The recast Energy Performance of Buildings Directive, published in the Official Journal of the European Union in May 2024 and designated Directive 2024/1275/EU, establishes the most ambitious requirements the construction and building services sector in Europe has encountered. For HVAC engineers, this legislation is not merely a legal text. It is a framework that directly determines how heating, ventilation, and air-conditioning systems are modelled, sized, and verified in new buildings and deep renovations. Understanding its technical implications is essential for any engineering practice operating in the EU member states or in the UK market, where equivalent trajectories continue to be adopted by national policy. NOVTRIQ Engineering Intelligence provides thermal analysis and HVAC system design services to projects across Europe, both remotely and on-site, and this article sets out the key technical obligations and their engineering consequences. | The EPBD 2024 revokes and replaces Directive 2010/31/EU and its 2018 amendments. The changes of greatest relevance to HVAC thermal analysis fall into five principal areas. First, the directive introduces the 'Zero Emission Building' (ZEB) category, replacing the 'nearly zero-energy building' (nZEB) concept. A ZEB must achieve a very low energy demand and cover that demand entirely with carbon-free energy, which redefines the acceptable load boundaries for heating and cooling systems. Second, member states are required to establish renovation trajectories that bring non-residential building stock to energy class E or above before 2030, and to class D before 2033. These thresholds translate directly into heating and cooling demand limits that HVAC systems must satisfy. Third, the directive introduces the Building Renovation Passport, a technical roadmap document that requires successive assessments of the building envelope and systems, implying periodic and documented dynamic thermal load analyses throughout the building lifecycle. Fourth, non-residential buildings with heating or air-conditioning systems of nominal output exceeding 290 kW must install Building Automation and Control Systems (BACS) of class B according to EN ISO 52120-1 before 2025, with the threshold extending to systems above 70 kW before 2027. Fifth, the directive reinforces the application of the Smart Readiness Indicator (SRI), which assesses a building's capacity to respond to grid signals and manage its thermal loads flexibly. | The harmonised calculation method that underpins compliance declarations under the EPBD across the majority of EU member states is EN ISO 52016-1:2017, formally titled 'Energy performance of buildings - Energy needs for heating and cooling, interior temperatures and sensible and latent heat load.' This standard defines two levels of calculation. The first is a simplified hourly method based on a 5-node resistance-capacitance (RC) model per zone. This model represents the zone as an air node, a thermal mass node for the envelope, a surface node for the envelope, a central structural mass node, and a node for walls in contact with the exterior. This representation captures thermal lag and attenuation of the building fabric, parameters that are critical for correctly sizing HVAC systems without over-engineering them. The second level is a detailed calculation that provides more precise representation of distributed thermal mass, radiation exchange between surfaces, and controlled natural ventilation. This is used in more complex projects or where the simplified level produces conservative results that would unfairly penalise the building's performance rating. | Several input parameters in EN ISO 52016-1 demand particular attention during the HVAC design phase. Occupancy schedules and internal gains, including lighting and equipment profiles defined by the standard for different building typologies, should not be applied without adaptation to the actual project conditions. Using default profiles without verification can lead to significant under- or over-estimation of latent loads. Ventilation airflow rates, their temperature and humidity, and infiltration rates through the envelope all affect both sensible and latent loads. The EPBD 2024 reinforces requirements for high-efficiency heat recovery in mechanical ventilation systems, making accurate infiltration modelling more consequential than it was under the previous regime. Effective thermal mass (Cm), calculated from the products of density, specific heat, and thickness of each thermally accessible layer from the interior, is a parameter that can substantially reduce peak load and therefore installed plant capacity when properly quantified. Solar gains through glazing are particularly sensitive to the solar factor (g-value) of the glass and to shading devices, both fixed and movable, and EN ISO 52016-1 includes a simplified shading calculation procedure for obstructions. | The indoor environment quality criteria that determine HVAC design parameters are set out in EN 16798-1:2019, which replaced EN 15251. This standard defines four categories of indoor environment quality (I to IV) based on the acceptable level of dissatisfaction, with operative temperature and CO2 ranges for each category. The category selected directly determines the design parameters for the HVAC system. For an office building designed to category II, which the standard recommends for new buildings and major renovations, the operative temperature range in summer without active cooling is 23 to 26 degrees Celsius, and the maximum CO2 concentration is set at 800 ppm above the external level. Sizing the system to maintain these ranges during the specified hourly percentile is the central task of the load calculation. According to the International Energy Agency (IEA), buildings account for approximately 30 per cent of global final energy consumption, with heating, ventilation, and air-conditioning systems representing the largest share of that demand in European climates. Given this significance, precision in thermal load calculation has a direct impact on both operational energy consumption and capital cost of plant. | A recurring error in professional practice is the application of global safety factors to the output of calculation standards without technical justification. This leads to over-sized systems with the associated problems of poor operation under partial load, higher energy consumption, and elevated maintenance costs. The correct procedure requires calculating the peak cooling load on a zone-by-zone basis using real hourly climatic data, preferably reference climatic years in accordance with ISO 15927-4 or an equivalent national method, and applying occupancy and equipment diversity factors grounded in the specific use of the building. For projects in the European market, NOVTRIQ uses hourly calculation tools consistent with EN ISO 52016-1, complemented by dynamic simulation where the complexity of the envelope or systems justifies it. | Although the EPBD 2024 does not explicitly reference BIM or digital twins, the complexity of Building Renovation Passports and the requirement to update energy analyses across the building lifecycle makes these technologies practically indispensable for efficient information management. Structuring geometric and parametric building information so that thermal calculation models are fed directly from a Common Data Environment (CDE) reduces transcription errors and ensures design change traceability. According to the IEA Energy Technology Perspectives Report 2023, the adoption of digital twins in building management could reduce HVAC energy consumption by between 10 per cent and 20 per cent in commercial buildings, through optimisation of operational schedules and predictive maintenance. | Demonstrating compliance with the EPBD 2024 requires a structured set of technical documentation. This includes a heating and cooling energy demand calculation report following a recognised method such as EN ISO 52016-1, with all input data documented and justified. An Energy Performance Certificate (EPC) issued by a qualified assessor under the national regulations of each member state is required, together with a declaration of conformity of the installed HVAC system with minimum performance requirements, for example under the EU Ecodesign Regulation for climate control equipment. Where BACS is mandatory, a classification report in accordance with EN ISO 52120-1 demonstrating class B or above must be produced. For renovation projects, the Building Renovation Passport must include the improvement roadmap and verification milestones. Producing these documents correctly requires close collaboration between the envelope design team, HVAC engineers, control system specialists, and energy certification professionals. NOVTRIQ structures its project teams to cover this technical interface coherently, with a single point of contact for the client throughout the process.