Can a slab be too thick to have UFH pipes in it?

[Thorfun]

that's great. thanks guys. I'll do some more research on the probes before pulling the trigger today or tomorrow.

[Nickfromwales]

If you use 16mm pipes for conduits for the probes, fit proper cap ends so they don’t back fill with the concrete slurry  

[Thorfun]

just spoke to Wunda technical support and their probes have 2 wires and he said they're not proprietary and should work with other systems. they work with the Heatmiser systems that Wunda also supply so I see no reasons why they shouldn't work with Loxone.

 

@Dan F I do notice that the Loxone ones have 3 wires though. do you know what the benefit of that would be? @Rob99? maybe this is something you would know about?

[Dan F]

54 minutes ago, Nickfromwales said:

Wunda don’t do the uber low temp pump and blending set atm

 

What is there special about low-temp pump, or is it the blender?  What would you reocmmened for low-temp UFH + cooling?

[Dan F]

26 minutes ago, Thorfun said:

@Dan F I do notice that the Loxone ones have 3 wires though. do you know what the benefit of that would be? @Rob99? maybe this is something you would know about?

 

Few things though:

- 1-wire is digitial and sends back exact temperature rather than any kind of analog signal. 

- Loxone polls sensor every x seconds.

- Sensor needs power.  Two options:

     i) It gets power via data line and stores it in internal capactitor

    ii) It has power supplied seperatly (thrid wire).

 

Ton of more detailed information on 1-wire protocol online, but loxone summarize the basics here: https://www.loxone.com/enen/kb/wiring-1-wire-devices/

 

 

[PeterW]

loxone uses a DS18B20 sensor, Heatmiser uses an NTC thermistor. You can apparently use the AI Extension to convert to digital but given 10m DS18 sensors are as cheap as chips why would you ..??

[Thorfun]

19 minutes ago, Dan F said:

 

Few things though:

- 1-wire is digitial and sends back exact temperature rather than any kind of analog signal. 

- Loxone polls sensor every x seconds.

- Sensor needs power.  Two options:

     i) It gets power via data line and stores it in internal capactitor

    ii) It has power supplied seperatly (thrid wire).

 

Ton of more detailed information on 1-wire protocol online, but loxone summarize the basics here: https://www.loxone.com/enen/kb/wiring-1-wire-devices/

 

 

thank you. will do more reading on this instead of my day job today. ? 

[Thorfun]

5 minutes ago, PeterW said:

loxone uses a DS18B20 sensor, Heatmiser uses an NTC thermistor. You can apparently use the AI Extension to convert to digital but given 10m DS18 sensors are as cheap as chips why would you ..??

if I knew what you were talking about it might be better. but, I think you're saying that I should forget the Wunda probes and either get the Loxone ones or buy cheap versions of a DS18 sensor online.

[PeterW]

So the loxone one is a 3 wire which @Dan F has said is essentially a DS18S20. You can get them with 10m extensions off eBay. 
 

NTC/PTC thermistors are ok but can suffer with long cables. 

[Thorfun]

3 minutes ago, PeterW said:

So the loxone one is a 3 wire which @Dan F has said is essentially a DS18S20. You can get them with 10m extensions off eBay. 
 

NTC/PTC thermistors are ok but can suffer with long cables. 

like this?

 

https://www.ebay.co.uk/itm/124433541502?hash=item1cf8d1297e:g:mTsAAOSwPKlfqoC-

 

how would you know if the quality is any good though? or do you simply install lots of them and if one fails then just disconnect it and wire up a different one!

[markc]

If a sensor fails you pull it out of the tube and slide in a replacement.

[Dan F]

6 minutes ago, PeterW said:

So the loxone one is a 3 wire which @Dan F has said is essentially a DS18S20. You can get them with 10m extensions off eBay. 
 

NTC/PTC thermistors are ok but can suffer with long cables. 

 

You also need to be careful with length of 1-wire branches, so I wouldn't be buying probes with 5 -10m lead, not if you want to get close to 20 sensors on a single run (and single loxone extension).   If you have any electric UFH in bathroom, you can also use these probes there and not need to rely on thrid-party control systems.

[Thorfun]

1 minute ago, markc said:

If a sensor fails you pull it out of the tube and slide in a replacement.

but the sensor is out the end of the conduit so it's in contact with the slab, right? so, therefore it won't pull out as it'll be concreted in?

[Dan F]

2 minutes ago, markc said:

If a sensor fails you pull it out of the tube and slide in a replacement.

 

Test all sensors and 1-wire wiring before plasterboarding though.  1-wire can be a bit fussy with grounding, length of branches etc. so you need to ensure not only the sensors work, but also that the wiring works, prior to boarding up and loosing access.

[Dan F]

2 minutes ago, Thorfun said:

but the sensor is out the end of the conduit so it's in contact with the slab, right? so, therefore it won't pull out as it'll be concreted in?

 

Look a bit more closely at the photo I shared.   The end of the UFH pipe (that the sensor gets pushed down into later) is closed with pliers and taped.  Or you can use caps as @Nickfromwales suggested.  But the point of the UFH pipe isn't just to position the sensor, but also to avoid concrreting them in.

Edited April 26, 2021 by Dan F

[Thorfun]

2 minutes ago, Dan F said:

 

You also need to be careful with length of 1-wire branches, so I wouldn't be buying probes with 5 -10m lead, not if you want to get close to 20 sensors on a single run (and single loxone extension).   If you have any electric UFH in bathroom, you can also use these probes there and not need to rely on thrid-party control systems.

 

hmm...but I don't have any soil pipes going under the slab like you did so I feel I need to run the sensors back to the plant/comms room rather that to where a wall will eventually be built and sticking up from the slab.

 

Just now, Dan F said:

 

Test all sensors and 1-wire wiring before plasterboarding though.  1-wire can be a bit fussy with grounding, length of branches etc. so you need to ensure not only the sensors work, but also that the wiring works, prior to boarding up and loosing access.

 

again, talking about sensors in the slab at the moment so once they're in they're not coming out!

[Thorfun]

1 minute ago, Dan F said:

 

Look a bit more closely at the photo I shared.   The end of the UFH pipe (that the sensor gets pushed down into later) is closed with pliers and taped.  Or you can use caps as @Nickfromwales suggested.  But the point of the UFH pipe isn't just to position the sensor, but also to avoid concrreting them in.

ahh....ok. I get it now. I assume that the caps wouldn't affect it's accuracy on temperature reading then?

[Dan F]

Just now, Thorfun said:

 

hmm...but I don't have any soil pipes going under the slab like you did so I feel I need to run the sensors back to the plant/comms room rather that to where a wall will eventually be built and sticking up from the slab.

 

You poke up your bit of UFH either in the service cavity of external wall, or within internal studwork or any boxed out areas.   Easier with SVP, but not a requirement.  It does take some measuring, but you'll need to measure up to work out where to put (and not to put) UFH runs anyway.

[Dan F]

2 minutes ago, Thorfun said:

ahh....ok. I get it now. I assume that the caps wouldn't affect it's accuracy on temperature reading then?

 

No, given:

i) pipes conduct heat very well.   (they are for UFH after all)

ii) slab temperature changes slowly, so any very minor lag from heating any air between pipe/sensor is absolutely nothing in comparison.

 

[markc]

7 minutes ago, Thorfun said:

ahh....ok. I get it now. I assume that the caps wouldn't affect it's accuracy on temperature reading then?

The pipe the sensor is in is burried in the slab, the tube and air in it will be at the same temp as the slab. sensor doesnt have to be in contact with the concrete or screed

[Thorfun]

13 minutes ago, Dan F said:

 

You poke up your bit of UFH either in the service cavity of external wall, or within internal studwork or any boxed out areas.   Easier with SVP, but not a requirement.  It does take some measuring, but you'll need to measure up to work out where to put (and not to put) UFH runs anyway.

thanks again Dan. really appreciate it. 

[jack]

1 hour ago, Thorfun said:

hmm...but I don't have any soil pipes going under the slab like you did so I feel I need to run the sensors back to the plant/comms room rather that to where a wall will eventually be built and sticking up from the slab.

 

1-wire sensors work best if you run them on a bus topology rather than star. 

 

One approach is bring each conduit up from the slab within a nearby internal wall or service void on an external wall, so that it finishes behind a small access plate (behind a door so it's out of sight). You then run a bus cable from Loxone, then access plate to access plate, terminating each 1-wire sensor cable to the bus behind its corresponding access plate. Having a few short stubs off a bus is far less problematic than having a full star topology, and the access panels allow replacement if necessary. Powering them independently rather than parasitically helps.

All that said, if you're only running a small number of sensors, star layout might be fine. Mine is a combination of star and bus with stubs (only about 5 sensors in all) and it works fine.  Unfortunately, one failed fairly early on and is in an inaccessible place, so I had to just cut it loose. Wish I'd had the foresight to use spare UFH conduit in the way you're proposing!

 

I bought these in 2017 and they seem to work fine: https://www.amazon.co.uk/dp/B00CHEZ250/  (no guarantees you'll get the same stock several years later, of course).

[Thorfun]

5 minutes ago, jack said:

 

1-wire sensors work best if you run them on a bus topology rather than star. 

 

One approach is bring each conduit up from the slab within a nearby internal wall or service void on an external wall, so that it finishes behind a small access plate (behind a door so it's out of sight). You then run a bus cable from Loxone, then access plate to access plate, terminating each 1-wire sensor cable to the bus behind its corresponding access plate. Having a few short stubs off a bus is far less problematic than having a full star topology, and the access panels allow replacement if necessary. Powering them independently rather than parasitically helps.

All that said, if you're only running a small number of sensors, star layout might be fine. Mine is a combination of star and bus with stubs (only about 5 sensors in all) and it works fine.  Unfortunately, one failed fairly early on and is in an inaccessible place, so I had to just cut it loose. Wish I'd had the foresight to use spare UFH conduit in the way you're proposing!

 

I bought these in 2017 and they seem to work fine: https://www.amazon.co.uk/dp/B00CHEZ250/  (no guarantees you'll get the same stock several years later, of course).

thanks @jack. I did see those ones on Amazon but they're only 1m cable length which seems a little tight to me. 

 

It's interesting that you mention powering independently rather than parasitically helps. I am just doing more reading on 1-wire and was interested to know the benefits of one over the other but I've yet to get that far in my reading.

 

I think I'll go for the approach of bringing a conduit near to a wall with back plates. those back plates could always be switches and Loxone seem to say that you can then use the other pairs of the CAT 7 cable for the switches.

 

from https://www.loxone.com/enen/kb/wiring-1-wire-devices/ that @Dan F linked previously....

 

 

so was thinking of running the probes to the location where the switch plates would eventually be. seemed quite a sensible idea.

[Thorfun]

so after reading this article https://www.best-microcontroller-projects.com/ds18b20.html it seems that the benefits of using parasitic power is that you only need 2 wires for the sensors but it says you need a pull-up resistor but I presume that the Loxone 1-Wire extension has that all covered. so using parasitic power requires on one twisted pair on a Cat6/7 cable leaving the rest spare for other uses but using separate power means you have to use another wire from another twisted pair.

 

the article does mention about delays when using parasitic power due to during a strong pull-up action no other communication can be made over the one-wire bus. so maybe if you have the spare twisted pair in your cable then separate power is the way to go.

[Thorfun]

put my plans in LoopCAD and came up with this:

 

 

 

I'll see how it compares to Wunda's design but I'm pretty happy with what I came up with.

 

doubt I need that loop in the WC but I figured what the heck!

 

was going to put 1 x temperature probe in each of the 4 main rooms just in case I decide to zone the basement. I ordered 5 of these at 3m length. it'll do me for now.

 

ps. all the internal walls are block so no penetration of the slab is required. which is why I'm comfortable running pipes under the walls in places.

Edited April 26, 2021 by Thorfun