Macro Flo Opening Types

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    MacroFlo Opening Types User Guide 6.0

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    Contents

    1. Introduction..................................................................................................................42. What Are Opening Types? ..........................................................................................53. MacroFlo Opening Types Manager Interface ............................................................ 5

    3.1. Add ..................................................................................................................................................... 53.2. Reference ID ...................................................................................................................................... 53.3. Description ......................................................................................................................................... 53.4. Exposure Type ................................................................................................................................... 63.5. Opening Category .............................................................................................................................. 6

    3.5.1. Custom/Sharp Edge Orifice....................................................................................................... 7

    3.5.1.1. Openable Area % ...................................................................................................................... 7

    3.5.2. Window/Door - Side Hung......................................................................................................... 7

    3.5.2.1. Openable Area % ...................................................................................................................... 73.5.2.2. Max Angle Open ..................................................................................................................... 7

    3.5.2.3. Proportions ................................................................................................................................ 7

    3.5.3. Window - Centre Hung .............................................................................................................. 7

    3.5.3.1. Openable Area % ...................................................................................................................... 7

    3.5.3.2. Max Angle Open ..................................................................................................................... 8

    3.5.3.3. Proportions ................................................................................................................................ 8

    3.5.4. Window - Top Hung................................................................................................................... 8

    3.5.4.1. Openable Area % ...................................................................................................................... 8

    3.5.4.2. Max Angle Open ..................................................................................................................... 8

    3.5.4.3. Proportions ................................................................................................................................ 8

    3.5.5. Window - Bottom Hung.............................................................................................................. 8

    3.5.5.1. Openable Area % ...................................................................................................................... 8

    3.5.5.2. Max Angle Open ..................................................................................................................... 9

    3.5.5.3. Proportions ................................................................................................................................ 9

    3.5.6. Parallel Hung Windows/Flaps.................................................................................................... 9

    3.5.6.1. Openable Area % ...................................................................................................................... 9

    3.5.6.2. Max Angle Open ..................................................................................................................... 9

    3.5.6.3. Proportions ................................................................................................................................ 9

    3.5.7. Window - Sash .......................................................................................................................... 9

    3.5.7.1. Openable Area % ...................................................................................................................... 9

    3.5.8. Sliding/Roller Door................................................................................................................... 10

    3.5.8.1. Openable Area % .................................................................................................................... 10

    3.5.9. Louvre...................................................................................................................................... 10

    3.5.9.1. Openable Area % .................................................................................................................... 10

    3.5.9.2. Coefficient of Discharge .......................................................................................................... 10

    3.5.10. Grille ........................................................................................................................................ 10

    3.5.10.1. Openable Area %............................................................................................................ 10

    3.5.10.2. Coefficient of Discharge.................................................................................................. 10

    3.5.11. Duct ......................................................................................................................................... 11

    3.5.11.1. Openable Area %............................................................................................................ 11

    3.5.11.2. Duct Length (m) .............................................................................................................. 113.5.11.3. Duct................................................................................................................................. 11

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    3.5.12. Acoustic Duct........................................................................................................................... 11

    3.5.12.1. Openable Area %............................................................................................................ 11

    3.5.12.2. Duct Length (m) .............................................................................................................. 113.5.12.3. Duct................................................................................................................................. 11

    3.6. Aerodynamic (or equivalent) Area.................................................................................................... 123.7. Crack Flow Coefficient (l s

    -1m

    -1Pa

    -0.6)............................................................................................. 12

    3.8. Crack Length (% of opening perimeter) ........................................................................................... 133.9. Opening Threshold Temperature (C).............................................................................................. 133.10. Degree of Opening (% Profile) ......................................................................................................... 133.11. OK .................................................................................................................................................... 143.12. Cancel .............................................................................................................................................. 14

    4. Wind Pressure Coefficients ......................................................................................154.1. What Are Wind Pressure Coefficients?............................................................................................ 154.2. Exposure Types ............................................................................................................................... 17

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    1. IntroductionThis document describes MacroFlo Opening Types, a program for specifyingthe air flow characteristics of openings such as windows and doors for use inthe bulk air flow simulation program MacroFlo.

    Please refer to theMacroFloUser Guide and the Apache User Guide for furtherinformation about MacroFlo.

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    2. What Are Opening Types?In the Virtual Environment, an opening is a window, door or hole created inModelIT. These objects may also be used to represent other types ofpenetration in the building fabric such as louvres and grilles.

    Opening Types provide a means for specifying the air flow characteristics ofwindows and doors for the purpose of analysing natural ventilation andinfiltration in MacroFlo. Holes represent a special category of opening withconstant and unmodifiable air flow characteristics, and are not associated withOpening Types.

    The air flow characteristics of an opening include its crackage, openable areaand exposure to the outside environment, as well as parameters indicating howits area varies with time and (optionally) with room temperature.

    The pressure / flow characteristics of openings such as louvres and grilles arewidely available from manufacturers (coefficient of discharge or Cd factors),however not so for windows. MacroFlo provides a default selection of pressure /flow characteristics for a wide range of opening types for the convenience of the user.

    MacroFlo Opening Types are attached to openings in the model using facilitiesprovided in the MacroFlo Application View.

    3. MacroFlo Opening Types Manager Interface

    3.1. A dd

    Add an opening type to the list. The initial properties of the new opening typewill be copied from the currently selected type.

    3.2. Reference ID

    An 8-character ID unique to the Opening Type. The Reference ID isconstructed automatically by the program from the Description.

    3.3. Des c r ip t ion

    A verbal description of the Opening Type.

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    3. 4. E x pos ur e T y pe

    Select an Exposure Type from the list to specify the exposure of the opening towind pressures. For details, see help on Wind Pressure Coefficients and theMacroFlo Methods manual. For buildings of more than 12.5m in height, useexposure types with names beginning High-rise. If the Opening Type is to beused for internal openings only, or if the effects of wind are to be ignored,select Internal.

    3.5. O penin g Cat egor y

    Select the category of opening to be represented by the type. Choose fromcustom/sharp edge orifice, window/door side hung, window centre hung,window top hung, window bottom hung, parallel hung windows/flaps,

    window sash, sliding/roller door, louvre, grille, duct or acoustic duct.

    Custom/sharp edge orifice is an idealised model of the real air flow/resistancethat occurs through building windows, doors and louvers which in realityinvolve more turbulent flow.

    To specify a realistic opening type in terms of real air resistance select thecategory and define the parameters that are displayed to calculate theAerodynamic (or equivalent) Area as a % of the gross opening area as drawnin ModelIT.

    Openable area and modelled elements:

    Typically users draw a different level of detail at different stages in the designprocess e.g.

    Early stage large ModelIT surface elements representing a grossstructural opening of which some sub areas may be openable;

    Detail stage many small ModelIT surface elements each representingan openable (or fixed window) element.

    In the examples above openable area may need to include the impact of framearea or obstructing elements in the openable area and/or define the openablearea in a large element that contains both openable and fixed parts.

    It is important not to confuse openable area with geometric free area whichmay not be in the plane of the wall.

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    3.5.1. Custom/Sharp Edge Orifice

    3 .5 .1 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doors(using this input method) that open by pivoting, the parameter should be an estimate of theequivalent area (a sharp edged orifice that has the same flow / pressure characteristics asthe window or door) or alternatively another window type which will account for this fact canbe selected.

    Openable Area can be any value from 0% to 100%.

    For custom/sharp edge orifice the aerodynamic (or equivalent) free area is taken directly as

    the openable area %.

    3.5.2. Window/Door - Side Hung

    3 .5 .2 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by pivoting, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leaf) the minimum cross sectionpresented by the opening to air passing through it.

    Openable area can be any value from 0% to 100%.

    3 .5 .2 .2 . M a x A n g l e O p en

    The maximum angle of opening of the window, degrees.

    Max angle open can be any value from 10 to 90.

    3 .5 .2 .3 . P r o p o r t i o n s

    The ratio of window/door length to window/door height.

    Proportions can be defined by selecting any option from Length/Height < 0.5, 0.5 =Length/Height < 1, 1 = Length/Height < 2, Length/Height > 2.

    3.5.3. Window - Centre Hung

    3 .5 .3 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by pivoting, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leaf) the minimum cross section

    presented by the opening to air passing through it.

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    Openable area can be any value from 0% to 100%.

    3 .5 .3 .2 . M a x A n g l e O p en

    The maximum angle of opening of the window, degrees.

    Max angle open can be any value from 15 to 90.

    3 .5 .3 .3 . P r o p o r t i o n s

    The ratio of window length to window height.

    Proportions can be defined by selecting any option from Length/Height = 1 or Length/Height> 2.

    3.5.4. Window - Top Hung

    3 .5 .4 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by pivoting, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leaf) the minimum cross sectionpresented by the opening to air passing through it.

    Openable area can be any value from 0% to 100%.

    3 .5 .4 .2 . M a x A n g l e O p en

    The maximum angle of opening of the window, degrees.

    Max angle open can be any value from 10 to 90.

    3 .5 .4 .3 . P r o p o r t i o n s

    The ratio of window length to window height.

    Proportions can be defined by selecting any option from Length/Height < 0.5, 0.5 =Length/Height < 1, 1 = Length/Height < 2, Length/Height > 2.

    3.5.5. Window - Bottom Hung

    3 .5 .5 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by pivoting, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leaf) the minimum cross sectionpresented by the opening to air passing through it.

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    Openable area can be any value from 0% to 100%.

    3 .5 .5 .2 . M a x A n g l e O p en

    The maximum angle of opening of the window, degrees.

    Max angle open can be any value from 10 to 90.

    3 .5 .5 .3 . P r o p o r t i o n s

    The ratio of window length to window height.

    Proportions can be defined by selecting any option from Length/Height < 0.5, 0.5 =Length/Height < 1, 1 = Length/Height < 2, Length/Height > 2.

    3.5.6. Parallel Hung Windows/Flaps

    3 .5 .6 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by pivoting, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leafs) the minimum cross sectionpresented by the opening to air passing through it.

    Openable area can be any value from 0% to 100%.

    3 .5 .6 .2 . M a x A n g l e O p en

    The maximum angle of opening of the window, degrees.

    Max angle open can be any value from 15 to 90.

    3 .5 .6 .3 . P r o p o r t i o n s

    The ratio of window length to window height.

    Proportions can be defined by selecting any option from Length/Height = 1, Length/Height =2 or Length/Height > 2.

    3.5.7. Window - Sash

    3 .5 .7 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by sliding, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leaf) the minimum cross sectionpresented by the opening to air passing through it.

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    Openable Area can be any value from 0% to 100%.

    For sash windows the aerodynamic (or equivalent) free area is taken directly as theopenable area %.

    3.5.8. Sliding/Roller Door

    3 .5 .8 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for window frames, partialopening and the obstructing effect of pivoting elements. In the case of windows and doorsthat open by sliding, the parameter should be set to an estimate of the throat area in theplane of the window (the hole created by the opening leaf) the minimum cross sectionpresented by the opening to air passing through it.

    Openable Area can be any value from 0% to 100%.

    For sliding/roller doors the aerodynamic (or equivalent) free area is taken directly as theopenable area %.

    3.5.9. Louvre

    3 .5 .9 .1 . O p e n a b l e A r e a %

    The area available for air flow, expressed as a percentage of the overall plane area of the

    opening. The value should usually be less than 100%, to allow for frames and bottomlouvres. It is essentially the duct face area.

    Openable Area Can be any value from 0% to 100%.

    3 .5 .9 .2 . C o e f f i c i en t o f D i s c h a r g e

    The coefficient of discharge, Cd, of the louvre used in the calculation of air flow through theopening (further details in the MacroFlo Calculation Methods manual).

    Coefficient of discharge can be any value from 0 to 0.6 Cd.

    3.5.10. Grille

    3.5.10.1. Openable Area %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for frames and bottomlouvres. It is essentially the duct face area.

    Openable Area can be any value from 0% to 100%.

    3.5.10.2. Coeff icient o f Disch arge

    The coefficient of discharge, Cd, of the grille used in the calculation of air flow through theopening (further details in the MacroFlo Calculation Methods manual).

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    Coefficient of discharge can be any value from 0 to 0.6 Cd.

    3.5.11. Duct

    3.5.11.1. Openable Area %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for frames and bottomlouvers. It is essentially the duct face area.

    Openable Area can be any value from 0% to 100%.

    3.5.11.2. Duct L ength (m)

    Enter length of the duct in metres, m.

    Duct length can be any value from 1m to 10m.

    3.5.11.3. Duct

    Define the type of duct.

    Duct can be defined by selecting any option from;

    Straight / one 90 bend / two 90 bends / three 90 bends no grille,

    Straight / one 90 bend / two 90 bends / three 90 bends - grille 50%,

    Straight / one 90 bend / two 90 bends / three 90 bends - grille 20%.

    3.5.12. Acoustic Duct

    3.5.12.1. Openable Area %

    The area available for air flow, expressed as a percentage of the overall plane area of theopening. The value should usually be less than 100%, to allow for frames and bottomlouvers. It is essentially the duct face area.

    Openable Area can be any value from 0% to 100%.

    3.5.12.2. Duct L ength (m)

    Enter length of the duct in metres, m.

    Duct length can be any value from 1m to 10m.

    3.5.12.3. Duct

    The type of duct.

    Duct can be defined by selecting any option from:

    Straight - free area 20% / 30% / 50% / 100% - no grille,Angled - free area 20% / 30% / 50% / 100% - no grille,

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    Straight - free area 20% / 30% / 50% / 100% - grille 50%,

    Angled - free area 20% / 30% / 50% / 100% - grille 50%,

    Straight - free area 20% / 30% / 50% / 100% - grille 20%,Angled - free area 20% / 30% / 50% / 100% - grille 20%.

    3. 6. A er ody nam ic ( or equiv alent ) A r ea

    Aerodynamic area represents the actual orifice area as a % of the grossphysical opening that will have the same pressure loss as the selected realopening type. This is calculated based on the values given for the selectedopening category.

    Further information regarding the calculation of aerodynamic (or equivalent)area for each category is given in the MacroFlo Calculation Methods userguide.

    3.7. Cr ac k F low Coef f ic ient (l s-1 m-1 Pa-0.6)

    A coefficient characterising the leakage properties of the crack. The flowcharacteristic is assumed to take the form:

    q = C L (0/)0.5P 0.6

    where:

    q is the air flow through the crack (l/s)

    C is the Crack Flow Coefficient (l s-1 m-1 Pa-0.6)

    L is the length of the crack (m)

    is the density of air entering the crack (kg/m3)

    0 = 1.21 kg/m3 is a reference air density

    P is the pressure difference across the crack (Pa).

    Representative measured values of the Crack Flow Coefficient for windowsand doors are given in Tables 1 and 2. These values are taken from AnAnalysis and Data Summary of the AIVCs Numerical Database. TechnicalNote AIVC 44, March 1994. Air Infiltration and Ventilation Centre. University ofWarwick Science Park. Sovereign Court, Sir William Lyons Road, CoventryCV4 7EZ.

    Table 1. Crack Flow Coefficients (l s -1 m-1 Pa-0.6) Windows

    Lower Quartile Median Upper QuartileWindows (Weatherstripped) Hinged 0.086 0.13 0.41

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    Sliding 0.079 0.15 0.21

    Hinged 0.39 0.74 1.1Windows (Non-weatherstripped)

    Sliding 0.18 0.23 0.37

    Table 2. Crack Flow Coefficients (l s -1 m-1 Pa-0.6) Doors

    Lower Quartile Median Upper Quartile

    Hinged 0.082 0.27 0.84External Doors (Weatherstripped)

    Revolving 1.0 1.5 2.0

    Hinged 1.1 1.2 1.4External Doors (Non-weatherstripped)

    Sliding 0.2

    Internal Doors (Non-weatherstripped) 1.1 1.3 2.0

    Loft Hatches (Non-weatherstripped) 0.64 0.68 0.75

    3. 8. Cr ac k Lengt h ( % of opening per im et er )

    The length of the crack around the opening, expressed as a percentage of theopenings perimeter length. Values greater than 100% are appropriate foropenings such as sash windows. This parameter and the Crack FlowCoefficient are used to calculate infiltration and air leakage rates for closedwindows and doors. Openings may be eliminated from the MacroFlo analysisaltogether by assigning zeros to either or both crack parameters and the

    parameter Openable Area (% of opening area).

    3.9. Op enin g Th resh old Temperatu re (C)

    This parameter allows for window opening to be controlled on the basis ofroom temperature. Opening Threshold Temperature is the temperature in theroom adjacent to the opening which, when exceeded, will trigger the openingof the window or door. Once open, it will remain so (possibly in varyingdegrees) until the Degree of Opening percentage profile falls to zero,regardless of subsequent values of the adjacent room air temperature. A low

    value for Opening Threshold Temperature (for example 0C) will ensure thatthe pattern of opening simply follows the Degree of Opening percentageprofile.

    An alternative, and for many purposes preferable, way to control windowopening on the basis of room temperature is by using a formula profile for theDegree of Opening profile, as described below.

    3.10. Degree of Opening (% Profi le)

    A percentage profile allowing the degree of window or door opening to be

    specified as a function of time. The profile may be selected from the list of

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    Project Percentage Profiles defined in APpro. Subject to the TemperatureThreshold control, the area of the opening will be varied by modulating the

    Openable Area with the Degree of Opening percentage profile. When theDegree of Opening profile is zero, or when the Threshold Temperature controldictates that the window or door is closed, the opening will be treated as acrack.

    Window opening can be controlled on room temperature, outside temperatureand other variables by setting the Degree of Opening profile to a profilecontaining a formula. A common type of formula for this purpose is:

    int(100*(ta/24))

    This opens the windows when the room air temperature exceeds 24C and(unlike the Temperature Threshold control) closes them immediately it fallsbelow this value. The formula should be assigned to the appropriate dailyprofile for the period of the day when the windows might be opened. If this typeof window opening control is used, the Opening Threshold Temperature shouldbe disabled by setting it to a low value such as 0C.

    See the section headed Formula Profiles in the APpro User Guide for furtherguidance on the use of formula profiles.

    3.11. OK

    Exit the MacroFlo Opening Types Manager and save the changes.

    3.12. Cancel

    Exit the MacroFlo Opening Types Manager without saving the changes.

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    4. Wind Pressure Coefficients

    4.1. W hat A r e W ind P r es s ur e Coef f ic ient s ?

    The pressure exerted by the wind on a building is a complicated function ofwind speed, wind direction and building geometry. The surrounding terrain andnearby obstructions can also be important factors. For practical purposes, windpressures are often estimated using wind pressure coefficients. Thesecoefficients relate the wind pressure on a building surface to the wind speed,using a relationship of the form:

    p = Cp v2 / 2

    where:

    p wind pressure (Pa)

    Cp wind pressure coefficient

    air density (kg/m3)

    V reference wind speed (m/s)

    Wind pressure coefficients may be obtained by a variety of means, including insitu measurements, CFD studies and wind tunnel experiments. Those used inMacroFlo are derived from wind tunnel experiments on simple building models.These experiments provide wind pressure coefficients for various types ofsurface (referred to as Exposure Types) for a range of relative wind directions(angles of attack). Exposure Types characterise both the geometrical aspectsof the surface (such as roof pitch) and the degree of sheltering by nearbyobstructions.

    In line with the convention adopted in the data used by MacroFlo, thereference wind speed (v) appearing in the pressure formula is normally the freestream wind speed at the building height. (For an exception to this rule, seebelow.) The variable v is estimated from the meteorological wind speed, u,using an empirical expression for the variation of wind speed with height andterrain type:

    v = u K ha,

    where:

    u meteorological wind speed at height 10m in open country (m/s)

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    h height above the ground (m)

    and a and K are coefficients taking the following values for different terrain

    types:

    TerrainType

    Description Exponenta

    LayerThickness(m)

    K

    Country Open terrain with scattered obstructionshaving heights generally less than 10 m,including flat open country typical of meteorological station surroundings

    0.14 270 0.7244

    Suburbs Urban and suburban areas, wooded areas, orother terrain with numerous closely spaced

    obstructions having the size of single-familydwellings or larger, over a distance of at least2000 m or 10 times the height of the structureupwind, whichever is greater

    0.22 370 0.4319

    City Large city centres, in which at least 50% ofbuildings are higher than 21m, over a distanceof at least 2000 m or 10 times the height of thestructure upwind, whichever is greater

    0.33 460 0.2097

    Data in this table is taken from ASHRAE Handbook of Fundamentals (2001).ASHRAE provide the following formula for wind speed at height h, based onthe assumption of a power law velocity profile (with exponent a) applying up to

    a height , where is the thickness of the atmospheric boundary layer:

    v = u (met/hmet)met (h/)

    where

    met = 270 m is the Layer Thickness for the meteorological site (assumed to beof type Country)

    met = 0.14 is the Exponent for the meteorological site (assumed to be of type

    Country)hmet = is the measurement height for the meteorological site (assumed to be 10m)

    In accordance with equations 2 and 3, the values of K appearing in the abovetable are calculated from

    K = (270/10)0.14 (1/)

    An alternative reference wind speed is used in cases not strictly covered by theexperimental data, namely buildings of more than 12.5m in height. In such

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    cases the reference wind speed depends on the height of the opening. Foropenings less than 12.5m off the ground, v is taken to be the free stream wind

    speed at 12.5m, or at the height of the building (whichever is the smaller). Foropenings above 12.5m, v is taken to be the free stream wind speed at theheight of the opening.

    4.2. E x po s ur e T y pes

    MacroFlo uses wind pressure coefficients taken from the Air Infiltration andVentilation Centres publication Air Infiltration Calculation Techniques AnApplications Guide. These coefficients, which are derived from wind tunnelexperiments, are recommended for use with buildings of up to 3 storeys (or

    about 12.5m). They are provided for a range of exposure types exposedwall, sheltered roof < 10 deg, etc and for 16 azimuthal angles of attack. Anexposure type must be set for all Opening Types.

    When selecting Exposure Types in the MacroFlo Opening Types Manager thefollowing considerations should be borne in mind:

    The terms exposed, semi-exposed and sheltered in the Exposure Typename refer to the degree of sheltering of the building by surrounding buildingsand other obstructions. Exposed denotes a building standing in open ground

    with no obstructions nearby, semi-exposed denotes a building with nearbyobstructions lower in height than the building itself, and sheltered isappropriate when the surrounding obstructions are of similar height to thebuilding.

    The terms long and short relate to the shape of the building viewed in plan.The experiments on which the wind pressure coefficients are based dealt witha square building and a rectangular building with a plan aspect ratio of 2:1.Short wall and long wall refer respectively to the walls on the short and longsides of the rectangular building, and wall refers to the walls of the square

    building. Long roof and roof refer respectively to the pitched roofs on therectangular and square buildings.

    When selecting appropriate exposure types for MacroFlo Opening Types, youshould make a judgement as to which of the available exposure types mostaccurately describes the exposure of the surfaces to which the Opening Typesare to be assigned.

    To cover flat roofs (which were not treated in the experimental study) threeadditional Exposure Types have been added: exposed flat roof, semi-

    exposed flat roof and sheltered flat roof. Wind pressure coefficients for these

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    Exposure Types have been estimated by extrapolating the availableexperimental data.

    An exposure type appropriate for internal openings, internal, is also provided.If applied to external openings, this exposure type sets all wind pressurecoefficients to zero, allowing you to investigate flow patterns in the absence ofwind pressures.