Siemens RVP331 Heating Controller

[sid]

Has anyone got any experience of using this (VERY EXPENSIVE) controller?

I'm looking for some specific information and rather than post all the complicated details here I'd prefer to discuss the set up directly.... but here's a brief outline before I get any complaints ...[;-)]

I've had my heating system modified this year by the addition of low temperature (hot water) underfloor heating in several new rooms. I have retained the radiator system in the older part of the house, therefore it's now a 2-zone system. I'm having a slight problem with, I think, a conflict of room sensors. I've discussed it with the 'chauffagiste' (no complaints about him, he's done good work so far) but I think I've been unable to explain myself properly and I'm a bit frustrated.

[Gluestick]

If the system is correctly zoned, then any sensor (e.g. room stat) should be controlling a motorised valve which permits- prevents circulation in that zone: only.

 

[sid]

Precisely. This is not a general query.

I can see I'm getting drawn into giving more details, but I need to chat to someone who has knowledge of the product. For example I'd like to check the connections and settings. There is a menu with 195 settings per heating circuit, so it's quite specific to the product.

I know what's required of the system; I specified in outline what I wanted.

The underfloor part has a motorised 3-way mixing valve. The radiators, which were already in place, have a more 'crude' non-motorised mixing valve (originally controlled by plugging in or taking out the plug... not even a timer!!!) and the work carried out by the engineer did not involve this original system, just the addition of the new part.

[Gluestick]

Had a rapid whiz through the tech spec (above) and I now have a sneaky feeling that this programmer requires matching sensors and valves etc. if it is to provide the very complex and multi-variable performance specified.

Additionally, it apparently needs certain boiler-specific devices, too.

Just a thought...............

 

[sid]

Thanks for that Gluestick.

I think I'll have to go back to the chauffagiste armed with my dictionary and try and explain my query to him. 

Sid

[Gluestick]

I believe that your controller is probably amongst the first of the new breed of CH programmers, which has been "Mapped", in the same way as a modern car's ECU. The Mapped ECU has a huge stored variety of settings for ignition timing, advance curves and mixture settings/compensation and guesses the optimal set of values according to the various detectors which are feeding data in. The latest mapped systems are car-specific; and the new generation of CH programmers are believe it or not, house-specific!

They learn! Thus in say January, the programmer "knows" how to adjust the temperature of the rooms, zones and boiler etc. To achieve this, needs a host of detectors, which include flowmeters, thermostats and etc. Additionally, other controls are fitted to avoid "Dead Cycling", which wastes fuel.

Boilers cycle, needlessly, when the jacket (and thus surrounding water) temp drops past the point where the boiler stat kicks in; despite the fact that none of the demand systems is calling for heat.

Condensing combi-type boilers solve this problem, as again, they are a demand based system.

The old High-Hysteresis Bi-Metal stats have mainly now, thankfully, been replaced with low-hysteresis electronic types: another cause of unnecessary boiler cycling and heat waste. Ther are many of the old type about, still however.

Hope you find someone who can work it out.

 

[Jc]

Condensing and combi boilers are two totally different types of boiler.

[Gluestick]

Well, Jc, then all these guys got it wrong, too![;-)]

http://www.worcester-bosch.co.uk/index.php?fuseaction=site.articleDetail2&con_id=130817

http://www.nef.org.uk/energyadvice/boilers.htm

http://www.worcester-bosch.co.uk/index.php?fuseaction=site.articleDetail2&con_id=125860

http://www.viessmann.co.uk/downloads/Vitodens.pdf

http://www.muswell-hill.com/foxandco/pages/boilertypes.htm

 

[Dave Plumb]

Is the 'old' part system now controlled by a 2 port valve and not the plug ?

if so check the brown and grey wires to the valve are not connected together from the room stat, only the brown must come from the stat and the grey connected to a dedicated permanant live tag,  its a common assumption they can be connected together as both need power so its not a problem, but can leed to feedback across to the other zone valve and turn  the other zone on with the thermostat closed 

Dave 

[sid]

Hi Dave

Sorry for the late response, I've only just spotted your message.

The radiator system (the old part) is controlled by a manual 4-way vanne melangeuse; there is no room thermostat for this part of the system, the water is maintained at a specified temperature by the new controller and strap-on (excuse the expression[:$]) sensors on the flow and return pipes, and then adjusted manually to get the required level of heating. Sophisticated eh? This is how the original system was installed and it even used to be a case of inserting/withdrawing an electrical plug for the boiler and the pump!

The new part (underfloor) is fully controlled with outside sensor, room thermostat and pipe sensors. There is an additional hot-water function too which operates independantly.

My query is about the room sensor, a Siemens QAW50, which doesn't appear to be connected to circuit 2, the underfloor part, but is connected to "A6" which is a common connector for both circuits... I think.

A6 probably will not mean much without a diagram, which could be tricky!

What I'm trying to confirm is whether the room sensor is calling for heat for both heating circuits, which I don't want it to do, and if so how do I limit it to the underfloor circuit?

I hope this makes sense!!!

Sid

 

[Dave Plumb]

Hi Ya Sid

Great fun eh,  I must admit I dont know this programmer off hand as i stoped using this type of compensation system a long time ago because it worked out you had great comfort conditions but with a large increse in running costs, maybe they have cured this now.

You say both circuits get hot, is this the old heating circuit and underfloor or is there another rad circuit, if the former the controls you have will also control the firing of the boiler  relative to the differance between the outside temperature and inside temperature and primary flow temperature and on and on all controlled by various thermostats fitted over the system, as the old system has a manual control a number of additional valves and thermostats would have to b fitted to give the same control on this other circuit.  Deep breath

Or as the underfloor heating will probably cycle most of the time you could fit a two port valve to the old circuit through a room thermostat, this would give you temperature control to turn the old circuit down but not allow you fire the boiler without the underfloor on.

If the latter is correct I can ask around and see if anyone knows if they can fire independently and whot the connection/positions should be

 

Hope this helps

 

Dave

[Michael]

 Sid. You should have two pumps on the system for a start,one for the general heating system the other tied up with the mixing/diverting valve on the underfloor heating circuits. the underfloor heating works on a lower temp than the rest of the circuits so its crucial all circuits are zone valved. I would do away with the melangeuse and install two zone valves, one for the rads the other for the primarys to ballon .Then with the system correctly installed you might  have a chance for your Electronic Temperature control unit to be wired up and work as its designed to.It do not surprise me that the QAW50 stat is wired up to both circuits,with half control what else could your plumber do.Not forgetting,carefull when messing about with the control unit wireing as there is low voltage side as well as mains side.Happy heating Michael..

[Jc]

I see some of the firms(Fox and co,for example agree with me).A combi boiler has not hot water tank in the circuit;it effectively becomes a multipoint water heater when some one turns on a tap.A condensing boiler may or not have a hot water storage tank;it refers to a type of boiler where the hot exhaust fumes are used to preheat the cold water entering the boiler to improve the efficiency.

[Jc]

Gluestick,When I finally got thro' to all the sites you mention,I found that they all agree with me-the first page of the Worcester/Bosch makes it very clear.

[Gluestick]

[quote user="Jc"]Condensing and combi boilers are two totally different types of boiler.[/quote]

Jc: this quote from the Worcester website: first page, top:

What is a combi boiler?

The high efficiency condensing combi or combination boiler is an ingenious space-saving idea, and an increasingly popular choice in UK homes. In fact, combis now account for well over half of all the new domestic boilers installed in Britain every year. "

Sorry: I don't understand what you are driving at? [8-)]

 

[sid]

Hi guys

Thanks for the latest postings. It's getting complicated, as I feared.

My system has THREE pumps, one for rads, one for underfloor and one for the domestic hot water (which is pumped into the existing 200 litre tank). It was for this reason that the Siemens controller was recommended, plus the underfloor runs at low temperature.

My original wish was that the room thermostat would control just the (new) part of the house with the underfloor heating, and I would manually adjust the rads. The hot water works fine. Previously we'd had problems with the hot water, sometimes on switching on the rads, all of the domestic hot water would be cooled by an unintentional reversed pumping!! That's cured now.

At the moment the system doesn't seem to cycle unnecessarily, but then maybe I wouldn't recognise that if it did! The underfloor heating works very well and I'm fairly sure so far that it's working out economically, but I'll know better after a full winter, but most importantly... we're warm at last! If anyone is thinking about underfloor heating it has a couple of immediately noticeable advantages, no radiators to take up wall space, your feet and legs are always warm and thus you tend to feel warm all over, and no convection currents to set up draughts.

I'm not concerned with the condensing/combi issue at the moment as I've decided to make do for now with the standard French-type oil boiler that we've got.

It would appear from the documentation that perhaps some room sensors (not mine) can be 'addressed' so that they are "circuit specific" if that makes sense, but mine just seems to be general to the whole system.

Without the help of someone with particular knowledge of this controller I'll have to go back to the engineer, which is probably what I should have done in the first place. It's just that I like to know HOW things work, not just switch them on and off.

Thanks again

Regards

Sid

[Gluestick]

Umm, that's one of my problems too, Sid: from the moment I disassembled my first clock! Not enough to know it did work: but needed to know why it did work!

Hope you soon sort out the problem.

Just a thought: have you drawn out a logic diagram; i.e. using Boolean approach? Might assist to dope it out.

 

[Dave Plumb]

The biggest drawback with the combi boiler is flow rate of hot water as they can only supply a fixed amount of flow ltrs at one time, can be a drag if more than one bathroom , kids or guests wantign to wash at the same time, But  condensing combi's  are very efficient and to help combat the flow rate problem a higher efficient and ingienious way is to fit the boiler instant hot water circuit to feed one tap outlet only, say, the most used during the day kitchen sink, pipe up the heating circuit as normal but from the boiler, off the heatting flow pipe take anouther circuit to your hot water storage  vessel, install 2 port valves and timer, wire the system to think the hot water circuit is anouther heating zone, this allows you to only heat the hot water vessel as needed during the evening without loss of heated water duiring the day when it would only be on for the kitchen sink, heating can be turned on when the chill sets in, if ever.  further savings could be made if the kitchen sink was big and you could sit in it to wash just like in the old days, no need for the old hot tank then at all.

Ps  if you go down that route dont forget to close the kitchen shutters[:)]

 

Dave

[Gluestick]

Good idea and neat solution, Dave.[:)]

As always, there's more than one way to kill a cat than forcing it take a bath in the kitchen sink with the sutters open! [blink]