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Topic: Heating automation (Read 1 time) previous topic - next topic

ralfeus

Hi
I've got an idea to automate heating in my apartment and now want to understand where I can start.
My heating system uses radiators with valves controlled manually now. I want to replace those manual ones with another, that could be controlled by Arduino.
I know there are "smart" thermostatic heads available on the market. But they use own controlling system, whilst I want to have it as a part of "smart home". So my idea is that:
- have electrically controlled radiator valves
- have Arduino module controlling valves
- have Arduino radio module (wifi, BT or pure radio) to get commands from central unit

The central unit would get data from temperature sensors and adjust temperature based on other data as well (time, day, outside temperature etc).

I've found out there are thermoelectric valves powered either by AC 230V or DC 24V. Both types are controlled by some specialized control units. I'm not sure whether such pieces can be controlled by Arduino, so hence the question: are there any heating radiator valves that can be controlled by Arduino?

Thank you

gilshultz

Most will work, you just have to design an interface.  Are you going to use bang bang regulation, proportional or pwm. You need to pick the appropriate actuator and the appropriate driver.  The hard part is installing the valve.  Since the valves will work without being piped in debug everything, this way you can see what is happening and will not have to get out the electric underwear.  
Good Luck & Have Fun!
Gil

ralfeus

Hi
Thanks for reply. Valve is already installed. Now it has manual head, which controls valves just by setting some level of temperature. So replacing those heads with electric ones should be a problem.

> Are you going to use bang bang regulation, proportional or pwm

No idea :-) Where can I read about difference?

> You need to pick the appropriate actuator and the appropriate driver.

And how to choose appropriate one?

steve1001

You should be able to find an actuator to replace your existing thermostatic valve heads. What make are they?
The thread is commonly an m30x1.5 I think.
The spindles inside the valve bodies seem to vary in length, so you may find a problem there, but you won't know until you try something.
I fitted some electric valve heads years ago on a job, but I am a bit vague on the wiring. The one I fitted were low voltage. A transformer supplied power to a room thermostat. The stat just  switched the power to the valves, on and off. 
If using a 240V actuator, I would think you just supply a 240V feed to it.
I had a quick search and found the Honeywell M4450A head. The wiring diagram for it suggests you just switch 240V to supply it. The manual suggests that the actuator has an opening and closing time, so there is some control circuitry in the head.
Maybe just splash out and buy a cheap head, and experiment with it.
All you need is the Arduino to control a relay; and the relay supplies the 240v to the actuator head.

Steve

ralfeus

Thanks
Do I understand correctly that its works on a simple principle: when it's powered it opens in some time (4-5 minutes), when it's not powered, it closes?

High voltage means I'd need to supply wiring for each radiator, which I'd like to avoid. Are there actuators, that use low voltage so they could be powered by a battery?

steve1001

Just google '12V Radiator Valve' and see actuators there are out there.

Also, search for 'Honeywell MT4-230-NC' and read the manufacturers data sheet.
In that data sheet, it says .. quote "When the operating current is applied, a PTC resistor heats up a wax element. After a delay, this wax element expands, causing stroke movement."

So, without power to the actuator head, the spindle in the radiator valve is up and open. When the head is powered, the wax element in the head gets heated up, via a resistor, and eventually expands. The head mechanism, which has expanded, then pushes down on the valve spindle, which closes off the flow of water through the valve.

I learnt something new today. Those heads are 'Linear Thermoelectric Actuators'. I always assumed there was some small motor in them!

I doubt if you will have much luck making a battery powered Arduino system for each radiator location. I would have the Arduino system in a remote location, powered via a transformer, and just run a 2 core bell wire along the skirting board to provide the valve head with power.

Steve
 

gilshultz

 


A water heater that maintains desired temperature by turning the applied power on and off (as opposed to continuously varying electrical voltage or current) based on temperature feedback is an example application of bang-bang control. Although the applied power switches from one discrete state to another, the water temperature will remain relatively constant due to the slow nature of temperature changes in materials. Hence, the regulated temperature is like a sliding mode of the variable structure system setup by the bang-bang controller.



Symbol for a bang-bang control

In control theory, a bang-bang controller (2 step or on-off controller), also known as a hysteresis controller, is a feedback controller that switches abruptly between two states. These controllers may be realized in terms of any element that provides hysteresis. They are often used to control a plant that accepts a binary input, for example a furnace that is either completely on or completely off. Most common residential thermostats are bang-bang controllers. The Heaviside step function in its discrete form is an example of a bang-bang control signal. Due to the discontinuous control signal, systems that include bang-bang controllers are variable structure systems, and bang-bang controllers are thus variable structure controllers.
Mathematically or within a computing context there may be no problems, but the physical realization of bang-bang control systems gives rise to several complications.


First, depending on the width of the hysteresis gap and inertia in the process, there will be an oscillating error signal around the desired set point value (e.g., temperature), often saw-tooth shaped. Room temperature may become uncomfortable just before the next switch 'ON' event. Alternatively, a narrow hysteresis gap will lead to frequent on/off switching, which is undesirable for, e.g., an electrically ignited gas heater.


Second, the onset of the step function may entail, for example, a high electrical current and/or sudden heating and expansion of metal vessels, ultimately leading to metal fatigue or other wear-and-tear effects. Where possible, continuous control, such as in PID control will avoid problems caused by the brisk physical system state transitions that are the consequence of bang-bang control.

The above from "https://en.wikipedia.org/wiki/Bang%E2%80%93bang_control"
Here is a very good explanation: https://www.fourmilab.ch/hackdiet/www/subsection1_2_3_0_5.html

Good Luck & Have Fun!

Gil




ralfeus

#7
Nov 18, 2019, 09:38 am Last Edit: Nov 18, 2019, 09:57 am by ralfeus
Thank's a lot! Now I'm much smarter :-)

May be last question. Documentation of actuators I've found don't contain the control design. There is only recommendation of specific control unit. What would be standard approach to figure out the control design? Find a documentation of the actuator or just go to datasheet of recommended control unit?

gilshultz

Sorry but I cannot answer that question, that is up to the system engineer to specify, probably you. My guess is you probably will go to a PID (Proportional Integral Derivative) controller with a variable actuator but that is your decision. I hope you are good at math if you get deep into it.  Stanford offered a course in the year 2000 time frame that was extremely good. To close the loop you will need at a minimum inside, outside and water temperatures.
Good Luck & Have Fun!
Gil


BlueRidgeDog

Thank's a lot! Now I'm much smarter :-)

May be last question. Documentation of actuators I've found don't contain the control design. There is only recommendation of specific control unit. What would be standard approach to figure out the control design? Find a documentation of the actuator or just go to datasheet of recommended control unit?
I have not had a radiator in a long time, but I recall my last ones were not on/off in response to the valve.  Opening it a little gave a little heat, opening it all the way gave max heat.

I would observe one of the off the shelf units (get a 12v one).  Put a scope on it and see what it does and why it does it.  Is it bang-bang (all or nothing) or is it doing a "open more if we are further from the setpoint". 

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