ABSTRACT
Heat recovery ventilation devices include rectangular plate cross-flow, hexagonal plate combined counter and cross-flow, rotary wheel sensible, sorption rotor hybrid sensible and latent heat exchanger. Currently, existing studies have produced no clear findings on which climatic conditions latent heat recovery would be optimal, and therefore sought to determine in which climatic conditions it would be suitable to use devices that perform latent heat recovery. This study analysed the performance of different heat recovery devices in different climatic conditions in a ventilation project of a sample hotel building. In the case study, while there is a useful heat recovery between 44.01 and 58.68 kW at low outdoor temperatures in devices with only sensible heat transfer, this value increases up to 158.42 kW, as the outdoor temperature rises. In the heat recovery device providing latent heat transfer, the amount of useful heat recovery varies between 51.34 and 352.16 kW at low outdoor temperatures, depending on the outdoor relative humidity, while this amount increases to 411.26 from 773.25 kW at high outdoor temperatures. Outdoor temperature and humidity levels required for latent heat recovery was also determined by orthogonal optimization method. By using the orthogonal optimization, the study found that under conditions of high temperature that exceeds 35 °C in outdoor ambient temperature, and high humidity that exceeds 60% relative humidity, usage of latent heat recovery devices caused significant differences in total heat recovery ratio. Analysis also concludes that these devices can be used under these conditions.
ABSTRACT
The possibility of unfavorable leakages, especially with infectious diseases, in heat recovery systems in air handling units (AHU) is an essential issue. Typical configurations of AHU are analyzed in this aspect, based on their pressure distribution. It is shown that analyzing only for the design conditions is insufficient and that the changing pressure drops of the air filters due to their nonuniform soiling should be taken into account. The novelty of this paper is in proposed method of considering these leaks in the Wells-Riley model, widely used in the literature for airborne transmission of infectious diseases, including the leakage correction factor fhrleak (outdoor fresh air correction factor) based on EATR (exhaust air transfer ratio). Using the proposed method, for typical rooms, on the example of the SARS-CoV-2 virus and its Delta and Omicron variants, it is shown that considering leaks in heat recovery systems in AHU increases the probability of pathogen transmission. The highest increase in the absolute value of the probability of infection is observed in the single office scenario (4.1%) and in the auditorium with a sick speaker scenario (2.7%). The highest increase in reproduction number is observed in the auditorium with a sick speaker scenario (2.69). Such significant changes in reproduction number, including its change from R < 1.0 to R > 1.0 (auditorium with sick speaker for Delta variant of the virus), are crucial from the point of view of considering event scenarios;they slow down or accelerate the pandemic. © 2023 Elsevier Ltd
ABSTRACT
The possibility of unfavorable leakages, especially with infectious diseases, in heat recovery systems in air handling units (AHU) is an essential issue. Typical configurations of AHU are analyzed in this aspect, based on their pressure distribution. It is shown that analyzing only for the design conditions is insufficient and that the changing pressure drops of the air filters due to their nonuniform soiling should be taken into account. The novelty of this paper is in proposed method of considering these leaks in the Wells-Riley model, widely used in the literature for airborne transmission of infectious diseases, including the leakage correction factor fhrleak (outdoor fresh air correction factor) based on EATR (exhaust air transfer ratio). Using the proposed method, for typical rooms, on the example of the SARS-CoV-2 virus and its Delta and Omicron variants, it is shown that considering leaks in heat recovery systems in AHU increases the probability of pathogen transmission. The highest increase in the absolute value of the probability of infection is observed in the single office scenario (4.1%) and in the auditorium with a sick speaker scenario (2.7%). The highest increase in reproduction number is observed in the auditorium with a sick speaker scenario (2.69). Such significant changes in reproduction number, including its change from R < 1.0 to R > 1.0 (auditorium with sick speaker for Delta variant of the virus), are crucial from the point of view of considering event scenarios;they slow down or accelerate the pandemic.
ABSTRACT
Energy recovery ventilators (ERVs) are the key equipment to fresh air ventilation, which is helpful for the control of respiratory diseases like COVID-19. In this paper, design optimization of the compact heat exchanger in a proposed heat recovery ventilator of the energy efficient building has been carried out and discussed. Appropriate theoretical models are required to evaluate system performance and potential energy savings. This is challenging because of the complexity of the preferred module combining cross- and counter-flow regions. The objective of the design optimization is to maximize the heat transfer effectiveness and to minimize the pressure loss of the compact heat exchanger with limited space. In this study, the allowable dimensions, heat transfer specifications and design requirements of the proposed heat exchanger are firstly defined. Then, the flow configuration, numbers, and dimensions of the air flow channels inside the heat exchanger are identified as the design parameters. A systematic design and optimization method for heat exchanger effectiveness improvement is explored. Furthermore, a detailed mathematical modeling is conducted and validated against the experimental results using the effectiveness-NTU method. It is found that the proposed modeling method is expected to be used to design of the compact heat exchanger. Finally, guidelines for improving the heat transfer effectiveness of air-to-air heat recovery ventilator were derived.
ABSTRACT
Covid-19 further revealed the significance of ventilation by air conditioning systems. Most common split heaters and resistance heaters recirculate the indoor air without ventilation process. Ventilation wastes energy consumption by the building. However, adding an air-to-air heat recovery unit seems a quick solution to reduce the wasted heat of the ventilation process. Nonetheless, recovery unit means further pumping power (pressure drop through the air-to-air heat exchanger), capital cost, additional fans and their electricity consumption, exergy costs and so on. Hence, the profitability of the recovery unit depends on outdoor temperature, desired indoor temperature, electricity price of the region, exergy loss and also the aforementioned factors. In this research the general standard Specific Exergy Costing theory is employed and simplified as an economic strategy for recovery ventilation. The model not only is able to predict the profitability of the ventilation process using air-to-air heat exchanger, but also it is an optimization tool for air-to-air heat recovery units as provided as a case study in this paper.
ABSTRACT
Mobilized thermal energy storage (M−TES) is a promising technology to transport heat without the limitation of pipelines, therefore suitable for collecting distributed renewable or recovered resources. In particular, the M−TES can be flexibly used for the emergency heating in the COVID-19 era. Though the M−TES has been commercializing in China, there is not any specific regulation or standard for M−TES systems. Therefore, this paper summarizes and discusses the existing regulations and policies concerning M−TES in the aspects of facility manufacture and operation, road transportation, and financial support and guidance. Furthermore, the suggestions were presented including necessary consensus on the development of M−TES among different departments, consideration of local conditions when drafting or revising regulations and policies, sufficient investment, or subsidy on the R&D of M−TES, and qualification recognition of M−TES companies and staffs.
ABSTRACT
A membrane-based enthalpy exchanger is a device used for heat and humidity recovery in ventilated buildings. The energy-saving potential of such a device is dependent on the parameters responsible for heat and moisture recovery. The trend is toward composite membranes, which are custom produced, and their parameters can be adjusted for a given application;therefore, the diffusion and sorption characteristics of such membranes are unknown. In order to obtain the values of the water vapor diffusivity of three investigated handmade membranes, a serial resistance model using a Field and Laboratory Emission Cell (FLEC) is proposed. Experiments were conducted to identify the resistance in each step of the moisture transfer process to extract the moisture diffusivity in the membranes. The calculated moisture diffusivities in the membranes were 8.99 × 10−12 (m2/s) for the membranes from cellulose acetate, 1.9 × 10−10 (m2/s) for the microporous PE/PUR membranes, and 1.53 × 10−11 (m2/s) for the PET/PUR microfibrous membranes. The obtained membrane diffusivities were then used in the proposed effectiveness-NTU-based model of an exchanger with a cross-flow arrangement to predict performance under various operating conditions. The results show that the highest latent effectiveness was found for the exchanger core made from the PE/PUR membrane and the lowest was for the one with the PE/PUR membrane core.
ABSTRACT
Climate change poses significant challenges, and the global community is not on track to meet sustainable development goals or the Paris Agreement to mitigate climate change. The COVID-19 pandemic and necessary government measures to curb the spread of the virus has put climate action on hold and shut down economies. The need for improved ventilation as an important mitigating factor against the risk of COVID-19 transmission has additional implications for costs and emissions for businesses. Leisure centres, as large users of water and energy, account for significant emissions and operational costs. However, there is scope for significant reductions in water and water-related energy demands and associated emissions and costs without impacting service quality and delivery. These reductions can be a promising response to the current challenges of climate change and post-COVID-19 economic recovery, particularly given current UK energy crises and inflation trends. We have been working with leisure centres to support them in improving energy efficiency through water-use efficiency as part of the cross-border, interdisciplinary Interreg Dwr Uisce research project on improving the energy performance and long-term sustainability of the water sectors in Ireland and Wales. In this paper, we discuss the potential of energy efficiency gains based on the framework on water management hierarchy which prioritises management actions in order of preference of implementation, where the next hierarchy should only be considered once all potential savings from the hierarchy above have been exhausted. We also discuss how these interventions are not one-size-fits-all – although leisure centres typically have the same water-use types, they differ significantly in age, size, location, building types and materials, functionality, and efficiency;and why therefore, interventions must be considered on a site-specific and case-by-case basis. © 2022 WITPress. All rights reserved.
ABSTRACT
This paper demonstrates the need and potential for using waste heat recovery (WHR) systems from infrared gas radiant heaters, which are typical heat sources in large halls, due to the increasing energy-saving requirements for buildings in the EU and the powerful and wide-spread development of the e-commerce market. The types of gas radiant heaters are discussed and the classification of WHR systems from these devices is performed. The article also presents for the first time our innovative solution, not yet available on the market, for the recovery of heat from the exhaust gases of ceramic infrared heaters. The energy analysis for an industrial hall shows that this solution allows for environmental benefits at different levels, depending on the gas infrared heater efficiency, by reducing the amount of fuel and emissions for domestic hot water (DHW) preparation (36.8%, 15.4% and 5.4%, respectively, in the case of low-, standard- and high-efficiency infrared heaters). These reductions, considering both DHW preparation and hall heating, are 16.1%, 7.6% and 3.0%, respectively. The key conclusion is that the innovative solution can spectacularly improve the environmental effect and achieve the highest level of fuel savings in existing buildings that are heated with radiant heaters with the lowest radiant efficiency.
ABSTRACT
The demand for electricity and power has been increasing with the increase of the population of the world. The Covid-19 Pandemic has affected the way of life of human beings starting last year. The pandemic and economic downturn also affected the electricity demand of the world, but this is only short-term. Once the lockdowns around the world ease and back to normal situation begin, demand for power and electricity shall continue to grow. The century-old Rankine cycle has been the basis for power plants widely used today. However, a modified Rankine cycle known as the Kalina cycle has been proving more efficient than the standard Rankine cycle and might be able to provide the additional power needed in medium and low-temperature sources and waste heat recovery. This paper look into the development of the Kalina cycle and the trends that might be of use for the global electricity requirement.
ABSTRACT
Since the outbreak of the worldwide COVID-19 pandemic, public transportation networks have faced unprecedented challenges and have looked for practical solutions to address the rising safety concerns. It is deemed that in confined spaces, operating heating units (and cooling) in non-re-circulation mode (i. e., all-fresh air mode) could reduce the airborne transmission of this infectious disease, by reducing the density of the pathogen and exposure time. However, this will expectedly increase the energy demand and reduce the driving range of electric buses. To tackle both the airborne transmission and energy efficiency issues, in this paper a novel recovery heat pump concept, operating in all-fresh air mode, was proposed. The novelty of this concept lies in its potential to be applied to already manufactured/in-service heat pump units as it does not require any additional components or need for redesigning the heating systems. In this concept, the cabin exhaust air is directed to pass through the evaporator of the heat pump system to recover part of the waste heat from the cabin and to improve the efficiency of the system. In this paper, a 0D/1D coupled model of a generic single-deck cabin and a heat pump system was developed in the Simulink environment of MATLAB (R2020b) software. The model was run in two different modes, namely the all-fresh air (as a baseline and a recovery heat pump concepts), and the air re-circulation mode (as a conventional heat pump concept with a 50% re-circulation ratio). The performance of these concepts was investigated to evaluate how an all-fresh air policy could affect the performance of the system, as well as the energy-saving potential of the proposed recovery concept. The performance of the system was studied under different ambient temperatures of -5 °C, 0⯰C, and 5⯰C, and for low and moderate occupancy levels. Results show that implementing the all-fresh air policy in the recovery and baseline concepts significantly improved the ventilation rate per person by at least 102% and at most 125%, compared to the air-re-circulating heat pump. Moreover, adopting the recovery concept reduced the power demand by at least 8% and at most 11%, compared to the baseline all-fresh air heat pump, for the selected fan and blower flow rates. The presented results in this paper along with the applicability of this concept to in-service mobile heat pumps could make it a feasible, practical, and quick trade-off solution to help the bus operators to protect people and improve the energy efficiency of their service.
ABSTRACT
The use of Stirling-cycle-based heat pumps in high-temperature applications and waste heat recovery at an industrial scale is of increasing interest due to the promising role in producing thermal energy with zero CO2 emissions. This paper analyzes one such technology as developed by Olvondo Technology and installed at the pharmaceutical company AstraZeneca in Sweden. In this application, the heat pump used roughly equal amounts of waste heat and electricity and generated 500 kW of steam at 10 bar. To develop and widen the use of a high-performance high-temperature heat pump that is both economically and environmentally viable and attractive, various analysis tools such as exergy analysis and life cycle assessment (LCA) can be combined. The total cumulative exergy loss (TCExL) method used in this study determines total exergy losses caused throughout the life cycle of the heat pump. Moreover, an LCA study using SimaPro was conducted, which provides insight into the different emissions and the overall environmental footprint resulting from the construction, operation (for example, 1, 8, and 15 years), and decommissioning phases of the heat pump. The combined results were compared with those of a fossil fuel oil boiler (OB), a bio-oil boiler (BOB), a natural gas-fired boiler (NGB), and a biogas boiler (BGB).