Hasil untuk "Heating and ventilation. Air conditioning"

Abdul Afram, F. Janabi-Sharifi

F. Oldewurtel, A. Parisio, C. Jones et al.

王峙锴, 王瑜, 李好奇 et al.

To address hypothermia in casualties in cold environments, this paper designs a solar-powered rewarming sleeping bag for casualties in extreme cold conditions using phase change materials ODE@CaF2MPCMs and Cu2O@n-C20, which release heat during phase change at low temperatures. Hot water simulation and human experiments were conducted. Results show that in the hot water simulation at 0, 4, and 8°C, with a 40°C initial phase change material temperature, the initial 37°C warm water can be maintained at around 36°C within 3600s, and the bilateral distribution of phase change materials has a higher heating rate than the unilateral distribution. In human experiments, at -5, 0, and 5°C conditions, the average temperature can be maintained at about 35°C within 3600s, and the unilateral distribution of phase change materials has better insulation than the bilateral distribution, with an average temperature increase of 2°C; at -15°C, the average temperature can be maintained above 32°C within 540 minutes. The temperature distribution uniformity analysis shows that the maximum coefficient of variation for unilateral distribution is 0.036, and for bilateral distribution is 0.053, indicating a relatively uniform temperature distribution inside the sleeping bag, with unilateral distribution being more uniform than bilateral distribution. Comprehensive performance assessment shows that the sleeping bag has excellent insulation but needs optimization in convenience; after repeated experiments at -5°C for 30 times, the temperature effect remains almost unchanged, with only a 0.05°C decrease in average human body temperature after 30 uses; moreover, the cost of the sleeping bag is only about 400 yuan, a single heating to 40 ° C consumes about 0.24 ° C , which is low and has good economic benefits.

Fazri Amir, Samsul Rizal, Razali Thaib et al.

Isolation rooms are crucial in healthcare facilities to prevent the spread of infectious diseases. Infectious diseases can be transmitted to humans from humans or through animals known as zoonoses. With the increase in the number of COVID-19 cases, isolation rooms have become one of the most critical facilities in hospitals. Maintaining the correct temperature and humidity in these isolation rooms is a challenge, considering the heating, ventilation, and air conditioning (HVAC) systems that continuously consume large amounts of energy. With the application of energy conservation methods, the total energy consumption of HVAC systems can be reduced. Many studies have shown that the heat pipe heat exchanger (HPHE) technology can contribute significantly to energy savings using HVAC systems. In this study, the effectiveness of an HPHE on an HVAC system in an isolation room was examined, and the total energy reduction was quantified. The HPHE consisted of two rows with ten heat pipes in each row, arranged in a staggered configuration with fresh air temperature and mass flow variations. The inlet fresh air temperatures varied at 32, 35, 37, and 40 °C and fresh air velocities at 1.2, 1.6, 2.2, and 2.6 m/s. Using a chiller, the inlet fresh air was cooled to a comfortable temperature zone, approximately 24.4–25.2 °C, in the isolation room. Notably, higher velocities decreased the effectiveness of the HPHE. An increase in the flow rate enhanced the system, thereby improving the heat recovery value. The increase in the inlet fresh air temperature from 32 °C, that yielded an energy saving of 1.23 W, to 40 °C, resulted in a further energy saving of 1.85 W. The application of the HPHE in the HVAC system in isolation rooms represents a significant innovation that contributes to a reduction in total energy consumption.

Fatma Mtibaa, K. Nguyen, Muhammad Azam et al.

Cui Zhiheng, Yang Changzhi

In this study, we utilize the life cycle assessment method to examine the relationship between the change in the energy efficiency ratio of air conditioners and the energy structure over the course of its operational years. We then develop a carbon emission model for air conditioners based on the dynamic life cycle assessment (DLCA). The carbon emissions of scroll-compressor-based household air conditioners filled with R410A refrigerant are studied. The results show that the introduction of dynamic parameters during operation has a significant impact on the life cycle carbon emissions. Unlike in the static assessment model, the changes in the energy efficiency ratio and energy structure can cause the total carbon emissions to fluctuate by 19.0% and -9.1%, respectively. The annual carbon emissions at the end of the air conditioning service life of the dynamic and static assessment models are 1.71 and 0.80 times the initial annual carbon emissions, respectively. The life cycle carbon emissions of air conditioners are mainly produced during the operation stage, accounting for 91.8% of the total emissions; 75.0% of the total carbon emissions in the life cycle is caused by the power consumption of equipment operation and 23.0% is from refrigerant leakage. Parameters such as the indoor temperature setpoint, refrigerant leakage rate, and refrigerant GWP have a significant impact on carbon emissions during the life cycle of an air conditioner. This study will contribute to the further optimization of carbon emission evaluation models in the HVAC field.

E. Uhde, T. Salthammer, S. Wientzek et al.

The SARS-CoV-2 pandemic, which suddenly appeared at the beginning of 2020, revealed our knowledge deficits in terms of ventilation and air pollution control. It took many weeks to realize that aerosols are the main route of transmission. The initial attempt to hold back these aerosols through textile masks seemed almost helpless, although there is sufficient knowledge about the retention capacity of fabric filters for aerosols. In the absence of a sufficient number of permanently installed heating, ventilation, and air conditioning systems, three main approaches are pursued: (a) increasing the air exchange rate by supplying fresh air, (b) using mobile air purifiers, and (c) disinfection by introducing active substances into the room air. This article discusses the feasibility of these different approaches critically. It also provides experimental results of air exchange measurements in a school classroom that is equipped with a built-in fan for supplying fresh air. With such a fan and a window tilted at the appropriate distance, an air exchange rate of 5/h can be set at a low power level and without any significant noise pollution. Heat balance calculations show that no additional heat exchanger is necessary in a normal classroom with outside temperatures above 10°C. Furthermore, a commercial mobile air purifier is studied in a chamber and a test room setup in order to examine and evaluate the efficiency of such devices against viable viruses under controlled and realistic conditions. For this purpose, bacteriophages of the type MS2 are used. Both window ventilation and air purifiers were found to be suitable to reduce the concentration of phages in the room.

Christian Utama, Sebastian Troitzsch, Jagruti Thakur

Abstract Demand-side flexibility (DSF) has been touted as a possible solution to the challenges in power system operation arising from increasing intermittent renewables penetration and the emergence of electric vehicles. In Singapore, where around 24 to 60% of electricity demand in buildings could be attributed to heating, ventilation, and air conditioning (HVAC) purposes, air-conditioned buildings represent a significant flexibility resource which could be used to provide DSF and help tackle these challenges. This study aims to investigate the DSF potential of Singapore’s building stock and to explore how this potential could be realized through demand-side bidding. To this end, a building energy modeling tool with explicit modeling of the relationship between occupant comfort and HVAC load with model predictive control, CoBMo, is used. CoBMo allows optimal load scheduling to be expressed as a linear programming problem: minimizing overall electricity cost while maintaining occupant comfort. A price-based market clearing model is developed to evaluate demand-side bidding implementation, for which a case study on Singapore’s Downtown Core district is developed. Three scenarios with possible future utility-scale photovoltaic (PV) penetration in Singapore’s electricity system are explored, alongside a sensitivity analysis and a comparison between centralized dispatch and demand-side bidding with price-quantity pairs and linear curves. Results of the analysis show that DSF potential varies between building types, depending on cooling load and occupancy schedule. When extreme price fluctuations happen in future Singapore electricity market with 10 GWp PV penetration, demand-side bidding could aid consumers to utilize their DSF potential by encouraging more effective energy use and in turn, reducing their total electricity cost.

Yu Yang, S. Srinivasan, G. Hu et al.

This article studies a scalable control method for multizone heating, ventilation, and air-conditioning (HVAC) systems to optimize the energy cost for maintaining thermal comfort (TC) and indoor air quality (IAQ) (represented by CO2) simultaneously. This problem is computationally challenging due to the complex system dynamics, various spatial and temporal couplings, as well as multiple control variables to be coordinated. To address the challenges, we propose a two-level distributed method (TLDM) with an upper level and lower level control integrated. The upper level computes zone mass flow rates for maintaining zone TC with minimal energy cost, and then, the lower level strategically regulates zone mass flow rates and the ventilation rate to achieve IAQ while preserving the near energy-saving performance of upper level. As both the upper and the lower level computation are deployed in a distributed manner, the proposed method is scalable and computationally efficient. The near-optimal performance of the method in energy cost saving is demonstrated through comparison with the centralized method. In addition, the comparisons with the existing distributed method show that our method can provide IAQ with only little increase of energy cost, while the latter fails. Moreover, we demonstrate that our method outperforms the demand-controlled ventilation (DCVs) strategies for IAQ management with about 8%–10% energy cost reduction. Note to Practitioners: The high portion of building energy consumption has motivated the energy saving for heating, ventilation, and air-conditioning (HVAC) systems. Concurrently, the living standards for indoor environment are rising among the occupants. Nevertheless, the status quo on improving building energy efficiency has mostly focused on maintaining thermal comfort (such as temperature), and the indoor air quality (IAQ) (usually represented by CO2 level) has been seldom incorporated. In our previous work with the similar setting, we observed that the CO2 levels will surge beyond tolerance during the high occupancy periods if only thermal comfort (TC) is considered for HVAC control. This deduces the IAQ and TC should be jointly considered while pursuing the energy cost saving target and thus studied in this article. This task is computationally cumbersome due to the complex system dynamics (thermal and CO2) and tight correlations among the different control components (variable air volume and fresh air damper). To cope with these challenges, this work develops a two-level distributed computation paradigm for HVAC systems based on problem structures. Specifically, the upper level control (ULC) first calculates zone mass flow rates for maintaining comfortable zone temperature with minimal energy cost, and then, the lower level strategically regulates the computed zone mass flow rates as well as ventilation rate to satisfy IAQ while preserving the near energy-saving performance of the ULC. As both the upper and lower level calculations can be implemented in a distributed manner, the proposed method is scalable to large multizone deployment. The method’s performance both in maintaining comfort (i.e., TC and IAQ) and energy cost saving is demonstrated via simulations in comparisons with the centralized method, the distributed token-based scheduling strategy, and the demand-controlled ventilation strategies.

G Balasubramanian, P. Chandrasekar, S. Albert Alexandar

N. Rosa, N. Soares, J. Costa et al.

Abstract Open-loop earth-air heat exchangers (EAHE) can be used as a passive contribution to reduce the energy demand of buildings for heating and cooling, by providing a thermal pre-conditioning of the required ventilation air. This paper aims to numerically assess the influence of three parameters on the overall thermal performance of an EAHE system for residential buildings in warm-summer Mediterranean climate: spacing between pipes, pipes diameter and flowing air velocity. ANSYS-CFX® was used to simulate the EAHE transient behaviour during heating and cooling operation modes, and to evaluate the influence of each parameter on the outlet air temperature and soil-air heat transfer rate. The numerical results were validated against experimental data and compared with previously obtained analytical results. It was concluded that for a certain pipe diameter and distance between adjacent pipes, the higher the air velocity the lower the thermal performance of the system, mainly for cooling. Results also showed that for a certain air velocity and pipe diameter, the distance between pipes can be reduced from 1.0 m to 0.5 m without compromising the EAHE performance, thus allowing a reduction of the land area needed for the EAHE pipes up to ca. 50%.

Aysan Shahsavar Goldanlou, Rasool Kalbasi, M. Afrand

Abstract Due to the high energy usage in buildings, researchers have sought to reduce energy consumption in this sector. In this regard, lower energy demands undoubtedly reduce the large amounts of energy consumed for heating, ventilation, and air conditioning (HVAC) in buildings. In this study, a novel design of the air handling unit (AHU) equipped with the primary and secondary heat recovery units was proposed to diminishing energy demand through the energetic and exergetic analysis. In the primary heat recovery unit, the incoming fresh air is pre-cooled to decrease energy usage in cooling coil whereas, in the second one, the cooling coil outlet air is preheated to diminish the heating coil load. Due to the installing energy recovery units, the cooling and heating coils load decreased by 21.65% and 81.17%, respectively, which improved the energy efficiency by 43.75%. Also, the total irreversibility was reduced by 24.56%, and the second law efficiency improved by 9.27%. The sensitivity analysis results revealed that the quota of ambient temperature and relative humidity, chilled water temperature, and the amount of ventilation were more effective than other input parameters.

Ammar Alkhalidi, Mohamad K. Khawaja, Dana Abusubaih

An already existing aquaponics facility in Jordan, named Khodra, will be used to evaluate the cooling and heating profiles to provide the best environment for plants and fish to thrive. A replica of the ‘Khodra’ facility will be simulated to be built in Qatar. Good ventilation rate with 50% green color shading was sufficient to reduce the temperature down by almost 10 degrees in ‘Khodra’-Jordan while using a heating, ventilation and air conditioning water-chiller based system reduced the humidity in the ‘Khodra’-Qatar greenhouse yet using AC split units was cheaper for the small size, 360 m2, of this specific greenhouse.

N. T. Myers, Leonardo Calderón, Brian T. Pavilonis et al.

Bioaerosol concentrations in residential buildings located in the Northeastern US have not been widely studied. Here, in 2011-2015, we studied the presence and seasonal variability of culturable fungi and bacteria in three multi-family apartment buildings and correlated the bioaerosol concentrations with building ventilation system types and environmental parameters. A total of 409 indoor and 86 outdoor samples were taken. Eighty-five percent of investigated apartments had indoor-outdoor (I/O) ratios of culturable fungi below 1, suggesting minimal indoor sources of fungi. In contrast, 56% of the apartments had I/O ratios for culturable bacteria above 1, indicating the prominence of indoor sources of bacteria. Culturable fungi I/O ratios in apartments serviced by central heating, ventilation and air-conditioning (HVAC) system were lower than those in apartments with window AC. The type of ventilation system did not have a significant effect on the presence of indoor culturable bacteria. A significant positive association was determined between indoor dew point (DP) levels and indoor culturable fungi (p <0.001) and bacteria (p <0.001), regardless of ventilation type. Also, residents in apartments with central HVAC did not experience extreme DP values. We conclude that building ventilation systems, seasonality, and indoor sources are major factors affecting indoor bioaerosol levels in residential buildings.

Yixiang Huang, Chengqiang Zhi, Qianru Zhang et al.

Chenghu Zhang, Yaping Li, Jianli Zhang

Xinyi Chen, Qinran Hu, Qingxin Shi et al.

As the penetration of renewable energy continues to increase, stochastic and intermittent generation resources gradually replace the conventional generators, bringing significant challenges in stabilizing power system frequency. Thus, aggregating demand-side resources for frequency regulation attracts attentions from both academia and industry. However, in practice, conventional aggregation approaches suffer from random and uncertain behaviors of the users such as opting out control signals. The risk-averse multi-armed bandit learning approach is adopted to learn the behaviors of the users and a novel aggregation strategy is developed for residential heating, ventilation, and air conditioning (HVAC) to provide reliable secondary frequency regulation. Compared with the conventional approach, the simulation results show that the risk-averse multi-armed bandit learning approach performs better in secondary frequency regulation with fewer users being selected and opting out of the control. Besides, the proposed approach is more robust to random and changing behaviors of the users.

Jun Bao, Yu Wang, Xinjie Xu et al.

Yi Man, Xinyu Zhang, Shuo Li et al.

Jiaen Luo, Zhaosong Fang, Lan Tang et al.