Condensation in Buildings - Australian Building Codes Board

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Information Handbook: Condensation in Buildings Figure 4.15 – Impact of indoor volume, air change rate and ducting of sources on indoor humidity water vapour content of indoor air (g/kg) 14 12 10 8 6 4 2 0 87% RH at 20°C from indoor sources from outdoor air 50% RH at 20°C 59% RH at 20°C 47% RH at 20°C 100m² / 0.5 ACH 100m² / 0.5 ACH 100m² / 2.0 ACH 100m² / 2.0 ACH 300m² / 0.5 ACH 300m² / 2.0 ACH / not ducted / DUCTED / not ducted / DUCTED / not ducted / DUCTED Floor area / Air change rate / Ducting of indoor sources The first four columns in Figure 4.15 show the effect on indoor vapour content of using ducting and increased ventilation to manage a daily release of 10 kg from indoor sources in a 100 m 2 dwelling (the 10 kg average value is based on typical rates of release shown in Figure 4.16). The last two columns (in darker blue) indicate the advantage of having a larger indoor volume. The water vapour content of the outdoor moist air (shown in the lower parts of the columns) sets the baseline for indoor water vapour levels and provides the major contribution in all of the examples. Choices about ducting arrangements and fresh air ventilation rates, however, make considerable differences to the average water vapour content indoors (shown by the overall height of each column). Whatever is not ducted to the outdoors or carried away by ventilation will be dispersed through the moist air volume in the building. In practice, it is unlikely that perfect mixing will occur, particularly when bathrooms and laundries are often behind closed doors. Indoor sources, concentrated in particular rooms, may raise the indoor water vapour content above the calculated average value. To recognise this possibility, an initial assessment of the impact of indoor water vapour generation can use a smaller building volume than is actually present. Similarly, assuming a low ventilation rate and low levels of outside exhaust will tend to amplify the effect of estimated water vapour releases indoors (as demonstrated by the varying examples in Figure 4.15). This approach is adopted in Section 4.6, using the psychrometric chart to highlight what may happen if indoor moist air finds its way to parts of the building fabric which are cooled to near-outdoor temperatures. DRAFT HANDBOOK Australian Building Codes Board Page 45
Information Handbook: Condensation in Buildings Figure 4.16 – Indoor sources of water vapour in dwellings and rates of release (Source: BRANZ 2012) Cooking: 5 kg per day – unvented, gas fired Laundering: 0.6 kg per day – unvented 2 hours of cooking per day washing every 5 days, drying every 10 days 1 kg per day Dishwashing: 1 kg per day 3 kg per day (if not vented outdoors) 2 kg extra if gas fired 0.2 kg per person per hour Washing 0.5 kg per load 1.5 kg per person (if not vented outdoors) Drying 5 kg per load (if not vented outdoors) Bathing/Showering: 6 kg per day for 4 people – unvented 0.5-1 kg per hour (if unflued) DRAFT HANDBOOK Occupants:5.5 kg per day for family of four absent / active / asleep 8 hours each Gas heating: 4 kg per day – if unflued (dog not included) Australian Building Codes Board Page 46
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Condensation in Buildings - Australian Building Codes Board

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