Energy Efficiency Of Air Conditioning Systems Research Articles

Automated fault detection and diagnosis of chiller water plants based on convolutional neural network and knowledge distillation

Automated fault detection and diagnosis (AFDD) plays a crucial role in enhancing the energy efficiency of air-conditioning systems; its quantitative impact has gained greater clarity in recent years. Deep learning has emerged as a promising tool for image classification, and its application in the context of AFDD of heating, ventilation and air-conditioning (HVAC) systems is gaining traction owing to its exceptional performance. However, the deployment cost of deep models in practical scenarios increases owing to the large number of parameters involved. This study uses knowledge distillation to significantly reduce the number of model parameters and the cost of model deployment without compromising the accuracy of AFDD. This case study builds a simulation model and 31 types of fault datasets based on an actual HVAC in Japan. We transformed the time series into two-dimensional image tensors via the Graham angle field to apply state-of-the-art image classification algorithms for AFDD. Based on these findings, it is evident that the proposed teacher model can achieve a remarkable top-1 accuracy of 88.45 % and top-5 accuracy of 99.78 %. Furthermore, the knowledge distillation algorithm performed equally well, if not better than the teacher model, with a top-1 accuracy of 88.12 % and a top-5 accuracy of 100 %. This was achieved with a significant reduction in the number of parameters by up to 56%.

Performance evaluation and users’ perception of courtyards role in indoor areas of mediterranean social housing

Cities confront two critical challenges: general overheating and inefficient use of energy resources within their housing buildings, both adversely affecting urban citizens' daily lives. To mitigate these issues, passive techniques offer promising solutions on enhancing building comfort levels from a sustainable approach. Although this energy efficiency of air-conditioning systems in buildings in warm climates has been extensively analysed, the influence of the microclimate of transitional spaces attached to them on this performance has not yet been properly assessed. Investigating the potential benefits of the implementation of courtyards within Seville's social housing infrastructure for passive conditioning purposes is one way of reducing this research gap. Furthermore, the study also includes the subjective perception of users' thermal well-being around these spaces and their own social relationship related to their use. The work relies on detailed data analyses carried out using DesignBuilder software to quantify the benefit effectively accrued from courtyard utilization. Concurrently, user surveys conducted help determine perceived thermal comfort aiding better configuration management and passive design strategies of urban social housing. Findings from monitoring and simulation reveal that courtyards work faultlessly as a highly effective and efficient passive cooling system whilst promoting energy efficiency up to 20,5%. Surveys confirmed these findings with data revealing significant improvements in thermal comforts perception inside courtyards and within indoor spaces adjacent to the courtyards. This research provides novel insights into how architects and urban managers might integrate passive strategies into future designs for optimizing comfort levels in social housing using courtyards as one possible environmental measure for achieving sustainability targets.

Smart Fuzzy Petri Net-Based Temperature Control Framework for Reducing Building Energy Consumption.

This study addresses the pressing issue of energy consumption and efficiency in the Kingdom of Saudi Arabia (KSA), a region experiencing growing demand for energy resources. Temperature control plays a vital role in achieving energy efficiency; however, traditional control systems may struggle to adapt to the non-linear and time-varying characteristics of the problem. To tackle this challenge, a fuzzy petri net (FPN) controller is proposed as a more suitable solution that combines fuzzy logic (FL) and petri nets (PN) to model and simulate complex systems. The main objective of this research is to develop an intelligent energy-saving framework that integrates advanced methodologies and air conditioning (AC) systems to optimize energy utilization and create a comfortable indoor environment. The proposed system incorporates user identification to authorize individuals who can set the temperature, and FL combined with PN is utilized to monitor and transmit their preferred temperature settings to a PID controller for adjustment. The experimental findings demonstrate the effectiveness of integrating the FPN controller with a convertible frequency AC compressor in significantly reducing energy consumption by 94% compared to using the PN controller alone. The utilization of the PN controller alone resulted in a 25% reduction in energy consumption. Conversely, employing a fixed-frequency compressor led to a 40% increase in energy consumption. These results emphasize the advantages of integrating FL into the PN model, as it effectively reduces energy consumption by half, highlighting the potential of the proposed approach for enhancing energy efficiency in AC systems.

A novel machine learning-based model predictive control framework for improving the energy efficiency of air-conditioning systems

The dynamic optimization of key setpoints (e.g., supply water temperatures of chillers and cooling towers, or indoor temperature and humidity) can track the efficient performance point of the air-conditioning system (ACS), thus obtaining a great energy-saving effect. The model predictive control is an effective way to precisely adjust these setpoints. However, most of the existing studies focused on simple linear strategies, e.g., experience-based, rule-based, or component-based, which results in unsatisfactory energy efficiency. Aiming at this, the paper proposed a novel machine learning-based model predictive control (MLB-MPC) framework with predictive inputs of disturbances. The framework first employed the grid search and cross-validation to optimize the total energy consumption prediction models (TECPMs), which were built by data-driven models (e.g., multiple linear regression, artificial neural network, support vector regression (SVR), and random forest). And then the optimization performances of each TECPM to the controlled variables were obtained by using different optimization algorithms (e.g., genetic algorithm, particle swarm optimization (PSO), and simulated annealing). Finally, the optimal match of TECPMs and optimization algorithms was achieved by trade-off among prediction accuracies, optimization accuracies, and optimization time. The case studies demonstrated that the optimal match for the MLB-MPC is SVR and PSO as they had the highest prediction accuracy (mean absolute percentage error of 2.5%) and shortest optimization time (41 ms/per) and optimization accuracies with little difference. After adopting the optimal match, the MLB-MPC with predictive disturbing inputs achieved a great energy-saving ratio of 7.1% for the ACS, which was only less than the MLB-MPC with ideal disturbing inputs by 0.4%. This indicated that exact predictions of disturbances (e.g., cooling load and outdoor wet-bulb temperature) are important for the MLB-MPC. The proposed MLB-MPC framework would provide a method for improving the energy efficiency of ACSs.

Enhancing Energy Efficiency of Air-Conditioning Systems in Hot Climates through Refrigerant Vapor Injection: A Study of Kuwait and GCC Countries

This study is aimed at investigating the potential of the refrigerant vapor injection (VI) technique to improve the energy efficiency of air-conditioning (AC) systems in hot climates, with a focus on Kuwait’s sustainability goals for 2035. The VI technique was found to significantly enhance heating and cooling systems by lowering compressor discharge temperature and improving cooling capacity, resulting in an enhanced coefficient of performance (COP). Data from previous experimental studies were analyzed to correlate the VI technique’s cooling COP with operating conditions at high ambient temperatures ranging from 20°C to 52°C. The results showed that the VI technique was applicable at high ambient temperatures, leading to improvements of up to 35.4% compared to conventional cooling systems. Empirical formulas, comprised of the temperature parameters (ambient, wet bulb, condensation, and evaporation temperatures), were developed to predict the COP of the VI cooling cycles with a maximum mean absolute error (MAE) of 3.81%. The results also showed that the VI technique enhanced the cooling COP by up to 28% when operating at 51.7°C and up to 34% during the hottest month in Kuwait (July) compared to the conventional cooling cycle. The empirical correlations were also applied to other Gulf Cooperation Council (GCC) countries to examine the impact of ambient humidity on cooling COP, with predicted increases ranging from 13.5% to 21.2%. Further experimental studies are recommended to fully evaluate the cooling impact of the VI system in GCC countries.

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.

Performance Analysis of Evaporation and Heat Wheel-Based Building Air Conditioning Systems

Abstract Air conditioning in composite weather is relatively more challenging and also carries importance as it resembles conditions of hot-dry, cold, and warm-humid climates. Bifurcation of cooling and ventilation tasks happens to be one of the attractive techniques to design energy-efficient air-conditioning systems. It deals with the concept of providing a dedicated outdoor air system (DOAS) in conjunction with the air-conditioning unit. This study establishes the electrical energy consumption behavior of a building air-conditioning unit when modifications are done along the air pathway of the desiccant-integrated DOAS. For a 511 m2 building situated in composite weather, simulations in energyplus are carried out after necessary validations with the available standards. Here, two modes are discussed: in the first one, an indirect evaporation cooler (IEC)-based system is analyzed, while in the second mode, a heat wheel has been studied. For regeneration, a solar collector and supplementary electrical heater are provided. For the dynamic pattern of site environmental conditions, variations of room air temperature, humidity, thermal load, electricity, thermal energy, and solar fraction have been studied. Current analysis demonstrates that approximately 2994 kWh of the total thermal energy delivered by solar collector and supplementary electrical heater system can be saved through heat wheel instead of IEC. The usage of a heat wheel in the airflow pathway of the desiccant-integrated DOAS can offer energy savings up to 5.04% of the electrical energy with respect to IEC-integrated DOAS. Furthermore, the suggested design delivers a higher solar fraction.

A novel integrated index for simultaneous evaluation of the thermal comfort and energy efficiency of air-conditioning systems

Energy efficiency and thermal comfort are the main factors reflecting the performance of air-conditioning units, but these characteristics have been evaluated separately in previous studies. Considering that the goal of an air-conditioning device is to provide thermal comfort, energy efficiency should be simultaneously evaluated with thermal comfort in a scientific and practical manner. Therefore, the thermal comfort effective energy performance factor, expressed as EER*/COP* (the effective energy efficiency ratio/coefficient of performance), was defined in this study as the ratio of the effective cooling/heating capacity (in terms of the spacing ratio, effective working period, likelihood of dissatisfaction, and cooling/heating capacity) to the total electric consumption. To verify the characteristics of the proposed index, typical cases were analyzed using different supply air angles and set-point temperatures for the heating mode of a room air conditioner. The effective COP* and COP** were then respectively defined by considering the overall thermal comfort and local discomfort. The COP* increased as the set-point temperature increased and the supply air angle approached vertical, indicating higher energy efficiency. The overall and local thermal satisfaction indices, as well as the effective COP* and COP**, also increased as the set-point temperature increased and the supply air angle approached vertical, respectively indicating the most comfortable and uniform environments. Therefore, the proposed index considering both the indoor environment and energy performance indicated that a lower set-point temperature, higher supply airspeed, and more vertical supply air angle provide optimal performance.

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.

Investigation on heat transfer and phase transition in phase change material (PCM) balls and cold energy storage tank

The phase-change based energy storage provides an excellent solution for the mismatch of energy production and consumption. Cold energy storage tanks filled with PCM balls could be applied in energy-efficient air-conditioning systems. The main advantage lies in the reduction of energy storage space demand compared with water-based cold energy storage. Clarifying the pattern of freezing process within the PCM balls is of critical importance for the design of energy storage tank. In the present work, experimental measurement is conducted to obtain the temperature variance and phase transition process of one PCM ball. With the aid of CFD simulation software, physical model of one PCM ball is established and well-validated with experimental data. The validated model is then used to simulate the thermal performance of cold energy storage tank filled with multiple PCM balls. Meanwhile, the influences of parameters involving in the diameter of the PCM balls (90, 90&60, and 60 mm), and the flow rate of chilled water in the tank are evaluated. The results indicated that higher freezing rate of PCM ball can be achieved by smaller diameter of the ball and faster flow rate of chilled water. Under the conditions set in this study, the optimal diameter of phase change balls is determined to be 90&60 mm. and the best inlet flow rate is 2.196 m/h. When PCM balls are concerned for cold storage systems, it is proposed to set the diameter carefully in terms of the capacity of cold energy (flow rate of chilled water) and the limit of freezing duration.

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.

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.

Designing, Modelling and Experimental Investigation of Direct Evaporative Cooling System Coupled With Commercial Desiccant Dehumidifier

Abstract With the increasing demand of clean and energy-efficient air conditioning systems, evaporative air cooling technique is gaining significant attention owing to less energy consumption and environmentally safe technology in comparison with conventional refrigerant-based air conditioners. In this study, commercial desiccant dehumidifier is coupled with experimentally developed direct evaporative cooling (DEC) system to first dehumidify the air and then pass it through DEC to achieve human thermal comfort level defined by ASHRAE standards. Under the climatic conditions of Islamabad, Pakistan, multiple experiments were carried out at different temperatures, flowrate, and relative humidity of air during November, when air temperature and relative humidity were in the range of 25–30 °C and 40–60%, respectively. To analyze the system performance under summer ambient conditions, indoor temperature was increased by 8–10 °C and relative humidity by 15–25% in laboratory. Experimental analysis showed that the system can provide human comfort level for a range of temperature 29–39.7 °C and relative humidity of 65–80% at flowrate of 180 m3/h. To achieve thermal comfort at higher humidity level, DEC is coupled with commercial desiccant dehumidifier. However, due to desiccant regeneration by an electric heater in the dehumidifier, the overall power consumption of the whole system increases up to 1.95 kW. Two well-known indices coefficient of performance (CoP) and energy efficiency ratio (EER) are used to analyze the system performance. Experimental analysis revealed that CoP decreases with the increasing specific humidity of air, decreasing ambient temperature, and flowrate.

Towards the development of energy-efficient poultry air conditioning system

Towards the development of energy-efficient poultry air conditioning system

Comparison of Energy Efficient Air-Conditioning Systems

The purpose of this paper is to provide a comparison of energy-efficient air-conditioning systems in an office building in a warm, tropical climate. Miami, Florida was the city used for the demonstration. A typical office building from the coast of Miami was selected and to do a proper assessment of the energy efficiency of different air-conditioning units, we designed the shell of the office building and simulated the energy usage in eQUEST software. The software then generated the results for examining the energy usage of each air-conditioning systems and allowed us to determine which would be the most energy efficient based on the results received.

Energy-efficient air conditioning system of a data processing center

BACKGROUND: Currently, because of the rapid development of digital technologies, an increasing amount of computer computing power is required where data processing centers are built, which sometimes require power consumption in the megawatt range. For stable year-round operation of data centers, reliable engineering is required, which includes air conditioning systems (ACS) for year-round use with a given level of reliability. Several traditional methods of data center cooling are available, namely, precision air conditioners based on vapor compression refrigeration machines (PCRMs) and systems with intermediate coolant (so-called chillerfancoil systems). However, in modern settings, when the required capacity of data centers increases every year and the framework for environmental friendliness and energy efficiency of installations becomes stricter, new, more energy-efficient, and environmentally friendly solutions for data center cooling is needed.
 AIM: This study aims to compare the proposed energy-efficient ACS with combined vapor compres-sion and indirect-evaporative cycle with the most commonly used ACSs in data centers and to deter-mine the boundaries of transition between the operating modes of the proposed ACS in a data center operating in Moscow as an example.
 METHODS: This study employs the following methods: analysis of existing data center cooling sys-tems, determination of a typical design set of outdoor air parameters in the region under consideration, and calculation by comparative analysis of the energy consumption of the proposed and traditional ACSs for data centers.
 RESULTS: From our study, the different ACSs currently used for data centers, namely, precision air conditioners and chillerfancoil systems are highlighted. The main components of each system, the advantages and disadvantages observed in the design, installation, and commissioning processes, and the operation of the systems are described. An alternative ACS that combines PCRM and indirect-evaporative cooling is proposed. The comparative analysis of the proposed scheme and traditional so-lutions demonstrates that the combined ACS allows significant reduction in the energy consumption for data-center cooling. Therefore, under the conditions in Moscow, the proposed system for a particu-lar year will consume energy that is two times less than a chillerfancoil system with free cooling and 2.5 times less than a system with precision air conditioners that operate on the traditional vapor-compression cycles.
 CONCLUSION: The comparative analysis of the proposed energy-efficient ACS with combined vapor compression and indirect-evaporative cycle with the most commonly used ACS in data centers con-firms its high energy efficiency and provides greater environmental safety. The boundaries of the tran-sition between the operating modes of the proposed ACS are determined in a data center that operates in Moscow as an example, which exhibits high energy efficiency and reliable operation.

Performance of oil-free water-cooled chiller for a shopping center air conditioning system

Many researches have been conducted on cooling equipment to reduce its energy consumption, maintenance and operation cost. Oil-free chiller uses a magnetic bearing compressor to avoid friction loss from the bearing’s contact surface. In comparison to a conventional compressor, the magnetic bearing of the motor, with the help of variable speed drive (VSD), runs more efficiently at partial loads. This paper presents the application of oil-free compressors in a chiller plant. The chiller plant also includes a chilled water system. In designing an energy-efficient air conditioning system it is important to choose proper chilled water and cooling water system. The evaporator is used to absorb the heat from the conditioned room while the condenser rejects the heat from the chiller to the environment through circulating cooling water. This research also aims to analyze the chiller plant for the air conditioning system operates in one of the shopping malls in Indonesia and how it affects the performance of the magnetic bearing chiller. The research also presents an analysis of the efficiency of the chiller plant, the coefficient of performance of each compressor, and their compliance with both national and international standards.

Energy performance analysis on segmented liquid desiccant air-conditioning system for bus spray-paint booths

A paint booth is the dominant energy consumer in a manufacturing plant. Large amount of conditioned air with accurate temperature and humidity is required in the spray-paint booth to guarantee constant product quality, which implies huge energy consumption for air-conditioning. However, there has been limited research on energy-saving design for air-conditioning systems applied in the spray-paint booth. In this study, a novel segmented liquid desiccant air-conditioning system is proposed for energy conservation in the spray-paint booths of a bus manufacturing plant. A mathematical model is built to simulate the performance of the proposed system during the cooling season. The advantages of the proposed system can be summarized in terms of the following two aspects: first, the segmented and cascaded configuration of the proposed system helps to reduce the cooling load from 2844.4 to 1078.0 kW under basic conditions when compared with the separated configuration; second, the adoption of the liquid desiccant dehumidifier helps to avoid reheating, and a reheating capacity of 630.8 kW in the current operating system could be saved by operating the proposed system under basic conditions. When operating the proposed system, a yearly primary energy saving rate of 40.7% can be achieved, while a yearly running cost saving rate of 35.6% can be achieved in this plant as compared to the current operating system. This study would provide valuable reference for energy-efficient air-conditioning system design for applications in spray-paint booths.

Experimental investigation of thermally activated glass fibre reinforced gypsum roof

Switch to energy-efficient air conditioning systems and the use of eco-friendly building materials would result in significant energy savings and reductions in CO2 emissions. Thermally activated building system (TABS) is a promising low-energy cooling technology, which provides better thermal comfort than the conventional air conditioning system. In TABS, cooled water circulated in the tubes embedded in one or any combination of roof, floor slab and walls, not only reduces the heat ingress but also cools the building. Integrating TABS with eco-friendly building materials like glass fibre reinforced gypsum (GFRG) could be an intertwining solution. A hybrid system that integrates TABS with GFRG roof is investigated in this study. The thermal behavior of this thermally activated glass fibre reinforced gypsum (TAGFRG) roof is analysed experimentally in terms of diurnal temperature gradients, thermal images of the interior and exterior roof surfaces, decrement factor and water temperature variations. The reinforcement zone of the TAGFRG roof handled a higher cooling load compared to that of air cavity zones. The diurnal temperature fluctuation of interior roof surface at the air cavity and reinforcement zones is reduced by 5.1 and 6.7 °C respectively by TAGFRG roof cooling.

Theoretical performance analysis of a new hybrid air conditioning system with two-stage energy recovery in cold winter

Abstract Energy recovery technologies can effectively improve the energy efficiency of air-conditioning systems and significantly reduce building energy consumption. In this paper, a parametric analysis and energy-saving potential evaluation for a new hybrid air conditioning system (HAC) is carried out theoretically based on developed models. The proposed HAC incorporates into a conventional mechanical vapor compression air conditioning system with an independent fresh air conditioner which is composed of a network of heat exchangers, including a packed bed and three air-water finned coils. Under cold winter climate, in the fresh air conditioner, a packed bed is coupled with a water-air heat exchange coil to form a total energy recovery loop. A run-around sensible energy recovery loop is also integrated in the system to produce a two-stage energy recovery effect. Moreover, a sprayer is installed upstream of the two-stage energy recovery process for fresh air humidification, and a fresh air recirculation duct is equipped for frost-free operation. In the parametric analysis, four independent affecting parameters are included: the air-to-water heat capacity ratio, the indoor temperature, the ambient temperature, and the ratio of recirculation fresh air. The energy-saving potential of the HAC is also evaluated for applications in seven typical cities located in middle-lower Yangtze River region of China over the winter period (December, January and February). The results show that compared with the conventional system with electric humidification, the HAC has an average energy saving rate of 44.0%, and its average power saving per hour is 13.41 W m−2.