Samantha Callos, Robert Schofield

We identified 3 peaks (26.4 Hz, 27 Hz, and 29.5 Hz) in DARM resulting from HVAC systems and the CS Chiller; 1 peak between 26.4 Hz and 27 Hz remains unidentified. See Fig. 1.

The first peak at 26.4 Hz's source has been found to be the office HVAC system, as shown in Fig. 2. There are two gaps corresponding to when Robert shut down the HVAC system (from alog 79888). Fig. 3 shows the peak at 26.4 Hz disappears in DARM for when the office HVAC is off vs when it is on.

The second peak varies between 26.5 Hz and ~26.7 Hz. It has yet to be identified, but we do know:

• It has a fundamental harmonic at 13.3 Hz.
• Its strongest, higher harmonics are its 3rd (53.2 Hz) and 6th (133 Hz) harmonic.
• It turns off and on all the time.
• It is seen by both accelerometers and microphones.
• It is seen everywhere.
• Places to look for it next include:
  • LSB
  • LExC
  • Elsewhere?

The third (27 Hz) peak's source is the mini splits HVACs controlled by the downstairs thermostat of the CER, as shown in Fig. 4 when the CER HVAC was shut down (alog 80049). It also shows the second round of shut downs of the office HVAC from alog 79888 which reconfirms the first peak. Fig. 5 shows the peak in the mics disappearing when the "downstairs" bank of the mini splits in the CER were turned off.

The fourth peak's source is the CS main chiller unit, Fig. 6, at 29.5 Hz. This shut down was done by Robert on June 29th, 2024 (alog 78749). A microphone placed across the road from the chiller pads showed that the 29.5 Hz peak seen in the permanent microphones is much louder near the chillers (see Fig. 7).

Finally, in Fig. 8, the coherence between DARM and floor accelerometers is shown for the peaks mentioned above.