Inside Air Temperature Research Articles

From Laboratory to Field: The Effect of Controlling Oscillations in Temperature on the Growth of Crops

Crops are grown in natural conditions. Environmental factors such as temperature, humidity, and light irradiance have a regular pattern. A grower chamber is usually used to test the effect of environmental factors on the crops. If crops were cultivated under fixed environmental conditions, the results would be different from that for plants that are grown in a natural environment. Limits in the capability of an apparatus mean that most studies use a fixed temperature, a fixed relative humidity, or a fixed light intensity. In an accumulated temperature study, Pak choi and strawberry were used to compare the difference between fixed and oscillating temperature conditions in a growth chamber. There were three temperature patterns: the high-temperature (HVT) oscillation pattern (day: 22–32 °C; night: 19–25 °C), low-temperature (LVT) oscillation pattern (day: 21–29 °C; night: 19–23 °C), and the fixed temperature (CT) regime (day: 25 °C; night: 22 °C). The light intensity was 80 μmol∙m−2s−1. The environments used for the Pak choi experiments were the HVT oscillation pattern, the CT pattern, and the inside air temperature for a net house. The strawberries had three treatments: the HVT and LVT oscillation patterns, and the CT pattern. The fresh weight of total plants, the leaf area, the leaf number, and the chlorophyll content were measured for the two crops. For strawberries, the fresh weight of the leaves and the Brix value were measured. The experimental results show that there is a significant difference in the growth characteristics for these three regimes. The results of the growth characteristics of Pak choi and strawberry for an oscillating temperature are better than those for a fixed temperature environment with a statistically significant difference. For the biological and agricultural experiments, an oscillating temperature in the growth chamber realistically simulates a natural environment.

Optimizing the Power Usage of Anti-Sweat Heaters in Glass-Door Refrigerators According to the Dew Point

Putting glass doors on the display cases of refrigerators is one of the most efficient ways to reduce the energy consumption of supermarkets. However, the glass fogs up when opening the door because of the difference in air temperature inside and outside of the refrigerator, thereby obscuring the view. To defog the glass, anti-sweat heaters (ASHs) are used. In this paper, the power usage of ASHs according to changes in the dew point (DP) inside a supermarket were evaluated for two types of ASH, i.e., the door-frame ASH and the glass ASH. The evaluation was based on measurements of the condensation on the glass doors of vertical display cases, used for the preservation of frozen foodstuffs. A mathematical model of the correlation between the ASH’s power usage and the DP was developed and used for predicting the long-term energy savings. The savings were calculated based on the measured DPs inside the supermarket, which were extrapolated over a longer time period based on their correlation with the outside DPs. Regulating the door-frame ASH according to the DP resulted in an 84.6% reduction in energy consumption and a 90.1% reduction in the case of the glass ASH, compared to the current state. The correlation between the DPs inside and outside the supermarket served as a basis for the proposed implementation of the power usage regulation of the ASH according to the DP.

Evaluation of Typical Volatile Organic Compounds Levels in New Vehicles under Static and Driving Conditions.

In modern societies, the air quality in vehicles has received extensive attention because a lot of time is spent within the indoor air compartment of vehicles. In order to further understand the level of air quality under different conditions in new vehicles, the vehicle interior air quality (VIAQ) in new vehicles with three different brands was investigated under static and driving conditions, respectively. Air sampling and analysis are conducted under the requirement of HJ/T 400-2007. Static vehicle tests demonstrate that with the increasing of vehicle interior air temperature in sunshine conditions, a higher concentration and different types of volatile organic compounds (VOCs) release from the interior materials than that in the environment test chamber, including alkanes, alcohols, ketones, benzenes, alkenes, aldehydes, esters and naphthalene. Driving vehicle tests demonstrate that the concentration of VOCs and total VOCs (TVOC) inside vehicles exposed to high temperatures will be reduced to the same level as that in the environment test chamber after a period of driving. The air pollutants mainly include alkanes and aromatic hydrocarbons. However, the change trends of VOCs and TVOC vary under different conditions according to various kinds of factors, such as vehicle model, driving speed, air exchange rate, temperature, and types of substance with different boiling points inside the vehicles.

Investigation on the cooling performance of a buoyancy driven earth-air heat exchanger system and the impact on indoor thermal environment

The feasibility and cooling performance of a pure buoyancy-driven earth-air heat exchanger system (B-EAHE) with the assistance of combined effect of solar chimney and thermal mass were verified and revealed by a full-scale experimental study. The experimental results showed that the EAHE pipe diameter plays an important role in the system performance, and the airflow rates reach peak values of approximately 252 m3/h and 166 m3/h for the EAHE pipes with diameters of 0.3 m and 0.2 m, respectively. The air temperature differences between the inlet and outlet of the EAHE were approximately 12.5 °C and 13.0 °C in maximum, and 4.8 °C and 4.78 °C in average for the EAHE pipes with diameters of 0.2 and 0.3 m. In addition, the amplitude of indoor air temperature was further attenuated under the regulation of the B-EAHE system. The air temperature inside reference chamber varies from 28.3 to 35.1 °C, while the air temperature inside test chamber with 0.3 m diameter pipe ranges from 28.5 to 30 °C, which is approximately 2 °C lower than that for test chamber with 0.2 m diameter pipe. Moreover, higher energy saving potential is justified by the 0.3 m diameter pipe with peak cooling capacity of 1179 W compared with the 0.2 m diameter pipe with peak cooling capacity of 629 W. It is concluded that the B-EAHE system is able to achieve 24 h periodically fluctuating natural ventilation and passive cooling, and to improve the indoor thermal environment greatly in hot summer conditions.

Impact of environmental factors on energy balance of greenhouse for strawberry cultivation

This study elucidated the effects of passive solar greenhouses on strawberry cultivation in temperate areas. The energy required to heat the greenhouse was calculated. Furthermore, the results of a field test performed in a temperate area in central Japan were presented. Environmental conditions such as the ambient temperature, solar radiation, and relative humidity were experimentally investigated. The results of this study indicate that the maximum temperature difference between the inside and ambient air temperatures was 16.4 °C during the evaluation period. The maximum reduction in solar radiation through a transparent vinyl sheet in the greenhouse was approximately 30% when compared with the ambient solar radiation. Additionally, heating requirements were estimated to achieve optimal cultivation conditions in the future. The monthly heating requirement of the greenhouse was between 60.0 and 327.6 MJ/(m 2 ･month), and the energy requirement for heating was found to be maximum in the extremely cold month of January. The energy required for controlling the optimum environment for sensitive plant cultivation was proposed. The proposed evaluation methods can also be applied to other regions for cooling. • Effect of passive solar greenhouse on strawberry cultivation is investigated. • Field test is performed in a temperate area in central Japan. • Greenhouse provides thermal comfort for strawberry crop during winter. • Heat energy required for optimum cultivation in an area is estimated. • Validity of energy analysis proposed in this study is demonstrated.

The potential of facade greening in mitigating the effects of heatwaves in Central European cities

This study investigates the potential of living walls in improving the climatic quality in the urban environment. To achieve this goal, numerical simulations using the urban microclimate modelling tool ENVI-met were conducted to analyse the distribution of air temperature, mean radiant temperature (MRT), relative humidity, and wind speed in a residential block in Stuttgart, Germany. The impact of the living wall on the interior air temperature was investigated as well. Before the simulations were conducted, the model was first validated against measured data collected in Weimar, Germany. The validation showed a fairly good agreement between the measured and simulated air temperature, MRT, relative humidity, and wind speed with an averaged respective mean absolute error (MAE) of 0.72 K, 2.67 K, 3.98%, and 0.30 m/s. The simulation of the residential area in Stuttgart indicated that facade greening has only a little impact on air temperature (−0.57 K). Yet, a reduced MRT by up to 3.04 K and a reduced interior air temperature by up to 3.8 K were observed. The living wall also had an impact on the relative humidity among the buildings, which was increased by a maximum of 5.07%. Only a marginal impact on airflow between buildings was observed when facade greening was implemented. Yet, air velocity directly in front of the foliage was reduced by an average of 0.25 m/s.

Developing an insulation box with automatic temperature control for PM2.5 measurements in cold regions

Low-cost PM2.5 sensors are now used worldwide to assess air pollution. However, their operation is generally challenging in severely cold regions like Siberia, Alaska, the Arctic, and Antarctica. We made an insulation box with automatic internal temperature control developed for a low-cost PM2.5 sensor to maintain a warm operational environment with four light-bulb heaters when the air temperature inside of the insulation box falls slightly below 5 °C under the current preset temperature setting. We confirmed the performance of the temperature controller with four light-bulb heaters in a −25 °C cold temperature room. In addition, we found that the insulation box must be attached to a small electric fan to forcibly ventilate the box to accurately reflect the external ambient air conditions into the insulating box. Our observations with the data from our low-cost PM2.5 sensor fitted with the insulation box were validated against the Sapporo National Ambient Air Monitoring Station (NAAMS) data in Sapporo, Japan, showing good correspondence with the hourly station-measured data. Then, we installed our PM2.5 measurement system on the roof of the International Arctic Research Center (IARC), University of Alaska Fairbanks, Alaska, USA, in June 2019. The sensor sufficiently captured two instances of significant increases in PM2.5 mass concentrations during the Alaskan wildfires in the summer of 2019. Our developed insulation box for low-cost PM2.5 sensors, called “the portable PM2.5 measurement system for cold regions”, will help assess air quality in many cold regions in future studies.

Feasibility of winter cultivation of fruit vegetables in a solar greenhouse in temperate zone; experimental and numerical study

Feasibility of winter-cultivation of fruit vegetables was studied in a solar double plastic covered greenhouse in a temperate zone. An experment for 24-hour-course including a cold night was performed and an unsteady numerical model was developed to predict microclimate in the greenhouse. Sensible heat term with separated air and leaf temperatures was applied to energy equation. Modeling of plant transpiration and outside boundary conditions were accomplished by applying a user defined function added to FLUENT. Comparisons between measured and simulated air/leaf temperatures showed a good agreement for the 24-hour-course. Simulations were performed to examine the feasibility of ensuring the inside air temperature higher than 12 ℃ (the lowest temperature limit for fruit vegetables) in inner greenhouse during the coldest winter night. When covering both the outer and inner films with quilts, it could overcome the night with the lowest outside air temperature of −18.6 ℃. A necessity of heat shield for north wall outside surface was confirmed. Results show that the double plastic covered greenhouse can be a good passive solar system for winter-cultivating the fruit vegetables in some temperate zones.

Energetic and economic analysis for improving greenhouse energy efficiency

Protected agriculture is one of the prominent agricultural techniques. It allows for creating an adapted microclimate to the plant growth, which leads to high quality and off-season production. Instead, a significant amount of energy is required. This study aims to provide the potential of energy saving based on the optimal selection of the greenhouse design under Fez City’s climatic conditions (Morocco). For this purpose, a dynamic model of a gothic-arch-shaped greenhouse is created in EnergyPlus environment. The impact of four different orientations (0°, 90°, 45° and - 45°) on greenhouse energy needs is first investigated. The selected design is further improved by using a thermal insulation blankets system operating during the coldest months and deploying from the sunset to sunrise. To define the prospect of the energy saving, two variables were primarily evaluated: the greenhouse inside air temperature variation and thermal loads prompted by creating the optimum microclimate for tomato plant. Finally, an economic analysis is performed. The results show that 0° relative north (longer axis) is the optimal orientation for a gothic-arch greenhouse and that the thermal insulation blankets allow for reducing 17 % of the greenhouse heating needs under the climate conditions of Fez

Spatial-temporal pattern in the cooling effect of a large urban forest and the factors driving it

This study evaluated the cooling effect of the 30.07 km2 Purple Mountain Forest (PMF) in Nanjing City, China. Data from fixed and mobile measurements of air temperature inside and outside of the PMF over 37 days were used to conduct a holistic analysis of spatial/temporal patterns in the cooling effect of forest and the factors driving this variation. The forest exhibited a maximum cooling effect of 8.4 °C throughout the study period. The average daytime cooling intensity was 4.1 °C in the central undeveloped area, decreased to 1.8 °C at the highly developed tourism zone, and further to 1.3 °C at the boundary zone and 0.3 °C in the outside built-up area. Cool air could extend 267 and 883 m into nearby built-up areas along two roads radiating from the forest boundary. The cooling intensity could increase by 1 °C for every 950 m reduction in distance to the central area, every 95 m increase in altitude, or for every 0.8 increase in leaf area index. Cooling was more pronounced in the nighttime than in the daytime and on sunny days than on cloudy and rainy days. Solar radiation and relative humidity were key factors affecting the cooling intensity. Rainfall could considerably increase the cooling intensity of subsequent sunny days at the tourism and boundary zones of the forest. The results of this research enhance our understanding of the cooling effect of large urban forests. Our results also have implications for urban planning and forest management in the context of global warming.

Thermal transmittance prediction based on the application of artificial neural networks on heat flux method results

Deep energy renovation of building stock came more into focus in the European Union due to energy efficiency related directives. Many buildings that must undergo deep energy renovation are old and may lack design/renovation documentation, or possible degradation of materials might have occurred in building elements over time. Thermal transmittance (i.e. U-value) is one of the most important parameters for determining the transmission heat losses through building envelope elements. It depends on the thickness and thermal properties of all the materials that form a building element. In-situ U-value can be determined by ISO 9869-1 standard (Heat Flux Method - HFM). Still, measurement duration is one of the reasons why HFM is not widely used in field testing before the renovation design process commences. This paper analyzes the possibility of reducing the measurement time by conducting parallel measurements with one heat-flux sensor. This parallelization could be achieved by applying a specific class of the Artificial Neural Network (ANN) on HFM results to predict unknown heat flux based on collected interior and exterior air temperatures. After the satisfying prediction is achieved, HFM sensor can be relocated to another measuring location. Paper shows a comparison of four ANN cases applied to HFM results for a measurement held on one multi-layer wall – multilayer perceptron with three neurons in one hidden layer, long short-term memory with 100 units, gated recurrent unit with 100 units and combination of 50 long short-term memory units and 50 gated recurrent units. The analysis gave promising results in term of predicting the heat flux rate based on the two input temperatures. Additional analysis on another wall showed possible limitations of the method that serves as a direction for further research on this topic.

Comparison of thermal response times of historical and modern building wall materials

The study aims to identify the main reason of the thermal response time difference between historical and modern buildings. Therefore, in this study, the thermal response time of historical and modern wall structures and its effect on the interior air temperature change was investigated parametrically. Considering the environmental conditions of Kocaeli province, Turkey, the thermal response time of a historical building wall made of a cut stone was compared with those of brick and gas concrete wall structures having the same overall heat transfer coefficient using the second-order lumped capacitance approach. The insulation thicknesses of the three different construction materials for U-values of 0.6, 0.4 and 0.2 W/m2K were calculated and temperature variations of indoor environment, wall and insulation material were analyzed. In addition, the required thicknesses of insulation material to obtain the same heat transfer coefficients were determined in case of using the 0.1 m thickness of cut stone, brick and gas concrete structure materials. The maximum and minimum amplitudes of the inside air temperature were recorded as 0.59 and 0.18oC for the aerated concrete in Case 3 and for the cut stone in Case 2, respectively. As a result, the walls with high thermal inertia are less affected by the changes in the environmental temperature although their U-value is relatively high. For this reason, it can be stated that one of the reasons why historical buildings have thick walls is to increase thermal inertia and thereby improve thermal comfort by reducing energy loss.

Passive window ventilation openings in every-day use

The integration of passive window ventilation openings (PWVO, small air inlets integrated in the window frame) with additional exhaust fans in the kitchen and bathroom(s) can ensure a user-independent basic air change rate in dwellings. The project reported on herein is focused on how well buildings with PWVO work in real life. Altogether 28 multi-family houses are investigated by site visits, a survey among the inhabitants and measurements in eight flats. The survey is conducted in the winter 2017/18 and addresses user ventilation behavior, thermal and acoustic comfort, IAQ and user satisfaction. The 270 completed questionnaires returned allow tentative inferences for future ventilation concepts. For instance, it is found that in dwellings heated with radiators, air draught caused by PWVO is reported less frequently then in dwellings with a floor heating. The measurements in the winter 2018/19 are twofold: short-term measurements with a focus on the volume flow rates, the airtightness and the relative pressures in the flats. Long-term measurements comprise CO2 concentrations, interior and exterior air temperatures and humidities and operation modes of the extract fans. In six out of eight flats the measured outdoor air flow rate covers only 35–80 % of the amount recommended by the Swiss building standards. The airtightness of all flats varies between qa50-values of 0.5 and 1.3 m3/(h m2) (±10 %). CO2 measurements show that in the sleeping rooms the mean is between 650 and 3′440 (±70–160) ppm.

Experimental and Computational Model for a Neonatal Incubator with Thermoelectric Conditioning System

This work describes the design, construction and testing of a thermo-electric conditioning device installed in a neonatal incubator with the aim of improving the precision in the regulation of the interior air temperature, reducing noise and interior vibration, and improving the life of the neonate. A simplified one-dimensional thermal model has been developed, made up of resistances and thermal capacities that simulate the thermal behaviour of all the elements of the system from end to end. All the equations of the model are obtained in a nodal way, allowing the mathematical relationship between the input and output to be known. This model makes it possible to improve temperature control, avoiding the deviations that occur in the traditional model controlled by sensors at both ends. The computational model allows to predict the variation of temperatures in transient and permanent regime. This model allows the design and sizing of the thermoelectric system for different outdoor environmental conditions and the selection of the number of Peltier modules needed to satisfy the heating demand of other incubators with different geometry and capacity. The results of the computational model show good agreement with the experimental tests, despite being a simplified 1D nodal model. The results obtained show a coefficient of operation (COP) of 1.38, achieving higher performance than the current traditional electrical resistance system (COP = 1). In addition, a CFD study has been carried out to check the air patterns, to see the temperature uniformity and to estimate the number of air changes per hour (HVAC) inside the incubator.

Experimental and CFD Investigation of a Modified Uneven-Span Greenhouse Solar Dryer in No-Load Conditions under Natural Convection Mode

An uneven-span modified greenhouse dryer was constructed and tested in no-load conditions under natural convection mode under the weather conditions of Marrakech, Morocco, for two distinct days. Moreover, a CFD evaluation of the uneven-span greenhouse dryer was performed as tool to visualize the air temperature distribution inside the dryer. For validating the CFD model, the temperature variations along the hours of the day were compared to the experimental results. A good agreement is obtained between the computed and measured inside air temperature with a difference not exceeding 8.46°C, with a correlation coefficient ( r ) and root mean square percentage deviations ( e ) 0.94 and 8.17, respectively. Furthermore, the maximum inside air temperature was measured to be 56°C and 52°C while the minimum inside relative humidity was measured to be 17% and 12%, for day-1 and day-2, respectively. The benefice of using asphalt as a floor covering material was revealed as an efficient way to heat the inside air at low solar radiations. The performances of the dryer were evaluated by the percentage of net heat gain variation as a way to validate the effectiveness of the dryer. This latter is found to be equal to 46% and 48% for the two days, respectively.

Controlling radiative heat flows in interior spaces to improve heating and cooling efficiency

SummaryHeating and cooling in buildings account for nearly 20% of energy use globally. The goal of heating and cooling systems is to maintain the thermal comfort of a building's human occupants, typically by keeping the interior air temperature at a setpoint. However, if one could maintain the occupant's thermal comfort while changing the setpoint, large energy savings are possible. Here we propose a mechanism to achieve these savings by dynamically tuning the thermal emissivity of interior building surfaces, thereby decoupling the mean radiant temperature from actual temperatures of interior surfaces. We show that, in cold weather, setting the emissivity of interior surfaces to a low value (0.1) can decrease the setpoint as much as 6.5°C from a baseline of 23°C. Conversely, in warm weather, low-emissivity interior surfaces result in a 4.5°C cooling setpoint decrease relative to high emissivity (0.9) surfaces, highlighting the need for tunable emissivity for maximal year-round efficiency.

Construction and Evaluation of Transfer Function of Marginal Soil Temperature on the South Side of Greenhouse under Different Linings

The marginal soil temperature on the south side of a greenhouse remains at low temperatures in winter for long periods, which affects crop growth and land-use efficiency, it is of great significance to grasp the influencing factors of soil temperature change to improve the marginal soil temperature on the south side of the greenhouse. This study was conducted in at typical greenhouse in the cold and arid area of northern China and used the Grey Relational Analysis (GRA) method, the relational degree between the marginal soil temperature on the south side of the greenhouse and environmental factors under different lining structures was analyzed, and established the soil temperature transfer function. The results show that soil temperature had the greatest correlation with the soil humidity and air humidity inside and outside the greenhouse, and the second greatest correlation was the relation with the air temperature inside and outside the greenhouse and the outdoor soil temperature; the lining structure could effectively reduce the relation between soil temperature and humidity inside and outside the greenhouse. Polystyrene extruded board (PEB) had a greater degree of relational reduction than other lining materials in the test. Through verification analysis, the mean absolute error of soil temperature of 5 cm was less than 0.85 °C, the average absolute error of soil temperature at 15 cm was less than 0.57 °C, and the average absolute error of soil temperature at 25 and 55 cm was less than 0.2 °C. In conclusion, the constructed soil temperature transfer function could be used to predict the variation trend of soil temperature, and the PEB material lining structure had good thermal insulation.

CFD Study of Airflow and Microclimate Patterns Inside a Multispan Greenhouse

Understanding and improving greenhouses requires the analysis and modelling of energy and mass exchange phenomena. The mastery of all these physical mechanisms can make it possible to propose technological solutions to control the greenhouse climate. This study presents an analysis and simulation of air flow, temperature and humidity patterns ,in ½-ha multi-span greenhouse with oblique side walls,covered by insect proof nets.The site is located in the coastal area of southern Morocco. The fundamental calculation of climatic conditions is based on CFD, wich uses the mass, momentum and energy conservation equations. The dynamic influence of the insect screens and tomato crop on airflow movement, was described ,using the concept of the porous medium approach proposed by Darcy and Forchheimer.The coupling of convective and radiative exchanges at the plastic roof cover is considered. A good agreement was observed between the measured and simulated values for inside air temperatures and relative humidity. Insect screens significantly reduced airflow and increased thermal gradients inside the greenhouse. The results clearly showed the heterogeneity of the greenhouse’s internal climate, which infects agricultural production in quantity and quality

CFD Comparative Study Between Different Forms of Solar Greenhouses and Orientation Effect

Only scarce studies that were adopted have considered two properties, the structure safety and energy, where the aero-dynamic and energetic phenomena were taken into account simultaneously in the agricultural greenhouses area. In fact, in this numerical study, the response of the greenhouse has been investigated in outside climate conditions, by considering the orientation relatively to the wind direction velocity and solar trajectory. A resolution of the physical problem combined between the thermal and dynamical fluid flow equations have been based on the Ansys Fluent software. The results showed that the difference between inside and outside air temperature of greenhouse has been strongly affected by the reorientation of the tunnel greenhouse structure, or by the design of the tunnel structure that was adopted in the dome and chapel shape. Moreover, the safety properties of greenhouse structure linked to the drag stress can be developed when based on the interaction fluid-structure analysis. In this view, a temperature profile evolution versus different heights inside greenhouse was highlighted. As well as like continues of our previous study of the drag evolution over tunnel design body proved by the results found in the literature will be compared with chapel and dome designs.

The Effect of Diffuse Film Covers on Microclimate and Growth and Production of Tomato (Solanum lycopersicum L.) in a Mediterranean Greenhouse

The efficient use of light is one of the most important factors for the development of greenhouse crops. It is increasingly necessary to use film covers that enhance transmittance and the proportion of diffuse light to generate a more homogeneous light distribution. The objective of this study was to evaluate the effect that an experimental film cover with high transmittance and high light diffusivity produces on the microclimate and the growth and yield of tomato crops (Solanum lycopersicum L.), compared with a commercial thermal film cover. The trial was developed during a spring–summer growing cycle in a multispan greenhouse divided into two compartments (sectors) separated by a vertical polyethylene sheet. In the East sector, a commercial film was installed (transmittance of 85% and diffusivity of 60%) and in the West sector, an experimental film was used (transmittance of 90% and diffusivity of 55%). The results show an increase in the marketable yield of 0.25 kg·m−2 in the sector with the experimental film, which represents 3.2% growth with respect to the commercial film. The photosynthetic activity measured in tomato leaves was 21.5% higher in plants growing in the sector with the experimental film, with had the highest transmittance. The increase in radiation transmittance of 14% produced greater photosynthetic activity without generating a higher inside air temperature at the crop level (at the height of 2 m above the floor). However, the mean temperature of the soil surface was statistically higher on the side with the diffuse experimental cover film, as a logical consequence of the higher level of intercepted solar radiation.