# Scottish Passive House: Insights into Environmental Conditions in Monitored Passive Houses
## 4 Results
### Ventilation  
Air flow rates at the mechanical ventilation grille terminals (supply and extract) were measured in each dwelling using a hooded anemometer. The results (Table 3) confirmed that the air supply and extract delivered to the internal spaces from the MVHR unit was balanced in one dwelling (TB1) and unbalanced in the remaining dwellings with a variance greater than the permissible 10% accepted by Passive House in dwellings DA2, DB1 and DB2. Generally, the MVHR units in Site A were imbalanced, which served to positively pressurise these homes, while the dwelling in Site B was found to be negatively pressurised. Both of these conditions could negatively affect the heat loss and the building fabric by drawing cold air through the fabric or forcing warm moist air out of the building, through infiltration pathways. Furthermore, the imbalance could negatively affect the heat exchange efficiency and require more heat input from the post heater (if available) subsequently requiring more energy to meet the space heating demand. MVHR units in a Passive House are sized based on proposed treated floor area, occupancy levels and an overall air change rate of 0.3 ac/h. Passive House also state a fresh air requirement of 30 m\({}^{3}\)/h per person (equivalent to 8.33 L/s/p) is to be provided for adequate indoor air quality conditions. The air flow rates in dwellings DA1 and DA2 (identical in dwelling size and design) in theory should be equal, the measured air flow rates revealed DA1 to receive 29% more supply air in normal mode and 40% more in boost mode than dwelling DA2. However, the supply air flow rate to individual rooms (Table 3 and Figure 9) indicated that in normal operation the supply rate to all rooms to be inadequate for more than one person, except for living room in DB1 and DB2 with supply air for two persons. If boost mode was utilised, then only dwelling DA1 would have sufficient air supply for two persons in all three supply rooms. In boost mode the extract rooms in DA1 were found to provide flow rates marginally above the Passive House extract air requirements of 60 m\({}^{3}\)/h (kitchen), 40 m\({}^{3}\)/h (bathroom) and 20 m\({}^{3}\)/h (WC). The correct extract air volume was provided in DB1 and DB2 but was found to be poorly distributed in the extract rooms with the greatest extract air being from the bathroom instead of the kitchen. This means there is potential for smells from the kitchen to be drawn to other extract points in the dwelling. The extract requirement in DA2 and TB1 was not met and the occupants in TB1 reported the lingering of kitchen smells. Figure 8: TB1 monthly minimum, maximum and mean temperatures by monitored room for 2013. The occupant in DA2 routinely switched off the MVHR unit for two reasons. The first was the mistaken perception that the MVHR unit was the heating system, and switching it off when feeling thermal comfort had been reached. Secondly the occupant complained of thermal discomfort from draughts arising from air delivery at the living room supply terminal. The air supply rate into the living room was measured as 9.06 L/s at a velocity of 1.39 m/s, suggesting the supply air is being delivered at too high velocity and, thus, not adhering to coanda-effect principles [19]. In dwelling TB1 the treated floor area of the dwelling is of a similar size to three-bedroomed DB1 and DB2 and has the lowest air supply rate of all the monitored dwellings. Additionally, Passive House principles require the boost mode of the ventilation system to be capable of achieving an air flow rate of 30% greater than the normal operational speed for a short period of time.