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Heating and cooling: Help me understand UFH actuators…

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    • CommentAuthorringi
    • CommentTimeDec 19th 2015
     
    (I am thinking of using them with a radiator based system with lots of zones, so will not have the thermal mass of the floor to even out the response.)

    I know that there are 3 types, 240v, 12v (or 24v) and 0-10v proportional.

    Firstly I have seen that at least some actuators take 3 minutes to open when they are powered. How does such a slow response allow a TPI thermostat to work, or any thermostat to keep the temperature constant in a room?

    How do I control a proportional actuator, it seems that standard thermostats don’t support them?

    Given a choose I would like a fully wired system, as I don't trust wireless to remain pain free and the building is at a stage where putting wires in is easy.
    • CommentAuthorcjard
    • CommentTimeDec 19th 2015 edited
     
    The system is balanced in terms of flow rate by use of taps on every pipe on the hot rail.. Flow depends essentially on loop lengh and desired heat emission is more a function of floor construction and covering and water temperature

    The actuator goes on the cold rail of the manifold and is essentially an electronic tap

    The thermostat sits in the room and the room temp is either above below or at the target temperature. Below temp the stat "calls for heat" and the actor opens. The stat continues in call mode until the temperature of the room is above the limit. It stops calling, the tap shuts, the heat source fades and the room cools, goes below the target temp, then the stat calls for heat again. Most stats should have a buffer zone, whereby for example they stop calling above 21 and start calling below 19 when striving for 20 degrees. This prevents rapid cycling on the actuator

    Having an actuator take 3 mins to open would also implement a buffer in case the stat does not, and it would avoid rapid flow rate changes in the system, noise etc. If your pump is an intelligent constant pressure one it will allow it to gradually change its output.

    Never read anything on proportional actuators but I guess it would likely be an extension of the buffering idea, so the stat can request incrementally smaller changes when it is operating in or near the buffer zone, rather than being on off, it could be 25%/75% and vary between 19.8 and 20.2

    Using them with a rad system shouldn't really be that much different, you still balance your radiators so the plumbing between rads could be thought of as one massive manifold. The actuators take the place of TRVs I presume, and as TRVs are proportional you may be better off wih proportional acts and stats that understand them
    • CommentAuthorwookey
    • CommentTimeDec 20th 2015 edited
     
    Posted By: ringiHow do I control a proportional actuator, it seems that standard thermostats don’t support them?


    Supply 0-10V, depending how open you want it :-)

    That's a standard control signal, available from various PLCs or a microcontroller.

    E.g, if using a microcontroller:
    This will convert a PWM to 0-10V: (from the last post on http://www.eevblog.com/forum/projects/0-10v-led-driver-control-with-microcontroller/ )
    http://www.falstad.com/circuit/circuitjs.html?cct=%24+1+5.0E-6+10.20027730826997+57+5.0+50%0Ag+128+224+128+272+0%0Aw+256+176+256+224+0%0Aa+256+160+400+160+1+15.0+-15.0+1000000.0%0Aw+400+160+400+224+0%0Ar+256+224+400+224+0+2000.0%0Ar+160+224+256+224+0+2000.0%0Aw+256+80+256+144+0%0AO+400+160+464+160+0%0Aw+128+224+160+224+0%0Ar+128+80+176+80+0+4700.0%0Ac+176+80+176+128+0+4.7E-5+3.746293688163822%0Ag+176+128+176+144+0%0Aw+176+80+256+80+0%0Aw+128+80+112+80+0%0AR+96+80+48+80+0+2+500.0+2.5+2.5+0.0+0.75%0Aw+96+80+112+80+0%0Ao+15+64+0+35+5.0+0.00625+0+-1%0Ao+12+64+0+35+5.0+9.765625E-5+1+-1%0Ao+7+64+0+34+10.0+9.765625E-5+2+-1%0A

    That site is a nifty little circuit simulator!

    The other (input) side of your microcontroller can speak serial or modbus or 1-wire or opentherm or I2C or whatever is trendy these days. Ideally someone has made a suitable gadget that does this already, but I've not been following this automation stuff recently (it's all 1-wire in my house, and connecting up the UFH actuators is a long way down my list. Ask me again in 2-3 years time :-)
    • CommentAuthorringi
    • CommentTimeDec 20th 2015
     
    Wookey, I was hoping for thermostats and UFH wiring center that did it all for me.
    •  
      CommentAuthordjh
    • CommentTimeDec 21st 2015
     
    Posted By: ringiWookey, I was hoping for thermostats and UFH wiring center that did it all for me.

    A thermostat doesn't really provide enough information for good control. Better to start with something that actually measures the temperature, like a thermistor. My MVHR post heater has a thermistor (well, two actually*) and its logic unit uses those inputs to vary the power supplied to the heating coil. I expect there are separate control units that support thermistor inputs that work in a similar way.

    * The second thermistor is used to limit the in-duct temperature.
    • CommentAuthorringi
    • CommentTimeDec 21st 2015
     
    djh,
    I consider a "thermostat" to be the box I put on the wall, that allows me to set how warm I want the room to be.
    •  
      CommentAuthordjh
    • CommentTimeDec 21st 2015
     
    Posted By: ringidjh,
    I consider a "thermostat" to be the box I put on the wall, that allows me to set how warm I want the room to be.

    Well, you're entitled to call things whatever you like, but it's generally more productive to use the same terminology as other people, especially when you're looking for advice, so there's less chance of misunderstanding. Wikipedia explains:

    A thermostat is an instance of a "bang-bang controller" as the heating or cooling system output is not proportional to the difference between actual temperature and the set temperature; the equipment runs at full capacity until the set temperature is reached, then shuts off. Increasing the difference between the thermostat setting and the desired temperature therefore does not shorten the time to achieve the desired temperature.

    The term is derived from the Greek words θερμός thermos, "hot" and στατός statos, "standing, stationary".

    It doesn't help that some manufacturers of 'smart' sensors call them stats. But generally, you need to look for a sensor that is capable of providing temperature measurements to the controller, as I said. And to a first approximation, if it's called a 'stat' then it doesn't do that.

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