Pictured below is a device we recently made to act as a fan controller for an apple storage room.This device has two waterproof DS18B20 temperature sensors connected to it and a relay to switch the power to a fan which drives air from outside the apple store to the inside.

Whenever the outside temperature is measured to be a couple of degrees cooler than the inside temperature, the fan is turned on to drive the cooler air into the store. When the temperature differential falls to zero – i.e. the inside and outside temperatures are equal or the inside is cooler, the fan is turned off again.

This device also has built in frost protection to prevent freezing air from being blown into the apple store. If the outside temperature falls below 2 degrees C, the fan is turned off if it is on, and remains off until the outside temperature has increased by a couple of degrees.

If you need any kind of thermostat, email neil@reuk.co.uk with details of your requirements.