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Article 2 - Climate considerations for the design of small lot houses.

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PURPOSE

Throughout Australia a number of new housing innovations continue to be delivered and tested in emerging communities and in suburbs experiencing redevelopment. Some of the more topical housing forms are the 'small lot' housing products which are typically built on 200m to 400m lots and can include terraces, duplexes and detached housing forms.

The thermal performance of each dwelling type as well as the broader performance of suburbs which contain a high proportion of small lots can be measured through AKLFlowDesigner. This article will seek to test a range of different design responses and their associated thermal performance at the single lot level. This article is focused on a typical single floor small lot dwelling and will investigate:

        •    The cooling benefits of roof insulation
        •    The different thermal performance of roof colours (light tiles vs dark tiles)
        •    The varied thermal performance of small lots based on different prevailing breezes

The analysis of the various matters presented in this article will provide a general introduction to a number of concepts relevant to sustainability assessments including environmental data, materiality, building design and thermal transfer. Accordingly, the processes described in this article rely on a number of fundamental scientific concepts including Fluid and Thermal Dynamics as well as climate science.

However, one the key advantages of using AKLFlowDesigner is that the program already contains the most important information relevant to these matters and can provide design insights without needing to develop new or customised data sets. The intuitive interface and familiar tool set allows users to undertake important simulations without needing a detailed understanding of the above noted concepts. Accordingly, this article will present a streamlined approach to determining climatic design performance with future articles providing more detailed scientific exploration of these concepts.

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APPLICATIONS

A project's climatic location, the use of various materials and construction techniques and the resulting reliance on mechanical cooling are all interdependent and should be considered holistically when undertaking planning and design exercises.

It is suggested that all levels of planning and design can benefit from an understanding of each matter which AKLFlowDesigner can assist with at all stages of the project development and assessment.

For example when undertaking strategic broad hectare planning investigations, due consideration should be given to the local micro and macro climate and its topographical context. In regions which experience significant heat and which have limited access to breezes, the delivery of some housing product types should be cautioned.

In these circumstances, due consideration and simulation of the project site might suggest different design and planning controls to increase setbacks, reduce site cover, or more focused design intervention to increase thermal comfort.

REFERENCE DESIGN

For this article a reference design has been prepared that represents a typical arrangement of a house on a small lot. The model has been prepared in SketchUp is available upon request vial email. Importing SketchUp files into AKLFlowDesigner is a simple and straightforward process however for reference purposes, the AKLFlowDesigner simulation files have also been prepared and are available to existing customers upon request.

The subject site is 12 meters wide and 26 meters deep creating a 312m² lot. A minimum of ~0.9m side setback has been achieved with the exception of the garage. A 2.0m rear setback has been sought to allow for a 8m² patio area. A 1.0m front setback has also been applied to allow for onsite gardens or planting areas. The ceiling height of the building is 2.5m and the slope of the hip roof is 15°degrees. The subject dwelling has the following features:

•    4 x Bedrooms
•    2 x Bathrooms
•    Double garage
•    Living and Dining areas
•    1 x Study
•    1 x Laundry

ENVIRONMENTAL CONDITIONS

The climatic conditions of any particular location in Australia can be recreated digitally using a number of parameters including temperature, humidity, wind speed, wind direction, cloud clover, radiant heat energy etc. EnergyPlus Weather (EPW) files contain specific climate information including many parameters which can be imported into AKLFlowDesigner using the solar radiation assessment option.

An intuitive way of viewing EPW files can be found via the online resource provided through the Berkley University of California Centre for the Built Environment’s online web CBE Clima Tool: a free and open-source web application for climate analysis tailored to sustainable building design. Version: 0.8.12. Betti G., Tartarini F., Nguyen C., Schiavon S. (2022).

This website not only allows for the review of multiple data sets, it also provides a world map identifying multiple locations where weather information has been recorded and compiled into EPW file formats. From this website you can download EPW files and use them in AKLFlowDesigner. The below image from the CBE Clima Tool website shows the extent of weather station data availability in Australia.

For this article, the reference design will be digitally located in Parramatta, New South Wales, Australia and will include average climate information recorded between 1997 and 2021. The location of the sensor is Long:151.017, Lat -33.8 and an elevation of 55m. It is likely that this information has been compiled from the Australian Bureau of Meteorology station 066124 – Parramatta North (Masons Drive). A link to this station is provided below:

http://www.bom.gov.au/climate/averages/tables/cw_066124.shtml

It is possible and sometimes preferred, that localised weather data is collected within the actual project site in a number of locations to establish a climatic baseline. Information from any weather station can be easily compiled into an EPW file with the assistance of a number of software tools including DesignBuilder Results Viewer among many others. Including EPW files in the simulation is simply achieved by identifying the downloaded files located under the Solar Analysis tab of the Analysis drop menu show in the image below.

MATERIALITY

The thermal properties of each construction material must be known to accurately simulate the performance of the reference design. Some analysis systems rely on a material’s SRI, or R / U values to determine thermal performance, however these values may not capture all of the thermal impacts related to the geometry of adjoining structures, the depth of overshadowing, humidity and material heat loss via convection. For example, it is difficult to determine the thermal performance of angled roofs which may be ventilated and contain insulation. See below the arrangement of a tile roof and ceiling both with and without insulation which would challenge many other software packages, but is inherently easy to simulate in AKLFlowDesigner.

One of the key advantages of AKLFlowDesigner is how it applies the materiality of each element to provide the most robust and comprehensive representation of construction materials. Specifically, AKLFlowDesigner calculates the following parameters of every material:

•    Density
•    Specific heat
•    Thermal conductivity
•    Absorptivity
•    Reflectivity
•    Solar absorptance
•    Solar reflectivity

This allows all elements of a model to be individually considered during an analysis with each component's thermal behavior being assessed. The layered image of the reference design below shows each of the geometries which have been used in this simulation. Each one of the geometry groups has its own materiality based on its actual real world equivalent performance. For example, plaster (gypsum) is used for the walls, timber (cedar) is used for the fences and clear float glass is used for the windows. By simply changing the applied materials for an element allows the different performance of each material to be assessed and compared.

An example of this would be determining the relative benefits of clear float vs heat absorbing green tint vs low-e multilayered glass.

AKLFlowDesigner comes with an extensive library which covers many different types of construction related materials. The library can be simply expanded to include any material type and Envision Urban and AKL continue to work together to build a library of key Australian design materials. The upcoming ‘Thermal Design and Materials’ article on this website will include a more extensive discussion of building materials and how they affect the performance of buildings.

The specific performance of construction materials is often published by the manufactures and can be acquired through a simple web search. In addition to this a number of industry groups and bodies also maintain and publish this information.

The below is an example of an industry web page which provided specific material information. https://www.greenspec.co.uk/building-design/insulation-materials-thermal-properties/

Academic institutions also frequently research the thermal properties of various materials and their application within the built environment. One article of particular relevance to Australia roofing typologies includes a focus on different concrete tile colours and their respective thermal parameters. The published paper can be found at the below link:

https://www.researchgate.net/publication/351150701_Effect_of_Roof_Tile_Colour_on_Heat_Conduction_Transfer_Roof-Top_Surface_Temperature_and_Cooling_Load_in_Modern_Residential_Buildings_under_the_Tropical_Climate_of_Malaysia

Farhan, S.A.; Ismail, F.I.;Kiwan, O.; Shafiq, N.; Zain-Ahmed, A.;Husna, N.; Hamid, A.I.A. Effect ofRoof Tile Colour on Heat ConductionTransfer, Roof-Top SurfaceTemperature and Cooling Load inModern Residential Buildings underthe Tropical Climate of Malaysia.Sustainability 2021,13, 4665

The article suggests that whilst white tiles reflect significantly more visible light than black tiles, the infrared emittance of light coloured tiles is almost the same to that of dark coloured tiles. Accordingly, the amount of heat that is transferred through a roof should also be analysed to determine an optimal design response for all small lot housing types. The below table summarises some of the research on tiles and provides a comparison of the key thermal properties of both light and dark coloured tiles.

	Light Coloured Tiles	Dark Coloured Tiles
Density	1890 (J.(kg.K)	1890 (J.(kg.K)
Specific heat	1000 (kg/m3)	1000 (kg/m3)
Thermal conductivity	0.836 (w/m.k)	0.836 (w/m.k)
Absorptivity	0.9	0.9
Reflectivity	0.1	0.1
Solar absorptance	0.27	0.943
Solar reflectivity	0.73	0.057

For the reference design, the material applied to the roof is a 3cm concrete brick with a dark grey colour. The impact that the colour of a roof has on not only the surface temperature of a building’s exterior, but also how much of that thermal energy transfers through to the remainder of the house can be quickly and easily determined using AKL FlowDesigner.

PERFORMANCE MEASUREMENT

A baseline should be established which can be used as reference point from which all future scenarios are compared. For this project, a base case which uses the solar information from the Paramatta EPW file is applied. Specifically, 10:00am on the morning of 21 January 2023 has been selected. The observed ambient temperature is 29º C with a relative humidity of 50%. Importantly, this baseline simulation does not include access to a wind resource and no breezes are present. To undertake this simulation in AKLFlowDesigner the ‘Pseudo Windless’ setting must be chosen.

Before specific results and measurement are derived, it is worthwhile reviewing all the calculated data which informs the outcomes of the simulation. Most of these are based on the transfer, retention and dissipation of thermal energy. Whilst many data layers exist in the simulations, four key metrics are presented in the below images to represent some of these energy insights.

The below images show the surface temperatures of both the interior and exterior and the heat of each individual building feature based on its location, size, materiality and design. Significant heat is seen on the exterior drive way, road, and paved footpaths. However, the highest concentration of heat can be observed on the eastern facing side of the roof which receives the highest direct amount of solar radiation. AKLFlowDesigner allows you to view all information within the model by live sectioning along any axis.

Cross sections can also be produced for all the data simply by locating the section plane in either the X,Y or Z axis and enabling the 'false colour' option. These insights confirm that a significant portion of the thermal energy from the roof is passed through to the interior rooms.

The above results show a concerning level of thermal stress across the simulation with internal and external spaces registering very high temperatures. The lack of available breezes, a dark roof colour and no insulation compounds this result. By comparison, the below results achieve a significant reduction in external surface temperatures as well as internal space temperatures by simply changing the roof tiles to be a lighter colour.

If more specific measurements are required, an array of ‘volumes’ can provide results which can be exported to CSV files and opened in Microsoft Excel. For the reference design a 1m³ volume has been placed approximately 0.75m above the internal floor height within each key room. For reference, the surface area of each key room within the reference design has been identified below:

•    Living Room                  ~ 23.5m²
•    Dining Room                 ~ 34.5m²
•    Garage                        ~ 35m²
•    Bed 1 (Master)              ~ 21m²
•    Bed 1 Bath 1(Ensuite)   ~ 12m²
•    Bed 1 WIR                     ~ 4m²
•    Bed 2                             ~ 12.3m²
•    Bed 3                             ~ 12.3m²
•    Bed 4                             ~ 9.6m²
•    Bath 2                            ~ 5.6m²
•    Office                             ~ 6.8m²
•    Pantry                            ~ 4.3m²
•    The centre of the road       NA
•    Footpath                            NA
•    Front lawn area, and         NA
•    Outdoor patio                    NA

Some areas have been excluded due to the transient nature of their use including hall ways and the laundry although these could be added simply if insights into their particular function was required. Using the defined volumes, the inclusion of insulation into the simulation again shows an improvement to the thermal performance of the reference designs. The most significant benefit occurs with the inclusion of insulation into a grey roof tile model. However the best overall configuration is the use of light colour roof tiles and insulation.The results for each of these scenarios are shown in the below graphs prepared in Microsoft Excel based on the CSV data exported from AKLFlowDesigner. As per the above, the observed ambient temperature is 29º C with a relative humidity of 50%.

Whilst insulation in the grey roof model significantly reduces the temperature, it still does not achieve the same temperature which the white roof tile model achieves with insulation. Whilst the difference is only approximately 3º C between the two roof colours in the model, this temperature difference is significant when considered across all the rooms within the reference design. Specifically, the additional amount of energy it requires to cool these areas through mechanical systems like air conditioning units is likely to be substantial.

It is important to remember that this simulation is based on a single dwelling. When the dwelling is placed within a more intensive urban setting, it is likely that the difference in surface temperate of the ceiling will compound the temperature stress throughout the entire suburb. This is known as the Urban Heat Island Effect and whilst not investigated in this article, it will be the focus of future published material.

PREVAILING BREEZES

A key climatic consideration that will influence the sustainability of the reference design is the project’s location and its relative access to prevailing breezes. The frequency, direction, speed, temperature and humidity of an available wind resource can have a profound impact on the human comfort provided by a design and the requirement for air conditioning or mechanical ventilation.

The previous simulations included a ‘pseudo windless’ scenario but it is worth simulating other wind variables which are likely to occur. Although AKLFlowDesigner primarily inputs EPW data related to solar radiation, the EPW files can be used to confirm standard wind resource observations. For example when using the CBE Clima Tool EPW viewer it is easy to determine the most likely wind direction and velocity experienced in a location.

It is suggested that the direction, speed, temperature and humidity of the prevailing breezes typically experienced during summer mornings, middays, and afternoons are the most important in determining the thermal stress experienced in housing forms. The below image shows the wind directions and wind speed for each hour of each day based on the averaged conditions for the location.

Whilst the above examples show that the most frequent prevailing breezes come from East, East - North, for the ease of comparing information, the reference design has been exposed to breezes predominantly from the East direction. To illustrate the positive cooling impact that that breezes provide, four typical scenarios have been simulated for the reference design. This includes the pseudo windless base case, as well as scenarios for 1.2m/s, 2.4m/s and 4.8 m/s all coming from the East direction. All of these scenarios occur at the same time of day (10am) and with the same ambient temperature / relative humidity, insulation and 3cm deep dark concrete roof tiles.

There are a number of ways to interrogate and present wind information using AKLFlowDesigner. The most common is X,Y,Z ‘false colour’ section planes. However, when reviewing information about wind flow some other useful tools are provided within AKLFlowDesigner. One of these is the ‘Particle Trace’ feature which uses arrows to shown the path of breezes within a simulation. The below animation has been produced by drawing a ‘Region’ close the surface of the road and animating the particles. The, size, colour and speed of the blue paper plane graphics (or arrows) reflect the velocity of the wind particles. Next to this is a 'streamlines' diagram which shows the entire path and velocity of the arrows from the paper plane graphic.

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It is worth noting the relationship between exterior airflow and the temperature of the internal rooms. Generally speaking, even without having windows or door open, the reference design significantly benefits from the breezes passing over and around the structure. The below images shows one cross section of wind behaviours over and along the roof of the building. Breezes will often follow the path of least resistance and connect areas of low pressure with those of higher pressure. The below image shows that high velocities are present over the roof compared to those that interact with the walls of the building.

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The below images show four different velocities of breeze engaging with the reference design. The loss of heat from a surface due to breezes passing over it is known as convection loss. In additional to convection loss, AKLFlowDesigner is above to visually represent the radiant convection heat flux or the amount of energy removed from a surface. These are shown for each of the below scenarios with a clear trend emerging showing that increased speeds increase the thermal loss of the roof surface. Again, the observed ambient temperature is 29º C with a relative humidity of 50%.

Further, it appears that with the reference design in this location, the potential reduction in thermal stress due to breeze access is at least as significant as the chosen roof colour.

CROSS VENTILATION AND BREATHING BUILDINGS

Opening the doors and windows in different combinations throughout the reference design achieves different levels of human comfort and associated temperature levels through the structure. This is due to the introduction of external breezes which are typically at the prevailing ambient temperature which is much cooler than the radiant internal temperature within the building.

The below image shows a closed scenario on the left with the breezes going over the building and accelerating over the roof surface. The image on the right highlights breezes from the same origin point but the scenario includes and open front door and an open rear door. This results in the breezes passing through the interior, albeit at a reduced velocity.

For each project the frequency, direction, temperature and speed of seasonal breezes should researched and analysed. Most of the time, weather readings will be recorded in only a single location within a particular precinct. It is important to note that the conditions recorded at a single location will be influenced by the movement of air relative to the elevation and aspect of the local terrain. Accordingly the orientation, design and materiality of small house products should be optomised to capture summer afternoon breezes and efforts should be applied to ensuring that they are not inappropriately located in areas which do not have access to winds.

To provide additional insights into the behaviour of breezes through and around small lot housing products, the below scenario has been prepared to evaluate the benefits of opening the front door and the rear door indicated below with the blue 'open door' icons. Each window and door within the reference model can be easily opened or closed by simply turning on and off each feature in AKLFlowdesigner. This allows for every conceivable scenario to be tested and analysed.

The above shows a series of cross sections that help understand the relative comfort achieved in both the internal rooms and external areas. The temperature and wind velocity slices show a strong correlation between rooms which receive cross ventilation and those with reduced temperatures. The wind speed slice shows that the speed of the breezes within the form are of higher velocities near the opened doors but also that breezes within the lounge room are still of a reasonable velocity. The Mean Radiant Temperature (MRT) shows some correlation with the temperature slice but given the enclosed nature of the space, the cooling effects of breezes are less clear. Therefore it is suggested that MRT has limited utility in determining interior comfort levels.

COMPARISONS

The potential of cross ventilation to reduce internal temperatures and reduce reliance on mechanical ventilation and air-conditioning is significant and should be tested during the structure planning, master planning and architectural design of housing forms on all projects in areas which experience high temperatures or are expected to in the coming decades.

The below comparison shows exactly the same building with the same materials and with the same front door and rear doors opened. However, one set of results if from a lot which is planned for a low point in an area of moderate undulation and therefore only receives breezes at approximate ~0.1 m / s. The other form receives a 4.8m / s breeze as it is located at a higher elevation where winds are not impeded by surrounding land-forms. Not only does the living room, kitchen and dining rooms receive a great reduction in temperature, all rooms in the house receive some benefit through the convection loss achieved between internal and external surfaces.

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4.8 m/s Breeze

0.1 m/s Breeze

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The below table incorporates the results from the above comparison as well as additional scenarios which investigated other wind speed profiles and also included some scenarios which change which windows and doors are open. In all scenarios the observed ambient temperature is 29º C with a relative humidity of 50%, the dark roofing tiles are the same and roof insulation is present.

The results show that passive cooling significantly increases with the increased velocity of available breezes. The design of the windward side of the house and size and location of the primary opening (the front door in this example) is particularly important when it comes to encouraging cross ventilation.

The below diagrams include additional details for the above scenarios and including an extra configuration for comparitive assessment. The fifth diagram set described as ''rear doors and windows open' with a 4.8 m/s breeze tests a scenario where many of the windows are opened on the side of the house and the rear door is open but the front door has been left closed. The results suggest that the relative cooling achieved may not be sufficient without a wide opening to the windward side of the structure.

Therefore, extra design emphasis should be placed on the entrances and openings on the windward side to ensure that whilst cross ventilation is encouraged, visual and acoustic privacy within the house is also maintained. AKLFlowDesigner makes the testing of specific design responses to these types of problems quick and efficient. Changes to the design can either be completed within AKLFlowDesigner utilising its own modelling tools, or specific elements can be removed and re-imported from external applications including SketchUp, Revit etc.

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CONCLUSION

Australia continues to endure extreme summer weather conditions including very high temperatures and humidity levels. Seasonal storms and cyclones compound this problem when they damage or destroy power line infrastructure and disrupt electricity supply. The result is potentially extensive periods of time where residents are unable to avoid uncomfortably hot conditions and will become susceptible to heat stress, fatigue and in extreme instances fatalities may occur. Whilst on site solar power generation can be configured to provide some backup power contingency in the case of extended blackouts, the retention capacity of onsite batteries are unlikely to support air conditioning usage for multiple days.

Therefore, the layout and materiality of housing products are vitally important and architectural expertise is crucial to ensuring all design considerations are appropriately considered when planning, assessing or developing new housing products. Well designed small lot products can achieve a good level of thermal comfort for occupants if they are well located and orientated.

Accordingly, the most robust software solutions should be utilised by architects, landscape architects and planners to ensure that all design assumptions are validated. AKLFlowDesigner provides the perfect platform to absorb common Australian environmental data sets, import design files from a range of platforms, and produce outputs which interrogate, highlight and confirm environmental performance.

FURTHER ANALYSIS

The above analysis provides a robust and accurate simulation of a built form reference design against the typical climatic conditions of Parramatta. However the mere measurement of temperature and wind speed are not in their own right appropriate criteria with which to judge human comfort.

Accordingly, Article 3 will built on the analysis prepared in this article and go further to provide a history on the evolution of various comfort criteria, and also suggest some performance benchmarks which may be appropriate for adoption in the review of development applications, and the certification process for a range of environmental accreditations.

Article 3 will also provide detailed information on the following topics.

        •    The efficiency of air-conditioning units based on their capacity and location (internal and external)
        •    The amount of energy in KiloWatts required to cool houses based on their design
        •    The conditions which may potentially lead to the failure of external air conditioning condenser units

• The placement and performance of vegetation including street and site based planting.
• The different performance of various soils and their associated irrigation profiles.

AKLFlowDesigner clients can access the most up-to-date pre-release of article 3 and the associated files within the file access portal located here.

ACADEMIC RESOURCES

Given the ongoing environmental challenges facing the design and development industries in Australia, it is imperative that future leaders are able to understand and contribute to matters of sustainability and human comfort. The following is a series of practical questions that are considered reasonable for students in the various planning and design fields to investigate and provide informed answers and solutions. AKLFlowDesigner supports academic institutions and their students through the provision of tertiary education licenses which are very affordable and powerful. Students who are interested in learning more about these topics should consult with their departments and urge their course administrators to investigate AKLFlowDesigner. Lecturers, researchers and tutors are encouraged to see which AKLFlowDesigner applications may suit their specific fields of interest by emailing here.

TOWN PLANNING AND URBAN DESIGN

Time to prepare models and undertake simulations : Approximately 10 hours

Investigate the relationship between standard planning controls and thermal performance. Specifically, determine what, if any impact controls such as setbacks and site cover ratios have on the internal and external areas of the reference design. Changes may be made to the dwelling to test what if any benefit may be achieved by reducing the footprint of the dwelling. Successful changes will retain or reduce the internal temperatures of the building and the external patio area. The below shows some typical examples of setback configurations which may be considered.

ARCHITECTURE - Question 1.

Time to prepare models and undertake simulations : Approximately 4 weeks

The reference model has a hip roof design, however many other roof forms are common throughout Australia. Change the roof form to see what, if any impact the design and shape of the roof has on the internal and external temperature of the dwellings. Also create a roof form which incorporates a weather proof ceiling opening via operable windows or other form. Determine what, if any thermal relief the ceiling opening provides in a 'pseudo windless' scenario when all other openings are closed.

ARCHITECTURE - Question 2.

Time to prepare models and undertake simulations : Approximately 1 term for third+ year students

Identify a recent or emerging residential estate with a variety of small lot housing products. Form a group of four students and have each student prepare a 3D model for a particular product based on site observations and online plans. Ensure that the housing types are generally similar in terms of height, size and setbacks. Apply materials with the same thermal attributes to all models ie. use the same timber, plaster, concrete, ceiling tiles etc. Run a thermal simulation using AKLFlowDesigner based on the same agreed upon climatic conditions / time of day / date and determine the temperature in each of the habitable rooms for each of the four chosen dwellings.

Note: It is important to provide attribution and comply with all copyright requirements when analyzing real world products. Results should not be published online and appropriate disclaimers should be included on all generated outputs. Permission should be sought from the intellectual property owners if there is any doubt regarding the use of the plans. Where appropriate students are encouraged to share their results with the original architects and developers via their course lecturer.

LANDSCAPE ARCHITECTURE.

Time to prepare models and undertake simulations : Approximately 4 weeks

Using the AKLFlowDesigner library of trees and shrubs, plant out the back yard, front lawn, and footpath with a variety of species at varying sizes. Using AKLFlowDesigner determine what the impacts of the additional planting was on the temperature, humidity and wind speed of the exterior arreas. What if any impact did the additional planting have on the internal temperature of the reference design? What was the difference in the wind speed, temperature and humidity of the breeze when it entered at the front of the property vs the conditions at the rear boundary.