B.5. Calculations of ventilation air balance <br>

B.5. Calculations of ventilation air balance

Ventilation air balance in program is used in area of building. It includes all compartments in building, both heated and non-heated. Program performs the air balance for whole building to calculate the ventilation air balance for compartment.

Applied algorithm assumes, that ventilation air is removed from flat as a result of operation of mechanical ventilation and is supplied to the building through leaks in building construction from outside as a result of subatmospheric pressure caused by operation of exhaust ventilation or/and is blown mechanically into compartments. The balance of ventilation air includes only streams of air resulting from declaring of streams exhausted from and blown into the compartment on the way of mechanical ventilation. The balance does not include hygienic and infiltration stream of air.

Balance of ventilation air in compartment includes following air streams:

- stream of air exhausted mechanically from compartment “Vexh”,

- stream of air blown mechanically “Vsup”,

- stream of air flowing into compartment from outside and/or from other compartments in building “Vmech,inf,i”. It is a stream of air flowing as a result of operation of mechanical installation. It occurs, when declared exhausted steam “Vexh” is bigger than blown stream “Vsup”. Then, to keep the air balance, into compartment flows an external air through leaks in building construction and/or from other compartments.

Ventilation air balance in compartment does not include following streams of air:

- stream of infiltrating air “Vinf”,

- minimal stream of ventilation air “Vmin” resulting from hygienic requirements in compartment.

These air streams are used for calculations of ventilation heat losses.

Ventilation air balance is calculated according to following guidelines:

1. For whole building is determined a total stream of air “Vmech,inf”, flowing through leaks in building construction (through windows and doors) as a result of operation of mechanical exhaust installation. It is calculated on the basis of difference between the sum of streams exhausted and blown mechanically. If the difference between exhaust and intake in building is equal to 0, then into building does not flow any additional external air. If the difference is > 0, then the stream “Vmech,inf” is divided into individual compartments of building with windows and external doors, on the basis of volume share of compartment in the sum of volumes of all compartments in the building. In this way for individual compartments is calculated the stream “Vmech,inf,i”.

2. In compartment are calculated other streams of ventilation air.

3. Hygienic stream of ventilation air results from normative requirements depending on the type of compartment and its cubic capacity. It can also be declared manually in order to adapt it to individual needs. Its volume participates in ventilation heat losses. It is not included in ventilation air balance.

4. Infiltrating stream of air flowing into compartment through leaks in windows and doors. Its value depends on air-tightness of building block, multiplication factor of exchanges at difference of 50 Pa between building interior and external environment and correction coefficients taking into account the grade of building shielding and height of compartments over ground level. Its volume participates in ventilation heat losses. It is not included in ventilation air balance.

5. Value of exhausted and mechanically blown stream of air is declared in program by the User on the basis of ventilation parameters.

6. Within compartment is calculated a stream of air, which can flow in/out to/from other compartments in the building. Additional stream of air flowing within compartments in the building depends on balancing of exhausted stream “Vexh” and blown streams „Vsup” + “Vmech,inf,i”. Temperature of inflowing air results from mixing of streams of air coming from individual compartments.

7. Stream of air flowing from the building is corrected in calculations of ventilation heat losses by temperature correction coefficient including mixing of air streams having different temperature values, flowing from various compartments.

Streams of ventilation air (“Vi”) calculated on the basis of the balance are used for calculations of ventilation heat losses . Its value depends on the presence of ventilation installation in the building.

If the mechanical ventilation has not been declared in compartment, then the stream of air Vi used in heat loss calculations is calculated as a max value from declared minimal stream of hygienic air “Vmin” and air infiltrating into compartment.

If the mechanical ventilation has been declared in compartment, then the stream of air Vi used in heat loss calculations is calculated as a max value from declared minimal stream of hygienic air “Vmin” and sum of infiltrating air streams “Vinf” and stream of air blown mechanically „Vsup” into compartment and flowing “Vmech,inf,i” as a result of air excess exhausted from compartment.

Calculation of ventilation heat loss for a building:

Lack of mechanical ventilation

For a building are summed maximal values Vi of hygienic and infiltrating air streams appearing in compartment. Summing is performed for all compartments in a building.

Declared mechanical ventilation in a building

For a building are summed maximal values Vi of air streams appearing in compartment. Summing is performed for all compartments in a building. For calculations is taken hygienic, infiltrating, blown mechanically and flowing as a result of excess of air removed from compartment stream of air.

If the algorithm of calculation of ventilation air balance can not be applied in calculated building for some reasons, it is necessary to declare to all compartments only minimal multiplication factor of air exchanges.