Development of Indoor Environment Comfort

1. Introduction

Indoor environment quality significantly affects occupants’ health and wellbeing, particularly thermal comfort and indoor air quality. To provide thermal comfort and indoor air quality is a challenging task due to the complicated physiological and psychological mechanisms underlying the thermal comfort demand and the complicated contaminant sources causing indoor air quality concerns, as well as the complicated relationship between thermal comfort and indoor air quality and the temporal variations in the demands of thermal comfort and indoor air quality. Thus, more studies on the mechanisms underlying indoor environment demands of thermal comfort and indoor air quality, as well as technologies for indoor environment demand management, are urgently required to ensure thermal comfort and indoor air quality. Moreover, to ensure thermal comfort and indoor air quality, an energy source is required to handle the thermal load and the contaminant load, which accounts for a large amount of building energy consumption and building carbon emissions. Given the carbon emissions reduction goals in 2030 and 2060, energy-efficient technologies and renewable energy are urgently required to reduce the carbon emissions related to the provision of thermal comfort and indoor air quality.

This special issue presents recent advances in indoor environment comfort to energy-efficiently provide thermal comfort and indoor air quality. This special issue consists of nine papers, with one review article and eight research articles, which includes the advancements in improving thermal comfort (e.g., the dynamic ventilation with fluctuating air velocity) and indoor air quality (e.g., controls for indoor infection risk and allergies) and the advancements in energy sources for indoor environment quality (e.g., renewable energy including solar energy and geothermal energy and the phase change materials-based natural cold source). The studied indoor environments include the general indoor environment, the residential indoor environment, the commercial indoor environment, the indoor environment with computing clusters, and the application scenarios include both cooling and heating. The authors are diverse, addressing both the domestic and international research questions (e.g., the “Yin Summer-Heat” Perspective in Traditional Chinese Medicine and the dust mite- and mould-caused allergies in New Zealand), with scholars from universities (e.g., Southeast University and Xi’an Jiaotong University) and engineers from research institutes and enterprises (e.g., Key Laboratory of Coal Resources Exploration and Comprehensive Utilization and Qingdao Haier Air Conditioner Co., Ltd.).

2. Overview of Contributions

2.1. Contributions Related to Indoor Environment Quality

Contribution 1 [1] provides a method to interpret indoor thermal comfort demand and helps avoid the overcooling problem due to the conventional air-conditioning design based on average comfort zones, which innovatively applies the traditional Chinese medicine concept of “Yin Summer-Heat” (including the pathogenic factors, constitutions, and health preservation principles) to interpret diverse environment perceptions, demands, and adaptive behaviors. Contribution 2 [2] provides a technology to improve thermal comfort, which experimentally reveals that dynamic ventilation with fluctuating air velocity physiologically improves the cold stimulation to the cutaneous cold receptors with an enhanced cooling effect by enhancing the convective heat transfer, and psychologically improves thermal satisfaction with the lower draft rate because of thermal preference (i.e., thermal alliesthesia) towards dynamic airflows.

Contribution 3 [3] provides a tool to identify different indoor pathogen transmission routes for indoor infection risk control, which can accurately predict the temporal variation in the infection risks via air and surface routes by incorporating the transmission and degradation characteristics of aerosols and surface particles. Contribution 4 [4] quantifies the relationship between indoor thermal conditions for dust mites to thrive and for mould spores to germinate, and provides a guideline of indoor thermal environment control for preventing indoor allergies related to dust mites and mould.

2.2. Contributions Related to Energy Sources for Indoor Environment Quality

Contribution 5 [5] provides an optimization method of the selection of the refrigeration plant, which integrates optimized equipment selection at the design stage with empirical performance analysis based on actual operation and achieves an energy efficiency ratio up to 5.4 (exceeding the Grade I efficiency threshold stipulated by the Chinese standard T/CRAAS 1039-2023). Contribution 6 [6] reviews the advancements in CO₂ transcritical cycle technology in building indoor environmental regulation, which highlights the benefits of CO₂ as a natural refrigerant with zero ozone depletion potential and low global warming potential and also highlights the high efficiency of CO₂ transcritical cycle technology with proper design and control optimizations.

Contributions 7 and 8 provide renewable energy, i.e., solar energy [7] and geothermal energy [8], respectively, for indoor environment management. Contribution 7 [7] proposes a building-integrated heat pipe-embedded prefabricated wall panel for low-carbon building cooling and hot water production, which collects the solar thermal energy on the wall to generate hot water with a water gain efficiency of 16.7% and improves the cooling efficiency with a reduction of 76.1% in the heat gain of wall heat transmission. Contribution 8 [8] proposes a soil heat deficit regulation-based cross-seasonal heat storage method with a medium–deep borehole heat exchanger for building heating, which expands the soil heat deficit to enhance the geothermal heat flux recovery and heat storage efficiency simultaneously for improved heating performance with an improvement in the geothermal extraction capacity of up to 56%. Contribution 9 [9] proposes a hybrid cooling strategy integrating outdoor natural cold air (as a continuous heat sink) with phase change materials (for transient heat peak absorption) to cool down the computing clusters with high power density of each chip, which reliably keeps the chip temperature below the safety threshold and achieves an energy saving of 75%.

3. Outlook

The above introduction demonstrates the systematic contributions of this special issue to the low-carbon development of thermally comfortable and healthy indoor built environments. This special issue mainly concerns the indoor environment quality regarding thermal comfort and indoor air quality, while visual comfort and acoustic comfort interact with thermal comfort and indoor air quality and coordinately regulate the overall indoor environment quality. Future developments in indoor environment quality should pay more attention to the interactive relationships among the multiple aspects of indoor environment quality for the optimal regulation of overall indoor environment quality with the help of advancements in artificial intelligence.