The project "Case Study: Simulation, Validation and Design Optimisation of ThermocillTM", delivered for Thermocill Ltd in 2020, addressed a practical energy challenge through computational fluid dynamics (CFD) and energy and thermal modelling. Rather than producing simulation images in isolation, the study was organised around the client's design questions: what controlled performance, where the principal risks or losses occurred, and how the design or operating strategy could be improved.

Thermocill is an energy savings product that is designed for installation under the window board and above the radiator in a room. It is made from recycled plastic materials and can be retrofitted to existing homes as well as new builds. In its operation, the product tends to direct the natural convection from the radiator to create a wall of warm air immediately in front of the internal side of the glazed window. In this project, the performance of the Thermocill was investigated based on the previously designed experimental condition. The main aim of the CFD simulation was to assess Thermocill’s effectiveness in a typical bedroom consisting of a radiator, a double-glazed window and a door. Several high-fidelity and transient simulations were conducted to reproduce the experimental conditions and to provide an insight into the details of Thermocill’s operation, particularly near the window. Subsequently, a design optimisation on several geometrical aspects of Thermocill were carried out. The CFD simulations successfully reproduced the experimental data and led to major changes in Thermocill’s design. Products such as Thermocill play an important role in decarbonisation of heating in homes in the UK, which is one of the priorities of the UK government in achieving net-zero emissions.

The methodology centred on a high-fidelity transient room CFD and thermal model reproducing the experimental Thermocill setup. The representation retained the radiator, window, room enclosure and the device geometry responsible for redirecting the natural-convection plume along the glazing. Boundary and operating conditions covered the tested room conditions, alternative product geometries, radiator operation and relevant envelope heat losses, with material, fluid and equipment properties assigned from the available design information. Resolution was concentrated in regions where steep velocity, thermal, concentration or phase gradients were expected, while the overall model remained efficient enough to compare several credible configurations. This balance allowed system-level performance to be linked to the local mechanisms responsible for it.

The assessment compared geometric changes intended to strengthen the warm-air curtain and improve manufacturability. Performance was judged using window-surface temperature, convective plume path, room temperature, heat loss, condensation or mould risk and agreement with experimental measurements. Results were reviewed through quantitative summaries and engineering visualisations, such as contours, vectors, streamlines, sections and time histories, selected to suit the physics. Important assumptions and operating uncertainties were considered so that the recommendations relied on repeatable comparative trends rather than a single nominal case.

For Thermocill Ltd, the principal value was a validated redesign that improved the product's contribution to domestic heat decarbonisation and retrofit performance. The final evidence linked each recommendation to the relevant model or process output, making it suitable for internal design reviews, supplier or contractor discussions and, where applicable, planning, safety or regulatory dialogue. The work also created a reusable baseline that can be updated as geometry, operating data or test results become available, reducing the cost and risk of later design iterations.