Motorised UFH manifolds for ordinary rads (vs evohome)

[gball]

As part of a whole house replumb, I am getting the copper microbore ripped out, and was considering replacing with point-to-point plastic - i.e. a F+R from a central location out to each room, rather than a traditional series circuit. I believe the plastic materials cost would be cheaper than the time cost of full copper on a normal loop.

This means I could run each rad off a manifold, and could potentially use motorised valve manifolds, making each room a zone.

I have seen motorised manifolds for UFH, but never for rads. Is there any reason they can't be used? I doubt the higher temp (60C) is a problem, but unsure if flow rates could be a problem.

I know the cost of 10+ programmer thermostats is far greater than 10 basic TRV's, but comparing it to an equivalent like Honeywell evoHome, it seems better to have the stat somewhere on the wall and not part of the rad.

 

[Dan Robinson]

I have this set up at home with Evohome - works very well using the underfloor controller to coordinate the circuits.

I wouldn't bother using the HR92 heads though. Just thermostats on the walls.

Then you can have nice slim lockshield valves on each end of the rad.

 

[gball]

Ah - I hadn't even realised evoHome could be used that way! So your setup is to NOT use the motorised heads/temperature sensors (even though you have rads), but to use the wireless thermostats, and the HCE80 zone controller to control the individual manifold valves?

A couple of questions:
1) With the different thermostats available, I can see either a temperature sensor (HCF82) which I guess means you need to use the main controller to boost a room; a HCW82 manual stat which looks like it will lock onto a specific +/- offset (i.e. you have to remember to turn it back down), and the DTS92 digital stat. Does the DTS92 allow you to boost the temperature, but then the controller resets it to standard afterwards? The advantage of the TRV was the ability to temporarily boost the temperature in an intuitive way.

2) One of the selling points of the TRV was the gradual closing of the valve as the setpoint is reached. As the UFH controller is a binary on/off device (due to the actuator), and the rads are faster to heat than UFH ... do you find the radiator cycles and the room temperature oscillates?

 

[Dan Robinson]

The valves open and close slowly which mitigates these problems - whether or not this is part of the control protocol I have no idea.

I use T87 and DT92 units in my house. i also have the OpenTherm bridge which adjusts the setpoint of the boiler. In theory.

The zones can be overridden by turning up the thermostat - which with the t87 is literally a case of turning it.

I have as an experiment added a bathroom rad into the controller and put an old HR82 on the manifold and it works perfectly. However I would have concerns about RF interference with multiple units being that close together.

I also have a second manifold that does have UFH on it. But I have sized the system to work at much the same temperatures.

 

[gball]

Ok, I'm now going to sound a bit dim - what's the difference between the T87 and the DT92 (apart from shape!!)

I know the T87 talks to the main controller over RF, and sends over both temperature, plus a 'local room boost' (i.e. turn the dial) But is the DT92 the same, only with pushbuttons? It looks like the DT92 is wireless, but back to a base unit; is it not really an Evohome unit?

 

[Dan Robinson]

Its all part of the same suite of controls.

For intents and purpose they do the same job.

 

[gball]

Thanks Dan, I've drawn up the options and costs for evohome (for 8 specific zones). It looks like a more intuitive system than the Heatmiser equivalent.

The two design options are either HR92 at £60 per radiator, or T87 at £80 per room + £20 per radiator. i.e. separate stats are only cheaper if there are a significant number of radiators in each room (1 rad/room x 8 = £480 vs £800; 2 rad/room x 8 = £960 vs £960 breakeven)

Are there any other factors to consider between the two options? I originally thought one downside was the temperature sensor being too close to the rad, but it looks like the HR92 can compensate for this. Also a separate mains actuator means longer battery life, but it sounds like the HR92 has decent battery life anyway!

 

[Dan Robinson]

Aesthetics and battery life are the main considerations.

 

[gball]

All sketched out - and thanks for help so far.

One more question on manifold sizing. I have a total of 19 rads on 16 loops across the house. I will be running off a heatbank so the CH will come out piping hot immediately.

From an outlet perspective, I have a concern that all 16 loops drawing at the same time may be more than a single pump can handle.

Now without a heatbank, the boiler power would probably be the limiting factor (slow flow rate is fine, if you drew the fluid faster, it would just come out at lower temp) But with a heatbank you can pull all the 80deg water as fast as you like.

1) Would running two manifolds from two pumps off two bosses be better to get greater total flow?
2) Assuming yes, can you slave zones to two different relays? i.e. zones 1-6 to boiler pump 1 and valves 1-8, and zones 7-10 to boiler pump 2 and valves 9-16.

Unfortunately the Ecohome pairing doesn't seem too clear on how many relays you can run (apart from the example of a CH and a separate DHW relay)

 

[simond]

Eh? So in a house with just 19 rads you think you'll need more than one pump?

Do you not think you might be better off getting an Evohome specialist close to you to come and quote for this?

We do 100s of Evos in our area (not in Berkshire) and if you go to the Honeywell site there is a list of firms with some Evo training and experience. Chances are, if they are into Evo they will be quite cute with central heating, and boiler plant generally.

Just like Dan and myself.

 

[Dan Robinson]

Indeed - there are quite a few technical alarm bells ringing there OP.

you can pull all the 80deg water as fast as you like

Nnnoooo.....

Ecohome pairing doesn't seem too clear on how many relays you can run

Yes it is - very clear.

Would running two manifolds from two pumps off two bosses be better to get greater total flow?

Yes and no...

can you slave zones to two different relays? i.e. zones 1-6 to boiler pump 1 and valves 1-8, and zones 7-10 to boiler pump 2 and valves 9-16.

This would get very very messy.

 

[gball]

Hi Dan, Simon,

I suspect you think I'm going to DIY this whole install - in fact, I'm definitely paying a professional plumber like yourselves (and a trusted one, who has worked on a previous system for me before) I'm just getting extra opinions as experts may have more views, and I'd rather be fully aware of the options as I continue talking with him.

I know it's fine to run dozens of rads on a single pump, zoned or unzoned - however the last heatbank I had installed had a simple design where each zone was individually pumped (4 in total), no motorised valves to worry about. And it works incredibly well, and rads heat up from cold in under a minute. I'm trying to recreate that wish, and the rad count is now 25.

I'm leaving the decision to the plumber, but appreciate your comments that help explain the less obvious pros/cons that I've been thinking through.