Heating Air Conditioning Research Articles

An experimental and theoretical investigation of refrigerant charge on a secondary loop air‐conditioning heat pump system in electric vehicles

Automotive air-conditioning heat pump systems are particular interest worldwide in energy conservation and emission reduction for electric vehicles, hybrid electric vehicles, and fuel cell electric vehicles. Refrigerant charge amount is a key factor for the air-conditioning heat pump system optimization affecting the condensing pressure and subcooling in both heating and cooling modes. In this paper, the influence of the refrigerant charge on system performances was investigated using the experiment method on a secondary loop air-conditioning heat pump system. The typical heat transfer and flow parameters were recorded, and both cooling and heating performances of the system were investigated and illustrated by pressure-enthalpy diagrams. The critical refrigerant charges were determined in both heating and cooling modes. Three typical void fraction correlation models were also applied for the refrigerant charge determination modeling as a system off-design method. Results show that the Hughmark void fraction correlation method has the best prediction of the critical refrigerant charge in both cooling and heating modes.

Model-Based Fault Detection and Diagnosis Using Convolutional Neural Networks in Heat Source System with Water Thermal Storage Tanks

Since a heat source system that produces and conveys the heat for air conditioning comprises various devices, and has complex controls, faults that impair performance occur. Heat source systems are customized, however, and are complicated to the extent that a ‘one-fits-all’ approach to fault detection and diagnosis (FDD) has not been established. Here we propose a novel method for FDD, using a fault database generated by a simulation, and using convolutional neural networks (CNNs) trained by the database. A real system, with a water thermal storage tank, was the object of this research. Firstly, system behaviors in response to faults were calculated, using a detailed simulation, and then a database was generated, using the simulation results with fault labels. There were 16 fault types in total, which included a condition without faults, four types of faults, and their combinations. The assumed four types of faults: were chiller deterioration by condenser fouling, improper sewage pump set value, heat exchanger fouling, and temperature sensor error at the supply side of the heat exchanger. Then, we preprocessed the database, and converted the data into images, with two axes of time series, and with items from one 24-hour data set as a representative image. Then, CNNs were trained by the database, and trained CNNs were tasked with the diagnosis of real data. The CNNs performed with 98.7% accuracy in training, and diagnosed the real data using probabilities. We reviewed the analysis of the real data, where the probability indicated the likely presence of a fault, and how the real data was similar to the fault severity assumed in the simulation. We concluded that this FDD method will help analyze real data, because it indicates faults emerging in the real data with probability, whereas conventional data analysis requires checking the data using expert knowledge.

Validation of Unsteady CFD considering Thermal Load Fluctuation in Office Room

In the design stage of air-conditioning equipment, by predicting the annual air-conditioning energy and heat load with high accuracy and by comparing multiple designed air-conditioning systems, it is possible to select optimal equipment and reduce capital investment. However, occasionally, it is difficult to predict energy consumption by means of energy simulation (ES) assuming that the thermal environment of the room is uniform, because of various reasons such as the influence of the uneven distribution of the pieces of equipment that act as heat loads, and mixing loss due to the air-conditioning system. In addition, when evaluating an air-conditioning system considering human comfort in a room, it is necessary to calculate a comfort index such as the Predict Mean Vote (PMV). In that case, it is important to predict the distribution of the thermal environment such as the bias in wall surface temperature. Therefore, attempts have been made to combine Computational Fluid Dynamics (CFD) with energy simulation for predicting the distribution of the thermal environment. However, in a few cases, measurements are made considering thermal load fluctuations in actual outdoor environments, and validation of CFD analysis is performed. Therefore, in this study, in a laboratory simulating an office, considering the effect of actual solar radiation, we measured the performance by changing the air-conditioning system of the perimeter zone and analysed the behaviour of thermal load in the room. Subsequently, by comparing the actual measurement results with the results of unsteady CFD analysis, the prediction accuracy of indoor temperature distribution and air-conditioning heat quantity was validated. As a result, it was clarified that the prediction accuracy of indoor temperature distribution is affected by how the airflow that was directed out of the air conditioner in the perimeter section collides with the window shade.

Techno-economic analysis of an air conditioning heat pump powered by photovoltaic panels and the grid

This work presents an environmental and techno-economic study of an inverter air conditioner simultaneously powered by photovoltaic panels and the grid, without batteries. The unit provides the thermal demand to an office in an administrative building located in Alicante (South East Spain).In comparison with other systems which also use renewable energy for air conditioning, this one presents significant advantages. It is comparatively simple, reliable, has low maintenance needs and its renewable energy production is entirely self-consumed, which avoids problematic interaction with the grid.The system has been monitored during one year to measure the thermal energy provided to the room, the electrical consumption of the device and the photovoltaic and grid contribution to it.Experimental results of some Key Performance Indicators are presented as a result of a one year data collection campaign. The measurements show a solar contribution of 54% to the electricity consumed by the system. As a result, the ratio between the thermal energy and grid electricity consumption during one year is SPFsys = 9.6. Consequently, the primary non–renewable energy consumption is drastically reduced to a 26% of the reference system (SPFref=2.5).Furthermore, the techno-economic study concludes that in spite of requiring a higher initial investment in the system, the saving produced by the lower electricity consumption, results in an annualized cost of 84% of the reference system cost.

Study on heat transfer performance of metro tunnel capillary heat exchanger

The metro tunnel capillary heat exchanger, which is to lay the capillary along the wall surface of the subway tunnel, is a kind of front end heat exchanger of the air conditioning heat pump system. The numerical simulation is used to analyze the heat transfer characteristics of the metro tunnel capillary heat exchanger with different pipe spacings. Combined with the system regulation and operation, the optimal pipe spacing suitable for the metro tunnel capillary heat exchanger was obtained. Through experimental tests, we concluded the law of temperature distribution and the heat transfer characteristics of the sand with the capillary heat exchanger were buried, the correctness of the simulated value was verified.

沖縄・某エネルギーセンターのブリリアント冷熱源システム （第1報）高効率システム構成

沖縄・某エネルギーセンターのブリリアント冷熱源システム （第1報）高効率システム構成

Development of congress tourism in the Krasnodar region

This article describes the main ones possible for the development of the MICE industry (Meetings, Insentives, Conferences, Exhibition) in the Krasnodar Territory in general and in Krasnodar in particular. The author substantiates the importance of the importance of congress and exhibition tourism in terms of changing the direction of tourist flows, filling the number fund of means of accommodation of the city and the region during the off-season. Also, the economic attractiveness of congress and exhibition tourism, requirements for hotels, as well as statistical data are described. The article analyzes in detail the most promising and important hotel companies providing services in the sphere of organizing exhibitions and conferences in the Krasnodar Territory: conference halls, Internet access (wi-fi), sound and sound amplification equipment, air conditioning (heating) and humidification systems , marker boards, projectors, flip charts, mobile presentation screens, simultaneous interpretation systems, indoor TV, modern stage lighting equipment. The author also analyzes the possibilities of developing congress and exhibition tourism in Krasnodar, where there is an enterprise – a clearly expressed regional leader of the industry – the exhibition and congress complex «Expo Yug». At the same time, the article describes not only the positive aspects of the development of congress and exhibition tourism, but also the problems from which the effective functioning of the entire tourist industry of the Krasnodar Territory depends.

Enhanced condensation heat transfer in air-conditioner heat exchanger using superhydrophobic foils

Air-conditioners have the highest energy consumption among the household appliances because of the improved thermal resistance by the filmwise condensation in summer and frosting in winter on the surface of hydrophilic foils of condensers. The wet foils are also easy to adsorb dirts and reproduce bacteria, further affecting people health in the room. Here, through chemical oxidation and subsequent chemical modification, we fabricated a novel air-conditioner fin-tube heat exchanger with superhydrophobic foils, which showed high performance in self-cleaning, anti-condensation, anti-frosting, anti-corrosion and environment stability, promising a good candidate for improving energy efficiency of air-conditioners in future. Enhanced condensation heat transfer were demonstrate on indoor and outdoor condenser in summer and winter, respectively. The results of testing revealed that the cooling capacity and heat transfer coefficient from superhydrophobic Fan Coil Unit (indoor condenser) increasing over 8 and 2% than conventional hydrophilic one under rated output working conditions. Moreover, the superhydrophobic outdoor condenser under the condition of frosting has higher energy conversion (over 85%) than the conventional hydrophilic one after 60 min.

Residential adaptive comfort in a humid continental climate – Tianjin China

The aim of this study was to understand occupant thermal comfort and air-conditioning (AC) usage behavior in mixed-mode dwellings in China. Longitudinal field measurements were conducted in 43 homes in Tianjin during the warm half of the year, May through November 2016. Room air temperatures and AC on/off events were recorded continuously using autonomous data-logging devices (iButtons). Occupants’ “right-here-right-now” thermal responses were collected through an online questionnaire delivered intermittently to their smartphones throughout the survey period. A total of 4157 AC events and 1697 online questionnaires were collected and then matched against concurrent indoor and outdoor temperatures. Results indicate that thermal sensations of the Tianjin residents were less sensitive to variations of the room temperature, compared to findings from previous studies conducted in offices. The indoor temperature limits corresponding to 80% thermal acceptability for our Tianjin residential sample were estimated to be 21.0 °C (the lower limit) and 27.3 °C (the upper limit). Average “trigger temperature” for AC cooling in summer was 27.6 °C resulting in a cooling of the room by 4.1 °C on average, and the average trigger temperature for AC heating in winter was 18.6 °C heating the room by 6.6 °C. Our analysis also indicated that the householder's education level and household income were associated with their AC usage decisions.

A Novel Approach to Feedback Control with Deep Reinforcement Learning

A novel deep reinforcement learning (RL) algorithm is applied for feedback control application. We propose Proximal Actor-Critic, a model-free reinforcement learning algorithm that can learn robust feedback control laws from direct interaction data from the plant. We show efficacy of the algorithm on a benchmark problem in Heating Ventilation and Air Conditioning (HVAC) heating system, with the RL controller achieving lower Integral Absolute Error (IAE) and Integral Square Error(ISE) as compared to baseline Proportional-Integral (PI) and Linear Quadratic Regulator (LQR) controllers. We also provide details on establishing feedback control problems within the deep reinforcement learning framework, including policy parameterization, neural network architecture and training procedures.

Correcting energy balance error in heat exchanger data by maximum likelihood method

In this paper, the uncertainty propagation during the heat exchanger performance data analysis is examined through Monte Carlo simulations. Using the simulation tool, different methods for averaging redundant heat transfer rate measurements for heat exchangers are compared in terms of the uncertainty propagation. When compared to the popular arithmetic mean method, it is found that the weighted linear averaging method is superior for minimizing the uncertainty of the average heat transfer rate, but not necessarily resulting in a minimized uncertainty for the overall performance characteristic (i.e. UA). Also, it is found that the calculated UA values from UA-LMTD method and effectiveness-NTU method are not exactly the same when there is an energy balance error in the redundant heat transfer rates. These issues are caused by the underlying discrepancies in the measured variables during the data reduction. In the present work, a full reconciliation of all measured variables is proposed which makes adjustments to not only heat transfer rates but also other underlying measurements such as mass flow rates and temperatures. The amounts of corrections to individual variables are determined by straightforward formulas derived from a constrained, weighted least squares method. From Monte Carlo simulations, these corrections to variables are confirmed to be the most likely errors with given uncertainties and observed energy balance error. The proposed method consistently yields a minimum uncertainty for both heat transfer rate and UA, and it also produces identical results from UA-LMTD and effectiveness-NTU methods. Using sample data for an air conditioning heat exchanger, the advantage of the proposed method is demonstrated.

太陽熱フル活用を目的とした空気式太陽熱集熱システムを用いた戸建住宅に関する研究 第2報 付加蓄熱体の設置による暖房消費エネルギー削減の検討

太陽熱フル活用を目的とした空気式太陽熱集熱システムを用いた戸建住宅に関する研究 第2報 付加蓄熱体の設置による暖房消費エネルギー削減の検討

Solar Heat Underground Storage Based Air Conditioning Vis-à-Vis Conventional HVAC Experimental Validation

This paper presents a comparison of air conditioners using the conventional heating, ventilation, and air conditioning heat pumps and the one using solar heat stored underground, also known as shallow geothermal air conditioning. The proposed air conditioner with solar heat stored underground reunites practical data from an implementation of the heuristic perturb-and-observe (P&O) control and a heat management technique. The aim is to find out the best possible heat exchange between the room ambient and the underground soil heat to reduce its overall consumption without any heat pump. Comparative tests were conducted in two similar rooms, each one equipped with one of the two types of air conditioning. The room temperature with the conventional air conditioning was maintained as close as possible to the temperature of the test room with shallow geothermal conditioning to allow an acceptable data validation. The experiments made both in the winter of 2014 and in the summer of 2015 in Santa Maria, South Brazil, demonstrated that the conventional air conditioner consumed 19.08 kWh and the shallow geothermal conditioner (SGC) consumed only 4.65 kWh, therefore, representing a reduction of energy consumption of approximately 75%.

Comparative performance analysis of different solar desiccant dehumidification systems

The transient performance of different configurations of solar desiccant cooling systems is analyzed and compared based on the concept of Finite Time Thermodynamics. The TRNSYS software is used to conduct the transient simulation, and the results are compared with the experimental data in literature. Solar desiccant cooling systems are studied in 3 different configurations, in which fresh air, conditioned air, and a mixture of fresh air and conditioned air enter the dehumidifier wheel, respectively. Also, the performance of desiccant cooling system is investigated in single-stage and double-stage configurations to consider the effect of the number of dehumidifier wheels. The coefficient of performance (COP) and exergy efficiency of different configurations are evaluated to determine the optimum arrangement. The highest COP is achieved for Dunckle configuration in ventilation mode and for Uçkan configuration in recirculation mode. The results indicate that the COP of single-stage systems is higher than double-stage in both recirculation and ventilation modes. The highest COP and exergy efficiency are achieved for Dunckle configuration in ventilation mode as 0.6 and 35%, respectively. Implementation of heat recovery system improves the performance of double-stage configuration more than the single-stage system. An economic analysis is performed to compare different configurations based on electrical energy saving and payback period. The result indicates that the Uckan and Dunckle configurations consume 50% lower electrical energy compared to air conditioning heat pumps with payback period of about 4 years.

Performance analysis of a novel liquid desiccant evaporative cooling fresh air conditioning system with solution recirculation

Liquid desiccant evaporative cooling air-conditioning (LDECAC) system, which combines both advantages of liquid desiccant and evaporative cooling technology, has a great potential to utilize low-grade heat for refrigeration and air conditioning. A novel LDECAC system is proposed to obtain lower supply air temperature and humidity ratio at the expense of less thermal energy consumption when used as a dedicated fresh air system. It consists of a liquid desiccant system with self-cycle solution at dehumidification and regeneration sides, a regenerative indirect evaporative cooler (RIDEC) and a direct evaporative cooler with adjustable by-pass flow. A parametric study on steady-state thermal performance of LDECAC system was performed based on the developed mathematical model. The performance was investigated by varying five key parameters: solution self-cycle ratio (Rs), working to intake air flow ratio (Ra), regeneration temperature, ambient air temperature and humidity ratio. The results show that the system can handle the process air to 17.9 °C and 9.2 g/kg with the thermal coefficient of performance of 0.56 under the design condition. The recommended value for Rs lies between 0.6 and 0.7 and that for Ra is 0.2 under the typical operating condition. The variable Rs control method is effective in response to the change of ambient air conditions. Performance comparison with the conventional LDECAC system shows that the novel system can utilize lower temperature heat source and achieve a higher thermal coefficient of performance.

Air-conditioning Usage Pattern and Energy Consumption for Residential Space Heating in Shanghai China

Air-conditioning (AC) is discontinuously used in Shanghai residential buildings during the winter time. The AC usage pattern, therefore, has great influence on its energy consumption. In order to figure out the space heating energy consumption for Shanghai residents, it’s necessary to have an accurate description of AC usage model. In this study, questionnaire surveys and continuous measurements of 10 residents were done in Shanghai. Based on the Marcov Chain and AC usage conditional probability model, the descriptive parameters under three different energy levels were calculated according to test data. Then, the AC energy consumption is calculated by DeST-h software for validation. The results of this paper can serve as a reference for AC heating energy consumption studies.

Indoor environment and adaptive thermal comfort models in residential buildings in Tianjin, China

This paper investigates air-conditioning (AC) usage patterns and adaptive comfort behaviors in a Chinese residential context. Field measurements were conducted in 43 homes in Tianjin from May 14th to November 20th in 2016. Indoor temperatures and AC on/off events were recorded. Occupants’ “right-here-right-now” thermal perception and adaptive behaviors were collected. 4,743 AC events and 1,697 online comfort questionnaires were collected. Average duration for AC cooling events in summer was 3.24 hrs per house and the average duration for AC heating events in winter was 0.96 hrs per house. Tianjin residents were less sensitive to indoor air temperature, compared to those in offices. The indoor temperatures corresponding to 80% thermal acceptability ranged from 21.0℃ to 27.3℃. We also derived statistical models to predict the likelihood of adaptive behaviors (i.e. turning on AC, turning on fans and opening windows or doors) with regard to outdoor air temperatures.

Comparison of a novel un-baffled and a conventional shell-and-tube dry-expansion evaporator

To overcome the disadvantage of the poor heat transfer performance of the conventional baffle shell-and-tube dry-expansion evaporator (BSTDEE), a novel un-baffled shell-and-tube dry-expansion evaporator (USTDEE), for use in air source heat pumps (ASHPs), was developed and investigated. An experimental platform was built to test the performance of the USTDEE-ASHP and BSTDEE-ASHP. Several parameters, including the overall heat transfer coefficient (U) of the USTDEE and BSTDEE, cooling capacity (Qe), heating capacity (Qc), and coefficient of performance (COP) of the ASHP were investigated. The results show that the COP of the USTDEE-ASHP is higher than that of the BSTDEE-ASHP. The refrigerant charge of the former unit is less than that of the latter, whereas the water pressure drop of the former is greater than that of the latter. With increasing evaporating temperature (Te), outside tube Reynolds number (Reo) and heat flux (qi), the heat transfer performance of the USTDEE is enhanced and is better than that of the BSTDEE. With an increase in condensing temperature (Tc), the heat transfer performance of the USTDEE and BSTDEE decreases, and the former is worse than the latter. This research indicates that the USTDEE has the advantages of higher heat transfer performance; compact volume and less heat transfer area and has broad prospects in air conditioning heat pump applications.

연결세경관을 이용한 휜관형 열교환기의 기계확관에 의한 전열특성

The fin and tube heat exchanger using a two-port tube has in air-conditioner heat exchanger because heat transfer performance. This study investigates the feasibility of a fin and tube heat exchanger using two-port copper tube by mechanical expansion. The optimum size of the tube-expanding bullet for the heat exchanger using two-port tube was through numerical calculation. The heat exchanger using a two-port tube was fabricated by mechanical expansion, and the heat exchanger performance was evaluated condensation and evaporation experiments. Compared to the heat exchanger of a conventional circular tube, the pressure drop per unit length of the heat exchanger with a two-port tube decreased. Compared to the heat exchanger using a conventional circular tube, the overall heat transfer coefficient of heat exchanger with a two-port tube increased up to 13% in the case of condensation, and up to 25% in the case of evaporation. The two-port tube heat exchanger outperforms conventional heat exchanger for air conditioner with a inner grooved circular tube.

Simplified model of finned-tube heat exchangers based on the effectiveness method and calibrated with manufacturer and experimental data

A simplified model for predicting the overall thermal performance of finned-tube heat exchangers considering water and air as hot and cold fluids, respectively, is investigated. The model is based on the classical ɛ-NTU method and the thermal convective resistance in each fluid is estimated after conventional-type (Nusselt number) empirical correlations. The model is calibrated with catalogue data of a heating coil. Calibrations of six families of model versions are performed by using different numbers of operating cases ranging from 2 to 320, some of them taking into account the influence of varying properties. The calibrated versions are tested for operating cases listed in the catalogue and the best performing versions are identified, such as the one calibrated with 24 cases and taking into account the effect of the fluid properties, which provided better accuracy than the versions calibrated in previous works. A test of the method robustness is conducted regarding the influence of the initial guessed values of the thermal resistances on the calibration procedure.The validity of the component model is further investigated by using a set of published experimental data for an automotive radiator covering ranges of practical interest of the mass flow rates of both air and water streams, and some versions providing excellent results are identified.The model based on a suitable version previously calibrated and tested is a promising procedure for the modular component simulation of finned-tube heat exchangers, when used as air conditioning heating coils or in other particular applications.