Cold Outdoor Research Articles

HEAT TRANSFER IN THE CHANNELS OF THE HEAT EXCHANGER INTENDED FOR THE RECOVERY VENTILATION SYSTEM OF THE ROOM

Air exchange, or ventilation, systems are created to ensure comfortable conditions in rooms in terms of temperature, humidity, and oxygen content in the air. In energy-efficient buildings, the organization of such a system should include energy-saving measures. Among such measures, it should be noted the use of a recuperative heat exchanger, which provides partial heating of the cold outdoor air from the warm air removed from the room in the winter. This paper examines the characteristics of the heat exchanger - recuperator, which is a system of coaxial cylindrical surfaces made of copper. That is, this heat exchanger is a system of annular channels of the "tube-in-tube" type. Technical characteristics are defined for this heat exchanger, which include: thermal power, that is, the amount of heat transferred in the heat exchanger from one heat carrier to another per unit of time; consumption of heat carriers; the temperature of the air removed from the room into the environment after the recuperator; the temperature of the outside air entering the room after the recuperator. The dependence of these characteristics on the number and sizes of annular channels in the heat exchanger and on the pressure drop between the inlet and outlet cross-sections of the channels is investigated. It was determined that the dependence of the degrees of heating and cooling of air flows in the heat exchanger channels on the pressure differences between the inlet and outlet cross sections of the channels are different for heat exchangers with different number of channels and different widths.

Experimental evaluations of Berkeley thermal sensation and comfort models in electric vehicle cabin under cold outdoor conditions

As the automobile industry is transitioning toward electric vehicles, manufacturers have started implementing local warmers alongside cabin heating, ventilation, and air conditioning (HVAC) systems for effective thermal comfort management. However, optimal operating strategies need to be developed for integrating local warmers with HVAC systems. Although the Berkeley models comprising local/overall thermal sensation and comfort models offer insights in this regard, they lack follow-up assessments for occupants transitioning from very cold states. In this study, Berkeley models were evaluated using two sets of experimental data collected in a transient vehicle cabin under cold outdoor conditions: test (A) with cabin HVAC alone and test (B) with both HVAC and local warmers. The findings confirm the satisfactory performances of the Berkeley models for predicting overall sensation and comfort, with a maximum root mean-squared error (RMSE) of 0.15. The local comfort model performed poorly with the original coefficients across both datasets (maximum RMSE of 1.96). Therefore, the model coefficients were regressed for the dataset from test A and validated against the dataset from test B to achieve a maximum RMSE of 0.49. With these regressed coefficients, it was observed that moving toward a neutral whole-body state diminished the potential to maximize local comfort. Conversely, the local sensation model showed poor agreement (maximum RMSE of 1.9); we confirmed that accurate adaptive setpoint temperatures are a prerequisite for ensuring good predictions from the model. These findings are expected to contribute toward future efforts in using Berkeley models to formulate effective local warmer–HVAC operational strategies in electric vehicles.

Enhancing frost-resistant and electrically conductive properties of bacterial cellulose-based IPN hydrogel wound dressings via photopolymerization: Towards epidermal sensor applications

Conventional wound dressings are limited in their application due to the difficulty of maintaining normal use in cold conditions and a lack of functionality. In this study, photopolymerization was employed to fabricate a wound dressing with the capacity to monitor vital signs in cold environments. Utilizing bacterial cellulose (BC) to form an Interpenetrating Network (IPN) structure, the dressing exhibits enhanced water retention and mechanical properties, with a notable increase in mechanical strength to 540.37 KPa. Moreover, it maintains excellent mechanical resilience and electrical conductivity (9.01 × 10−3 S/cm) even at temperatures as low as −20 ℃. Incorporation of positively charged quaternary ammonium salts imparts potent antibacterial properties to the hydrogel against Staphylococcus aureus and Escherichia coli by electrostatically adsorbing to and disrupting negatively charged bacterial cell membranes, resulting in the leakage of internal fluids. The efficacy of the hydrogel in promoting wound healing was validated through rat-infected wound models. Hematoxylin and eosin (H&E) staining confirmed a reduction in inflammation at the wound site, improved wound healing, and a marked increase in the wound healing rate. Moreover, the hydrogel has remarkable electrical conductivity (1.25 × 10−2 S/cm), enabling the detection of subtle signals (e.g., strain 0.25 %) crucial for emergency wound management to prevent infections. Of significant importance, these hydrogels can function as electrodes for monitoring electrocardiogram (ECG) signals and respiratory status, facilitating timely assessment of vital signs in casualties. This innovative hydrogel wound dressing holds promise for simultaneously monitoring human vital signs and treating wounds in cold outdoor settings, thus offering broad applications in the realms of wound management and dressing for cold outdoor sports.

Open-cycle thermochemical energy storage for building space heating: Practical system configurations and effective energy density

Salt-hydrate thermochemical materials (TCM) are promising candidates for energy storage systems for building space heating due to their high theoretical energy density and the need for low regeneration temperature. However, water vapor is required to drive the hydration process of the TCM reactor, which poses a challenge during winter when water vapor is typically scarce. Using indoor air directly lowers the building's humidity to an unconformable level in practice, while the cold outdoor air contains limited moisture. Here we consider different integration strategies for open-cycle TCM reactors in buildings and develop a model to simulate their thermal performance across diverse buildings and climates, specifically for building space heating. The potential energy densities and the levelized cost of storage of the TCM reactor are evaluated in practical scenarios to demonstrate the load-shifting potential of TCM systems for heating applications. We use a strontium chloride (SrCl2)-based composite as the baseline and explore the impact of various reactor and material changes to the energy density and levelized cost of storage.

Ventilation performance of induction displacement units in indoor spaces within cold regions

Efficient ventilation systems play a crucial role in reducing occupants' exposure to indoor contaminants, including particles potentially carrying viruses like SARS-CoV-2. Displacement ventilation systems have demonstrated their effectiveness in improving indoor air quality during cooling modes. However, traditional displacement ventilation systems often struggle to achieve satisfactory distribution of contaminant concentrations during heating modes. To address this issue, this study focused on enhancing the ventilation performance of a dual-coil displacement-induction unit. Through a combination of experimental measurements and computational fluid dynamic (CFD) techniques, the study examined airflow and contaminant concentration distributions in an environmental chamber conditioned by these units. The results demonstrated good agreement between measured and simulated data, validating the CFD model. Further evaluation in a 25-occupant classroom under cold outdoor conditions showed that the dual-coil unit could achieve satisfactory ventilation performance in heating modes with proper design, comparable to traditional displacement ventilation in cooling modes. Additionally, the unit's versatility allows it to accommodate a wide range of air conditioning applications, from heating to cooling, making it a promising solution for displacement ventilation in various environments.

Laser-induced carbonization strategy for designing efficient dual-layer solar wastewater evaporator

Solar water evaporation technology is of great significance in alleviating the problem of clean water shortage. However, interface evaporation materials are crucial for solar evaporator and are hindered by high costs, complex processes, and environmental issues. In this work, a simple, fast, and environmentally friendly laser-induced carbonization strategy was used to convert commercial polypropylene into porous carbon materials in a one-step process, and assembled with natural bamboo to form an efficient dual-layer evaporator. The residual carbon nanotubes catalyst in the carbonized products further enhance its evaporation performance. The water evaporation rate of the evaporator under one sun is 1.93 kg·m−2·h−1. In addition, the evaporator has an evaporation rate of 1.62 to 1.85 kg·m−2·h−1 for wastewater containing methylene blue, carmine, CuCl2 and FeCl3. This strategy not only overcomes the limitations of traditional polymer carbonization methods but also allows for size adjustment based on the quantity of bamboo, and has been successfully applied to wastewater evaporation experiments under cold outdoor weather conditions. The proposed strategy not only elucidates the carbonization mechanism of polymers under laser irradiation, but also provides a new approach for the field of solar water evaporation.

Understanding Outdoor Cold Stress and Thermal Perception of the Elderly in Severely Cold Climates: A Case Study in Harbin

This study collected data through microclimate monitoring, surface temperature measurements, and questionnaire surveys, and used indicators, such as the universal thermal climate index (UTCI), surface temperature (Ts), and wind chill temperature (tWC), to determine the thermal comfort threshold of the elderly in severely cold climates and evaluate their cold stress. The results indicated that (1) the neutral UTCI (NUTCI) for elderly individuals in winter was 13.3 °C, and the NUTCI range was from 1.4 to 25.2 °C; (2) the intensity of elderly individuals’ physical activity affected the magnitude of risk of whole-body cooling, with duration-limited exposures corresponding to 0.5, 3.3, and over 8 h for light, moderate, and vigorous activity levels, respectively; (3) the tWC in all four spaces was below −10 °C, potentially inducing discomfort or even frostbite in the elderly; (4) for a 10 s touch, the maximum Ts (−17.2 °C) of stone was lower than the numbness threshold (−15.0 °C), while that (−15.1 °C) of steel materials remained below the frostbite threshold (−13 °C), posing risks for the elderly during physical activity. This study’s results will provide valuable insights and theoretical references for the landscape design of urban park activity spaces for elderly individuals in cold climate regions.

Thermal comfort characteristics of a catalytic combustion heater under wind-chilled exposure

Heating in wind-chilled environments is a serious task. The catalytic combustion heater (CCH) provides more efficient and cleaner in combustion compared to conventional heaters with high pollutant emission and low energy utilization. In this paper, the heating ability of CCH on human body in a wind-chilled environment (apparent temperatures between −14.8 °C and 12.4 °C) was investigated by collecting skin temperature and subjective thermal evaluation data from 23 subjects. The impact of cold air on localized heating of body parts by CCH was clarified using decision trees and dimensionless correlation coefficients. A human-computer interaction regulation strategy was proposed to simultaneously satisfy the requirements of effective heating, low energy consumption, and low pollution. Finally, CCH and a commercial heater were compared in terms of heating effectiveness and energy consumption in a real outdoor environment. The results showed that CCH effectively solved the problem of excessive cold extremities, and the temperature difference between thoracoabdominal area and extremities was reduced by 57.5–87.9% to within 2 °C. In a strong convective environment, wind speed was the decisive factor (coefficient of 0.95), inducing 46% radiant heat loss. Inputting personnel subjective perception, dynamic environmental parameters, and pollutant thresholds to adjust the injected gas flow enabled intelligent control. In a real cold scenario, the CCH saved 65.9% of energy compared to a commercial heater when achieving the same heating effect. This study provides a reference for the application of catalytic combustion technology in cold outdoor heating and also provides an important theoretical basis for the construction of heating strategies for CCH.

Full-scale numerical simulation and experimental validation of the thermal environment under the heating mode in an air-conditioned room

The numerical simulation of the air flow of the room equipped with the crossflow fan air conditioners has been conducted a lot. However, the simulation of the air flow distribution under the heating mode has always been difficult to match the experimental data well, due to the fact that both the air temperature and the flow are affected by the buoyancy. In addition, very few full-scale simulations were conducted. To precisely predict the air flow and temperature distribution of the room with the crossflow fan air conditioner, a full-scale steady numerical simulation was conducted with the Computational Fluid Dynamics (CFD) package. The full-scale physical model was constructed strictly according to the real settings, including the detailed components of the air-conditioner, such as the crossflow fan and the heat exchangers. The Shear-Stress Transport (SST) k-ω turbulent model was selected to simulate the low Reynold flow near the inner surface of the room, and to simulate the high Reynold and transitional flow near the fan blades of the air-conditioner. The porous medium model was used to simulate the heat exchange fins in the air-conditioner. Furthermore, an experiment under the same condition was also conducted to verify the accuracy of the simulation. Results showed that the simulated supply air flow rate was 537.48 m3/h, producing a 4.97% deviation from the experiment result. Meanwhile, the upward movement of the supply air from the outlet of the air-conditioner was observed, leading to higher air temperatures in the upper region of the room. Furthermore, among all 210 measured temperature data points in the room, 149 data points had the deviation within ±5%, and 194 data points had the deviation within ±10%. 9 abnormal data points with greater deviation near the door were detected, which might be resulted from the outdoor cold air leakage through the crack between the door and the floor in the experiment. Conclusively, the full-scale numerical simulation in this study produced an accurate and reliable solution to predict the air temperature distribution in buildings, thus providing a potential method for the design or optimization of the air-conditioners.

Correction: Shao et al. Outdoor Cold Stress and Cold Risk for Children during Winter: A Study in China’s Severe Cold Regions. Buildings 2022, 12, 936

It is very unfortunate that there were mistakes in the original publication [...]

Indoor Environmental Quality, Pupils’ Health, and Academic Performance—A Literature Review

Classrooms have more students per square meter than other buildings such as offices, making them more crowded. In addition, children respire more than adults and are in contact with one another more often. For appropriate student comfort, wellbeing, and health, including reducing the risk of transferring communicable diseases (for example, COVID-19) in the school setting, adequate ventilation and thermal comfort is recommended, along with regular cleaning, especially of high-contact surfaces. However, this may lead to increased energy usage, especially in mechanically ventilated schools. While natural ventilation conserves energy, its usage may be limited in temperate regions, especially during the cold seasons, as more energy will be required for heating in order to achieve thermal comfort. In the tropics, natural ventilation alone may be insufficient for students’ thermal comfort due to the possibility of unconditioned warm or cold outdoor air entering the classroom environment. Additionally, natural ventilation is difficult to control, as there may be overventilation or underventilation due to the ventilation rate being dependent on the outdoor environmental condition such as windspeed. This current traditional literature review appraises previous indoor environmental quality (IEQ) literature on ventilation, thermal comfort, moisture and mold, and cleanliness in schools. Furthermore, a further review was performed on the effect of IEQ (indoor air quality and thermal comfort) on student health and academic outcomes in order to summarize existing knowledge that can help other researchers avoid research duplication and identify research gaps for future school IEQ studies.

Integrated asymmetric cellulose aerogel membrane with triple thermal insulation and unidirectional liquid penetration for personal thermal management

With the rapid development of personal thermal management, there is an urgent need for an advanced material that can effectively integrate various thermal functions to keep body warm and cope with the cold outdoor environment. Herein, a multifunctional cellulose based asymmetric modification aerogel membrane (ACAM) encompassing thermal insulation, thermal radiation reflection, solar adsorption, and directional perspiration has been fabricated via bottom-up assembling biomass sisal fibers and pulp fibers into cellulose aerogel membrane, followed by spin-coating ionic liquid modified graphene (IGNs) and silver nanowires (AgNWs) on both sides of the cellulose aerogel membrane, respectively. The results showed that the temperature on the IGNs side is 14.2 °C higher than that of the cotton cloth after 30 s of sunlight exposure. Compared with pure cellulose aerogel membrane, the AgNWs side of ACAM has lower infrared emissivity and higher infrared reflectivity, and the temperature is reduced by 3.2 °C in indoor environment. In addition, the ACAM has asymmetric wettability, which facilitates the transfer of sweat from the hydrophobic side to the hydrophilic side and perspiration penetration was achieved in 10.6 s to obtain the comfort of wearing. The ACAM also exhibits excellent breathability, easy preparation and controllable functional structures. This work may provide a new idea for heat management and dynamic moisture to ensure maximum comfort in very harsh environments.

Short-term association between outdoor temperature and the hydration-marker copeptin: a pooled analysis in five cohorts

Whereas outdoor temperature is linked to both mortality and hydration status, the hormone vasopressin, measured through the surrogate copeptin, is a marker of cardiometabolic risk and hydration. We recently showed that copeptin has a seasonal pattern with higher plasma concentration in winter. Here, we aimed to investigate the association between outdoor temperature and copeptin. Copeptin was analysed in fasting plasma from five cohorts in Malmö, Sweden (n=26,753, 49.7% men, age 18-86 years). We utilized a multivariable adjusted non-linear spline model with four knots to investigate the association between short-term temperature (24h mean apparent) and log copeptin z-score. We found a distinct non-linear association between temperature and log copeptin z-score, with both moderately low and high temperatures linked to higher copeptin concentration (p<0.0001). Between 0°C and nadir at the 75th temperature percentile (corresponding to 14.3°C), log copeptin decreased 0.13 z-scores (95% CI 0.096; 0.16), which also inversely corresponded to the increase in z-score log copeptin between the nadir and 21.3°C. The J-shaped association between short-term temperature and copeptin resembles the J-shaped association between temperature and mortality. Whereas the untangling of temperature from other seasonal effects on hydration warrants further study, moderately increased water intake constitutes a feasible intervention to lower vasopressin and might mitigate adverse health effects of both moderately cold and hot outdoor temperatures. Swedish Research Council, Å Wiberg, M Stephen, A Påhlsson, Crafoord and Swedish Heart-Lung Foundations, Swedish Society for Medical Research and Swedish Society of Medicine.

A waste textiles-based multilayer composite fabric with superior electromagnetic shielding, infrared stealth and flame retardance for military applications

The challenge of developing multifunctional military tent fabrics with low-cost, stable electromagnetic shielding and infrared stealth in complicated environments is enormous. Herein, a novel aluminium-flammability carbonized waste cotton-carbon felt (A-FCWCF) composite fabric consisting of hydrophobic flame-retardant fabric, carbonized waste cotton felt and carbon fiber felt was prepared via a simple yet low-cost stitching process. The resulting composite fabric was extensively investigated for its stability and applicability in a complicated environment. Due to the significant conductivity and impedance mismatches, the A-FCWCF composite fabric displayed exceptional EMI-shielding properties, plus an X-band EMI rating of 82.63 dB. Moreover, the A-FCWCF composite fabric presented excellent infrared stealth performance at room and extremely cold outdoor temperatures, owing to its high porosity and low emissivity. The functional finishing on the A-FCWCF composite fabric also made it stable flame retardate and hydrophobic. Furthermore, the EMI-shielding and infrared stealth performances of A-FCWCF composite fabric were almost unaffected even if subjected to environmental stability, mechanical properties and weather resistance tests, making it a promising candidate for tough natural environments. Overall, this low-cost and simple preparation strategy of multi-layer stitched multifunctional fabric can revolutionize the production of military materials, improving functionality even in the most complex environments.

Tri-Layered Bicomponent Microfilament Composite Fabric for Highly Efficient Cold Protection.

Functional thin fabric with highly efficient cold protection properties are attracting the great attention of long-term dressing in a cold environment. Herein, a tri-layered bicomponent microfilament composite fabric comprised of a hydrophobic layer of PET/PA@C6 F13 bicomponent microfilament webs, an adhesive layer of LPET/PET fibrous web, and a fluffy-soft layer of PET/Cellulous fibrous web is designed and also successfully been fabricated through a facile process of dipping, combined with thermal belt bonding. The prepared samples exhibit a large resistance to wetting of alcohol, a high hydrostatic pressure of 5530 Pa, and brilliant water slipping properties, owing to the presence of dense micropores ranging from 25.1 to 70.3µm, as well as to the smooth surface with an arithmetic mean deviation of surface roughness (Sa) ranging from 5.112 to 4.369µm. Besides, the prepared samples exhibited good water vapor permeability, and a tunable CLO value ranging from 0.569 to 0.920, in addition to the fact that it exhibited a very suitable working temperature range of -5°C to 15°C. Additionally, it also showed excellent clothing tailorability including high mechanical strength with a remarkably soft texture and lightweight foldability that suitable for cold outdoor clothing applications.

Individual Factors that Affect the Perceived Thermal Comfort Condition during Heating Seasons

This paper investigated the effect of individual differences and the type of heating system on the perceived thermal comfort condition, neutral temperature, and thermal sensitivity in cold outdoor air conditions. Three types of individual factors, such as gender, temperament, and thermal past experience, were studied and compared in this paper. According to the results, temperament and thermal past experience directly influenced the occupants’ thermal preference and indirectly influenced the thermal sensation by affecting their clothing level. However, the effect size of such variations was negligible. The type of heating system had the most significant impact on the neutral temperature, with a mean difference of 2.8°C. Individual factors did not have a direct impact on the neutral temperature. However, thermal sensitivity was influenced by an individual’s temperament. Occupants with a cold temperament were more sensitive to the variation in the running mean outdoor temperature (Trm) than those with a warm temperament. When the results were compared with the predictions by the adaptive thermal heat balance (ATHB) and the predicted mean vote (PMV) models, it indicated that if the control condition over the heating system became limited, there would be no (i.e., very low) behavioral, physiological, and psychological adaptation. However, by creating an opportunity to control the heating system, thermal adaptation could be reached at a lower temperature under cold outdoor air conditions.

東京都内の機械換気設備を有する小学校普通教室における新型コロナウイルス感染症対策としての環境調節が換気量および温熱環境へ及ぼした影響

Air temperature and CO2 concentration were measured in classrooms with ventilation system from April 2018 through March 2022. It is assumed that, under the COVID-19 circumstances, windows of the classrooms, where ventilation system was working, were basically kept open throughout a year. The average air temperature at foot level was 11°C during winter period because of cold outdoor air infiltration. The estimated ventilation rate tended to decrease during winter period. However, the estimated ventilation rate per person more than 30 m3/h was obtained in case of half number of pupils in the classroom with Hybrid-Flexible lesson for the whole day.

Research on indoor thermal comfort and energy consumption of zero energy wooden structure buildings in severe cold zone

Indoor thermal comfort level not only affects the indoor thermal environment but also affects building energy consumption. Generally speaking, the higher the thermal comfort of the building, the greater its energy consumption. Therefore, in severe cold zone with the most stringent thermal engineering standards in China, how to reduce building energy consumption while improving building thermal comfort is of great significant for the building in this region to achieve zero energy consumption. In order to achieve this research goal, this paper designs two kinds of wooden structure buildings with water-passing wall in severe cold zone. Through combination of simulation and scale model experiments, the performance of water-passing wall, thermal comfort performance of wooden structure building, and building energy consumption were studied. The research results indicate that the water-passing wall of the wooden structure building has good thermal stability and thermal insulation performance, which can isolate outdoor cold in winter. Moreover, due to the function of water-passing wall, the two kinds of wooden structure buildings have high thermal comfort levels throughout the year, with occupants feeling uncomfortable for no more than 6% of the year. It is compared with the energy consumption before the water supplying to the wall, the total energy consumption of the two kinds of wooden structure buildings were reduced by 44.3% and 46.2% respectively. Therefore, these two kinds of wooden structure building can pursue higher thermal comfort with lower energy consumption, it has high energy-saving benefits.

Performance of a Phase Change Material Battery in a Transparent Building

This research evaluates the performance of a Phase Change Material (PCM) battery integrated into the climate system of a new transparent meeting center. The main research questions are: a. “Can the performance of the battery be calculated?” and b. “Can the battery reduce the heating and cooling energy demand in a significant way?” The first question is answered in this document. In order to be able to answer the second question, especially the way the heat loading in winter should be improved, then more research is necessary. In addition to the thermal battery, which consists of Phase Change Material plates, the climate system has a cross-flow heat exchanger and a heat pump. The battery should play a central role in closing the thermal balance of the lightweight building, which can be loaded with hot return or cold outdoor air. The temperature of the battery plates is monitored by multi-sensors and simulated by the use of PHOENICS (Computational Fluid Dynamics) and MATLAB. This paper reports reasonable agreement between the numerical predictions and the measurements, with a maximum variance of 10%. The current coefficient of performance for heating and cooling is already high, more than 27. There is scope for increasing this much further by making use of the very low-pressure difference of the battery (below 25 Pascal), low pressure fans and the ventilation system as a whole.

중국 지린성 옌지시(吉林省延吉市) 조선족 고령자의 의생활 및 자각적 온열 감각

This study explores self-identified thermal perception and wearing habits of elderly Korean Chinese in Yanji city, Northeast China. Responses from a total of 193 participants were analyzed: 51 males and 142 females. Participants answered thirty-one questions concerning the following: wearing habits, thermoregulatory behavior, selfidentified cold tolerance, thermal perception, and heating conditions, etc. The results showed that the indoor temperature in Yanji was kept sufficiently warm during the heating period due to district heating, but a high percentage of respondents wore thermal underwear not only outdoors but also indoors. And only 14.7% of respondents said they were not vulnerable to cold (male 25.5%, female 10.8%, P = 0.022). Nevertheless, when asked what outdoor temperature they thought that it was cold in winter, they answered that the temperature was below -16.2 ± 8.2℃, which is very low. Interestingly, 76.6% answered that they preferred indoor temperature in winter above 24℃, which is relatively warm. 98.9% said they were supplied with district heating in the winter. Over many years, elderly Korean Chinese have adapted to both high indoor temperatures and harsh outdoor cold. Accordingly, it seems that their wintertime indoor and outdoor thermal perception have developed separately in winter.