Thermal Comfort, Environmental Quality, and Energy Consumption in the Built Environment

The built environment is a cornerstone of human well-being, influencing health, productivity, well-being, and a sustainable life [1,2,3,4]. As societies strive to mitigate climate change and enhance healthy living, the interplay between thermal comfort, environmental quality, and energy consumption has become a focal point for researchers and practitioners alike. This Special Issue of Energies brings together cutting-edge research that addresses these interconnected challenges, offers innovative solutions to optimize building performance, and highlights the need for prioritizing occupant needs.

1. The Interplay of Key Factors

The delicate balance between thermal comfort, environmental quality, and energy efficiency is a central theme in modern building design. However, achieving these goals often seems to conflict with the imperative to reduce energy consumption, particularly in the race towards a net-zero society and with tightening global sustainability targets.

Buildings account for approximately 40% of global energy consumption and contribute over 30% of CO2 emissions, with a significant proportion used for thermal comfort provision [5]. The high energy consumption of air conditioning systems is largely due to the uniform control of indoor temperature regardless of building location, despite evidence suggesting this rigidity is unnecessary for ensuring occupant comfort [6,7]. Substantial energy savings could be achieved by allowing for wider ranges of indoor temperature fluctuation while maintaining satisfactory comfort levels [4,6,8,9,10].

The papers in this Special Issue exemplify the multidisciplinary approaches required to navigate these challenges. The presented research highlights how technological innovation and holistic design can reconcile these competing priorities, from advanced ventilation systems to biophilic design and renewable energy integration.

2. Key Contributions from the Special Issue

2.1. Optimizing Ventilation for Energy Efficiency, Comfort, and Sustainable Cooling Solutions

The study “Testing Method for Non-Isothermal Radial Wall Jets from Ceiling Diffusers Used in Building Ventilation” [11] addresses a critical issue in variable air volume (VAV) systems: the risk of cold air dumping during low-flow conditions. The authors provide a framework for minimizing discomfort while maintaining energy efficiency by introducing a method to assess non-isothermal jet behavior.

Similarly, “Ventilation Methods for Improving Indoor Air Quality and Energy Efficiency in Multi-Family Buildings in Central Europe” [12] underscores the limitations of natural ventilation in retrofitted buildings. Simulation results emphasize the superior performance of mechanical ventilation systems, substantially improving indoor air quality (IAQ) while reducing heating energy requirements, an essential finding for Central Europe’s extensive stock of thermally retrofitted residential buildings.

Expanding the scope to outdoor thermal environments, the work “Cooling of Air in Outdoor Areas of Human Habitation” [13] explores evaporative cooling coupled with photovoltaic (PV) systems as a sustainable alternative to conventional compressor-based cooling systems for urban outdoor spaces. With solar energy meeting 81% of the cooling demand, this solution emerges as the most efficient and environmentally friendly solution. This approach not only mitigates urban heat island effects but also optimizes energy use through renewable resources.

Recent advances in outdoor evaporative cooling technologies have further demonstrated their effectiveness in hot climates, with systems capable of lowering the dry air temperature to 95% of the wet-bulb temperature [14]. Moreover, the development of modular and context-aware evaporative cooling systems for outdoor urban environments represents a promising approach to mitigating heat stress in public spaces while minimizing water consumption through intelligent control systems [15].

These studies emphasize the importance of implementing smart ventilation strategies that adapt to occupancy and climate conditions, as well as innovations aimed at addressing challenges posed by climate change. Considering the changing climate, the demand for comfort cooling is increasing, making the sustainable provision of such cooling one of the crucial challenges for the future built environment.

2.2. Innovative HVAC Control and Air Distribution Strategies

“Influence of Control Strategy on Heat Recovery Efficiency in a Single-Duct Periodic Ventilation Device” [16] demonstrates how simple sensor-based adjustments can improve heat recovery efficiency by over 10%. Balancing air supply and exhaust cycles significantly enhanced system efficiency and reliability under real-world conditions. This cost-effective decentralized solution shows promise for widespread implementation in existing residential buildings, aligning energy savings with indoor environmental quality.

The use of sensor-based adjustments presents a complementary step to model predictive control (MPC). MPC has emerged as a promising approach for optimizing HVAC system operation. MPC strategies can significantly reduce energy consumption while maintaining or improving occupant comfort through predictive algorithms that anticipate building needs based on weather forecasts, occupancy patterns, and thermal dynamics [17]. MPC implementation could yield energy savings of ~20%, though practical challenges remain in developing accurate predictive models and integrating these systems with existing building management systems [18].

“Innovative High-Induction Air Diffuser for Enhanced Air Mixing in Vehicles and Personalized Ventilation Applications” [19] introduces a diffuser that improves air entrainment by 48% compared to traditional diffusers, reducing temperature disparities in vehicle cabins. This technology enhances the thermal comfort of vehicle occupants and has broader applications for personalized ventilation [20] in offices and other enclosed spaces.

2.3. Biophilic Design and Occupant Well-Being

The integration of biophilic design elements has shown significant potential for improving occupant well-being [21]. The research “Effect of Indoor Green Walls on Environment Perception and Well-Being of Occupants in Office Buildings” [22] highlights the dual benefits of biophilic design: improving air humidity and occupants’ perception of the indoor environment while also enhancing psychological well-being. Green walls matched the performance of standalone humidifiers while fostering a more positive work environment. The findings reinforce the importance of nature-based solutions in sustainable building design and compliment similar findings carried out worldwide [23,24].

3. Towards Integrated Solutions

The diversity of research in this Special Issue is a testament to the cross-disciplinary impact of this issue. It also reflects the complexity of creating energy-efficient, comfortable, and healthy buildings. Several overarching themes emerge:

• Adaptability: Systems must respond dynamically to occupancy, climate, and user preferences and adaptability [5,25] (e.g., sensor-controlled ventilation, VAV adjustments).
• Renewables Integration: Solar energy and passive cooling strategies can decouple comfort from high energy consumption. Simultaneously, it is becoming imperative to incorporate circular economy principles like building repurposing and material reuse [26].
• Human-Centric Design: Occupant well-being should drive innovation, whether through biophilic elements or novel, personalized systems [27,28]. Context-specific and dynamic systems can be the future of indoor thermal comfort [29].
• Holistic Retrofitting: As shown in the multi-family building study, deep energy retrofits must prioritize the indoor environmental quality alongside the energy efficiency of the space [30]. This is also an important change introduced into the 2024 recast of the Energy Performance of Buildings Directive, EU [31].

4. Conclusions

This Special Issue underscores the transformative potential of interdisciplinary research in shaping the future of the built environment. By bridging the gap between energy efficiency and occupant-centric design, the featured papers provide actionable insights for architects, engineers, and policymakers. As the world transitions toward net-zero buildings, the lessons from these studies will be invaluable in creating spaces that are not only sustainable but also conducive to human health and productivity.

As part of the second edition of this Special Issue, we invite researchers to build upon these findings and continue exploring innovative approaches to harmonizing thermal comfort, environmental quality, and energy consumption in the built environment. For instance, the scalability of evaporative cooling in humid climates or the long-term maintenance of green walls warrants further exploration. Additionally, the integration of artificial intelligence for real-time system optimization presents an exciting frontier.