Do you intend to have CO2 sensors as an optional add-on to the emonTH? Our clients need to monitor CO2 levels in addition to Temp/Humidity and we are looking at how best to accommodate this and bring the data into emonCMS. Ideally, an emonTH with a CO2 sensor is our best route.
Also, in your image of the CO2 sensor, I noticed it is AC-powered. Does the sensor require AC power or can it be battery-powered like the emonTH?
Thanks,
Gordon
Hello Gordon. Our plan is to make it easier to attach the I2C CO2 sensor we’ve used here when we get the next batch of emonTH2 units manufactured but this is unfortunately quite some time away. I imagine you would want more than a couple of these? The firmware I have written so far is not low power, hence these have been powered by USB.
I wonder if there are any zigbee devices out there that you could integrate with a zigbee dongle of some kind in the mean time?
Hi Trystan,
thanks for the update. When you suggest “quite some time” are you thinking of months or years? Having something late this year would work for me.
Regarding Zigbee, I’ll need to look into this. We would plug the ZigBee dongle into the emonPi2 - correct?
Thanks,
Gordon
I will review the stock and get back to you on timescales.
Yes that’s correct. @glyn.hudson integrated a room temperature sensor last year using this approach I think, I will check with him how he did this.
Correct, but there’s a bit of setup required. Zigbee dongle is not supported out of the box:
@TrystanLea
I’m following up to see if there has been any progress on a CO2 sensor that can attach to the emonTH. I experimented with Zigbee, but in the end, it became too much of a science project with a limited range compared to 433 Mhz.
I’m now testing the Ecobee Premium thermostat with many great features, including Air Quality, along with an API interface, but the price point is high and the API has a monthly fee.
My preference is to keep things simple and remain in the Open Energy ecosystem and in most cases CO2 measurements are sufficient. Do you think you would have a product to test within the next couple of months?
Keep up the great work!
Thanks,
Gordon
I can’t remember if you use Home Assistant, but if you do there are a couple of devices that work with HA and you can send the data on.
For me, the simplest solution is to get a couple of WEMOS D1s & SCD40/41 (plus a case) from Aliexpress and roll your own with either ESPHome or Tasmota. Either will send the data to emoncms by MQTT.
SCD40 SCD41 Gas Sensor Module Detects CO2 Carbon Dioxide Temperature And Humidity In One Sensor I2C Communication - AliExpress 502 (I’d just get the cheaper 40)
LOLIN D1 Mini V4.0.0 - WEMOS WIFI Internet of Things Board based ESP8266 4MB MicroPython Nodemcu Arduino Compatible - AliExpress 502 (Stupidly cheap)
Another option is the Building A Better Smart Home – Everything Smart Technology presence One as it has an optional CO2 sensor (but probably needs HA to work easily).
FWIW, I just bought one (actually a ‘Lite’ rather than a ‘One’) and after some faffing it works straight into my Home Assistant Green. I export some other data from HA to my emoncms system, but despite adding the CO2 readings to my config file, they aren’t being sent to emoncms. I haven’t found out why not yet.
2 posts were split to a new topic: No sign of data from Home Assistant
Just a note to @grod55 I will get back to you about this soon, apologies! I need to review EmonTH stock and timing for prototypes etc.
Hi Bryan,
I do not use HA, so I thank you for the info. Assuming I try cobbling together the first three items in your list, is there any sample code I need to integrate? I have very rudimentary coding skills (I’m more of a plug-it-in and configure-it guy).
Thanks,
Gordon
Tasmota is just a download, if you connect the sensor it should auto-detect it. No code, only mid-level assemble, download, config skills.
I’d suggest ESPHome as you can more easily configure MQTT to send the data (I think). There is now a web based uploader so reasonably easy to do - configured with YAML.
Tasmota is similar (and has a scripting facility which I think can be used to send a specific MQTT message). I then use Node-RED to parse the standard data output from Tasmota and send that to emoncms.
OK, I have a q about ACH numbers. Do we believe one air chance takes all the air out and replaces it (with air from outside, or some other room), or does it actually leave 1/e th of the original air there. Exponential decay.
Eg if I replace my black coffee with milk I can throw it all away, and refill the cup (one cup change), but doing that with a room full of air is a non starter. Vacuum being hard on the occupants. If I empty out half my coffee, and refill with milk, and then do it again, I have thrown away a cup full, but have 25% of my black coffee left in there. Do it drop by drop and nearly half will be left.
So is an air change really only about half a room full??
That’s the definition, anything else would not make a lot of sense, as you also explain with your example.
The important part is that you have to bring that volume up to the internal temperature, so 1 ACH in a 100 m3 room means you have to warm up 100 m3 of air per hour from outdoor to indoor temperature.
Thanks, yes I thought thru to that conclusion later. However it does make a difference (to energy loss) if you are NOT continuously heating, since the air in the room gets colder, so delta T to outside goes down. The second airchange, like the 50% coffee, loses less heat energy. Guess that is why people think turning the heat off saves energy… If your energy loss is mostly air change, it will. If you are mostly radiating it away, not so much.
We need to be really careful on how to word this. We have overall three processes. First there’s heat loss due to conduction, which is proportional to T_in-T_out. Second, there’s the air change that is also proportional to T_in-T_out. Both of these lead to an exponential decay in temperature if no heating is on, and you could not really differentiate which is dominating just by looking at temperature. So essentially they are “indistinguishable” in that model and you save energy by not heating independent of which of those two dominates.
You also bring in “radiation”, but I’m assuming you really meant the conductive heat losses mentioned above. Radiation also happens and is proportional to the difference of the fourth power of house surface temperature to background temperature. This is not air temperature but really the temperature of the surroundings, which is equal to air temperature mostly but a clear sky in winter has a radiative temperature of far far below 0°C so radiative losses through the roof can be higher. As far as I am aware, those heat losses are typically completely neglected. If there’s no clear sky but everything in the background (trees etc) is at air temperature, and the house external surface is also at air temperature then there will be no radiative losses at all.
Yes, I was using ‘radiation’ inappropriately to cover conduction, convection, and all the other losses from the fabric through walls, floor etc.
The difference with that and ACH is that if you let the fabric get cold (lose energy) one day you are going to have to put it back in. If, however, you are having a lot of air changes with cold air while you are out, there is little to no cost … the only air you need to reheat is whatever is in the building when you next want it warm, you don’t have to heat all the stuff that went through the building while you were not heating.
All the air changes remove heat from the fabric and cool down the house. Cold air comes in and is heated up, taking energy from the fabric and also the warm air inside. Whether the cooling is via conduction or air change doesn’t really matter - the heat stored in the house (air + fabric) is removed, and the heat loss of both is proportional to the current difference between outside and inside temperature.
My heat loss survey gives two numbers, one for conduction and one for ventilation. Both are in W/K and the cooling down of the house would look the same as long as the sum of those two was identical.
If you have your house at 20°C and left it without heating for a day it would end up at the same temperature if the heat loss was purely conductive or purely from ventilation as long as the heat loss coefficients in W/K are the same. It would also take the same energy to reheat the house.