@MarkSiddallRIBA @BarryMcCarron Another independent result confirming [Uhlig 2014]. The measurements have been made in a region with high radon actcivity in the soil. With HRV running, indoor Rn-activity just around the values of external air. Without HRV: see yourself. 
@MarkSiddallRIBA @BarryMcCarron What removes Rn also removes other indoor air pollutants: VOC,smells,dust (&the germs connected to dust).The removal rates are similar. Of course,also indoor CO2 is reduced(although that's not a 'pollutant').In one sentence: Indoor air in passive houses has an improved quality.
@MarkSiddallRIBA @BarryMcCarron Important remark: It's not just the HRV. It's all of the following:
(1) really air tight envelope
(to avoid uncontrolled leckage: e.g. Rn coming in)
(2) pure balanced fresh air ventilation (no recirc. air)
(3) quality approved (i.e. PH certified) HRV system
(1) really air tight envelope
(to avoid uncontrolled leckage: e.g. Rn coming in)
(2) pure balanced fresh air ventilation (no recirc. air)
(3) quality approved (i.e. PH certified) HRV system
@MarkSiddallRIBA @BarryMcCarron Methodological question: How can it even be smaller than the value in external air? Part of the activity comes from Rn-decay nuclei (e.g. Po-218); these are metals & tend to condensate on dust particles caught by the HRV filter.
