AIR HANDLING UNITS


Operational challenges and diff erent defrosting techniques when running traditionally designed reversible heat-pumps in wintertime (a - left). Typical integrated HP design with one heat exchanger positioned on the ‘cold’ side of the thermal wheel operating in reverse cycle defrost with reduced capacity and airfl ow. (b- centre) Close-proximity electric heaters are used to defrost the frozen evaporator (c - right), and reheaters are used to increase the supply air temperature during decreased recovery and reverse cycle defrost.


Heating-led optimisation does not mean neglecting cooling performance. In warmer periods, the system prioritises a sequence of free cooling and night cooling before an energy-effi cient DX cooling cycle is applied. When mechanical cooling is required, the unit operates at higher evaporation temperatures, which reduces latent cooling and lowers energy input. This results in an improved indoor climate for occupants, less strain on the system, and lower energy consumption. Comparisons between traditional HVAC designs, with separate chiller and boiler installations, and modern AHUs with integrated reversible heat pumps show around 20% lower energy use overall, and can show a seasonal coeffi cient of performance in heating mode of more than 11. In a typical offi ce building, this translates into signifi cant operating cost savings and a reduction in CO₂ emissions of up to 37% from energy use alone. These are not marginal improvements, but fundamental gains that directly support both cost control and decarbonisation targets.


Regulation and sustainability drivers The regulatory landscape reinforces the case for heating optimised AHUs. Minimum Energy Effi ciency Standards already prohibit leasing of commercial buildings below EPC rating E, with proposals to raise the minimum to B by 2030. Achieving that benchmark requires signifi cant improvements in operational performance. Integrated reversible heat pumps support this by addressing both carbon emissions and running costs in a single investment. Operating with lower GWP refrigerants such as R454B, these systems reduce environmental impact by 78% and 31% compared to legacy R410A and R32 designs. They also qualify for all available BREEAM credits under Pol 01, Impact of Refrigerants, and carry full ISO Environmental Product Declarations covering embodied carbon. These third-party credentials give consultants and property owners confi dence that the solution contributes not only to operational effi ciency but to wider sustainability and compliance goals, including the building sector’s overall strive for increased material and natural resource effi ciency. The fi nancial case is strengthened when systems are designed with accurate local climate data. One of the most common specifi cation errors is the assumption that maximum outdoor temperature and maximum relative humidity occur simultaneously, but in reality, they don’t. Oversizing based on


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"Comparisons between traditional HVAC designs, with separate chiller


Thermocooler HP DX layout


this assumption increases capital cost and creates instability in part load operation, which is where most systems spend the majority of their running hours. As an example, changing design criteria from 30°C/50% RH to 32°C/60% RH may seem a minor adjustment, but it can drive a 55% increase in required cooling capacity. The result is higher investment cost, less stable operation and reduced fl exibility in variable air volume systems. Heating optimised AHUs designed with correct cooling data avoid this trap, delivering more predictable operation and lower lifetime costs. For a long time, reversible AHU integrated systems have


been treating heat as a secondary function. That approach is no longer suffi cient. The industry now has access to systems that are designed for heating from the outset, ensuring stable supply air conditions, avoiding defrost interruptions and reducing both capital and operating costs, while still providing suffi cient comfort cooling. For consultants and contractors, this is a chance to specify solutions that meet client expectations for comfort, resilience and sustainability without compromise. For building owners, it is an opportunity to achieve faster paybacks, higher EPC ratings and greater asset value.


While not neglecting the need for comfort cooling, the industry is moving towards a heating-fi rst philosophy in AHU design, one that better refl ects our climate and regulatory pressures. By embracing this shift, we can deliver systems that are simpler to install, cheaper to run and aligned with long- term carbon goals. Sometimes the most eff ective innovation comes not from refi ning existing compromises, but from rethinking the problem altogether. In the UK, the problem is heating. Now, we have technology designed to meet it.


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and boiler installations, and modern AHUs with integrated reversible heat pumps show around 20% lower energy use overall, and can show a seasonal coeffi cient of performance in heating mode of more than 11."


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