aeraulic load losses in ventilation systems are irreversible loss of energy because the loss is converted into heat or noise :
Suction ventilation calculation software Mecaflux pro3D:
Ventilation renews and cleanses the indoor air and provides fresh air necessary for well being of the occupants.
- Natural ventilation by temperature difference, using convection of cold air taken from outside that rises when warmed, This ventilation can be calculated as for pulling up a flue with a heat input (power generator) corresponding to the heat in the rooms.
- Mechanical ventilation is to create a dynamic air movement with a fan, which compensates the aeraulic head loss related to flow in air ducts.
The nine principles of ventilation(INRS)
• Wrapping at maximum area pollutants
• Capter au plus près de la zone d'émission
• Collecting at closer to the emission zone
• Using the natural movements of pollutants
• Induce sufficient air velocity
• Uniformly distributing the air speed at the zone
• Compensate for air outlets with corresponding air inflow
• Avoid the air currents
• Reject the polluted air outside of the areas of fresh air inlet
regulation based on two principles: :
• Aeration should be general and permanent ;
• It must scan the entire housing with installed air inlets in the main rooms and outlets placed in service rooms.
|extracts Flow rates expressed in m3/h|
|Number main rooms||kitchen||Bathroom||Other bathroom||single WC||WC multiple|
|5 et plus||135||30||15||30||15|
When the ventilation is ensured by a mechanical device that automatically module housing air renewal, so that the rate of indoor air pollution do not constitute any health hazard, and the condensation can be avoided, except transiently, the rates defined in the table above may be reduced.
• If it is a CMV (controlled mechanical ventilation) Single flow the minimum flows to respect are :
|Nb main rooms||1||2||3||4||5||6||7|
|Total minimum flow in m3/h||35||60||75||90||105||120||135|
|Minimum flow in kitchen m3/h||20||30||45||45||45||45||45|
•And if it is a humidity controlled ventilation, minimum ventilation rates are further reduced :
|Nb main rooms||1||2||3||4||5||6||7|
|Total minimum flow in m3/h||10||10||15||20||25||30||35|
Office premises without physical work
25 m3 per hour
Local restoration, sale, assembly
30 m3 per hour
Workshops with local light physical work
45 m3 per hour
Other workshops and local
60 m3 per hour
- Local non-specific pollution: Pollution mere presence of man
- To specific local pollution: pollution from the emission of harmful or embarrassing products
- Local ventilation: capture pollutants as close as possible to their source
- General Ventilation: dilution of the pollutant with a new air into the workroom
- Natural ventilation: ventilation only made by external opening
- Mechanical Ventilation: ventilation performed by mechanical devices, provides fresh air flow.
- Mechanical local non-specific pollution ventilation : Minimum flow of fresh air per person depending on the local
The hourly rate of brewing - or HRB - is the number of times the air is renewed in a room for a period of one hour.. Unlike the hourly turnover rates, the air flow in the room is not new and can come from an air intake followed by filtration.
For example, with a system of supply and return air with a flow rate of 30 m³ per hour, the HRB will be 3 for a room of 10 m³..
hourly turnover rates – HTR – is the number of times the air is changed in a room for a period of one hour. Unlike the hourly rate of brewing, the air blown into the room is new.
For example, with a system of supply and extract with a flow of 30 cubic meters per hour, HTR will be 3 for a room of 10 m³.
Mechanical ventilation is the cause of two types of energy expenditure:
- Energy expenditure of the fan
Expenses related to the fan is calculated by multiplying the engine power (in kW) by the annual operating time (8760 hours if the operation is continuous). This corresponds to the major losses in the air ducts and minor head loss of the system and fan efficiency
- The cost of heat (in winter) corresponding to the need to heat the air renewed
Expenses related to heating (E Wh / year) can be calculated as follows:
- 0.34 = constant wastage for ventilation W/K/ (m³/h) (W: Watt - K: Kelvin)
- Flow = airflow m³/h.
The flow is generally not known,it is calculated from the ratio of the air volume of the building, which is renewed in one hour. The basis of calculation may be 1 vol/h, which means that all air from the building is renewed in an hour..
- DDU (Degree Days unified) K.day/year = measure calculated for each department, equal to the difference between the mean temperature of the day and 18 ° C, every day.
- 24 hours / day to reduce the ratio in hour.
E = 0.34 * Flow * DDU * 24
Exemple : Building with a living area, heated of 2 380 m² (ceiling height 2.50m). Consumption of heating : 563 000 kWh. The CMV (controlled mechanical ventilation) is a power of 1150 W and renews the air up to 1 vol/h.
E = 0.34 * 5 950 * 2 321 * 24 = 112 689 190 Wh =>112 689 kWh
This consumption represents about 20% of annual heating consumption of condominiums.