Steve Molloy from Daikin explores how well-designed HVAC systems can contribute to thermally resilient commercial buildings as the Earth continues to warm.
With four of the UK’s hottest years on record occurring between 2022 and 2025, the conversation around climate control in the built environment has become increasingly urgent. Indeed, according to a report published by the Climate Change Committee in May, the UK is ‘built for a climate that no longer exists’ and current heat mitigation policies are unlikely to be sufficient in the face of rising temperatures.
The landmark report advocates for greater use of mechanical cooling in public buildings, particularly in those intended for vulnerable populations such as care homes and schools, and calls for the Government to set a maximum temperature for work environments.
For architects working in commercial spaces, the report is another clear signal of the direction of travel: overheating is no longer an operational issue to be managed but a key design priority that must be considered in the earliest stages of a project. Decisions made at RIBA Stage 1 and 2 about building orientation, glazing strategy and structural thermal mass will either ease or compound the demands placed on any mechanical system. Getting the building envelope right is vital, of course, but the mechanical strategy should be given equal consideration and as the mercury continues to rise, it should be equally ambitious.
After all, a carefully planned HVAC system must perform against a wide breadth of criteria. It must deliver thermal comfort year-round, contribute meaningfully to carbon reduction targets and remain capable of performing reliably in ambient conditions significantly warmer than today’s. Crucially, decarbonising the heating and cooling of commercial buildings is inextricably linked to the question of thermal resilience. A design that solves the overheating problem through energy-intensive cooling, powered by the grid without regard for carbon content, is only a partial solution.
Heat pumps are the most credible pathway to low-carbon heating and cooling in commercial buildings, and the technology has matured. Air-source heat pumps (ASHP) extract heat from ambient air and remain the dominant choice in the UK market, where a suitable water source or appropriate geology for ground or water source alternatives is not always available. Ground and water source systems offer more consistent year-round performance given the stability of ground and water temperatures relative to air and are worth investigating where site conditions permit.
A key design advantage of heat pumps is that the refrigerant cycle can be reversed for cooling, making a single technology capable of addressing the full thermal comfort range. For buildings with complex or mixed requirements, four-pipe multipurpose configurations can deliver heating and cooling simultaneously to different zones, capturing and redistributing heat rather than rejecting it; particularly efficient during seasons when some spaces require warming and others need cooling.
Achieving domestic hot water temperatures above 70°C has historically been a constraint on full heat pump specification in commercial projects, but advances in refrigerant technology such as the development of high-temperature heat pump products have largely resolved this.
Several design considerations are non-negotiable, beginning with a fabric-first approach. The lower flow temperatures at which heat pumps operate make building envelope performance a critical variable, not a secondary concern. Electrical infrastructure must be assessed early as heat pumps increase demand significantly, and engagement with the Distribution Network Operator should happen at the earliest possible design stage to avoid abortive work. Plant footprint, noise and the risk of cold air recirculation from air-source discharge must be resolved in the layout.
For offices, hotels, retail and education buildings, Variable Refrigerant Volume (VRV) air-to-air heat pump systems offer a practical and efficient route to integrated heating and cooling in new builds. Direct expansion systems respond immediately to changing indoor conditions, a compelling advantage in buildings where solar gain, occupancy and IT loads can shift rapidly.
Heat recovery configurations allow simultaneous heating and cooling in different zones, recapturing rejected energy and redistributing it where needed. Compact refrigerant pipework and a self-contained installation make VRV systems straightforward to integrate structurally, and the industry’s ongoing shift towards lower GWP refrigerants like R-32 makes them particularly suited for projects seeking BREEAM, LEED or WELL.
As temperatures continue to rise, the challenge facing architects is no longer simply how to reduce operational carbon, but how to ensure buildings remain comfortable, healthy and productive throughout their lifetime. Thermal resilience and decarbonisation should be viewed as complementary objectives rather than competing priorities. By considering building fabric, mechanical systems and electrical infrastructure as part of a unified design strategy from the earliest project stages, commercial buildings can offer resilience and support the transition to a lower-carbon built environment.
Steve Molloy is sustainability & commercial solutions manager at Daikin