Abstract :
Two new units are proposed for the evaluation of indoor air quality using the decibel concept, which give a much better approximation of the human perception of odour intensity, compared to the CO2 and TVOC concentration scales: the decicarbdiox and the decitvoc. On the Psycho-Physical Scale according to Yaglou, the weakest odour that can be detected by the human smell sensors is equal to 1 and corresponds to the lower limit of percentage dissatisfaction (PD) of 5.8% and is equivalent to (a) a CO2 threshold concentration of 485 ppm — O dB (odour CO2) — dCd (decicarbdiox), and (b) a TVOC threshold concentration of 50 μg/m3 — O dB (odour TVOC) — O dTv (decitvoc). The upper limit is determined by the initial value of toxicity (a) CO2 — 15,000 ppm — 134 dCd, and (b) TVOC — 25,000 μg/m3 — 135 dTv. It is supposed that optimal values corresponding to PD=20%, admissible values to PD=30% for unadapted and adapted persons and that long-term tolerable values (determining SBS range) and short-term tolerable values (beginning of toxic range) are stated as well. The same figures used to evaluate noise can be used to evaluate air quality, additionally the contribution of individual constituents (at present acoustic and odour) to the overall quality of the environment can be ascertained. The new units dCd and dTv can express an increase or decrease in air contamination, i.e. by using air cleaners, new building materials, etc. The proposed system of dCd and dTv is compatible with BSR/ASHRAE 62-1989 R which can be used to determine the required volume of fresh air for ventilation by an improved method which takes into account different levels of required indoor air quality.
