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IEQ-2 AIR DISTRIBUTION EFFECTIVENESS

 

Technical Clarification

Application of SANS 10400-O

Technical Clarification Number
IEQ02-T-OB1-442

Guidance
2012-04-02

Wherever ‘SANS 10400-O’ is referred to within the IEQ-2 credit, this relates to SANS 10400-O:1990 for the purposes of Green Star SA – Office v1 rating tool. It is the project team’s responsibility to ensure however that the latest relevant building regulations are complied with for statutory purposes.

 

Credit Interpretation Request

Alternative credit criteria - naturally ventilated & mixed-mode ventilated spaces

Credit Interpretation Request Number
IEQ2-C-OB1-0310

Ruling
2012-01-10

The Credit Interpretation Request (CIR) seeking approval of the proposed alternative credit compliance methodology, is conditionally approved. The CIR Review Panel agrees with the opinion of the Project Team that the current Credit Criteria for ‘naturally ventilated spaces’ is flawed and prohibitive to Project Teams. The CIR Review Panel and Technical Advisory Group (TAG) provide the following alternative Credit Criteria for naturally ventilated and mixed-mode ventilated spaces, which are based on the proposed methodology with amendments;

Naturally Ventilated Spaces
• 3 points are achieved for IEQ-1 Ventilation Rates;
AND
• 90% of the Office UA achieves an air change effectiveness (ACE) greater than 0.80, measured in the breathing zone, in accordance with ASHRAE 129-1997: ‘Measuring Air Change Effectiveness’, for the ‘Performance Climatic Condition’ of the site.

Mixed-Mode Ventilated Spaces
A space that is ventilated by both natural ventilation and mechanical ventilation must satisfy the Credit Criteria for mechanical ventilation only. As it is likely for the majority of climate zones within South Africa that mixed-mode ventilated spaces will operate predominantly in mechanical ventilation mode for the occupied hours, it is more important that the mechanical ventilation system is assessed for air change effectiveness.

Additional Guidance - Naturally Ventilated Spaces
The space must be shown through modelling to satisfy the air change effectiveness requirements during a ‘Performance Climatic Condition’, a condition which is, for the purposes of modelling, representative of key climatic characteristics of the site. The Performance Climatic Condition is comprised of the mean ambient temperature, median wind speed and prevailing wind direction experienced at the project site during working hours of 7am to 6pm (weekdays only).

Mean ambient temperature must be the average temperature during working hours of 7am to 6pm (weekdays only). This must be derived from acceptable weather data.

Median wind speed must be the median (or 50th percentile) of all hourly wind speed values during working hours of 7am to 6pm (weekdays only). These wind speeds are scalar and independent of direction. This must be derived from acceptable weather data.

Prevailing wind direction must be the direction represented by the highest frequency direction of all hourly wind direction values during working hours of 7am to 6pm (weekdays only). Only hourly wind directions where the wind speed is greater that 1m/s should be considered. Hourly wind directions that are greater than 1m/s should be binned into 8 cardinal points (N, NE, E, SE, S, SW, W, & NW). The cardinal point bin which contains the most hourly values will represent the prevailing direction that must be used in the simulation. This must be derived from acceptable weather data.

Acceptable weather data is considered as that deemed compliant in the Green Star SA – Office v1 Energy Calculator Guide:
1. Test Reference Year (TRY) data if the building location is within 50km of a TRY location; OR
2. Measured data at a resolution of no more than 1 hour sampling intervals from institutional weather stations within 50km of the building location; OR
3. Meteonorm data; OR
4. Weather data approved by CIR.

 

Technical Clarification

Air Change Effectiveness and 'Shell & Core' spaces

Technical Clarification Number
IEQ2-T-OB1-0359

Guidance
2012-01-10

The following guidance is provided for spaces delivered as ‘Shell & Core’, as defined in the Green Star SA Office v1 Technical Manual.

The air change effectiveness within a naturally ventilated, mechanically ventilated or mixed-mode ventilated space is highly influenced by the distribution of supply/inlet locations and exhaust/outlet locations. Where a space is not provided with specific supply/inlet locations and exhaust/outlet locations, as evidenced through the provision of a fully documented design within the tender documentation (Design rating) or as installed As Built documentation and commissioning reports (As Built rating), compliance with the Credit Criteria cannot be demonstrated.

 

Technical Clarification

Air Change Effectiveness calculation methodology

Technical Clarification Number
IEQ2-T-OB1-0315

Guidance
2011-08-24

Air change effectiveness can be calculated according to Equation (4) from the ASHRAE Standard 129 – 1997, as follows –

E = Tn / A avg (1)
where
E = the air change effectiveness (The target is > 0.95)
Tn = the nominal time constant
A avg = the arithmetic average of the ages of air measured at breathing level within the space.

The nominal time constant can be calculated according to the definition in paragraph 3 of the Standard. “nominal time constant: the indoor air volume of a space or building divided by the rate of outdoor air supply..”, as follows –

Tn = [Vz] /[Qa] (2)
Where
Qa = the rate of outdoor air supply into the zone [m3/s]
Vz = the volume of the zone [m3]

• The values for air supply flow rate, Qa is obtained from the mechanical drawings and
• Age of air at breathing level, Aavg can be determined by CFD analysis. Thus it is possible to solve for E, in equation (1).

Note that regarding air flow rates above, the Green Star SA – Office V1 Technical Manual prescribes rates as for minimum turn-down.

 

Technical Clarification

CFD Modelling & Deemed-to-satisfy split approach

Technical Clarification Number
IEQ2-T-OB1-0305

Guidance
2011-08-04

A project may choose to use a combination of CFD modelling and the deemed-to-satisfy approach (where applicable) for different air-conditioned areas, as long as the CFD modelling does in some reasonable and conservative way account for the influence adjoining areas could have on airflows to and from the area for which the CFD modelling is undertaken.

 

Erratum

Green Star SA - Office v1 Technical Manual: Page 47 - 52

Erratum Number
IEQ2-E-OB1-0145

Guidance
2011-01-06

Title of Credit, change the title 'Air Distribution Effectiveness' to 'Air Change Effectiveness' in the top title bar.

 

Erratum

Green Star SA - Office v1 Technical Manual: Page 49

Erratum Number
IEQ2-E-OB1-0147

Guidance
2011-01-06

Documentation Requirements, documentation table, Design section, for naturally ventilated spaces, change "Tender architectural drawings" to "Tender drawings".

 

Erratum

Green Star SA - Office v1 Technical Manual: Page 50

Erratum Number
IEQ2-E-OB1-0148

Guidance
2011-01-06

Documentation Requirements, description of documentation, changed the bold "Tender architectural drawings" to "Tender drawings".

 

Erratum

Green Star SA - Office v1 Technical Manual: Page 50

Erratum Number
IEQ2-E-OB1-0149

Guidance
2011-01-06

Documentation Requirements, description of documents, changed the description of "As built drawings" to read "As built drawings of each typical space indicating floor area, ventilation system and key elements of the ventilation or air conditioning system. For naturally ventilated spaces, for each typical naturally ventilated space, with ventilation openings, inlets and outlets clearly indicated and dimensioned.”

 

Erratum

Green Star SA - Office v1 Technical Manual: Page 48

Erratum Number
IEQ2-E-OB1-0150

Guidance
2011-01-06

Documentation Requirements, third paragraph, delete "Actual occupant density and standard hours of occupancy of 50 hours a week must be used".

 

Erratum

Green Star SA - Office v1 Technical Manual: Page 47

Erratum Number
IEQ2-E-OB1-0169

Guidance
2011-01-06

Credit Criteria, under Naturally ventilated spaces heading, change "for at least 90% of each space" to "for at least 95% of each space."

 

Technical Clarification

Schematic mechanical drawings

Technical Clarification Number
IEQ2-T-OB1-0116

Guidance
2010-11-16

In the absence of 'schematic mechanical drawings', mechanical plan drawings are deemed an acceptable substitute provided that all of the information required to be communicated within the 'schematic mechanical drawing' is contained, and clearly identified, within the mechanical plan drawing. The intent of 'schematic mechanical drawings' is to clearly communicate essential information pertaining to mechanical air or water distribution systems. Project teams are to ensure that ALL the equivalent essential information expected on a schematic mechanical drawing is clearly identified on the mechanical plan drawing.

 

Technical Clarification

Definitions - "occupied hours”, “standard hours of occupancy” and "standard working hours"

Technical Clarification Number
IEQ2-T-OB1-0110

Guidance
2010-11-02

For the purpose of this credit, “occupied hours”, “standard hours of occupancy” and "standard working hours" are defined as equivalent and equal to the operational profile of the ‘HVAC plant’ as detailed in the applicable Energy Calculator & Modelling Protocol Guide. This definition is applicable to both mechanically ventilated spaces and naturally ventilated spaces (irrespective of the inclusion of HVAC plant or not). Please note these definitions do not amend the ‘Occupancy’ profiles as defined in the applicable Energy Calculator & Modelling Protocol Guide.

 

 

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