# Performance Analysis of the Demand-Based Ventilation in a Nordic Apartment Building
## 2 Materials and Methods  
### Building Description  
A building in Helsinki, Southern Finland, was selected for the analysis. It was built in 2019 and has a complex structure, and one staircase was chosen for the analysis. The staircase has five floors with a floor height of 3 m, the first floor is non-residential, and the 4 above are residential. The ventilation system is a centralized demand-based balanced mechanical system with heat recovery, shown in Figure 1.  
The designed air change rate is 1 1/h at the apartment level, with a minimum of 0.5 1/h on room level. The air is supplied in the living rooms and bedrooms and extracted in the bathrooms, toilets, storages, and kitchens. Supply airflow rates are chosen according to occupancy, room type or floor area, whichever value is higher. The exhaust airflow rate is set to be equal to supply. The apartment airflow rates for studio, two-, three- and four-room apartments are 27 L/s, 37 L/s, 42 L/s and 50 L/s, respectively. The apartment floor area for the studio, two-, three- and four-room apartments are 32.5 m\({}^{2}\), 41.3 m\({}^{2}\), 64.5 m\({}^{2}\), and 87 m\({}^{2}\), respectively. The kitchen hood has two operating modes: normal with 8 L/s and boosting with 25 L/s. In the boosting mode in the two-, three- and four-room apartments, the increased airflow in the kitchen hood is compensated by decreasing the exhaust airflow rate in the bathroom and toilet by closing one of the exhaust air valves. In the studio, the supply airflow rate is increased by opening an additional supply diffuser to compensate for the additional kitchen exhaust airflow rate needed in boosting mode. The exhaust airflow rate of studio bathrooms cannot be reduced due to the minimum required airflow rate demand, shown in Figure 2.  
Figure 1: Scheme of the ventilation system in the case building. AHU: Air Handling Unit. The ventilation ductwork is designed so that apartments connected to the same staircase are served by a single air handling unit (AHU). In that AHU's serving area, the ductwork has separate control zones. Each control zone has the same set of apartments on 4 different floors, shown in Figures 2 and 3. The apartments located above and below each other are identical and have joint branches of exhaust and supply ventilation ducts. The AHU maintains a constant static pressure in the exhaust (140 Pa) and supply (110 Pa) ventilation plenums, controlled by adjusting the speed of the fans. At the apartment level, the boosting technology is introduced in two ways: apartment airflow increment and borrowing. In the studios, the total airflow rate (both supply and exhaust) is increased by 30% in the boosting mode. An on/off damper is installed in the living room branch to supply more air in the boosting mode. The damper is closed in the normal mode. The borrowing principle is used in the two, three and four-room apartments. The boosting exhaust airflow of the kitchen range hood is compensated by reducing the bathroom exhaust. In the bathroom branch, the damper is closed when the boosting mode is activated, and opened in the normal mode. The characteristics of components of the ventilation system of the apartment and branch levels are presented in Tables 1 and 2. The ducts are the same size as the corresponding components. The k-values are presented for each component in the normal operation mode to represent its resistance characteristics in accordance with Equation (1). The airflow rate values are based on the commissioning documentation of the case study building and are equal for the supply and exhaust sides. The kitchen hoods have two k-values, one for normal mode and the other for boosting, and these values are identical for each hood. The balancing dampers have one fixed k-value and are adjusted to the normal mode. Figure 2: Airflow rate of rooms in differently sized apartments on one floor during normal and boosting modes.