The required amount of fresh air for ventilation of residential buildings
Slovenian legislation states that the required air exchange rate for ventilation of buildings,
when they are not occupied is 0.2 hˉ¹. This dilutes the pollutants emitted by substances and devices.
In a time when people are present in the building, one must provide 0.5 air exchanges per hour.
If this does not corresponds with the required quantity of fresh air per person (20 to 40 m³/h per person),
exchange rate should increase. Since only windows and doors with high tightness (class 3) can be used
according to the regulations, we cannot provide the necessary amount of fresh air when windows are closed,
as we can usually do in older buildings. The perceived poor air quality causes users to respond by opening windows.
These often remain open no matter what the air quality is what have impact on building energy consumption.
Therefore mechanical ventilation with the controlled fan operation (usually on the basis of air humidity,
which is a good indicator of air pollution) is more appropriate. Even more efficient is mechanical ventilation
with heat recovery system that transfers heat from waste air to fresh air. Heat losses due to ventilation of
the building can be reduced, depending on the type of heat recovery and building tightness, for 50% to 90%.
Natural ventilation of buildings is therefore allowed, but it is not energy-efficient!
Methods and systems of ventilation in the Cell
In addition to natural ventilation, two mechanical ventilation systems are used in the Cell.
Natural ventilation of the living area and the attic is designed separately and is used out of heating season.
The window on the facade has smaller part, which can be left open even when it rains or when there are no residents in the Cell.
Roof window has a ventilation cavity with protection against precipitation. Due to large height differences between windows, natural ventilation is more intense than usual.
Residential unit with attic has also a system for mechanical ventilation.
The system is integrated into the outer wall and its transparent cover also allows
air heating with solar energy. In the residential unit there are distribution channels
for extraction of waste air and intake of fresh air. Both channels have integrated fans
and dampers in order to prevent uncontrolled ventilation. The system is activated according
to the temperature of fresh supply air, which is heated by solar energy, and CO2
and volatile organic compounds (VOC) content in the air in the Cell. More about this:
>monitoring >building management system.
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Channels are made of porous material and their length allows proper absorption of sound transmitted by fan.
Sound pressure level during fan operation increases for less than 5 dB and is not higher than 35 dB,
which corresponds to the requirements for the bedroom. Learn more: >monitoring >
reports.
Sanitary and technological unit are ventilated by a mechanical system with heat recuperator,
which is made from two consecutive plate heat exchangers. With two exchangers significantly
higher heat recovery effectiveness is achieved. Noise emissions in this system are reduced with a sound insulated housing.
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Effectiveness of mechanical ventilation systems
In the case of mechanical ventilation, energy efficiency is evaluated on the basis of the effectiveness
of the heat transfer in the heat exchanger and depending on the amount of electricity required for operation
of the system (fans and control unit).
The heat recovery effectiveness of the residential unit`s ventilation system is between ~ 50 % during night time
and up to 200 % + in clear weather conditions because the air is preheated with solar energy.
Due to two in series mounted plate cross-flow heat exchangers (this is the case when air flows of
exhaust and fresh air in a heat exchanger are perpendicular) in the sanitary and technological unit
mechanical ventilation system, the heat transfer effectiveness increases to 90%.
In both systems the fans with 24 V DC motor were used, with power of 5 W. Thus we have reached, that the ratio of transferred heat and electricity consumption (COP) is between 23 and 28,
which exceeds the requirements for the systems in the passive buildings.
