Air Heat Recovery Research Articles

Integrated battery thermal management and CO2 control in electric buses using recirculated air and waste heat recovery

In recent years, electric vehicles (EVs) have significantly progressed due to their environmental protection and energy-saving advantages. However, maintaining indoor thermal comfort and effective battery thermal management are critical considerations for EVs. Unlike conventional vehicles, EVs cannot use waste heat and depend on heat pump systems for winter heating and summer cooling. This research proposes a novel system to reduce the energy consumption of heat pump systems by using recirculated air while addressing the challenges of battery temperature management and maintaining safe CO2 concentrations in the cabin. The primary objectives of this research are threefold: first, to ensure passenger comfort through an integrated approach that includes cabin CO2 concentration safety; second, to recover heat from recirculated cabin air to save energy and control battery temperature; and third, to comprehensively analyze the performance of the Electric Vehicle Thermal Management System (EVTMS) using precise Computational Fluid Dynamics (CFD) analysis and mathematical modeling. This study will significantly enhance the understanding of energy consumption related to CO2 concentration control; an aspect previously overlooked in the literature. It will develop a battery temperature management strategy that leverages bus exhaust heat. These contributions will aid in achieving both passenger comfort and battery stability in electric buses, providing practical insights for the design and optimization of thermal management systems for future electric buses.

Improvement of Air Purification and Heat Recovery Systems for Industrial Emissions

Improvement of Air Purification and Heat Recovery Systems for Industrial Emissions

Thermal and electrical performance analysis of a lightweight micro CHP system for recreational vehicles

For comfortable use of a Recreational Vehicle (RV), there is a need to supply electrical energy to recharge the batteries and supply the installed equipment, as well as thermal energy, for hot water and ambient heating. A conventional solution for supplying electrical energy is the installation of photovoltaic modules combined with connection to an electrical grid, when possible. Water heating is generally done using a passage gas heater or hybrid gas/electric storage heater. Imported vehicles have gas heating and many other vehicles have diesel heaters. To develop an alternative to currently available energy supply methods, this work proposes the creation of a cogeneration system for RVs. From a literature review, a research gap was identified in relation to micro CHP devices for RVs. In the development of this work, a micro CHP prototype was created, with 980 W of maximum electrical power, consisting of a single-cylinder internal combustion engine, an automotive alternator and heat exchangers for heat recovery. The prototype was enclosed and instrumented, allowing to evaluate the thermal power obtained in water flowing through exhaust gases, lubricating oil and cooling air heat recovery systems, in addition to measuring the electrical power of the alternator. Operational tests were carried out with 46 different test conditions, combining variations in the engine speed (N) and in electrical load. The prototype electrical efficiency reached 10.18 % ±0.2 % at 3008 rpm with 83 % load. The maximum electrical power was 0.746 kW±0.015 kW at 3637 rpm and 100 % load. The maximum thermal energy recovery rate was 3.267 kW±0.039 kW. Utilization factor reached 65.57 % ±0.33 % at 3208 rpm with 63 % load. Compared to traditional means of providing electrical power and thermal power for RVs, the prototype proved to be more advantageous when the demand is for electrical power and space heating. However, for conditions in which the demand is for electrical power and water heating, or just electrical power, the current solutions available are still more efficient.

Performance evaluation and multi-objective optimization of a hybrid earth-air heat exchanger and building-integrated photovoltaic/thermal system with phase change material and exhaust air heat recovery

The current study explores the feasibility of employing an integrated system comprising an earth-air heat exchanger (EAHE) unit and a photovoltaic/thermal (HPT) system equipped with a phase change material (PCM) to fulfill the heating, cooling, and electrical loads of a building. In this arrangement, ambient air is heated during cold months by passing it through the EAHE and PCM-based HPT systems, and during hot months, it is cooled by passing through the EAHE unit. Additionally, in warm months, the air exiting the building is utilized to lower the temperature of the PV panels. The electricity generated by the PV panels is harnessed to meet a portion or the entirety of the building's electrical demand. Following the identification of factors influencing the system performance, the multi-objectives genetic algorithm (MOGA) approach is employed to ascertain the optimal values of these parameters, aiming to concurrently maximize both the thermal and electrical output of the HPT-EAHE system. The findings indicated that the optimal HPT-EAHE system can fulfill 132693.3 kWh of heating demand for the building during cold months, address 26536.1 kWh of cooling needs during hot months, and generate 9242.2 kWh electrical power throughout the entire year.

Study on the Applicability of Green and Efficient Refrigeration and Air Conditioning Based on Exhaust Air Heat Recovery Technology

With the sustained and stable development of the national economy, China has stepped into a new stage of green emission reduction. Under the environment of comprehensively promoting the market share of green and efficient refrigeration products, the popularization and use of exhaust air heat recovery technology in different fields will further promote the green and efficient transformation of the refrigeration industry, improve the industry's independent innovation technology, and accelerate the construction of ecological civilization. This project firstly analyzes the research background, reviews domestic and international research, and clarifies the research background and current situation; secondly, it builds a comprehensive evaluation system for green refrigeration development based on three major energy-saving concepts, and measures the level of green refrigeration development in China's first-tier cities; secondly, it applies empirical evidence based on the data of three districts and cities, namely, Beijing, Shanghai, and Guangzhou, in the period of 2011-2021, to analyze the effect of the exhaust heat recovery technology on the development of high-efficiency green refrigeration. Then, based on the data of Beijing, Shanghai and Guangzhou from 2011 to 2021, we use the empirical analysis to analyze the effect of exhaust air heat recovery technology on the development of high-efficiency green refrigeration.

Condensation risk-based applicability analysis and design of a dynamic thermal insulation window with ventilated airflow in different climates

The exhaust air insulation glazing system (EAIG) integrates exhaust air heat recovery and dynamic insulation to minimize heat loss/gain through the window by allowing the exhaust air to be ventilated through the air gap between two glass panels. However, condensation may form on the internal glazing surface of EAIG during winter. How to prevent the occurrence of condensation and improve technical feasibility of EAIG for various climatic conditions has not been addressed. A numerical model was developed to determine the hourly glazing surface temperatures of EAIG and identify whether condensation will form or not during winter. The condensation probability of EAIG was quantitatively estimated considering various window orientations and climatic conditions. Furthermore, the effectiveness of some potential measures for preventing condensation in EAIG was also investigated. The results indicate that outdoor weather conditions significantly influence the condensation of EAIG. For a climate with a relatively mild winter, slight condensation occurs within the EAIG, while in severe cold climate, long-term condensation with a probability of 45.4 % occurs, which detrimentally affects the practical application of EAIG. Moreover, reducing indoor humidity and adding a low-e coating can effectively reduce condensation probability and expand technical feasibility of EAIG for various climatic conditions. In severe cold climates, the condensation probability decreases from 45.5 % to 6.5 % when employing an additional low-e coating. The findings in this study are beneficial to providing a design guideline for engineers and architectural designers, and enhancing the applicability of EAIG in various climatic conditions.

Analysis of measures to increase the energy efficiency of educational buildings of the national university of water and environmental engineering

The implementation of energy-efficient measures at the National University of Water and Environmental Engineering (NUWEE) was started since 2000. The buildings of NUWEE are located in different parts of Rivne city and Rivne region. Buildings № 1-7 were selected by the Ministry of Education and Science of Ukraine for financing their thermal modernization as part of the loan project "Higher Education of Ukraine. Energy efficiency and sustainable development" with the aim of increasing their energy efficiency. The authors analyzed the measures to increase the energy efficiency of the educational buildings of the NUWEE, namely, the installation of thermal insulation of facades, roofs, floors on the ground and first surfaces, replacement of windows and doors, installation of thermal insulation of pipelines, modernization of automated thermal energy regulation units (ATERU), heating system and lighting, implementation of the energy monitoring and dispatching system, installation of the ventilation system with exhaust air heat recovery. Implementation of the proposed measures will reduce energy consumption and related costs by 60 %, namely by 6,232 MWh/year (compared to the baseline level of energy consumption of 10,286 MWh/year). It will result increasing of the buildings’ comfort and functionality. After the implementation of the described measures, the increase of the energy efficiency class of educational buildings is predicted. The implementation of energy-efficient measures will also lead to the reduction of greenhouse gas emissions by 50 %, namely by 1,648 t/year. Measures that can pay off as soon as possible are the implementation of thermal insulation of pipelines, modernization of ATERU and lighting, implementation of energy monitoring and dispatching systems. The longest payback period will require the installation of ventilation air heat recovery, but this measure is necessary in view of the current reduction in heat energy costs for heating the external supply air in the cold period of the year.

Calculation of a heat exchanger using heat pipes in the exhaust air heat recovery system

Objective. The purpose of the work is to develop practical recommendations for the design and manufacture of a heat exchanger using heat pipes, which could find widespread use in heating, ventilation and air conditioning systems at facilities for various purposes. Method. The research is based on methods of thermodynamic analysis, full-scale and computational modeling of processes and objects of refrigeration and cryogenic technology, air conditioning and life support systems. Result. The implementation of the practical recommendations studied in the work on the use and design of heat exchangers using heat pipes in ventilation, heating and air conditioning systems will provide significant savings in energy spent on heating and/or cooling the air supplied to the room served by the HVAC system. To reduce heat loss in a building, it is rational to maintain air balance and compensate for the exhaust air with an organized influx of outside air, to heat which the heat of the removed exhaust air is utilized. Conclusion. Compared to a heat exchanger based on a glycol recuperator, a regenerator using heat pipes is less energy-intensive, requires virtually no maintenance, and is also more energy efficient due to the absence of a pumping device that requires electricity in the design. At the same time, the ability to completely separate the supply and exhaust ventilation flows of the regenerator on heat pipes is preserved, which is extremely in demand in medical institutions, due to the need to comply with strict sanitary standards.

Energy modeling and experimental validation of heat pump operating modes in exhaust air heat recovery. Part 2. Energy, economic and environmental indicators

Energy modeling and experimental validation of heat pump operating modes in exhaust air heat recovery. Part 2. Energy, economic and environmental indicators

Constructing year-round energy-efficient fresh air handling unit with exhaust air heat recovery using multi-condition design

Traditional fresh air handling units with exhaust air heat recovery insufficiently utilize exhaust air waste energy, and are designed under the design-load condition, which are unable to efficiently adapt to the varying fresh air conditions for both the energy consumptions of compressors and fans. To promote energy efficiency, a fresh air handling unit with exhaust air heat recovery is constructed in this study by grade matching of loads and waste and natural energies under different typical fresh air parameter conditions, and the improved year-round efficient system configuration is determined by combining the configurations obtained under each typical condition. In addition, numerical models are adopted to calculate the energy and economic performances of the system in an office building in Nanjing, China, and a traditional system is also analyzed for performance comparison. The main conclusions are as follows: 1) The improved system configuration is determined to be a heat-recovery device plus a two-stage heat pump that can operate close to a separately designed configuration under various cases, thereby ensuring efficient operation throughout the year; 2) Compared with a traditional fresh air handling unit for fresh air load treatment with a variable refrigerant flow system in Nanjing, China, the annual saving rate of the proposed system is 14.4 %; 3) Compared with the traditional system, the static payback period is 1.1 years.

Experimental and numerical study of a natural convection indirect solar dryer with PCM tubes: Dynamic, thermal and nutritional quality analysis

A natural convection solar dryer was investigated in this paper with a storage unit in the form of copper tubes filled with Paraffin wax as a PCM, experimentally and numerically using the ANSYS Fluent software. The storage unit was placed in a side-mounted plenum chamber for air uniformity and heat recovery. The validations made for the drying chamber’s temperature with and without storage, the outlet air temperature, and velocity of the SAH, show good accordance with the experimental results, which promote the use of this method in investigating the solar dryer numerically. The drying of orange slices in different modes were studied; open sun drying, in a solar dryer with and without PCM. The drying time required to reduce the moisture content from 81.19% (wb) to 19% (wb) was respectively 216 h, 144 h, and 168 h. In terms of the quality of orange slices, the open sun drying showed the poorest quality in terms of color, texture, shape, and odor. However, all these properties were enhanced with the solar dryer, particularly with the use of PCM tubes. The most valuable nutritional value of oranges is vitamin C, which was measured per slice in all mentioned cases. One fresh orange slice contains 11.34 mg of vitamin C, while it contains 7.77 mg, 7.34 mg, and 5.99 mg in the drying cases with and without PCM as well as in open sun drying respectively.

Comparative analysis of the energy performance of an air handling unit with two-stage heat recovery operating in the different climatic zones of Bulgaria

A comparative analysis was carried out to establish the energy performance of an air handling unit (AHU) for two-stage heat recovery of the exhaust air. The seasonal coefficient of performance (SCOP) was calculated when AHU is operating in heating mode, as well as COP for the entire unit on an annual basis, taking into account the specific features of the different climatic zones in the Republic of Bulgaria. The results have been compared with the BIN-temperature data for an average climate provided in EN 14825 (Table 37) in order to find out how far this standard will give reliable results for the Bulgarian climate, both in terms of energy consumption and SCOP.

Energy saving potential of latent heat exchanger-integrated dual core energy recovery ventilator

High-efficiency energy recovery ventilators (ERVs) have a significant impact on the conservation of building energy. In particular, the importance of the latent cooling performance of ERV which used in hot, humid climates has been growing. To enhance the latent heat recovery performance of the existing ERVs and attain satisfactory sensible heat recovery performance as well, a dual-core energy recovery ventilation unit combining a hollow fiber membrane-based latent heat exchanger (M-LHX) and a sensible heat exchanger (SHX) was proposed in a previous work. This study evaluated the energy saving potential of the proposed ventilation unit integrated air-conditioning system via a series of building energy simulation. As the reference system, a conventional ERV with a flat-plate membrane enthalpy exchanger was chosen. The M-LHX and SHX in the proposed ventilation unit enable decoupled sensible and latent heat recovery of outdoor air. Energy simulations were conducted for a single-story office building located in South Korea, which is one of the humid regions during the summer. The simulation results showed that the proposed ventilation unit could reduce 15.9, 14.4, and 14.1% of building air-conditioning loads in summer, intermediate season, and winter, respectively, compared with the reference ERV. This is because the proposed ventilation unit provided energy benefits by recovering more latent heat from the M-LHX and comparable amount of sensible heat from the SHX than the reference system. Accordingly, the proposed system presented the annual primary energy savings of 10.6% over the reference system, although the proposed system consumed more fan energy.

Numerical simulation for energy and exergy analysis of a novel turbulator in a heat recovery system filled with hybrid nanofluid

This study utilizes numerical simulation to assess the efficacy of a novel turbulator (NT) on Energy analysis (performance thermohydraulic) and exergy efficiency (ηex) of a dual-tube, heat exchanger (H.E) filled, two-phase method (TPM) ZnO-MWCNT /water, hybrid nanofluid (H.N.F). This system can be used for the novel exhaust air heat recovery system consisting of a nanofluid-based building integrated photovoltaic/thermal system or an earth-water heat exchanger. The pressure-based solver problem is employed to simulate nanofluid (NF) steady flow. ZnO-MWCNT/water TPM HNF is simulated using the Eulerian model. Inlet Reynolds number (Re) changes 10,000 to 28,000, volume fraction (φ) of ZnO and MWCNT nanoparticles (NPs) varies from 1% to 3%, and the pitch ratio (λ) of the NT is assumed to be 0, 0.25, 0.50, and 1. The discretization of the equations is done using the second-order upwind method for more accuracy in the calculations and the SIMPLE algorithm is utilized to couple the velocity (V) and pressure (P) equations. Also, the results demonstrate that the thermal performance (TP) is highly dependent on the changes in φ and Re of the HNF entering dual-tube HE. Besides, the pressure drop (Δp) is strongly dependent on the inlet V in the dual-tube HE. In addition, the use of a NT is desirable for 10,000 < Re < 28,000 and 1% < φ < 3%. Finally, the ηex of the dual-tube HE with a NT with λ = 4 is A better version by 47.22% and φ = 3% and Re enhances 10,000 to 28,000.

Research on Multiple Energy-Saving Strategies for Existing Coach Stations: A Case of the Xi’an Area, China

In the context of China’s dual-carbon goals, energy efficiency in public buildings has become a focal point of public concern. As large-scale public transportation buildings, the indoor thermal comfort and the current state of energy consumption of coach stations are increasingly being emphasized. This research used existing coach stations in the Xi’an region as the object; through on-site investigations and field tests of indoor thermal environments in winter and summer seasons, it was found that the coach stations had energy waste and high energy consumption; the enclosure structures had poor thermal performance; and the stations lacked effective energy-saving measures. Energy-saving transformation strategies were proposed from two aspects: enclosure structures and renewable energy utilization. Using DeST-C for energy consumption, the external walls, roofs, insulation materials, and glass materials were simulated, and nine different combinations of energy-saving schemes were simulated using orthogonal experiments. The optimal scheme was selected based on the comprehensive energy-saving rate and economic analysis results, which included using 80 mm XPS external insulation for the external walls, low-e hollow glass for the windows (low transmittance type), and an 80 mm PUR board for the roof insulation. The energy-saving rate of this scheme was 26.84%. The use of rooftop solar photovoltaic power generation and fresh air heat recovery devices can effectively reduce building energy consumption, and the investment payback period is less than 5 years. The research applications have practical significance for improving the indoor environment of existing coach stations and saving energy consumption.

Improving the environmental efficiency of glass furnace chimneys using heat recovery technologies

Purpose. Improving the conditions for dispersing harmful emissions from gas-consuming industrial furnaces based on the development of new complex methods for their greening using modern energy-saving technologies. Methodology. The known methods of heat exchangers and chimneys thermal calculation and methods for dispersing harmful emissions from thermal-energy plants in the environment were used. Findings. Calculative studies were carried out on improving the chimneys operation safety of glass furnaces of regenerative type when using technologies for waste heat recovery of furnace gases using water-heating and air-heating heat exchangers and chimneys of various designs. The influence of design features of chimneys on their operating modes when using heat recovery technologies with water and air heat recovery units has been studied. In order to improve the environmental efficiency and operational reliability of chimneys, it is proposed to use the thermal method of bypassing part of exhaust gases from regenerators past the heat recovery equipment in the heat recovery technologies. The effectiveness of this method for improving the dispersion in the ground-level of harmful emissions from furnaces when using the proposed heat recovery systems has been analyzed. Originality. For the first time, the application efficiency has been investigated of the proposed greening methods to improve the dispersion conditions of harmful emissions of gas-consuming glass furnaces in the environment under the conditions of using heat recovery technologies. Practical value. The results obtained will be used in the development of energy-efficient gas-consuming thermal installations for technological purposes.

Optimizing indoor air quality and noise levels in old school classrooms with air purifiers and HRV: A CONTAM simulation study

Efforts at the national level are being made to improve the indoor air quality of school classrooms. Air purifiers and heat recovery ventilation (HRV) are commonly used to achieve this objective. However, the noise generated by these systems often disrupts classes, leading students to be hesitant in utilizing them. This study proposes an operating method to minimize noise while improving indoor air quality through CONTAM simulations. The method involves operating the HRV in low wind mode during class time and strong wind mode during break time. The dissatisfaction rate (measured by the duration in which the CO2 concentration exceeded 1500 PPM) was minimal, with a rate as low as 0.2% over one year of occupancy. In the case of fine dust PM2.5, operating the air purifier 1 h earlier than occupancy time, while maintaining the existing HRV operation, resulted in a low dissatisfaction rate (PM2.5 concentration exceeded 15 μg/m3 during occupancy time for one year) of 2.6%. According to student reports, the use of weak wind mode during class and strong wind mode during break time resulted in reduced annoyance from the equipment noise. They expressed overall contentment with the experimental noise level, as long as the indoor air quality was improved. The study findings provide an effective and feasible approach to satisfying both noise and indoor air quality requirements. Furthermore, the methodology adopted in this study can be valuable for developing appropriate air purifier facility capacities in different schools.

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

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

The urgent task of mass construction of «passive houses» in Ukraine

An analysis of energy consumption per m2 of housing showed that in the EU countries the average value of energy for heating is about 95 kWh/(m2) per year, while in Ukraine this value is about 200-250 kWh/(m2) per year. The main mechanisms for reducing energy costs for heating residential premises in the EU countries are shown and the dynamics of this decrease to the level of 15 kWh/(m2) per year is disclosed. The role of the «passive house» strategic building standard (nZEB) as a pioneer in reducing residential energy consumption is shown. Data on the number of "passive houses" built around the world, and data on single houses of this type in Ukraine are given. The urgent task need for the use of the "passive house" standard in Ukraine to reduce the consumption of thermal energy for heating housing, as well as harmful emissions into the atmosphere, has been identified. The topic of availability in our country of local constructive and heat-insulating building materials, technologies and engineering systems was discussed. The basic principles of creating a "passive house", its main digital technical characteristics are listed and it is shown that they are suitable for the climatic conditions of Ukraine. Recommendations are given on the use of structural and thermal insulation materials, special windows, air tightness, mechanical ventilation with exhaust air heat recovery and design of buildings without cold bridges. It has been determined that a "passive house" with simple engineering heating (cooling) systems is more sustainability and anti-crisis. The main methods for calculating a "passive house" are analyzed, the need to involve additional 3D modeling programs is determined to obtain more accurate numerical characteristics of the building and the choice of engineering systems. It is emphasized that the creation in Ukraine of entire eco-settlements from such houses will affect the general increase in the awareness of our society, broad awareness of new technologies and, as a result, the breakdown of the inertia of the entire system and the introduction of new, innovative building codes, which will entail the mass construction of "passive houses”, significant savings in energy resources throughout the country, reducing harmful emissions and improving the quality of life of people.

An experimental study of thermal performance of the radiant ceiling cooling in office building in Thailand

This paper investigated the radiant ceiling cooling in office buildings in a tropical hot humid climate. Full-scale experiments were conducted in an outdoor laboratory chamber to observe the indoor thermal conditions and the envelope heat gain from the intermittent operation of the installed radiant chilled panels (RCP) coupled with an outdoor air unit (OAU). The radiant system was also modeled by using a simulation software namely Transient System Simulation Software (TRNSYS), and the calculation results from the model were compared to the experimental observations. In the simulation part, the validated TRNSYS model was adopted to assess the radiant system performance in a typical office environment under the four schemes of combinations of the technology options for the OAU and the building envelope. The perceived comfort from the radiant cooling was assessed based on the thermal sensation of the local subjects acclimatized to hot humid climate. The energy consumption of the radiant cooling was also apprised as opposed to the conventional mixed-air system. The simulation results presented an insight into the importance of the exhaust air heat recovery and the envelope insulation on energy saving and human comfort improvement for the radiant cooling.