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Conventional air conditioning in buildings consumes substantial energy contributing to an increase in greenhouse gas emissions, which aggravates global warming. Kirigami envelopes with reflective surfaces offer a promising option to reduce indoor heat gain. So far none has performed outdoor testing of kirigami envelopes nor numerical simulation to understand how they interact with the environment. To understand the impact of the geometric design of the kirigami shading system on both daylighting and temperature variation in the indoor environment, a series of prototypes and simulations is devised to investigate the real‐time shading behavior in an outdoor environment. Large‐scaled and silver‐coated kirigami‐based envelopes of different cut patterns and stretching ratios are fabricated and placed in front of custom‐designed chambers equipped with six thermo‐sensors. Simulation is performed to investigate the effect of light modulation and hence temperature inside the chamber, which corroborates with the experiments. The indoor daylighting pattern and temperature are significantly influenced by the geometry of the stretched kirigami envelope, and overall, both the indoor temperature and the spatial distribution of illuminance are more uniform compared with that without the kirigami envelope. These results indicate that the installation of kirigami envelopes can improve building energy saving and occupants' comfort. [ABSTRACT FROM AUTHOR]

Much of human exposure to ozone takes place indoors. However, few studies have focused on human ozone exposures in normally occupied residential houses in the U.S. urban environments. Only rare studies have explored the implication of building envelope design variables on outdoor ozone penetration. Our study reveals the extent to which outdoor ozone penetrates and persists in the occupied houses in one of the most ozone-polluted cities, as influenced by building characteristics, building geometry, envelope design variables, window conditions and urban meteorology conditions. Through a set of analysis and variable regressions, we found that (1) the ratios of indoor to outdoor ozone concentration (I/O) were higher with windows open (0.700 ± 0.13) than with the windows closed (0.53 ± 0.22); (2) the indoor ozone concentration is typically elevated when the outdoor ozone concentration is high; and (3) design variables such as exterior envelope finishes, wall surface area and window-to-wall ratio are reasonably effective predictors. Our results of health risk evaluation suggest that the observed levels of indoor ozone exposure could pose a considerable risk to human health. Further work is needed to discover how building envelopes can be designed, constructed and maintained to support occupant health. [ABSTRACT FROM AUTHOR]

It is widely accepted that most people spend the majority of their lives indoors. Most individuals do not realize that while indoors, roughly half of heat exchange affecting their thermal comfort is in the form of thermal infrared radiation. We show that while researchers have been aware of its thermal comfort significance over the past century, systemic error has crept into the most common evaluation techniques, preventing adequate characterization of the radiant environment. Measuring and characterizing radiant heat transfer is a critical component of both building energy efficiency and occupant thermal comfort and productivity. Globe thermometers are typically used to measure mean radiant temperature (MRT), a commonly used metric for accounting for the radiant effects of an environment at a point in space. In this paper we extend previous field work to a controlled laboratory setting to (1) rigorously demonstrate that existing correction factors used in the American Society of Heating Ventilation and Air-conditioning Engineers (ASHRAE) Standard 55 or ISO7726 for using globe thermometers to quantify MRT are not sufficient; (2) develop a correction to improve the use of globe thermometers to address problems in the current standards; and (3) show that mean radiant temperature measured with ping-pong ball-sized globe thermometers is not reliable due to a stochastic convective bias. We also provide an analysis of the maximum precision of globe sensors themselves, a piece missing from the domain in contemporary literature. [ABSTRACT FROM AUTHOR]

We present results of a radiant cooling system that made the hot and humid tropical climate of Singapore feel cool and comfortable. Thermal radiation exchange between occupants and surfaces in the built environment can augment thermal comfort. The lack of widespread commercial adoption of radiant-cooling technologies is due to two widely held views: 1) The low temperature required for radiant cooling in humid environments will form condensation; and 2) cold surfaces will still cool adjacent air via convection, limiting overall radiant-cooling effectiveness. This work directly challenges these views and provides proof-ofconcept solutions examined for a transient thermal-comfort scenario. We constructed a demonstrative outdoor radiant-cooling pavilion in Singapore that used an infrared-transparent, lowdensity polyethylene membrane to provide radiant cooling at temperatures below the dew point. Test subjects who experienced the pavilion (n = 37) reported a "satisfactory" thermal sensation 79% of the time, despite experiencing 29.6 ± 0.9 °C air at 66.5 ± 5% relative humidity and with low air movement of 0.26 ± 0.18 ms1. Comfort was achieved with a coincident mean radiant temperature of 23.9 ± 0.8 °C, requiring a chilled water-supply temperature of 17.0 ± 1.8 °C. The pavilion operated successfully without any observed condensation on exposed surfaces, despite an observed dew-point temperature of 23.7 ± 0.7 °C. The coldest conditions observed without condensation used a chilled water-supply temperature 12.7 °C below the dew point, which resulted in a mean radiant temperature 3.6 °C below the dew point. [ABSTRACT FROM AUTHOR]

In this study, we enhance the understanding and design of a radiant cooling technology for outdoor comfort in tropical climates, originally proposed by R.N. Morse in 1963, in this journal. We investigate a type of radiant cooling methodology whereby the cold temperature source is physically separated from the outdoor environment by an insulated enclosure using a membrane transparent to infrared radiation. The enclosure isolates the radiant cooling surface from ambient conditions, allowing the radiant surface to be cooled significantly below ambient dew point temperatures without incurring condensation. For this new study, a Fourier Transform Infrared (FTIR) Spectroscopy analysis on three candidate membrane materials is undertaken and a prototype experimental test panel is fabricated. Our study shows that for a 5°C chilled panel temperature, the exterior membrane surface temperature reaches 26°C in a 32°C / 70% RH environment resulting in an effective mean radiant temperature of 15.8°C. These results provide new evidence in support of Morse's original proposal, that such panels could provide significant radiant cooling without condensation in humid environments. Radiant cooling products based on the studied technology may offer an ability to provide thermally comfortable conditions in hot environments without the energy required for dehumidification. [ABSTRACT FROM AUTHOR]

[Display omitted] • ASHRAE et al. recommends increasing indoor fresh air supply to mitigate COVID-19 spread. • Increased fresh air supply may double energy costs when operating a conventional HVAC system. • We propose an HVAC solution which couples novel radiant systems with natural ventilation. • We estimate this solution would address thermal comfort needs in all major climate zones. • Where adopted, this solution could reduce building HVAC energy demand by 10–45%. Radiant cooling-assisted natural ventilation is an innovative technical approach that combines new radiant cooling technology with natural ventilation to increase fresh air delivery into buildings year-round with minimal energy cost and improvment of air quality. Currently, the standard paradigm for HVAC (heating, ventilation and air conditioning) is based on central air systems that tie the delivery of heating and cooling to the delivery of fresh air. To prevent heat loss, the delivery of fresh air must be tightly controlled and is often limited through recirculation of already heated or cooled air. Buildings are designed with airtight envelopes, which do not allow for natural ventilation, and depend on energy-intensive central-air systems. As closed environments, buildings have become sites of rapid COVID-19 transmission. In this research, we demonstrate the energy cost of increasing outdoor air supply with standard systems per COVID-19 recommendations and introduce an alternative HVAC paradigm that maximizes the decoupling of ventilation and thermal control. We first consider a novel analysis of the energy costs of increasing the amount of conditioned fresh air using standard HVAC systems to address COVID-19 concerns. We then present an alternative that includes a novel membrane-assisted radiant system we have studied for cooling in humid climates, in place of an air conditioning system. The proposed system can work in conjunction with natural ventilation and thus decreases the risk of indoor spread of infectious diseases and significantly lowers energy consumption in buildings. Our results for modeling HVAC energy in different climates show that increasing outdoor air in standard systems can double cooling costs, while increasing natural ventilation with radiant systems can halve costs. More specifically, it is possible to add up to 100 days' worth of natural ventilation while saving energy when coupling natural ventilation and radiant systems. This combination decreases energy costs by 10–45% in 60 major cities globally, while increasing fresh air intake. [ABSTRACT FROM AUTHOR]

The indoor environment directly affects health and comfort as humans spend most of the day indoors. However, improperly controlled ventilation systems can expend unnecessary energy and increase health risks, while improved thermal and air quality can often result in higher energy consumption. One way to approach this dilemma is by understanding the effectiveness of the variables influencing indoor air quality (IAQ) related health and comfort. The objective of this paper is to highlight evidence and variables from empirical and deterministic models, which are combined in analytical models that current machine learning techniques often overlook. This paper reviews the analytical models and identifies the corresponding input variables, discussing their application in models based on artificial neural networks (ANNs) and reinforcement learning (RL). ANN and RL models have accurately described non-linear systems with uncertain dynamics and provided predictive and adaptive control strategies. The first part of this study focuses on the most common thermal comfort models and their variables, mainly related to steady-state and adaptive models. The second part reviews typical models of determining indoor air pollutants and their relationship with ventilation requirements and health effects. Forty-five works closely related to the field are summarized in multiple tables. The last part identifies the factors needed to predict thermal comfort and IAQ. • Analytical models and its variables of IAQ related thermal comfort are discussed. • Analytical models and its variables of IAQ related health are investigated. • ANNs have emerged as the most used technique to define building sensing systems. • RL is an efficient one for improving human-building interaction. • Improving thermal comfort and health while lessening energy use is feasible. [ABSTRACT FROM AUTHOR]

Mean radiant temperature is central to our understanding of the radiant heat exchange between the human body and surrounding environment. This paper will present a review of the concept's evolution including its qualitative definition, methods of quantitative evaluation and corresponding challenges. In the process, this review suggests that more effort needs to be invested in addressing the geometric complexities of radiant heat transfer in research into MRT; the ASHRAE definition is broad and is liable to simplification, and research which uses the definition relies on a variety of simplifications, often without acknowledging the degree of geometric complexity which exists in reality. Existing means of obtaining an estimate of mean radiant temperature range from direct measurements using globe thermometers or net radiometers, to computational simulations, and are widely used for studies within indoor and outdoor environments. Previous literature studying the correlation between air temperature and MRT has found equivalence ratios, the relative importance of convection to radiation, ranging from 0.71 to 1.4, however, it is often assumed to be 1.0 in current research practices. We also identified a rapid increase in the usage of MRT in biometeorological studies during the last ten years on top of the increased usage in indoor environment sensing and modeling in light of recent developments in heating and cooling systems. Recent efforts to include the short-wave component in indoor MRT characterization have shown an increase in cooling capacity of radiant floors from 32 to 110 W/m2; significantly decreasing peak energy demand. • We have expanded the conclusion section with both numerical conclusions and expanded discussions on the limitations of existing MRT usages. • Included new citations that covers the latest development of MRT research and standardization effort (ASHRAE Standard 55-2017, for example). • Adding new illustration of the MRT as a concept in relation to the human body geometry. • Expanded review on how indoor MRT variations due to shortwave radiation are characterized [ABSTRACT FROM AUTHOR]