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planning:building_services:ventilation:basics:types_of_ventilation

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planning:building_services:ventilation:basics:types_of_ventilation [2015/09/01 10:07] – [The convenient solution: supply and exhaust air systems with heat recovery] wfeistplanning:building_services:ventilation:basics:types_of_ventilation [2022/05/22 19:20] (current) – [The convenient solution: supply and exhaust air systems with heat recovery] wfeist
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   * Wind and airflow caused by temperature differences fluctuate too much in Central Europe. In a house which is not leaky enough for sufficient air exchange during periods with small windforces, intolerable draughts are still caused during periods with strong winds (following picture).   * Wind and airflow caused by temperature differences fluctuate too much in Central Europe. In a house which is not leaky enough for sufficient air exchange during periods with small windforces, intolerable draughts are still caused during periods with strong winds (following picture).
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   * New constructions in many countries such as Germany are so airtight that air exchange through leaks in the nevelope is insufficient for good indoor air quality. This also applies for modernised buildings with new windows.     * New constructions in many countries such as Germany are so airtight that air exchange through leaks in the nevelope is insufficient for good indoor air quality. This also applies for modernised buildings with new windows.  
-  * Apart from that, condensation damage can occur due to the warm air escaping through cracks.\\+ 
 +  * Apart from that, condensation damage can occur due to the warm air escaping through cracks.
 \\ \\
 |{{ :picopen:nat_ventilation.png?400 }}| |{{ :picopen:nat_ventilation.png?400 }}|
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 Accordingly, the air quality is usually poor and there is an increased risk of high air humidity.  Because we cannot perceive the indoor air quality ourselves and it is not possible for us to estimate the amount of fresh air actually supplied through open windows,  it is difficult, even for an expert, to achieve "just the right" amount of air exchange. Accordingly, the air quality is usually poor and there is an increased risk of high air humidity.  Because we cannot perceive the indoor air quality ourselves and it is not possible for us to estimate the amount of fresh air actually supplied through open windows,  it is difficult, even for an expert, to achieve "just the right" amount of air exchange.
   * If ventilation is insufficient, the air quality will be poor and there will be a risk of condensation occurring.   * If ventilation is insufficient, the air quality will be poor and there will be a risk of condensation occurring.
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   * If too much ventilation takes place, the air will become too dry and energy consumption will become excessively high.   * If too much ventilation takes place, the air will become too dry and energy consumption will become excessively high.
  
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     * If the window is opened wide for long enough, the stale indoor air will be replaced by fresh outdoor air.     * If the window is opened wide for long enough, the stale indoor air will be replaced by fresh outdoor air.
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     * When the air replacement is complete, the windows doesn't need to be kept open any longer (replacing of fresh air with fresh air?).     * When the air replacement is complete, the windows doesn't need to be kept open any longer (replacing of fresh air with fresh air?).
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     * Window ventilation provides this kind of just one complete air exchange each time it takes place.     * Window ventilation provides this kind of just one complete air exchange each time it takes place.
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     * If this is done twice a day, this means two air replacements in 24 hours or an average air change of 2 / 24 h<sup>-1</sup> which is less than 0.1 h<sup>-1</sup>.     * If this is done twice a day, this means two air replacements in 24 hours or an average air change of 2 / 24 h<sup>-1</sup> which is less than 0.1 h<sup>-1</sup>.
  
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 Moisture is continuously being released into the room, especially at night. Moisture is continuously being released into the room, especially at night.
   * If the air is not replaced, the relative air humidity increases – these periods of increased humidity can be seen clearly.   * If the air is not replaced, the relative air humidity increases – these periods of increased humidity can be seen clearly.
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   * One can also see that each time the window is opened for air exchange, the humidity level drops (valleys). The residents open the windows for airing more than twice a day  - but in spite of that the humidity keeps increasing and for long periods of time it remains above 60%.     * One can also see that each time the window is opened for air exchange, the humidity level drops (valleys). The residents open the windows for airing more than twice a day  - but in spite of that the humidity keeps increasing and for long periods of time it remains above 60%.  
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   * The green curve shows the indoor air humidity near the inner surface of the external wall.  A relative air humidity level of more than 80% is often present here.  These are the conditions which encourage mould growth (area in blue).   * The green curve shows the indoor air humidity near the inner surface of the external wall.  A relative air humidity level of more than 80% is often present here.  These are the conditions which encourage mould growth (area in blue).
  
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 Systematic examination of homes has shown that proper distribution of fresh air in all rooms and safe dehumidification of kitchens and bathrooms is possible through **controlled ventilation**. Systematic examination of homes has shown that proper distribution of fresh air in all rooms and safe dehumidification of kitchens and bathrooms is possible through **controlled ventilation**.
   * In this way the fresh air is directly supplied to the living room, office and bedrooms. These rooms are equipped with at least one supply air inlet.   * In this way the fresh air is directly supplied to the living room, office and bedrooms. These rooms are equipped with at least one supply air inlet.
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   * As in exhaust air systems, the kitchen, bathroom and toilet as well as other areas with high humidity and odours are ventilated directly through the extract air outlets.   * As in exhaust air systems, the kitchen, bathroom and toilet as well as other areas with high humidity and odours are ventilated directly through the extract air outlets.
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   * There is a directed flow throughout the house: the fresh air first enters the main living rooms (see illustration), from here it flows through the transferred air zones (usually corridors) into the humid areas. The humid areas have relatively high air changes so that e.g. towels can dry more quickly.\\   * There is a directed flow throughout the house: the fresh air first enters the main living rooms (see illustration), from here it flows through the transferred air zones (usually corridors) into the humid areas. The humid areas have relatively high air changes so that e.g. towels can dry more quickly.\\
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 Ventilation can also take place if a simple exhaust air system and external air inlets are used.  The external air inlets let fresh (cold) air in the required amounts into the rooms.  However, for the Passive House the ventilation heat losses that would be caused by the disposal of the unused extract air would be much too high.  It would only be possible to adjust the energy balance with a high heating output. Ventilation can also take place if a simple exhaust air system and external air inlets are used.  The external air inlets let fresh (cold) air in the required amounts into the rooms.  However, for the Passive House the ventilation heat losses that would be caused by the disposal of the unused extract air would be much too high.  It would only be possible to adjust the energy balance with a high heating output.
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 +===== Heat Recovery with a Counterflow Heat Exchanger =====
  
 **In Central Europe, Passive Houses only work if a highly efficient heat recovery system is also present**  This recovers the heat from the exhaust air and using a heat exchanger, transfers it back into the supply air without mixing the air flows. Today, modern ventilation technology allows a heat recovery rate of  between 75 and 95 %. This is possible due to counterflow heat exchangers and special energy-efficient fans (with so-called EC motors with a particularly high effectiveness), so that the recovered heat is 8 to 15 times the electricity consumed.\\ **In Central Europe, Passive Houses only work if a highly efficient heat recovery system is also present**  This recovers the heat from the exhaust air and using a heat exchanger, transfers it back into the supply air without mixing the air flows. Today, modern ventilation technology allows a heat recovery rate of  between 75 and 95 %. This is possible due to counterflow heat exchangers and special energy-efficient fans (with so-called EC motors with a particularly high effectiveness), so that the recovered heat is 8 to 15 times the electricity consumed.\\
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 \\ \\
 |{{ :picopen:heat_exchanger_ir.png?400 }}| |{{ :picopen:heat_exchanger_ir.png?400 }}|
-|//**Thermographic image of an opened counterflow heat recovery\\ unit. The actual heat exchanger can be seen as a hexagon.\\ It recovers more than 75% of the perceptible heat from\\ the extract air. (Image: PHI).**//|\\+|//**Thermographic image of an opened counterflow heat recovery\\ unit. The actual heat exchanger can be seen as a hexagon.\\ It recovers more than 75% of the sensible heat from\\ the extract air. (Image: PHI).**//|\\
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 The highly efficient ventilation units developed for the Passive House have also proved to be effective  in **modernisations of existing buildings**. Here they contribute to the improvement of the air quality, and ensure that mould growth does not occur at weak points in external building components, as well as helping to save energy. The highly efficient ventilation units developed for the Passive House have also proved to be effective  in **modernisations of existing buildings**. Here they contribute to the improvement of the air quality, and ensure that mould growth does not occur at weak points in external building components, as well as helping to save energy.
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-An additional possibility for improving the efficiency of ventilation systems is offered by the **subsoil heat exchanger**: on average, the ground is warmer in winter than the surrounding air, and colder in summer.  Fresh air can therefore be pre-heated or pre-cooled using the earth.  This can take place directly through air ducts (air-to-soil heat exchanger) or indirectly by means of a hydraulic system (brine-carrying subsoil heat exchanger).\\ 
  
 In hot climates, air-to-air counterflow heat exchangers can also help to recover "cool temperature" from the exhaust air and to reduce the temperature of the supply air, if the fresh air is uncomfortably hot. But this requires low energy fans in order to reduce heat loads caused by the ventilators. Humidity recovery, which is possible with special types of heat exchangers, is another highly efficient option in extreme cold and/or extreme hot and humid climates.\\ In hot climates, air-to-air counterflow heat exchangers can also help to recover "cool temperature" from the exhaust air and to reduce the temperature of the supply air, if the fresh air is uncomfortably hot. But this requires low energy fans in order to reduce heat loads caused by the ventilators. Humidity recovery, which is possible with special types of heat exchangers, is another highly efficient option in extreme cold and/or extreme hot and humid climates.\\
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 ===== Conclusion ===== ===== Conclusion =====
  
-Passive Houses always have an integrated home ventilation system with heat recovery, and often this is the central component of the complete building services. Only high quality ventilation technology is suitable for the Passive House. The Passive House Institute has [[http://www.passiv.de/03_zer/Komp/Lueft/Lueft_F.htm|summarised these (in German) in the requirements for central ventilation units]]: Apart from a high heat recovery rate, low electricity consumption, and hygienically faultless and very quiet operation must be guaranteed.\\+Passive Houses always have an integrated home ventilation system with heat recovery, and often this is the central component of the complete building services. Only high quality ventilation technology is suitable for the Passive House. The Passive House Institute has [[https://passivehouse.com/03_certification/01_certification_components/02_certification_criteria/02_certification_criteria.htm |summarised these (in German) in the requirements for central ventilation units]]: Apart from a high heat recovery rate, low electricity consumption, and hygienically faultless and very quiet operation must be guaranteed.\\
 \\  \\ 
 ===== Literature ===== ===== Literature =====
planning/building_services/ventilation/basics/types_of_ventilation.1441094851.txt.gz · Last modified: 2015/09/01 10:07 by wfeist