Authors

Akshit Gupta (Researcher at Institute for Renewable Energy, Eurac Research)
LinkedIn profile

Francesco Babich (Senior Researcher at Institute for Renewable Energy, Eurac Research)
LinkedIn profile

(Note: opinions in the articles are of the authors only and do not necessarily reflect the opinion of the EU).

Introduction

Ventilation in buildings is crucial in creating a thermally comfortable indoor environment with acceptable indoor air quality (IAQ). For thermal comfort, ventilation has a direct impact on air temperature, relative humidity, and air velocity, while for IAQ ventilation affects the concentration of indoor air contaminants such as carbon dioxide (CO2), particulate matter (PM), and volatile organic compounds (VOCs). To ensure optimal conditions, it is vital to have reliable tools for predicting ventilation performance before constructing a building. While for smaller rooms it can often be reasonable to assume a well-mixed air (that means conditions in the room are uniform), larger spaces such as theatres, atriums or hotel lobbies require a more detailed understanding of the indoor parameters to assess the ventilation effectiveness, and thus the conditions experienced by people. 

This article provides an overview of methods used for predicting ventilation performance in buildings and discusses recent applications in European research projects and industries throughout Europe, to enhance indoor air quality, thermal comfort, energy efficiency, and overall building performance. This includes experimental, analytical, multizone network, zonal models, and Computational Fluid Dynamics (CFD) models, as explained below along with their industrial applications. 

- Analytical models: simplified conservation equations from fluid dynamics and heat transfer, case-specific approximations. The European construction industry often employs analytical models in the design phase of energy-efficient buildings. These models help architects and engineers to estimate airflow rates and indoor air quality in various building types. These models are valuable tools for HVAC system design and retrofitting projects. 

- Experimental models: economical, mimic real conditions with scaled parameters for similarity, used for data validation, and transitioning to numerical models. Industries, especially in healthcare and education sectors, use small-scale experimental models to test localized ventilation solutions. This approach allows for efficient testing and optimization of ventilation strategies in specific settings. European HVAC manufacturers and building operators often conduct full-scale experiments to validate the performance of ventilation systems. This practice ensures that newly installed systems meet design specifications and regulatory requirements. 

- Multizone models: assume uniform conditions in a zone, to predict airflow, air exchange, energy, and pollutants. See Figure 1. The European real estate and construction industry leverages multizone models to assess ventilation efficiency in large commercial buildings and residential complexes. These models aid in optimizing HVAC system operation for improved comfort and energy efficiency. 

- Zonal models: divide larger space into cells, to predict the distributions of air temperature, based on measured airflow patterns or mass and energy balance equations. Various industries in Europe, including pharmaceutical and manufacturing, employ zonal models to address non-uniform airflow conditions. Zonal models help ensure consistent indoor air quality and temperature in spaces with complex layouts. 

- CFD models: solve conservation equations and provide the spatial distribution of physical parameters. See Figure 2. In many building industry applications, CFD models are applied to optimize HVAC system design, evaluate natural ventilation strategies, and analyse indoor air quality, by simulating spatial attributes such as airflow, temperature, contaminants, and comfort parameters. 

​

Figure 1. Multizone network models. Credits: Francesca Avella.

​

Figure 2. CFD model. Credits: Akshit Gupta 

In recent studies, analytical and empirical models have made limited contributions to the literature. Small- and full-scale experimental models are mainly used for data validation, while multizone models are improving and are essential for predicting overall building ventilation. Zonal models have limited applications and may be replaced by coarse-grid fluid dynamics models. CFD models are the most popular and contribute significantly to the literature. They are primarily used for studying indoor air quality, natural ventilation, and stratified ventilation, which are challenging to predict using other methods. There is a growing trend of using full-scale experimental models for data validation and then employing validated computer models, particularly CFD, for predicting ventilation performance or designing ventilation systems in buildings. 

Overview of European policies/initiatives and industry applications

EU policies and directives recognise the importance of Indoor Environment Quality (IEQ) and ventilation in buildings to create healthier indoor environments, and the interconnection between building sustainability, energy performance and occupant health. Some initiatives and research projects in Europe are dedicated to the advancement of ventilation prediction methods in diverse sectors.: 

- The EU Renovation Wave Strategy:  focuses on how to increase the rate and depth of energy-related building renovations to enable the decarbonisation of the sector. It places a strong emphasis on tackling the worst performing buildings, addressing energy efficiency as well as comfort and IEQ.  
- Energy Efficiency Directive (EED): The EED sets out requirements for member states to improve energy efficiency, including in buildings. It indirectly impacts IEQ by encouraging measures that may involve ventilation system upgrades to reduce energy consumption while maintaining good indoor air quality. 
- Energy Performance of Buildings Directive (EPBD): The EPBD, at the time of writing (November 2023) under revision, aims to make sure that buildings in Europe are fit for the Green Deal climate ambition, and to reach the target of at least -60% emissions reduction by 2030 in the building sector. Among the main measures in the new proposal, is the gradual introduction in Member States of minimum energy performance standards, a new more ambitious standard for new buildings or provisions related to the modernisation of buildings, including ventilation. The proposed revision requires installation of measuring and control devices for the monitoring and regulation of IAQ in new buildings or existing buildings undergoing major renovations. 
- Several EU Funding programmes support or have supported the improvement of sustainability in the buildings sector, including indoor comfort and air quality. These are the Horizon Europe programme, the LIFE Programme, INTERREG Europe, COST (European Cooperation in Science and Technology), or the Erasmus+ Programme among others. initiatives also These programs, together with national funding programmes and initiatives, drive technological advancements in the field of ventilation and IAQ solutions. 
- City Initiatives: EU and national programs support City Initiatives, encompassing urban development, sustainability, and technology integration. Some initiatives, such as ‘Smart Cities’ and ‘Green City Accord’, focus on urban sustainability and promotes healthier, energy-efficient, and sustainable indoor environments within smart city infrastructure. These initiatives encourage cities to implement strategies for clean air, which can include improved ventilation and IAQ measures. 

European projects

Several European research and innovation projects have been promoting energy-efficient, smart, and healthy buildings. Below some of the European Commission-supported projects and actions.

Horizon Europe EDIAQI (official website EDIAQI) studies indoor air pollution in European cities, using short-term, high-intensity measurements and long-term, large-scale monitoring. The project will aim to understand the sources, routes of exposure, and health effects of indoor air pollution. Main results:

• Indoor Air Pollution (IAP) characterisation

• Data management tools and pollution monitoring

• Toxicological data

• Hybrid digital twin for modelling air pollution

H2020 Cultural-E (official website Cultural-E) aims to define modular and replicable solutions for Plus Energy Buildings (PEBs), accounting for climate and cultural differences, while engaging all key players involved in the building life cycle. Cultural-E is developing technologies and solution sets that are tailorable to specific contexts and energy demands, as well as performing a comprehensive optimisation of the value/cost ratio of Plus Energy Buildings. Main results are:

• Design tools, to provide an interactive map of the different European geo-clusters to shape a common basis for the development of technology solutions-set for different climates and cultural factors.

• Smart technologies such as the cloud-based House Management System, smart hybrid ventilation system, smart air movement system, and decentralized Packed Heat Pump system. 

• Methodologies, to help designers to maximize the solutions co-benefits according to the specific context.

• Policy recommendations, to accelerate the transition from nZEBs to Plus Energy Buildings.

EU FESR New-Air aimed to systemise companies and research institutions operating in the field of quality and control of the built environment in order to define new approaches and technologies that improve the healthiness of indoor environments and thermal comfort by reducing energy consumption. Main results are:

• New IEQ (Indoor Environmental Quality) monitoring system.

• Categorisation of the major indoor pollution sources, and dissemination at the provincial level.

• Development of a system for controlled natural ventilation.

• New machine and new strategies for residential mechanical ventilation (VMC).

• Control system capable of coordinating different systems and guiding the user: the residential "building management system" (BMS).

H2020 ReCO2ST (official website ReCO2ST) aims to better building & living. It applies an easy 3-step approach to building renovations, resulting in major savings and heightened standards of living, at a near-zero energy coefficient. Main results are:

• Cool Materials: Reflective surfaces reduce energy use and CO2 emissions.

• Cooling Evaporative Ventilated Facade: Ventilated facade with cooling evaporative effect for energy savings.

• Intelligent Energy Management System: Controls indoor air quality, energy, and comfort effectively.

• HVAC Systems: Innovative ventilation systems maximise comfort and energy efficiency.

• Nature-Based Technologies: Indoor air treatment with plant-based solutions for improved air quality.

• PV Integration: Solar systems designed for maximum efficiency and energy harvesting.

• Smart Windows: Renovation includes advanced windows for energy optimisation.

• Vacuum Insulation Panels: Ultra-thin insulation panels enhance energy efficiency.

H2020 Surefit (official website Surefit project) aims to demonstrate fast-track renovation (40% reduction in implementation time) of existing domestic buildings by integrating innovative, cost-effective, and environmentally conscious prefabricated technologies. The project is about to reach the target of near zero energy through reducing heat losses through the building envelope and energy consumption by heating, cooling, ventilation, and lighting, while increasing the share of renewable energy in buildings. Main results are:

• Fast track renovation of domestic buildings.

• Prefabricated technologies.

• Target on near zero energy buildings.

• Increase the share of renewable energy in buildings.

• Innovative technologies involving heating & cooling systems, hot water, lighting, power generation.

• Smart control systems.

• Demonstration in 5 buildings in different climates.

• Development of guidelines and operational tools.

• Innovative business models.

Conclusion

In today's context of increasing emphasis on energy efficiency, sustainability, and indoor environmental quality, European initiatives and research and innovation funding programs play a pivotal role in advancing ventilation prediction methods. These programs support innovation in different key methods of ventilation prediction, ranging from analytical models to CFD, fostering the development of smarter and more energy-efficient buildings. The importance of these efforts cannot be overstated, as they contribute to healthier indoor environments, reduced energy consumption, and lower carbon emissions, aligning with Europe's commitment to a greener future and improved well-being for its citizens. These endeavours empower researchers and industries to address the pressing challenges in building ventilation and shape a more sustainable tomorrow.