Section J Case Study series: Building façade Building ......651-500 Aluminium Curtain Wall – Captive (6mm Evantage SuperGreen #2 /12mm Air Gap/6mm Clear) with a whole-of-window

52 SUMMER 2020 • ECOL IBR IUM

PEER-REVIEWED TECHNICAL PAPERS

F O R U MF O R U M

Section J Case Study series: Building façadeBuilding façade performance and impact on HVAC design and building energy

By Grace Foo, M.AIRAH, Principal Consultant DeltaQ*

and Hongsen Zhang, M.AIRAH, EnerEfficiency

INTRODUCTIONBuilding fabric Deemed-to-Satisfy (DTS) provisions are covered under Part J1. It includes roof and ceiling construction, roof lights, floors and wall-glazing constructions. The focus of this case study will be Part J1.5 Walls and Glazing, because it represents the section of greatest change between the 2016 National Construction Code (NCC) and the current NCC. In previous versions of the NCC, these requirements were split across multiple parts of the code, and the opaque elements were considered independently from glazing performance. Wall-glazing construction is now considered as a single building element for compliance within Part J1.5 of Section J.

Although not covered within this case study, it is important to note that other building fabric requirements related to roof, ceiling and floor insulation must also be complied with within Part J1 of the 2019 NCC Section J.

CASE STUDY DETAILSThe fictional building is a 10-storey office building located in Sydney. The building fabric is a curtain wall construction, with opaque spandrel glass. A sample of the north elevation drawing for the building is shown in Figure 1. The plant room is located on level 5.


F O R U MF O R U M

* Questions regarding this paper should be directed to this author.

Extract from the 2019 National Construction Code Volume One Section J Part J1.5.

Figure 1. Elevation drawing on Northern façade.

SUMMER 2020 • ECOL IBR IUM 53


F O R U MF O R U M

Relevant details are:

• Curtain wall vision glass component is selected to be a G.James Series 651-500 Aluminium Curtain Wall – Captive (6mm Evantage SuperGreen #2 /12mm Air Gap/6mm Clear) with a whole-of-window performance Uw = 3.20 and SHGCw = 0.28. The vision glass is 3.0m height x 1.5m width. The glass only performance (from the manufacturer, assessed using NFRC 100-2001) is SHGCg=0.30 and Ug = 2.0.

• The spandrel glass panel component is affixed with a non-thermally broken aluminium frame system, double-glazed glass panel with similar performance to the vision glass performance except without low-e coating. The spandrel panel is typically 0.9m height x 1.5m width. The spandrel panel detail provided by the architect shows a 50mm gap between the glass panel and aluminium back-pan supporting the wall insulation (75mm thickness

with insulation bag-value of R=2.0). See Figure 2

• The level 5 plantroom external wall uses aluminium spandrel panels.

• There is no external shading designed at this stage, but the architect is open to incorporating external horizontal overhangs as required.

• For the purposes of this case study, it is assumed that the dimensions of the wall-glazing construction are identical on all facades (north, east, west and south).

CALCULATING THE WALL‑GLAZING U‑VALUEThe ABCB façade calculator V1.1 is used to determine compliance to Section J requirements. The vision glass details are categorised as the glazing system, and the spandrel panel is considered external wall construction, therefore classified under Wall Systems.

The vision glass performance is taken from the manufacturer and set up as a User-Defined glass type in the Façade Calculator. Note that the Façade Calculator also provides options for generic default glass constructions (e.g., double-glazed unit with single low-e coating) and their glass-only performance. The inputs to the Façade Calculator are shown in Figure 4.

The spandrel panel configuration can be matched with default Configuration 3 in Specification J1.5b, which outlines how spandrel panel thermal performance is calculated. This means that the spandrel panel R-value can be taken as a deemed value using Method 1. Despite an insulation bag-value or R=2.0, once thermal bridging from the aluminium framing is accounted for, the adjusted R-value of the spandrel

Figure 2. Vertical section of spandrel panel arrangement.

Figure 3. Manufacturer curtain wall selection – whole of window energy performance.


F O R U M

panel is only 1.09 (Figure 5). Note that if the spandrel panel configuration cannot be matched to the four configurations in Specification J1.5b Method 1, the Specification J1.5b provides an alternative Method 2 to calculate the Spandrel panel U-value using the following equation:

Usp = Ucs Acs + ΣUes Aes + ΣUƒs Aƒs

Acs + ΣAes + ΣAƒswhere:

Acs = the area of the centre region of the spandrel panel;

Aes = the area of the edge region of the spandrel panel, where the edge has a defined width of 127mm;

Aƒs = the area of the frame region of the spandrel panel;

Ucs = the U-value of the centre region of the spandrel panel;

Ues = the U-value of the edge region of the spandrel panel, where the edge has a defined width of 127mm;

Uƒs = the area of the frame region of the spandrel panel;

Usp = the Total system U-value of the spandrel panel.

Section J requirements include the wall-glazing total U-value and solar admittance. The discussion in the previous session showed how the wall-glazing total U-value considers

both the U-value of the wall component (which is a function of the wall insulation R-value), and the U-value of the window component.

CALCULATING THE WALL‑GLAZING SOLAR ADMITTANCESolar admittance is a function of the window-to-wall ratio, shading multipliers affected by the properties of external shading and the window system Solar Heat Gain Coefficient (SHGC). Previously, the information relating to glazing SHGC was entered in the Façade Calculator (Figure 4) and no external shading is designed for this building. The next step is to input information regarding the total glazing area and total wall plus glazing area, to calculate the window-to-wall ratio. This information is entered separately for each façade in the Façade Calculator (Figure 7).

In the case study, we have assumed that each façade has identical geometry to simplify the demonstration of this concept. In practice, each façade would typically have a slightly different vision glazing type and opaque wall area and assessed as a separate reference row in the Facade Calculator. For traditional window-wall constructions, certain facades may have exceptionally low window-to-wall ratios where the core area

(housing lift foyers, toilets, plantrooms and risers) of the floor plate is designed to span one façade.

In Figure 7, the overall window-to-wall ratio for this building is 64% on each façade. Note that the wall-glazing construction surface area for the level 5 plantroom is excluded from the wall area because the plantroom is considered in the non-conditioned zone, and therefore the wall-glazing construction does not form the building envelope. The internal walls, floors and ceiling of the plantroom form part of the envelope and therefore are to be assessed as internal walls, floors and ceiling as appropriate to where they join to a conditioned space. The plantroom could be part of the conditioned zone, and hence the wall areas would then be included if the plantroom was used as a return air plenum.

CHECKING DESIGN FOR COMPLIANCEThe Façade Calculator automatically does the background calculations to determine if the building’s wall-glazing U-value and solar admittance performance for each aspect (north, east, south and west) of the building complies with the Section J Part J1.5 requirements. When compliance for each aspect is determined individually, this is labelled “Method 1” in Specification J1.5a.

Part J1.5 states the compliance levels for this building to be:

• Total system U-value must not exceed 2.0

• Total R-value requirements for the wall component (<80% of total wall-glazing construction area) is at least 1.0

Figure 5. Wall system inputs in the ABCB Facade Calculator.

Figure 4. Glazing Systems inputs in the ABCB Façade Calculator.

Figure 6. Extract from NCC Volume One Specification J1.5b showing the spandrel panel configurations where deemed values can be used. Configuration 3 is used in this case study.


F O R U M

• Solar admittance of the external wall-glazing construction must not exceed 0.13

Figure 7 shows that the building meets the average wall R-value requirement (achieved R-value=1.09). Figure 8 shows that wall-glazing U-values and solar admittance do not comply with building code requirements on a standalone aspect basis (Method 1). Even when a whole-of-building approach (Method 2) is taken, the building is unable to comply.

MODIFYING DIFFERENT PARAMETERS TO ACHIEVE COMPLIANCESeveral measures can be tested on the building fabric design to achieve compliance. These are investigated sequentially:

1. Reduce the window-to-wall ratio by adjusting the glazing and spandrel panel height. The vision panel height is reduced from 3.0m to 2.5m and

spandrel panel height increased from 0.9m to 1.4m. The width of each panel is left unchanged at 1.5m. Figure 8 shows that reducing the window to wall ratio from 64% to 52% on each aspect helps reduce the building’s total U-value but still does not comply with the U-value requirement of 2.0.

2. A higher performance vision glazing was sought from the same supplier and product line, with improved window U-value resulting in a different glazing selection. However, the higher SHGCw (therefore, solar admittance) associated with this change will require

Figure 9.Facade Calculator results when the window-to-wall ratio is reduced to 52%.

Figure 7. Wall-glazing area inputs into the ABCB Façade Calculator.

Figure 8. Façade Calculator results using Method 1 (individual aspects approach) and Method 2 (whole-of-building approach).


F O R U M

further adjustments by installing external shading. Figure 10 shows that changing the vision glass performance from Uw=3.2 to Uw=2.8 was beneficial in helping the building comply with its U-value requirements.

3. Finally, external shading in the form of sunshades on the northern façade to minimise solar admittance is considered. Advice is sought from the architect confirming that permanent horizontal overhangs on

the northern and western façades are possible. The shading multipliers table found in Table 7a and Table 7b of Specification J1.5a provide some guidance regarding ideal projection depth and ratios to maximise shading multipliers. Ideally the gap between the base of the sunshade and top of the vision glass is as small as possible, and the projection depth to be as close as possible to the total height of the glazing system. In this case, the projection depth (P) was chosen to be

half of the total glazing system height (H) including the gap (G). The gap (G) was chosen to be as small as practical, so that the sunshade is as close as possible to the top of the glazing. These details are seen in Figure 11. Figure 12 shows that while the solar admittance requirements on the east and south aspects are still not met (hence failing the compliance test using Method 1), the introduction of Method 2 whole-of-building approach shows that the AC Energy Value of the modified proposed design is lower than the DTS reference. As such, the wall-glazing design complies with Section J requirements, albeit a few issues that should be noted:

a) In reality, the projection depth of 1.35m shown in Figure 11 may not be possible due to structural concerns and adherence to Australian Standards limiting the maximum projections from the building for such structures.

b) The sun angle is low as it passes from the east to west orientations across all seasons. As such, it may be more practical to consider the use of vertical shading devices on the eastern and western facades instead of horizontal shading. The use of vertical shading devices is not an option under the Section J Specification

Figure 12. Results and impact of adding external shading to the northern and western aspects.

Figure 11. External shading inputs to the Facade Calculator.

Figure 10. Facade Calculator results when the vision glass is changed to an improved window U-value and reduced window SHGC.


F O R U M

J1.5a(7) and will likely require a different Performance Solution. The CAMEL heat load software has a function that allows for an equivalent horizontal shading projection to be input to the façade calculator, based on different shading options built into the program. This allows a simple performance-based solution to be used via the outputs.

c) With consideration to the two issues above, a building with high glazing surface area is likely to find it difficult to comply using the DTS method. It is therefore more likely that such buildings will seek to use one of the Verification Methods (energy and thermal simulation) to demonstrate compliance.

INVESTIGATION INTO THE IMPACT OF CHANGING BUILDING FABRIC PERFORMANCE ON HVAC DESIGN AND THERMAL COMFORTHVAC&R professionals typically do not have direct input into building façade design. In this section of the case study, we will use a simulation software package to examine the impact of changing building fabric attributes, particularly glazing properties, on HVAC equipment, building energy consumption and occupant comfort. Two climate zones have been chosen:

• Climate zone 2 (Brisbane) – warm humid summer, mild winter

• Climate zone 6 (Melbourne) – mild temperate

A typical Australian office building was modelled as the base case for this study. The simulation follows DTS provisions in Section J of NCC2019. The base model has these characteristics:

• 10-storey building with underground carpark

• 56% Window-to-wall ratio (WWR)

• 31.6m by 31.6m floorplate, 4 perimeter zones, 4 centre zones and 1 core area

per floor, the total floor area is about 9,985.6m². The total NLA is 9,000m².

• HVAC: Variable air volume (VAV) system with central cooling and heating plant

• Floor to ceiling height 2.7m

• Plenum height 0.9m

Diagrams of such a building as shown in Figure 13 and Figure 14:

Building constructionDouble glazing with the characteristics shown in Table 1 was used in the simulation.

The following opaque constructions were used in the simulation are shown in Table 2 below. The thickness of external wall used in the simulation is equivalent to 21mm K12 insulation, with thermal bridging from the lightweight steel frame.

Figure 13: View of simulation model. Figure 14: Floor plate showing zones

Construction description

Material (from outside to inside)

Thickness (mm)

U-Value (W/ m²·K) SHGC

External window

Tinted glass 6

2.71 0.21Argon 12

Clear glass 6

Table 1: Glazing characteristics for the best practice model

Construction description

Material (From outside to inside)

Thickness (mm) U R

External wall

Steel cladding 0.7

1 1Insulation 12.1

Air cavity 100

Plasterboard 10

Internal partition

Plasterboard 12.5

1.86 0.54Air cavity 50

Plasterboard 12.5

Internal floor Concrete 150 3.57 0.28

Underground carpark floor

U-value correction layer 176.50.26 3.84

Concrete 150

Floor above the carpark

Concrete 1500.44 2.27

Glass fibre 70

Ceiling Fibreboard 30 1.37 0.73

RoofConcrete 100

0.24 4.16Board 68

Table 2: Opaque construction details for the best practice model

Note that the total U-Values above include the surface resistances and represent typical figures in the building stock. The R-Value of the underground carpark floor has been adjusted using EN-ISO 13370 method.


F O R U M

The impact of thermal bridging on the overall wall construction R-value is calculated using the NCC façade calculator as shown in Figure 15.

Building loads The building loads are as follows:

• Occupancy. 10m² per occupant. Sensible load of 75W/m² and 55W/m² latent load.

• Equipment. 11W/m²

• Lighting power density. The lighting power density of 4.5W/m² distributed equally between plenum and zone.

VentilationThe ventilation rate during occupied hours was set at 7.5L/s/person.

Weather fileThe IWEC weather file appropriate to the region was used. The building was modelled in Brisbane and Melbourne.

Modelling softwareModelling was executed in Integrated Environmental Solutions Virtual Environment (IES<VE>), which was developed by Integrated Environmental

Solutions Limited and has passed BESTEST accreditation. The program has been widely used in Australia and has widespread international acceptance.

SchedulesOccupancy, lighting and equipment operation schedules were modelled in accordance to Section J Specification JVc.

HVACHeating plantCondensing boilers were used in the modelling. The heating hot water temperature reset was modelled to be 80°C when the outside dry bulb is 4°C above design heating temperature, 60°C when the outside dry bulb is 14°C above design heating temperature and linear in between. The rated gross boiler efficiency was modelled to be 90%

Cooling PlantWater cooled chillers with variable speed drive-controlled compressors were used in the modelling. The in-built water-cooled chiller curves in IES were adjusted to match the COP requirement of NCC 2019. The in-built chiller performance curve

takes into account the COP variation, which is dependent on the part-load, entering condenser water temperature and chilled water temperature. The chilled water temperature was linearly reset from 6°C to 10°C when the outside air dry bulb drops from 25°C to 10°C. The chilled water pump, condenser water pump and cooling tower fan was sized based on NCC requirements.

AHU configurationFive AHUs were provided for each facade and for the centre zones. The cooling supply air temperature was reset from 12°C to 22.5°C when the average zone temperature changes from 24°C to 23°C. The heating supply air temperature was reset from 30°C to 22.5°C when the average zone temperature changes from 21°C to 22°C.

Zone temperature controlThe zone temperature control was reset to 22.5°C with a dead band from 21.5°C to 23.5°C and 1°C proportional bands either side of this. The VAV box minimum turndown was set to 30% for perimeter zones and 50% for centre zones.

Figure 15. Wall system inputs in the ABCB Facade Calculator.


F O R U M

ScenariosFour scenarios were modelled:

Scenario 1 – Non-compliant U-value of the windows: The U-Value of windows was modelled to be 5.7. The SHGC remains unchanged at 0.21. This window is a single-glazed unit with non-thermally broken aluminium frames.

Scenario 2 – Non-compliant SHGC of the windows: The SHGC of windows was modelled to be 0.42. The U-Value remains unchanged. This window is a clear double-glazed unit.

Scenario 3 – WWR enlarged: The WWR was increased from 56% to 75%. The glazing performance is the same as the base case. The equivalent wall-glazing system U-Value in the scenario is 2.28 (non-compliant) and the solar admittance is 0.16 (non-compliant).

Scenario 4 – WWR enlarged with compliant solar admittance: The WWR was increased from 56% to 75%. The SHGC of the glazing was modelled to be 0.17 to achieve the compliant solar admittance (<=0.13). Note that the U-Value of the glazing remain unchanged. As a result, the total system U-Value of wall-glazing construction is not compliant in this scenario. The glazing unit is an argon-filled double-glazed unit with low-e and low-iron coating. The wall-glazing system U-Value in the scenario is 2.28 and the solar admittance is 0.13.

IMPACT ON HVAC DESIGN (COOLING CAPACITY/HEATING CAPACITY)The results are shown in Figure 16.

While heat load estimation software was not used for HVAC plant sizing in this case study, the modelling results using IES<VE> show that the peak cooling, heating and airflow requirements increase when glazing performance deteriorates or when a large amount of glazing is used in a building. From a HVAC design perspective, the impacts of deteriorated building fabric design are:

• Increased peak cooling capacity and heating capacity is required. This translates to larger chiller and heating plant systems with modular design and good part load performance.

• Reduced U-value performance associated with swapping a double-glazed unit to a single-glazed unit has substantial impact on heating plant peak capacity (>50% increase), even in a warm climate such as Brisbane.

• Increased airflow capacity is required. This translates to larger ductwork and fan sizes required, including riser spatial requirements.

· Reduced SHGC performance generally has a greater impact on

the eastern and western perimeter zones, though it can be seen that in a warmer climate like Brisbane, this has substantial impact on the centre zone and north façade too.

· In a cooler climate such as Melbourne, a higher glazing SHGC value is beneficial for the southern perimeter zone, where peak airflow requirements reduce. However, note that recent work by this author examining the impact of climate change on building HVAC plant design found that increased cooling capacity (central plant and air distribution) will be required.

IMPACT ON ENERGY CONSUMPTIONFrom an energy consumption and emissions perspective, the results in Figure 18 and Figure 19 show that increased building HVAC consumption is largely driven by increased central plant energy consumption (chillers and boilers).

The additional operational expenditure incurred can be quantified using an average tariff of 18c/kWh for electricity and $14/GJ for gas. Figure 20 shows that compared to climate zone 6, the energy expenditure increase is higher in climate zone 2 in all scenarios, except for scenario 2 where the decrease in (gas-fired) heating energy associated with increased solar heat gain during winter

Figure 16. Modelling results showing peak cooling, heating and airflow requirements (relative

difference from base case) – Climate Zone 2.

Figure 17. Modelling results showing peak cooling, heating and airflow requirements (relative

difference from base case) – Climate zone 6.


F O R U M

in Melbourne is insufficient to counteract the increase in (electrical) cooling energy in summer. As such, it is still important to prioritise good SHGC performance in a cool climate.

IMPACT ON THERMAL COMFORTFigure 21 and Figure 22 show the results for thermal comfort in the form of predicted mean vote (PMV). The metric used is a PMV between -1 and +1, referenced from the NCC Section J Verification Methods thermal comfort requirements. This criterion is equivalent to a predicted occupant average vote feeling slightly warm (+1) and slightly cool (-1). It can be seen that in climate zone 2 (warm humid summer, mild winter), reduced glazing performance does not substantially impact thermal comfort,

except for the eastern façade when the glazing ratio is increased (Scenario 3) and across the occupied space when SGHC performance is sacrificed (Scenario 2).

Conversely, thermal comfort improves in climate zone 6, except for the western and south façade when wall-glazing U-value performance is increased. It should be caveated that the corresponding improvement in absolute terms is quite small – specifically, it represents an improvement from PMV±1 for 97% of the time to 100% of the time.

CONCLUSIONThe 2019 National Construction Code Section J requirements for wall-glazing construction are substantially different from previous versions of the code. While the approach is now

simplified with only four aspects (north, east, south, west) requiring assessment and greater flexibility allowed for with the whole-of-building assessments (Method 2), stringency has also changed

such that highly glazed buildings such as those using curtain wall construction will find it difficult to comply unless thermally broken framing and extensive external shading devices are employed. Non-thermally broken aluminium spandrel panels will struggle to achieve an adjusted R-value above 1.0. The impacts of thermal bridging is now explicitly addressed in the building code and practitioners must calculate the adjusted U-value (or R-value) of the wall-glazing, floor or roof construction, instead of using a simplified and unadjusted insulation bag R-value to comply.

The first part of the case study demonstrated the use of the Façade Calculator to assist designers in this process (to avoid the use of a Verification Method or JV3), showing how a simplified curtain wall construction complied using sequential adjustments to reduce glazing to façade ratios, improve glazing U-values and reduce solar admittance through the use of external shading. In the end, the building complied with Section J on a whole-of-building basis.

The second part of the case study demonstrated the impact of changing building fabric performance on HVAC plant design, building energy consumption and occupant thermal comfort. These were modelled in

Figure 18. Modelling results showing annual HVAC plant energy consumption (relative to base case) – Climate zone 2.

Figure 19. Modelling results showing annual HVAC plant energy consumption (relative to base case) – climate zone 6.

Figure 20. Annual energy expenditure based on modelling results in climate zone 2 and 6.


F O R U M

climate zone 2 and 6 using an energy simulation software package IES<VE>, using an office building geometry used in preliminary 2019 Section J revision simulation work. The modelling results showed that changing glazing system and building façade attributes has a varying degree of impact for buildings in different climate zones. In a warmer humid climate like Brisbane (climate zone 2), thermal comfort reduces with poorer glazing performance but a cooler climate like Melbourne (climate zone 6) may experience improved thermal comfort albeit very small when considered in absolute terms, when building façade solar admittance is increased. This observation does not account for global warming caused by climate change. However, the consistent conclusions that can be drawn regardless of climate zones are:

• HVAC plant capacity requirements (peak demand) will increase, particularly cooling and air distribution plant.

• Building energy consumption will increase, along with energy operational expenditure.

Practitioners are encouraged to prioritise good building fabric design, which has a longer lifecycle (40 to 60 years) relative to HVAC plant (15 to 20 years). Good building fabric design will enable efficient HVAC plant

and control to occur – avoiding the use of HVAC plant as a band-aid solution to counter thermal comfort issues related to poor building fabric design.

Finally, it is important to note that other building fabric requirements related to roof, ceiling and floor insulation must also be complied with within Part J1 of the 2019 NCC Section J. ❚

ABOUT THE AUTHORSGrace Foo, M.AIRAH, is principal consultant at DeltaQ, a boutique energy management and sustainability consultancy. Foo was a key technical coordinator behind the updates to the NCC 2019 energy efficiency requirements (Section J). She led a large interdisciplinary team conducting research, energy modelling and economic analysis in the fields of building fabric, lighting, and HVAC systems. In the past decade, she has delivered successful energy efficiency projects, with the capability to convert technical recommendations into cost-effective and commissionable projects where investment performance can be measured and proven. Grace is also experienced in delivering policy work for several projects commissioned by federal government agencies, state and local governments, and various government-owned corporate entities. Foo has Climate Active Carbon Neutral qualifications, is a Certified Measurement and

Verification Professional (CMVP), Certified Energy Efficiency Leader, NABERS Auditor, Supervisor and Trainer, and Independent Design Review panel member. She is currently undergoing WELL Accredited Professional accreditation.

Hongsen Zhang, M.AIRAH, is the director at EnerEfficiency. He is an energy efficiency consultant with 20 years of academic and industry experience. Zhang is a leading energy modeller in the industry. He has completed more than 50 simulation projects for both new and existing buildings and intensively used simulation to support policy development projects. He is one of the key technical contributors for the NCC2019 Section J revision project. He was the simulation team leader in that project. A NABERS Independent Design Review panel member, Zhang has published 15 peer reviewed papers in the field of HVAC and energy efficiency in buildings. In 2018, he was awarded AIRAH’s W.R. Ahern Award for the best technical paper published in Ecolibrium by an AIRAH member.

Figure 21. Modelling results showing thermal comfort changes relative to base case – Climate Zone 2.

Figure 22. Modelling results showing thermal comfort changes relative to base case - Climate Zone 6.

ACKNOWLEDGEMENTSThe contributions of Ken Thomson, M.AIRAH, in reviewing the case study is gratefully acknowledged.

This project is supported by the Australian Government Department of Industry, Science, Energy and Resources through the Climate Solutions Package.

Documents

Section J Case Study series: Building façade Building ......651-500 Aluminium Curtain Wall – Captive (6mm Evantage SuperGreen #2 /12mm Air Gap/6mm Clear) with a whole-of-window