Fan assised radiators and water flow control?

[ericmark]

Old house had fan assisted radiator, (Myson) fitted around 1980 so quite old, as was the boiler, however there were a list of advantages and disadvantages and on the down side is water is not switched off when room is warm, it just switches off the fan.

Mixing water flow control and air flow control is hit and miss, having a fan assisted radiator which still controls water flow would seem better if not fitting fan assisted radiators to all rooms.

However the question is how will it work where radiators are often only just warm? The add on system https://www.radfan.com switches on/off it seems as radiator warms up or cools down, but how does that effect the radiators TRV?

 

[foxhole]

Why is it a disadvantage .? Pump needs to run on after stat is satisfied.
Trv should be unaffected as air flow near rad will be about the same .
Why are rads just warm? Boiler temp should keep them stable temp?

 

[ericmark]

Why is it a disadvantage .? Pump needs to run on after stat is satisfied.
Trv should be unaffected as air flow near rad will be about the same .
Why are rads just warm? Boiler temp should keep them stable temp?

That does not seem correct? I thought boiler temperature is maximum temperature any radiator will reach, but under normal operation the TRV restricts flow, so radiator should be a lot cooler than boiler unless using OpenTherm or similar which will reduce water temperature when demand is low?

If the fan gradually increased speed as the radiators got warmer I can see they would work without a problem, however it seems just two settings on and off, now radiator will naturally increase flow as it gets warmer with thermo syphon of air, and air should naturally circulate in the room which is why mounting a thermostat on opposite wall works, the fan needs to increase the air flow, the venturi effect can mean fans will suck the air around them so possibly do not need to fill the deflector tube, but two fans with width shown one wonders if they will circulate air through room or just the device, possibly they will help as deflecting air from wall, but as to heating room faster, not so sure a processor fan from a computer is fast enough to be better than standard thermal circulation, and if using a more powerful fan then would think it would need to be multi speed so it matched heat output of radiator.

I tried to use an upright fan to blow air from TRV end to lock shield valve end to increase radiator output, I used a thermostat connected to return pipe to activate fan, it of sorts worked, however it caused the TRV head to continually modify flow rate and it cooled radiator too much, so fan was switching on/off all the time, and batteries went flat in the TRV. It was this experiment which makes me think it will not work, the Myson radiator does not restrict water flow, and the heat exchanger matrix is more like a car radiator painted black and with huge amounts of cooling fins, switching them off means the output is near zero so there is a thermostat which just controls the fan, newer models have multi-speed fans, my old model has a manually variable speed fan.

So I can see with a double radiator how a unit which is thermostatically controlled blowing from bottom of radiator so monitoring temperature of return air and with TRV turned to maximum you could extract more heat from a standard radiator, however all it does if the radiator was correct size is speed up time to heat room, and in theory the faster you heat the room the less energy is required as you can start heating the room latter, however to be able to control when a room is heated means having a valve which is timed, so you would need an electronic TRV head to be able to use the faster speed.

So the fan needs to work with the eTRV head not against it, so a IFTTT link to the eTRV head seems most likely method. However that does not exist.

 

[foxhole]

TRV controlls flow not temp of water, temp set is achieved and it shuts off but supply too it remains at boiler set temp.
You will not extract more heat from the radiator, merely speed the warm air movement from it.
I have plinth heater, the fan runs whenever the hot water temp is detected the temp controlled by room stat.

 

[ericmark]

I am told by RadFan that it does not run fast enough to alter temperature of return water, I suppose that means it just moves heat around the room. Also told it starts running when radiator at 42 deg C and off at 38 reg C I have not measured temperature of radiator, at this time of year they are never hot, I am told TRV's fully open and fully close, I think that is unlikely, however even if they do, the result is radiators maintain temperature without getting very hot as to if hot enough I will need to measure.

With modulating boilers the water temperature varies, I am lead to understand best practice is for the TRV to tell a central hub the heat it requires and in turn the central hub often called a thermostat as it often shows temperature, and in turn this tells the boiler what temperature is required by connection to the bus, old or cheap systems don't do this, but there is nothing to say fans only suitable for old or cheap systems.

So how it works would very much depend on the system used for control.