Ventilation Ventilation efficiency is typically 0.5…0.8 with displacement ventilation, whereas a level of 0.3…0.45 can be reached by using mixing ventilation. Better ventilation efficiency means, in addition to energy savings, improved indoor air quality in the occupied zone and thus improved performance of the workers.
Supply airflow patterns for different supply air temperaturesIsothermal air supply Warm air supply Cool air supply • a longer period for the use of free cooling • better air quality in the occupied zon. Heater A displacement ventilation system can be applied also for heating in commercial buildings if the heating demand is low. However, in heating mode the system operates like a mixing ventilation system. The extraction point should not be located directly above the supply unit, to prevent short-circuiting of warm supply air to exhaust. The most typical applications for heating integration are industrial or similar buildings and lobby areas where the activity level and clothing differ from, e.g., those of the office environment. Cooling With displacement ventilation, the room air temperature increases with the height in the space. Thermal conditions and air quality are actively controlled only in the occupied zone. The air temperature and contaminant level are higher in the upper zone.Depending on the breakdown of heat gains and the height of the space, the temperature difference between the supply and exhaust air is 5 to 12 °C. Since cool air is supplied directly to the occupied zone, special attention should be paid to analysis of the potential draught risk close to the units.
Typical displacement ventilation application Thermal displacement ventilation is based on cool air supply at low level and stratification of room air temperature and contaminants as a result of the natural buoyancy forces created by the heat sources. Traditionally the system has been designed as a dedicated outdoor air system. There are two alternative concepts used in a displacement ventilation system: • horizontal low-velocity supply • floor-mounted diffusers.The extraction point of the exhaust air is located above the occupied zone – preferably close to professional ceiling level.A displacement system is preferable for the following situations: • the specific airflow rate per unit of floor area is high (as in lobbies, theatres, and conference rooms) • high contaminant loads exist, as in industry and smoking areas • the height of the space is more than 3 metres. Description Operation The advantages of displacement ventilation over totally mixing ventilation system are: • lower cooling energy and capacity demands to maintain equal thermal conditions in the occupied zone.

Displacement ventilation system Displacement ventilation system

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