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Thermal comfort

Richard Tibenham, Building Performance Specialist at IES on keeping workplaces safe and productive in extreme weather

It has recently become clear that the UK is somewhat unequipped for maintaining ideal working conditions under extreme hot weather events. There is no maximum working temperature, and until the government makes moves to legislate it is an employer’s responsibility to ensure facilities are safe, comfortable and fit for purpose. This applies both in the warm summer months and colder winter months.

The answer here is not simply to install more air conditioning or space heaters as these active climate control measures are incredibly carbon-intensive and only serve to exacerbate the root issue.

One solution is the implementation of passive strategies, assessed and implemented using data and technology-informed decisions. Every building is different and there is not a one-size-fits-all list of techniques, which is why the use of performance modelling technology is vital in the planning process. While passive measures are most effective when considered from the earliest stage of planning, some measures can be added to existing buildings to help create comfortable conditions while using minimum energy.

Form, orientation, glazing ratios, shading strategy, and the inclination and orientation of roofs can all offer very significant energy efficiency and thermal comfort opportunities at negligible additional capital cost.


Commissioned as part of the Scottish Net Zero Public Buildings Standard, consultants at IES have developed a guide to Dynamic Simulation Modelling in the application of dynamic modelling within a NZC design brief. These models are theoretical, but employ far more detailed data inputs than ‘compliance models’, allowing far greater accuracy and insight.

Upon project completion, using a process known as calibration, these theoretical models can be developed from a static representation of a building or portfolio into a fully-fledged ‘digital twin’ which mirrors the behaviour and dynamics of its real-world counterpart.

By capturing and feeding real-world operational data from buildings back into the digital twin and combining this with the unique power of physics-enabled simulation, machine learning and AI, a highly accurate digital asset can be created which evolves with the building itself.

When using energy modelling, different weather files can be selected to examine how the building will perform under varying circumstances to future-proof building performance, particularly where passive ventilation and cooling solutions are being tested.


Building orientation: with the long axis of the building in an east-to-west orientation, a building can gain the greatest exposure to solar heat gains from the south, for direct solar heat gain and energy yield. Glazing an office building to the north, with high internal heat gains and high overheating risk, will reduce solar heat gains.

Floor layout planning: should consider the availability of sunlight and solar heat gain on different aspects of the building. Consideration of the unique requirements of different activity types and their relationship to the sun can be helpful. For instance, it could be beneficial to locate office areas, for instance, on the north elevation, where large windows will provide ample daylight without incurring an overheating risk. Likewise, hotel rooms, which typically incur low internal heat gains will benefit from a south facing exposure, for winter time solar heat gain.

Self-shading and external shading features: especially on southern facades, help to reduce overheating in the summer months, but these need to be tested so they are correctly sized and shaped to work in balance with daylighting strategies. This can be done with modelling technology that calculates the size and angles necessary to block and allow the sun, based on the exact positioning of the building and time of year.

Window-to-wall ratio: depends on the floor area, latitude and climate. Windows should ideally be specified to permit maximum passive solar heat gain and be no larger than is necessary to permit sufficient daylight. Doing so maximises daylight availability and solar heat gains, whilst limiting conductive heat transfer.

Whole building ventilation strategies: that are modelled through the whole building allow for heat to be recovered for warmth, and natural ventilation used to cool. For cooling, this would involve ensuring windows are positioned on the side of the prevailing wind and that the air can then circulate once in the building. Mechanical ventilation can be used to limit heat loss during the winter months but can also be used to limit heat gain via ventilation during the summer. Mixed-mode strategies, which allow natural ventilation to operate under suitable conditions, help to reduce the energy demand of operating ventilation system fans.

Thermal mass: allows buildings to absorb, store and later release heat. This can be beneficial to help stabilise internal temperatures, but is not always essential. A well-insulated building with a good solar shading strategy should not become excessively hot, unless high internal heat gains are present. Buildings with high internal heat gains, such as offices, tend to benefit more from high thermal mass structures.

Passive design features to keep buildings comfortable in extreme heat are extensive and no two buildings will be best suited to the same measures. Technology and energy modelling allows access to accurate predicted operational performance information. Otherwise, there is the risk of misallocating capital on solutions which do not deliver, creating uncomfortable conditions for building occupants and impacting poorly on their health and productivity.

About Sarah OBeirne

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