C1-Air Transfer 2024-2025 PDF

An Erasmus Mundus International Joint Master Degree C1 - Heat and mass transfer in buildings. High energy performance building envelopes Air transfer Department of Energy Engineering University of the Basque Country MSc in Smart Cities and Communities Air transfer 3  Air...

An Erasmus Mundus International Joint Master Degree C1 - Heat and mass transfer in buildings. High energy performance building envelopes Air transfer Department of Energy Engineering University of the Basque Country MSc in Smart Cities and Communities Air transfer 3  Air transfer 1. Introduction to air infiltration in buildings 2. Basic concepts and terminology 3. Characteristics and classification of cracks in buildings 4. Fundamentals of air movement 5. Distribution of air leakages 6. Measurements of air flow due to infiltrations 7. Calculation of air infiltrations Table of contents 4  3.1. Introduction to air infiltration in buildings 3.1. Introduction to air infiltration in buildings WHY? 3.2. Basic concepts and terminology How? Where? 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air Why? What? movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 5  3.1. Introduction to air infiltration in buildings 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement Buildings cannot spontaneously and 3.5. Distribution of air leakages continuously maintain the 3.6. Measurements of airflow due comfort conditions inside to infiltrations them. 3.7. Calculation of air infiltrations We don't design buildings as well nowadays as we did years ago’. Heat and mass transfer in buildings. High energy performance building envelopes 6  3.1. Introduction to air infiltration in buildings 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings Energy expenditure (energy poverty risk) 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Climate change Heat and mass transfer in buildings. High energy performance building envelopes 7  3.1. Introduction to air infiltration in buildings Most of the measures adopted have been aimed at reducing heat losses through 3.1. Introduction to air infiltration in buildings the building envelope. 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 8  3.1. Introduction to air infiltration in buildings 3.1. Introduction to air The improvement in the level of insulation has led to a infiltration in buildings reduction in transmission losses and, therefore, in total 3.2. Basic concepts and losses. terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air However, the relative weight of each type of movement loss has changed. 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 9  3.1. Introduction to air infiltration in buildings Efficiency of It is important to consider 3.1. Introduction to air ventilation system infiltration in buildings the airtightness of buildings. 3.2. Basic concepts and terminology IAQ 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages Energy consumption 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Airtightness Design of HVAC system Heat and mass transfer in buildings. High energy performance building envelopes 10  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 11  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration  Air exchange: It is to renew the indoor stale but thermally conditioned air in buildings using outdoor clean but thermally not conditioned air. To thermally 3.2. Basic concepts and terminology conditioning the air, it is necessary to use energy. It is possible to renew the 3.3. Characteristics and classification of cracks in buildings air by ventilation or infiltration. 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations stale clean air air stale air clean air Heat and mass transfer in buildings. High energy performance building envelopes 12  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration  Air transfer: This is the air that goes from a local within a building to in buildings another local of the building. This can happen intentionally or not, through 3.2. Basic concepts and terminology cracks or through openings. 3.3. Characteristics and classification of cracks in buildings IAQ 3.4. Fundamentals of air movement 3.5. Distribution of air leakages  Ventilation: It is the process by which clean air is provided intentionally 3.6. Measurements of airflow due removing the indoor polluted air to maintain an appropriate indoor air to infiltrations 3.7. Calculation of air infiltrations quality. This can be achieved by natural or mechanical ventilation. Heat and mass transfer in buildings. High energy performance building envelopes 13  3.2. Basic concepts and terminology  Natural ventilation: Natural ventilation occurs due to pressure differences 3.1. Introduction to air infiltration in buildings produced by natural sources. Air flow through open windows and doors, air 3.2. Basic concepts and terminology inlets or any other opening installed intentionally. 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 14  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 15  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 16  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 17  3.2. Basic concepts and terminology  Mechanical ventilation: In this case, air flows intentionally due to the 3.1. Introduction to air infiltration in buildings pressure difference generated by mechanical systems: fans or range hoods for 3.2. Basic concepts and terminology example. 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 18  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations https://www.youtube.com/watch?v=hIszVpFukCw Heat and mass transfer in buildings. High energy performance building envelopes 19  3.2. Basic concepts and terminology Exhaust ventilation systems work by depressurizing 3.1. Introduction to air infiltration your home. The system exhausts air from the house in buildings while make-up air infiltrates through leaks in the 3.2. Basic concepts and building shell and through intentional, passive vents. terminology 3.3. Characteristics and Typically, an exhaust ventilation system consists of a classification of cracks in buildings single fan connected to a centrally located, single exhaust point in the house. 3.4. Fundamentals of air movement A better design is to connect the fan to ducts from 3.5. Distribution of air leakages several rooms, preferably rooms where pollutants 3.6. Measurements of airflow due to infiltrations are generated, such as bathrooms. 3.7. Calculation of air infiltrations Adjustable, passive vents through windows or walls can be installed in other rooms to introduce fresh air rather than rely on leaks in the building envelope. Heat and mass transfer in buildings. High energy performance building envelopes 20  3.2. Basic concepts and terminology Supply ventilation systems use a fan to 3.1. Introduction to air infiltration in buildings pressurize your home, forcing outside air into the building while air leaks out of the building 3.2. Basic concepts and terminology through holes in the shell, bath, and range fan 3.3. Characteristics and ducts, and intentional vents (if any exist). classification of cracks in buildings Typical supply ventilation system has a fan and 3.4. Fundamentals of air movement duct system that introduces fresh air into 3.5. Distribution of air leakages usually one -- but preferably several -- rooms 3.6. Measurements of airflow due that residents occupy most (e.g., bedrooms, to infiltrations living room). This system may include 3.7. Calculation of air infiltrations adjustable window or wall vents in other rooms. Heat and mass transfer in buildings. High energy performance building envelopes 21  3.2. Basic concepts and terminology Balanced ventilation systems, if properly designed 3.1. Introduction to air infiltration and installed, neither pressurize nor depressurize in buildings your home. Rather, they introduce and exhaust 3.2. Basic concepts and approximately equal quantities of fresh outside air terminology and polluted inside air. 3.3. Characteristics and classification of cracks in buildings It usually has two fans and two duct systems. 3.4. Fundamentals of air Fresh air supply and exhaust vents can be installed movement in every room, but a typical balanced ventilation 3.5. Distribution of air leakages system is designed to supply fresh air to bedrooms 3.6. Measurements of airflow due to infiltrations and living rooms where occupants spend the most time. It also exhausts air from rooms where 3.7. Calculation of air infiltrations moisture and pollutants are most often generated (kitchen, bathrooms, and perhaps the laundry room). Heat and mass transfer in buildings. High energy performance building envelopes 22  3.2. Basic concepts and terminology Ventilation Pros Cons System 3.1. Introduction to air infiltration Can draw pollutants into living space in buildings Not appropriate for hot humid climates Rely in part on random air leakage 3.2. Basic concepts and Relatively inexpensive and simple to install terminology Exhaust Work well in cold climates. Can increase heating and cooling costs May require mixing of outdoor and indoor air to avoid 3.3. Characteristics and drafts in cold weather classification of cracks in Can cause backdrafting in combustion appliances. buildings 3.4. Fundamentals of air Relatively inexpensive and simple to install movement Allow better control than exhaust systems Can cause moisture problems in cold climates Minimize pollutants from outside living space Will not temper or remove moisture from incoming 3.5. Distribution of air leakages Prevent backdrafting of combustion gases from air Supply fireplaces and appliances Can increase heating and cooling costs 3.6. Measurements of airflow due Allow filtering of pollen and dust in outdoor air May require mixing of outdoor and indoor air to avoid to infiltrations Allow dehumidification of outdoor air drafts in cold weather. 3.7. Calculation of air infiltrations Work well in hot or mixed climates. Can cost more to install and operate than exhaust or supply systems Balanced Appropriate for all climates Will not temper or remove moisture from incoming air Can increase heating and cooling costs. Heat and mass transfer in buildings. High energy performance building envelopes 23  3.2. Basic concepts and terminology  Infiltration: It is the outdoor air that enters a building through cracks and 3.1. Introduction to air infiltration in buildings openings that have not been intentionally placed. 3.2. Basic concepts and terminology  Exfiltration: It is the indoor air that goes out from a building through cracks 3.3. Characteristics and classification of cracks in and openings that have not been intentionally placed. buildings 3.4. Fundamentals of air Infiltration and exfiltration occur due to the pressure difference created by movement 3.5. Distribution of air leakages natural forces (temperature difference and wind) or mechanical forces (fans). 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Infiltration Exfiltration Heat and mass transfer in buildings. High energy performance building envelopes 24  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 25  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 26  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 27  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 28  3.2. Basic concepts and terminology 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 29  3.2. Basic concepts and terminology Urban wind flow patterns with various simple buildings shapes and spacings 3.1. Introduction to air infiltration Isolated roughness flow in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Wake interference flow Skimming flow Heat and mass transfer in buildings. High energy performance building envelopes 30  3.2. Basic concepts and terminology Urban wind flow patterns with various simple buildings shapes and spacings 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 31  3.2. Basic concepts and terminology  How is ventilated an enclosure has a significant effect on indoor air 3.1. Introduction to air infiltration in buildings quality, thermal comfort and energy consumption. 3.2. Basic concepts and terminology Infiltration helps to ventilate buildings, but 3.3. Characteristics and classification of cracks in buildings infiltration occurs in an unintended and 3.4. Fundamentals of air movement uncontrolled manner. 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations It will be more intense when the driven forces are higher: 3.7. Calculation of air infiltrations  Indoor/outdoor temperature difference: Cold winters/hot summers.  Wind effect: Very windy regions or zones. Heat and mass transfer in buildings. High energy performance building envelopes 32  3.2. Basic concepts and terminology  The commercial, office and institutional buildings have mechanical ventilation 3.1. Introduction to air infiltration in buildings and air conditioning systems that pressurize the building avoiding air 3.2. Basic concepts and terminology infiltrations. 3.3. Characteristics and classification of cracks in  In case of the residential buildings, window opening and infiltration are the most buildings 3.4. Fundamentals of air common ways to ventilate buildings. movement 3.5. Distribution of air leakages  When air infiltration occurs, as it is uncontrolled, the air can enter to the building 3.6. Measurements of airflow due to infiltrations from the polluted areas. This must be avoided. 3.7. Calculation of air infiltrations  The airflow rate due to infiltration is changeable throughout the year, and window opening is also dependent of the weather and user’s behaviour. Heat and mass transfer in buildings. High energy performance building envelopes 33  3.2. Basic concepts and terminology  Airtight buildings are needed to increase thermal comfort and reduce energy use of the buildings. 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in Proper buildings 3.4. Fundamentals of air Thermal design of the movement comfort ventilation 3.5. Distribution of air leakages 3.6. Measurements of airflow due system to infiltrations 3.7. Calculation of air infiltrations Energy IAQ (Health) Efficiency Heat and mass transfer in buildings. High energy performance building envelopes 34  3.3. Characteristics and classification of cracks in buildings 3.3.1. Airflow through cracks 3.1. Introduction to air infiltration  The number of cracks and their characteristics will largely depend on the type of in buildings construction (materials used, type of building, etc.). 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 35  3.3. Characteristics and classification of cracks in buildings 3.3.1. Airflow through cracks 3.1. Introduction to air infiltration in buildings Typical leakage paths in a residential building are: 3.2. Basic concepts and  Penetrations through the exterior walls, such as exhaust vents, hose bibs and mail terminology slots 3.3. Characteristics and classification of cracks in  Window and door frames buildings  Switch and sockets plates 3.4. Fundamentals of air movement  Gaps between exterior doors and the frames 3.5. Distribution of air leakages  Recessed lights 3.6. Measurements of airflow due to infiltrations  Attic and crawlspace hatches 3.7. Calculation of air infiltrations  Fireplace dampers  Heating registers along the floor or ceiling  Plumbing penetrating exterior walls under sinks Heat and mass transfer in buildings. High energy performance building envelopes 36  3.3. Characteristics and classification of cracks in buildings 3.3.1. Airflow through cracks 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 37  3.3. Characteristics and classification of cracks in buildings 3.3.1. Airflow through cracks 3.1. Introduction to air infiltration in buildings  Airflows through cracks is due to a pressure difference (P) between both sides of 3.2. Basic concepts and terminology the crack.. 3.3. Characteristics and classification of cracks in buildings P1 3.4. Fundamentals of air P2 movement 3.5. Distribution of air leakages  The aerodynamics of this flow is complex because it depends on several factors: 3.6. Measurements of airflow due to infiltrations  Crack size and configuration. 3.7. Calculation of air infiltrations  Characteristics of the flow through the crack.  Pressure difference across the crack. Heat and mass transfer in buildings. High energy performance building envelopes 38  3.3. Characteristics and classification of cracks in buildings 3.3.1. Airflow through cracks 3.1. Introduction to air infiltration  The flow can be laminar, transitional or turbulent. in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations  The type of regime depends on the size of the crack. Heat and mass transfer in buildings. High energy performance building envelopes 39  3.3. Characteristics and classification of cracks in buildings 3.3.1. Airflow through cracks 3.1. Introduction to air infiltration  By classifying openings within two general types, it is possible to specify simple in buildings formulae to relate the flow rate to the pressure difference. 3.2. Basic concepts and terminology a) openings with a typical dimension larger than approximately 10 mm. 3.3. Characteristics and classification of cracks in b) cracks, or small openings with a typical dimension less than approximately 10 mm. buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 40  3.3. Characteristics and classification of cracks in buildings 3.3.2. Large cracks and openings 3.1. Introduction to air infiltration  In the case of large free areas, for example large cracks or vents, for normal in buildings pressures the flow is turbulent. 3.2. Basic concepts and terminology  So, the air flow rate through the opening or crack is proportional to the 3.3. Characteristics and classification of cracks in square root of the pressure difference through the crack or opening. buildings 3.4. Fundamentals of air movement ·∆ Standard orifice flow equation 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations  : Discharge coefficient of opening. 3.7. Calculation of air infiltrations  : Flow area  : Pressure difference across the crack or opening.  : Air density at a reference temperature and pressure, and. Heat and mass transfer in buildings. High energy performance building envelopes 41  3.3. Characteristics and classification of cracks in buildings 3.3.2. Large cracks and openings 3.1. Introduction to air infiltration in buildings  In the case of sharp-edge orifices, the discharge coefficient can be considered 3.2. Basic concepts and independent of the Reynolds number and equal to 0.61. terminology 3.3. Characteristics and classification of cracks in  Anyway, because the variability on the pressure difference and the geometry of the buildings openings this value of the discharge coefficient has not been seen for most buildings. 3.4. Fundamentals of air movement  The effective leakage area (ELA), can be determined by Blower-door test. 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 42  3.3. Characteristics and classification of cracks in buildings 3.3.3. Small cracks and openings 3.1. Introduction to air infiltration in buildings  The flow is laminar in the case of narrow cracks compared with the their depth. 3.2. Basic concepts and terminology  The Couette flow equation is defined as follows for this kind of openings: 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due  𝑏: Length of the crack 𝑚. to infiltrations 3.7. Calculation of air infiltrations  ℎ: Height of the crack 𝑚.  𝐿: Depth of the crack in flow direction 𝑚.  𝜇: Absolute viscosity of the air 𝑃𝑎 · 𝑠. Heat and mass transfer in buildings. High energy performance building envelopes 43  3.3. Characteristics and classification of cracks in buildings 3.3.3. Small cracks and openings 3.1. Introduction to air infiltration in buildings  For cracks between large and small, the flow is not fully laminar or 3.2. Basic concepts and terminology turbulent, it is in transition region. 3.3. Characteristics and classification of cracks in buildings  The previous expressions are gathered into a single power-law equation: 3.4. Fundamentals of air movement 3.5. Distribution of air leakages Crack flow equation 3.6. Measurements of airflow due to infiltrations  : Flow coefficient. 3.7. Calculation of air infiltrations ·  : Flow exponent. Heat and mass transfer in buildings. High energy performance building envelopes 44  3.3. Characteristics and classification of cracks in buildings 3.3.3. Small cracks and openings 3.1. Introduction to air infiltration in buildings  “ ” is function of the crack geometry. 3.2. Basic concepts and terminology  While “ ” is dependent on the flow regime, its value is “0.5” when the flow 3.3. Characteristics and classification of cracks in buildings is fully turbulent and “1” when it is laminar. 3.4. Fundamentals of air movement  The fact that measured data typically result in an intermediate value 3.5. Distribution of air leakages (between 0.6 and 0.7) indicates that neither of these two limits is a good 3.6. Measurements of airflow due to infiltrations explanation. In general the value equal to 0.67 is accepted. 3.7. Calculation of air infiltrations Bibliography Heat and mass transfer in buildings. High energy performance building envelopes 45  3.3. Characteristics and classification of cracks in buildings 3.3.3. Small cracks and openings 3.1. Introduction to air infiltration in buildings  Some authors suggested a quadratic flow equation: 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings  “𝛼” and “𝛽” are flow coefficients and can be obtained from experimental tests. 3.4. Fundamentals of air movement  The laminar flow is represented by the first term on the right-hand side of the 3.5. Distribution of air leakages expression, and the second term represents the turbulent flow. 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations  When the air flow rates are low the laminar term is more important, while the airflows are larger the second term becomes important. Heat and mass transfer in buildings. High energy performance building envelopes 46  3.3. Characteristics and classification of cracks in buildings 3.3.3. Small cracks and openings 3.1. Introduction to air infiltration in buildings  The crack flow equation and the quadratic equation have been used in order 3.2. Basic concepts and terminology to obtain the air flow rates across the building envelopes. 3.3. Characteristics and classification of cracks in  Researchers compared the air infiltration rates obtained using both buildings equations: 3.4. Fundamentals of air movement 3.5. Distribution of air leakages The results were identical when the pressure difference across the crack 3.6. Measurements of airflow due was higher than. to infiltrations 3.7. Calculation of air infiltrations The performance of the crack flow equation was higher at low pressure differences (of the order existing under normal environmental conditions). Heat and mass transfer in buildings. High energy performance building envelopes 47  3.3. Characteristics and classification of cracks in buildings 3.3.4. Analogy between cracks and ducts 3.1. Introduction to air infiltration in buildings  The pressure drop along any duct for any flow regime (laminar, turbulent or 3.2. Basic concepts and transition) can be expressed as follows: terminology 3.3. Characteristics and · classification of cracks in (*) buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 𝑓: Darcy friction factor (-). 𝐿: Length of the duct 𝑚. 3.6. Measurements of airflow due to infiltrations 𝐷 : Inner diameter of the duct 𝑚. c: Velocity of the fluid 3.7. Calculation of air infiltrations 𝜌: Density of the fluid. Heat and mass transfer in buildings. High energy performance building envelopes 48  3.3. Characteristics and classification of cracks in buildings 3.3.4. Analogy between cracks and ducts 3.1. Introduction to air infiltration  The flow rate through a duct can be calculated as follows: in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and  The friction factor can be obtained using the following expression: classification of cracks in buildings 3.4. Fundamentals of air movement 𝑅𝑒: Reynolds number (-). For example in 3.5. Distribution of air leakages 𝐴, 𝑀: Constant values dependent on the flow regime. laminar flow 3.6. Measurements of airflow due 𝑓= to infiltrations 3.7. Calculation of air infiltrations Reynolds number can be calculated by: Heat and mass transfer in buildings. High energy performance building envelopes 49  3.3. Characteristics and classification of cracks in buildings 3.3.4. Analogy between cracks and ducts 3.1. Introduction to air infiltration in buildings  Introducing the previous three equations into the first one (*) 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 50  3.3. Characteristics and classification of cracks in buildings 3.3.4. Analogy between cracks and ducts 3.1. Introduction to air infiltration  Introducing the previous three equations into the first one (*) in buildings 3.2. Basic concepts and 𝜋·𝑑 𝑑 terminology 𝑉̇ = · 2· · υ ·𝜌 · ∆𝑝 4 𝐴·𝐿 3.3. Characteristics and classification of cracks in buildings This term term gathers This term is This term 3.4. Fundamentals of air the parameters related function of the depends on movement to the geometry of the fluid the pressure 3.5. Distribution of air leakages 3.6. Measurements of airflow due duct. properties. difference. to infiltrations 3.7. Calculation of air infiltrations As “M” depends on the flow regime, the three terms in the equation depends on the flow regime. Heat and mass transfer in buildings. High energy performance building envelopes 51  3.3. Characteristics and classification of cracks in buildings 3.3.4. Analogy between cracks and ducts 3.1. Introduction to air infiltration in buildings  The flow through a crack is more complex than through a simple duct. 3.2. Basic concepts and terminology  By measurements, it has been proved that the relationship between flow rate and 3.3. Characteristics and pressure difference can be expressed by power law. classification of cracks in buildings 3.4. Fundamentals of air movement  Considering the air as an ideal gas and neglecting the influence of the pressure to 3.5. Distribution of air leakages calculate its temperature, the following expression is obtained: 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations  So the airflow rate through the crack also depends on the average temperature of the air across the crack. Heat and mass transfer in buildings. High energy performance building envelopes 52  3.3. Characteristics and classification of cracks in buildings 3.3.4. Analogy between cracks and ducts 3.1. Introduction to air infiltration in buildings  To make it easier the use of the previous expression, it is introduced a 3.2. Basic concepts and terminology correction factor “ ”. 3.3. Characteristics and classification of cracks in · buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages  The correction factor is calculated considering 20ºC as standard condition 3.6. Measurements of airflow due to infiltrations ( = 293.15 K). 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 53  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings  It is very difficult to classify cracks, but there are two basic methods. 3.2. Basic concepts and terminology  The first method is to classify the crack according to the component type. This has 3.3. Characteristics and classification of cracks in been done for many years. buildings 3.4. Fundamentals of air movement  The flow coefficient and the flow exponent are given to each component using 3.5. Distribution of air leakages measurement results. 3.6. Measurements of airflow due to infiltrations  In this case, the form of the crack does not refer to the geometry of the crack itself, it 3.7. Calculation of air infiltrations is referred to the behaviour of the component. Heat and mass transfer in buildings. High energy performance building envelopes 54  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings  The paths in walls, roofs and floors share similar characteristics in comparison to 3.2. Basic concepts and terminology windows: they are quite long. 3.3. Characteristics and classification of cracks in  Considering windows, two groups should be considered: single and double- buildings 3.4. Fundamentals of air pane windows, regardless of the material, shape or construction. movement 3.5. Distribution of air leakages  In the case of doors, the shape of the cracks is similar compared to single- 3.6. Measurements of airflow due to infiltrations pane windows, but the behaviour is different. 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 55  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Source: Liddament – Guide to energy efficient ventilation Heat and mass transfer in buildings. High energy performance building envelopes 56  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 57  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 58  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings  The second method is to classify the cracks in relation to their geometry. 3.2. Basic concepts and terminology  The cracks were classified as straight, L-shaped and multi-cornered by Hopkins et 3.3. Characteristics and classification of cracks in al., Etheridge and Baker. buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 59  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations P.H. Baker; S. Sharples; I.C. Ward. Air Flow 3.7. Calculation of air infiltrations Through Cracks Building and Environment Volume 22, Issue 4, 1987, Pages 293-304 Heat and mass transfer in buildings. High energy performance building envelopes 60  3.3. Characteristics and classification of cracks in buildings 3.3.5. Classification of crack forms 3.1. Introduction to air infiltration in buildings  This second method can be applied when it is known the type of the cracks present 3.2. Basic concepts and terminology in a building. 3.3. Characteristics and classification of cracks in  However, this is rarely known in the case of a real building, so it is not clear the buildings reliability of the method. 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 61  3.4. Fundamentals of air movement  The driving force for the air leakage is the pressure difference across the crack or 3.1. Introduction to air infiltration opening. in buildings 3.2. Basic concepts and terminology  The pressure difference can be produced by 3.3. Characteristics and classification of cracks in the action of the wind, buildings 3.4. Fundamentals of air the temperature difference (stack pressure) and movement 3.5. Distribution of air leakages by a mechanical ventilation system. 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 62  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration in buildings  The flow of air around a building creates a wind pressure on the building. 3.2. Basic concepts and terminology  The distribution of pressure at the surface of a building will depend upon the 3.3. Characteristics and following: classification of cracks in buildings 3.4. Fundamentals of air (a) the shape of the building; movement 3.5. Distribution of air leakages (b) the wind speed and direction relative to the building; 3.6. Measurements of airflow due to infiltrations (c) the location and surroundings of the building, particularly upstream terrain 3.7. Calculation of air infiltrations and the presence of other buildings or similar large obstructions in close proximity. Heat and mass transfer in buildings. High energy performance building envelopes 63  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration  The wind pressure intensity depends on the air density, wind speed, and building in buildings 3.2. Basic concepts and shape characteristics expressed as a pressure coefficient, Cp. terminology 3.3. Characteristics and  The general expression of the wind pressure intensity is given by: classification of cracks in buildings 1 3.4. Fundamentals of air 𝑝 = ·𝐶 ·𝜌 ·𝑐 𝑃𝑎 2 movement 3.5. Distribution of air leakages 𝐶 : Static pressure coefficient (-). 3.6. Measurements of airflow due to infiltrations 𝜌 : Density of air at outdoor temperature. 3.7. Calculation of air infiltrations 𝑐: Wind speed at height of the crack or opening. Heat and mass transfer in buildings. High energy performance building envelopes 64  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration in buildings  The coefficient “𝐶 ” defines the relative pressure over a surface corresponding to the 3.2. Basic concepts and effect of the wind. terminology 3.3. Characteristics and classification of cracks in  Its values can be positive or negative. When it is positive there is overpressure, while buildings negative value indicates that the pressure over the surface is lower than atmospheric 3.4. Fundamentals of air movement pressure. 3.5. Distribution of air leakages 3.6. Measurements of airflow due  Pressure coefficients are generally calculated from data obtained through to infiltrations experimental testing, wind tunnel, or full-scale tests, on various building shapes and 3.7. Calculation of air infiltrations heights. Heat and mass transfer in buildings. High energy performance building envelopes 65  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration in buildings  It is normally assumed to be independent of wind speed but varies according to wind 3.2. Basic concepts and terminology direction and position on the building surface. 3.3. Characteristics and classification of cracks in buildings  The pressure coefficient “𝐶 , ” at point “𝑘 𝑥, 𝑦, 𝑧 ” with reference dynamic pressure 3.4. Fundamentals of air “𝑝 ” related at height “𝑧 ”, for a given wind direction “∅” is defined as follows: movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due , to infiltrations 3.7. Calculation of air infiltrations Where Heat and mass transfer in buildings. High energy performance building envelopes 66  3.4. Fundamentals of air movement 3.4.1. Action of the wind Source; [Liddament] – A guide to energy 3.1. Introduction to air infiltration efficient ventilation in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 67  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration in buildings  In addition to the static pressure coefficient, it is necessary to consider the wind speed. 3.2. Basic concepts and terminology  Wind is highly turbulent and gusting, so average speed is considered. 3.3. Characteristics and classification of cracks in  The speed of the wind changes with height from the ground as well as the buildings roughness of the terrain. 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 68  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration  The average speed profile can be obtained using the following expression: in buildings 3.2. Basic concepts and 𝑐 terminology =𝑐·𝐻 𝑐 3.3. Characteristics and classification of cracks in 𝑐 : Average wind speed at height “𝐻” above the ground. buildings 3.4. Fundamentals of air 𝑐 : Average wind speed measured at a weather station height, normally 10 m movement 3.5. Distribution of air leakages above the ground. Terrain c a 3.6. Measurements of airflow due to infiltrations Open flat country 0,68 0,17 𝑐 and 𝑎: Factor depending on the terrain. 3.7. Calculation of air infiltrations Country with scattered 0,52 0,20 wind breaks Urban 0,35 0,25 City 0,21 0,33 Heat and mass transfer in buildings. High energy performance building envelopes 69  3.4. Fundamentals of air movement 3.4.1. Action of the wind 3.1. Introduction to air infiltration  There are other expressions to evaluate the wind speed at height above the ground. in buildings 𝐻 3.2. Basic concepts and 𝑐 𝛼 10 terminology = · 𝑐′ 𝛼′ 𝐻′ 3.3. Characteristics and 10 classification of cracks in buildings 𝑐: Measured wind speed. Terrain description 𝛼 𝛾 3.4. Fundamentals of air movement 𝐻 : Height of the wind speed measurement Water with at least 5 km of 0,10 1,30 3.5. Distribution of air leakages 𝑚. unrestricted expanse Flat terrain with some isolated 0,15 1,00 3.6. Measurements of airflow due 𝛼 and 𝛾: Factors are the terrain parameters. obstacles to infiltrations Primed values are referred to the location of Rural area with low buildings, 0,20 0,85 3.7. Calculation of air infiltrations trees, etc. Bibliography the weather station, and unprimed values Urban, industrial or forest areas 0,5 0,67 referred to the location of the building. Centre of large city 0,35 0,47 Heat and mass transfer in buildings. High energy performance building envelopes 70  3.4. Fundamentals of air movement 3.4.2. Stack pressure 3.1. Introduction to air infiltration  In addition to wind pressure, the pressure due to buoyancy must be taken into in buildings account. 3.2. Basic concepts and terminology  This is due to temperature difference between indoor and outdoor air of a building. 3.3. Characteristics and classification of cracks in buildings  This is actually due to the difference in densities caused by the difference in 3.4. Fundamentals of air movement temperatures. 3.5. Distribution of air leakages  The density difference due to temperature difference generates pressure gradients 3.6. Measurements of airflow due to infiltrations within outdoor and indoor zones and also within internal zones. 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 71  3.4. Fundamentals of air movement 3.4.2. Stack pressure 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations If the outdoor air is colder than indoor air, the outdoor air enters to the building 3.7. Calculation of air infiltrations through cracks at lower parts of the building, and indoor warm air leaks through cracks at a higher level. When the indoor air is colder than outdoor air, the flow direction is the opposite. Heat and mass transfer in buildings. High energy performance building envelopes 72  3.4. Fundamentals of air movement 3.4.2. Stack pressure  The level at which the transition between inflow and outflow occurs is the neutral 3.1. Introduction to air infiltration in buildings pressure plane (NPP) or neutral pressure level (NPL). 3.2. Basic concepts and terminology  At the height of the NPP, the pressures inside and outside are the same. 3.3. Characteristics and classification of cracks in  The height of the NPP depends on the distribution and flow characteristics of the buildings cracks and it is changeable. 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 73  3.4. Fundamentals of air movement 3.4.2. Stack pressure 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 74  3.4. Fundamentals of air movement 3.4.2. Stack pressure 3.1. Introduction to air infiltration  The pressure due to buoyancy (stack pressure) is equal to: in buildings 𝑝 =𝑝 −𝜌·𝑔·𝑧 →𝑝 −𝑝 =𝜌·𝑔·𝑧 3.2. Basic concepts and terminology 3.3. Characteristics and 𝑝 : Pressure at the reference height 𝑧 𝑃𝑎. classification of cracks in buildings 𝜌: Air density. 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 𝑔: Acceleration due to gravitation. 3.6. Measurements of airflow due to infiltrations 𝑧: Height from the reference level*. 3.7. Calculation of air infiltrations * Commonly, the stack pressure is expressed relative to a consistent datum such as ground level or the level of the lowest opening Heat and mass transfer in buildings. High energy performance building envelopes 75  3.4. Fundamentals of air movement 3.4.2. Stack pressure 3.1. Introduction to air infiltration in buildings  The variation of the pressure in relation to the height can be defined as follows: 3.2. Basic concepts and terminology 𝑑𝑝 = −𝜌 · 𝑔 3.3. Characteristics and 𝑑𝑧 classification of cracks in buildings  Considering air as an ideal gas and because 𝑝 ≈ 𝑝 , the indoor/outdoor pressure 3.4. Fundamentals of air movement difference due to stack can be defined as follows: 3.5. Distribution of air leakages 𝑝 𝑝 𝜌 𝑇 𝑇 3.6. Measurements of airflow due 𝜌 = 𝑎𝑛𝑑 𝜌 = → = →𝜌 =𝜌 · to infiltrations 𝑅 ·𝑇 𝑅 ·𝑇 𝜌 𝑇 𝑇 3.7. Calculation of air infiltrations 𝑇 ∆𝑝 = 𝑝 − 𝑝 = 𝜌 − 𝜌 · 𝑔 · 𝑧 = −𝜌 · 𝑔 · 𝑧 · 1 − 𝑇 Heat and mass transfer in buildings. High energy performance building envelopes 76  3.4. Fundamentals of air movement 3.4.2. Stack pressure  According to the previous expression, the stack pressure difference between two 3.1. Introduction to air infiltration in buildings vertical cracks separated by a vertical distance “𝑧” will be: 3.2. Basic concepts and terminology 𝑇 𝑝 = −𝜌 · 𝑔 · 𝑧 · 1 − 3.3. Characteristics and 𝑇 classification of cracks in buildings 𝜌 : Density of the outdoor air. 3.4. Fundamentals of air movement 𝑇 : Outdoor air temperature 𝐾. 3.5. Distribution of air leakages 𝑇 : Indoor air temperature 𝐾. 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations  When indoor/outdoor temperature difference is equal to 20 K and the vertical Bibliography distance between two cracks is 5 m, the stack pressure is equal to 4,3 Pa. The pressure difference due to wind will be the same if the wind speed is equal to 5 m/s. Heat and mass transfer in buildings. High energy performance building envelopes 77  3.4. Fundamentals of air movement 3.4.3. Mechanical air infiltration 3.1. Introduction to air infiltration in buildings  Mechanical extract ventilation systems generate a relative negative pressure 3.2. Basic concepts and situation indoors, while mechanical supply systems create a relative positive terminology pressure situation referred to outdoors. 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement  The air infiltration or exfiltration created by 3.5. Distribution of air leakages those ventilation systems can be determined 3.6. Measurements of airflow due to infiltrations using the fan curve and building air leakage 3.7. Calculation of air infiltrations curve. Heat and mass transfer in buildings. High energy performance building envelopes 78  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration  The sum of the pressure due to wind, stack and mechanical ventilation system acts in buildings over the building envelope. 3.2. Basic concepts and terminology  It is necessary to consider the sign of each component of the pressure. 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 79  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration  As an exhaust fan, buoyancy causes a decrease in the indoor pressure. in buildings 3.2. Basic concepts and  Once it is known the indoor/outdoor pressure difference we can get the total terminology 3.3. Characteristics and airflow rate (infiltration + ventilation) through the building envelope: classification of cracks in buildings 𝑉̇ = 𝐶 · ∆𝑝 =𝐶· 𝑝 +𝑝 +𝑝 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 𝑉̇ = 𝑉̇ + 𝑉̇ + 𝑉̇ 3.6. Measurements of airflow due to infiltrations  𝑉̇ is the airflow rate due to unbalanced ventilation system: exhaust or supply 3.7. Calculation of air infiltrations fan only. Heat and mass transfer in buildings. High energy performance building envelopes 80  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration in buildings  The previous expression is obtained considering the simple summation of pressure 3.2. Basic concepts and difference across a crack or opening. terminology 3.3. Characteristics and  As said before, the value of “𝑛” is between 1 and 0,5, but it is considered 𝑛 = 0,67 as classification of cracks in buildings a good approximation when there are no measurement data. 3.4. Fundamentals of air movement  The expression can be used to calculate the total infiltration airflow rate when the 3.5. Distribution of air leakages ventilation system is unbalanced: exhaust or supply ventilation system. 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 81  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration in buildings  When the ventilation system is balanced (the supplied and exhausted airflow rates 3.2. Basic concepts and by the mechanical ventilation system are the same), the ventilation system does not terminology affect to the total pressure. 3.3. Characteristics and classification of cracks in buildings  The total airflow rate in the case of balanced ventilation system can be calculated as 3.4. Fundamentals of air movement follows: 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations 𝑉̇ : The airflow rate provided by the balanced ventilation system. Heat and mass transfer in buildings. High energy performance building envelopes 82  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration in buildings  This method used to calculate the total airflow rate considers that the internal 3.2. Basic concepts and pressure is influenced by the wind and stack in the same way. terminology 3.3. Characteristics and classification of cracks in  This is not always the true, the effects of wind and stack pressures are not a buildings linear combination. 3.4. Fundamentals of air movement  So the actual pressure difference through a building envelope can only be 3.5. Distribution of air leakages obtained by iteration. 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations  In order to not use complex iterative models some methods of superposing stack and wind effects were proposed. Heat and mass transfer in buildings. High energy performance building envelopes 83  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration in buildings  The simple linearity method: 𝑉̇ = 𝑉̇ + 𝑉̇ 3.2. Basic concepts and terminology ⁄ 3.3. Characteristics and  The quadrature method: 𝑉̇ = 𝑉̇ + 𝑉̇ classification of cracks in buildings 3.4. Fundamentals of air ⁄ ⁄ movement  The simple pressure addition method: 𝑉̇ = 𝑉̇ + 𝑉̇ 3.5. Distribution of air leakages 3.6. Measurements of airflow due ⁄ ⁄ ⁄ to infiltrations  The iterative method: 𝑉̇ = 𝑉̇ + 𝑉̇ + 𝐵 · 𝑉̇ · 𝑉̇ where 𝐵 ≈ −0,33 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 84  3.4. Fundamentals of air movement 3.4.4. Total air infiltration 3.1. Introduction to air infiltration in buildings  The four models were tested using constant concentration tracer gas technique, 3.2. Basic concepts and using two houses to measure air infiltration due to wind and stack separately. terminology 3.3. Characteristics and classification of cracks in  According to the measurements, the quadrature method produced similar buildings results as iterative and simple addition methods. 3.4. Fundamentals of air movement 3.5. Distribution of air leakages  When the simple linearity equation was used the air infiltration was 3.6. Measurements of airflow due overestimated up to 50%. to infiltrations 3.7. Calculation of air infiltrations  Regarding the results of the study, the researchers recommended the use of the pressure addition method because its simplicity and reliability. Heat and mass transfer in buildings. High energy performance building envelopes 85  3.5. Distribution of air leakages  Different research works tried to define the distribution of air leakages or cracks 3.1. Introduction to air infiltration through different parts of the envelope. in buildings 3.2. Basic concepts and  The percentage in relation to the total air leakage percentage are the following terminology according to ASHRAE: 3.3. Characteristics and classification of cracks in buildings Walls: Air leakages through walls represents between 18% and 50% of the total air 3.4. Fundamentals of air leakages through the envelope. Those air leakages are located in wall/floor, movement window/wall and wall/ceiling joints, electric sockets and plumbing penetration. 3.5. Distribution of air leakages Ceilings: Air leakages in ceilings are ranged 3-30% of the total air leakages. In the 3.6. Measurements of airflow due case of the highest floors in a building, they are an important cause of heat losses. to infiltrations Lights, wiring and plumbing penetration are the most important source of air leakages 3.7. Calculation of air infiltrations in ceilings. Heat and mass transfer in buildings. High energy performance building envelopes 86  3.5. Distribution of air leakages Ventilation systems: They represent between 3% and 28% of the total air leakages: air handling units, ductwork, air inlets (for kitchen for example or 3.1. Introduction to air infiltration in buildings boilers) ,… It is important to notice that it is necessary to generate pressure 3.2. Basic concepts and terminology difference to transport air through ductwork. This pressure difference can be 3.3. Characteristics and higher than 10 times the pressure difference across the envelope of a building. classification of cracks in buildings Doors and windows: Air leakages in doors and windows represent between 6% 3.4. Fundamentals of air movement and 25% of the total air leakages. In the case of windows, air leakages depend on 3.5. Distribution of air the type of windows. Windows with weatherstrips show a higher performance. leakages 3.6. Measurements of airflow due Chimneys: Obviously, it depends on whether or not there is a chimney in the to infiltrations building. The air leakages in chimneys can represent around 30% of the total. It is 3.7. Calculation of air infiltrations very convenient to seal the chimneys when not in use. Heat and mass transfer in buildings. High energy performance building envelopes 87  3.5. Distribution of air leakages Air grilles: The air leakages through these elements represents between 2% and 3.1. Introduction to air infiltration in buildings 12% of the total air leakages. When the ventilation and air-conditioning systems 3.2. Basic concepts and are not in use is convenient to close them using manual devices, but the elements terminology used do not work properly. 3.3. Characteristics and classification of cracks in buildings Diffusion through walls: Air leakage through walls is less than 1% of the total. 3.4. Fundamentals of air movement The rest of the mechanisms are much more important. 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 88  3.5. Distribution of air leakages 3.1. Introduction to air infiltration in buildings 3.2. Basic concepts and terminology 3.3. Characteristics and classification of cracks in buildings 3.4. Fundamentals of air movement 3.5. Distribution of air leakages 3.6. Measurements of airflow due to infiltrations 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 89  3.5. Distribution of air leakages Tendency in relation to the characteristics of the building  The airtightness of a building is determined by the test called in colloquial language 3.1. Introduction to air infiltration in buildings “Blower-door” test (EN 13829). 3.2. Basic concepts and terminology  In the case of doors and windows the test used to define their airtightness is EN 3.3. Characteristics and 1026. classification of cracks in buildings  This type of test is widely used in countries such as the United States, Canada, the 3.4. Fundamentals of air movement Nordic countries, France, Germany,... 3.5. Distribution of air  Data collected over the years allowed to determine the influence of different leakages parameters on the airtightness of buildings. Among them, the construction year, size 3.6. Measurements of airflow due to infiltrations of the building, location of the building, presence of ductwork and construction type. 3.7. Calculation of air infiltrations Heat and mass transfer in buildings. High energy performance building envelopes 90  3.5. Distribution of air leakages Tendency in relation to the characteristics of the building  The most important parameters are the year built and the size of the building.