Refrigerant gases are used to provide a means of cooling the evaporators in freezers and air conditioning for plant rooms and chiller plants. Historically CFC refrigerant gases such as R11, R12 and R22 have been used. CFC’s are ozone depleting gases and are now being phased out and replaced by ozone friendly gases such as R134, R404 and R407.
There are two basic techniques used for the detection of CFC, HFC and HCFC gases:
These use specially doped substrates and are run hot. When the gas passes over the sensor it changes the electrical characteristics of the semi-conductor and hence changes the response from the sensor. The sensors are low cost but suffer from basic problems which make them unreliable in their use:
Most chemicals, including all refrigerant gases absorb infra-red energy. Often these wavelengths are specific to individual chemicals or the wavelengths can be selected to monitor whole groups of chemicals including refrigerants. Monitoring the absorption of infra-red energy at selected wavelengths provides an accurate method of measuring low levels of these gases. The sensors are more expensive but do not suffer the problems associated with cheaper technologies such as: