Response time for thermal actuators

[SimonHa]

I've got 24V thermal actuators (Emmeti) on an UFH manifold that is driving 7 radiator zones.

I've found they take about 3-4 mins to open and 4-5 mins to close. This is within their spec, but does mean that the zones aren't very responsive and means that the HA control of the rads could be quite crude (in theory - I haven't got that far yet). I suppose for UFH systems the heat up time is so long that this isn't relevant, but it does make radiators seem a bit tardy. I see the flow goes from 0 to full in about 30 seconds so I wonder if it's worth trying to slacken the heads, or drill out the pad slightly, so that the pins are already partially extended - has anyone else tried a trick like this?

In particular, SWBO expects the boiler to fire up as soon as the override button is jabbed  ... perhaps someone can suggest a boiler soundtrack arrangement to make the heating seem more responsive    (like the little flap wheels that are supposed to be in cash machines so that you "know it's counting the money")


Simon

[Baz]

You could try a recording/playback sound effect chip to mimic the boiler.
When TV was first invented I believe the then President of the USA was too thick to understand the tube would take a minute to warm up so didn't come on instantly. They rigged the TV to be on constantly and just connected the on/off to be a brilliance control. The tube was replaced every few weeks in case it burned out as he probably couldn't take the concept of something breaking through abuse.

[Dyslexicbloke]

Have considered any sort of proportional control …
A wax head is going to be slow and I doubt that it could be changed with any amount of drilling.

There is perhaps a plan that would compensate for that.

If you feed pulses to the head, Pulse Width Modulation (PWM), you should be able to maintain a partially open state and vary that with respect to the current heating demand.

Essentially you would need to create a PID loop but, given the extremely slow response rate of the valve heads I doubt you would need anything much more complex than a recycle timer and a relay.

I would be happy to elaborate if you are interested…

Alistair

[ecogeorge]

I've got 24V thermal actuators (Emmeti) on an UFH manifold that is driving 7 radiator zones.

I've found they take about 3-4 mins to open and 4-5 mins to close.
Simon

Puzzled as to why you consider 3-4 mins slow 
Don't ever get underfloor then , - change mins into hours !
Surely zones are never so cold you want/need heat that instantly.
Why are you controlling radiators from an underfloor heating manifold?
You could always replace the actuators with straight forward 24v solenoids for either on or off operation.
rgds George.

[SimonHa]

Alistair: yes, I suppose some kind of pulsing mechanism could work - I've got flow meters on the manifold so it would be fairly easy to calibrate. Ultimately I'm hoping to finely control the boiler flow temperature (at the moment I can just switch between "normal" weather-compensated mode, and a "low" 45C flow mode) when the house is reaching temp so perhaps on/off valves will be OK.

George: well, it is still 3-4 mins extra when you've come to a cold house, especially when each zone is small and only has a few litres in the pipes to heat. Yes, it does get very cold here - it's an old stone house so insulation is challenging (see my various posts) - in fact, the trap in the downstairs bath froze in the bathroom the other day (central heating pipes haven't quite reach there yet... tuit shortages)! I didn't even know you could get a 24V solenoid with a M30 threaded head - can you suggest a manufacturer?

I'm using an UFH manifold "upside down" as I have a centrally located boiler room and 7 zones (plus DHW) to control and so this seemed more elegant (and cheaper/easier to install) than a row of 2-port valves. The system was designed over a year ago but if I were doing it again, especially if the boiler wasn't in the centre of the house, I think I'd seriously consider those Conrad/Pegler etc radio controlled motorised valves (particularly once they have sorted out the ticking noise issues) on the rads instead of a manifold.

Thanks for the feedback!

Simon

[ecogeorge]

A

George:  I didn't even know you could get a 24V solenoid with a M30 threaded head - can you suggest a manufacturer?

Fit the solenoid to the pipe not the "only use our fittings"manifold !!
If you are 16mm pipe use 16mm - 1/2" bsp fittings (Bosta)- then use off the shelf 1/2 solenoid with coil voltage to suit.
Simples -squeak.

[Dyslexicbloke]

Have you considered operating things differently …
Personally I wouldn’t switch the system off at all, just reduce its flow temp but it doesn’t matter either way.

Weather the system boiler and pump are on, at a drastically reduced flow temp, or completely shut down you could simply leave the valve heads powered up, allowing them to close only when a zone was approaching its set-point, essentially they would be open by default.

If you do it that way then as soon as the boiler and pump fire up all zones will receive heat immediately, assuming they are cold enough.

Just a thought
Al

[wookey]

Both thermal actuators and motorised valves are embarassingly inefficient (4-5W consumption per valve all the time they are on). Much better to use the HR20 or pegler terrier type motorise-to-position valves, or motor-on/motor-off standard-type motorised valves - then you only use power when changing the settings. The major advantage of the HR20 type fittings is that they are relatively cheap as well as modulating. If you have 7 zones on for say 3hrs/day on average in the heating season that's 19kWh/yr just to run your valves.

[SimonHa]

Both thermal actuators and motorised valves are embarassingly inefficient (4-5W consumption per valve all the time they are on). Much better to use the HR20 or pegler terrier type motorise-to-position valves, or motor-on/motor-off standard-type motorised valves - then you only use power when changing the settings. The major advantage of the HR20 type fittings is that they are relatively cheap as well as modulating. If you have 7 zones on for say 3hrs/day on average in the heating season that's 19kWh/yr just to run your valves.

Thanks for your replies Al & Wookey.

Manifold: I chose an UFH manifold in favour of building a bank of valves for installation time/cost, number of joints and overall neatness (especially true having seen what the plumber managed for a row of 6 air vents under the bath). Advantages of the manifold/central zone control that I hadn't anticipated are that you can more easily balance the zones using the flow meters without and you can isolate a zone without having to depressurise or drain down the rest of the system.

Actuators: When I was planning my new heating system with my plumber over a year ago I didn't know about HR20s. If I did it now, maybe I'd have a large radial circuit with Pegler i-temp motorised TRVs (though they do currently have the noise/ticking issue though this will presumably be improved in the next generation).

Power consumption: yes, we had a discussion here: http://www.navitron.org.uk/forum/index.php/topic,12111.0.html (I've also got a 24V transformer). It is mitigated by the boiler room being within the house, plus, although the actuators waste energy, this is still a tiny fraction of the energy used by the boiler (yes, I know we go to great lengths to reduce electric power).


Simon
PS. To be honest this question has gone off my radar anyway. I'm having more of an issue now with radiator/pipe noise when only one zone is open (presumably due to excessive pressure/flow speed) - probably system boiler design doesn't really expect this yet (mine has an integrated single speed Grundfos 15/50 - I'm trying to see if an Alpha2 could be fitted...)

[Brandon]

an alpha 2 ought to fit provided you have space available for the extra length of the can, this might be an issue if it is within the boiler.

[SimonHa]

an alpha 2 ought to fit provided you have space available for the extra length of the can, this might be an issue if it is within the boiler.

Ah, great, thanks for the info Brandon.

Am I right in assuming that the pump head and pump body are very likely to be the same size between a regular UPS and an Alpha2 - I'm guessing they should be (why re-invent the wheel). The reason I ask is that, yes the pump is inside the boiler, but also has an auto air vent built into the body. The upgrade is only really feasible if it's possible to simply remove the pump head and replace it with the Alpha2 head, keeping the body as is.

I'd been looking into the depth of the pump - from pipe centre to end of case (H2) is 129mm for the Alpha2 and 102mm for the UPS. From peering into the case it might just fit, but there's a plastic pillar that supports the control box very close. After speaking to Viessmann they say it might fit too but that it could affect the DHW reheat performance (I'm not convinced but will have to do the pressure calculations for the cylinder first). Plus it might not go down well in the 5 year warranty department

I am going to have to try to do something though next summer - all the effort we put into having nice smooth bends is all going to waste when only 1 or 2 zones are running!

Simon

[Iain]

Hi Simon

PS. To be honest this question has gone off my radar anyway. I'm having more of an issue now with radiator/pipe noise when only one zone is open (presumably due to excessive pressure/flow speed) - probably system boiler design doesn't really expect this yet (mine has an integrated single speed Grundfos 15/50 - I'm trying to see if an Alpha2 could be fitted...)

Have you a bypass valve fitted to your boiler
Similar http://www.screwfix.com/prods/34127/Plumbing/Central-Heating-Controls/Honeywell-Bypass-Valve-22mm

This would reduce the pressure/flow in the system when only one zone is open. I think they are fitted as standard on most boilers now. Probably easier to retrofit than changing the pump. Could be fitted anywhere in the system, between the flow/ return pipes.
Iain

[SimonHa]

Have you a bypass valve fitted to your boiler
Similar http://www.screwfix.com/prods/34127/Plumbing/Central-Heating-Controls/Honeywell-Bypass-Valve-22mm

Yes, according to both my plumber and Viessmann one is built into the boiler.

Aside: I do wonder whether we'll see the bypass disappear over time - creating a short circuit for the heat can't be great for real-world efficiency although I suppose the boiler will stop heat demand fairly soon (possibly leading to short cycling though). Looking at this as a non-expert, the future would appear to be varying the flow temp to suit heat load* (as mentioned earlier and presumably most suitable in buildings with uniform heat losses and load) or variable pump speeds. For older houses with a range of insulation levels, or larger houses with variable room occupation, I think it has to be the second approach.

* some controllers (e.g. Open Therm) do this already based on the response of the room with the thermostat in it

[KLD]

Simon, which Viessmann boiler is it, and which controller? Ours has the Vitotronic200, and that controller wants to know about the pump. I doubt you can just swap the pumps in these units. I also seem to remember that the pump and the built-in three way valve share one body.
Incidentally, the Vitodens 200-W gas boiler does not have a bypass valve built in.

Klaus

[SimonHa]

Simon, which Viessmann boiler is it, and which controller? Ours has the Vitotronic200, and that controller wants to know about the pump. I doubt you can just swap the pumps in these units. I also seem to remember that the pump and the built-in three way valve share one body.
Incidentally, the Vitodens 200-W gas boiler does not have a bypass valve built in.

Hi Klaus
It's the "entry-level" Vitodens 100-W WB1B and heat is switched on by the 240V "1" line (via the 4 wire actuators which in turn are controlled by my 1-wire network). With this model basic weather compensation is built into the boiler electronics rather than a Vitotronic controller. Mine is the system boiler with a single speed pump (and only a L/N/E connection to it). Note the WB1B combi version has a 2 speed pump which can be set via the control panel to stage 1 or 2 (fixed).

I think there may be other gubbins apart from the air vent in the body of the pump - I think a head replacement is the only viable option (plus sounds least controversial - all the head has to do is spin at an appropriate speed).

My earlier comment was wrong - re-reading my Viessmann emails I see they say the Alpha2 pump won't fit unless it's a smaller rating which may affect the DHW reheat performance. (I wouldn't be so worried about that but actually I can't see a smaller bodied Alpha2 anyway). They definitely said "the boilers are equipped with an internal by-pass valve so there is some compensation".

As it happens I took some photos of the boiler internals before it was fitted (a bit sad really!). From the "pump_elec" one you can perhaps see that the boiler electronics pivot forward - there's a white case/front panel, with a black tray covering the PCB and having all the cutouts for the cable grips, then a (not shown) sort of elongated black rectangular box cover which clips over the top. "pump_front" shows that the only substantial thing that might be a little in the way is the white plastic post that supports the electronics box pivot (and used by the clip). "pump_side" shows how tight it might be - I'd need 27mm in front of the existing pump. You can see that the panel pivot clip could easily be shortened (then might need a flat screwdriver to unclip it rather than by finger) but the back of the cover definitely looks in the way. Potentially only cosmetic implications though...

"Pimp my boiler"?

Simon