Building thermal simulation for passive and active solar systems

With skyrocketing gas and electricity prices, many property owners that are planning to build a high-end houses are willing to invest in house energy efficiency. Our approach is to assist architects to use our service to first minimize heating and cooling demand of the house and then size a cost effective renewable system for the house.

Every new house needs to comply to National Construction Code (NCC) energy efficiency provisions to be able get building permit. Most architects satisfy these provisions with 6 Star rating which doesn’t provide any real-life data for the building . Our solution is what is called Verification using a Reference Building Method in NCC (Section and it replaces the 6-Star rating with a 3D realistic modelling (TRNSYS) that provides hour by hour heating and cooling loads. Geoflow then liaises with the architect to develop optimised cost effective solutions, to further reduce building heating and cooling demand. Below is an example of an off-grid house in Moorabool. Working in conjunction with the architect, Geoflow managed to significantly reduce the house energy demand to less than half of its initial value under 6 Star provisions.

While satisfying the NCC energy efficiency requirements, our modelling software (TRNSYS) enables us to further investigate active solar solutions like solar thermal for space heating and hot water storage tank or solar electricity and battery storage or geothermal solution, etc. Geoflow models the dynamic interaction between the building and the proposed energy system(s) for a typical year, so that the long term cost saving of the solution is determined. Our engineers properly model the building energy system(s) to enable architects to confidently assess different design options – not based on rules of thumb or guesses, but on actual kWh’s and $ savings. This ensures that home owners achieve the pre-quantified benefits from their energy efficiency investment. Contact us to discuss how we can assist you with your large residential building design.


Passive Solar Design

We defines passive house as a house that requires cost effectively, minimum amount of mechanical heating or cooling. Homes that are passively designed take advantage of natural climate to maintain thermal comfort. 


With passive solar design we try to limit the heat gains in summer and heat losses in winter through climate sensitive design of building envelope. A house built using passive solar design principles will generally be much less reliant on artificial heating and cooling and will therefore use less energy and cost less to run. Passive house design is essential for houses that are planned to be off grid. Lowering building demand allowing to lower the capital investment on solar electricity and battery and solar thermal heating/cooling and hot water storage tanks. 


The key principles of passive solar design (with the correct order) are as follows: 

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1- Orientation and siting

2- Zoning and layout

3- Thermal mass

4- Common building elements, such as walls, floors and roofs

5- Floor type and materials

6- Windows and glazing

7- Shading, including use of eaves

8- Convection and ventilation

9- Insulation

10- Landscaping and vegetation.


Note for the order of different principles above as it is the key for a cost effective passive house design. Home owners don’t need to invest several tens of thousands on excessive and unnecessary insulation where a proper modelling and design can reveal cheaper options to better take advantage of natural climate at lower installation costs. 


At GeoFlow Australia, we use TRNSYS software to model all building’s thermal details in 3D. TRNSYS is the most advanced thermal modelling software that is used in industry and research for implementation of new innovative energy systems. Modelling in 3D allows to consider almost all the details for the building thermal modelling. It also minimizes errors in modelling as you can see the building in 3D and compare it with architect’s plans. Neighbouring buildings and objects can be exactly modelled and shading effects can be assessed for any time of the year. Internal heat gains by occupants and schedule of operation can be modelled as requested by home owners every details. The most important final output of modelling is hourly building heating and cooling demand and electricity/gas/hot water consumption. 


At Geoflow we want to achieve lowest building energy demand with cheapest energy efficiency options. For instance we won’t consider triple glazing with aluminium frame and thermal break where a double glazed UPVC window can deliver similar saving at half the cost. We model different energy efficiency options and assess annual hourly building loads and savings for each option and let the architects/builders/home owners decide based on annual cost saving which options they want to take. 


Because the climate varies so much across Australia, passive design is not a single set of strategies all of which are applied equally in every house and climate. For instance higher shading is desirable in warmer climate where it can lead up to increased annual demand in mild and cool temperate. Same applies on different types of glazing. Warm climates should minimize heat gain from glazing where in cool temperate different type of glazing are used to increase solar heat gain during the day. At Geoflow, we use appropriate strategies in our modelling to take into account the climate and specifics of the site to minimize the heating and cooling requirements of the building, cost of running the building and consequently the carbon footprints of the building.


In the following summary of key points for different passive house design principles are discussed. 


Co-benefit of hourly energy modelling

The co-benefit of GeoFlow’s passive solar modelling is to use data from passive house modelling to design your renewable energy system. Sometimes, for some people this co-benefit becomes the major focus. One of the key outputs of GeoFlow’s energy modelling is hourly energy outputs. These hourly outputs can be used to find peak demand, annual total heating/cooling demand, annual total electricity to run appliances and annual total hot water demand. The software can also show any heat loss/gain from any part of building envelope like window, walls, etc., for any time of the year which comes handy when comparing options like different glazing from different manufacturers. 

Output of building thermal modelling – hourly heating and cooling for the building

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These hourly outputs are the key for proper design of renewable energy system as source of energy. With conventional energy sources like grid electricity, split heating, gas heating, etc, annual demand is not a design factor as they are unlimitedly available as long as you pay for the bills. However, with renewable energy generation for yourself, it is important to know hourly and annual demand for energy to be generated to cost-effectively spend the available capital. Renewable energy generation system for your house includes but not limited to solar electricity, battery storage, geothermal and solar thermal heating/cooling. Oversizing and wrong design, could cost a lot of capital investment which could have been used more cost effectively. 


TRNSYS software allows to model almost any energy source system like geothermal, solar electricity and solar hot water to be designed for best satisfaction of the building demand for every hour of the year. In other word, our passive solar design enables us to use data from passive house modelling to use for your solar hot water and electricity generation and storage design. 




Table below shows the Minimum insulation according to NCC for major cities climate zones

General insulation principles:

Bulk insulation is more effective above ceiling that under roof. Reflective foil is more effective under a roof than above ceiling. Walls can be effectively insulated with bulk and /reflective foil insulation. However, if the foil the effectiveness of foil insulation will be reduced if there is not enough still air gap in front of foil


In heating dominant areas, unwanted shading from eaves is probably the most important factor affecting the thermal design of the house. As shown in picture below, the area immediately below a horizontal building element like an eave is virtually permanently in shade. In climates that can benefit from solar gains for heating in winter, it is important to ensure that any fixed horizontal shading device doesn’t keep top of glazing in permanent shade. A shaded area of glass makes no contribution to winter solar gain and can lead to large amount of heat losses to ambient.

Even use of thermal mass elements in permanently shaded area are useless as they are never exposed to warmth. It is important that eaves dot restrict the solar access of mass elements. Thus in climate zones where heating predominates, top of window must be far enough below the eave to prevent overshadowing at mid-winter. Providing a clearance between horizontal overhangs and top of window is an important low cost strategy thermal performance of the house.

Geoflow Modeling Software

Here description of modelling tools used by Geoflow are presented so our clients can rest assured that we don’t use rules of thumb at cost of our clients.

TRNSYS Software for 3D building thermal modelling

We use TRNSYS 3D building modelling which allows to draw multizone building with considering thermal mass, self-shading, external shading and internal view factors for radiation exchange. The data we need for modelling is the building plans, elevations and specifications if they are available.

TRNSYS is the most comprehensive suite of tools that allows modelling the building, geothermal heating and cooling, solar electricity, solar thermal and any other thermal phenomena in a single model and assess interaction of different systems on each other.

 3D simulation with TRNSYS

6-Star Energy Bands

According to the NatHERS star rating protocol, star bands are introduced for NatHERS building modelling approach to assign star rating for residential buildings. Figure below represents the star bands for 67 different cities in Australia. For instance Melbourne is called climate region 21 and to achieve 6 star rating, building must not consume more than 114 MJ/m2 or 31.6kWh/m2. In other words, theoretically, a 200m2 6-star building in Melbourne annual heating and cooling energy demand shall be about 200*31.6kWh/m2= 6320 kWh.

The below star bands (hyperlink to star band figure) are valid for a house of 200m2. For smaller or bigger houses, the star rating is adjusted to consider surface area of the house. For bigger houses, this adjustment is like a fixed penalty for house star rating regardless of quality of building thermal fabric.

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NatHERS Star bands (Source: FirstRate5 Software manual, page 16, published Jan 2015)

 Star rating adjustment with building foot print area