No, this is not the case. We often surfaced at night to recirculate with fresh air. In fact, this is done so often that the first thing we do is turn the clocks 12 hour forward so our day shift when everyone was working occurred at night. We need to surface to recharge the lead acid battery off the diesel engine as well, which was done to make sure that kept working well. I did this when newly qualified as an electric plant operator and it was difficult for me to do correctly.