Outdoor Temperature Difference Research Articles

Evaluating the Ventilation Performance of Single-Span Plastic Greenhouses with Continuous Screened Side Openings

Natural ventilation is the most cost-effective environmental control method for protected horticulture. To overcome the issues associated with high temperatures in greenhouses, analyzing their ventilation characteristics and maximizing their natural ventilation performance are essential. Therefore, in this study, the natural ventilation performance of arched single-span plastic greenhouses with screened side openings was empirically investigated. Three identical single-span plastic greenhouses were used in this study, each with different side-opening heights. Temperature and wind-speed data were collected, and the ventilation-volume flow rate was calculated considering both buoyancy and wind forces. The natural ventilation performance of the greenhouses was strongly and positively correlated with the ventilation-area ratio and outdoor wind speed. The ventilation rate increased linearly with an increase in the ventilation-area ratio and high outdoor wind speeds. However, the association between ventilation performance and indoor–outdoor temperature differences was not strong. When the ratios of ventilation areas in the greenhouse were changed to 0.08, 0.19, and 0.29, the average indoor–outdoor temperature differences were 14.0, 10.1, and 7.7 °C, respectively, and the ventilation rates were 0.0081, 0.0196, and 0.0315 m3 s−1 m−2, respectively. The proportion of wind in the total ventilation performance was high with a low ratio of ventilation openings and high outdoor wind speeds. However, the proportion of the buoyancy was high, with a high ratio of ventilation openings and a large indoor–outdoor temperature difference. Overall, this study provides foundational insights for optimizing the design and evaluation of ventilation openings in greenhouses, considering the outdoor wind speed.

Potential Regenerative Impact of Implementation of Cultural Vernacular Elements (Rowshan) in Jeddah, Saudi Arabia

The present study aims to explore rowshans as essential vernacular architectural elements in designing houses in very hot-dry climates such as Jeddah, Saudi Arabia, to determine their most significant effects on air movement, ventilation, and mitigating cooling loads. A comprehensive combination of building performance simulation and computational fluid dynamics (CFD) analysis was used to model a room with six different sizes of rectangular openings and quantify rowshans’ potential as passive elements in providing occupants with comfort and reducing energy use. Analysis of the passive element revealed the thermal performance and natural ventilation in single-family homes for the Jeddah climate, created by outdoor and indoor temperature, airspeed, and pressure differences in the room model, were improved, lowering sensation temperature for inhabitants’ comfort. The results highlight the beneficial effects of rowshans in lowering a house’s temperature during the daytime: from November to April, at noon, indoor air temperature (IAT) could reach a 15% to 22% reduction in the north orientation. The findings also show that rowshans with 5 × 5 cm opening grids can keep the air volume flow rate within an acceptable range and keep the room in the comfort zone range for 42.3% of hours annually, equal to 3704 h. An implication of these results is the possibility of establishing housing design criteria that can enhance efficiency and thermal comfort conditions, lower the cost of operations, provide occupants with satisfaction, and reduce emissions to regenerate the environment, leading to affordability and sustainability in the Jeddah region.

Research on heat pipe air-conditioner with soil heat exchanger for base station

The refrigeration system accounts for 40-60% of the total energy consumption of the base station, so an effective energy-saving technology is much needed. This paper proposes a heat pipe air-conditioner with an additional soil heat exchange unit. When the indoor and outdoor temperature difference is small, the indoor heat can be scattered to the soil to achieve energy-saving effect.

Experimental Study of a Pump-Driven Microchannel-Separated Heat Pipe System

The current situation of high energy consumption in data centers places high demands on the energy consumption and heat-dissipation efficiency of cooling technology. This article studies the steady-state flow and heat-transfer characteristics of a pump-driven separated heat pipe system from an experimental perspective. After designing and selecting the pump-driven microchannel-separated heat pipe system, an experimental platform is built to test the pump-driven microchannel-separated heat pipe system under variable operating conditions. It is found that the optimal filling rate range of the system is 75% to 95%, and the optimal condensing air volume is 4250 m3/h. The relationship between the circulating mass flow rate and the heat-transfer capacity of the heat pipe system is comprehensively influenced by the resistance of each section and the heat-transfer coefficient at the heat exchanger. When the indoor and outdoor temperature difference increases from 10 °C to 30 °C, the heat transfer increases by 261.5%, and the working medium of R410a has a better heat-transfer performance than R134A at outdoor temperatures ranging from 0 to 15 °C. The results contribute to the application of pump-assisted microchannel heat pipe systems in data center machines, which provide guidance for the application of cabinet-level thermal management.

Effect of the urban microenvironment on the indoor air temperature of the residential building stock in the Helsinki region

Due to climate change, there is an increased risk of apartment overheating. In Nordic countries, heatwaves have not been common in the past and hence apartments are not equipped with mechanical cooling systems, so wise urban design might be a solution. This study evaluated the influence of the urban microenvironment on residential building indoor air temperature via green view index (GVI), floor area ratio and distance from the sea. We analyzed a large dataset of over 2000 apartments in the Helsinki region during summers of 2018 and 2021, where severe heatwaves were presented, and combined it with the aforementioned parameters. In the method used, closely situated buildings were clustered into groups by the microenvironment parameters. The results showed consistent correlations between clustered groups and microenvironment parameters, where the best-performing group had an indoor air temperature of about 1 °C lower than the average during the summers and 0.7 °C lower during the severe heatwaves. Building groups with higher GVI demonstrated a greater ability to endure long heatwaves, where combined influence of other urban microenvironment factors was significantly reduced. A substantial influence of sea distance and floor area ratio was observed during short heatwaves in the middle and late summer. The indoor temperature difference of the groups was compared to the average outdoor temperature difference of group areas based on the Finnish Meteorological Institute HARMONIE-AROME weather model implemented with the SURFEX module. The results revealed a consistent correlation between predicted outdoor and indoor temperatures and their distribution of group-to-area differences.

Performance Study of Booster-Driven Hybrid Cooling Units for Free Cooling in Data Centers

In the data center, using ambient energy cooling technology can effectively reduce the average power use efficiency, and the heat pipe as an effective use of ambient energy device has attracted much attention. For the dynamic heat pipe, reducing the power consumption of the pump effectively is the key to improving the efficiency. In this paper, the rotary booster is selected as the gas phase booster device of the heat pipe unit, the standard unit of the rotary booster is improved, and three types of boosters are obtained, including two improved boosters and one standard unit. Comparative test studies are conducted on three different types of boosters, and the power of the booster shows a downward trend with the increase in indoor and outdoor temperature differences (outdoor temperature decreases). With the increase in indoor and outdoor temperature differences, the cooling capacity increases first and then decreases. When the indoor and outdoor temperature difference is greater than 20 °C, the suction pressure of the booster is greater than the saturated condensing pressure force under outdoor ambient temperature, and the work of the booster decreases. Among the three types of boosters, the medium pressure ratio booster energy efficiency ratio (EER) is the largest. After throttling the standard unit, results show that its cooling capacity unit increases, but the booster power also increases, and the EER is still smaller than that of the improved unit.

Building Energy Saving for Indoor Cooling and Heating: Mechanism and Comparison on Temperature Difference

Reducing the heat transfer temperature difference via reasonable indoor temperature determination and air conditioning system design is a confirmed building energy-saving approach for space cooling and heating. However, the energy-saving mechanism cannot be explained scientifically and comprehensively while maintaining the cognitive level of the heat transfer law. In this paper, based on the same climatic conditions and decreasing range of indoor and outdoor temperature difference, the yearly and monthly absolute energy-saving amount (ESA) and relative energy-saving ratio (ESR) are investigated and compared for cooling and heating, respectively, to reveal the energy-saving mechanism for cooling and heating from the microscopic perspective. Two new concepts, including ESA by temperature difference and behavioral ESA by measure itself, are defined. The yearly ESA for cooling or heating caused by the decreasing of temperature difference is composed of those two factors. For cooling, the contribution rate of the behavioral ESA at those moments within the decreasing range of the temperature difference can be up to 78%, while for heating is only 7%. This work can provide theoretical support for building energy system design optimization and method reference for energy-saving analysis of building air conditioning systems with temperature difference considerations for cooling and heating, respectively.

Estimation of Natural Ventilation Rates in an Office Room with 145 mm-Diameter Circular Openings Using the Occupant-Generated Tracer-Gas Method

Natural ventilation in a building is an effective way to achieve acceptable indoor air quality. Ventilation dilutes contaminants such as bioeffluents generated by occupants, substances emitted from building materials, and the water vapor generated by occupants’ activities. In a building that requires heating and cooling, adequate ventilation is crucial to minimize energy consumption while maintaining healthy indoor air quality. However, measuring the actual magnitude of the natural ventilation rate, including infiltration through the building envelope and airflow through the building openings, is not always feasible. Although international and national standards suggested the required ventilation rates to maintain acceptable indoor air quality in buildings, they did not offer action plans to achieve or evaluate those design ventilation rates in buildings in use. In this study, the occupant-generated carbon dioxide (CO2) tracer gas decay method was applied to estimate the ventilation rates in an office room in Seoul, South Korea, from summer to winter. Using the method, real-time ventilation rates can be calculated by monitoring indoor and outdoor CO2 concentrations without injecting a tracer gas. For natural ventilation in the test room, 145 mm-diameter circular openings on the fixed glass were used. As a result, first, the indoor CO2 concentrations were used as an indicator to evaluate how much the indoor air quality deteriorated when all the windows were closed in an occupied office room compared to the international standards for indoor air quality. Moreover, we found out that the estimated ventilation rates varied depending on various environmental conditions, even with the same openings for natural ventilation. Considering the indoor and outdoor temperature differences and outdoor wind speeds as the main factors influencing the ventilation rates, we analyzed how they affected the ventilation rates in the different seasons of South Korea. When the wind speeds were calm, less than 2 m/s, the temperature difference played as a factor that influenced the estimated ventilation rates. On the other hand, when the temperature differences were low, less than 3 °C, the wind speed was the primary factor. This study raises awareness about the risk of poor indoor air quality in office rooms that could lead to health problems or unpleasant working environments. This study presents an example of estimating the ventilation rates in an existing building. By using the presented method, the ventilation rate in an existing building can be simply estimated while using the building as usual, and appropriate ventilation strategies for the building can be determined to maintain the desired indoor air quality.

The mathematical model of kitchen smoke exhaust system in high-rise residential buildings considering the Influence of Stack effect

In high-rise buildings with large indoor and outdoor temperature difference, neglecting the effect of stack effect in smoke exhaust shafts may cause calculation error of the fluid network model. In this paper, the mathematical model of kitchen smoke exhaust system considering the influence of stack effect was put forward and it can be inserted different range hood sub-models. Compared with the results of six working conditions of the model without considering the stack effect, the error of the proposed model were reduced by 7.6%, 4.3%, 4.1%, 2.8%, 2.4%, and 2.1%. While the indoor and outdoor temperature difference varies from −5 °C to 49 °C, the effect of stack effect on the pressure in the flue and the flow rate for each user was studied for six operating rates s. The results show that under the combined effect of stack effect and flue resistance, the static pressure of the kitchen smoke exhaust system showed a low-high-low distribution, and the maximum static pressure in the flue moved toward the bottom with the increase of temperature difference. User flow rates exhibit a low-high-low-high distribution, with an increased flow rate in the bottom users and the largest flow rate in the top users.

Identification of Factors Determining Household PM2.5 Variations at Regional Scale and Their Implications for Pollution Mitigation.

Indoor PM2.5, particulate matter no more than 2.5 μm in aerodynamic equivalent diameter, has very high spatiotemporal variabilities; and exploring the key factors influencing the variabilities is critical for purifying air and protecting human health. Here, we conducted a longer-term field monitoring campaign using low-cost sensors and evaluated inter- and intra-household PM2.5 variations in rural areas where energy or stove stacking is common. Household PM2.5 varied largely across different homes but also within households. Using generalized linear models and dominance analysis, we estimated that outdoor PM2.5 explained 19% of the intrahousehold variation in indoor daily PM2.5, whereas factors like the outdoor temperature and indoor-outdoor temperature difference that was associated with energy use directly or indirectly, explained 26% of the temporal variation. Inter-household variation was lower than intrahousehold variation. The inter-household variation was strongly associated with distinct internal sources, with energy-use-associated factors explaining 35% of the variation. The statistical source apportionment model estimated that solid fuel burning for heating contributed an average of 31%-55% of PM2.5 annually, whereas the contribution of sources originating from the outdoors was ≤10%. By replacing raw biomass or coal with biomass pellets in gasifier burners for heating, indoor PM2.5 could be significantly reduced and indoor temperature substantially increased, providing thermal comforts in addition to improved air quality.

Analysis on construction technology of large steel structure building thermal insulation engineering

In order to solve the need of maintaining temperature in large steel structure buildings, the author proposes a method of applying new materials, this method is used to analyze the properties of exterior insulation materials for steel structure buildings. Combining with the need of heat preservation in large steel structure cold storage, the author puts forward a new construction technology and applies it into practice by combining autoclaved gas technology, the advantages and disadvantages of organic and inorganic materials on heat preservation effect are analyzed, through the value engineering formula of maximum efficiency analysis, the minimum life cycle cost, in the ideal place, time to play the necessary function of the product. Finally, the experimental samples adopted the author?s method are compared with the ordinary samples. The experimental results show that the absolute value of indoor and outdoor temperature difference under the construction process is significantly greater than that under the current construction process, the highest temperature reached 29.2? and the lowest was 25.6?. In conclusion, the method adopted by the author can greatly help the current construction technology and reduce the loss of enterprises.

Development of an automatic opening system for sliding and casement windows to control the natural ventilation rate

Under the influence of COVID-19, ventilation is recommended to reduce the risk of infection in the room. Window openings can increase the ventilation rate caused by indoor and outdoor temperature differences. However, there is a concern that opening the window in the air-conditioned room will increase the heating and cooling loads due to air leakage. In addition, it is difficult to maintain an adequate ventilation rate because the outdoor temperature changes from time to time. To solve this problem, we have developed an automatic opening system to control the natural ventilation rate. This system can control the adequate ventilation rate for the room by adjusting the opening area of the window automatically. In this study, the control equations for the system for sliding windows were derived, and actual measurements were taken with the system. Additionally, the flow coefficients of the casement windows were numerically analyzed. Then, the control equation for the system for casement windows was derived from the relationship between the opening angle and the flow coefficient. As a result, the ventilation rate could be controlled using an automatic opening system for the sliding windows. Also, the flow coefficient of the casement window could be approximated by a sinusoidal function of the opening angle.

Thermal performance and economy of PCM foamed cement walls for buildings in different climate zones

Using phase change material (PCM) into the building envelope is considered an effective thermal energy storage strategy to improve building thermal performance and reduce space heating/cooling loads. However, different phase transition temperatures and climatic conditions have a huge impact on application effect. This paper investigates the effects of walls containing PCM foamed cement on thermal performance and economy of single-story building in 5 different climate zones in China. The temperature, energy storage, energy consumption and the payback period for PCM foamed cement wall are analyzed by numerical simulation. The results indicate that the PCM foamed cement moderates the indoor and outdoor temperature differences in all 5 climate zones. Among which, Harbin (severe cold region) had the best increase in the south wall inner surface average temperature in January with an increase of 0.378 °C. The optimal phase transition temperature is close to the local annual average temperature except Harbin, and the energy saving rates are 20.17 % (Beijing), 15.87 % (Shenzhen), Shanghai(22.26 %), 37.02 % (Kunming). The shortest payback period is 5.95 years for the application of PCM foamed cement in Harbin, but in Kunming (mild region) at the current price, the investment cannot be recovered.

Numerical study on transient airflows and air exchange induced by door motion in thermally stratified environment

Door motion has been identified as a contribution factor for containment transport between indoor and outdoor, but the combined airflow characteristics due to door motion, ventilation airflow and thermal effects have not been clarified. This paper investigated transient airflow characteristics and amount of air exchange induced by hinged door motions in thermally stratified environment with displacement ventilation using dynamic CFD simulation. The results show that about 40% amount of air exchange occurs in the first phase when door angle β < 30° although the consumed time is only 15% of the whole door motion process. Indoor and outdoor air temperature difference and rotation speed of the hinged door are two important influencing factors. When the door motion is slow enough and temperature difference is above 3 °C, the thermal convective flow could significantly affect the airflow pattern through the doorway. When there is no indoor and outdoor temperature difference, the amount of air exchange increases linearly with door motion speed. Under combined effects of buoyancy force and door motion, a moderate door speed results in minimum air exchange. The door motion only affects the air temperatures near the door. The overall thermal stratification in the displacement ventilated room is not significantly destroyed by a single door open and close cycle. The findings could provide suggestions for reducing door motion induced contaminant transport, and enhance understanding of dynamic disturbance effects in thermally stratified environments.

Operation optimization of the coaxial deep borehole heat exchanger coupled with ground source heat pump for building heating

• The transient numerical model of the coaxial heat exchanger is established. • Operation optimization method for the heat pump system is developed. • The underground heat transfer model is validated using test data from literature. • The operation of the system before and after optimization is compared. Geothermal is considered to be one of the most promising renewable sources for district heating. Ground source heat pump systems coupled with the coaxial deep borehole heat exchanger have been widely applied because of their high efficiency. However, in order to reduce the total energy consumption of the system, there are few studies on the optimization of the water flow rates in the coaxial deep borehole heat exchanger by time to meet the load change during the heating season. In this paper, an optimization method for the two flow rates which are set at two time periods respectively every day in the coaxial deep borehole heat exchanger during the operation of the ground source heat pump system is proposed. The application of the method is to determine the applicable flow rates when the temperature of the next day is predicted. Space heating of a building (located in Tianjin, China) is taken as a scenario, comparisons were carried out on system operation before and after optimization, which shows that the method has a good effect on the energy-saving operation of the system. After optimization, the total power consumption of the system is reduced, the total performance coefficient of the equipment as well as the temperature difference between the inlet and outlet of the underground heat exchanger is increased, and the trend of flow rates changes with time is the same as the indoor and outdoor temperature difference.

Evaluating Indoor Carbon Dioxide Concentration and Ventilation Rate of Research Student Offices in Chinese Universities: A Case Study

This work provides a case study on the indoor environment and ventilation rate of naturally ventilated research student rooms in Chinese universities. In the measured room, air temperature, relative humidity and carbon dioxide (CO2) concentration were monitored during the heating period for 4 weeks. The number of indoor occupants, occupied time of the room and window/door-opening cases were simultaneously recorded. Results showed the research student room was occupied for an average of 12.0 h each day. Due to a large indoor and outdoor temperature difference during the heating season, and occupants’ adaption to indoor environment, indoor occupants seldom open windows/doors for ventilation. Air exchange of the room only by air infiltration cannot meet the ventilation requirement. As a result, an average of 77.6% of measured CO2 data each day exceeded 1000 ppm during occupied time. In fact, according to CO2 data, it was observed that window/door opening could effectively decrease indoor CO2 concentration. Therefore, intermittent window/door opening or CO2-based demand-controlled ventilation facilities were suggested for improving indoor air quality of such rooms. Additionally, special attention should be paid to other possible outdoor pollution.

Lab-scale reproduction test method for temperature-driven movement of through-thickness cracks in concrete exterior walls for crack repair evaluation

Crack repair is an important process for extending the service life of buildings. Crack movement is one of the factors that affect the durability of crack repair; however, there is no existing method to evaluate the repair under the influence of crack movement. To this end, this paper proposes a lab-scale crack movement reproduction test method to evaluate the effectiveness and durability of the repair. The movement of cracks penetrating the thickness of the concrete wall (through-thickness cracks) was monitored on both the indoor and outdoor sides. The results showed that the through-thickness cracks produced a bending-like movement with movement amplitudes of about 0.03 to 0.08 mm, driven by indoor and outdoor temperature differences; the resulting deterioration pattern in the repair area was a combined outcome of temperature and mechanical loading. The reproduction experimental method was established in reference to numerical simulation. Experimental results verified that the proposed test method satisfies the relationship between movement amplitude and the temperature difference, restraining force, and initial crack width in actual buildings. In addition, the method is stable, with a coefficient of variation of 7.73% in the movement amplitude for ten experimental groups. Furthermore, it was suggested that reducing the temperature gradient in the wall cross-section can reduce the deterioration caused by crack movement.

Thermal and energy performance of a user-responsive microalgae bioreactive façade for climate adaptability

As a recent trend in the energy-efficient architecture, microalgae bio-reactive façades can control buildings’ thermal loads by the responsiveness to solar radiations and adaptive variations in culture density. Although these smart systems can provide adaptable shading during the year, they cannot meet the varying thermal comfort needs of building users in a short time because the microalgae medium’s culture remains almost unchanged during the day. This paper reports on an innovative method that helps microalgae bioreactive façade respond to solar radiation and users’ thermal needs in a short time. To achieve it, a smart window panel will be introduced, which contains two remotely-controlled adjustable bioreactors which can regulate the algae medium in height based on the users’ thermal needs. This novel panel can serve as a bio-adaptable sunshade integrated with the building facade. Thus, the internal building thermal loads can be adjusted via the height of the bioreactor façade. Experimental and simulation research was conducted to compare the thermal performance of bioreactor facades at different microalgae medium height levels in the BSk climate zone. The results indicate that indoor and outdoor temperature differences for full, ¾, ½, and ¼ medium height level every 15-minute time interval are 12.55, 11.50, 10.87, and 6.53, respectively, indicating that the full-height level has the most influence to control the thermal load of the system. According to the results, the bioreactor façade with adjustable medium height greatly impacts building thermal control in a short time.

Evaluation of an automatic opening window system to maintain adequate ventilation rates

Under the influence of COVID-19, it is recommended to ventilate to reduce the risk of infection in the room. In an air-conditioned room, opening windows increase the ventilation rate that caused by indoor and outdoor temperature differences. However, there is a concern that opening windows in the air-conditioned room will increase the heating and cooling loads due to air leakage. In addition, it is difficult to maintain the adequate ventilation rate. To solve this problem, we developed an automatic window opening system to control the natural ventilation rate. This system can be controlling the adequate ventilation rate for the room by adjusting the opening area of window automatically. The purpose of this study is to confirm the effectiveness of this system and to understand its performance. In this study, analysis was done to calculate the adequate opening width in Japan, and actual measurements were conducted to understand the operating performance of this system. As a result, it was confirmed that sensible heat load due to ventilation was reduced with this system, and the ventilation rate could be controlled by this system.

Analysis on influencing factors and energy saving potential of photovoltaic curtain wall preheating fresh air system in severe cold area

In the general building air conditioning load, the fresh air load accounts for more than 30%, especially in the severe cold areas in the north, with long winter and large indoor and outdoor temperature difference, the fresh air heat load will account for a larger proportion in the air conditioning system load. Making full use of renewable energy can effectively reduce building energy consumption. In this paper, the air flow field distribution in the ventilation duct of photovoltaic curtain wall is numerically simulated by fluent simulation software, and the air distribution form and temperature field distribution in the system cavity under different ambient temperature, cavity thickness and tuyere position are analyzed and compared, so as to obtain the influence of different influencing factors on the performance of the fresh air preheating system, and combine the photovoltaic curtain wall preheating fresh air system and electric heating system to explore its energy-saving potential. The results show that when the cavity thickness is greater than 400mm, the reduction range of photovoltaic curtain wall temperature becomes smaller, and the overall temperature distribution of the cavity tends to be uniform. When the ambient temperature is different, with the increase of ambient temperature, after the fresh air passes through the photovoltaic curtain wall preheating system, the temperature difference at the inlet and outlet of the air flow channel decreases, and the maximum temperature difference decreases from 4.6k to 3.4K.The combination of photovoltaic curtain wall and electric heating is used to preheat the fresh air. Compared with the traditional method, the same fresh air load is treated, and the energy-saving rate is 60% ∼ 70%. It shows that using photovoltaic curtain wall to preheat the fresh air can achieve better results, which provides guidance for putting forward more appropriate, economic and energy-saving design schemes in the project.