Sensor that captures absolute humidity?

Hello there,

I am new to Smartthings hope the community can help.

I am trying to find accurate sensors which intergrate well with smarttings and measure absolute humidity (without having to convert rel. humidity and temperature into abs. humidity).

Thanks very much.

the the Aeotec multiple purpose sensor 6

I have one and it works really well, does temp, humidity, lux, uv, motion and also tamper

Interesting. All sensors I’ve seen so far (including the Aeotec mentioned above) provide relative humidity (0 to 100 %) versus absolute (g/m3). It would probably be relatively easy to add the formula to a custom Device Type Handler (DTH) for someone experienced with them but that wasn’t what you were looking for. Good luck!

Thanks very much for the swift replies.

Thats exactly the issue. There does not seem to be a shortage of sensors measuring relative humidity but for serious climate control this is unfortunately not enough.

What is your use case? What do you mean serious climate control?

I have this sensor from monoprice:
https://www.monoprice.com/product?p_id=15902

Also these Xiaomi Aqara WSDCGQ11LM Temperature Humidity Sensors which can be a pain to add and keep online.

https://us.gearbest.com/access-control/pp_626702.html

ah yes… DOH… the Aeotec one does relative humidity… silly me… soz

Relative humidity is what is given by the sensors because that is what is useful to people. Absolutely humidity means absolutely nothing. Relative humidity is what is used because it measures your level of comfort relative to the temperature in the room. The exact same absolute humidity means something very different at 5C vs 40C. But if you’re talking about climate control of your home, you’re talking a VERY narrow window of temps. So, whether you use relative or absolutely humidity won’t really matter. You’re going to get the same outcome. I’m curious why you think you NEED absolute humidity.

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Thanks for your feedback. What you say is unfortunately only 50% of the truth. Serious climate control requires both rel. and absolute humidity. If you want to avoid mold at home you have to understand temperature, dew point and absolute humidity indoor and outdoor. Relative humidity does not help at all - pure physics.

Best

Just curious why you’re averse to using a conversion? Would be pretty easy to modify a DTH to convert to absolute, or to do the conversion on the rules side using something like webCoRE.

I’ve not seen a smart sensor that outputs absolute humidity natively, so a conversion somewhere might be your only option.

I’m not convinced you really need absolute humidity for climate control though. I worked for many years doing water damage restoration and mold remediation, and from that I understand the sciences of quickly drying homes and preventing mold pretty well. I could care less how much actual water there is in the air in my home, I’m much more concerned with how saturated the air is and what the dew point is relative to the current temperature.

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That is not correct. Unless you let your home fluctuate between -10 C and 30 C, absolutely humidity would be immaterial. Your home is kept in such a small range of temps, relative humidity is all you need. What is the difference in absolute humidity between a RH of 50% at 20C and a RH of 50% at 17C? 1.4 g/m3!!!

You keep saying “serious climate control”. Well, if this was such a necessary component of serious climate control, what systems use absolute humidity?

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Guys - Thanks very much, very helpful. I take it there is no native solution for my Problem with Smartthings.

@Ryan780: I had a simple question and would very much appreciate no comment if no solution / answer to my question. If you want to questions physics - pls. go ahead.

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not only do we help people with their solutions we also want to make sure their solutions are not unnecessarily over engineered, ST is about keeping things as simple as possible to meet the real world needs. If you want to implement something that is not only unnecessary but also a waste of time then please go ahead.

Just out of curiosity I would like to hear your physics that answers the question that @Ryan780 has.

Also you have not given us a real world problem that you are trying to solve, so given that there is no absolute humidity sensors that work with ST we cannot possibly give you a solution, apart from use some algorithms in code to get exactly what you could possibly need.

Even if you have reptiles that need a very closely monitored humidity environment, I can’t comprehend why absolute would be necessary.

Unless you have an environment that you want to monitor the has such a large temperature fluctuation then I too cannot see why you would need it.

The important thing with home control is to remember that as others have said, your temperature variation is not enough to need to know absolute.

Perhaps you could educate us by telling us what your real world situation is.

Are you a physics lecturer, perhaps looking to setup an experiment for your students? or a scientist looking to setup an exponent of some sort? Thats about the only reasons I could possibly comprehend why you would need this.

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I’m a firm believer in physics, which is why these comments confuse me. You clearly understand that absolute humidity can be calculated from RH, temperature, and barometric pressure based on your first post. You also claim that serious climate control requires knowledge of dew points and absolute humidity levels, yet also claim that knowing the RH is useless. How is RH useless if it can be used to give you the very things you claim are required knowledge? Why is it so critical that the indoor sensor output absolute humidity without any calculations? Does that mean you’ve found an outdoor sensor that measures both absolute humidity and dew point and have another way to measure indoor dew point directly, or is calculating the outdoor absolute humidity, outdoor dew point, and indoor dew point ok, but not the indoor absolute humidity?

FWIW I looked through the code in the DTH I’m using for my Xiaomi/Aqara sensors, and it would be super easy to add a calculation to get it to output absolute humidity based on the measured RH, temp, and barometric pressure. It would literally only require adding a single line of code. I’d be happy to edit a DTH to do this for you if you really want me to.

If you choose a different sensor that doesn’t measure barometric pressure you’ll need to let me know the average barometric pressure for your area to use for the calculation. Even drastic changes in pressure have minimal impact on the absolute humidity (less than the accuracy or resolution of the sensors), so using the average pressure should be fine.

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Ditto, I am very interested as I have been investigating residential radiant cooling for a while now and it’s important to control humidity in those situations to avoid condensation on your ceiling/walls.

Radiant cooling for a residential application in a moderately humid climate like San Antonio can be a challenge. Even here in the dry Sonoran desert it can be problematic if the house isn’t properly insulated and sealed, or if you have people coming and going into and out of the house frequently, or if the DOAS isn’t designed and installed properly. It’s much easier to implement in large commercial applications.

And for monitoring of a radiant cooling system to prevent condensation I’d be paying attention to the dew point more than anything else. As long as the water temperature for your radiant system stays above the dew point there shouldn’t be any condensation issues.

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Great info! The plan was to shoot for < 0.7 ACH50 with the fewest opening windows (and some strict, no leaving doors open rules!), along with one or more ERVs.

I figured that we would probably need a controllable dehumidifier before the outside intake on the ERV and potentially another controllable dehumidifier on the inside intake of the ERV so that there’s lots of control over the humidity levels, though like you say, dew point is the critical value but I want to monitor basically everything, can’t hurt to have as much data as possible!

My biggest concern is having the inside intakes (extracting indoor air) in the bathrooms where humidity is potentially at its highest, being mixed/transferred in the ERV to the incoming outside air.

The ERV’s I’ve dealt with had desiccant wheels which help control humidity of all intake air. Whether you add a controllable dehumidifier to the outside intake or inside intake or both really depends on how much make up air the system is designed to use on average. If you do only one, you’d want it on whichever side will handle more air. Around here that’s typically the inside intake, but that’s in large part due to the extreme summer temperatures here.

And yes, having as much data as possible is always good, but be wary of making the controls too complex or you can easily end up with a sort of feedback loop. Monitor everything you possibly can, but try to simplify so that only a couple of parameters are acting as triggers.

Are you planning on ceiling panels or a slab system?

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Ceiling panels, nothing in the slab, all radiant heating/cooling done from the ceiling though I get that heating would technically be more “effective” in the slab, just want to keep complexity down and not have two separate systems and effectively double the work.

I didn’t realise desiccant wheel style could do ERV and de-humidification duties, if they can in “one unit” then that would avoid additional units, additional complexity and duct work. I was looking at one (or more, will need to calculate based on final square footage covered, etc) of the Panasonic Intelli-Balance 100 ERVs.

I love this info, thank you!

Good choice, ceiling panels are vastly more efficient/effective for cooling, which is likely more important in TX. It will be very important to have a good radiant barrier above the panels, and really high levels of insulation in your ceilings. I’d even consider looking into using foil backed decking for the roof structure. It can be hard to install with the air gap required to gain the radiant effects, and can lead to condensation in the roof if not designed properly, but when properly implemented it can really help.

Pretty much all ERV’s perform some level of dehumidification in summer months (and humidification in winter months). Energy exchange from transfer of moisture is a huge part of how and ERV’s work. Looking at the spec sheet for that Panasonic it appears to be a fixed plate style (they call it a “capillary core” though), which will also dehumidify the air significantly in the summer. One advantage of enthalpy wheels over most other styles is slightly higher efficiency because it can do both sensible and total heat transfer. Some fixed plate systems can do both sensible and total heat transfer if they use hydroscopic materials though, which the Panasonic very well might. Didn’t dig into the spec sheet deeply enough to confirm though.

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