The amount of water vapour removal depends on the relative humidity and temperatures of indoor and outdoor air. It is critical to maintain a comfortable level of humidity in winter (indoor: temperature 20°C, relative humidity (rh) 60 per cent; outdoor: temperatures between 0°C-10°C, rh 70 per cent). In this case, the exfiltration rate of water vapour mass MR varies between:

3.8 g m-3 • VR (m3 h-1) ^ MR ^ 7.0 g m-3 • VR (m3 h-1) [10.2]

where VR = n • V is the volume rate of the exchanged air.

The lower limit correlates to 10°C outdoor air temperature, the upper value describes the case for 0°C. Correspondingly, an air exchange rate per person of 30 m3/h will remove between 110 g/h and 210 g/h of water vapour. This rate of removing water vapour is quite sufficient for most of the cases where humidity is generated in dwellings. Only for more intensive showers, cooking, cleaning, washing and drying activities will higher humidity loads occur, which have to be removed by additional ventilation measures (intended actions such as opening of windows, setting the highest possible mechanical ventilation rate and activation of an extra fan). Table 10.1.1 gives the typical emission rates of water vapour due to various sources.

Table 10.1.1 Typical emission rates of water vapour for some sources

Source of water vapour Evaporation rate (g/h)

Persons (sedentary activity) 40-60

Persons (average activity) 60-120

Persons (exhausting activity) 120-200

Bath approximately 700

Shower approximately 2500

Cooking 600-1500

Potted plants 7-15

Drying laundry (4.5 kg washer drum), spinned dry 50-200

Drying laundry (4.5 kg washer drum), dripping wet 100-500

Aquarium (per m2 water surface) 30-50

In a typical household with 4 individuals, approximately 12 kg of water vapour is emitted over 24 hours.

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