Question: I'm analysing the technologies for an IoT device that would need to be installed in a commercial environment. The requirement is to install thousands (or maybe even tens of thousands) of small sensors/devices in a commercial setting, like a hotel, or an office building. I need these devices to have bidirectional connectivity to a central server/control dashboard. The connection doesn't have to be super fast, but it should be reliable.

No power usage restrictions present, but I also don't want to considerably stress the existing infrastructure or spend lots for a new one.

So, what are my options? The following ones come to mind:

1. Wi-Fi. The obvious choice, but it has the following issues:
a) Too many of the devices in the same area will definitely stress the radio space, cause interference and possibly make the connections unreliable for both iot devices and the existing devices (computers, tablets, phones, printers, whatnot)
b) Might need lots of routers/repeaters to cover large areas, which may impact the cost of the project.
2. ZigBee. Has issues with WiFi in the same space, also kinda limited in number of devices? Will also require specialised hardware and bridge to IP network for control dashboard.

Mesh networks also have their limits.

I'd love to hear opinions, ideas, suggestions and resources to look into.

Answer: 
LoRaWAN matches the requirements of...

1. Hosting 1000s of devices
2. Not super fast. 300 bps to ~20 Kbps
3. Simple star-of-stars topology
4. Operates in sub-GHz ISM band (863—925MHz). So no interference to WiFi
5. Covers more than a kilometre

Ref.: <https://lora-alliance.org/about-lorawan>
LoRaWAN is a great option, as mentioned above. But the complexity does not end there, in terms of the databases to be used, with that number of devices publishing data at all times, it is a very good option to think in an elasticsearch database.