Air-conditioned Buildings Research Articles

Experimental and Numerical Study on the Dynamic Thermal Response of Building Interior Decoration Coatings during Intermittent Air-Conditioning in High U-Values Buildings in China

Interior decorating coatings (IDCs) are the heat-transfer medium between indoor air and building walls, which mainly form the cooling load and are important in an indoor built environment. To explore the impacts of the precooling process of IDCs on indoor thermal environment of occupants during intermittent air conditioning, this paper investigated the dynamic thermal response of IDCs. Three representative coating materials were integrated to the external insulation wall and internal insulation wall, and their interior surface temperatures were experimentally tested under intermittent air conditioning operation in southern China. Moreover, a heat transfer model was established and verified to analyze the influences of IDC on the thermal response of the interior surface. During the pull-down process, the cold was accumulated in the IDC layer with small thermal diffusivity and could not be transferred into the wall inside, so that the largest temperature reduction was obtained, meaning that the indoor thermal environment could meet the setpoint in a short time. According to modelling calculations, the thick IDC with volumetric specific heat capacity less than 1 × 105 J/(m3·K) and small thermal conductivity integrated to the internal insulation wall was beneficial to increase the thermal response rate and had the better energy-saving efficiency.

Thermal design of energy piles for a hotel building in subtropical climate: a case study in São Paulo, Brazil

The use of shallow geothermal energy through energy piles for the air-conditioning of buildings is increasing worldwide. This type of renewable energy technology is still not utilized in Brazil, where the hot dominating weather regions and the air cooling demand predominate. In this case of unbalanced heat transfer to the ground, the efficiency of the system may decrease with time due to the excessive heat injection into the soil. In order to investigate the possibility of an efficient application of this technology in São Paulo city, a balanced use of the ground for a ground-source heat pump (GSHP) system utilizing energy piles is evaluated in the present paper. Energy foundations were designed to meet the balanced heating and cooling loads (air conditioning and water heating) of a hypothetical business hotel building located in a site at the campus of the University of São Paulo, where thermal response tests (TRTs) were conducted on different types of energy pile. The number of energy piles required to supply the building thermal loads were estimated using the pile heat exchanger modelling software PILESIM 2.1 and compared with an analytical model prediction. The evaluations were done for three different types of pile tested at the site chosen for this study: micropiles, steel pipe, and continuous flight auger (CFA) piles. The results indicate that the ground heat extraction should be considered for the use of GSHP systems with energy piles in air cooling-dominated scenarios similar to the case studied here.

High thermal conductivity concrete for energy piles

Research is increasingly focusing on thermal properties of concrete with the aim of reducing the heat exchange between buildings and environment. On the other hand, concretes with high thermal conductivity could have interesting applications in the field of thermo-active ground structures as Geothermal Energy Piles (GEPs). This kind of foundations represent an environmentally friendly technology that allows exploiting the heat of the shallow earth surface to supply renewable energy for the air conditioning of buildings. GEPs are needed for structural and geotechnical reasons and allow recovering the installation costs connected to vertical boreholes. Concrete drilled or driven piles are equipped with a Primary Circuit (PC) of high-density polyethylene plastic pipes attached to the reinforcement cages. Thermal energy is extracted from or injected into the ground thought a carrier fluid that flows into the pipes of the PC. To improve the heat exchange between the pile and soil the thermal properties of the concrete should be considered as design parameters. Concrete thermal conductivity, contrary to what happens for the buildings, should be increased to optimise the thermal performance of the GEPs. Different solutions that modify the mix design of concrete are proposed to the aim of increasing the thermal performance of GEPs.

Interactive analysis of green building materials promotion with relevance to energy consumption and greenhouse gas emissions from Taiwan’s building sector

Service and residential sectors have become significant sources for reducing greenhouse gas (GHG) emissions relevant to the electricity demand for heating, ventilation & air conditioning (HVAC) in buildings. In Taiwan, the energy efficiency (or energy saving) in buildings is a very important issue because the service and residential sectors in this subtropical/tropical island region are the primary sources of GHG emissions. Therefore, the main purpose of this work was to present an interactive analysis of Taiwan’s energy consumption, GHG emissions from the services and residential sectors, and the certified green building materials (GBM) during the period of 2005–2020 based on the official statistics. Furthermore, the policy for promoting the GBM products with high thermal insulation performance and their compulsory specifications were also addressed. On average, the service and residential sectors accounted for about 15% of total domestic energy consumption during this period. By contrast, the electricity consumption shared around 35% in 2020, and also indicated a decreasing trend from 2005 to 2020 due to the governmental policy for improving energy saving and energy efficiency through the establishments of greenhouse buildings (GB) and GBM. In line with international trend of low-carbon buildings, the Taiwan government has promoted the GBM labeling system under the promulgation of relevant regulations since the early 2000s. A total of 2668 GBM labels have been issued over the years of 2005–2020, showing that the number of approved and issued GBM reached a record high in 2020. In summary, the certified high-performance GBM products indicated significant increases since 2013 under the regulatory promotion. The new and/or retrofitted buildings will adopt the certified GBM with high insulation performance totally by 2030 under the sustainable development goals (SDGs).

Multi-objective optimization of setpoint temperature of thermostats in residential buildings

Determination of the optimum setpoint temperature of thermostats in various climates is a problem in air conditioning of residential buildings. In this paper, a new method is developed to optimize the setpoint temperature of thermostats in different climates of Iran. Design variables in the optimization process are heating setpoint, cooling setpoint, thickness, and thermal conductivity of insulations in the building envelopes. The optimization goals are minimizing energy consumption and cost of insulations in addition to maximizing thermal comfort of occupants. Thus, the static payback period (SPP) and the predicted percentage dissatisfied (PPD) indices are selected as objective functions which should be minimized in the optimization process. The methods applied to attain these objectives are numerical modeling by EnergyPlus software, Grouped Method of Data Handling (GMDH) type of Artificial Neural Network (ANN), and Non-Dominated Sorting Genetic Algorithm II (NSGA-II). Therefore in this process, first, EnergyPlus is used to train the neural network. Afterward, the GMDH-type neural network is applied to derive polynomials computing the objective functions from the design variables. Then, Pareto optimal points for the objective functions are obtained through using these polynomials and NSGA-II multi-objective optimization. Finally, the optimum design point is selected for different cities. According to the results, type and thickness of insulation integrated in the building envelopes affect the static payback period and thermal comfort of occupants. For all the climates of Iran, the most appropriate insulation is XPS and the optimum heating setpoint of thermostat is 22 °C. Also, the optimum value for the cooling setpoint pertains to the type of climate, so that this value for Bandar Abbas, Yazd, Tehran, Rasht and, Tabriz is, respectively, equal to 24.5, 24.7, 25.2, 25.3, and 25.6 °C. Moreover, thermal comfort of occupants increases with thickness of insulation, except for Bandar Abbas whose PPD is almost constant. The most value of PPD reduction with insulation thickness is related to Tehran where by increasing the insulation thickness from 1 cm to 5 cm, PPD decreases up to 53%.

The comfort and energy impact of overcooled buildings in warm climates

Around 18% of global carbon emissions can be attributed to building heating or cooling, driven by the adoption of “international” thermal comfort standards such as ASHRAE-55, which imply an homogenous indoor environment. We argue that the importation of such standards to warm climates results in indoor cold discomfort due to “overcooling”: a phenomenon anecdotally recognised worldwide but not studied or defined systematically. Unlike under- or over-heating, overcooling is the purposeful over-expenditure of energy, that creates conditions of cold thermal discomfort. We examine data for warm and temperate climates from a global thermal comfort database spanning 27 countries with over 90,000 occupant responses to investigate overcooling of air-conditioned buildings. We suggest that overcooling is best defined by taking the intersection of thermal sensation and preference and, using this definition, we find that 17% of building occupants in the examined data can be classed as being overcooled. We estimate the cooling energy demand of overcooling imposed through the adoption of the ASHRAE-55 standard using computer simulations that move building occupants from being overcooled to comfortable. The results suggest around 15% of cooling energy demand could be saved through a simple upward adjustment of set-point temperatures by 2 °C in warm climates. Such an adjustment in the Global South, which contains the majority of the warm regions of the Earth, could have a dramatic impact on the evolution of future cooling energy demand which is expected to triple by 2050.

Innovative strategy of passive sub-ambient radiative cooler through incorporation of a thermal rectifier to double-layer nanoparticle-based coating

Although various types of radiative cooling have been investigated, providing more cooling efficiency is always a challenge. One of the most critical challenges of radiative coolers is the ability to cool during the daytime against direct sunlight. In this work, the efficiency of the radiative cooler is increased by proposing an innovative design consisting of a thermal rectifier, an emitter with high emissivity in the “sky window,” and a solar reflector. Radiative and optical properties of selective surfaces were used to achieve thermal rectification. The spectroscopy (IR-Vis) tests were used to measure the optical-radiative properties of the present design structure, as well as their performance in the simulation software, was analyzed. An apparatus with the ability to measure the temperature at five simultaneous points and a digital data logger were designed and built to compare the cooling power of different samples experimentally. First, an experiment was performed to measure the temperature of different samples in winter (February) and summer (September) on the roof of a building in the southwest sky of Tehran (Iran). Site measurements showed that the temperature of the rectifier-cooler was at least 4.6 °C lower than the sample without the rectifier during the day. Also, the temperature difference between the no-coated and black samples reaches up to 7 and 17°C, respectively. Moreover, the resistance of the samples to the thermal shock was evaluated and characterized. Results show more thermal shock resistance in the rectifier-cooler, which reduces the body's stress and thus decreases its fatigue and failures. Further studies showed this structure has a reflectance of about 90% in the solar range and an emittance of about 0.7 in the sky transparency (8–13 μm spectrum). This new method has the potential to apply in a confined or extensive area, which provides a practical step towards achieving an industrial approach for radiation cooling technology, including building air conditioning, automotive industries, space industries, etc.

Numerical study on the heat performance of enhanced coaxial borehole heat exchanger and double U borehole heat exchanger

• The BHEs model considering the multilayer properties and groundwater flow. • An enhanced coaxial model with intermittently laid spiral ring fins was proposed. • The heat transfer performance of the vertical BHEs was evaluated. • The influence level of different factors on heat transfer performance was analyzed. • The influence of groundwater flow on the ground temperature field was analyzed. Borehole heat exchangers (BHEs) are widely used in various building air conditioning and heating systems. It has always been the unremitting pursuit of researchers to provide solutions for energy conservation by improving the heat transfer efficiency of BHE. In this work, comprehensively considering groundwater seepage in the surrounding rock and soil and the difference of heat transfer performance between various layers of rock and soil, three-dimensional geometric models of double-U BHE and enhanced coaxial BHE with intermittently laid spiral ring fins were established. The established model was verified by the drilling, geothermal, thermal response data collected through filed tests and the actual operating data of the system. The heat transfer performance and influencing factors of the two BHEs models under different working conditions were simulated by improving and replacing the double-U BHE model by means of equivalent buried pipe cross-sectional area. The results showed that the linear meter heat transfer of the enhanced coaxial BHE was significantly better than the linear meter heat transfer of the equivalent U BHE. The average linear meter heat transfer of the enhanced coaxial BHE can reach 1.46 times and 1.45 times of the equivalent U BHE under winter and summer working conditions, respectively. Finally, the results of the sensitivity analysis of single factor showed that the inlet temperature/inlet fluid heating power is the most significant impact on the heat transfer performance, followed by the inlet flow rate, and the hydraulic gradient of groundwater seepage has the least impact. The results obtained can provide a new type of the buried pipe structure that can be used as a reference for improving the heat transfer performance of BHEs in the simulation and experiment conditions.

Daily personal exposure to black carbon in different microenvironments in Hanoi, Vietnam

Daily personal exposure to black carbon (BC) in different microenvironments in Hanoi, Vietnam was quantified for the first time. In this study, a portable instrument, microAethe® model AE51, was used to continuously measure BC concentrations in various microenvironments within buildings and transportation modes. Overall average daily personal exposure to BC from those microenvironments was 5.46 µg/h. The highest BC exposure was during commuting 13.48 µg/h and 5.74 µg/h for the motorcyclist and car driver, respectively. In building environments, the highest BC exposure was 3.98 µg/h in a coffee shop with smoking; the lowest BC exposure was 1.54 µg/h in a hospital department; while BC exposure in an office was 1.92 µg/h. The level of BC exposure in an apartment was strongly influenced by building ventilation modes. They were 3.58 µg/h and 2.15 µg/h with doors/windows open and closed, respectively. Our finding confirmed that commuting contributes disproportionately to the total BC exposure due to the high level of BC during traffic/travel. Building ventilation and air conditioning can significantly affect indoor BC levels and should be considered as a measure to reduce BC exposure within buildings in Hanoi.

Evaluation of thermal comfort in mixed-mode buildings in temperate oceanic climates using American Society of Heating, Refrigeration, and Air Conditioning Engineers Comfort Database II

A comprehensive understanding of occupant comfort in mixed-mode (MM) buildings is crucial for the design of MM buildings which are being proposed as a low-energy solution to combat the global warming without compromising comfort. Current comfort standards are mainly for naturally ventilated (NV) or air-conditioned (AC) buildings, and there is a significant gap in standards for MM buildings. With comfort databases playing a major role in the development of thermal comfort models, the recently published ASHRAE Global Thermal Comfort Database II is utilised, in this research, to investigate the thermal sensation and occupant’s behavioural adaptations in MM buildings in temperate oceanic climates and to develop an adaptive thermal comfort model based on the outdoor environmental conditions. The Fanger's PMV model was found to underpredict the actual thermal sensation of the occupants while the occupant adaptivity was found to be lower than that predicted by the adaptive models of Standard 55 and EN15251/EN 16798-1. Furthermore, based on the results of this study and the various impediments faced, recommendations are proposed for future comfort surveys so that more detailed and conclusive studies can be conducted for wider applications using open-source thermal comfort databases. Good understanding of occupant comfort is necessary to reduce building energy consumption without compromising comfort. This article explores the use of ASHRAE Comfort Database II for determining occupant comfort in MM buildings in temperate oceanic climates and the limitations faced therein. A practical and publicly accessible database developed based on the recommendations from this study will improve thermal comfort models and enable better prediction of occupant comfort while improving energy efficiency substantially.

A new perspective for understanding actual anthropogenic heat emissions from buildings

The magnitude and timing of heat emissions from buildings can be substantially different than the corresponding energy consumption profile. Indeed, the definition of anthropogenic heat needs rethinking if our goal is to understand the role of buildings in heating of the urban environment, and to identify opportunities to reduce that heating. Here, we introduce a new definition of anthropogenic heat emissions from buildings. Specifically, we contend that a more useful definition must compare total sensible heat emissions from a building and its surrounding land with the emissions that would have been generated from the same land without a building. This definition includes convection from all building surfaces, heat emissions from the building air conditioning system, and infiltration/exfiltration of heat. It also considers shading of other buildings and the ground surface. The proposed framework is intended not to replace existing waste heat emissions approaches within atmospheric models, but rather to provide a separate approach for truly understanding the role of building construction, materials, and operations in affecting the urban environment. We implement this framework through urban building energy model simulations to estimate the actual hourly profiles of anthropogenic heat from an archetype office building of 3 different heights in four US cities in varied climate regions. In the summer season, 6 story buildings are responsible for a sensible heating of the environment that is three to four times the magnitude of their energy use. For 2 story buildings 62 to 69% of this sensible heating in summer is due to convection from the roof surface alone, while less than 29% is due to waste heat from air conditioning systems. So, the rooftop surface is twice as important as the building energy use in determining the extent to which a building warms the surrounding environment. These results demonstrate the flawed nature of thinking of anthropogenic heat from buildings solely from the perspective of energy use or emissions from heating and cooling equipment. The proposed framework is of crucial importance in understanding how buildings affect their surrounding thermal environments. Ultimately, it can inform strategies to mitigate heat emissions as it quantifies the role of façade and rooftop construction materials and their thermal and radiative properties.

Impacts of life satisfaction, job satisfaction and the Big Five personality traits on satisfaction with the indoor environment

Providing indoor environmental quality (IEQ) that satisfies building occupants is an essential component for sustainable and healthy buildings. Existing studies mainly analyse the importance of environmental factors on occupant satisfaction, but often overlook the influence of personal factors. Here, we aim to explore the impact of personal factors like life satisfaction, job satisfaction, the Big Five personality traits, sex, and age on occupant IEQ satisfaction. We conducted a cross-sectional assessment in nine air-conditioned commercial buildings in Singapore and surveyed 1162 individuals on their satisfaction with 18 IEQ parameters. Using proportional odds ordinal logistic regression, we found that occupants with higher job and life satisfactions were, respectively, 1.3–2.3 and 1.3–2 times more likely satisfied with the 18 IEQ parameters. The odds ratios (OR) for overall environment satisfaction and job and life satisfaction were 2.1 (95% CI: 1.8–2.6) and 1.9 (95% CI: 1.6–2.3). We speculate that occupants’ satisfaction with their job and the overall environment are entwined, meaning that a better workspace could improve job satisfaction and vice versa. We observed some associations between the Big Five personality traits and some IEQ parameters, but the corresponding effects were small. Due to the substantial relationship between job and overall workspace satisfaction observed in this study, we recommend including job satisfaction questions in future post occupancy evaluations (POEs).

Air-conditioning in New Zealand: power and policy

Policies, codes, standards and voluntary ‘green’ assessments have exacerbated cooling demand in New Zealand’s commercial buildings. Building codes allow designs to use single glazing on the facade, voluntary ‘green’ criteria are not higher than the legal minimum in the code and inexpensive energy for commercial buildings all contribute to an increasing use of air-conditioning. Legal standards for the energy efficiency of the building envelope of commercial buildings have not significantly changed in over a quarter of a century and, over much of the same time, the cost of electricity (the predominant form of energy in New Zealand used to heat and cool buildings) has decreased for commercial buildings. These factors have led to an increased dependency on air-conditioning in commercial buildings. This increase in energy demand is unnecessary and can be reduced through policies, codes, and standards that reduce solar gain and use mixed-mode ventilation. The reduction in air-conditioning demand will improve energy security and reduce greenhouse gas emissions. <em><strong>Policy relevance</strong></em> Inaction by successive governments (influenced by industries and lobby groups) has resulted in an energy culture in New Zealand that has moved air-conditioning from being a luxury to a dependency. The presented analysis makes a case for improving building standards to reduce commercial buildings’ dependency on air-conditioning. New requirements could reduce energy demand by specifying a maximum energy allowed for cooling and a set of practical measures (<em>e.g</em>. the use of natural ventilation, reduction of solar gain by the use of shading, consideration of orientation, maximum amounts of glazing in facades and higher performance specifications for glazing).

Feasibility analysis and feature comparison of cold thermal energy storage for off-grid PV air-conditioned buildings in the tropics

Cold thermal energy storage (CTES) is a cost-efficient storage approach for PV powered air-conditioning systems in tropical buildings. However, the feasibility and performance of different CTESs, including chilled water storage, ice storage, PCM cooling storage, and building thermal storage, are still unclear for off-grid PV air-conditioned buildings.In this study, an off-grid PV system with battery and CTES is proposed, including the operation strategy to manage the energy-storage process. To implement all CTES-types, a co-simulation model, which integrates the system model with the ARX (autoregressive with exogenous input) cooling-load model, is constructed to enable the interaction between supply- and demand-side. Based on the minimization of net present cost and the constraint of a certain required solar fraction, an optimization method is developed to find the optimal system-configuration. Moreover, an office, a hotel, and a residence are selected for a case study.The results indicate that CTES is feasible for higher solar fraction. The feasibility ranking of building type is (from high to low): residence, hotel, and office. In the most suitable case (residence), the maximum reduction of system costs (compared to battery-only system) is 49.76%, 41.77%, 44.31%, and 22.78%, respectively, for chilled-water storage, ice storage, PCM cooling storage, and building thermal storage. These values are 22.48%, 12.00%, 17.42%, 2.60% for the hotel, and 19.26%, 11.57%, 13.64%, 4.06% for the office. In addition, the sensitivity analysis shows that the increasing cost of both PV-array and CTES-device affects the feasibility of CTES negatively, while the increasing battery cost is a positive factor. Compared to the cost of the PV-array and the CTES-device, the battery cost represents the most significant effect-factor for feasibility.

Performance and economic evaluation of CO2 (R744) air conditioning system driven by compressed air engine

Traditional building air conditioning uses electricity or thermal energy to drive the refrigeration cycle. The energy released by the expansion of compressed air can also be used for driving the refrigeration cycle. Moreover, the expanded low-temperature air can be used in the air conditioning system too. In this paper, three forms of CO2 air conditioning systems driven by novel reciprocating piston compressed air engines were designed, namely EAGC (Exhaust Air for Gas Cooler), EAS (Exhaust Air for Sub-cooler), and EASC (Exhaust Air for Space Cooling), to analyze the performance and economics of CO2 air conditioning systems combined with compressed air energy storage technology. Twenty-seven typical cities were selected in different climate regions in China to evaluate the systems' performance and running cost under outdoor temperature changes and different electricity prices. The results show that compared with the electricity-driven CO2 air conditioning system, the three systems can greatly improve the system COP (Coefficient of Performance) but still cannot reach the performance level of the conventional freon refrigeration systems. However, in cities like Beijing and Shanghai with the large peak-to-valley electricity price difference, EASC system compared to the electricity-driven R410A air conditioning system running costs are lower, the average running cost per hour can be saved 11.96% and 16.35%, respectively. This means that the CO2 air conditioning system with compressed air energy storage technology has a certain economic application value and can be popularized on reasonable occasions. This innovative system design can help solve the contradiction between supply and demand of building energy, realize leisure energy consumption, and reduce the economic cost of energy consumption on the demand side.

Field study on human thermal comfort and indoor air quality in university dormitory buildings

Field studies on the environmental conditions and occupant thermal comfort were carried in air-conditioned buildings and no air-conditioned building in Xi’an, China. The present study aimed to explore the effect of indoor thermal history on the thermal adaptation and indoor air quality of occupants. Based on a field study, 550 and 580 data sets were obtained in naturally ventilated (NV) and spilled air-conditioned dormitory buildings (SAC), respectively. The physical environment parameters and subjective responses were explored. Most of the environment in NV mode were warmer than the current standard upper limit (28 °C). The neutral temperature of the NV group was 26.7 °C, 1.5 higher than that of the SAC group (24.6 °C). The upper limit of 80% acceptable temperature range was 29.2 °C for the NV group, 1.7 °C higher than that of the SAC group (27.5 °C). Compared to the SAC group, a warm indoor thermal history of the NV group produced a shift to higher neutral temperature and higher acceptable temperature. Differences were found in the indoor environment quality and in the occupant’s subjective satisfaction between the two groups. Compared to PMV model, the adaptive model was more applicable to spilt air-conditioned building.

A review on phase change materials (PCMs) for thermal energy storage implementations

With the rapid developments in the industry and technology, the energy need is increasing. 80% of the CO2 emission in the atmosphere is caused by the use of fossil based fuel and this situation has a serious impact on climate change. Therefore, energy researchers/engineers mainly work on the development and improvement of the techniques in order to use renewable energy sources more effectively. In this context, intensive studies have been carried out in order to use the energy from the sun in the most efficient way, by active or passive means when it is needed. Because solar energy is a discontinuous energy source within day and seasons, its storage in thermal form is one of the commonly used techniques. The most effective and easiest way to achieve this is to exploit from phase change materials (PCM) directly or by developing them as a composite. In this context, PCMs are used in various research areas of energy storage and thermal management systems. Since, particularly, approximately 40–45% of the energy consumption in the world is corresponding to the consumed amount for heating, cooling and air conditioning in buildings, the use of PCMs in buildings directly or by integrating them with building materials makes them more important in terms of energy saving. For this purpose, the number of studies on the use of effective phase change materials (PCMs) that have the ability to store/release solar energy in the form of latent heat is increasing. In this short review, general information about PCMs that can passively store thermal energy is presented. The diversity of PCMs, the selection criteria in practical applications, the difficulties of use, the solvation ways and also their potential utility areas were summarized.

An Experimental Study of Indoor Air Quality Enhancement Using Breathing Walls

Recently, many studies have focused on studying indoor air quality, especially with the outbreak of COVID-19, which is one of the reasons for the increased need to improve indoor air quality. Many ideas and applications are available to incorporate nature into buildings to improve indoor air quality (IAQ) and thus secure a higher percentage of natural ventilation and pollution reduction. One of these ideas is to use "breathing walls" (BWs), which are envelope components based on porous materials. They decrease energy consumed for heating, ventilation, and air-conditioning of buildings. The study discusses the effect of using the BW approach on thermal comfort in buildings. Moreover, the improvement in the IAQ when using two models - one using BWs (applying natural and industrial materials together on the BWs, which are composed of wooden concrete hollow bricks (WCHBs)), and the other model built with solid traditional bricks (STB) - was studied through an experiment to compare air temperature, carbon dioxide (CO₂) concentration, indoor relative humidity and thermal behavior. The experiments were conducted on the two models for five months in the summer of 2019, and the results of both models were compared. From the results, it may be concluded that the model with BWs exhibits improved thermal behavior than the model with traditional bricks by recording on average three to five degrees lower than the outside temperature. Moreover, the relative humidity is lower in the WCHB model than in the STB model by ~41.66% in the same conditions; however, the CO₂ concentration (ppm) in the WCHB model was lower than that in the STB model by ~28.5% in the same conditions.

Evaluation of energy utilisation efficiency of central air conditioning in large buildings based on entropy weight-cloud model

In the evaluation of the energy use efficiency of the existing large air conditioners, the problems of low accuracy and high time cost are presented. The structure and movement mechanism of air conditioners in large buildings are analysed to obtain efficiency evaluation results. The covariance matrix was used to obtain the evaluation index of energy utilisation potency in air conditioners. Through proportion of influencing factors, the function relationship between indoor temperature change and cooling load change was determined based on the distribution of cooling load in large buildings. The entropy weight-cloud evaluation model was built to complete the evaluation and analysis of utilisation potency. Through comparative analysis, we can see that error of energy evaluation for air conditioner is less than 3%, and that need time cost is small.

Evaluation of energy utilisation efficiency of central air conditioning in large buildings based on entropy weight-cloud model

Evaluation of energy utilisation efficiency of central air conditioning in large buildings based on entropy weight-cloud model