At 08:20 UTC, in agreement with Dattilo, Passaquieti and Soldani, I turned off the CEB AHU ventilation of the clean rooms, for energy saving (pict1).
To ensure the overpressure of the clean rooms of SIB2 I sealed, with tape, the communication door between SIB2 and the Clean Room (Pg). The door is now sealed and locked. In case of need, contact the Clean Op team.
The contamination levels of the CEB clean rooms are constantly monitored by a particle counter positioned in Class100 (plot attached).
Concerning the CEB CleanRoom AHU "off condition" assessment.
A few observations concerning the behaviour of the clean area parameters and the achieved environmental noise reduction during the switch off.
The ClearRoom AHU has been kept off continuously for about 3 weeks, from December 16 to January 10.
Figure 1 shows the behaviour of the temperature and humidity of the Class 1 and Class 100 areas. Also the dust particle counters are shown but are not to be considered because likely unattendible. Figure 1 shows a long time stretch since the beginning of October.
At the end of October the temperature and humidity start fluctuating replicating the outside temperature (Figure 2). This is consequent to the closing of the warm and cold water flows into the HVAC heat exchangers but keeping the air fans running (energy saving test). In this configuration the inlet external air (which is substantial) temperature and humidity parameters are no more compensated by the heat exchanger control loops. The "problem" is the large external air flux, which although it has been set to the "minimum", looks still too large, as verified with inspection (Vincenzo and Davide). The replacement of the external air shutter with one with a more sutable range is planned.
When, between Dec. 16 and Jan 10, also the air fans have been turned off the temperature and humidity are more stable and the temperature stabilize at about 22 deg, that is +4deg respect to the HVAC full operation condition. This better stability is probably due to the fact that the external air inlet circulation reduces when the fans are stopped.
Figures 2,3,4 and 5 describe the reduction of noise in the CEB hall consequent to the switch off. Some vibration and acoustic lines disappear from the CEB floor (Figure 1) and vacuum chambers, in particular DT and IB (Figure 3). These lines have been identified, see https://tds.virgo-gw.eu/ql/?c=18442 or the LineDB. In particular disappear the infamous 18.5 and 16.4 Hz lines. Figures 4 and 5 are intensity maps of the NN-seismic-array (@Level 2) at the 18.5 Hz line, taken when the CleanRoom AHU is ON and then OFF, respectively. Note that there switching off the CR AHU causes no evident reduction of broadband noise, neither in seismometers or microphones (Figure 1, TOP plot). We know that the broadband acoustic and seismic noise in the CEB floor below ~10Hz is dominated by the HALL AHU. To complete the assessment of the CleanRoom AHU off condition the air contamination parameters need to be examined as well.
This morning, at 09:42 UTC, with D. Soldani, we turned OFF the Air Handling Unit (CEB AHU) ventilation of CEB Clean Rooms for energy-saving reasons.