Energy Efficient Air Conditioning Research Articles

Potential for Electrical Energy Savings in AC Systems by Utilizing Exhaust Heat from Outdoor Unit

This study explores the potential of utilizing waste heat from air conditioning systems, one of the largest consumers of electrical energy. Currently, most of the waste heat generated by outdoor units is typically released into the environment without being utilized, leading to missed energy-saving opportunities. This study analyzes the potential for improving electrical energy efficiency in air conditioning (AC) systems by harnessing this waste heat. Two primary approaches are evaluated: the first is the use of waste heat for domestic water heating, and the second is the conversion of heat into electrical energy using thermoelectric generators (TEG). The results of this research indicate that both methods have the potential to improve overall energy efficiency significantly. However, challenges related to conversion efficiency and integration of these technologies with AC systems require further, more specific studies. These findings are expected to contribute to more efficient and environmentally friendly cooling systems by optimizing technology and overcoming barriers to wider implementation.

Design of ionic liquids as a desiccant for the liquid desiccant type air conditioning system

Abstract Recently, liquid desiccant air conditioners (LDACs) have gained rapidly growing interest as an important candidate for an energy-efficient air conditioner. By enabling moisture absorption from the air, ionic liquids (ILs) can serve as a novel desiccant source for LDACs. For insights into the design and optimization of ILs to this end, we herein present a survey of studies on dehumidification and other relevant properties of ILs and offer some molecular perspective on their feasibility as a desiccant.

Artificial neural networks for predicting the performance of heat pumps with horizontal ground heat exchangers

A Ground Coupled Heat Pump (GCHP) is a highly energy efficient heating, ventilation, and air conditioning (HVAC) system that utilises the ground as the heat source when heating and as the heat sink when cooling. This paper investigates GCHP systems with horizontal Ground Heat Exchangers (GHEs) in the rural industry, exemplifying the technology for poultry (chicken) sheds in Australia. This investigation aims to provide an Artificial Neural Network (ANN) model that can be used for GCHP design at various locations with different climates. To this extent, a Transient System Simulation Tool (TRNSYS) model for a typical horizontal GHE applied in a rural farm was first verified. Using this model, over 700,000 hourly performance data items were obtained, covering over 80 different yearly loading patterns under three different climate conditions. The simulated performance data was then used to train the ANN. As a result, the trained ANN can predict the performance of GCHP systems with identical (multiple) GHEs even under climatic conditions (and locations) that have not been specifically trained for. Unlike other works, the newly introduced ANN model is accurate even with limited types of input data, with high accuracy (less than 5% error in most cases tested). This ANN model is 100 times computationally faster than TRNSYS simulations and 10,000 times faster than finite element models.

Development and validation of a model for an air-to-air air conditioner

Air conditioning units are responsible for a significant amount of global warming, with demand predicted to triple by 2050. Mathematical models aid in designing energy efficient air conditioners that can contribute to climate change mitigation. This study presents a steady-state model for a air-to-air air conditioner. The proposed model can assist in reducing the number of experiments and optimizing the efficiency of air conditioning systems. It utilizes a bottom-up approach to solve for compressor, condenser, capillary tube, and evaporator sub-models. The compressor is modelled using polynomial equations to determine refrigerant mass flow rate and power consumption based on operating temperatures. Heat exchanger models are solved using finite volume approach and reliable correlations are used for void fraction, friction factor, and heat transfer coefficient calculations. The closing equations are the mass conservation, i.e. constant refrigerant charge, and the equivalence between the mass flow rate sucked by the compressor and the one that flows through the capillary tube, while the evaporating and condensing pressures are the independent variables. The capillary tube is modelled using semiempirical correlations. The model is validated against experimental data at various operating conditions and shows a ±7% agreement for predicted cooling capacity.

Comparative study on performance of counter-flow dew-point indirect evaporative cooling systems via a more realistic and experimentally validated three-dimensional model

Dew-point indirect evaporative cooling (DPIEC) technology is designed and applied as a low carbon-emission and high energy-efficient air conditioning (AC) solution without employing non-environmentally friendly refrigerant and mechanical compressor for cooling in building sector. A more realistic three-dimensional (3-D) model of the DPIEC that better captures the fundamental thermodynamic of its operation is proposed. It considers the variability of air thermal properties and is employed to investigate the DPIEC's performance for three possible arrangements. The 3-D model is classified as configurations 1, 2 and 3 based on the relative flow direction between primary/secondary air and spray water. Experimental results indicate that the model can well evaluate the thermodynamic performance. Additionally, the influence of crucial factors on the performance is parametrically studied by employing three performance indexes. Comparison reveals that configuration 1 can achieve the highest effectiveness and cooling capacity. Results also show that the secondary-to-primary air ratio should be confined to around 0.3 to achieve maximum cooling capacity, and the optimal channel gap should be limited to the range from 3 to 4 mm. Comparatively, the relative flow direction between the spray water and the primary/secondary air has a greater effect on the thermodynamic performance than the spray water inlet velocity.

Factors influencing purchase intention towards energy efficient air conditioners: a study of Indian households

PurposeThis study aims to examine the antecedents of purchase intention toward energy efficient air conditioners by incorporating the theory of planned behavior (TPB) with two additional constructs, i.e. environmental concern and personal norms. TPB is one of the most widely used theoretical framework to study consumer behavior.Design/methodology/approachThe study applied a quantitative technique using a survey method by distributing self-administered questionnaires among the Indian households who have purchased energy efficient air conditioners in the past six months or had enquired to do so. The study collected data from three select regions: Delhi and NCR, Punjab and Tri-city. The collected data of 424 respondents have been analyzed using confirmatory factor analysis and structural equation modeling.FindingsThe study posits that normative factors such as subjective norms and personal norms have a relatively higher influence on purchase intention. Despite the significant existence of environmental concern, the study did not find environmental concern directly influencing purchase intention.Research limitations/implicationsThe sample size of the study is too small and pertains to specific regions. Thus, it could hinder the generalizability of the results. Advertisement appeals should be related with enhancement of self-esteem in terms of making responsible and valuable contribution to environment protection through the purchase of energy efficient air conditioner.Originality/valueThere are a few studies in the Indian context studying consumer’s purchase intention toward energy efficient air conditioners to which this study adds. The study provides an important contribution to marketers in developing strategies for increasing purchase intention toward energy efficient air conditioners in view of their stage in the product life cycle, diffusion of product and influence of normative factors.

ADOPTION OF ENERGY-EFFICIENT AIR CONDITIONERS AND THE PRINCIPAL-AGENT PROBLEM: EVIDENCE FROM CHINA

As an important measure for households’ adaptation to climate change, air conditioning is becoming more and more prevailing in developing countries, which implies a larger demand for electricity and highlights the role of energy-efficient air conditioners (ACs) in energy saving. Using household-level data from China, this paper investigates the determinants of households’ adoption of energy-efficient ACs, with a focus on the role of the split-incentive (principal-agent) problem between homeowners and renters in the adoption of energy-efficient ACs. The results show that the principal-agent (PA) problem does exist in the adoption of energy-efficient ACs in Chinese households, with renter-occupied dwellings being about 10.2% more likely to have low energy-efficient ACs installed in dwellings, compared to homeowner-occupied dwellings. Moreover, the increased energy consumption and carbon emissions due to the PA problem in AC investment are calculated based on the estimated agency effect.

Comparative analysis of energy-efficient air conditioner based on brand

The availability of numerous air conditioners in the market with various brands and types often leads consumers to be unaware that the purchased air conditioner may be inefficient in terms of energy usage. This research aims to determine the most energy-efficient air conditioner based on the brand of air conditioners available in the market. The research method consists of four stages: data collection, data preprocessing, data analysis, and interpretation of results and conclusions. The data used in this study was obtained from the database of the Directorate General of New, Renewable, and Energy Conservation (EBETKE), which consists of 11 AC brands sold in the market. Data analysis was performed using data distribution analysis techniques, standard deviation calculations, and correlation analysis between variables, such as the Pearson's correlation coefficient. The results of this study show that the AC brand with the highest average efficiency value is Mitsubishi Electric, with a value of 16.36 Energy Efficiency Ratio (EER), while the AC brand with the lowest average efficiency value is GREE, with a value of 5.640 (EER). Each AC brand has a different average efficiency value, with significant variations. From the correlation heatmap results, the AC power does not appear to significantly affect the AC efficiency value, where AC with lower power tends to have higher efficiency values, but there are also AC with high power and high efficiency values. Additionally, the cooling capacity value also appears to have a small effect on the AC efficiency value, where AC with lower cooling capacity tends to have higher efficiency values. However, some AC brands have high cooling capacity values but also have high efficiency values. This study also shows a moderate correlation between the AC efficiency value and the AC's annual energy consumption value, where AC with higher efficiency values tends to have lower annual energy consumption values.

Review of liquid desiccant air dehumidification systems coupled with heat pump: System configurations, component design, and performance

Vapor Compression Systems (VCS) are the most common air conditioning technology. VCS cool the air to its dew point temperature (overcooling) to remove water vapor in the air through condensation and then reheats the air back to the comfort temperature for direct use. The VCS process is inefficient due to overcooling and reheating. Liquid Desiccant Dehumidification (LDD) is a potentially energy-efficient air conditioning. LDD removes water vapor in the process air using liquid desiccant’s high-water affinity. It hybrids with sensible cooling to control temperature and humidity separately. The LD in the LDD becomes weak after dehumidification. The LDD needs additional heating to regenerate the weak Liquid Desiccant (LD) to a high concentration for dehumidification.Earlier versions of the LDD systems use highly concentrated liquid desiccant (large water removal capability) to dehumidify the air by only dealing with latent load. It leads to highly elevated temperatures above 60 °C of heat sources (combustion or electric resistance-based heating) for regeneration. The energy needed for the elevated temperature heat resource significantly reduces or demolishes the benefit of LDD systems. In the recent two decades, researchers have investigated a new configured LDD system that couples an LDD with a heat pump at both dehumidification and regeneration sides for better efficiency.The heat pump provides cooling (from the evaporator) for both dehumidification and sensible cooling and simultaneous heating from the condenser for regeneration. The highly integrated system (HP-LDD) with improved efficiency enables the LDD to operate at lower concentrations and temperatures in dehumidification and regeneration.This paper depicts the working principle behind HP-LDD and its heating and cooling requirements. It reviews the comparison between the HP-LDD systems and the conventional LDD systems regarding system configurations, component design, energy efficiency, and dehumidification performance characteristics. The main findings from the review include the preferred use of packed bed over membrane-based dehumidifiers, the use of internally cooled dehumidifiers enabled by the HP cooling capacity, the high dispersion of HP operation conditions, and the dependence of dehumidification performance on various dehumidifiers. An outlook for future research on HP-LDD strategies is presented based on the reviewed works and their limitations.

Boosting the air conditioning unit performance using phase change material: Impact of system configuration

Boosting the energy efficiency of air conditioning (AC) systems will considerably impact on lowering domestic power consumption. Innovative methods are being developed to enhance AC performance. One promising method involves integrating phase change materials (PCM) with the AC systems. The significant PCM charging period is a primary limitation of coupling AC systems with PCM in the previous research. The current study aims to investigate the impact of coupling an AC unit with various PCM container configurations (e.g., parallel plates, staggered and aligned tubes, and elliptical tubes) on PCM charging and discharging, and AC performance. During the nighttime, the low ambient temperature is charged inside the PCMs. Then, during the daytime, the hot ambient air is cooled by passing through the cold PCM heat exchanger before passing over the unit condenser. A complete dynamic mathematical model for the proposed system is constructed and solved numerically using ANSYS software. Results indicate that applying the cylindrical arrangement lowers the solidification time of the PCM at night by approximately one-third compared to the plate arrangement. Also, raising the inflow air temperature of the air-PCM heat exchanger increases the air temperature difference through the heat exchanger and saving percentage of the AC's power and decreases the PCM's charging and discharging time. For inflow air temperatures of 318.15 K, 313.15 K, and 308.15 K, the maximum average percentage of saved power is around 25 %, 18.7 %, and 12.5 %, respectively for 2 h working and around 8.4 %, 7.2 %, and 6.3 %, respectively for 8 h working of the AC unit. Cylindrical configuration is preferable for daily use of AC systems as the charging process can be achieved through the nighttime.

Preferred green home features by potential buyers in Sibu Sarawak

Green concept was gaining attention since 1960s, with research and development initiatives been allocated to ensure its evolvement, for enhancing the minimization on the impact of global warming and greenhouse gases emissions. Enormous green home features be introduced worldwide, but such features were not collated into a single piece of information, and the preference of home buyers varies according to the culture, living environment, and personal preferences. This research aims to examine the relative importance of green home features to potential home buyers in Sibu, Sarawak. Purposive and random sampling methods were adopted as the participants need to meet the requirement of having intention to purchase a house in Sibu in the next five years. Quantitative online questionnaire survey was distributed to the potential home buyers with 118 valid responses returned (response rate 29.57%). The results indicated that air quality, energy saving lighting, and energy efficient air conditioner were the three most preferred features by the respondents. This research could contribute to the knowledge gap of the preferred green home features by the potential home buyers in Sibu, and hence, serve as a piece of supporting document to the developers, to meet buyers’ demand and further increase the supply of green home in Sibu.

Energy-efficient air conditioning system using a three-fluid heat exchanger for simultaneous temperature and humidity control

Room air conditioners are unable to simultaneously control the temperature and humidity of the air supply. Although temperature-regulating dehumidifiers can simultaneously control the temperature and humidity, they have complex refrigerant pipelines, and the heat exchanger exhibits air resistance when the reheat demand is low. This study proposes an air conditioning system for simultaneous temperature and humidity control, using a three-fluid heat exchanger. The supply air temperature is adjusted by changing the air volume ratio and cooling water flow rate through the three-fluid heat exchanger, which is used as the condenser. Free cooling can be realized by supplying low-temperature cooling water to treat the return air. Numerical models were built to simulate the performance of the devices in the system, and were validated by experimental results. The temperature-regulating performance and energy consumption under different conditions were numerically calculated using a case-studied air-conditioned room in Beijing. The results are summarized as follows: 1. The proposed strategy can regulate the supply air temperature over a wide range of temperatures. 2. Compared with those of the temperature-regulating dehumidifier system, the compressor and fan energy consumption of the proposed system are reduced by 19.1% and 15.5%, respectively, with a total energy-saving rate of 15.8% in the cooling season. 3. Compared with those of the room air conditioner system, the compressor energy consumption of the proposed system is reduced by 11.5%, and the energy-saving rate of the entire system is 6.3%. The initial investment of the proposed system does not increase significantly compared with conventional systems, and the refrigerant pipeline and valves can be simplified, resulting in acceptable economic performance for the proposed system.

Use of membrane energy exchanger in ventilation: Odour sensory measurement

Membrane energy exchanger (MEE) for a new generation of energy efficient heating, ventilation and air conditioning (HVAC) systems has attracted wide attention. As MEE has been increasingly employed, extensive studies of heat and moisture transfer features have been carried out. Nevertheless, odour transfer through MEE, which may cause odour nuisance and complaints regarding indoor environment, is seldom studied. For most applications of MEE in ventilation, MEE is presumed to be able to prevent the pollutants transfer including volatile organic compounds (VOCs) and odours, despite a lack of clear scientific evidence. This study measured the potential odour transport through an MEE by using an odour sensation panel. The sensory measurement shows the percentage of dissatisfied could reach 84% for the odour source of waffle mix powder in extract air. In comparison, the percentage of dissatisfied is 5% when there is no odour source. The sensory air acceptability, odour intensity and hedonic tone for the supply air using MEE are assessed by a panel for different odour sources in the extract air. The findings of this study indicate that the odours generated from, such as cooking and cleaning in kitchens and in bathrooms, are likely to be undesirably transferred to the supply air through the tested polypropylene membrane exchanger, which may lead to a poor perception of the indoor environment. It may be particularly important to pay attention to the odour transfer through MEE when the odours originate from a kitchen. More studies for different membranes are recommended in the future.

Enhancement of Chiller Performance by Water Distribution on the Adiabatic Cooling Pad’s Mesh Surface

Evaporative cooling is widely recognized as an energy efficient and environmentally-friendly air conditioning solution, and it has drawn a lot of market interest in recent years. However, this technology is accompanied by several challenges. For instance, insufficient evaporation due to poor and non-homogenous water distribution of the pre-cooling pad significantly reduces the cooling performance. The aim of the study is to develop a technique for numerical simulation of the distribution of a droplet liquid (water) on the mesh surface of an adiabatic cooler to improve the performance of air conditioning equipment. Modern computer-aided design (CAD)/computational fluid dynamics (CFD) programs were used to solve the issue. For the mathematical modelling of the medium motion, non-stationary Navier–Stokes equations were used. Parameters such as heat, mass transfer, and the efficiency of liquid droplet spraying were determined. The current study presents CAD modelling, conducted in SolidWorks platform, of water distribution on the adiabatic cooling pad’s mesh surface for improving air conditioning equipment performance. This study provides the methodology for computer modeling and numerical calculation of the parameters of adiabatic cooling, such as modelling of water atomization process. The results show that the use of additional metal mesh intended as cooling pads increases the mass transfer coefficient by Sh ≈ 15–40%; heat transfer coefficient Nu increases by ≈20–40%; and the atomization efficiency increases by ≈30–40%. The installation of metal pad mesh allows for equalized uniformity of the water distribution. The results imply that there are more opportunities to optimize the parameters of adiabatic cooling, which should be evaluated in further research on the subject.

Optimizing air conditioning systems by considering the grades of sensible and latent heat loads

Traditional air conditioning systems uniformly treat all the sensible and latent heat loads of buildings by the lowest temperature chilled water, resulting in low efficiencies. Previous researchers proposed the temperature grades of staged loads and various energies, and the systems operate efficiently after being designed by grade matching. However, the method includes latent heat load with sensible heat load as the corresponding temperature grade; thus, the energy efficiency of the system designed can still be further improved. The latent heat systems have been experimentally improved, but the extent of applying appropriate humidity sinks and cooling and heating sources is unclear, and they are not comprehensively designed with sensible heat systems in the entire air conditioning systems. In this study, the humidity grade for the latent heat load and humidity sink is defined. A method for converting humidity grade to temperature grade is developed to obtain the potential of utilizing different humidity sinks, and cooling and heating sources in both sensible and latent load treatments. A grade-matching method is proposed to realize a more energy-efficient air conditioning system. A case study of an office building is used to demonstrate the method. The system designed using the proposed method improves energy-saving rates for heat pumps by 34.0% and 11.2% compared with the typical system (where latent and sensible heat subsystems are separately designed) and the system designed by the previous method (where the air treatments are limited to condensation dehumidification), respectively. This method is conducive to the more reasonable utilization of natural and waste cooling and heating sources for air treatment, and it reduces the capacities and energy consumptions of electric heat pump systems, resulting in significant energy savings.

The rebound effects of energy-efficient air conditioners: buy more, bigger, or use longer?

The rebound effects of energy-efficient air conditioners: buy more, bigger, or use longer?

A novel design, implementation and performance evaluation of the first electronic expansion ejector for energy saving of a mini split air conditioner controlled by inverter

Due to the global warming impact, which has resulted in rising energy costs, it has become vital to adopt energy-efficient air conditioners and improve their performance at a low power consumption rate, which is considered a big challenge. Ejectors have received much attention over the last decade because of their simplicity, cheap maintenance, high operating capacity, low-temperature handling, no risk of blockage, and longer lifespan at reduced costs. For the first time in the current study, a novel electronic ejector as an expansion device is designed and implemented in conjunction with a mini-split air conditioner that uses the refrigerant R-410A and is controlled by an inverter.The effects of several design and operation factors, such as primary nozzle diameter, primary nozzle length, mixing throttle diameter, capillary tube diameter, capillary tube length, air average velocity, external air temperature, and conditioned space thermal load, are also considered. The study aims to investigate the system performance by integrating a new electronic ejector technology that may be used as an expansion device in conjunction with an inverter-controlled air conditioner. According to the findings, the electronic ejector has a greater COP and saves more energy than the electronic expansion device. Dimensionless correlations of COP and EER incorporating the experimental results are also obtained.

Solar Desiccant Cooling System as an Alternative Solution for Net-Zero Energy Buildings (NZEBs) in the Tropical Regions

The development of energy-efficient cooling systems is a major challenge for Net-Zero Energy Buildings (NZEBs) in tropical climates. This study proposes a solar-assisted two-stage hybrid desiccant cooling system as an energy-efficient air conditioning (AC) system for use in tropical NZEBs. TRNSYS software was used to simulate the proposed model for application in a classroom with a high latent load (51%). The simulation results were analysed in terms of air properties, energy allocation, and potential energy savings. It was discovered that using two-stage dehumidification instead of one-stage dehumidification reduced regeneration temperature from 72 °C to 63 °C, which leads to considerable reduction in backup heater energy consumption. This study shows that by means of the proposed model instead of a fan coil unit, thermal comfort and energy savings of 37% can be achieved.

Energy-saving potential and cost-effectiveness of active energy-efficiency measures for residential building in warm-humid climate

The commitment for energy-efficiency improvement becomes increasingly important in the context of global initiatives for sustainable development, and buildings have a great potential in this regard. As part of achieving energy-efficiency in residential buildings, the present study has analyzed the energy-saving potential and economic viability of adopting active energy efficiency measures (EEMs) on a detached family house in warm-humid climate of South India. The EEMs considered were selective air-conditioning (AC), lighting control, thermostat setting, mixed-mode ventilation, and energy-efficient AC, lighting and appliances. The modeling and simulations were performed by a reliable software (DesignBuilder, V.6) to estimate the annual energy consumption of the building with and without EEMs. The individual and combined contributions of EEMs in reducing the building's energy performance index (EPI) were quantified, and their economic viability was assessed in terms of discounted payback period (DPP). The results showed that about 63.5% reduction in EPI was possible by implementing the proposed EEMs, and the DPP for the additional investment was estimated to be 4.94 years.

Experimental investigation of an integrated absorption- solid desiccant air conditioning system

Separate handling of sensible and latent components of building loads can be an energy efficient approach compared to simultaneous management of both. This paper presents a detailed experimental analysis of an energy efficient air conditioning system using solid desiccant integrated with absorption system for separate building thermal load handling. The experimental system consists of silica-gel based solid desiccant for latent load handling, whereas the gas fired air-cooled NH3-H2O absorption chiller is used to handle sensible load of the space. A chilled water-cooling coil heat exchanger is installed on the process side of desiccant cooling system to integrate it with the absorption chiller. The performance of integrated absorption- solid desiccant system is compared with a standalone conventional desiccant air conditioning system with a direct evaporative cooler considering it as baseline system under wide range of operating conditions including air temperature, air humidity, and regeneration temperature. The comparative analysis is performed in terms of supply air temperature, cooling capacity, and coefficient of performance. The experimental results exhibit that supply air temperature of the integrated system is 15.2 °C compared to 24.6 °C achieved by conventional desiccant system. Moreover, COPth of the integrated system is also 50–55% higher than its counterpart and it is almost comparable with double-effect absorption chiller. It is concluded that the integrated system using separate load management approach is more efficient for HVAC applications.