second condition)
2) heating is being called for. The motorised valve direct to the boiler must be closed and the one to the heating system must be open.
Some conservative people use the solar controller to drive a relay, which then controls the pump. That reduces the current the solar controller is switching and thus makes it less likely that the relay on the controller will fail and an expensive new solar controller will be needed (or a very fiddly repair on the circuit board). Obviously don't try and connect a variable speed solar pump output to a relay, though it would be possible to use a variable speed output to drive a power transistor or other electronic "relay". Set the solar output to 100%. There is a school of thought that of/on control is a better approach for solar, rather than variable speed. The relative merits probably depend on the length of pipe run and thus heat losses.
--
David Hansen, Edinburgh
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wrote:

It seems not - the Resol manual states that "The thermostat function works *independently* from the solar operation". This suggests to me that this second relay output would merely replace the store thermstat which already controls the boiler. The advantage however could be that I could set an on/off range thus maximising the burn time of the boiler, (e.g. boiler heats the store if the temp is below 65 C, and continues heating until temp reaches 75 C... this would be similar to installing two store thermostats at slightly different heights up the cylinder.that I have read about elsewhere). The interesting thing is that Resol talk about controlling this 'thermostat function' with sensor 3 at the top of the cylinder. - I can't see how this could be useful, and I think I'd have to make sensor 3 the half-way-up sensor?
On another issue, this rapidly dumping heat into the heating system definitely isn't working as I'd hoped. We went away last weekend and left the room stat in frost mode. When we returned the programmable room stat (house temperature) said 13C. Top of heat store said ~75C and bottom of store ~50C (IIRC). Turning on the heating (pump) starts the process nicely, but within 5 minutes my kitchen plinth heater fan turned itself off indicating that the temperature of the water in the pipes had dropped below 40c [room stat barely reached 14C by this stage]. This is not quite what I'd hoped... it's not a deal breaker, and could probably be sorted by adding a lower thermostat, but nevertheless doesn't give me the sooper-dooper quick heat up I'd hoped for, (and had promised the missus!)
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On Wed, 17 Dec 2008 11:53:56 -0800 (PST) someone who may be snipped-for-privacy@googlemail.com wrote this:-

I'm surprised, but it is a while since I read the manual,

The boiler should have come on by then, though five minutes is a short time to use up so much of the heat.
--
David Hansen, Edinburgh
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wrote:

David, The two valves are motorised, and I agreed with your idea that the motorised valve seemed redundant... hence I set it right up to max. I've since found it's purpose (!); it of course allows fluid to flow after both zone valves have closed, but whilst the boiler is still in it's pump run-on cycle. I was getting a lot of banging and noise from the boiler - my conclusion is that with the pump on setting 1 there is not enough static pressure to overcome the auto bypass valve when set on 0.5bar, and hence I was getting local boiling within the boiler at the end of the call for heat.
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Mike, the thing about thermal stores is that the individual functions are quite hydualically separate. The boiler only heats the store. The CH pump only heats a CH loop, the DHW is separate again. The solar loop is separate. They have no interaction with each other. The only common point is the store which is a wonderful neutral point.
To get it to work as you want you will need to change pipework. This is what you must do.
a) Take the boilers flow to the top alternative energy connection. b) Take the return of the boiler to the bottom alternative energy connection. c) Put the pump on the return to the boiler with a check valve just after the pump to stop gravity circulation.
d) The current boiler flow, half way up the store, re-direct to the flow of the rad system loop. e) The current boiler return, below the flow take to the CH return. Install on the flow a Wlio Smart auto variable speed pump with check valve in front of it. f) Install a Magnaclean filter on the CH return to the store. This is ESSENTIAL g) Put TRVs on all rads, the Smart cope with this. h) Remove the zone valves and by-pass valve. i) Remove the stat timer in the living area, as TRVs all around
That is the pipework sorted. A normal thermal store setup. The stat is in the wrong place. Is there a spare cyl stat probe point on the cylinder? Or is there a spare tapping not used that can be converted to a probe point? If so, where on the cylinder? A Surrey flange in CH return tapping may be useful to insert a probe point, so all is not lost. Having two stats will prevent boiler cycling.
Now, what you have is a boiler that only heats the store. And a CH loop that only takes heat from the store. The two functions are hydraulically separate.
There appears to be enough water volume between the CH flow and return tappings in the store. The average rad system is 100 litres. So it looks like it can dump 100 litres of hot water in the rads.
If the solar controller has a relay to cut out the boiler when there is useful solar heat then it "may" be worth wiring that in. Sometime when they cut out the boiler there is not enough useful solar heat and the store is too cool. I would be inclined not to play with the boiler and leave it alone and allow the solar coil to give some pre-heated water at the bottom of the store.
The main ST 6400 timer can time the store to come on earlier in the morning via the DHW function, so you have a store of ready hot water to dump into the rads, when the CH function switches on the CH pump.
Using two stats to prevent boiler cycling requires a relay. It may be wise to put in CH pump interlock, using spare relay contacts. When the boiler is reheating the CH pump is cut out.
Over to you.
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You may want to use the redundant zone valves in creating two CH zones, one upstairs and one down after the pump, and no check valve. Best have a single stage timer for each. Timer energises the zone valve and the end switch turns on the pump. Having TRVs all around will require no wall room stats in the house.
Of course there may be some pipe changes in the CH circuit to create two zones.
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wrote:

<SNIP RECOMMENDED CHANGES>
F.A.O. Dr Drivel & David Hansen, (and the rest of the group),
The more I look at the way the store operates, the more I see the sense and simplicity of the separacity of the boiler and heating hydraulic systems that you both recommend. Unfortunately I may have mislead you slightly by referring you to the photo in the boiler manual, rather than the specific layout of the bosses on my particular cylinder, so if you have time and patience to look at the following then I would greatly appreciate it;
My cyclinder is here; http://tinyurl.com/cekdub and http://tinyurl.com/cprkfy
In case of parallax error in the photos then the connections are at the following heights (cm) [measured from the bottom]
Solar Coil Return 25 Solar Coil Flow 37
'Boiler' coil (unused) 52 'Boiler' coil (unused) 68
DHW coil in 112 DHW coil out 130
Then there are the following bosses which I believe are all open to the main body of the cylinder; 27cm = F&E connection 38cm = currently unused (to right in 2nd picture) 53cm = Currently flow to radiators/return to boiler via pump 69cm = currently unused (to right in 2nd picture) 88cm = Currently boiler flow 88cm = Additional unused boss (this is a 28mm boss I think)
Electric Immersion Heater is at 47cm Cylinder Thermostat is at 75cm Sensor pocket at 38cm Sensor pocket at 74cm Sensor pocket at 130cm
Top of cylinder is 150cm
I'm thinking that your recommendations would be to use the 53cm/88cm pair of connnections for boiler return/flow and the 38cm/69cm pair of connections for radiator return/flow - does that sound about right?
Another couple of questions for the group;
- It has been suggested that I could probably help cut down on disturbances to the cylinder stratification caused by the pumped fluid if I connected the boiler flow to a length of perforated copper tube which is then pushed into the cylinder. The theory being that the boiler flow would not be such a single 'jet' of water into the cylinder, but a series of smaller jets spread across a wider area. ... would it be worth doing this for boiler return / heating flow / heating return too? - Comments?
- I see Dr Drivel often recommends a twin thermostat (with latch) way of controlling the heating of the thermal store - I'm thinking I could use the 'after heat' function of my existing Resol controller to achieve a similar effect. This function lets me say - "If sensor temperature falls below x then fire boiler...... keep firing until temperature y is met". Any comments on this arrangement?
- Dr D also recommends check valves in the system. I don't see how the valve in his point (e) would work... wouldn't it be in the wrong direction? - surely to prevent thermosyphoning it would also prevent normal pumping of the fluid through the heating system? - maybe I don't understand the check valve correctly.
- Could I plumb in the changes so as to create anti-thermosyphon traps, (u-bends), and thus do-away with the check valves all together? [Bear in mind the cylinder & boiler are in the loft and all rads are on the floors below].
Your help is very much appreciated.
Many thanks, Mike
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On Tue, 3 Feb 2009 15:39:21 -0800 (PST) someone who may be snipped-for-privacy@googlemail.com wrote this:-

From a quick skim, that is what I would do.

Some cylinders/stores are fitted with something similar. If you are handy and want to try this then it shouldn't take too long to make.

That is the normal way of doing it. Ideally the temperatures will be lower if solar output is available.
--
David Hansen, Edinburgh
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Where are the alternative energy connections as per the Gledhill diagram?

Worth doing. Face the boiler flow upwards towards the DHW coil.

If it works independently of the solar control then that is fine. Gledhill do it on the Systemate and Boilermates.

The CH. Have a Smart pump, pump "away" from the cylinder. The flow of the CH circuit. You could put and anti circulation loop in the pipework.
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As the CH would come out of the cylinder and then head downwards, (remember cylinder is in loft), then I presume I could get away without a check valve or anti circulation loop on this circuit?
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wrote:

As the CH would come out of the cylinder and then head downwards, (remember cylinder is in loft), then I presume I could get away without a check valve or anti circulation loop on this circuit? <<<<
A bit iffy. Sometimes you can get circulation through just one rad. I would put one in to be sure. The check valve is cheap enough or a loop in the pipe work.
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