Guidance for a setup in a cold chamber

Hi guys,

My name is Juan, from Spain, I am a complete beginner on this topic of home automation systems and sensors. I came across with OPENHAB for two reasons: first, I love open source projects, and second, this community seams to be very active. So here are questions, to see if any of you can help me.

I am starting a pilot project on a cold chamber where meat is stored at a specific temperature (roughly -10 degrees). Here, I should install a set of sensors in order to measure three variables:

  • Temperature (and humidity may be useful too)
  • Electric energy consumption of the chamber (currents, voltages, energy demand, etc)
  • Measuring the time when the door is open

I need to access to the data of those sensors remotely, so those sensors need to have the capability either to send their own data to a cloud server, either send the data to another “hub device” which is in charge of gathering all the information from the different sensors and send those data to a cloud server. For the cloud server, I was thinking to setup an Amazon Web Services server. The idea with the project is to perform some data analyticis over the data gathered in order to understand better the performance of the cold chamber: see variations of energy consumption with temperature settings, how the door opening may affect to the temperature, etc.

Pretty much this is the idea of the project. What I need from you guys is some guidance about how to start. For instance, what sensors providers should I use for my project? What models would works? Do you have any paper, blog entry, or wathever where somebody has done something similar? No need to say, the idea is to use OpenHAB set of tools in order to integrate all the sensors and data, so, the sensors that I use at this stage should be “compatible” or can be managed from OpenHAB.

Thanks in advance for your help,


My physics is rusty; can you have humidity at below freezing temperatures?
No harm in having a sensor, anyway.

Your sensor needs are pretty standard for home automation equipment, with the exception of the temperature; not all commercial indoor sensors are usable below freezing. So you’ll be looking for an “outdoors” rated device.
The other stuff will presumably live outside the chamber?

You have a wide choice of how to connect your devices to openHAB, it would likely be best to choose one common technology e… all zwave or all KN etc.

Hi rossko57,

Thank you for your reply, it is very informative for a beginner like me

The chamber won’t be all the time at freezing temperature, but yes, we can live without the humidity sensor. And yes, the other stuff (energy and door sensor) will live outside.

Can you recommend a provider/manufacturer, hopefully based on the US, from which we can get the three sensor we are looking for: temperature, door open/close, energy?

If you are ok with DIY type projects, which this kind of project seems, you might want to look at something like the DS18B20 (Google is your buddy) type sensor. They are cheap and can be obtained sealed with a long lead cable making it waterproof. They can withstand temps well below freezing.
Of course you would need some type of controller to hook it to, a Raspberry Pi or a esp8266 or whatever. (it is a sensor only)
Seems outdoor rated (withstand freezing temps) consumer grade sensors are not super common.
Say you go for a Pi or esp8266, you could hook simple wired contact switches to it as well for the door.
Energy consumption would need some other technology but many smart plugs report voltage/current. Depends on what voltages the cold camber runs on. There are also smart meters which hook to supply lines with a spring clamp so no direct electrical connection needed (I know nothing about, just seen) These type device often run on wifi or zwave. (zwave would require a zwave controller)
The local storage of data or cloud connection is another layer of the puzzle. How important is accessing the data remotely? How important is not losing data? These types of questions would play into my choices. The Raspberry Pi could run a MQTT server as well as handle sending the data to a cloud. The esp8266 could also send data to a remote MQTT server… lots of options

Well… me thinks you have lots of reading and research to do. This is a somewhat complex project for a complete noob but if you are a crafty techie type guy, it is do able. All could probably be realized with off the shelf components as well but you would probably spend more then it would cost leaving th door open on the cold chamber a few times by mistake :wink:

Hi Andrew_Rowe

Thank you for your reply ! As you said, as a techy guy I hope to grab the concepts quickly. However, for this project, I was thinking to start with off the shelf devices rather than DIY devices (that most probably comes at the next stage). In your experience, can you give me a couple of manufacturer’s name from which I can get the three sensors I am looking for?

Couple questions might get you started
What do you intend to use as a controller on which to install OpenHAB?
OpenHAB can be run on a PC with Windows, Mac or Linux or a SBC such as Rasberry Pi and a variety of other platforms
What is the power source of the chill chamber? 120v, 220v or ???
How will the controllers and sensors communicate? wired, wifi or radio?


Here are my answers:

What do you intend to use as a controller on which to install OpenHAB?
A raspberry pi most probably

What is the power source of the chill chamber? 120v, 220v or ??

How will the controllers and sensors communicate? wired, wifi or radio?
Between the sensors and the controller should be wireless (radio sounds interesting).
Between the controller and me, the operator/analyst, I guess that it should wifi or 4g.

Thanks again for your replies !!

Could you not integrate this as an all in one…
Sensors on the gpio pins of the pi, pi powered from the chambers control panel.
Humidity is going to increase when the unit is on defrost (assuming electric or hot gas), and also when the door is opened so a sensor would be handy.
Openhabcloud for remote access.
Just gotta work out WiFi or wired for the pi

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yeah like I said, I don’t know of consumer grade temp sensors that can handle freezing temps. I’m sure you can find one but I have no experience

Hi delid4ve,

Thanks for your reply.

Here in the following link you can see the arrangement of the devices in the room. As you can see, temperature and door sensors are separated from the controller-raspberry pi, so these two have to be connected with the controller wirelessly while the energy sensor may be concected with the controller by wire.

Any suggestions about suitable off the shelf devices that I may acquire in order to start playing with the concept… are very welcomed. This kind of tentative “purchase list” is what I need the most at this time. It is best if we can buy all the components from the same store/manufacturer… but the other option would work also…

Thanks !

Does the pi have to go there though??
I mean, I would rather wired sensors if it were me.
What’s the building like? False ceilings for cable runs?

I own a refrigeration business also btw :wink: so I’m with two minds here :joy:

Dave that sounds great !

Actually the PI does not have to be there, close to circuit center… just it make sense to me, but I may be wrong of course.

And yes, there is option to have all the sensors wired to the PI … again, it makes sense to me to have sensors connected wireless… but due to my lack of knowledge, I dont if this requirement may suppose other kind of headaches…

Only 1 Ethernet cable to run back for remote access.
Sensors will have less issues due to connectivity.
Wired sensors cheaper than wireless
No flat batteries in your sensors or extra power requirements
Vast options for wired sensors
If it’s just the Coldroom (depends on condensing unit whether separate supply but could run cable back with the pipework) to monitor energy usage this can be done at the panel and again connected to the pi.

Dave, those sounds like good reasons to think about starting with wired sensors. Can you recommend a store/manufacturer from which acquire the three sensors: temperature, energy and door. Of course, the three sensors have to be controllable from PI via the OpenHAB…

You might want to check out the very affordable Xiaomi Aqara temperature sensors. The manufacturer claims they can withstand up to -20 °C. I can’t confirm that myself, but I use two of them indoors and they work pretty well. I’m not sure how accurate they really are, but it sounds like your project doesn’t need too precise data, so they should be fine. Maybe they’re very accurate after all, I just never bothered to find out. The Aqara series also contains door sensors and other stuff. I don’t know if the door sensor also withstands sub-zero temperatures, but you can just attach that to the outside of the door anyway.

All sensors use Zigbee for wireless communication and the internal battery should last for at least a year, probably longer. Getting the Aqara hub is likely the easiest setup, but if you don’t want your data to end up on some Chinese server, you can get a cheap CC2531 USB dongle in combination with zigbee2mqtt that you can plug directly into your Raspberry Pi; just make sure it’s not too far away.

For cloud access, just use the Openhab Cloud Connector. You won’t need your own server.

Hi Leon,

Thank you for your reply and recommendations ! Have had experience with energy/power sensor in order to gather data like voltages, current draws, loads, etc? If so, what of them would you recommend for this project?

Sorry, I have no power measurement devices myself, so I can’t recommend anything specific. Many smart plugs have power measurement functionality built in, so if the power supply for the cooling system runs through a standard wall socket, just get one of those. If not, you can also easily find smart current meters that you can hook directly into the wire. Just watch out for the correct number of phases because a powerful cooling system might use more than one.
Either way, I don’t think there’s a lot you can do wrong on that end; just take whichever one you like. Make sure it can handle the current though.

Something to also consider is were to install it. If there is a single wire somewhere that is hooked up to the entire cooling system and nothing else, this is where you want to put the meter. If not, you’ll need to get multiple meters and add the measurements together in OpenHAB, but this is pretty straight forward by putting them in a group with an aggregation function.

Depends on your location. I don’t use a raspberry pi at all so I haven’t researched the GPIO pins but you should be able to integrate something like these (both go down to -40. I have very little experience with the programming side of things with the pi so you’ll need to do some research.
Would just need to heat shrink a length of cable of mount them in a box.

It could be one of two:
Power to control panel, which feeds indoor (evaporator) and outdoor (condenser), or
Power to control panel which feeds indoor, separate power to outdoor (controlled purely on a pump down system)