Fridges are good for 25L buckets but as cooling and heating is achieved using air for heat transfer its not much good once you are brewing batches of 50L or more, it is pretty much impossible to control the exothermic head generated by yeast, or to crash cool a large batch of beer using a fridge and tube heater.
This is where direct temperature control comes in, commercial breweries typically use jacket fermenters and these can be easily replicated on the smaller home brew scale. For the temperature control the best thing to us is a STC 1000 which is then used to switch the cooling and heating device. For Cooling, a Maxi or similar is ideal. For heating i use a soil heating cable. Both heating (soil cable) and cooling (copper coil) are shown below on a More Beer 14G conical
The conical is then wrapped in Armaflex insulation shown below, this setup allows the fermented beer to be crash cooled to 2-3deg.