Air-conditioned Buildings Research Articles

Microencapsulated phase change material incorporated light transmitting gypsum composite for thermal energy saving in buildings

The increased energy consumption for specific applications, including heating, cooling, air conditioning and lighting of residential and commercial buildings accelerate the research efforts concentrated on developing thermal energy storage capacity of buildings materials in recent years. Likewise, the development of light-transmitting building elements is a novel energy-saving technique that enhances lighting efficiency in buildings. In light of these, the current study seeks to design an untried microencapsulated phase change material (MPCM) integrated glass fiber reinforced gypsum composite with sufficient light-transmitting properties and thermal energy storage capacity. In this research, a multi-scale investigation of light-transmitting gypsum composite was conducted experimentally with physical, mechanical, chemical, microstructural, thermal, light transmittance and solar thermoregulation tests. The gypsum composite is formed from α-gypsum, water, polymer admixture, alkali-resistant glass fiber (AR-GF), several concentrations of MPCM, and plastic optical grids to allow light to transmit through the board. Although higher fractions of MPCM yielded an apparent decrease in mechanical strength test results, 5 wt% introduction of MPCM to the reference matrix reduced the compressive and flexural strength of specimens by 1 and 8 %, respectively. The results verified a reduction trend in thermal conductivity of composites with MPCM loading. DSC investigations revealed that the melting temperature and the regarding latent heat storage capacity of gypsum composite with 15 wt% of MCPM are 17.76 °C and 19.2 J/g, respectively. Light-transmitting gypsum composites showed up to ~10 % light transmittance, that can greatly increase the efficiency of lighting in buildings. The produced gypsum composites with MPCM kept the test room cooler during the highest temperature, while it provided a warmer room during the nighttime for an extended time. The study's findings are applicable to increase thermal comfort by reducing the significant temperature variations in buildings and improving artificial lighting efficiency, encouraging the design of sustainable building applications.

Air-conditioning cost savings, CO2 emission benefits and return on investment by using waste in porotherm bricks in hot-arid and warm-temperate climates

Building energy consumption has dramatically increased globally during the last few decades. This energy is primarily utilized to keep air-conditioned buildings at a comfortable temperature. As the worldwide demand for energy increases, net-zero or green buildings will undoubtedly become more and more crucial to address challenges related to climate change. It is well-known in this regard that the use of thermal insulation materials inside the building can contribute with temperature management and thermal comfort by preventing heat transmission. The present study examines the thermo-economic aspects of porotherm blocks filled with discarded insulations. Six different types of insulation were therefore investigated, and each was inserted into the porotherm brick cavities, including plastic powder, tire powder, cloth powder, leather powder, rockwool, and coconut pith. The effects of these newly developed brick configurations on air-conditioning costs, carbon dioxide emissions and payback time are compared to those of conventional porotherm blocks and burnt clay bricks. Thermo-physical properties of the aforementioned insulating materials, as well as porotherm brick and burnt clay brick, were established by experimental analysis. The thermo-economic analysis was carried out based on the number of degree-hours of heating and cooling to determine the building's annual energy usage. The thermo-economic performance of insulation-stuffed porotherm bricks was evaluated in two locations in India with distinct climatic characteristics: (28.57° N 75.12° E) New Delhi (warm-temperate climate) and (28.00° N 73.30° E) Bikaner (hot-arid climate). The rockwool porotherm brick wall demonstrated the best results in terms of lower unsteady transmittance, greater air conditioning cost-savings, appropriate payback spans, and improved yearly carbon mitigation values of 0.29 W/m2K, 0.83 $/m2, 0.95 years, and 15.65 kg/kWh, respectively, in hot-dry climates.

Design Selection Method of Exhaust Air Heat Recovery Type Indirect Evaporative Cooler

In order to promote the engineering application of indirect evaporative cooling (IEC) in the field of building air conditioning, as well as reduce air conditioning energy consumption and carbon emissions, this paper proposes a fresh air unit using indirect evaporative cooling to achieve heat recovery from exhaust air, which gives the recommended values of air and spray water operation parameters. The indirect evaporative cooler heat and mass transfer mathematical model and numerical solution procedure were made. In summer outdoor design conditions, the fresh air outlet state parameters, cooling capacity, fresh air cooling load, wet bulb efficiency and enthalpy efficiency were numerically solved for thirty typical cities from five climate zones of China. In addition, also based on the model results for the cities in China, two representative operating conditions points of medium and high humidity were selected. Eight models of fresh air unit coolers in the air volume range of 1000–10,000 m3/h commonly used in engineering were simulated to obtain the optimal heat transfer area and size selection of ERIEC heat exchangers for fresh air units, and economic analysis was performed. The results show that the wet bulb efficiency ranges from 0.67–0.98, and increases as the outdoor design wet bulb temperature decreases; the enthalpy efficiency ranges from 0.76–1.29, and increases as the outdoor design wet bulb temperature increases; and the fresh air load that the exhaust air heat recovery type indirect evaporative cooler can bear ranges from 55–100%, which could largely decrease the cold load of the matched surface cooler. As demonstrated, the energy-saving effect is remarkable.

Unravelling the impact of courtyard geometry on cooling energy consumption in buildings

At present, the energy used for air conditioning in buildings in urban areas accounts for over 36% of total global energy consumption. Energy efficiency has become a critical factor in the urban planning of cities worldwide. Courtyard buildings in hot cities are a prime example of the approach used in traditional vernacular architecture to mitigate the effects of extreme weather. However, given the challenge of guaranteeing accurate modelling of microclimates within these courtyards, their impact on energy demand in buildings has been routinely overlooked by energy certification tools.This work examines three empirical case studies selected in Seville city (Spain), where temperatures during the summer months are extreme. The case studies selected display distinct geometric variations, and the primary objective of the research is to assess the influence of this geometric factor on the cooling energy demand of the building indoors. To achieve this, a validated methodology combining experimental and numerical data was implemented to evaluate the energy performance of buildings with courtyards. Different simulations were conducted to detect the impact of individual courtyard features. The results show a reduction in cooling demand of 8–18% depending on the geometry of the courtyard. Analysis was also carried out on the influence of the floor level and the orientation of adjacent rooms, revealing differences of 15% and 22%, respectively. The main conclusion of the research is that the use of courtyards as functional devices, paying particular attention to their geometry, is a key factor in the cooling energy demand of buildings.

CFD Evaluation of Thermal Conditioning in a House of Social Interest with a Solar Chimney Arrangement in Guanajuato, Mexico

The aim of using electromechanical air conditioning in buildings is to maintain thermal comfort for its occupants; however, this type of air conditioning represents 40% of the total energy consumption of a building, generating economic and environmental impacts, because fossil fuels are the main source of energy. To reduce the use of electromechanical conditioning, it is possible to take advantage of the climatic conditions of the region to improve its performance. Due to the small number of works that quantitatively support measures aimed at improving the thermal behavior of houses in an integral way and the growth of mass construction in Mexico, in the present work, a solar chimney is incorporated in a typical type of social interest housing in Guanajuato. The incorporation of the solar chimney was simulated by using computational fluid dynamics (CFD) using ANSYS and evaluated by ASHRAE Standard 55-2017. The selected arrangement induces air flow inside without the need for external flow and obtains speeds of 0.2 m/s; thus, it could be considered for rooms within comfort zones up to an operating temperature of 29 °C according to the ASHRAE Standard 55-2017, PMV method.

A comprehensive scheduling model for electric vehicles in office buildings considering the uncertainty of charging load

The access of electric vehicles (EVs) has a profound impact on the operation and scheduling of building energy system. However, due to the fixed schedules of EV charging load, few studies concerned on the coordination strategy between EVs and other potential flexible load in office buildings. In this study, uncertainty sources of EV charging load are extracted from sensitivity analysis based on regression method, and then the uncertainties are introduced into the charging load prediction model based on Monte Carlo method. A optimal scheduling model embedded with the uncertainty of charging load, with the joint operation of building air conditioning system, photovoltaic system and EVs, is proposed for building demand response period. The results show that the operation strategies obtained from the proposed model embrace the advantages of small load variance, high flexibility, low operating cost and large photovoltaic power consumption capacity. The arrival non-guarantee rate is reduced from 12.23% to 6.55% and the charging non-guarantee rate is reduced from 24.03% to 9.39%. On the basis of EV orderly charging and the air conditioning pre-cooling, 7.57–61.67% of the 8:00 startup load can be transferred to night, and the original load variance can be reduced by 3.06–17.81%.© 2017 Elsevier Inc. All rights reserved.

An overview of water proofing system in concrete structures

Water Proofing is one of the methods to prevent leakage problems in buildings. For toilets, terraces, water tanks, and outdoor spaces, several methods of water proofing are suitable. Due to the concrete's tendency to shrink, fractures typically occur in the screed of the roof. However, the surface fracture will be partially repaired by casting the concrete in panels. This also happens due to temperature variation. Crystalline admix water proofing with water stops, water proofing with Atactic Polypropylene membrane, and injection are the water proofing systems most commonly used in basements. Using non-shrinking cementitious grout for waterproofing, concrete must have crystalline admixtures made of cementitious powder and water. For toilets in non-sunken places, water proofing with an elastomeric cementitious coating is used. In sunken areas, brick jelly cement concrete with inherent water proofing compound is used. Waterproofing without insulation and waterproofing with insulation are typically used in terraces. There are typically two different types of buildings: Air-conditioned buildings and Non Air-conditioned buildings. Buildings with air conditioning need to be insulated. Extruded polystyrene with geotextile mat is used as over deck insulation. Injection grouting is used in water tanks on the side walls and base slab. On the top surface of the slab and the outside face of the wall throughout the whole area, holes must be drilled using a pneumatic hammer in a zigzag pattern. Generally artificial area and extended basement needs to treat with proper water proofing system. Membrane is used to waterproof the landscape regions. Soil is used to fill in landscaped areas, and there will be a drainage layer to remove water. Materials should be made entirely of recycled polypropylene. In this paper it deals with the different types of water proofing system.

Energy Consumption Forecasting of Urban Residential Buildings in Cold Regions of China

Long-term predictions of the energy consumption of a building can be a reference in formulating energy conservation policies to achieve carbon neutrality. However, existing research on the prediction of energy consumption of urban buildings mainly adopts top-down or bottom-up single models that do not consider the coupling effect of macro and micro factors. Therefore, a coupled top-down and bottom-up prediction model has been proposed in this paper. The applicability of the proposed method was investigated based on residential buildings in Beijing, China. First, based on a top-down methodology, the energy consumption data of residential buildings in Beijing were investigated using an urban statistical yearbook, and the energy consumption of residential buildings under different energy-saving policies was analyzed. Second, micro factors, such as envelope parameters, personnel behavior, air conditioning, and electrical usage of typical residential buildings, were investigated. Subsequently, a simulation model of residential building energy consumption was constructed according to the survey data. The actual and simulated values for 2017 were 0.264 GJ/m2 and 0.252 GJ/m2, respectively. Finally, pessimistic and optimistic scenarios are proposed using the Human Impact, Population, Affluence, Technology (IPAT) model. The energy consumption of residential buildings in Beijing for the next decade was predicted under different scenarios by adopting the gray prediction method and multiple regression analysis, which was verified using the back-propagation neural network algorithm. In the baseline scenario, the projected 2021 heating energy consumption value was 13.4 kgce/m2 with a relative error of 6.52%.

사무실 건물의 다기능 히트펌프 적용에 대한 성능 및 에너지 소비량 분석

This study aimed to evaluate the energy consumption performance of a multi-functional air-source heat pump for the indoor air-conditioning, heating, and hot water supply of an office building. Based on the investigation, four heat pump system configurations are proposed for the comparative evaluation of each system. Two reference systems are used for comparisons in the energy performance evaluation. The detailed thermal load for a 100 ㎡ office building was conducted using commercial energy simulation tools. Thermodynamic theoretical equations were used for heat pump simulation. The results show that case 2, the cascade heat pump system, can reduce primary energy consumption by 41.7 % and 54.0 % when compared with two reference systems and showed the highest energy-saving performance in the proposed cases. This study validated the use of the multi-functional cascade heat pump system for use in an office building.

A review of data-driven fault detection and diagnostics for building HVAC systems

With the wide adoption of building automation system, and the advancement of data, sensing, and machine learning techniques, data-driven fault detection and diagnostics (FDD) for building heating, ventilation, and air conditioning systems has gained increasing attention. In this paper, data-driven FDD is defined as those that are built or trained from data via machine learning or multivariate statistical analysis methods. Following this definition, this paper reviews and summarizes the literature on data-driven FDD from three aspects: process, systems studied (including the systems being investigated, the faults being identified, and the associated data sources), and evaluation metrics. A data-driven FDD process is further divided into the following steps: data collection, data cleansing, data preprocessing, baseline establishment, fault detection, fault diagnostics, and potential fault prognostics. Literature reported data-driven methods used in each step of an FDD process are firstly discussed. Applications of data-driven FDD in various HVAC systems/components and commonly used data source for FDD development are reviewed secondly, followed by a summary of typical metrics for evaluating FDD methods. Finally, this literature review concludes that despite the promising performance reported in the literature, data-driven FDD methods still face many challenges, such as real-building deployment, performance evaluation and benchmarking, scalability and transferability, interpretability, cyber security and data privacy, user experience, etc. Addressing these challenges is critical for a broad real-building adoption of data-driven FDD.

Radiative-Cooling Composites with Enhanced Infrared Emissivity by Structural Infrared Scattering through Indium Tin Oxide Nanoparticles in a Polymer Matrix.

Radiative cooling has attracted tremendous interest as it can tackle global warming by saving energy consumption in heating, ventilation, and air conditioning (HVAC) in buildings. Polymer materials play an important role in radiative cooling owing to their high infrared emissivity. Along this line, numerous studies on optically optimized geometries were carried out to enhance the selective wavelength absorption for high infrared emissivity; however, the polymer material itself relatively was not investigated and optimized enough. Herein, we investigate the infrared radiation (IR) absorption coefficient of various polymer types, and introduce a new concept of radiative-cooling composites. By dispersing the IR scattering medium in a polymer matrix, IR can be effectively scattered and attenuated by the polymer matrix. Indium tin oxide was utilized as the IR scattering medium in a cellulose acetate polymer matrix in this report. The window film was made with this composite and showed an effective cooling performance by outdoor thermal evaluation. This composite opens a new venue to endow materials with enhanced radiative-cooling property regardless of the polymer types.

Study on an air conditioning system with the use of natural cooling

Issues of microclimate mitigation in Uzbekistan during the summer period require urgent resolution. It should be noted that currently there are very few researches, as well as practical recommendations related to the formation of a favorable microclimatic environment in cities with a hot climate. The simplest and most economical way of cooling, in dry and hot climates, is the evaporative cooling of a dry air stream. One of the possible ways to increase the efficiency of the system is the use of night evaporative cooling of water, followed by its accumulation for daytime cooling in heat-insulated batteries. The conducted experiments testify that rather simple and cheap natural sources of cold can be used along with machine cold sources for air conditioning of residential buildings in Uzbekistan.

Retrofitting of a High-Rise Residential Building for Energy Efficiency with OTTV as an Assessment Tool

Buildings account for nearly 50% of the total energy consumption. The use of air-conditioning is one of the major influencers to the high energy consumption in buildings. To tackle this high energy consumption, buildings are required to be more energy efficient. This study aimed to investigate the retrofitting of existing residential building for energy efficiency by using the Overall Thermal Transfer Value (OTTV) as an assessment tool. Various retrofitting measures were involved, including varying the colour of the opaque wall with different solar absorptivity, the U-value and shading coefficient of the Glazing system, and the type and projection of the external shading. The results showed that applying the retrofitting measures individually (i.e., using light colour with low solar absorptivity, replacing the glazing system to have lower shading coefficient and U-value, and the installation of external shading systems with low shading coefficient) can decrease the OTTV by 26% to 33.4%. However, combining these measures managed to decrease the OTTV by up to 75.6% (i.e., the OTTV decreased from 82.87 W/m² to 20.19 W/m²). This can improve the building energy efficiency as it contributes to less cooling load for the air-conditioned buildings, while it provides a better indoor environment in non-air-conditioned buildings.

Study on Electrical Services and Control for Heating, Ventilation and Air-conditioning in Buildings

In modern age of technology, the concept of energy saving and environmental comfort raise the building services and controls as a significant issue during the design, installation, operation and management. Proper electrical services and sound control systems, especially for Heating, Ventilation and Air-conditioning (HVAC) sections, can not only make our lives more convenient and pleasant, but also increase the energy efficiency in the view of sustainable development.

Extending the use of adaptive thermal comfort to air-conditioning: The case study of a local Japanese comfort model in present and future scenarios

The use of setpoint temperatures based on adaptive thermal comfort models has been identified as an efficient energy saving measure in the latest years. The recent studies applying adaptive setpoint temperatures consider ASHRAE and EN16798-1 international models. However, this study has considered a local Japanese adaptive comfort model instead. Therefore, this study analyses the energy demand resulting from the application of a local Japanese comfort model and compares it with the energy demand resulting from the use of the worldwide ASHRAE Standard 55 adaptive model and other fixed setpoint temperatures. Building energy simulations have been performed considering all different climate zones in the territory of Japan, and also considering full air-conditioning and mixed-mode building operation modes, as well as present and future scenarios under the influence of climate change, namely Representative Concentration Pathways (RCP) 2.6, 4.5 and 8.5 for years 2050 and 2100. Results show that energy savings ranging between 29 and 52% and 33 and 78% could be achieved by using setpoint temperatures based on the Japanese local adaptive comfort model respectively in full air-conditioning mode and mixed-mode. These results were obtained using the adaptive model for free running buildings, therefore assuming high levels of adaptation. In the context of climate change, the total energy demand decreases in cold climates between 14 and 65% and 18 and 91% for full air-conditioning mode and mixed mode respectively, while in warm climates, it increases between 8 and 36% and 17 and 51%, again respectively for full air-conditioning mode and mixed-mode. Therefore, the use of setpoint temperatures based on the Japanese local adaptive comfort model is identified as a very efficient energy saving strategy.

A Review on Adaptive Thermal Comfort of Office Building for Energy-Saving Building Design

The thermal environment quality of office buildings has an important role because thermal comfort is directly related to human productivity. Thermal comfort conditions are influenced by climate, location, and the built environment; hence, comfort standards are required to assist building designers in creating a comfortable indoor environment for building occupants. In this context, the present study analyzes the adaptive thermal comfort studies conducted in office buildings from various countries. A large number of research articles selected from the Scopus database were considered for this study. Based on the analysis, outdoor climatic conditions have a greater influence on indoor thermal conditions in naturally ventilated than in air-conditioned office buildings. The temperature required for comfort is as low as 17.6 °C and as high as 31.2 °C in naturally ventilated buildings. An adaptive comfort equation for naturally ventilated and air-conditioned office buildings has also been proposed to predict the indoor comfort temperature. Various studies show that a substantial amount of energy can be saved by changing the set point and natural ventilation. Furthermore, this study successfully provides hearty evidence that there is a need for climate-specific standards on thermal comfort for energy-efficient design development because existing comfort standards might not be applicable to all climates.

Experimental and numerical investigation of novel light weight concrete panels made with aerogel and phase change materials

Silica Aerogel (SAG) mortar is an ultra-lightweight cementitious composite. It has high heat-insulating properties, which helps to reduce building heating energy consumption. However, it may also increase overheating and peak cooling demand in buildings during summer due to low thermal mass to store thermal energy. Therefore, this study aimed to increase the thermal energy storage capacity of silica aerogel lightweight concrete panels (SAGP) by integrating Capric Acid (CA) Phase Change Materials (PCM). The CA was absorbed in Hydrophobic Expanded Perlite (HEP) porous materials to develop form stable capric acid hydrophobic expanded perlite (CAHEP) composite to prevent PCM leakage when melted. Various lightweight Heat Resistive and Storage Panels (HRSP) panels were developed by replacing sand with SAG and CAHEP composite at different volume fractions. Then, the thermophysical properties and thermal performance of those HRSPs were evaluated using appropriate standards and established methods. The results showed that the integration of 60% CAHEP in SAGP resulted in 43% and 56% higher thermal storage and inertia, respectively, compared to the reference SAGP without CAHEP. The developed HRSPs also have acceptable compressive strength and drying shrinkage for thermal insulating and plastering applications. Numerical simulation showed that the application of HRSPs on the interior surface of a typical Victorian house reduced annual energy use and greenhouse gas emissions by 9.14% and 24%, respectively, in air-conditioned buildings; and reduced summertime thermal discomfort hours by 42 h in a free running house during a heatwave period. Finally, the life cycle assessment revealed that HRSPs have lower environmental impacts than SAGPs. Thus, HRSPs can be a sustainable alternative to lightweight concrete panels.

Advanced Method of Variable Refrigerant Flow (VRF) Systems Designing to Forecast On-Site Operation—Part 1: General Approaches and Criteria

All the energetic management and controlling strategies in ambient air conditioning systems (ACS) are aimed to match design load to current needs. This might be achieved by determining a rational value of design thermal load without overestimation that can minimize its deviation from the actual values. The application of variable refrigerant flow (VRF) systems with speed-regulated compressors (SRC) is considered as the most advanced trend in building air conditioning due to the ability of SRCs to cover changeable heat loads without lowering their efficiency. The level of load regulation by SRC is evaluated as the ratio of the load range, regulated by SCR, to the overall design load range. With this, the range of actual changeable loads is usually supposed to be covered by SRC entirely while keeping the rest, unregulated, and load range unchangeable. However, to confirm this, the rest load range behind the regulated one should be investigated to estimate the efficiency of SRC operation. Therefore, the approach to dividing the overall thermal load range of ambient air conditioning into the ranges of changeable and unchangeable loads to compare with those covered by SRC is used. From this approach, the method of rational designing and shearing a design refrigeration capacity in response to current loading, based on the principle of two-stage ambient air conditioning, has been widened on the VRF systems to estimate the efficiency of SCR application. This was realized by imposing the load ranges regulated by SRC onto the ranges of changeable and unchangeable loads within the overall range of actual loading. The proposed innovative criteria and indicators for rational shearing the load ranges to match current duties and load level evaluation can reveal the reserves for improving the efficiency of SRC compressor operation and the ACS of VRF type as a whole.

A New Type in TRNSYS 18 for Simulation of Borehole Heat Exchangers Affected by Different Groundwater Flow Velocities

Heating ventilating air-conditioning (HVAC) systems have been increasingly widespread in Italy: they can exploit renewable energies, are energy efficient systems, do not directly consume fossil fuels, and in the post-pandemic era, have also been subject to incentive processes by the Italian government. In South Tyrol, subject to harsh climates in both the winter and summer seasons, ground-source heat pump (GSHP) systems can be an excellent solution for the air conditioning of buildings. Unfortunately, too often, the design of HVAC systems with borehole heat exchangers (BHEs) is not adequate, and therefore, an innovative and expeditious numerical solution is proposed. A new numerical element (named Type285), written in Fortran code, was developed for TRNSYS 18 and able to implement the main features of BHEs and the surrounding aquifer. Type285 was compared with numerical models present in the literature (using hydrogeological software such as MODFLOW) and validated with the experimental data. The demonstration of the exchanged energy increase between the BHE and subsoil due to the increase in the groundwater flow velocity was carried out and evaluated. The choice to simulate BHE in TRNSYS using Type285 can be a fast and advantageous solution for HVAC system design.

Special issue on “Optimal design and operation of energy systems”

Special issue on “Optimal design and operation of energy systems”