MacroFlo Opening Types User Guide <Virtual Environment> 6.0

(1)

MacroFlo Opening Types User Guide

(2)

1. Introduction... 4

2. What Are Opening Types? ... 5

3. MacroFlo Opening Types Manager Interface ... 5

3.1. Add ... 5

3.2. Reference ID ... 5

3.3. Description ... 5

3.4. Exposure Type ... 6

3.5. 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

3.5.2.2. Max Angle Open ° ... 7

3.5.2.3. Proportions ... 7

3.5.3. Window - Centre Hung ... 7

3.5.3.2. Max Angle Open ° ... 8

3.5.4. Window - Top Hung ... 8

3.5.4.2. Max Angle Open ° ... 8

3.5.5. Window - Bottom Hung... 8

3.5.5.2. Max Angle Open ° ... 9

3.5.6. Parallel Hung Windows/Flaps... 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) ... 11 3.5.11.3. Duct... 11

(3)

3.5.12. Acoustic Duct... 11

3.5.12.1. Openable Area %... 11

3.5.12.2. Duct Length (m) ... 11

3.5.12.3. Duct... 11

3.6. Aerodynamic (or equivalent) Area... 12

3.7. Crack Flow Coefficient (l s-1m-1Pa-0.6)... 12

3.8. Crack Length (% of opening perimeter) ... 13

3.9. Opening Threshold Temperature (ºC)... 13

3.10. Degree of Opening (% Profile) ... 13

3.11. OK ... 14

3.12. Cancel ... 14

4. Wind Pressure Coefficients ... 15

4.1. What Are Wind Pressure Coefficients?... 15

(4)

1. Introduction

This document describes MacroFlo Opening Types, a program for specifying

the air flow characteristics of openings such as windows and doors for use in

the bulk air flow simulation program MacroFlo.

Please refer to the

MacroFlo

User Guide and the Apache User Guide for further

information about MacroFlo.

(5)

2. What Are Opening Types?

In the Virtual Environment, an opening is a window, door or hole created in

ModelIT. These objects may also be used to represent other types of

penetration in the building fabric such as louvres and grilles.

Opening Types provide a means for specifying the air flow characteristics of

windows and doors for the purpose of analysing natural ventilation and

infiltration in MacroFlo. Holes represent a special category of opening with

constant and unmodifiable air flow characteristics, and are not associated with

Opening Types.

The air flow characteristics of an opening include its crackage, openable area

and exposure to the outside environment, as well as parameters indicating how

its area varies with time and (optionally) with room temperature.

The pressure / flow characteristics of openings such as louvres and grilles are

widely 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

<VE> user.

MacroFlo Opening Types are attached to openings in the model using facilities

provided in the MacroFlo Application View.

3. MacroFlo Opening Types Manager Interface

3.1. Add

Add an opening type to the list. The initial properties of the new opening type

will be copied from the currently selected type.

3.2. Reference ID

An 8-character ID unique to the Opening Type. The Reference ID is

constructed automatically by the program from the Description.

3.3. Description

(6)

3.4. Exposure Type

Select an Exposure Type from the list to specify the exposure of the opening to

wind pressures. For details, see help on Wind Pressure Coefficients and the

MacroFlo Methods manual. For buildings of more than 12.5m in height, use

exposure types with names beginning ‘High-rise’. If the Opening Type is to be

used for internal openings only, or if the effects of wind are to be ignored,

select ‘Internal’.

3.5. Opening Category

Select the category of opening to be represented by the type. Choose from

custom/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/resistance

that occurs through building windows, doors and louvers which in reality

involve more turbulent flow.

To specify a realistic opening type in terms of real air resistance select the

category and define the parameters that are displayed to calculate the

Aerodynamic (or equivalent) Area as a % of the gross opening area as drawn

in ModelIT.

Openable area and modelled elements:

Typically users draw a different level of detail at different stages in the design

process e.g.

 Early stage – large ModelIT surface elements representing a gross

structural opening of which some sub areas may be openable;

 Detail stage – many small ModelIT surface elements each representing

an openable (or fixed window) element.

In the examples above openable area may need to include the impact of frame

area or obstructing elements in the openable area and/or define the openable

area in a large element that contains both openable and fixed parts.

It is important not to confuse openable area with geometric free area which

may not be in the plane of the wall.

(7)

3.5.1. Custom/Sharp Edge Orifice

3.5.1.1. Openable Area %

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 window frames, partial opening 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 the equivalent area (a sharp edged orifice that has the same flow / pressure characteristics as the window or door) or alternatively another window type which will account for this fact can be 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. Openable Area %

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 window frames, partial opening and the obstructing effect of pivoting elements. In the case of windows and doors that open by pivoting, the parameter should be set to an estimate of the ‘throat’ area in the plane of the window (the hole created by the opening leaf) – the minimum cross section presented by the opening to air passing through it.

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

3.5.2.2. Max Angle Open °

The maximum angle of opening of the window, degrees.

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

3.5.2.3. Proportions

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. Openable Area %

(8)

3.5.3.2. Max Angle Open °

3.5.3.3. Proportions

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. Openable Area %

3.5.4.2. Max Angle Open °

3.5.4.3. Proportions

3.5.5. Window - Bottom Hung

3.5.5.1. Openable Area %

(9)

3.5.5.2. Max Angle Open °

3.5.5.3. Proportions

3.5.6. Parallel Hung Windows/Flaps

3.5.6.1. Openable Area %

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 window frames, partial opening and the obstructing effect of pivoting elements. In the case of windows and doors that open by pivoting, the parameter should be set to an estimate of the ‘throat’ area in the plane of the window (the hole created by the opening leafs) – the minimum cross section presented by the opening to air passing through it.

3.5.6.2. Max Angle Open °

3.5.6.3. Proportions

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. Openable Area %

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 window frames, partial opening and the obstructing effect of pivoting elements. In the case of windows and doors that open by sliding, the parameter should be set to an estimate of the ‘throat’ area in the plane of the window (the hole created by the opening leaf) – the minimum cross section presented by the opening to air passing through it.

(10)

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

3.5.8. Sliding/Roller Door

3.5.8.1. Openable Area %

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 window frames, partial opening and the obstructing effect of pivoting elements. In the case of windows and doors that open by sliding, the parameter should be set to an estimate of the ‘throat’ area in the plane of the window (the hole created by the opening leaf) – the minimum cross section presented by the opening to air passing through it.

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

3.5.9. Louvre

3.5.9.1. Openable Area %

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 bottom louvres. It is essentially the duct face area.

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

3.5.9.2. Coefficient of Discharge

The coefficient of discharge, Cd, of the louvre used in the calculation of air flow through the opening (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 the opening. The value should usually be less than 100%, to allow for frames and bottom louvres. It is essentially the duct face area.

3.5.10.2. Coefficient of Discharge

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

(11)

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

3.5.11. Duct

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 bottom louvers. It is essentially the duct face area.

3.5.11.2. Duct Length (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

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 bottom louvers. It is essentially the duct face area.

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

3.5.12.2. Duct Length (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,

(12)

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. Aerodynamic (or equivalent) Area

Aerodynamic area represents the actual orifice area as a % of the gross

physical opening that will have the same pressure loss as the selected real

opening type. This is calculated based on the values given for the selected

opening category.

Further information regarding the calculation of aerodynamic (or equivalent)

area for each category is given in the

MacroFlo Calculation Methods user

guide

.

3.7. Crack Flow Coefficient

(l s-1m-1Pa-0.6)

A coefficient characterising the leakage properties of the crack. The flow

characteristic is assumed to take the form:

q = C L (ρ

0

/ρ)

0.5

ΔP

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)

Ρ

is the density of air entering the crack (kg/m

3

)

ρ0

= 1.21 kg/m

3

is a reference air density

ΔP

is the pressure difference across the crack (Pa).

Representative measured values of the Crack Flow Coefficient for windows

and doors are given in Tables 1 and 2. These values are taken from An

Analysis and Data Summary of the AIVC’s Numerical Database. Technical

Note AIVC 44, March 1994. Air Infiltration and Ventilation Centre. University of

Warwick Science Park. Sovereign Court, Sir William Lyons Road, Coventry

CV4 7EZ.

Table 1. Crack Flow Coefficients (

l s-1m-1Pa-0.6)

– Windows

Lower Quartile Median Upper Quartile

(13)

Sliding 0.079 0.15 0.21

Hinged 0.39 0.74 1.1

Windows (Non-weatherstripped)

Sliding 0.18 0.23 0.37

Table 2. Crack Flow Coefficients (

l s-1m-1Pa-0.6)

– Doors

Lower Quartile Median Upper Quartile

Hinged 0.082 0.27 0.84

External Doors (Weatherstripped)

Revolving 1.0 1.5 2.0

Hinged 1.1 1.2 1.4

External 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. Crack Length (% of opening perimeter)

The length of the crack around the opening, expressed as a percentage of the

opening’s perimeter length. Values greater than 100% are appropriate for

openings such as sash windows. This parameter and the Crack Flow

Coefficient are used to calculate infiltration and air leakage rates for closed

windows and doors. Openings may be eliminated from the MacroFlo analysis

altogether by assigning zeros to either or both crack parameters and the

parameter Openable Area (% of opening area).

3.9. Opening Threshold Temperature (ºC)

This parameter allows for window opening to be controlled on the basis of

room temperature. Opening Threshold Temperature is the temperature in the

room adjacent to the opening which, when exceeded, will trigger the opening

of the window or door. Once open, it will remain so (possibly in varying

degrees) 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 0ºC) will ensure that

the pattern of opening simply follows the Degree of Opening percentage

profile.

An alternative, and for many purposes preferable, way to control window

opening on the basis of room temperature is by using a formula profile for the

Degree of Opening profile, as described below.

3.10. Degree of Opening (% Profile)

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

(14)

Project Percentage Profiles defined in APpro. Subject to the Temperature

Threshold control, the area of the opening will be varied by modulating the

Openable Area with the Degree of Opening percentage profile. When the

Degree of Opening profile is zero, or when the Threshold Temperature control

dictates that the window or door is closed, the opening will be treated as a

crack.

Window opening can be controlled on room temperature, outside temperature

and other variables by setting the Degree of Opening profile to a profile

containing 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 24°C and

(unlike the Temperature Threshold control) closes them immediately it falls

below this value. The formula should be assigned to the appropriate daily

profile for the period of the day when the windows might be opened. If this type

of window opening control is used, the Opening Threshold Temperature should

be disabled by setting it to a low value such as 0°C.

See the section headed Formula Profiles in the APpro User Guide for further

guidance on the use of formula profiles.

3.11. OK

Exit the MacroFlo Opening Types Manager and save the changes.

3.12. Cancel

(15)

4. Wind Pressure Coefficients

4.1. What Are Wind Pressure Coefficients?

The pressure exerted by the wind on a building is a complicated function of

wind speed, wind direction and building geometry. The surrounding terrain and

nearby obstructions can also be important factors. For practical purposes, wind

pressures are often estimated using wind pressure coefficients. These

coefficients relate the wind pressure on a building surface to the wind speed,

using a relationship of the form:

p = C

p

ρ v

2

/ 2

where:

p

wind pressure (Pa)

Cp

wind pressure coefficient

Ρ

air density (kg/m

3

)

V

reference wind speed (m/s)

Wind pressure coefficients may be obtained by a variety of means, including in

situ measurements, CFD studies and wind tunnel experiments. Those used in

MacroFlo are derived from wind tunnel experiments on simple building models.

These experiments provide wind pressure coefficients for various types of

surface (referred to as Exposure Types) for a range of relative wind directions

(angles of attack). Exposure Types characterise both the geometrical aspects

of the surface (such as roof pitch) and the degree of sheltering by nearby

obstructions.

In line with the convention adopted in the data used by MacroFlo, the

reference wind speed (v) appearing in the pressure formula is normally the free

stream wind speed at the building height. (For an exception to this rule, see

below.) The variable v is estimated from the meteorological wind speed, u,

using an empirical expression for the variation of wind speed with height and

terrain type:

v = u K h

a

,

where:

(16)

h

height above the ground (m)

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

types:

Terrain Type Description Exponent a Layer Thickness δ (m) K

Country Open terrain with scattered obstructions having 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, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger, over a distance of at least 2000 m or 10 times the height of the structure upwind, whichever is greater

0.22 370 0.4319

City Large city centres, in which at least 50% of buildings are higher than 21m, over a distance of at least 2000 m or 10 times the height of the structure 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 on

the assumption of a power law velocity profile (with exponent a) applying up to

a height

δ, where δ is the thickness of the atmospheric boundary layer:

v = u (δ

met

/h

met

)

αmet

_(h/δ)

α

where

δ

met

= 270 m is the Layer Thickness for the meteorological site (assumed to be

of type ‘Country’)

α

met

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

‘Country’)

h

met

= is the measurement height for the meteorological site (assumed to be 10

m)

In accordance with equations 2 and 3, the values of K appearing in the above

table are calculated from

K = (270/10)

0.14

(1/δ)

α

An alternative reference wind speed is used in cases not strictly covered by the

experimental data, namely buildings of more than 12.5m in height. In such

(17)

cases the reference wind speed depends on the height of the opening. For

openings 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). For

openings above 12.5m, v is taken to be the free stream wind speed at the

height of the opening.

4.2. Exposure Types

MacroFlo uses wind pressure coefficients taken from the Air Infiltration and

Ventilation Centre’s publication Air Infiltration Calculation Techniques – An

Applications Guide. These coefficients, which are derived from wind tunnel

experiments, are recommended for use with buildings of up to 3 storeys (or

about 12.5m). They are provided for a range of exposure types – ‘exposed

wall’, ‘sheltered roof < 10 deg’, etc – and for 16 azimuthal angles of attack. An

exposure type must be set for all Opening Types.

When selecting Exposure Types in the MacroFlo Opening Types Manager the

following considerations should be borne in mind:

The terms ‘exposed’, ‘semi-exposed’ and ‘sheltered’ in the Exposure Type

name refer to the degree of sheltering of the building by surrounding buildings

and other obstructions. ‘Exposed’ denotes a building standing in open ground

with no obstructions nearby, ‘semi-exposed’ denotes a building with nearby

obstructions lower in height than the building itself, and ‘sheltered’ is

appropriate when the surrounding obstructions are of similar height to the

building.

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 with

a 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 long

sides 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 the

rectangular and square buildings.

When selecting appropriate exposure types for MacroFlo Opening Types, you

should make a judgement as to which of the available exposure types most

accurately describes the exposure of the surfaces to which the Opening Types

are to be assigned.

To cover flat roofs (which were not treated in the experimental study) three

additional Exposure Types have been added: ‘exposed flat roof’,

‘semi-exposed flat roof’ and ‘sheltered flat roof’. Wind pressure coefficients for these

(18)

MacroFlo Opening Types User Guide <Virtual Environment> 6.0