I think the ideal control setup is individual electronic control for each zone - where zone is a single room in a conventional house, or maybe part of a room in an open plan layout. If the individual controls are networked back to the boiler - you can have a system where the boiler fires when any zone needs heat.
Yes, the electro-thermal-hydraulic actuators are nominally on-off. However, they have a slow opening and closing rate - and if you switch them on and off rapidly then you will get a very crude proportional control. If you have a sensitive stat with a very minimal hysteresis then it can turn the valve head on/off with quite small changes in temperature, and you may just get something close to what a basic TRV does.
IIRC we used Honeywell valves and actuators, and I checked with them on this - they said there's no restriction on duty cycle.
The ones we used had an on-delay of up to 2 minutes - ie if the wax was completely cold then it could take up to 2 minutes to open the valve. Similarly, there's a closing delay which could be up to 5 minutes if the wax was "fully hot". But switch the power off when it's only partially open and it'll start to close again quite quickly - and similarly, if you turn the power on while the valve is still closing then it'll start to open quite quickly.
So combine them with a very sensitive stat and I think they'd work - but you'd need to try it to find out. After a quick look, it does seem like they've been updated a bit since I was working with them - example here. You need to match the stroke with the valve - for the fan coil units we were using 4 port valves and 8mm stroke actuators, for radiator valves, they tend to be shorter stroke so you'd want the 4mm version.
Yes, the electro-thermal-hydraulic actuators are nominally on-off. However, they have a slow opening and closing rate - and if you switch them on and off rapidly then you will get a very crude proportional control. If you have a sensitive stat with a very minimal hysteresis then it can turn the valve head on/off with quite small changes in temperature, and you may just get something close to what a basic TRV does.
IIRC we used Honeywell valves and actuators, and I checked with them on this - they said there's no restriction on duty cycle.
The ones we used had an on-delay of up to 2 minutes - ie if the wax was completely cold then it could take up to 2 minutes to open the valve. Similarly, there's a closing delay which could be up to 5 minutes if the wax was "fully hot". But switch the power off when it's only partially open and it'll start to close again quite quickly - and similarly, if you turn the power on while the valve is still closing then it'll start to open quite quickly.
So combine them with a very sensitive stat and I think they'd work - but you'd need to try it to find out. After a quick look, it does seem like they've been updated a bit since I was working with them - example here. You need to match the stroke with the valve - for the fan coil units we were using 4 port valves and 8mm stroke actuators, for radiator valves, they tend to be shorter stroke so you'd want the 4mm version.