Description
In order to ensure a given class of cleanliness in clean rooms, the system of supply and exhaust ventilation must provide a certain level of air exchange.
The air exchange rate is the ratio of the volume of air entering the room to the volume of the room itself. The higher the air exchange rate, the more efficiently aerosol particles are removed from the room, the source of which is located in the cleanest room - these can be people working in the room, and equipment, and the process.
In case of insufficient air exchange, no matter how high-performance finishing filters are used to filter the air entering the room, it is impossible to achieve the required cleanliness class of the room, since the intensity of aerosol sources and air pollutants will be higher than the speed of their removal by the ventilation system.
How to measure air consumption and air exchange rate
The approach to determining the frequency of air exchange is quite simple, there are several methods for measuring air flow, which are used depending on the configuration of the clean room and the equipment available. One of the methods is to measure the average air flow rate near the final filters or in air ducts using a hot-wire anemometer. Knowing the average air velocity and the cross-sectional area of the duct or finishing filters, it is easy to calculate the volume flow.
It is possible to conduct direct measurements of the volumetric flow rate using a balometer, a special instrument equipped with a casing that collects the entire volume of air that has passed through the filter. The use of a balometer greatly simplifies and speeds up the measurement of the volumetric flow rate at the air distribution devices in the event that the measurements with a thermal anemometer are hampered by the presence of air distributors, diffusers or a highly turbulent air flow.
After measuring the speed / flow rate of air through all final filters and air distributors, the air exchange rate is calculated. The air exchange rate can be assessed separately for supply and exhaust air.
The results of measurements of flow rate, volume flow rate and air exchange rate
The test report includes information on the measured flow rate at each diffuser, the volume flow rate of air through the inflow and exhaust, the rate of air exchange in the room, as well as the compliance of the measured values with the requirements of the design and regulatory documentation.
