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daft question, maybe, but ... not sure I'm quite understanding how RVA001 / Radiator Valve Actuator is used .. is it just a replacement for the usual TRV top, so Cortex can do something a bit smarter than a wax TRV can do ... and is the result actually usefully better ??
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Yes. The RVA has a heating coil round the wax element, this allows the valve to be actuated electrically by heating the wax. It's obviously slower than using a motorised actuator but cheaper and probably quieter.
Because Cortex can control the heating coil you can do all the extra stuff, variable profiles by time of day and occupancy, automatic fallback, dial-up/web control, inhibit on windows or doors open, boost heating on outside temperature etc that a dumb TRV can't. You can zone your controls down to individual radiators and also have boiler efficiency controls like load building etc.
In theory you may get a degree of proportional control by PWM of the heating coil, but linearising the response may be a challenge. It's not clear whether it's worth it.
Certainly controls my heating better than TRVs plus single room stat did.----------------------
www.gumbrell.com -
ah - ta muchly ... power consumption worries me a little, maybe unnecessarily !Comment
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The RVA can be set to normally closed or open. So it will only be powered when you want it to be which in my case will be when it needs to be open. The power per valve is <5W IIRC, less than a zone valve and is significantly less than the power to drive the radiator its controlling which fr me will typically be 1.2kW!
i.e. don't worry about it :-)JonSComment
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so, that's whenever the heating's required in the room, so say 5W x 18 hours for 100 days a year times say six rooms at say 10p per kWhr = 5x18x100x6x0.10/1000 = about £5 per annum ...
reason for my interest is that (so far) I've failed to find a speed variable pump that can be controlled by Cortex in any useful way - via (say) a QOA - all I've found have been either variable but only manually pre-setable to set speeds or regimes or self-modulating on the basis of internal pressure differentials ... so, a possibility for Plan B is to maybe use one of the latter in conjunction with a RVA mounted on (say) a VUL valve :
with Cortex commanding the RVA & valve to throttle the flow & the pump responding to the pressure differential that that develops (more throttling => slower pumping) ...
don't like this , though, because the RVA is slow acting & achieving intermediate settings seems to be possible only via so-called pulse-pause signals & consequent quasi-continuous control (*)
no, I'm not convinced, either !!
(*) the datasheet actually says :
With a ‘pulse-pause’ clock signal, which effects a periodic open/close position, a quasi-continuous control system can be achieved with a cycle duration of 4 minutes. Permissible cycle duration: either < 4 min or > 12 min. Using the auxiliary contacts (which are available as an accessory and can be fitted later), a circulation pump or a heat counter, for instance, can be switched on. The auxiliary contacts switch between 35% and 50% stroke. The rating for these auxiliary contacts is 3 A for ohmic load and 2 A for inductive load. The contacts close when the stroke reaches 35% or 50%.Last edited by chris_j_hunter; 18 March 2009, 01:30 AM.Comment
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Chris,
I vaguely remember commenting on something like this elsewhere in the forums: in factoring the energy usage/cost of these actuators you should also consider that if used in the true logic setting then they will be drawing power when heat is being demanded. Energy use by the actuator is therefore contributing to room heating in a tiny way and therefore not 'additional'. The only difference is that it is electrical energy so if you are using some other fuel for the hot water then I guess this contribution is a little more expensive than its equivalent sourced by, say, gas. Of course if we move more to nuclear/wind power then I suppose it could be considered a lower carbon contribution
Regarding the datasheet about pulse modulation - I should just point out to anyone reading that this is the Sauter data sheet not ours. As David suggests it would be possible to do this in principle but probably needs some study to work out the linearisation mapping and probably unwarranted in general situations. However there are proprtional motorised drives from Sauter as well as other manufacturers (which we ourselves don't stock). These are typically 1-10V input so could in theory be positioned by a QAO module.Comment
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completely agree, on all counts !
just a bit odd that they talk about pulse modulation with this sort of device & yet not really make it clear (*) how to achieve it / achieve useful results - why didn't they simply refer to their other valves for when proportional operation might be required ?
using auto-adjusting pumps & throttle valves seems a bit of a strange way of adjusting heat flows, but I guess it's a natural development on from using fixed rate pumps with TRVs, just as the TRVs were a natural step on from manually adjustable valves - all in the days before electronics - the main driver for them, I suppose, was compatibility & retrofit !
(*) the not-very good translation from the original Schweizerdeutsch doesn't help, of course !Last edited by chris_j_hunter; 18 March 2009, 08:53 AM.Comment
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PS: just to tie the loose-ends ...
there are two Sauter options for achieving 0-10V continuous control :
motorised AXM117S :
thermal AXS111S:
the term continuous having a double meaning ... the 0-10V must be continuously applied, and the adjustment between extremes is continuous - not sure of the resolution though !
both are retrofitable onto their VUL unit control (as against on-off) valves :
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