Hot water cylinder control

[alldone]

Does anyone have any experience with interfacing a hot water cylinder into Idratek.

We are planning a new, solid fuel (automated coal boiler) central heating system and are planning on replacing our electrically heated & small hot water cylinder with a larger cylinder that can be indirectly (coil) heated. Electricity will remain as a backup and for use in summer (+/- solar, see below) when the coal boiler is off.

I am planing to use cortex/reflex control of the zone valves and boiler switching and to dump excess heat from boiler over-run (which is longer than gas due to waiting for coal currently in boiler to be burnt) into the cylinder.

We could just use a standard hot water cylinder thermostat feeding an idratek digital input and then switching the 3kW element (=13 amps). It would be nice to have a more sophisticated control, ideally with some sort of cylinder temperature monitoring into cortex.

We ideally need a unit with 2 temperature probes (one for top and one for bottom of cylinder, go into pockets into the cylinder), temperature output readable somehow (analog or direct to PC).

Anyone have any ideas? or who has anything like this.

I have been considering "smart" solar controllers such as those made by senztek

http://www.senztek.com/index.php?option=com_content&view=article&id=48&Itemid=70

or sorel

http://www.sorel.de/en/products/temp-difference-controller-tdc/general-information/

The senztek one is available as a "free" upgrade also with a free solar panel at the moment in New Zealand with a green glo cylinder purchase but the technical info is limited and I think the PC connection (not mentioned on the website but available as an optional extra) is monitoring only (datalogging and comms). I have a copy of the installation instructions as a PDF if anyone is interested.

The sorel controllers are available with ethernet and bidirectional control but price is Euros400+ which seems a bit steep.

[chris_j_hunter]

Interesting question, that's still open for us, too - in our case with the DPS controller - not sure how smart they really are, in the way they work (no presence sensing, no weather compensation, no family-friendly interface or push-button) ... to have them stand-alone or working with and/or backing-up Cortex control is not easy to decide !

[Karam]

Presently the typical method used to get temperature values from various points in the tank is to use thermistors wired into a QAI (analogue input) module. In some cases inserted in pockets that came as a part of that tank, or, less ideal, on the tank skin through the insulation. Cortex has control behaviour to which such sensors can be connected such the tank temperature can be made to follow different values at different times (for hot water).

Cortex does have heat dump features - have a look at the help files to see if it will fit in with your system.

[ludditeal]

I have just started doing some of this but early days. I have a 210L Navitron/Newark cylinder with 50mm of insulation (should have been more but they c**ked up) fed from a gas boiler and a solar panel. It has 2 solar pocket sensors.

I used a 4 sensor QAI as Karam mentions with 4 thermistors inserted into pockets that I cut into the insulation. At the moment I am just using the top one as a signal to the boiler to bring the hot water up to temperature in the evening.

If I was doing it again I would order extra temperature pockets for the sensors in the tank. The 2 existing solar pockets are 2 closed tubes set into the tank wall which lead to the centre of the water column. I am seeing a significant variation in the temperature (20 degreees+) which is recorded from inserting the thermistors in the existing pockets as opposed to putting them against the tank wall. I have overcome this by applying an offset to the recorded tank wall temperatures to get to what I believe is the real core water temperature. Somewhere in the garage I have some thermal paste which I want to try and see if that improves the readings but couldn't find it the other day.

I went for the navitron TDC3 solar contoller which does include a heat dump facility but I intend to use this in parallel to Idratek as a failsafe. The version with IP connectivity was way too expensive for me and as I was planning Idratek figured I would use that for recording info.

Regards
Allan

[chris_j_hunter]

how about using something like these :

http://www.rapidonline.com/Electronic-Components/Sensors/Thermal-Sensors/Pipe-clip-temperature-sensors/76422/kw/

clipped onto inlet & outlet pipes ?

[alldone]

The cylinders easily available in New Zealand usually have two pockets, top and bottom for inlet/outlet temperature. There are quite a lot of solar ready cylinders available due to relatively high penetration of the technology (and sun levels) here.

I am very tempted to go the full idratek route and not have a failsafe controller. I am planning on having the full battery backed-up power supply and all reports seem to indicate a high level of reliability of reflex/cortex etc. We may or may not have solar as the added benefit is relatively small in our situation (the solid fuel boiler we are planning is inexpensive to run vs high capital cost of solar) and we may have difficulty getting planning permission for the panels due to a listed building (or have to put them in a less than ideal location thanks to trees (also listed) etc).

[drod]

Hi All,

I placed my boiler/cylinder under Cortex control over the weekend, which has prompted some further questions about how best to work it.

The system I have comprises a Vaillant boiler feeding a hot-water supply to goes to both the hot-water cylinder and some underfloor heating manifolds. The feed to the cylinder is controlled by a zone value just before the cylinder.

I've taken an input from the cylinder thermostat and used that to open the zone valve and fire the boiler. When up the temp the signal drops and closes the valve and shuts the boiler down.

This is working to a point, but what I find is that the cylinder thermostat doesn't appear to be very reliable. It happily sends a 'call for heat' signal whenever the boiler needs to be fired, but doesn't always send a 'satisfied' signal when the temperature is reached. The end result being that The boiler fires for hours and the hot water appears to be way above the set temperture.

I've checked the stat output with a meter to confirm it's a problem there and not with any logic I've used! I've also lowered the temperature setting to see if that makes any difference.

I was wondering how to get a more reliable sensing mechanism and came across this thread. A further problem is that the cylinder is a stainless one encased in a plastic casing, so I can't get to the cylinder walls to measure anything.

I wondered if anyone has used the clip-on pipe thermostats that Chris mentions below, or is there a better way to do things?

Thanks, Dave

[Karam]

I suppose its an obvious question .. but can the thermostat be replaced? It sounds like it might be faulty from what you say. If the thermostat can be replaced then can something else go into its location?

[drod]

Thanks for that - yes, I'd thought of that too but wondered about changing the way the system was monitored to give something more accurate, rather than just swap out the device.

[Gumby]

If you pull out the existing thermostat you'll probably find a pocket. You may well be able to fit a thermistor in there and get the wires out, since thermostats often have quite a loose fit with a clamp screw.

You'd still want an overheat cutout in circuit, many cylinder stats have both variable and cutout ones in the same package.