By Eamonn Ryan
The following article is derived from an ASHRAE UK presentation on ASHRAE UK chapter’s upcoming Hot Climate Design Guide, by Frank Mills, FASHRAE and professional consulting engineer. This is Part 5 of an eight-part series.

In older cities many buildings are historic and listed, whereby achieving net-zero goals presents additional challenges. Freepik
In older cities many buildings are historic and listed, whereby achieving net-zero goals presents additional challenges. Older buildings were often not designed with energy efficiency in mind, and retrofitting them to meet modern standards can be difficult and expensive. However, passive solar design principles can be applied to even traditional buildings to help reduce their energy consumption. For example, buildings can be retrofitted with more efficient insulation, energy-efficient glazing and shading systems to minimise heat gain and loss. The use of passive solar atriums can also help capture and distribute solar energy within the building.
By combining these passive strategies with modern hybrid cooling and heating systems, even historic buildings can achieve significant reductions in energy use, bringing them closer to net-zero emissions.
The role of strategic planning and passive cooling
The John Darling Mall school is an excellent example of how thoughtful architectural design can address both the comfort and functionality of outdoor spaces, particularly in hot climates. This semi-external area, though not intended to be a teaching space, serves as a sheltered zone where students can relax or socialise. The design allows the space to be naturally warmed by the sun during sunny days, while offering shelter when it rains, demonstrating the importance of providing versatile outdoor areas in hot climates that can be used year-round without needing artificial heating or cooling systems.
In the ASHRAE UK Hot Climate Design Guide, Mills highlights several effective strategies for designing energy-efficient buildings in such climates. One important method is the Lighting and Thermal (LT) method. This approach takes into account the balance between the glass and fabric of a building’s exterior, ensuring that energy consumption related to both lighting and thermal comfort is minimised. This method was originally developed at Cambridge University and is designed to assist in the early-stage strategic analysis of building energy use, especially for non-domestic structures.
The LT method is simple to use, relying on basic calculations rather than complex computer programs. It helps designers quickly assess the potential energy efficiency of a design and identify areas for improvement without requiring advanced technical tools. In practice, it offers guidance on optimal building orientation, window placement and fabric selection, all of which are crucial elements in minimising the energy demands of buildings in hot climates.