Can The Antman Heat Dump be adapted for Unvented?

[Brompton]

I will shortly be installing a 210 litre unvented cylinder, which will be connected to an existing 25 x 58 solar array. A heat dump will be required as the solar takes the bottom of the existing vented 210 cylinder to 80 degrees in summer. The intention was/is to utilise the Antman heat dump (S Plan+) modified to accomodate the controls attached to the cylinder (eg so that the high level stat cuts the solar pump and central heating pump at the preset temp). Have a Registered Plumber/Heatiing engineer and his recommended electrician on board, who originally confirmed that they could design/install the system. Electrician now saying that he has been advised by an instructor on a training course that a) you shouldn't install an unvented system which needs a heat dump and b) the Antman system won't work.
It seems to me that there are plenty of unvented systems around with a heat dump achieved by putting a diverter valve in the solar loop and an attic radiator - so a) is wrong. However I would prefer not to dump heat into the attic - but utilise  the central heating system on the Antman model.
Has anybody designed/installed an unvented system with a modified Antman type heatdump? 
Thanks

[Philip R]

Hello Brompton,

A good while back, you had an issue with flow rates to the shower. I guess the unvented cylinder was the solution?

The unvented cylinder people make duel coil cylinders for the purpose of solar heating!. The controls supplied incorporate an energy cut out ( a thermostat driving a motorised valve, to turn off heat input to cylinder at about the 80deg C mark, before the overtemperature device dumps the contents out the D1D2 tundish assembly).
The Antman scheme will operate the heat dump which is external to the cylinder, just driving the primary solar medium through an external heatdump, via another motorised valve. I therefore do not understand what the electricians issue is?? it sounds like he knows nothing about the requirements of G3 and his friendly heating installer should intervene. ( and enlighten him!).

If he will not install it then PM me.

Regards, PhilipR

[Iain]

Hi
I use a similar heat dump on my unvented. I think they are worried that you are relying on the heat dump to protect the cylinder. I still have all the safety thermostats fitted so that if the heat dump fails the safety stat will cut the solar pump to stop any more input.
Heat dump at about 80degC and the safety cut out is at 90 degC as well as the tundish vent. I am using the boiler coil to "heat dump" with the boiler pump.
Providing you have all the supplied safety stats fitted the heat dump is an "extra" so makes it even more safe.
Iain

[guydewdney]

I have an unvented, with an antman system.

I use the over heat thermostat (built in) to fire up the CH, and kill the boiler via a relay. This also protects the cylinder from teh overheat situation from my WBS - connected via a heat exchanger, and down hill (so cannot gravity feed).

plus the antman system of overheat = CH on but boiler off mode.

Not sure if its to regs - but then again, I dont care - as most of the regs are for idiots, and Im not an idiot. My wbs install - no leaks, no problems, but not to spec as I used a custom made 7 to 6" flue (after checking with mfr that it would run OK) - which is illegal - meanwhile- fully qualified installer put WBS in with no  cement in the flue - leaks everywhere, exhaust paint to colour the flue....

[Brompton]

Philip
Thanks - and yes I decided in the end to go for a mains pressure system as I was concerned about the possibility of improving and extending the vented system only to find that it didn't perform well enough, and then having to go unvented after the house had been put back together. I have also recently discovered that my existing Navitron vented 210 litre solar cylinder has a boiler heated capacity of 93 litres - which I think will prove to be too small in winter for a 4/5 bed, 2 bathroom house (and the expected demand in due course from 2 teenage daughters). Newark have suggested a min of 155 litres boiler heated volume in a 210 litre unvented solar cylinder - which can be achieved by putting the boiler coil lower down than in the standard cylinder.

Iain/Philip
I think in part this situation has arisen because I have put forward the heat dump arrangement and pointed them in the direction of the Antman wiring diagrams and at the same time pointed out that they need to take into account any modifications necessary to deal with the unvented cylinder (and in particular what I called the high level stat - probably better called the energy cut out). I think the electrician has no problem with the Antman wiring diagrams, but because he doesn't fully understand how the heat dump works he is struggling with any modification.  I ws working on the idea that the energy cut out stopped the central heating pump - but see now that it just closes a valve to prevent further heat input to the cylinder. Either way it seems to me that this will stop the heat dump (which is not ideal but unavoidable - and not a problem insofar as if the heat dump is operating it should prevent the cylinder temp getting to the energy cut out temp) However the Antman model for vented systems uses the solar controller to stop the solar pump at a set maximum temp - and as you both say with unvented this should be done by the energy cut out (otherwise you open up the possibility of the heat dump stopping and the solar pump continuing to operate) I have also suggested that because I have an east/west set up the TDC 3 Controller will not have enough spare capacity to deal with the heat dump switching - and that he should be looking at a higher spec controller eg Resol.

You have both confirmed what I thought - that the Antman model will work with unvented - and furthermore that changes to the wiring from the vented system diagrams will be less complcated than I thought. I think the next step is a meeting with the heating engineer and the electrician - without the renewables instructor.

Thanks for your help.

[Antman]

Thanks Guys. Brompton and I discussed on PM but I am not sufficiently familiar with unvented systems to comment definitively so I suggested posting here.

There is no reason why (for belt and braces) and assuming the solar controller uses a standard mechanical relay output to trigger the HD, that you don't add an additional mechanical cylinder stat electrically in parallel. This will protect against solar controller failure or (more likely) the customer incorrectly fiddling with the programmed parameters. The latter has more serious consequences with unvented systems so could usefully but guarded against.

Antman

[Brompton]

Antman
Thanks - but I don't quite follow this - I was working on the basis that if the energy cut out on the cylinder cut the power to the solar pump once the (energy cut out) preset temp was reached (say 85 degrees) the solar pump couldn't restart until the cylinder termp dropped below 85 degrees. I can't think how any changes to the solar controller settings would overide this - am I missing something?
Regards
Mike

[Antman]

Maybe I am not understanding what you mean by 'energy cut-out'.

I was belt-and-braces ensuring that the HD works for all energy input sources, failures, and covering the possibility that someone fiddles with the controller settings once the installer has set them. E.g. it is possible to set the controller to continue loading the store beyond the normal max temp up to the absolute max - usually 90-95C.

Antman

[ericw]

Doesn't an external high limit N/C thermostat have to be in series with the solar pump so that if things go totally pear shaped the solar pump is not allowed to run so preventing more energy being transferred into the cylinder.
The setting for this thermostat needs to be higher than any "start the solar pump to dissipate energy" setting that might set in the controller.

[Iain]

Hi Eric
Yes there is are 2 manually resetable safety stats on my cylinder(I think preset at 90degC).1 for the solar pump and 1 for the boiler circuit

all the safety thermostats fitted so that if the heat dump fails the safety stat will cut the solar pump to stop any more input

Wired up as a standard unvented with the heat dump as an extra.
Iain

[Brompton]

Antman
I think Eric W and Iain have confirmed that it can/should be wired so that the energy cut out/high limit thermostat will overide any "instruction" to the solar pump coming form the solar controller.
I have spoken with the plumber and electrician and think that between them they can sort it.
Mike

[Iain]

Hi
Will try and attach my wiring diagram to see if it is any use to you.
The safety cut out is just in series with the solar pump supply wire.(over on the far right)
Iain

[Brompton]

This saga continues. The Navitron/Newark supplied unvented dual coil cylinder came with only one dual aquastat - a controlable thermostat (0 - 70 degrees) with a high level cut out (85 degrees). It seems that this can only be used to control /limit the heat supplied by the boiler and that another high level stat will be required to cut the power to the solar pump. The plumber is saying that he has only ever seen unvented dual coil cylinders with two high level stats - and the cylinder has two adjacent ports. Unfortunately we can't use the second port due to space constraints - but could use the secondary return port which is higher up the cylinder. Spoken with both Navitron and Newark to try and confirm that a second high level stat is required - Newark don't really know(they have spoken with MacDonald Engineering who design the cylinder who will only refer us to instructions on the Gledhill website) but they have agreed to supply a second dual aquastat f.o.c (this could be installed with the controllable element disabled). Navitron have said that they cannot advise - but have sold many of these cylinders without this coming up as an issue.
The inference is that these cylinders are being routinely installed with only one dual aquastat. Does anybody know how the high level stat in the dual aquastat can be used to cut the power to both the solar pump and close the two port valve in the boiler hot water circuit? Using the solar controller to cut the power to the pump in an overheat situation seems inadvisable given that the max temp can be altered by the user.
Thanks

[solar_cambridge]

If you only have one high level stat, then you could wire the boiler and solar through it. Then if the cylinder overheats it cuts off the power to everything. That meets the regs as you have removed the energy sources.  I did a kinspan solar cyl last week and it did have two pockets at the top for two stats, but they were very close together and the stats only just fitted.

[Brompton]

Thanks.
Do you know whether it is possible to wire the boiler through the controlable thermostat and the high level stat but the solar only through the high  level stat - I don't want the power to the solar pump being cut at 60 degrees. I am being told this isn't possible - if this is right I am puzzled as to why Navitron/Newark are supplying the cylinder with only one dual stat (and why they are apparently not getting regular requests for an additional stat)