More zones please?

[Milleniumaire]

I currently have a heating system with 3 zones; hot water, UFH and radiators.

I would like to add another UFH zone and possibly a further UFH zone in a few years.

My system comprises of the following:
Vaillant ecoTEC plus 637 system boiler
Vaillant uniSTOR (260 I think)
Vaillant VRC 430 weather compensator & thermostat (positioned in hallway)
Vaillant VR 61 wiring centre
Vaillant VR 81 (positioned in kitchen for UFH)
Wunda UFH 4 port manifold (3 ports used) with built in pump - used for kitchen only
15 radiators (with TRV's) throughout the house, over 3 floors (temperature controlled by VRC 430)
There are three 2 port valves; one for each zone.

I'm considering having wet underfloor heating installed into a bathroom as part of a refurbishment project. This is on the first floor and the opposite side of the house to the kitchen, which already uses UFH. The bathroom is 5m x 2.3m in size.

I would appreciate advice on the best way to accommodate the additional UFH zone?

Thanks.

 

[ericmark]

The problem with what your aiming for, is most boilers are modulating no on/off, so only way to combine the two is a water store, with a water store you can have as many pumps and valves as you want, but a motorised valve in the main turns on/off, and the boiler wants to turn up/down.

Radiators are easy, the standard TRV turns up/down, and if you want to have more control then an electronic head. But underfloor heating tends to be on/off, if most of the water goes through radiators then it still works, but as the amount increases through the floor then if you want boiler to modulate as it is designed, it needs a buffer in the form of a water tank.

 

[Dan Robinson]

What?

 

[Milleniumaire]

Hi ericmark, thanks for providing information to my question, unfortunately I don't fully understand what you are saying, but you seem to be suggesting that my boiler isn't designed to cope with UFH?

My current setup, containing a mix of UFH and radiators works perfectly. The existing UFH, which was added around 3 years ago as part of an extension, doesn't seem to have caused any problems and this is quite a large area (kitchen, sitting and dining) fed by three loops of pipe from a manifold on a circuit controlled by a zone valve. The proposed new UFH is a much smaller area, so I wouldn't have thought this would make that much difference to how the overall system works.

I had assumed it would need to be on it's own zone, with a zone valve because it will have its own manifold, with built in pump and a thermostat, but I'm happy to be corrected. Multiple zones and Vaillant systems don't seem to be compatible, especially when you want 4 or more zones!

Obviously I really don't want to be changing the boiler just because I have introduced an extra UFH zone and I'm reluctant to use electric UFH matting, although this would be much easier and cheaper to install.

 

[Milleniumaire]

Just spoken to my Brother-in-law as he purchased a new house a couple of years ago, which has UFH throughout. Coincidentally his boiler is a newer version of my Vaillant ecoTEC plus 637 system boiler, which suggests these boilers are perfectly suited to running a traditional system or full UFH or a combination? Of course, it could be the builder/heating engineer that designed this system picked the wrong boiler, but given my Brother-in-law says it works brilliantly and in his opinion is far better than a traditional system using radiators, it would appear not.

 

[Dan Robinson]

Ignore Eric - he has as much of an idea on heating design as a carrot.

How far in metres would the pipe run be from the existing manifold to the bathroom?

 

[Milleniumaire]

Ignore Eric - he has as much of an idea on heating design as a carrot.

Phew! I really like the boiler and it has been solid as a rock since an external expansion vessel was fitted a few years ago, which resolved the F.75 errors we used get, especially at this time of year.

I will measure the distance when I get home tonight. I assume you are wondering if it is possible to run another loop from the existing manifold to the bathroom?

 

[Dan Robinson]

Indeed.

 

[Milleniumaire]

I had wondered that myself, however, I'm not sure how a new bathroom thermostat would be wired up as obviously we want the bathroom temperature to be independently controlled.

Currently, there is a VR 81 in the kitchen/dining/sitting area and I believe this is wired (into the VR 61?) and therefore controls the opening of the zone valve to the UFH manifold. The manifold doesn't use electronic actuators for each loop, so this means the loops are always "open" and it is therefore the zone valve (and the pump on the manifold) that controls the flow of hot water through the three loops currently in use.

I assume this setup would need to be changed, possibly to use electronic actuators for all the loops, so that two different thermostats could control which actuators are opened, or something like that?

Also, I wasn't sure if another VR 81 could be added to the system as the VR 61 only supports 3 zones (1 x DHW and 2 x CH). I believe the VR 81 is also controllable by the VRC 430, so there are probably limitations on how expandable my existing Vaillant kit is.

I am expecting replacement controllers will probably be required to make this new setup possible and I know they aren't cheap

 

[Milleniumaire]

Out of curiosity, it would appear that traditional heating systems don't usually have multiple zones, possibly two; hot water and heating. Consequently, the heating system usually has a single thermostat that controls ALL the house heating. We recently visited a new housing development and they had a separate thermostat upstairs and downstairs, so I would guess that would have been three zones (including DHW). Since the addition of the UFH in the extension, we also have three zones.

For a house built with only UFH it would appear that actuators on the manifold are the zones, so each room might have a different loop and thermostat connected to one of the ports on the manifold?

I assume a multi-zone setup struggles to use weather compensation? I say this as I know my VRC 430 only provides one heating curve and I therefore assume this affects the whole house (radiators and UFH). There's a lot of assumptions here as I'm not 100% sure how these systems work, but I'm always keen to try to understand them.

Our boiler is very good at regulating the house temperature throughout the year and I've always assumed this is partly due to the use of weather compensation. As I'm trying to introduce more UFH I'm wondering if the weather compensation side of things is actually causing a problem due to the necessity to use all Vaillant controls, which are very expensive and don't appear to be very flexible in terms of adding zones.

 

[Dan Robinson]

Sub zoning your system controls probably won't NETT you any gains, so if the hydraulic side is OK, just hook the bathroom in and let it run with the rest of the system.

Otherwise, thing will get expensive quickly.

 

[Dan Robinson]

Otherwise, pull it all out and use Evohome and put the new bathroom zone on a single room manifold piped off the rad circuit.

Again, not cheap.

 

[MeldrewsMate]

As I'm trying to introduce more UFH I'm wondering if the weather compensation side of things is actually causing a problem due to the necessity to use all Vaillant controls, which are very expensive and don't appear to be very flexible in terms of adding zones.

I'm not a fan of Vaillant controls, but as you have them let's continue in that vein.
Weather compensation will work just as well with UFH as with rads, in that it reduces the boiler flow temperature to better match the heat output from the rads to the heat losses from the building. Keeping the flow temperature as low as possible improves economy.
The rads will typically run at 45 to 55C when outside temp is 15C, but UFH rarely needs temperatures above 55C, so it won't suffer in your case.
Hot water generation needs boiler flow temp of typically 65C, and there is usually a way that the controller increases the flow temp when hot water is demanded. Clearly that part works on your system.

@Dan Robinson has asked if it is practcable to run a pair of UFH pipes from your kitchen manifold to the new bathroom. You'll need about 70 m of UFH pipe for your floor area, so the run shouldn't be greater than 20m from your present manifold. Then you'll need a method (cable better than RF in my opinion) to get the thermostat signal to the UFH control system (usually near to UFH pump), and four UFH actuators so that the bathroom can be heated seperately from the kitchen.

 

[Milleniumaire]

Hot water generationneers boiler flow temp of typically 65C, and there is usually a way that the controller increases the flow temp when hot water is demanded. Clearly that part works on your system.

Yes, I think my boiler gives hot water priority over the heating side as I've noticed in the mornings when getting showers, the zone valves for the CH and UFH tend to be closed even when the temperature requirements of the CH or UFH haven't yet been met.

Then you'll need a method (cable better than RF in my opinion) to get the thermostat signal to the UFH control system (usually near to UFH pump), and four UFH actuators so that the bathroom can be heated seperately from the kitchen.

That makes sense, but I'm not quite sure how the bathroom thermostat would be connected up. The existing two thermostats use eBus, so the VRC 430 "knows about" the VR 81 and the VR 81 controls the opening of the UFH zone valve and turning on the manifold pump.

If an additional bathroom thermostat is added to the mix, this would also need to open up the UFH zone valve and turn on the manifold pump, as well as opening up the actuator for the bathroom loop. I assume the existing VR 81 would also have to open up the existing three UFH loops (which would have actuators fitted).

I'm not sure how two thermostats would be used to control the same zone valve and manifold pump, but different actuators and (potentially) have different temperature settings. This all sounds like it would need to be setup "outside" of the VR 61 wiring centre?

 

[MeldrewsMate]

According to Vaillant VR61 data sheet only one VR81 (remote thermostat) can be used with the VR430 controller and VR61 combination. As you already have a VR81 in the kitchen the addition of a second VR81 will not be allowed. It's all a bit Teutonic and thus inflexible.

Do you have the Wunda control box, which controls the UFH pump and powers the UFH zone valve? If so you may wire a 'standard' roomstat to it, and power the actuators from it.