Thermostat
Also known as: room thermostat, digital thermostat, cold room controller
Short definitionThe device that reads room temperature through a sensor and switches cooling on and off against the set point. Digital models also manage defrost, the evaporator fan and alarms.
The logic is simple: cooling starts when the measured temperature exceeds the set point by the differential and stops when it comes back down to the set point. This differential is called hysteresis and is around 2 K in most rooms. A mechanical thermostat only opens and closes a contact. A digital cold room controller brings the compressor, fan, defrost heater and alarm outputs together in one unit.
The main values entered at commissioning are room temperature, hysteresis, defrost interval, maximum defrost time and termination temperature, drip time, fan delay and alarm limits. If the defrost interval is wrong, either the evaporator ices up or energy is wasted. The room sensor goes not in front of the air discharge but at a point that sees the average air of the room. The defrost sensor is placed between the fins.