# Performance Analysis of the Demand-Based Ventilation in a Nordic Apartment Building
## 3 Results
### Performance with the Improved Design Concept  
The analysis of the standard ventilation system design shows a satisfactory operation in the normal mode and a significant imbalance of the supply and exhaust airflow rates in the apartments in the boosting mode. In all apartment types, the kitchen hood exhaust ventilation is unable to provide the designed 25 L/s airflow rate when two or more apartments in the same line are boosting. The range hood has two k-value settings. The principle of the standard balancing strategy is that the boosting mode k-value of the kitchen hood is obtained when only one apartment is boosting in the apartment line. The origins of the practical issues in the supply branches of studios and two-, three- and four-room apartments are the same. The control system does not adjust the k-value of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Apartment Type** & **2.5 1/h** & **1 1/h** & **0.5 1/h** \\ \hline Studio apartment & \(-\)4.4 Pa & \(-\)15.4 Pa & \(-\)39.8 Pa \\ \hline
2-room apartment & \(-\)1.6 Pa & \(-\)5.5 Pa & \(-\)15.4 Pa \\ \hline
3-room apartment & \(-\)0.9 Pa & \(-\)3.3 Pa & \(-\)12.7 Pa \\ \hline
4-room apartment & \(-\)0.7 Pa & \(-\)2.5 Pa & \(-\)6.4 Pa \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The pressure difference in the apartments with different airtightness levels. the components in the boosting mode, resulting in too high or too low apartment branch resistances, respectively. In Figure 6, a proposed solution is presented. The one-position dampers are replaced with two-position dampers in the exhaust branch of two-, three- and four-room apartments, and the supply branch of studio apartments. The two-position dampers are set to have different k-values for normal mode and boosting mode. The k-value for normal mode is obtained for all apartments in the branch simultaneously. The k-value for boosting is then obtained with only one apartment in the branch boosting and the rest in normal mode. The branch-level damper settings are presented by a k-value that is obtained when all apartments in the branch are in boosting mode. The kitchen hood has two settings for the k-value as well. The k-value for the normal mode is obtained when all hoods in the branch are in the normal mode. The k-value for boosting is obtained with only one apartment in the branch boosting, and the same value is used in every hood in the branch. The results of applying the new, improved concept are shown in Figure 7. The overall presentation methodology is similar as in Figure 3. In Figure 7, the two-room apartment and studio airflow rates are presented at different operation modes. The solution where the dampers are replaced with two-position ones but the balancing strategy is the same as in the original design fails to match the target values due to the decrement of the airflow rate of kitchen hood while more apartments are boosting. As a result, it is causing an ineffective performance of kitchen hoods and hence system imbalance. The combined solution with a damper replacement and modified balancing strategy shows the ability to maintain the airflow rate values within 10% of the target value. The maximum supply and exhaust imbalance on the apartment level is around 10%. Both concepts are presented to show that issue should be addressed in the complex. In the case study building, the kitchen hood exhaust branch is designed to be capable of providing the required airflow rates in cooking mode. Thus, the most demanding boosting modes have not been taken into account, resulting in the shortage of the airflow rate. The results show that proper airflow balancing is essential even in a well designed ventilation system, and the strategy should be created concerning all possible ventilation system modes. Furthermore, in general, the system inherited the CAV design with minor changes, presented by local airflow control on the apartment level through on/off dampers.