Having decided that I don't like plumbing enough to do a CH system, and also don't have the time - I'm looking at choices of boilers and controls... The 2 GasSafe plumbers who are quoting both favour Worcester-Bosch and I have no problem with that - they were on my list of 2 with Viesmann.
So I'm looking at a combi with mostly radiators, one fan convector and 2 instances of underfloor heating - one of which *must be on it's own zone*. Someone (John R IIRC, or might have been Andrew) kindly informed me about the concept of the eBUS control bus that WB use (along with others).
So I think my choices come down to (architecturally) to:
1) Native WB "Wave" contoller (but can it handle more than one zone - unclear)? How easy is it to OR other demand signals into an eBUS system?
2) Third party eBUS controller
3) Homebrew using either ZWave + ZWave "TRVs" for per room control - or simpler homebrew with perhaps 1-2 NEST controllers.
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Any interesting suggestions for 2 and has anyone used 1?
I prefer the simplicity akin to an amplifier with a 1V PP input will last forever. iPhone doct - what, 10 years before everything changes...
So perhaps get the boiler with it's most brain dead controller that takes a weather compensator sensor - and just worry about providing it with L,N,E and demand-L
And there seem to be issues with too many devices on a lot of these systems, if you have a head and a stat in every room...
The weather compensator on mine uses the ebus to connect it to the boiler, and then a separate dedicated analogue cable to connect the external temperature sensor to the boiler
(which was slightly annoying as I had misread the instructions and not realised the sensor was wired to the boiler rather than the weather compensator - so ended up needing to run another cable at the last minute)
Mine is a system boiler, so no hot tap switch. The demand comes over the ebus on which sits a pair of stats, and the interface box to the mains two port valves. (although the boiler does have contacts to use normal controls).
I was going to say that the controller (combined prog stat, system interface, and weather compensator) would need to pass along flow temperature data as well - but thinking about it, it must be an indirect way of doing it, since the sensor is connected to the boiler. (but the controller knows what heating curves to apply to select the required flow temperature)
In hardware terms, probably - its just a variation of a single wire serial bus combining power and data.
In software terms the boiler[1] is preconfigured to recognise a number of different setups depending on what is connected to it. So it can cope with the concept of two heating zones and a hot water one. Those heating zones can be "uncontrolled" i.e. normal zones with a stat, or controlled ones where the system controls blending valves etc for setting mix temperatures on UFH.
[1] or possibly the controller - not sure who has the real brains in this system!
To add extra heating zone beyond the two would require more traditional multiplexing of one of the "built in zones".
Alternatively you may find with third party controls, you can do more than with the Vaillant options.
The main stat/controller/compensator box acts as the main interface to the whole setup (its also a stat for one of the zones). It can take you through reams of configuration of pretty much everything. So in normal 7 day style prog stat you can choose what times and what days you want normal heating or setback temperature. When you want the cylinder to be charged and to what temperature (also things like anti salmonella cycles to heat it to a higher temp one day per week). The main box lets you set all this independently for both heating zones. (the stat for the second zone is a far more basic affair with a rotary controller and a LCD that can't do much more than report temperature and let you tweek the current temp up or down). The stat for the cylinder is a thermistor sat in a pocket in the cylinder - so the system can see the actual stored water temperature in real time rather than just "satisfied / not satisfied". Hence it can make more informed decisions on reheating - say not kicking in the moment it sees a small drop in store temp, but getting more serious if it sees bigger ones, and also modulating recharge primary flow temperature during the reheat to maintain condensing efficiency for as long as possible. It can run timed secondary circulation loop pumps as well.
(its interesting to note that even with my "uncontrolled" (i.e. normal; S+ plan style zones) the control system still maintains the concept of individual flow temperatures for each zone even though it has no mechanism for actually achieving them. So if you stick it in "engineer mode" and look at the states and tellbacks it might think that it wants a 50 degree flow upstairs, and a 55 degree one downstairs!)
Here is one of the areas where the documentation lets it down a bit - there is loads of detail on each component, but much less big picture overview stuff. I expect there is nothing to stop you using the conventional stat contacts in the boiler in parallel with the ebus stuff (although you may lose the weather compensation capabilities for those zones). I also get the impression that you can use other makers controls with the boiler (which some recommend on the ground that they are somewhat less "Germanic")
I assumed UFH still needs a mixer - or, with the right controls and valves, can smart boilers supply UFH at the correct temperature of flow (say 40C)? As in: Switch the diverter valves to UFH and modulate the temperature right down, run for a while. Then switch the valves to the rads and jump the temperature up?
They do that WRT to the DHW vs rads which often have 2 different thermostats on older dumb boilers.
If a mixer is still needed, it sounds like it would be more expedient to keep the logic simple :)
In other words, complexity at the controls end *might* offer simplicity at the pipes and and a mixer for 2 UFH circuits is actually a lump of mechanics I'd be happy not to see...
There certainly have been boilers which can directly feed UFH at a lower temperature (which improves boiler efficiency). AFAIK, they switch between two outputs when both are calling for heat at different temperatures. Someone on here had one (might have been the late Andy Hall).
I have mixed UFH with radiators by having the UFH only loosely thermally coupled to the floor, so it can run at radiator flow temperature without you burning your feet. In this case, it's under a suspended floor, and done by snaking microbore up and down between the floor joists, suspended an inch or two under the floorboards. I have not done this on a ground floor over an unheated subfloor space - you would need to insulate under the joists in that case. This method doesn't bring the benefits of low running temperature, and wouldn't be suitable for heating a concrete slab.
While the boiler can certainly do low flow temperatures, I don't think it could operate a mixed rads and UFH setup just by itself.
I get the impression (and since I don't have UFH, this was not something I spent any time looking at) that the extra ebus control box can drive mixer controls to derive the UFH flow temp required, while the boiler supplies water at the temp required for the rads.
Mine certainly has lots of UFH related stuff you can configure, but I suspect it only works when you have the ebus controls. (there are loads of options for drying out new UFH screeds - slowly warming them up over a period of weeks etc)
It does sound *very* much like KISS would be a good idea...
If the boiler has a weather compensator but otherwise simple controller, that should win in respect of producing a hotter flow on cold days and less hot on warmer days - optimising efficiency.
Perhaps it can be a little more clever with a full-monty set of controls, but if it gets 2/3rds the way there...
Somehow I feel happier with a small box with some relays on DIN rail OR-ing a few zone demands together.
Then the setup would be:
A = Programmer/stat (conservatory UFH) -> valve at mixer B = Programmer/stat (shower room UFH) -> valve at mixer
C = A||B -> mixer pump
D Main house programmer/hall stat (hall is in the middle, this would actually work)
E Extra boost for conservatory with wet fan heater (prob just a time delay button aka communal hall light switch)
F = C||D||E -> boiler demand
That's pretty simple. And boiler independent. I'd probably use a NEST for D.
Then me and the plumber can actually understand what it's doing!
Well, even using the ebus controls one might argue from an installation and use point of view its still fairly "simple"
Whats probably worth investigating is what happens when you hook up a weather compensator controller, but then skip all the other bits, and just use normal mains controls.
Ideally the controller would then just operate as a programmer / prog stat, but also affect the flow temperature even if the call for heat is external to it.
You tend to find that the weather compensation and the more sophisticated controls come as a package ;-)
If you have valve switch contacts etc available, then you possibly don't even need the relays.
Where the mixer is just a normal three port thermostatic blending valve with manual knob adjustment of temperature?
Yup that sounds doable.
Well more likely just you (depending on the plumber!) - but that is a good start.
Completely useless... It's all glossy marketing bullshit - nothing I can find saying "here are some controller options for multiple zones with a mix of UFH". Even the specifier section is marketing BS.
Giving them a call now to see if they can make a suggestion from their range...
They have no "smart" controls (ebus) that can handle more than one zone. None of their ebus controllers can be stacked up in multiples on the bus.
And if I put their FW100 weather compensator on and lock it "on"[1], it will apparently run the pump 24/7 to monitor the flow temperature.
[1] This is the only way to get the boiler to run with a simple demand signal.
So, from this, I conclude, at least as far as ebus is concerned, it's overrated and inflexible. I did enquire if WB sanctioned any 3rd party controllers and the answer was, no, although they knew their existed.
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