Various industrial processes usually take place in the air and they require different parameters of air quality and accuracy of its maintenance.

In present there are no rigorous analytical methods for reliable determination the actual accuracy of maintenance of air quality parameters on condition that they change orderly or stochastically. The harmonic analysis of exponents of periodical increase and decrease of parameters is proposed. It can be used for the estimation of  fluctuations and precision of maintenance of various air quality parameters, first of all, in precision technological V and AC systems.

Suggested method of temperature calculation under changing periodical heat load at the premises is illustrated by the example of high-precision V and AC system operating the area of grinding and test of optical devices.