Usage Of Air-conditioning System Research Articles

Energy saving potential of screen walls in high-rise residential buildings in hot and humid climates

About 33% of the total energy produced, is consumed by the building sector. Especially, 75% of the energy gets utilized by the residential buildings within the building sector. The increased usage of air conditioning systems to cool the indoor environment in hot-humid climatic regions increases the energy requirements of residential buildings. To be specific, high-rise residential buildings are known to be highly energy intensive. It is possible to mitigate the heat transfer into the indoor environment in high-rise residential buildings by shading the opaque facades. Since mutual shading or shading by adjacent building may not be possible at all times for high-rise residential buildings, screen wall can be used to shade the buildings to reduce its energy requirements and provide thermal comfort for the occupants in the indoor environment. In this background, the aim of the current research work is to find out the embodied energy, involved in the implementation of screen wall, and its effectiveness in reducing the operational energy requirements for space cooling in high-rise residential buildings. The option of screen wall and its benefits over conventional building envelope are emphasized in this study through a simulation study. A bedroom in a high-rise residential building in Chennai was chosen for conducting the detailed analysis and the analysis was carried through simulation for one year. The research design includes the modelling of the selected residential building in IES-VE software and validating the results through field measurements. Energy saving analysis was conducted through simulation to determine the energy saved in space cooling by shading the opaque façades with screen wall. For one year, 7.88MWh energy reduction was attained from the installation of screen wall over opaque surfaces at the set indoor temperature i.e., 27°C for 8 hours during night time using air-conditioning. The embodied energy was calculated for the installation of metal sheet over opaque façade and for shading as screen wall and the outcomes were compared with the energy savings in space cooling with the application of screen wall. The payback period for the embodied energy of the screen wall installation was determined in terms of operational energy saved in space cooling through screen walls. The analysis revealed that the payback period is one year. Due to COVID-19 pandemic, people staying at indoors in residential buildings has increased up to 90% during day time, which in turn results in high energy demand. Screen wall acts as a skin for the buildings and shade entirely from the sun. It helps in reducing the energy usage for space cooling in residential buildings, which eventually reduces the carbon footprint.

Impact of different urban canopy models on air quality simulation in Chengdu, southwestern China

Urban air pollution has emerged as a prominent public health concern in megacities and highly developed city clusters. Accurate modelling of urban air quality over complex terrain is challenging due to heterogeneous urban landscapes and multiscale land-atmosphere interactions. In this study, we investigated the applicability of urban canopy models in the Weather Research and Forecast (WRF) model and assessed the impacts of implementing these models on the urban air quality simulation in the Community Multiscale Air Quality (CMAQ) model over the megacity Chengdu, southwestern China. The land use and land cover of Chengdu were updated in WRF by using the land-use products in 2017 from the Moderate-resolution Imaging Spectroradiometer (MODIS). Sensitivity experiments with various urban canopy models were conducted to investigate the feasibility of different urban canopy models on WRF-CMAQ simulations. We found that the SLAB model significantly underestimates NO2 and PM2.5 concentrations, with mean fractional bias in winter (summer) reaching 52.93% (−50.34%) and −102.82% (−23.12%), respectively. Such large biases are mainly attributed to overpredicted wind speeds resulting from the flat structure in the SLAB model. In contrast, the BEM (a multilayer urban canopy model coupled with air-conditioning systems) model yields the best model performance in both winter and summer, with mean fractional errors of 33.15% (38.96%) and 34.10% (33.15%) for NO2 and PM2.5 in winter (summer), respectively. The UCM (a single-layer urban canopy model) model illustrates good performance in summer, with MFBs of 25.61% for NO2 and 19.03% for PM2.5, while NO2 and PM2.5 concentrations are overestimated in winter, with MFBs of 62.58% and 38.19%, respectively. In contrast, BEP (a multilevel urban canopy model)-modelled NO2 (MFB: 37.18%) and PM2.5 (MFB: 18.72%) correlate well with observations in winter, while significantly overestimated air pollutant concentrations in summer with MFBs of NO2 and PM2.5 of 49.70% and 44.50%, respectively. In general, the BEP model and the BEM model are well suited for air quality simulations over Chengdu in winter, and the BEM model could be considered for air quality simulations in summer. Furthermore, we assessed the effects of extensive usage of air conditioning systems in Chengdu during summertime, and the results suggest that using air conditioning systems facilitates the dispersion of air pollutants over Chengdu. This study pinpoints the limitations of default WRF configurations and tests the applicability of urban canopy models in the WRF-CMAQ model over Chengdu, in addition highlighting the crucial role of urban canopy models in urban meteorological-air quality simulations.

Theoretical and experimental development of cooling load temperature difference factors to calculate cooling loads for buildings in warm climates

In Mexico, electricity consumption is highest during the summer due to the usage of air conditioning systems. Considering that half of Mexico has warm climatic conditions and more than 30% households are equipped with some kind of air conditioning equipment, accurate cooling load calculations would directly affect energy efficiency, indoor thermal comfort and suitable heating, ventilation, and air conditioning design. The cooling load temperature difference/solar cooling load/cooling load factor (CLTD/SCL/CLF) method provides a reasonably accurate estimation of total heat gains through a building envelope; however, it is restricted to climatic conditions in the United States and a small number of construction materials. This study aims to determine the CLTD values for flat roofs and walls of buildings for different climatic zones in Mexico, such as Monterrey, Veracruz, and Mexicali, and for different construction materials that typically used in Mexico. We used the complex finite Fourier transform to solve the one-dimensional transient heat transfer model. We ran experimental setup in Monterrey to validate the mathematical model developed in this work. Additionally, we verified the theoretical model with the previously reported studies and compared them with CLTD values calculated using the correction factor proposed by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) methodology. From these results, we can conclude that applying the CLTD method with the correction factor overestimates cooling loads through walls and roofs for typical buildings and Mexican climatic conditions. The average difference between ASHRAE-derived values and the obtained CLTD values was 10 °C.

A Study on the Evaluation Tendency of Thermal Sensation in Tropical Region - Targeting short time residents -

Climate change is getting more and more serious issue in the world. This is known as caused by the increase of carbon dioxide. To stop the increase, many countries agreed to the Paris Agreement in 2015. When to discuss the climate change, temperature drop and increase are focused more often. The big change of the temperature, especially the rise of the temperature, causes the more usage of air conditioning system, and it also causes more energy consumption. In addition, the usage of the air conditioning system is affected by both indoor and outdoor thermal environment. The temperature setting of air conditioning system tends to be lower in the countries situated in tropical region than the countries in the other region. This happens because the thermal sensation of human is easily affected by the outdoor environment. For that reason, to grasp the tendency of thermal sensation in outdoor space is important. In addition, the tendency of short time residence is necessary to wipe out the influence of the thermal environment adjustment by long time living. For that reason, this research targeted the thermal evaluation tendency of short time residents in Bangkok and carried out subject experiments in outdoor spaces to develop landscape design method. As the result of analysis, a different tendency was grasped at one of the measuring points with open sky.

Developments of Thermochromic VO2–Based Thin Films For Architectural Glazing

Investigation on properties of vanadium dioxide (VO2) thin films has received significant attention as it is a thermochromic material potentially for applications on architectural glazing in order to reduce energy consumption from usage of air-conditioning system. Most studies have focused on the hysteresis behavior of thermochromic VO2 thin films that occurs at a certain phase transition temperature. Although large area coating techniques have recently been developed, there are still many obstacles in trying to deploy energy-efficient windows. Hence, this work concisely reviews on VO2 thin films as thermochromic materials, and developments on preparation methodologies in order to enhance the thermochromic characteristics of VO2 thin films.

ANALYZING AND EVALUATING A PMV-BASED THERMAL COMFORT MODEL IN CONTROLLING AIR CONDITIONING SYSTEM

The usage of air conditioning system to create a thermally comfortable environment in tropical countries is often a must, not necessarily luxurious any longer. However, the extreme usage of the system will lead towards higher consumption of energy and higher cost. A promising energy efficient model developed based on the Predictive Mean Vote (PMV) is analyzed and evaluated here to distinguish its workability. This model only requires the user to enter their respective PMV value (from -1 to +1) and the respective parameters will be inserted into the air conditioning system, which is based on the standard thermal comfort ISO 7730. Analyses and evaluations were done based on the measurements from human subjects and their feelings towards the surroundings were recorded to see the performance of the model. From here, more than 91% of the subjects agree with the parameters used in defining their thermal comfort. This proves the workability of the model towards controlling the air conditioning system in creating a thermal comfort ambience at lower energy consumption, and further simulative investigations are appreciated before implementation.