The ventilation systems of clean rooms consume a lot of energy, especially power for the ventilating fan, refrigerating capacity for cooling and dehumidification in summer as well as heating for warming and steam for humidification in winter. Therefore, the question comes up again and again whether one might switch off the ventilation of the rooms overnight or when they are not used in order to save energy.
It is not advised to switch off the ventilation system completely, it is rather advised not to do it. Premises, pressure conditions, microbiology, everything would be out of control during that time. This would make the subsequent measures for the restoration of the GMP-compliant state very complex because each time a requalification would be necessary to reach the normal GMP-compliant state.
But a reduction in the performance of the ventilation systems (reduction of the air volume by reducing the performance of the ventilation system) is possible, and is already carried out in some companies. Here too, however, the GMP-compliant state must be achieved prior to using the clean room again and this procedure must be validated.
For this purpose the following points must be observed:
The reduction can only be carried out so far that the clean room specific limits prescribed for the relevant case are not violated in general. These limits have to be defined in each case for the operating status and the reduction mode including permissible minimum and maximum values, such as clean room class (particle count with equivalent particle size), product specific values (temperature, relative humidity), pressure conditions (pressure difference between the rooms). Note that the values in reduction mode have to be chosen in such a way that the facility has reached the GMP-compliant state in due time before production begins (integration of a time program). This state depends on different parameters such as building material and performance of the system etc. The pressure conditions should be maintained all the time, this means that a reversion of the flow direction is not allowed.
Furthermore, the installation of an independent clean room monitoring system is recommended in any case in order to constantly monitor and document the above mentioned clean room specific parameters. Thus, the conditions of the area concerned can be monitored and documented at any time. In the case of deviations (reaching of a limit) and in the individual case it is possible to access the measurement and control technology of the ventilation system and to carry out the relevant adjustments.
During the reduction attention should be paid to ensuring that no unpredicted external interfering influences such as the entry of persons are allowed. For this the installation of a corresponding entry control is advised. In the case of an electronic locking system the entry authorisation can be linked with the above mentioned time program as well as with the independent clean room monitoring system so that entry is authorised only subject to compliance with the predefined requirements.
In principal, both states must be qualified first and then requalified in regular intervals and the customary measurements for the regular operating status such as the recovery time measurement in case of a complete failure of the facility must be carried out. In the case a clean room monitoring system exists it is in principal not required - as mentioned above - to carry out further measurements at the start of operations after reduction mode if the procedure is validated. Special focus should be put on the procedure of restarting since temporary reversions of the flow direction are possible, for instance.
All in all about 30 % of the energy costs can be saved depending on the mode of operation and the shift model but additional investment costs might have to be offset.