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| Multi-circuit water floor heating controller |
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| elcaron:
Hi, I would like to get some input for a project I am currently planning. Introduction I just moved into a new apartment with central water floor heating, which is currently controlled by bi-metallic thermostats. Unfortunately, I am quite underwhelmed by the performance. Since the house is reasonably well insulated, and the stone floor has very high heat capacity, we have bang-bang controller cycles >1d, so some days, the floor is cold, some days it is warm, temperature under- and overshoots ... it is not pleasant. I could probably counteract this be limiting the flow, but then I would waste power in the high efficiency pump. (Essentially that should be equivalent to current limiting with a resistor.) So something has to be done. Unfortunately, I have only 3 power cable wires available to the thermostats, one color-coded PE. With this, I am not willing to install any digital controllers that rely on 3 wires for L, N, L-switched cables. It seems that I will have to cook up something myself. About myself I am a mainly theoretical physicist in research. My electronics skills are developed as hobby, but reasonably well backed by my profession. Firm in algorithms and coding. DIY state of the art I found e.g. this project. It is a nice project, but I would like to solve it little differently. What is available - European style (round 60mm) outlet sockets in each of 7 rooms that currently hold the bimetallic themrostats ... - ... each directly connected with 3x1.5mm² power cable (blue,brown,yellow-green) to the room with the circuit distributor and the valves. Cable length <20m. - 9 water circuits, each with a 230V 2W valve, opening and closing time about 3min. No half open state available and probably non desired for pump-efficiency reasons (see above). 3 of the circuits are in a single room and are currently controlled by one thermostate (valves wired in parallel). What I have come up with by now I would like to place a new unit in the thermostat sockets, each one equipped with an 0.96" oled screen, a BME680 and probably an ESP12. I would like to power the unit over the brown and blue wires with 5V (LDO to 3.3V at unit), and use the green-yellow one for single wire data transfer for long term compatibility (don't want to base it on wifi if I do not have to). At the controller, I want to aggregate the data and and implement a PID-style controller that controls all the circuits in ~30min PWM intervals to keep a relatively stable ground temperature. What I not have made my mind up about fully - I would prefer to keep the 230V valves. Due to the PWM, I would like to avoid mechanical relays. On the other hand, some SSR might have problems with the low current. - I am not sure yet how to transfer the data bidirectionally over ~15m power cable on a single wire. Open-drain with MOSFETs and strong pullups? What protection should I place? Schmitt trigger? ESD protection? Or would 1-wire work reliably with a driver like the DS2482? I would be very happy if I would get away only one hardware version without revisions, so I would like to get this right on the first try. Programming will be interesting enough. Any ideas on the unclear parts? Issues? Improvements? |
| Zero999:
Sorry, I can't be a huge help with this, since it's not something I've done before. The one thing which stood out to me is using the green & yellow wire for data transfer, which would violate the wiring regulations anywhere in Europe. The green and yellow wire shall only be used as a protective earth connection, never for power or data. Rather than using the earth wire for data, it's possible to transmit it over the mains cable, which is perfectly safe, if done properly. |
| coppercone2:
This is a problem i have too. I find myself opening the window with a fan right now. My solution is gonna be to weigh it less for full room heating and compliment it with air vents lol. The floor is too much to monkey around with imo. |
| alanambrose:
Hi, I'm in the middle of reverse engineering my own setup, which is an Uponor 'Smatrix Base' thing so I'm starting to understand these systems. They're actually medium complicated - in that they involve a mix of heating in the 5-20kW range; valves, actuators, flow limiters, pumps, filling, draining, by-pass, blending valves; fail-safes; overall thermostat limiters; flow balancing; pump exercise etc etc etc .... besides the electronics, and room thermostats see e.g. http://www.pexa.com.tr/manifold/ I'm not sure how much control you have - is this a system you have complete control over, or are you piped hot water from some central source and you only have control over the valves and thermostats? Bang-bang will work fine - my system takes 9 hours to raise the temperature 1 degree C. The stat resolution is 0.1 degree F (about 0.05 degree C) so bang bang should keep within say 0.2 degrees and switch maybe every 1/2 hour. Suggest checking out the commercial systems (for residential) if only to see how they all hang together. Rolling your own won't be crazy difficult but there are some important things to get right to avoid overly heating your pipes etc. You'll see commercial systems with 24V or 230V actuator valves, rs485 or wireless data from sensors to controller etc. Maybe you can finesse a solution out faster and simpler - e.g. it sounds like your thermostats simply have too much 'dead time'. Alan |
| jbb:
This is interesting. I’d like to clarify a couple of things. 1) do you have all the valves in one location? You imply you want a central controller. 2) do you have access to both ends of the wiring without too much trouble? I agree that yellow/green should remain protective earth for safety (and wiring compliance) Getting power and data over 2 wires is a classic problem. What exactly do you want to send / receive? Two schemes for two-wire power+comms which come to mind are a classic 4-20mA current loop (very popular in industrial plants and building management) and some 2-wire version of LIN (found this app note, don’t know how good it is). For pretty much any such scheme, you have limited power available at the slave node, so I suggest a non-backlit LCD for the ‘thermostats.’ Reducing power dissipation here also reduces self heating and improves temperature measurement accuracy. Example 1: the electronics in a 4-20mA device must consume <4mA. With a standard linear regulator, your budget is around 3.5mA @ 3.3V, which is enough to run a micro, small LCD (no backlight) temperature sensor and a couple of buttons. Example 2: 4-20mA device with switching power supply. Assuming 12V drop across device, power budget is 3.5mA * 12V * PSU efficiency (say 75%). This nets you around 32mW, or approx 10mA at 3.3V. Still not enough to run an OLED |
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