Dew point sensors for underfloor heating: how and where to install them?

Hello,

since I would like to have underfloor heating with passive cooling function, I apparently also need dew point sensors. Where are these actually installed? Directly cast into the screed mounted on the water pipe? How can they be replaced in case of a defect? How many of these sensors are needed? One per floor? Are there particularly sensible points where these sensors are installed? For example, where the (cooling) pipe loops are laid particularly close together because the greatest cooling capacity is introduced there? Do these cables usually go directly to the control unit of the heating system or to the room thermostats? Do heating manufacturers recommend special types or can you choose freely? Is there a reputable manufacturer that has proven itself here?

I would be grateful for some answers.

In my underfloor heating system with cooling function, which I find absolutely great and enjoy very much in the summer, I have an extra sensor in the living room. It looks like a room thermostat / mini control unit but does nothing except display some data and measure humidity / temperature. I have one sensor in the whole house. The sensor is part of the heat pump installation, so also from the heat pump manufacturer.

A dew point sensor belongs in the floor covering.

A dew point sensor belongs in the floor covering.

Could you be a bit more specific? Do you really mean the covering (I have parquet) or the floor structure? Then in the screed or in some other way?

Opinions differ when it comes to implementation. Some install dew point monitors in the heating circuit (I’m not sure if it’s the supply or return line), while others install sensors in the screed, where dew point failure first occurs and could cause the greatest damage, especially if a calcium sulfate screed is used, as it cannot tolerate moisture for long or at all. According to my heating engineer, the option with the additional dew point monitor in the supply/return line is the simpler one but has two disadvantages: 1. You will never know exactly how "wet" the floor structure really is or will become during cooling, and 2. because of that, you will always have to operate with a "safety margin" regarding the supply temperature to be absolutely sure that dew does not form somewhere in the floor. So if you want to run the system at maximum capacity and without risk in cooling mode, you won’t avoid installing several sensors in the screed. It wasn’t worth it to us, which is why we preferred to run only 20 degrees through the floor instead of 17 or 18 degrees. However, depending on the prevailing conditions, that is also no 100% guarantee against dew! If the floor is already at 26 degrees and you then run 20-degree water, that could probably already cause dew as well.

Hello
You need to deal with this topic more intensively than with familiar heating systems.
First and foremost: in my opinion, a combined heating/cooling phase via the floor has not become established.
The ideal, because most effective, form would be underfloor heating plus ceiling cooling.
Please keep in mind that the temperature difference in a warm summer with high humidity can only be small. Precisely because of the dew point already mentioned in another form. However, this does not occur in the screed but on the surface of the covering.
With ceramic tiles, this means that (if undershot) during cooling operation the risk of slipping or sliding due to water film formation should not be underestimated; conversely, with, for example, 28°C room temperature and 75% relative humidity, you cannot expect major cooling results.
Why not?
Well, at 28/75 (see above) the dew point (on the surface) is around 23°C.
If you allow a safety margin of 3°C (a usual value), then the supply temperature of the cooling unit may only be 23°C + 3°C = 26°C.
Anyone can imagine that the cooling result with only 2°C temperature difference (air to floor) can hardly contribute to a feeling of relief through cooling effect.
And even if, at lower humidity, the supply temperature can be lowered further, then with sufficient probability you will have to deal with "cold feet." And that in summer.
Dew point sensors are a tricky matter.
I still remember a legal case I worked on as an expert.
The sensors built into the screed were supposed to transmit their data via app and thus suggest safety regarding the moisture content of the installed parquet as well as of the heating/cooling screed.
To cut a long story short:
There is no common sorption isotherm for all screed types and all parquet types!
That means the sensor may show whatever it wants, but it cannot provide reliable values specifically.
My corresponding inquiries with the manufacturer also remained unanswered regarding the measurement principle until the end.
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Conclusion:
If possible, look for another way than the heating/cooling combination via the floor.
You will not be happy with it and will most likely be annoyed by the costs of the unpleasant setup.
Better have one or more air conditioning units installed for the hot summer days that can reliably perform their tasks.
By "air conditioning unit" I mean devices based on the heat pump system.
Best regards and wishing you a wise decision: KlaRa