The building industry, which uses the most electricity, has a significant potential to contribute to energy consumption reduction. Commercial structures use more energy than other types of structures because of their productive and logistic features. In these types of structures, one of the main energy consumers is the HVAC system which comprises of heating, ventilation, and air conditioning, especially in arid conditions. Energy-efficient environment friendly HVAC system conception and execution can significantly lower the use of energy and support ecologically sound growth in business establishments. On the other hand, inadequate implementation of methods for reducing energy use may lead to a decline in the welfare of the environment. Therefore, in order to achieve energy efficiency and maintain the optimum degree of temperature regulation, a comprehensive energy conservation strategy is needed. To accomplish this goal, model predictive control strategy-based methodologies are used in this work. To estimate how much energy will be used in commercial buildings, four deep learning-based methods are utilised: radial basis function networks, multi-layer perceptrons, artificial neural networks, and back propagation neural networks. To further cut down on energy use, four distinct control mechanisms are used. The performance of the suggested solution is examined using performance measures like Mean Absolute Error and Mean Absolute Percentage Error.
Ahmad F. Zueter, Ahmad S. Dalaq, Mohammed F. Daqaq
This study introduces an innovative ventilation system, which leverages an origami-inspired structure to improve and regulate natural airflow driven by the stack effect, with applications in underground mines and buildings. The proposed system retrofits chimneys and/or exhaust risers with expandable origami units that dynamically modulate their geometric features (height and vent area) to control buoyancy-driven ventilation independent of external wind or solar conditions. The efficacy of the proposed concept is evaluated using a three-dimensional computational model that focuses on how the geometric design of the deployable stack and varying atmospheric conditions affect the volumetric airflow through the stack in both its fully expanded and contracted states. The results show that the ventilation rate increases by up to 25\% with each doubling of the height of the origami stack. % These findings highlight the potential of leveraging origami-inspired structures for adaptable and controllable energy-efficient ventilation, which is particularly beneficial in energy-intensive applications and/or remote, off-grid locations.
Antoine Gaillard, Detlef Lohse, Daniel Bonn
et al.
The COVID-19 pandemic caused a paradigm shift in our way of using heating, ventilation, and air-conditioning (HVAC) systems in buildings. In the early stages of the pandemic, it was indeed advised to reduce the reuse and thus the recirculation of indoor air to minimize the risk of contamination through inhalation of virus-laden aerosol particles emitted by humans when coughing, sneezing, speaking or breathing. However, such recommendations are not compatible with energy saving requirements stemming from climate change and energy price increase concerns, especially in winter and summer when the fraction of outdoor air supplied to the building needs to be significantly heated or cooled down. In this experimental study, we aim at providing low-cost and low-energy solutions to modify the ventilation strategies currently used in many buildings to reduce the risk of respiratory disease transmission. We find that ultraviolet germicidal irradiation (UVGI) modules added to the HVAC system are very efficient at inactivating pathogens present in aerosols, leading to good indoor air quality even with significant indoor air recirculation. Moreover, we show that an optimal placement of the air exhaust vents relative to air supply vents can improve the ventilation efficiency, with significant consequences in terms of energy savings.
In the past decade, the use of renewable energy for heating and residential and greenhouse cooling structures has gained much interest due to the energy crisis, population growth, and the quantity of demand. This paper investigates heat transport and thermodynamic equations for a residential and greenhouse structure to simulate and examine the performance of a soil air conditioning system using fluid flow rate, pipe diameter, length, and fluid type features. The results show that the air-driven ventilation systems during summer outperform the rest of the HVAC systems. Moreover, decreasing the diameter and prolonging the pipeline positively affects the ventilation system's performance. In addition, the airflow rate positively correlates with our HVAC performance. We studied the performance of the air-conditioning systems in 4 cities in Iran. The Rasht's ventilation system is claimed to be the most effective for heating, and the Abadan cooling system showed outstanding results. We also compared the expenses of the soil cooling and conventional HVAC systems.
Stochastic versions of a classical model for natural ventilation are proposed and investigated to demonstrate the effect of random fluctuations on stability and predictability. In a stochastic context, the well-known deterministic result that ventilation driven by the competing effects of buoyancy and wind admits multiple steady states can be misleading. With fluctuations in the buoyancy exchanged with an external environment modelled as a Wiener process, such systems tend to reside in the vicinity of global minima of their potential, rather than states associated with metastable equilibria. For a heated space with a leeward low-level and windward high-level opening, sustained buoyancy-driven flow opposing the wind direction is unlikely for wind strengths exceeding a statistically critical value, which is slightly larger than the critical value of the wind strength at which bifurcation in the deterministic system occurs. When fluctuations in the applied wind strength are modelled as an Ornstein-Uhlenbeck process, the topology of the system's potential is effectively modified due to the nonlinear role that wind strength has in the equation for buoyancy conservation. Consequently, large fluctuations in the wind of sufficient duration rule out the possibility of sustained ventilation opposing the wind direction at large base wind strengths.
This work leverages the U.S. Federal Aviation Administration's Traffic Flow Management System dataset and DV8, a recently developed tool for highly interactive visualization of air traffic data, to develop clustering algorithms for categorizing air traffic by their varying flight paths. Two clustering methodologies, a spatial-based geographic distance model, and a vector-based cosine similarity model, are demonstrated and compared for their clustering effectiveness. Examples of their applications reveal successful, realistic clustering based on automated clustering result determination and human-in-the-loop processes, with geographic distance algorithms performing better for enroute portions of flight paths and cosine similarity algorithms performing better for near-terminal operations, such as arrival paths. A point extraction technique is applied to improve computation efficiency.
Abstract Despite the advantages of building enclosure systems for improving ventilation efficiency and reducing energy consumption, there is a large difference in performance from the central heating, ventilating, and air-conditioning (HVAC) system. This study investigated the performance of a smart window-integrated ventilation (SWV) system in conjunction with a centralized HVAC system for enhancing indoor air quality (IAQ) and thermal comfort in a typical single-occupancy office. To evaluate the performance of two coupled systems, IAQ and thermal comfort in an office were analyzed for satisfying seasonally optimal ventilation scenarios using computational fluid dynamics simulations. A set of scenarios for case study was determined by outdoor temperature, supply airflow rate and temperature, and operation strategy of the two systems. Numerical results showed that using the SWV system as an aid to the HVAC system was more effective in winter than in summer for improving IAQ and thermal comfort. Only in the summer, the SWV led to poor IAQ. In spring and autumn, there were scenarios in which the SWV system performed similar to the HVAC system. Therefore, depending on indoor and outdoor conditions, the SWV system can be a good choice as an auxiliary means of the HVAC system or for single operation.
The solidification/melting model of FLUENT software was used to numerically study the influence of contact angle and mass fraction on the freezing process of pure water and sodium chloride solution on the cold surface. Meanwhile, copper was chosen as the hydrophilic surface and nanometer film as the hydrophobic surface, and the freezing process of droplets under different surface characteristics was experimentally studied. The results show that the freezing characteristics of the droplet on the surface of the plate are related to the surface contact angle and mass fraction. When the solution mass fraction is fixed, a smaller contact angle results in a faster droplet freezing rate and a shorter complete freezing time. At the beginning of the freezing process, the smaller the contact angle, the lower the bottom temperature of the droplet. When the freezing time and the droplet height were the same, the temperature and liquid fraction on the surface of the droplet were lower than those inside the droplet. At the same contact angle, the solution mass fraction is inversely proportional to the initial freezing temperature of the droplet and directly proportional to the complete freezing time. The comparison between the experimental results and the simulation results shows that the freezing time of different mass fractions of sodium chloride droplets exhibits the same trend when the contact angle is 60° and 100°, but the experimental value is greater than the simulated value.
Heating and ventilation. Air conditioning, Low temperature engineering. Cryogenic engineering. Refrigeration
Understanding ventilation strategy of a supercavity is important for designing high-speed underwater vehicles wherein an artificial gas pocket is created behind a flow separation device for drag reduction. Our study investigates the effect of flow unsteadiness on the ventilation requirements to form (CQf) and collapse (CQc) a supercavity. Imposing flow unsteadiness on the incoming flow has shown an increment in higher CQf at low free stream velocity and lower CQf at high free stream velocity. High-speed imaging reveals distinctly different behaviors in the recirculation region for low and high freestream velocity under unsteady flows. At low free stream velocities, the recirculation region formed downstream of a cavitator shifted vertically with flow unsteadiness, resulting in lower bubble collision and coalescence probability, which is critical for the supercavity formation process. The recirculation region negligibly changed with flow unsteadiness at high free stream velocity and less ventilation is required to form a supercavity compared to that of the steady incoming flow. Such a difference is attributed to the increased transverse Reynolds stress that aids bubble collision in a confined space of the recirculation region. CQc is found to heavily rely on the vertical component of the flow unsteadiness and the free stream velocity. Interfacial instability located upper rear of the supercavity develops noticeably with flow unsteadiness and additional bubbles formed by the distorted interface shed from the supercavity, resulting in an increased CQc. Further analysis on the quantification of such additional bubble leakage rate indicates that the development and amplitude of the interfacial instability accounts for the variation of CQc under a wide range of flow unsteadiness. Our study provides some insights on the design of a ventilation strategy for supercavitating vehicles in practice.
<p>Template energy calculation models that have been produced by the Building Energy End-use Study (BEES) team are used to quickly and reliably model commercial buildings and calculate their energy performance. The template models contain standardised equipment, lighting, and occupancy loads; cooling and heating requirements are calculated using an ideal loads air system. Using seven buildings, Cory et al. 2011a have demonstrated that the template models have the potential to closely match the monthly energy performance of detailed (individually purpose built) models and the real buildings. Three of these models were within the ±5% acceptable tolerance to be considered calibrated. The four template models that were not within the acceptable tolerance have been identified to have complex Heating, Ventilation, and Air Conditioning (HVAC) systems that the ideal loads air systems could not replicate. Because HVAC systems consume one of the largest proportions of energy in commercial buildings, this has a significant impact on the reliability of the template models. To address this issue, a set of detailed HVAC systems were needed to replace the ideal loads air systems. Due to HVAC system parameters not being collected by the BEES team and the lack of published modelling input parameters available, it is unknown what values are reasonable to use in the models. This study used a Delphi survey to collect real building information of the commonly installed HVAC systems in New Zealand commercial buildings. The survey formed a consensus between HVAC engineers that determined what the most commonly installed systems are and their associated performance values. The outcome of the survey was a documented set of system types and modelling input parameters that are representative of New Zealand HVAC systems. The responses of the survey were used to produce a set of HVAC system templates that replace the ideal loads air systems. The HVAC template models updated the software default parameter values with values that are representative of commonly installed systems in New Zealand. The importance of the updated input values was illustrated through a comparison of the calculated monthly energy consumption. The resulting difference in energy consumption using the updated parameter values is typically <5% monthly; at worst it is 75% for Variable Air Volume (VAV) system in the Wellington climate during June.</p>
This special issue, ‘Building Environmental Control for the Wellbeing of Occupants’ was initiated in response to the increasing demand for a better environmental control for the wellbeing of occupants, and in consideration of the government policy and the introduction of Chinese standards on ventilation for environmental control of indoor environments, which have been reviewed. The environmental control for the wellbeing of occupants is especially needed in consideration of the performance criteria for passive near-zero energy buildings required in China, and the Chinese standard GB/T 50668-2011, on ‘Indoor Environmental Quality for Assessment of Energy-efficient Buildings’. This special issue is derived from papers selected from the 11th International Symposium on Heating, Ventilation and Air Conditioning held on 12–15 July 2019 in Harbin, China. The selected papers were modified and extended and then peer reviewed for presentation as journal papers for the special issue. Heating, ventilating and air conditioning (HVAC) systems are of great importance to improve indoor environment quality (e.g. indoor air quality, thermal comfort, etc.). However, it may cause significant energy consumption, accounting for more than 50% of the total building energy consumption, especially for public/non-residential buildings. Moreover, considering the dynamic and non-uniform distribution characteristics of indoor environment parameters, e.g. pollutant concentration, temperature and humidity, HVAC systems may not satisfy the actual demand of the environment requirement. Thus, there is a need to develop correlated HVAC control strategies and techniques based on the perspective of indoor environment, health and wellbeing of occupants as well as energy efficiency. This is also the main goal of this special issue, i.e. new technologies for environmental control for the wellbeing of occupants. Technologies such as ground source heat pump, uncertainty-based robust control for HVAC systems, dehumidification systems, heat storage as well as ventilation design for underground space environments, etc. are considered. The following parameters that pose a demand on HVAC systems should be included: Indoor Air Quality and Ventilation systems. Air pollution could have many adverse effects on human health. The behaviour of indoor air pollutants emissions is of great importance to regulate air quality and assess health risks, such as fine and ultrafine particular matters (PM10 and PM2.5), 9 formaldehyde, VOCs, airborne fungi, nitrogen oxides (NOx), 14 ozone (O3) 15 and radon. Also carbon dioxide (CO2) 18,19 concentration should be included for consideration as this has a significant relationship with ventilation efficiency, occupants’ respiratory index related to tiredness and sick building syndrome symptoms. Besides, indoor environment could be influenced by outdoor pollution. High indoor PM concentrations were found to be highly influenced by outdoor levels. Building ventilation is an effective method to remove pollutants and dilute stable air. Natural ventilation through window openings could remove around 23% of indoor formaldehyde. However, ventilation air is a source of indoor PM2.5. Air filtration technology with good filtration performance and antibacterial function has been widely developed to reduce indoor contamination. Air curtain systems have been
Pouria Bahramnia, Seyyed Mohammad Hosseini Rostami, Jin Wang
et al.
Nowadays, by huge improvements in industrial control and the necessity of efficient energy consumption for buildings, unified managing systems are established to monitor and control mechanical equipment and energy usage. One of the main portions of the building management system (BMS) is the cooling and heating equipment called heating and ventilation and air-conditioning (HVAC). Based on temperature slow dynamic and presented uncertainty in modeling, a model predictive control (MPC) strategy to track both temperature and humidity is proposed in this study. The main goal of this study is to provide a framework to describe temperature and humidity elements required for dynamic modeling. Following that, by utilizing a predictive approach, a control strategy is obtained, which optimizes the tracking error of two interactional channel and performs the effort control by minimizing the optimization index. Other articles have mostly only had control over the temperature variable, but in our article, we tried to study the equations of temperature and humidity as well as their interference and according to the ASHRAE standard, both temperature and humidity controls must be accurate. The humidity was the novelty in our article. Simulation results proved the effectiveness of the proposed approach compared to the conventional proportional-integral controller. Evidently, the key idea behind the control objective is providing the comfort condition while consuming the least possible energy.
Thermoelectric (TE) air cooling is a solid-state technology that has the potential to replace conventional vapor compression-based air conditioning. In this paper, we present a detailed system-level modeling for thermoelectric air conditioning system with position-dependent (graded) and constant material properties. Strategies for design optimization of the system are provided in terms of cost-performance trade-off. Realistic convection heat transfer at both sides of the system are taken into account in our modeling. Effects of convection heat transfer coefficients, air flowrate, and thermoelectric material properties are investigated with varying key parameters such as TE leg thickness, module fill factor, and input current. Both constant material properties and graded properties are considered for the TE materials, and they are compared in terms of the degree of cooling, coefficient of performance (COP), and power consumption. For graded materials, we employ one-dimensional finite element methods to solve the coupled electrical and thermal current equations with arbitrary profile of material properties varying with position along the TE legs. We find that graded materials can enhance the degree of cooling, but only at the expense of COP, compared to the case of constant property materials. With constant material properties of ZT = 1 and relatively low electric current, the power consumption of TE cooler can be lower than those of conventional air conditioners at an equivalent cooling capacity. Considering additional advantages such as demand-flexible operation, low noise, and high scalability, thermoelectric cooling could be a competitive technology for future air conditioning applications.
This article presents a new, holistic model for the air traffic management system, built during the Vista project. The model is an agent-driven simulator, featuring various stakeholders such as the Network Manager and airlines. It is a microscopic model based on individual passenger itineraries in Europe during one day of operations. The article focuses on the technical description of the model, including data and calibration issues, and presents selected key results for 2035 and 2050. In particular, we show clear trends regarding emissions, delay reduction, uncertainty, and increasing airline schedule buffers.
Joey Reinders, Ruben Verkade, Bram Hunnekens
et al.
Mechanical ventilators sustain life of patients that are unable to breathe (sufficiently) on their own. The aim of this paper is to improve pressure tracking performance of mechanical ventilators for a wide variety of sedated patients. This is achieved by utilizing the repetitive nature of sedated ventilation through repetitive control. A systematic design procedure of a repetitive controller for mechanical ventilation is presented. Thereafter, the controller is implemented in an experimental setup showing superior tracking performance for a variety of patients.