27 October 2022
As energy prices rise and the race to Net Zero Carbon rages on, high-tech options may often seem like the only solution. However, it is important to remember the fundamental reasons behind building energy usage. By fully understanding the way buildings behave, it becomes easier to reduce existing building energy consumption and easier to design more energy efficient new buildings. As presented in the article “Energy efficiency: The unsung hero of Net Zero Carbon” by Anneli Tostar, Laure Ferrand, Tessa Lee and LeAnna Roaf, reducing consumption through energy efficiency measures is an essential step towards Net Zero.
With the ongoing impacts of climate change, there is an additional need to design resilient buildings that will continue to perform in 30 or 50 years. Rising temperatures will increase the burden on our cooling systems and increase the need for passive solutions.
Passive solutions – Factors that are already there to be used such as natural ventilation, daylight, external shading, passive heat gains
Retaining a desired environment
Creating an internal environment that is conducive to human wellbeing and appropriately tailored to building use requires a design that takes what is already provided by nature and augments it.
When a building is designed in a way that is comfortable and pleasant to be in, you might not realise why it feels that way. If you had to imagine an uncomfortable or unpleasant room, however, it is more obvious what is causing it. I have a few guesses for what might come to mind:
- The room is either stiflingly warm and stuffy, or so cold you have goosebumps.
- There might be an unpleasant smell, such as cleaning chemicals or mould.
- It could be dark and dingy, or the glare from the sun through the window might blind you at certain times of day.
No matter why the environment feels unpleasant, you will be wishing that the space was designed or operated better. We must aim to create spaces that are enjoyable to be in, in the most sustainable way possible.
Heating & Cooling
Thermal comfort cannot be efficiently achieved with a one-size-fits-all solution. Depending on location and time of year, the situation can vary significantly, so a bespoke approach needs to be taken for each building. That doesn’t mean that the fundamental principles aren’t universal – they very much are.
Before trying to immediately control the temperature with building heating and cooling systems, it is best to utilise the already available forms of heat gain/loss. In general, for a building these fall under one of the following types:
- Internal heat gain: Waste heat produced by objects within the space such as people, lights, electrical and cooking equipment.
- Solar gain: Heat transmitted as part of sunlight that enters through windows.
- Conduction: Heat transferred by conduction through walls, windows, doors, floors, and roofs.
- Ventilation: Heat transferred during exchange of air between inside and outside.
Each of the above are important individual contributors to achieving desirable thermal conditions, however they should be considered as a whole, as part of a holistic design strategy so that one aspect does not act counter to the goal (for example a well-insulated but “leaky” building will still lose significant amounts of heat during colder periods). Design standards, such as Passivhaus, are based around this concept of holistic passive design, whereby optimised construction can lead to minimal heating and cooling requirements.
Humans have a great ability to adapt to different temperatures but only when the change is gradual. Overly relying on mechanical heating or cooling means your body doesn’t have the chance to adapt to the outside temperature and will experience the uncomfortable shock when you exit or enter a building.
Only once the above elements are understood within the context of a specific building and use, should mechanical heating or cooling strategies be implemented. In a typical UK office, passive measures related to heating and cooling can reduce total energy consumption by more than 60% (Link).
The supply of fresh air in internal environments is essential to occupant wellbeing. Lack of ventilation results in a build up of harmful pollutants in the air such as CO2, particulate matter and TVOC’s (Toxic Volatile Organic Compounds). While levels of these pollutants can be reduced by minimising their sources (such as paints and cleaning products for TVOCs), there will always be a need to refresh the air. Therefore, to reduce energy consumption it is essential to supply fresh air as efficiently as possible.
Using openable windows can provide this, with the bonus of free cooling, although the design must account for times when it is too hot outside, and any issues with noise or air quality. Appropriate sizing of fans and ductwork along with limiting ventilation rates to optimal levels based on usage of the space allows for fan energy consumption to be minimised where mechanical ventilation is needed. In a typical UK office, passive measures related to ventilation can reduce total energy consumption by more than 25% (Link).
Achieving the necessary levels of light to ensure occupant wellbeing requires maximising the availability of daylight and then supplementing with efficient and bespoke artificial lighting. Levels of daylight vary significantly by location and time of year; this means that lighting design choices must be well-thought-out to ensure the needs of occupants are met. External and internal shading should be used to combat glare and reduce unwanted solar gain.
Glazing areas should be designed to maximise daylight, while also minimising the risk of overheating and heat loss. Positioning glazing as high on the façade as possible allows maximum daylight penetration, whereas low level glazing increases solar gain without providing much daylight benefit (your building will be too hot while still being dark). Artificial lighting should only be considered once natural daylight has been fully utilised. Efficient LEDs should be used to provide optimum levels of light based on the use requirements of the space, with daylight and occupancy-based controls to allow for the reduction of unnecessary energy consumption. In a typical UK office, passive measures related to lighting can reduce total energy consumption by more than 40% (Link).
Bringing it back to Net Zero
Considering our current global challenges, it is essential to ensure that our buildings are designed to use energy as efficiently as possible. As we have seen, significant energy savings can be achieved purely through passive measures, and these principles apply to all building types. These energy savings are often more significant than those which can be solely achieved with high-tech measures such as heat pumps. Therefore, while both are necessary, passive measures should be prioritized and integrated early within building design to ensure reduced need for mechanical systems. Apart from reducing unnecessary energy consumption, designing our buildings to act in harmony with the external environment establishes a resilience and adaptability that will persist through any future climatic changes. Embedding a thorough understanding of the fundamental ways in which our buildings behave into a design strategy reduces energy bills, aids alignment with Net Zero Carbon and creates climate change resilience.
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