It’s great having the Tempest station, it works marvellously, but I need to extend my temperature readings to include greenhouses - and it’s quite an overkill to have another full station in there, both in terms of cost and features.
Question: are there any Hub-compatible simple temperature and humidity sensors I could use as addons to the existing installation, for example in greenhouses?
The WeatherFlow Air sensor is exactly what you are looking for…but unfortunately it (and the Sky wind/rain/sunlight sensor) were discontinued when the one-piece Tempest system was released. There may be a few floating around on the used market if you search.
Since you have greenhouses, I would suggest looking at a LoRa-based agricultural system for monitoring their internal temperatures/humidities instead of trying to find a bunch of old WF Air sensors…
You might look at the sensors and hub from SensorPush https://www.sensorpush.com/. I have found them to be extremely reliable. I even buried one to get ground temperature!
Most inexpensive is likely going ecowitt - their temp+humidity sensors are quite good. Add an inexpensive gw1200 gateway and you can have as many as 8 sensors plus things like soil temp+moisture sensors. Cooking up a quick weewx or home assistant setup is pretty easy to do, but you could just use the Ecowitt phone/tablet app to view the data if you want.
One downside - the gateway needs internet connectivity to China for heartbeat, so put it on an IoT VLAN if you can do so. Not likely much different security risk of a WF Hub but you can’t be too safe I guess…
Cost these days would be approximately $35 for the gateway and $15 each for up to 8 indoor sensors and one outdoor sensor. The gateway also measures T+H+P and connects via 2.4GHz wifi to your LAN, so that adds up to 10 sensors per gateway if you need that many. Given you have greenhouses, I wouldn’t worry about using their indoor sensors in there.