Smart ventilation toward an assessment of airflow imbalance and supply temperature set-points

Many countries have mandated the use of mechanical ventilation with heat recovery to limit heat loss in residential buildings. Nearly all these devices use temperature sensors to modulate bypass dampers and adjust heat recovery. These controls track a reference temperature for the supply or return air while maintaining exhaust temperatures above freezing. As a result, nearly all air-handling units (AHUs) come equipped with temperature sensors before and after the heat exchanger for both airflows. As Figure 1 indicates, these temperatures are often labelled ‘outdoor’ (or ‘intake’), ‘extract’ (or ‘room’), ‘inlet’ (or ‘supply’) and ‘exhaust’. Nearly all AHUs indicate the position of the bypass damper around the heat exchanger, and if the AHU has a heating coil, the data will indicate the temperatures before or after the coil as well as its valve opening position. Using some basic knowledge about the physical design of the heat exchanger, data analysis can indicate the physical flows of heat and mass in the system. After applying several filters to the data, an energy balance can indicate the balance of airflows and required adjustments to the fan speeds to improve this balance. For most AHUs, these controls operate autonomously, but nearly every unit provides a potential communication link via Modbus, BACnet, KNX, or internet API. For this research, we used an API to access data from 40 apartment-level AHUs and developed a novel method to assess their performance with regards to airflow balance and supply temperature configuration.