Making proactive building decisions with Passive Design Modelling

October 10, 2023

What is Passive Design Modelling?

Passive design is a sustainable building design approach that harnesses and capitalises on natural resources and building elements to reduce energy consumption and improve indoor comfort. The goal of passive design is to create a building that requires minimal energy to maintain a comfortable indoor climate.

Passive building design principles include optimising the form and orientation of the building, using high-performance windows and insulation and thermal performance of the construction elements, utilising the thermal mass of the building and maximising natural ventilation and daylight. So before any energy-efficient heating and cooling systems or green energy solutions are even considered, the first step is to model the building and project how it will perform.

Passive Design Modelling uses computer simulations to analyse the building’s performance under different conditions, real time weather data and scenarios. This allows us to test and compare different design options and make informed decisions based on data. This is where building performance modelling comes in.

Understanding Building Performance Modelling

Building Performance Modelling (BPM) is a broad term that encompasses various techniques and tools used to analyse and optimise building performance. It includes energy modelling, daylight modelling, thermal modelling, and computational fluid dynamics (CFD).

Energy modelling is the most common type of BPM and is used to predict and evaluate a building’s energy consumption and carbon emissions. It takes into account the building’s geometry, materials, occupancy, and HVAC systems. Daylight modelling is used to optimise natural light levels in the building and reduce the need for artificial lighting. Thermal modelling is used to evaluate the building’s thermal performance and identify potential heat loss or gain. CFD is used to analyse the airflow and ventilation in the building and optimise indoor air quality.

This is a powerful design tool that gives us the ability to model and anticipate the movement of light, air and energy in and around a building before its form or orientation are set in stone - or glass or steel for that matter.

Of course, how light, heat and energy is transferred through a building will change when people are introduced into the equation. The same goes for external factors like the weather, and where exactly the structure is going to be located geographically. The beauty of building performance modelling is that it lets us take all of this in account in our decision making.

Climate change is impacting our decisions

It used to be that, in Ireland, our biggest concern was keeping the heat in when it came to building design. That meant a focus on tightly sealed buildings with insulation that retained heat. But with a rise in global temperatures, and 2022 being the hottest year in Ireland on record, the need to keep buildings cooler is becoming more relevant now.

Passive cooling uses natural and non-energy-intensive techniques

One of the main strategies of Passive Design Modelling is passive cooling, which uses natural and non-energy-intensive techniques to reduce the building’s cooling load. Passive cooling strategies include shading, natural ventilation, thermal mass, and evaporative cooling.

Every building is different, so building performance modelling technology is vital in the planning process. Not long ago, air conditioning would have been the go-to cooling option in well-insulated buildings, but its operation can be costly, both financially and environmentally with the carbon emissions it produces.

Shading is used to block direct sunlight from entering the building and reduce solar heat gain. It can be achieved through the use of overhangs, shading devices, or vegetation. Natural ventilation is used to provide fresh air and reduce the need for mechanical ventilation. It can be achieved through the use of operable windows, vents, or stack effect. Thermal mass is used to absorb and store heat during the day and release it at night. It can be achieved through the use of high-density materials such as concrete or masonry. Evaporative cooling is used to reduce the air temperature by evaporating water. It can be achieved through the use of water features or evaporative cooling towers.

Performance modelling of passive cooling measures is most effective when carried out at the earliest stages, to ensure the correct decisions are made before it is too late to make effective changes. At each stage of the design phase, as decisions are made, modelling will help to meet energy and cost targets and mitigate the risk of a performance gap occurring between planned energy use and actual operational use.

Where passive design modelling helps with critical decisions

Passive design is most effective when considered early in the design process – even better if it can be done before the planning application stage given some of the decisions that will need to be made around window size and external shades, etc.

  • Building orientation: The direction a building faces affects how much more natural light it will take in during the winter months and how much in shade the interior will experience in the summer months. There is a balance to be struck here.

  • Floor layout: Where machinery and equipment is located in a building affects its internal temperature.

  • External shading: Overhangs and shadings can reduce overheating in the summer months. Their effectiveness can be calculated using modelling.

  • Ventilation: In passive design, whole building ventilation strategies allow for heat to be recovered for warmth, and natural ventilation to be used to cool.

  • Thermal mass: Certain building materials can absorb, store and later release significant amounts of heat.

It can help with critical decisions throughout the building design process. It can help evaluate different options and select the most energy-efficient and cost-effective solutions. Passive Design can also help identify potential problems and optimise the building’s performance before construction begins.

Passive Design Modelling can also help with compliance with building codes and regulations. Many building codes and regulations require buildings to meet certain energy efficiency standards.

We reshape the way building performance is thought about

Passive Design Modelling is an effective approach to building design that prioritises energy efficiency and sustainability. By optimising the building’s orientation, layout, and materials, it can help achieve maximum energy efficiency in building projects.

Metec is an engineering consultancy that delivers an end-to-end building performance optimisation service, from concept through to detailed design and delivery onsite.

If you would like to know more about the power of passive design and building performance modelling to make better decisions, get in touch with the sustainability team at Metec Consulting Engineers today.

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