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Measuring temperature on bathroom floor


Ole
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Hi!

 

Does anyone have a good solution for monitoring the floor surface temperature on a bathroom floor that can't use a regular floor sensor? I am finding it surprisingly difficult to find a surface sensor that I can just tape to the floor underneath a shelf and connect to a Z-wave unit. Or is there another solution that is even better?

 

Cheers!

Ole

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What kind of accuracy do you expect?

 

IMHO the least amount of effort would be a Fibaro D/W 2 because it has a temp sensor built in. The sensor would not be in direct contact with the floor so measures something between air temp and floor temp. Plus, it has a bug which causes "spikes". There's a post about that problem:

 

 

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The "Flood Sensor" does not have the "spike" issue but it also has the sensor a bit above the floor

 

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But for myself, I wanted really good results, I would do some DIY

 

I would buy a few known brand DS18B20 from a reputable source, for example:

 

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Oh My! I bought several of those years ago, they were about 1 1/2 EUR each. Corona + chip shortage + war -> 5 EUR.

 

Do not be tempted to buy from unknown sources or buy any of the "waterproof sensors". Read this first!

 

 

I would then think long and hard about how to make it waterproof and get it glued to the floor. :D

 

You can attach a few of those to the smart implant

 

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You would also need a small power supply that meets regulations for bathrooms in your country.

 

It would be "mains operated" (I prefer that to battery devices) and the 12-24 V supply would make it safe...

 

Does this help?

 

 

 

 

 

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  • On 6/2/2022 at 1:01 PM, petergebruers said:

    What kind of accuracy do you expect?

     

    IMHO the least amount of effort would be a Fibaro D/W 2 because it has a temp sensor built in. The sensor would not be in direct contact with the floor so measures something between air temp and floor temp. Plus, it has a bug which causes "spikes". There's a post about that problem:

     

     

    Please login or register to see this link.

     

    The "Flood Sensor" does not have the "spike" issue but it also has the sensor a bit above the floor

     

    Please login or register to see this link.

     

    But for myself, I wanted really good results, I would do some DIY

     

    I would buy a few known brand DS18B20 from a reputable source, for example:

     

    Please login or register to see this link.

     

    Oh My! I bought several of those years ago, they were about 1 1/2 EUR each. Corona + chip shortage + war -> 5 EUR.

     

    Do not be tempted to buy from unknown sources or buy any of the "waterproof sensors". Read this first!

     

     

    I would then think long and hard about how to make it waterproof and get it glued to the floor. :D

     

    You can attach a few of those to the smart implant

     

    Please login or register to see this link.

     

    You would also need a small power supply that meets regulations for bathrooms in your country.

     

    It would be "mains operated" (I prefer that to battery devices) and the 12-24 V supply would make it safe...

     

    Does this help?

     

     

     

     

     

    Thank you for taking the time Peter! I was looking at something like the Secure SES302 and connect a NTC surface sensor to it. It has a default report interval of 5 minutes which should be ok for controlling the floor heating. I am now looking for a good quality NTC sensor that can be taped or otherwise fastened to the floor. It doesn't have to be the exact temp of the floor as I could just use offset. The only sensor by Secure is one for water tanks and pipes, not for flat surface. Any tips for one of those?

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    Posted (edited)
    42 minutes ago, Ole said:

    which should be ok for controlling the floor heating

    Ah! Originally you said "for monitoring the floor surface temperature" which I consider to be a totally different thing. But that is not a problem, just a misunderstanding.

     

    42 minutes ago, Ole said:

    Secure SES302 and connect a NTC surface sensor to it

    I agree, for controlling a heater, any heater, the right way to do it is to use a thermostat - because those devices can operate on their own, do not depend on algorithms running on a gateway that might be unreachable or rebooting etcetera.

     

    42 minutes ago, Ole said:

    Any tips for one of those?

    Unfortunately, I use "classic water based radiator heating" and no floor heating. I am not qualified to give you recommendations. I try to know where my limits are ;)

     

    That said, I monitor this forum and I know a lot has been said about "heatit" thermostats, their HCx compatibility and fir;ware versions... So thread carefully but this might be a starting point for you to do some research

     

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    But I don't see a sensor specifically to mount on a floor.......... Isn't such a device usually embedded or in a tube in your floor? Just talking out loud.

     

    Their thermostats can be configured for different values of NTC, default is 10 k but they also do 47 k.

     

    I actually have a bag full of NTCs in various sizes and specifications but none of them in a "sealed" package, so most of mine look like this

     

    1392849607_Screenshot2022-06-03at14_08_46.png.3387620796eef1a4636dd6d1466f1ae7.png

     

    When I look on aliexpress for "NTC Thermistor Temperature Sensor 3950 waterproof" you typically get one of those in a sealed metal tube with 1 or 2 m of wire, like this:

     

    2080380637_Screenshot2022-06-03at14_13_22.png.ded8cbbb39393612f5047e9cb979abe3.png

     

    Is this really waterproof? I do not know! For long term stability it is very important to seal an NTC, without that its properties will change over time.

     

    If it is for monitoring, I would choose the DS18B20 because it is a digital sensor and very stable over time. I do not know about thermostats using such a digital sensor, to control underfloor heating :(

     

    To make it a little bit more complicated, NTCs do not only have a resistance value at 25 C, they also have a "beta coefficient" which tells how steep its temperature curve is. If you do not see it mentioned, a typical value is 3900

     

    If I use "waterproof" and "ntc" as a search criterium on TME then I find this sensor which might do what you want, if you find a thermostat to go along with it:

     

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    Looks like this:

     

    2048002791_Screenshot2022-06-03at14_25_48.png.226ce55b2a6edaac1248d2b01d0fc3ba.png

     

    So..... Nah.... Not ideal because the question remains, how to properly make contact with the floor.

     

    You want my honest opinion? I think measuring and controlling under floor heating is not something trivial and I am not the right person to ask. But I do like to chat about temperature sensing and control.

     

    Is there an "under floor heating specialist" on this forum?

     

     

     

     

    Edited by petergebruers
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    @Ole, you would need to install it into the floor to get correct temperature to not risk burning the floor. Guys behind underfloor heating need to tell you maximum temperature. Here in Czech it is something between 25-30°C, depending on floor material.

     

    Honestly, I would choose thermostat for underfloor heating, that can do temperature measurements and limit floor temperature and do the regulation. With KNX system we can use device (such as

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    ) with temperature sensors connected and set Group adress (very simmilar to association) and connect temperature of the floor to heat regulator. I do not know any devices that can do that via Z-Wave.

     

    1 hour ago, petergebruers said:

    Is there an "under floor heating specialist" on this forum?

    I'm not expert but we do sometimes work with them to get system (those we sell), not just Fibaro, ready.

     

    1 hour ago, petergebruers said:

    If it is for monitoring, I would choose the DS18B20 because it is a digital sensor and very stable over time. I do not know about thermostats using such a digital sensor, to control underfloor heating :(

    That is one way to measure temperature, but you would need to write regulator into Home Center, but I would not like such regulator to be dependant on Home Center.

     

    1 hour ago, petergebruers said:

    1 or 2 m of wire

    For underfloor heating you would need 3 meters. 1,5 m down to floor and 1,5 meter into the floor.

     

    1 hour ago, petergebruers said:

    Their thermostats can be configured for different values of NTC, default is 10 k but they also do 47 k.

    We do MCO Home thermostats (MH7 and MH8). For those you can do only 15k Ohm. Manytimes in retrofitting you with thermostat change no one want to dig old sensor from the floor. So I teach trainees with heating background to get tables for converting from anything to 15k Ohm. It is not that accurate, but close enough.

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  • Thanks to you both for your input. And yes there has been some misunderstandings and I probably wasn't clear. My problem is as follows: I have a Z-Wave thermostat that controls the floor heating, but I do not have a in-floor tube to insert a NTC floor sensor into and therefore it only operates based on the air temperature in my bathroom. When the sun hits that side of the house, the air temperature rises and the floor heating is switched off for several hours causing the floor to get cold. So therefor I switched the thermostat to power regulator mode and thought I could monitor the temperature on the floor surface to change the gain on the power regulator using scenes. And the sensor doesn't need to be 100 % waterproof as that part of the floor is always dry. And if it gets wet I have bigger problems than to replace a broken sensor ;)

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    Posted (edited)

    Ah, I had a hunch about what you were trying to do but your post certainly makes it 100% clear to me!

     

    On 6/7/2022 at 10:40 AM, Ole said:

    I have a Z-Wave thermostat that controls the floor heating

    Okidoki, so the manual of that thermostat should make it clear what kind of sensor it expects. The 10k NTC is certainly popular but I wouldn't try to guess it.

     

    On 6/7/2022 at 10:40 AM, Ole said:

    but I do not have a in-floor tube to insert a NTC floor sensor into

    Okay, to be on the safe side here, this is not my field of expertise. @jakub.jezek seems to agree with me that the usual, and probably "correct" position of the sensor is in the concrete floor, actually somewhat close to the heating element. The idea behind that is ... building materials are often surprisingly good "insulators". Let me rephrase that, between good conductors like metals and insulation material, brick and concrete are bad conductors. So putting your sensor on top of the concrete will make it respond too late (later than a sensor in the concrete) and it will measure too low in case the temp inside the floor matters. For the last part, I do know water heated systems are not like electrical systems, a safety unit on the water pipe will prevent overheating of the floor.

     

    But since that is not an easy fix, and your "air temp sensor" did not cause any troubles besides the fact that it does not control the floor the way you want... You got that covered or by design it is not a big issue.

     

    But please do check if your concept is safe.

     

    On 6/7/2022 at 10:40 AM, Ole said:

    When the sun hits that side of the house, the air temperature rises and the floor heating is switched off for several hours causing the floor to get cold.

    Yup, totally understand that problem and in control theory this is what causes people's headaches: delays in the response, delays in the measurement. You need a more "predictive" algorithm and I agree with you, having only the air temperature will make it more difficult than having that one but also the floor temp. Although I think the floor temperature can be somewhat predicted by the power you send to it, and the time that power is on. The thermal constant of the system is based on the amount of building materials.

     

    On 6/7/2022 at 10:40 AM, Ole said:

    So therefor I switched the thermostat to power regulator mode and thought I could monitor the temperature on the floor surface to change the gain on the power regulator using scenes.

    I have never tried to control such a system, the closest I get is my "3D printer". The firmware is based on "Marlin" (on Github) and it uses a PID algorithm. You can find lots of resources online but they often omit some important stuff. For example, Marlin PID does not have a "Integral Windup Protection", instead it uses a simple switch from bang-bang control to PID control.

     

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    I added windup control to the algorithm for my printer, it does outperform the original algorithm, but that does not make me an expert :D

     

    I think it is worth researching that topic if you have not done so. Simply put The "P"roportional part is what gives you basic control, but is has no long term vesion and does not anticipate. So you add "D"erivative (aka differential) control which is kind of a predictor. The D can slow down the heating because it takes into account the fact that the heating at the surface does not stop when you turn of the heater. The "I"ntegral part knows that the P part always needs an "error" and can never reach target and helps by slowly adding a correction.

     

    On 6/7/2022 at 10:40 AM, Ole said:

    And the sensor doesn't need to be 100 % waterproof as that part of the floor is always dry. And if it gets wet I have bigger problems than to replace a broken sensor ;)

    Okay, they are cheap and replaceable. But keep in mind that some Z-Wave modules use a non-isolated power supply so the sensor might actually be "live". It is one of the reasons I've already mentioned the "Fibaro smart implant + power supply that meets regulations for bathrooms in your country.". I expect a properly designed module for under floor heating to meet that requirement, but generic modules (the old Qubino on/off thermostat comes to mind) can be mains referenced.

    Edited by petergebruers
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