As we discussed in one of our previous articles, energy use in buildings is extremely relevant in the climate change conversation. Direct carbon emissions in buildings represent, globally, 6–7% of the total. However, much of their contribution to total emissions comes indirectly through energy use, resulting in contribution of 12% of total emissions[1].
When looking only at energy-related emissions globally, buildings are responsible for approximately 28%[2]. To explore and find the best efficiency-related solutions, it’s key to understand that human thermal comfort (an essential part of health and well-being) is at the centre of energy use, which explains why most energy is put into Heating, Ventilation and Air-Conditioning (HVAC), even if energy end-use does vary significantly across countries. But how exactly are thermal comfort and energy use related?
Take a look at the image above. The building envelope represents, of course, the boundaries of the area where thermal comfort must be kept at the desired levels for human activities, and the arrows represent the movement of thermal energy (heat). These inflows and outflows generate continuous changes in the thermal state of the indoor environment, since they never really all switch off at once. Instead, they are controlled by engineers, occupants, and facility managers to try and reach a dynamic steady state, or put more simply: a set-point at which we feel comfortable. For example, we’ll open a window if we’re hot at midday, which increases air change and thus heat loss, which we must compensate for at night by switching the heating system on (if temperature drops). These changes govern our energy use.
Engineers and designers must precisely understand what certain choices in location and position, shape, material, or technology mean for each of these inflows and outflows. Think of this as setting the thickness of each arrow by design. Some examples of specific measures that increase efficiency (or reduce the thickness of the arrows):
Solar Radiation
- Glazing position and size according to climate
- Overhangs in sun-prevalent direction
- Movable shadings (controllability is key)
Envelope
- High insulation materials
- Additional layers
Internal heat gains
- Renewal of equipment to higher-efficiency products to avoid unwanted thermal gains
Air exchange
- Blockage of unwanted apertures: sealing materials (note: minimum air flow must be maintained to guarantee indoor air quality)
- Minimisation of amount of external-facing surface joints
Understanding the physical principles of indoor well-being, and thus energy use in buildings, is vital for boosting energy efficiency in the built environment. From an environmental point of view, reduction of energy use is crucial to fight the climate crisis. By incorporating and controlling the thermal variables in the energy model in the design phase of a building, when changes are easiest and most impactful, the best solutions can be selected before it’s too expensive (either economically or environmentally) to change them.
Mateo Barbero
co-founder
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[1] IPCC Fifth Assessment Report
[2] IEA (2019), The Critical Role of Buildings, IEA, Paris https://www.iea.org/reports/the-critical-role-of-buildings
