MacroFlo Opening Types User Guide <Virtual Environment> 6.0

Transcription

1 MacroFlo Opening Types User Guide <Virtual Environment> 6.0 Page 1 of 18

2 Contents 1. Introduction What Are Opening Types? MacroFlo Opening Types Manager Interface Add Reference ID Description Exposure Type Opening Category Custom/Sharp Edge Orifice Openable Area % Window/Door - Side Hung Openable Area % Max Angle Open Proportions Window - Centre Hung Openable Area % Max Angle Open Proportions Window - Top Hung Openable Area % Max Angle Open Proportions Window - Bottom Hung Openable Area % Max Angle Open Proportions Parallel Hung Windows/Flaps Openable Area % Max Angle Open Proportions Window - Sash Openable Area % Sliding/Roller Door Openable Area % Louvre Openable Area % Coefficient of Discharge Grille Openable Area % Coefficient of Discharge Duct Openable Area % Duct Length (m) Duct Page 2 of 18

3 Acoustic Duct Openable Area % Duct Length (m) Duct Aerodynamic (or equivalent) Area Crack Flow Coefficient (l s -1 m -1 Pa -0.6 ) Crack Length (% of opening perimeter) Opening Threshold Temperature (ºC) Degree of Opening (% Profile) OK Cancel Wind Pressure Coefficients What Are Wind Pressure Coefficients? Exposure Types Page 3 of 18

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. Page 4 of 18

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 Reference ID An 8-character ID unique to the Opening Type. The Reference ID is constructed automatically by the program from the Description Description A verbal description of the Opening Type. Page 5 of 18

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 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. Page 6 of 18

7 Custom/Sharp Edge Orifice Openable Area % 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 % Window/Door - Side Hung Openable Area % 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% Max Angle Open The maximum angle of opening of the window, degrees. Max angle open can be any value from 10 to 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 > Window - Centre Hung Openable Area % 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. Page 7 of 18

8 Openable area can be any value from 0% to 100% Max Angle Open The maximum angle of opening of the window, degrees. Max angle open can be any value from 15 to Proportions The ratio of window length to window height. Proportions can be defined by selecting any option from Length/Height = 1 or Length/Height > Window - Top Hung Openable Area % 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% Max Angle Open The maximum angle of opening of the window, degrees. Max angle open can be any value from 10 to Proportions 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 > Window - Bottom Hung Openable Area % 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. Page 8 of 18

9 Openable area can be any value from 0% to 100% Max Angle Open The maximum angle of opening of the window, degrees. Max angle open can be any value from 10 to Proportions 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 > Parallel Hung Windows/Flaps Openable Area % 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. Openable area can be any value from 0% to 100% Max Angle Open The maximum angle of opening of the window, degrees. Max angle open can be any value from 15 to Proportions 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 > Window - Sash Openable Area % 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. Page 9 of 18

10 Openable Area can be any value from 0% to 100%. For sash windows the aerodynamic (or equivalent) free area is taken directly as the openable area % Sliding/Roller Door Openable Area % 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. Openable Area can be any value from 0% to 100%. For sliding/roller doors the aerodynamic (or equivalent) free area is taken directly as the openable area % Louvre Openable Area % 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% 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 Grille Openable Area % 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% 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). Page 10 of 18

11 Coefficient of discharge can be any value from 0 to 0.6 Cd Duct Openable Area % 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% Duct Length (m) Enter length of the duct in metres, m. Duct length can be any value from 1m to 10m 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% Acoustic Duct Openable Area % 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% Duct Length (m) Enter length of the duct in metres, m. Duct length can be any value from 1m to 10m 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, Page 11 of 18

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% 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 Crack Flow Coefficient (l s -1 m -1 Pa -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 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 -1 m -1 Pa -0.6 ) Windows Page 12 of 18 Lower Quartile Median Upper Quartile Windows (Weatherstripped) Hinged

13 Windows (Non-weatherstripped) Sliding Hinged Sliding Table 2. Crack Flow Coefficients (l s -1 m -1 Pa -0.6 ) Doors Lower Quartile Median Upper Quartile External Doors (Weatherstripped) Hinged Revolving External Doors (Non-weatherstripped) Hinged Sliding 0.2 Internal Doors (Non-weatherstripped) Loft Hatches (Non-weatherstripped) 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) 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 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 Page 13 of 18

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 OK Exit the MacroFlo Opening Types Manager and save the changes Cancel Exit the MacroFlo Opening Types Manager without saving the changes. Page 14 of 18

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: u meteorological wind speed at height 10m in open country (m/s) Page 15 of 18

16 h height above the ground (m) and a and K are coefficients taking the following values for different terrain types: Terrain Type Description Country Open terrain with scattered obstructions having heights generally less than 10 m, including flat open country typical of meteorological station surroundings Suburbs City 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 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 Exponent a Layer Thickness δ (m) K 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 ) α met (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 Page 16 of 18

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 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, semiexposed flat roof and sheltered flat roof. Wind pressure coefficients for these Page 17 of 18

18 Exposure Types have been estimated by extrapolating the available experimental data. An exposure type appropriate for internal openings, internal, is also provided. If applied to external openings, this exposure type sets all wind pressure coefficients to zero, allowing you to investigate flow patterns in the absence of wind pressures. Page 18 of 18