The rigorous design of HVAC installations now demands considerably more than sizing equipment from empirical rules. The recast Energy Performance of Buildings Directive, published in May 2024 as Directive 2024/1275/EU, establishes a concrete roadmap towards zero-emission buildings across the entire EU property stock. Within this context, EN ISO 52016 has become the reference standard for calculating heating and cooling energy needs and for determining hourly HVAC loads. This article examines the methodology that standard establishes, the obligations that derive from the EPBD, and why a well-executed thermal analysis is indispensable for complying with both. | The EPBD 2024 introduces several requirements that directly affect the thermal modelling of HVAC systems. First, all new buildings must achieve zero-emission building (ZEB) status from 1 January 2028 for public-sector premises and from 1 January 2030 for all others. The Directive defines a ZEB as a building with very high energy performance, with any residual energy needs met exclusively from renewable sources. Second, each EU Member State must publish a national building renovation plan that includes quantified targets for 2030, 2040 and 2050, with explicit reference to the percentage reduction in primary energy demand. Third, the Directive reinforces periodic inspection obligations for boilers, heat pumps and air-conditioning systems, requiring performance reports that include indicators such as COP and SEER measured under real operating conditions. Fourth, the Smart Readiness Indicator (SRI) is extended in scope, evaluating the capacity of HVAC systems to respond to grid signals and adjust consumption dynamically. Fifth, renovation passports are generalised, each of which must include an energy roadmap based on calculations conforming to the ISO 52000 series for the building in question. According to the European Commission, buildings account for approximately 40 per cent of total energy consumption in the EU and 36 per cent of energy-related greenhouse gas emissions, figures that justify the regulatory ambition of the EPBD and demonstrate why precise thermal load calculation is not an academic exercise but a practical obligation with direct legal and economic consequences. | EN ISO 52016, formally titled 'Energy performance of buildings: Energy needs for heating and cooling, internal temperatures and sensible and latent heat loads', is structured in two principal parts. ISO 52016-1:2017 defines the calculation method for heating and cooling energy needs, hourly internal temperature, and sensible and latent loads. It includes both a detailed hourly method and a simplified monthly method. ISO 52016-2:2017 addresses the explanation and interpretation of ISO 52016-1 requirements, providing additional guidance on the selection of boundary conditions and the validation of results. The hourly method of ISO 52016-1 models building thermal dynamics using a resistance-capacitance (RC) network, representing each envelope element as a node network with defined thermal properties. Each thermal zone is characterised by the thermal resistances of each envelope layer (walls, roofs, floors and glazing), the effective thermal capacity of the building mass classified across five inertia levels from 'very light' to 'very heavy', hourly internal gains from occupants, lighting and equipment, solar gains calculated through solar transmittance factors (g-value) and incident irradiance on each orientation, and the ventilation and infiltration flow rate expressed in air changes per hour or in cubic metres per hour per zone. The output of the model is an hourly vector of heating and cooling needs for each zone and for the whole building, which feeds directly into HVAC system sizing and into the calculation of the energy performance indicator (EPB rating) required by the EPBD. | The standard permits use of the monthly method, inherited from the quasi-steady-state approach of ISO 13790, for simplified calculations in residential buildings with regular geometry. However, the monthly method introduces significant errors in several circumstances: when the building has high thermal inertia and the occupancy cycle is intermittent, as in office buildings, schools and sports facilities; when there is a high proportion of glazing on south- or west-facing facades, generating solar gain peaks that the monthly average artificially smooths out; when the HVAC system operates in nocturnal free-cooling mode or with pre-heating and pre-cooling strategies that are only visible at hourly resolution; and when hourly operative temperature is being assessed to verify thermal comfort in accordance with EN 16798-1. In these cases, the hourly method of ISO 52016-1 is the appropriate approach and is frequently the only one accepted by competent authorities for energy certification of new-build projects of any complexity. According to the technical report of the Joint Research Centre of the European Commission on EPBD implementation, several Member States already require the dynamic hourly method for non-residential buildings with a floor area exceeding 1,000 square metres, making dynamic simulation a de facto requirement for a growing share of the European market. | The energy needs calculated by ISO 52016 represent the net building demand, that is, the energy that the HVAC system must supply or extract at the boundary of the conditioned space. Translating this into equipment selection requires an additional step: calculating the design peak load, which determines the nominal capacity of boilers, chillers, air-handling units and terminal devices. This peak calculation is typically carried out in accordance with EN 12831-1 for heating and in accordance with the ASHRAE Handbook of Fundamentals chapter on cooling and heating load calculations, or with the procedures derived from EN ISO 52016, for cooling. In all cases the input data are identical: envelope characteristics, occupancy and use profiles, site climate data, and exterior design conditions. Early-stage estimation tools allow orders of magnitude to be established before the full model is available, reducing the risk of oversizing or undersizing with their associated capital and operational costs. | One of the most established trends in current engineering practice is the integration of the energy model with the building information model (BIM). When the BIM model is properly structured according to ISO 19650 standards, geometric and material data can be exported directly to energy simulation tools such as EnergyPlus, IDA ICE or DesignBuilder, eliminating manual data re-entry and reducing transcription errors. The subsequent step is the building digital twin, in which the energy model is fed real-time data from temperature, humidity, occupancy and consumption sensors. This permits continuous comparison of actual performance against ISO 52016 model predictions, identification of performance gaps, and continuous adjustment of HVAC control algorithms. In the context of the EPBD, the digital twin can become the tool underpinning the renovation passport, providing a historical database of real building performance that complements the normative calculations. | Data centres represent a special case within HVAC thermal analysis, because their internal loads dominate over envelope loads and they operate at high power densities continuously. The Energy Efficiency Directive (EED, Directive 2023/1791/EU) imposes on data centres with an installed load exceeding 500 kW the obligation to report indicators such as PUE (Power Usage Effectiveness), WUE (Water Usage Effectiveness) and ERF (Energy Reuse Factor) to national authorities. According to the International Energy Agency (IEA), global data centre energy consumption stood at approximately 200 TWh in 2022, with projections indicating sustained growth driven by artificial intelligence and cloud computing. For these projects, thermal analysis must address residual heat management, evaluation of free-cooling strategies, and the possibility of heat recovery for tertiary uses, all within the framework of the EED. | The professional workflow recommended for projects subject to the EPBD and EN ISO 52016 comprises the following sequence. In Phase 1, data collection, the engineer gathers architectural drawings, material specifications, usage profiles and reference climate data conforming to EN ISO 15927-4 or to the climate datasets approved by the competent authority of the relevant Member State. In Phase 2, construction of the ISO 52016 model, thermal zones are defined, envelope properties assigned, solar factors calculated, and the model's coherence with the BIM model verified where available. In Phase 3, simulation and sensitivity analysis, the annual hourly calculation is executed, critical months and days are identified, and the sensitivity of demand to variations in insulation level, ventilation rate or the presence of shading devices is evaluated. In Phase 4, integration with HVAC system design, the hourly demand vector is combined with the design peak load calculation to size equipment and verify that the EPB rating meets the ZEB threshold defined by the Directive. In Phase 5, documentation and certification, all assumptions, input data and results are compiled in a format acceptable to the national certification authority, including the validation traces required by ISO 52016-2. This structured approach ensures that thermal modelling serves not only as a design tool but also as auditable regulatory evidence, consistent with the increasing legal weight that the EPBD and its transpositions in Member State legislation place on quantitative building energy performance analysis.