question: How don't we run out of air to breathe if we don't open windows in our house for long periods of time?
comment: Your house is more exposed to the outdoors than you imagine. While it's mostly water-tight, it's far from air tight. Generally your attic is opened to the outdoors as well as your basement or crawl-space.
passages: Air is circulated through ductwork, which may be made of sheet metal or plastic "flex" duct, and is insulated or uninsulated. Unless the ducts and plenum have been sealed using mastic or foil duct tape, the ductwork is likely to have a high leakage of conditioned air, possibly into unconditioned spaces. Another cause of wasted energy is the installation of ductwork in unheated areas, such as attics and crawl spaces; or ductwork of air conditioning systems in attics in warm climates.
  
  Section::::Home furnaces.
   BULLET::::- Slow temperature changes: with ventilation and heating systems switched off, a passive house typically loses less than per day (in winter), stabilizing at around in the central European climate.
  
  BULLET::::- Quick return to normal temperature: opening windows or doors for a short time has only a limited effect; after apertures are closed, the air very quickly returns to the "normal" temperature.
  
  BULLET::::- Some have voiced concerns that Passivhaus is not a general approach as the occupant has to behave in a prescribed way, for example not opening windows too often. However modelling shows that such concerns are not valid.
   Keeping birds inside a house protects them from predators such as hawks and foxes. Some houses are equipped with curtain walls, which can be rolled up in good weather to admit natural light and fresh air. Most growout houses built in recent years feature “tunnel ventilation,” in which a bank of fans draws fresh air through the house.
   Some of the important limitations of wind driven ventilation:
  
  BULLET::::- Unpredictability and difficulties in harnessing due to speed and direction variations
  
  BULLET::::- The quality of air it introduces in buildings may be polluted for example due to proximity to an urban or industrial area
  
  BULLET::::- May create a strong draught, discomfort.
  
  Section::::Buoyancy-driven ventilation.
   Research aiming at the development of natural ventilation systems featuring heat recovery have been made as early as 1993 where Shultz et al proposed and tested a chimney type design relying on stack effect while recovering heat using a large counterflow recuperator constructed from corrugated galvanized iron. Both supply and exhaust happened through an unconditioned attic space, with exhaust air being extracted at ceiling height and air being supplied at floor level through a vertical duct.
   Air changes are often cited as a means of preventing condensation in houses with forced ventilation systems often rated from 3 - 5 ACH though without referencing the size of the house. However, where ACH is already greater than 0.75 a forced ventilation system is unlikely to be of use at controlling condensation and instead insulation or heating are better remedies. Seven out of eight houses studied in NZ in 2010 had an ACH (corrected for ventilation factors) of 0.75 or greater. The presence of forced ventilation systems has been shown in some cases to actually increase the humidity rather than lower it. By displacing air inside a dwelling with infiltrated air (air brought in from outside the dwelling), positive pressure ventilation systems can increase heating (in winter) or cooling (in summer) requirements in a house. For example, to maintain a 15 °C temperature in a certain dwelling about 3.0 kW of heating are required at 0 ACH (no heat loss due to warmed air leaving the dwelling, instead heat is lost due to conduction or radiation), 3.8 kW at 1 ACH and 4.5 kW are required at 2 ACH. The use of roof space for heating or cooling was seen as ineffectual with the maximum heating benefits occurring in winter in more southerly regions (being close to the South Pole in these southern hemisphere reports) but being equivalent only to about 0.5 kW or the heating provided by about five 100 W incandescent light bulbs; cooling effects in summer were similarly small and were more pronounced for more northerly homes (being closer to the equator); in all cases the values assumed that the ventilation system automatically disengaged when the infiltrating air was warmer or cooler (as appropriate) than the air already in the dwelling as it would otherwise exacerbate the undesirable conditions in the house.
   Compared to the, on average, 23 number of branchings of the respiratory tree in the adult human, the mouse has only about 13 such branchings.
   BULLET::::- In hot, humid climates, unconditioned ventilation air will deliver approximately one pound of water each day for each cfm of outdoor air per day, annual average. This is a great deal of moisture, and it can create serious indoor moisture and mold problems.
  
  BULLET::::- Ventilation efficiency is determined by design and layout, and is dependent upon placement and proximity of diffusers and return air outlets. If they are located closely together, supply air may mix with stale air, decreasing efficiency of the HVAC system, and creating air quality problems.
   BULLET::::- Maximize wind-induced ventilation by siting the ridge of a building perpendicular to the summer winds
  
  BULLET::::- Widths of naturally ventilated zone should be narrow (max 13.7 m [45 feet])
  
  BULLET::::- Each room should have two separate supply and exhaust openings. Locate exhaust high above inlet to maximize stack effect. Orient windows across the room and offset from each other to maximize mixing within the room while minimizing the obstructions to airflow within the room.
  
  BULLET::::- Window openings should be operable by the occupants
  
  BULLET::::- Consider the use of clerestories or vented skylights.
  
  Section::::Wind driven ventilation.
   One way to measure the performance of a naturally ventilated space is to measure the air changes per hour in an interior space. In order for ventilation to be effective, there must be exchange between outdoor air and room air. A common method for measuring ventilation effectiveness is to use a tracer gas. The first step is to close all windows, doors, and openings in the space. Then a tracer gas is added to the air. The reference, American Society for Testing and Materials (ASTM) Standard E741: Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution, describes which tracer gases can be used for this kind of testing and provides information about the chemical properties, health impacts, and ease of detection. Once the tracer gas has been added, mixing fans can be used to distribute the tracer gas as uniformly as possible throughout the space. To do a decay test, the concentration of the tracer gas is first measured when the concentration of the tracer gas is constant. Windows and doors are then opened and the concentration of the tracer gas in the space is measured at regular time intervals to determine the decay rate of the tracer gas. The airflow can be deduced by looking at the change in concentration of the tracer gas over time. For further details on this test method, refer to ASTM Standard E741.
   The volume of air that moves in "or" out (at the nose or mouth) during a single breathing cycle is called the tidal volume. In a resting adult human it is about 500 ml per breath. At the end of exhalation the airways contain about 150 ml of alveolar air which is the first air that is breathed back into the alveoli during inhalation. This volume air that is breathed out of the alveoli and back in again is known as dead space ventilation, which has the consequence that of the 500 ml breathed into the alveoli with each breath only 350 ml (500 ml - 150 ml = 350 ml) is fresh warm and moistened air. Since this 350 ml of fresh air is thoroughly mixed and diluted by the air that remains in the alveoli after normal exhalation (i.e. the functional residual capacity of about 2.5–3.0 liters), it is clear that the composition of the alveolar air changes very little during the breathing cycle (see Fig. 9). The oxygen tension (or partial pressure) remains close to 13-14 kPa (about 100 mm Hg), and that of carbon dioxide very close to 5.3 kPa (or 40 mm Hg). This contrasts with composition of the dry outside air at sea level, where the partial pressure of oxygen is 21 kPa (or 160 mm Hg) and that of carbon dioxide 0.04 kPa (or 0.3 mmHg).
   BULLET::::- Ruth – Ruth's extra large hole cannot accommodate her window, and by the time the window can even remotely fit, Ruth's window frame now has four 2x4s on all sides, yet there is still a gap big enough to put two fingers in on all sides. Ruth's solution of using a lumber shim does not help either.
  
  Section::::Episode 3: Sealing the Deal.:Insulation.
   Section::::Primary intervention for children.
  
  Children up to five years of age spend 90% of their time at home. Globally, 50% of pneumonia deaths among children under five years of age are due to particulate matter inhaled from indoor air pollution. Many homes around the world used solid fuels for cooking. These fuels release large amounts of carbon monoxide and fine particulate matter. These chemical irritants when inhaled may cause different pulmonary conditions ranging from pulmonary epithelial cancer or acute pulmonary tract infection.
  
  Section::::Kenya and modern energy.
   During heavy breathing, exhalation is caused by relaxation of all the muscles of inhalation. But now, the abdominal muscles, instead of remaining relaxed (as they do at rest), contract forcibly pulling the lower edges of the rib cage downwards (front and sides) (Fig. 8). This not only drastically decreases the size of the rib cage, but also pushes the abdominal organs upwards against the diaphragm which consequently bulges deeply into the thorax (Fig. 8). The end-exhalatory lung volume is now well below the resting mid-position and contains far less air than the resting "functional residual capacity". However, in a normal mammal, the lungs cannot be emptied completely. In an adult human there is always still at least 1 liter of residual air left in the lungs after maximum exhalation.
   The majority of infants who have survived following an incidence of bronchopulmonary dysplasia will eventually recover near-normal lung function, since lungs continue to grow during the first 5–7 years and the damage caused by bronchopulmonary dysplasia is to some extent reversible (even in adults). However, they are likely to be more susceptible to respiratory infections for the rest of their lives and the severity of later infections is often greater than that in their peers.
   Since almost all of the air circulation (transpiration) happens in the roots as does almost all of the energy production, the roots must be able to breathe easily. Overwatering will drown a typical houseplant. The air is pulled through the soil by the breathing of the roots. Air must be able to flow through the soil.
  
  Section::::Data for some common houseplants.:Water requirement.
   The alveoli are the dead end terminals of the "tree", meaning that any air that enters them has to exit via the same route. A system such as this creates dead space, a volume of air (about 150 ml in the adult human) that fills the airways after exhalation and is breathed back into the alveoli before environmental air reaches them. At the end of inhalation the airways are filled with environmental air, which is exhaled without coming in contact with the gas exchanger.
  
  Section::::Mammals.:Ventilatory volumes.
   For humans, the typical respiratory rate for a healthy adult at rest is 12–18 breaths per minute. The respiratory center sets the quiet respiratory rhythm at around two seconds for an inhalation and three seconds exhalation. This gives the lower of the average rate at 12 breaths per minute.
  
  Average resting respiratory rates by age are:
  
  BULLET::::- birth to 6 weeks: 30–40 breaths per minute
  
  BULLET::::- 6 months: 25–40 breaths per minute
  
  BULLET::::- 3 years: 20–30 breaths per minute
  
  BULLET::::- 6 years: 18–25 breaths per minute
  
  BULLET::::- 10 years: 17–23 breaths per minute
  
  BULLET::::- Adults: 12-18 breaths per minute
   For standards relating to ventilation rates, in the United States refer to ASHRAE Standard 62.1-2010: Ventilation for Acceptable Indoor Air Quality. These requirements are for "all spaces intended for human occupancy except those within single-family houses, multifamily structures of three stories or fewer above grade, vehicles, and aircraft." In the revision to the standard in 2010, Section 6.4 was modified to specify that most buildings designed to have systems to naturally condition spaces must also "include a mechanical ventilation system designed to meet the Ventilation Rate or IAQ procedures [in ASHRAE 62.1-2010]. The mechanical system is to be used when windows are closed due to extreme outdoor temperatures noise and security concerns". The standard states that two exceptions in which naturally conditioned buildings do not require mechanical systems are when:
   In many air distribution arrangements, air is neither uniform nor perfectly mixed. The actual percentage of an enclosure's air which is exchanged in a period depends on the airflow efficiency of the enclosure and the methods used to ventilate it. The actual amount of air changed in a well mixed ventilation scenario will be 63.2% after 1 hour and 1 ACH. In order to achieve equilibrium pressure, the amount of air leaving the space and entering the space must be the same.
  
  formula_1
  
  Where:
  
  BULLET::::- "ACPH" = number of air changes per hour; higher values correspond to better ventilation
   Forced ventilation to increase ACH becomes a necessity to maintain acceptable air quality as occupants become reluctant to open windows due to behavioural changes such as keeping windows closed for security.
   Wind driven ventilation can be classified as cross ventilation and single-sided ventilation. Wind driven ventilation depends on wind behavior, on the interactions with the building envelope and on openings or other air exchange devices such as inlets or chimneys. For a simple volume with two openings, the cross wind flow rate can be calculated using the following equation:
  
  formula_2
   Many if not most uses of ACH are actually referring to results of a standard blower door test in which 50 pascals of pressure are applied (ACH), rather than the volume of air changed under normal conditions. The Passive House standard requires airtightness so that there will be less than 0.6 ACH with a pressure difference between inside and outside of 50 Pa.
  
  Section::::Effects of ACH due to forced ventilation in a dwelling.
   In physiology, dead space is the volume of air which is inhaled that does not take part in the gas exchange, either because it remains in the conducting airways, or reaches alveoli that are not perfused or poorly perfused. In other words, not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, wasting that part of the inspiration which remains in the conducting airways where no gas exchange can occur. In humans, about a third of every resting breath has no change in O and CO levels.
   Room pressure can be either positive or negative with respect to outside the room. Positive pressure occurs when there is more air being supplied than exhausted, and is common to reduce the infiltration of outside contaminants.
  
  Section::::Ventilation.:Natural ventilation.:Airborne diseases.
  
  Natural ventilation is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza and meningitis. Opening doors, windows, and using ceiling fans are all ways to maximize natural ventilation and reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.
  
  Section::::Air conditioning.
  
presuppositions: Houses are air-tight when the windows aren't open. Your house can only get air to breathe through open windows.
corrections: Houses are not air-tight even when the windows aren't open. Your house can get exposure to the outdoors through the attic and basement.
raw_presuppositions: Houses are air-tight when the windows aren't open. Your house can only get air to breathe through open windows.
raw_corrections: Houses are not air-tight even when the windows aren't open. Your house can get exposure to the outdoors through the attic and basement.