Evaluation of supply temperature set-points and airflow imbalance using smart ventilation data

The installation of central mechanical ventilation with heat recovery (MVHR) in renovated apartment buildings presents considerable challenges, primarily due to insufficient space for ductwork. Consequently, many renovation projects are installing decentralised MVHR units, catering to individual apartments. Many of these devices offer the option of communicating with their controllers via Modbus, BACnet, KNX, or internet APIs, provided the necessary resources are available for the connection. Unlike central MVHR units, which offer the opportunity for centralised commissioning and maintenance, these decentralised units are frequently located in suspended ceilings or cabinets in refurbished apartments. This placement makes them challenging to access without a coordinated effort. Therefore, monitoring these decentralised MVHR units via available communication links – a concept commonly referred to as 'smart ventilation' - proves to be more convenient and less labour-intensive. Most MVHR units come with standard data sets, which typically include supply and exhaust fan signals and temperature sensors located before and after the heat exchanger for both the supply and exhaust airflows. The controller uses these temperature measurements, as depicted in Figure 1, to adjust the bypass damper's opening position, thereby modulating heat recovery. This adjustment aims not only to achieve the specified supply temperature set-point but also to prevent frost accumulation by raising the exhaust temperature when necessary. During the commissioning phase, the installer seeks to balance the supply and exhaust airflows to maximise heat recovery and minimise infiltration or exfiltration. However, reaching the specified airflows for each zone proves difficult. Even when achieved, this balance could degrade over time due to dust accumulation on components or occupants' interference with the valves. 'Smart ventilation' data can be used to optimise heat recovery by ensuring balanced supply and exhaust airflows. By performing an energy balance, 'virtual sensors' can be created to indicate the airflow balance. In this study, we utilized 'smart ventilation' data from 100 apartments in Frederikshavn, Denmark, to assess the supply temperature set-points and airflow balance.