Investigation of the performance of mock-target IR thermography for indoor air temperature measurements under transient conditions

Abstract

Mock Target IR Thermography for indoor air temperature measurement has been proven as an effective methodology for steady-state conditions. This method uses vertical poles of known emissivity placed in a space to measure air temperature by employing IR thermography. Compared to thermocouple / point-by-point measurement, this technique allows obtaining air temperature values in a continuous line. Several poles can be installed in a space ensuring the collection of a large amount of air temperature data entries by taking a single IR image, whereas measurements in large spaces with hundreds of thermocouples would require complicated wiring and data collection hardware. However, for this approach to be more widely considered, such measurement techniques should be adaptable for transient conditions as well, as air temperature can fluctuate and change due to external climatic conditions, occupancy or faults in HVAC equipment. This work aims to investigate if IR Thermography which was only tested in steady-state conditions can be applied to conditions of transient variation of indoor air temperature. For this purpose, measurements under lab conditions and numerical analysis with the use of finite element modelling (FEM) were performed. Specifically, measurements were carried out by using both Mock Target IR thermography and thermocouples, to investigate the precision of IR-obtained transient data. The experiments were conducted in the environmental chamber under controlled conditions. Three types of heating systems (underfloor heating, radiator heating, and ventilation heating) were investigated to ensure that the method is tested under conditions of different heat-emitting devices, as well as different convection and radiation ratios. Validated numerical models were developed using the FEM Multiphysics approach, to extend the scope of the assessment under various conditions and to observe the difference between the mock target pole temperature and air temperature. It was concluded that the mock target IR Thermography performance was accurate for the case of transient air temperature, as well as for different rates of temperature change, with an average temperature deviation of 0.4 [%] according to the experimental measurements and 1.74 [%] based on the numerical simulations.