Air temperature fluctuations in rooms

Field measurements of instantaneous air temperature and velocity were performed in 19 rooms with exhaust, mixing and displacement type mechanical ventilation. Large air temperature fluctuations, up to 3 °C, were measured in rooms with exhaust mechanical ventilation and window slots. In the remaining rooms the standard deviation of the temperature fluctuations was less than 0.5 °C. The frequency of the temperature fluctuations which contribute up to 90% of the measured standard deviation of the air temperature was in the range 0.2–1.2 Hz. Large spatial temperature gradients were not identified. A distance of 20–30 mm between the velocity sensor and the sensor used for temperature compensation does not seem to have an impact on the accuracy of the low velocity measurements. However, the air temperature fluctuations may decrease the accuracy of the measurements due to the different time constants of the velocity sensor and the sensor for the temperature compensation. The air temperature fluctuations will cause fluctuations of the heat flux through the skin of the occupants and this may increase their draught sensation.