Care to share make/model information with us? How much you paid, where extra parts can be had, etc?
Well it's all pretty basic I'm afraid, but FWIW here's our setup. Our print room is just 90 square meters (about 1000 square feet I think), we're in an industrial unit, so that area is self contained with a false ceiling using insulated tiles. There's a dirty great big 3 phase air conditioning unit to keep things cool, but obviously that sucks moisture out of the air, a lot. To monitor the room, we have a Sensormetrics Neon 100, which is basically a small box connected to the network that monitors humidity and temperature. These (temperature, humidity) are displayed on one of the monitors used by the proofing team (in the office) and any alarms for out of "q-zone" get emailed through to me. We use a Prem-i-air PCMH45 humidifier and I get spare parts from Electrovision UK (we're in the UK). That puts out 1.8 litres (a little over 3 pints) an hour and can be plumbed into the mains. It has a built in humidistat and that seems to work accurately enough for us. I like the product as it's simple and reliable, it's basically a big wheel with pads, a reservoir, a motor and a powerful fan. We tried an ultrasonic one before this (a high end domestic unit) and it wasn't anywhere near up to the job. I think Prem-i-air is an American product, so no doubt you can find a local supplier.
Sorry, that's probably a lot more low tech than you were thinking, but it works for us!