displacement ventilation

This study introduces a novel conceptual design of a mobile DV cooling unit that is aimed to support the ventilation and reinforce the thermal stratification in DV rooms. Supplying filtered chilled air from at low height, the portable DV unit (PDV unit) functions as if it is a typical DV diffuser. Moreover, the PDV unit employs heat exhausted from the heat pump to reinforce the temperature gradient by injecting the hot air flow in the upper zone of the room. Utilizing the exhaust air makes the PDV unit entirely ductless which adds to its flexibility placed in to balance the airflow.

Airborne transmissions take place as a transport of virus or bacteria via the aerosol flow in rooms. The distribution of aerosols tends to be evenly distributed if the flow in the room is fully mixed. The aerosols distribution will be different if the room air is stratified. A vertical temperature distribution may create stratified layers with either lower or higher concentrations of exhalation from the infected person.

Children spend the majority of their weekdays in classrooms that often have low indoor air quality and limited financial resources for the initial and running costs of mechanical ventilation systems. Designing effective natural ventilation (NV) systems in schools is difficult due to the intense use of the classroom spaces and the dependence of NV on building geometry and outdoor conditions. Building thermal and airflow simulation tools are fundamental to predict NV system performance in the design phase.

An accurate temperature gradient calculation is essential for displacement ventilation (DV) system design, since it directly relates to the calculation of the required supply air flow rate. Inaccurate temperature prediction can cause the poor thermal comfort and w sizing of the ventilation and cooling systems.

The ventilation system removes pollutants effectively, and the resultant vertical temperature difference in the room greatly affects the indoor air distribution. A reasonable air distribution system is essential to provide a satisfying indoor air quality (IAQ) for the occupants, of which air quality in the breathing microenvironment plays a major role in occupant health, as they are exposed to this region directly.

An accurate temperature gradient calculation is essential for displacement ventilation (DV) system design, since it directly relates to the calculation of supply air flow rate. Several simplified nodal models were developed and implemented in the various building simulation programmes in order to estimate the temperature stratification in rooms with displacement ventilation. However, the most commonly used models do not count the types and locations of the typical heat loads in rooms with displacement ventilation.

Drøbak Montessori lower secondary school is Norway’s first plus-energy school and also the first school built after the Norwegian Powerhouse-concept, www.powerhouse.no. This concept implies that the building shall produce more renewable energy during the lifetime of the building, than used for materials, production, operation, renovation and demolition.  

Displacement ventilation (DV) is an alternative to conventional mixing ventilation in various types of rooms. DV is superior to mixing ventilation when it comes to removing contaminants and surplus heat in a room if designed and applied correctly. In the design process of a space with DV it is necessary to have design methods and simulation tools that can predict the vertical contaminant stratification that arise.

The impact of clothing, breathing and body posture on the thermal plume above a thermal manikin was investigated. Measurements of air velocity and temperature above the manikin were performed at four different heights above a sitting and a lying manikin. The results obtained from tests above the sitting manikin show an inverse proportion between the thermal insulation of clothing and the air velocity in the thermal plume. Air velocity in the thermal plume with the breathing function switched on equalled 90-98% of the values obtained for non-breathing experiments.

This study developed a drift-flux model for particle movements in turbulent indoor airflows. To account for the process of particle deposition at solid boundaries in the numerical model, a semi-empirical deposition model was adopted in which the sizedependent deposition characteristics were well resolved. After validation against the experimental data, the drift-flux model was used to investigate human exposures to particles in three normally-used ventilation types: mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD).