Halton - displacement design guide
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Ventilation Ventilation efficiency is typically 0.50.8 with displacement ventilation, whereas a level of 0.3Ņ0.45 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 Օ better air quality in the occupied zon. Heating 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: Е horizontal low-velocity supply floor-mounted diffusers.The extraction point of the exhaust air is located above the occupied zone Ֆ preferably close to 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) Օ 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: Օ lower cooling energy and capacity demands to maintain equal thermal conditions in the occupied zone. >

Less suitedBest suitedVentilation ratesIf the specific airflow rate is low, chilled beams are the most recommended solutions for commercial buildings.A displacement ventilation system is a recommended solution for spaces where the occupancy rate or contaminant load is high.Space heightIn low spaces (< 3 m), displacement ventilation is not extremely beneficial as compared to a mixing ventilation system.In high spaces (> 3 m), a displacement ventilation system operates effectively.Heat loadsEspecially in commercial buildings, a high cooling load (> 90 W/m > 2 ) leads to a high airflow rate....

Shift-zone-based-design Calculation of the rising convection flow The shift zone method should be used in cases where heat sources release contaminants into the air and the air quality is the main concern.The height of different heat sources is defined. The rising convection airflow rate is calculated using theoretical plume equations. The heat loads are assumed to be either point or line sources. The location of the virtual origin needs to be defined when the shift zone method is used. Contact your local Halton sales office for further information on the shift zone calculation method. >...

In a kitchen, for example, vertical low velocity supply air displaces the excess heat from the appliances into the high level, to the extraction units.With low-turbulent air supply, the ventilation efficiency is higher than for mixing ventilation, due to beneficial flow conditions near critical extraction points. Ceiling cooling elements combined with displacement ventilation It is necessary to emphasise the difference between the air distribution method and the room air conditioning systems. Low velocity air supply combined with cooling elements e.g., passive beams at ceiling level ֖...

Energy-efficiency The temperature gradient in the room space improves the energy-efficiency because only the occupied zone is actively controlled. Also, the relatively high supply temperature improves the utilisation ratio of free cooling. The temperature gradient between extracted and supply air is typically 4 10 ŰC in commercial buildings and 10 12 ŰC for industrial applications. In spaces where there is no air conditioning but the ceiling height is high enough, displacement ventilation provides lower occupied zone temperatures and better energy-efficiency than a mixing system. Design...

Air distribution principle and supply unit types Displacement ventilation requires a low air velocity supply with limited induction. The air supply can be either horizontal or oriented vertically below a low velocity unit. The extraction point needs to be as high as possible but always above the occupied zone. The low velocity units require a certain wall area, or space in the floor. Typical standard unit types are: wall- mounted, corner-mounted, free-standing, and floor- mounted. Special attention must be paid to the adjacent zone around the supply unit when the unit type and location are...

Cooling load calculations with dynamic energy simulation Dynamic energy simulation should be conducted in order to estimate cooling load accurately. Simplified steady-state calculations typically overestimate the actual demand. Thermal mass plays an important role when the cooling load is computed. The effect of the thermal mass is even more significant when night-time ventilation or cooling is introduced. In commercial buildings, accurate calculation of the solar load is one of the most important factors. The equipment load is the most crucial in industrial buildings.It should be noted...