Energy-efficient Ventilation Research Articles

CFD modelling of transient thermal performance of solar chimney used for passive ventilation in a building

The paper analysed the 24 hour performance of a solar chimney placed on a building roof in Krakow, Poland. The solar chimney was an element of as a passive ventilation system allowing energy efficient night ventilation during the summer season. The chimney was built as an air duct. Three walls of the chimney were made of glass and faced toward the sun, the opposite wall was made of a concrete absorber. The system worked in two stages: day and night. The absorber located in the chimney was heated during the day, and cooled during the night. During the night phase, the released heat provided a draft contributing to passive ventilation.Absorbers with different thermal capacities were studied. Simulations were conducted for three different absorber thickness 10 cm, 20 cm or 30 cm. The simulations were carried out using the Ansys Fluent simulation software. The hourly results of temperature distributions in the chimney allowed the authors to determine the optimal absorber thickness for the passive ventilation system. Calculations showed that the chimney with the absorber that was 10 cm thick was the optimal among analysed solutions. The absorber is warmed up to the highest temperature, up to 82°C, and induces air flow which lets removing even 3820 m3 of air during the night.

Energy efficient ventilation units: The role of the Ecodesign and Energy Labelling regulations

Energy efficient ventilation units: The role of the Ecodesign and Energy Labelling regulations

Performance evaluation of CO2-based ventilation control to reduce CO2 concentration and condensation risk in residential buildings

As the airtightness of a building envelope gets higher to achieve energy efficiency, the necessity of appropriate ventilation for residential buildings is continually increasing. Many residential buildings are equipped with energy recovery ventilators (ERV) for energy-efficient ventilation; however, the ERVs are usually operated by occupants' manual control, which often leads to insufficient or unnecessary ventilation. Because it is difficult to operate an ERV during nighttime, when occupants cannot control the system, a residential building can suffer from poor indoor air quality and increasing condensation risks. Herein, a CO2-based ventilation control strategy was implemented in an existing ERV system for residential buildings. Considering that most ERV systems operate with a central control, the appropriate CO2 sensor location (or representative room) was investigated in a mock-up residential building. Comparative experiments were conducted to evaluate the control performances in terms of indoor air quality (CO2 control performance) and fan energy consumption. Experimental results showed that a living-room-based control can maintain an overall CO2 concentration in the entire space at acceptable levels. It was also shown that a living-room-based control resulted in reduced ventilation energy if the CO2 dispersed through open bedroom doors. The CO2-based ventilation control was modified to mitigate the condensation risk while minimizing the possibility of fan noise or cold draught. Through mock-up experiments on a modified CO2-based ventilation control, it was shown that CO2 concentrations can be maintained at acceptable levels and condensation risks can be mitigated even when the outdoor temperature decreases to −15 °C.

Cooling energy simulation and analysis of an intermittent ventilation strategy under different climates

Energy use on heating, ventilation and air conditioning (HVAC) accounts for about 50% of building energy use. To have a sustainable built environment, energy efficient ventilation systems that deliver good indoor environmental quality are needed. This study evaluates the cooling energy saving potential of a newly proposed ventilation system called Intermittent Air Jet Strategy (IAJS) and compares its performance against a mixing ventilation (MV) system in a classroom located in three cities with different climates, Singapore with ‘hot and humid’, Ahvaz with ‘hot and dry’ and Lisbon with “moderate” climate. The results show a significant reduction of cooling energy need and flexibility in control strategies with IAJS as a primary system in hot and humid climates like Singapore. Hot and dry climate with short cool periods like Ahvaz show possible application and considerable energy savings with IAJS as a primary system under optimized variable setpoints, but moderate climates have an increased risk of occupant discomfort likely due to increased draft especially during the cool season. Thus, IAJS as a secondary system that operates only during cooling season may be conducive for moderate climates like Lisbon. Additionally, the results show that supply fan energy savings can also be realised if well implemented.

Coupling of earth-to-air heat exchangers and buoyancy for energy-efficient ventilation of buildings considering dynamic thermal behavior and cooling/heating capacity

Energy-efficient technologies such as earth-to-air heat exchangers (EAHEs) and buoyancy-driven natural ventilation (BV) are employed for space conditioning. However, a fan is required in conventional EAHEs for air circulation, and BV normally serves as a passive cooling measure in temperate transitional seasons. This paper proposes the coupling of EAHEs and the buoyancy generated inside a building to achieve passive and autonomous ventilation without requiring any mechanical system. A model is developed to investigate the effects of the coupled system, with a primary focus on the dynamics of the airflow temperature, flow rate, and cooling/heating capacity provision. The model results are in good agreement with those of the computational fluid dynamics simulation. The model is applied in a hypothetical building located in a hot-summer/cold-winter region (Chongqing, China). The proposed coupled scheme is superior to the BV in hot and cold seasons. The indoor air temperature, ventilation flow rate, and cooling/heating capacity are found to fluctuate asynchronously. The cooling capacity is 56.3 kWh for the hottest day, and the heating capacity is 111.1 kWh for the coldest day. The maximum cooling or heating capacity is nearly achieved at the hottest or coldest times with the help of ventilation flow rate fluctuation.

Javanese House’s Roof (Joglo) with the Opening as a Cooling Energy Provider

Natural ventilation and air movement could be considered under the heading structural controls as it does not rely on any form of energy supply or mechanical installation but due to its importance for human comfort, it deserves a separate section. Air infiltration can destroy the performance of ventilation systems. Good ventilation design combined with optimum air tightness is needed to ensure energy efficient ventilation. Ultimately, ventilation needs depend on occupancy pattern and building use. A full cost and energy analysis is therefore needed to select an optimum ventilation strategy.The contains of paper is about the element of Javanese house (the roof) as the element of natural ventilation and a cooling energy provider. In this research, The Computational Fluid Dynamics Program, is used to draw and analysis. That tool can be track the pattern and the direction of movement of air also the air velocity in the object of ventilation of the roof Javanese house based. Finally, the ventilation of the roof of this Javanese house can add the velocity of air at indoor, average 0.4 m/s and give the effect of cooling, average 0.7°C.

Experimental study of a local ventilation strategy to protect semi-exposed relics in a site museum

Indoor environmental controls are critical considerations when preserving artifacts in museums. Controlling the indoor environment of site museum buildings with large space layout typically consumes large amounts of energy. Most of the energy load needed to preserve relics is dissipated throughout the non-occupied space, because the environments that contain the relics occupy relatively little space compared to the entire exhibition hall. In this study, an energy efficient local ventilation system was proposed to independently control the environment of a funerary pit, which was preserved within a museum separate from the large exhibition hall. An experimental hall, which consists of a funerary pit and an experimental local ventilation system, was built to simulate a site museum building. Experiments were conducted to investigate the system’s performance and to validate its ability to preserve historical terracotta figurines in their semi-exposed pits within the exhibition hall. The study evaluated the stability of the conservation environment and the system’s energy usage by assessing the effects of the ventilation rate. The experimental results showed that the local ventilation system provides an energy-saving strategy supporting the environmental control of the funerary pit. The LV system significantly decreased temperature fluctuations in the funerary pit and temperature differences across semi-exposed relics. The system could be used to control the local preservation environment of the funerary pit separately from a large space exhibition hall.

The application of the Pinch method for the analysis of the heat exchangers network in a ventilation system of a building

Intensive use of energy is related to the inefficient use of processes in building engineering systems. In well-insulated non-residential buildings ventilation systems are among the most energy intensive HVAC systems. The main components of an energy (and exergy) efficient ventilation system are heat exchangers. The paper presents the analysis of process integration possibilities in a ventilation system. Only air heating for ventilation purposes is analysed. The method of Pinch technology, mostly used for industrial process integration, is adopted for a ventilation system of a building for the first time. In the paper, several different cases of integration are analysed by using actual BMS data of a shopping centre. The results confirmed that process integration influences the thermodynamic efficiency of the system and that integrated systems consume less energy and exergy in comparison with the non-integrated ones. The case study shows that the seasonal energy demand of the system before integration is 26% higher compared to integrated system and the exergy demand is 45% higher.

Numerical investigation of the energy performance of an Opaque Ventilated Façade system employing a smart modular heat recovery unit and a latent heat thermal energy system

The building sector is responsible for more than 40% of the EU’s total energy consumption. To reduce the energy consumption in buildings and to achieve the EU’s fossil fuel saving targets for 2020 and beyond 2050, the energy efficient retrofitting strategies are critically important and need to be implemented effectively. This paper presents a dynamic numerical investigation of the energy performance of an innovative façade integrate-able energy efficient ventilation system (E2VENT) that incorporates a smart modular heat recovery unit (SMHRU) and a latent heat thermal energy system (LHTES). A number of component simulation models, including SMHRU, LHTES, Cladding and Building Energy Management System (BEMS), were developed and then integrated using the TRNSYS software which is an advanced building energy performance simulation tool. On this basis, sizing, optimisation and characterisation of the system elements including the HVAC system and insulation layer thickness were carried out. The overall energy efficiency of the E2VENT system and its impact on the energy performance of a post-retrofit building were then investigated. In particular, the heating and cooling energy performance of the E2VENT façade module was numerically studied at five different climatic conditions in Europe. Furthermore, the innovative E2VENT retrofitting was compared with traditional retrofittings in terms of the energy efficiency and primary energy savings. It was found that the innovative E2VENT solution can achieve 16.5–23.5% building primary energy saving and compared to the traditional retrofitting, the E2VENT solution can achieve two times less primary energy consumption. Thanks to this efficiency the development of this solution for buildings retrofit is promising.

OPERATING CHARACTERISTICS OF ADSORPTIVE REGENERATOR OF LOW-POTENTIAL HEAT AND MOISTURE BASED ON COMPOSITE SORBENTS ‘SILICA GEL – SODIUM SULPHATE’ AND ‘SILICA GEL – SODIUM ACETATE’ SYNTHESIZED BY SOL – GEL METHOD

The operating characteristics adsorptive regenerator of low-potential heat and moisture based on composite sorbents ‘silica gel – sodium sulphate’ and ‘silica gel – sodium acetate’ synthesized by sol – gel method are studied. Sorption heat regenerator operating and environmental test results are shown. Flows switch-over time is observed to depend on airflow rate and temperature differential between warm and cold ends of regenerator in steady-state conditions. Time dependences of absolute and relative humidity on the warm and cold regenerator ends are shown to be of periodic nature when both of sorbent used. Time dependences of temperature are observed to be periodic nature on warm and cold ends of regenerator and between holders with sorbent. Amplitude of time dependences of absolute and relative humidity and temperature for ‘silica gel – sodium acetate’ are stated to be less than observed when composite ‘silica gel – sodium sulphate’ used. Correspondence of temperature and humidity time dependences and sorbent sorption capacity is shown. Correlation between heat-regeneration-coefficient-dimensionless temperature differential and moisture-regeneration coefficients-dimensionless humidity differential dependences is approximated with fair accuracy for engineering calculation by linear polynomials of degree 2. Similarity of polynomials described both of dependences is shown to result from close interrelation between heat and mass transfer processes. These coefficients are shown to be capable of task-oriented variation in sufficient wide ranges by changing of half-cycle time, sorbent granules sizes and its amount. The investigation results can be used for development energy-efficient ventilation systems for residential and storage premises.

LATENT HEAT ENERGY STORAGE DEVICE AS А PART OF THE VENTILATION SYSTEM OF INDIVIDUAL HOUSE

Energy efficient ventilation systems allow to minimize the heat energy consumption for heating supply air, which is very relevant in the context of rising energy prices. It is dealt with the variant of the installation seasonal phase-change heat storage device in the system of ventilation with recuperation of heat energy. Preliminary engineering calculations were perfomed and the quantity of heat storage material (water) necessary for the operation of the ventilation system was determined. The diagrams of change the temperature of the air at the output from the accumulator and distribution of water and ice during the heating period were given. In the article the calculation of seasonal heat storage device on the basis of the water in the supply air ventilation systems are considered , which allows to minimize costs of thermal energy for heating the outside air before it enters to the premises of the house. It is proved that in modern economy conditions development the energy-efficient ventilation system is a promising direction of research and implementations.

Modeling heat and mass transfer in cross-counterflow enthalpy exchangers

Membrane-based enthalpy exchangers are an upcoming technology in energy efficient building ventilation systems. Evaluation of system performance and potential energy savings require appropriate theoretical models. This is challenging since the favored module geometry combines areas of cross- and counter-flow. With CFD simulation tools it is possible to accurately discretize such geometries. However, these models cannot be applied in process simulations. To overcome such limitations, we replace the complex module geometry by a combination of standard cross- and counter-flow units. Transition terms linking 1D- and 2D-discretization are introduced. In addition, governing equations of heat and mass transfer are presented. The final set of equations is solved using Aspen Custom Modeler®, which is a commercial tool comprising an extensive fluid property data base. After the model is validated by means of experimental data, the final set of equations is used to investigate the impact of boundary layer resistance on water vapor transport.

Assessment of mechanical exhaust in preventing vertical cross-household infections associated with single-sided ventilation

Single-sided natural ventilation is an energy efficient ventilation strategy that could provide satisfactory indoor air quality and thermal comfort. However, one of its possible negative influences is the cross-infection between households due to the two-way airflow. The present study aims at assessing the efficacy of mechanical exhaust (ME) devices to eliminate this possible cross-infection. CFD method was employed to simulate the buoyancy driven single-sided natural ventilation and the cross-contamination. Different occupant behaviour scenarios, such as ME-on centrally or ME-on individually, were compared with the no-ME case. It is found that mechanical exhaust could reduce the outflow of indoor air and increase the inflow of fresh air. However, the weakened outflow tends to be more attached to the façade and the re-entry risk may be increased. As the exhaust rate is large enough, the two-way airflow will turn into one-way inflow, and accordingly the vertical cross-household infection can be avoided. With ME-on in both floors, a low exhaust rate of 5 h−1 could reduce the presence of the tracer from the lower floor in the upper floor by an order of magnitude. But if the ME is on only in one of the two floors, the re-entry of outflow to the upper floor may be aggravated at some specific exhaust rate. Therefore, in epidemic seasons, appealing residents to switch on their individual exhaust fans, or alternatively switching on a central exhaust system is recommended. The results will contribute to the control of airborne transmission infectious diseases in high-rise residential buildings.

Developing a method to improve the energy efficiency of modern buildings by using traditional passive concepts of resource efficiency and climate adaptation

Around the world, humans have adapted building forms over the course of centuries to fit external, locally specific parameters such as climate, topography and available building materials. Thus, these structures are generally erected using locally available resources and adapted to fit the regional climate. These concepts were critical in the time before industrialization when neither the building materials, nor the energy and technology necessary for mechanical climate control systems, were available. Even though numerous studies on the concepts of traditional passive climate control exist, the applicability of these concepts in modern buildings is generally not explored. This study addressed this gap in the research by developing a method as a tool to improve the energy efficiency of modern buildings by integrating traditional passive concepts into the planning process. The paper describes an exemplary investigation of traditional residential buildings in the Upper Town of Thessaloniki, which has been the basis for developing the tool. The results of this case study showed that adding traditional concepts to the current legal requirements would improve indoor comfort and thus building energy performance. The tool could also be used for educational purposes to make students of the built environment aware of the great diversity of energy efficient heating, cooling and ventilation methods present in tradi tional buildings. This presents them with the opportunity to practice applying such alternative building designs and make comparisons with the alternatives.

Energy-efficiency impacts of an air-quality feedback device in residential buildings: An agent-based modeling assessment

A key factor to energy-efficiency of heating in buildings is the behavior of households, in particular how they ventilate rooms. Energy demand can be reduced by behavioral change; devices can support this by giving feedback to consumers on their behavior. One such feedback device, called the ‘CO2 meter’, shows indoor air-quality in the colors of a traffic light to motivate so called ‘shock ventilation’, which is energy-efficient ventilation behavior. The following effects of the ‘CO2 meter’ are analyzed: (1) the effect of the device on ventilation behavior within households, (2) the diffusion of ‘CO2 meter’ to other households, and (3) the diffusion of changed behavior to households that do not adopt a ‘CO2 meter’. An agent-based model of these processes for the city of Bottrop (Germany) was developed using a variety of data sources. The model shows that the ‘CO2 meter’ would increase adoption of energy-efficient ventilation by c. 12% and reduce heating demand by c. 1% within 15 years. Technology diffusion was found to explain at least c. 54% of the estimated energy savings; behavior diffusion explains up to 46%. These findings indicate that the ‘CO2 meter’ is an interesting low-cost solution to increase the energy-efficiency in residential heating.

Geometrical and kinematic analysis of turbulence in jets for energy efficient ventilation

Geometrical and kinematic analysis of turbulence in jets for energy efficient ventilation

Impacts of dynamic interactions on the predicted thermal performance of earth–air heat exchangers for preheating, cooling and ventilation of buildings

Earth–air tunnel ventilation is an energy efficient ventilation technique that makes use of relatively stable soil temperature in shallow ground for preheating and cooling of supply air to a building. During operation, an earth–air heat exchanger interacts with the soil and atmosphere and the performance varies with the soil and atmospheric conditions. A computer program has been developed for modelling of coupled heat and moisture transfer in soil and for simulation of the dynamic thermal performance of an earth–air heat exchanger for preheating and cooling of a building. The impacts of dynamic interactions between the heat exchanger, soil and atmosphere are illustrated from the comparison of the heat transfer rate, heat exchanger temperature and supply air temperature through the heat exchanger for both preheating and cooling. It is shown that neglecting the interactions between the heat exchanger, soil and supply air would over predict the thermal performance of an earth–air heat exchanger. Neglecting the interactions between the soil surface and atmosphere while assuming axi-symmetric distributions of heat and moisture transfer as well as soil properties around the heat exchanger is not only unrealistic but also would fail to produce reliable data for long-term operational performance of the earth–air heat exchanger installed in shallow ground. The performance of an earth–air tunnel ventilation system can be enhanced when operated for both winter preheating and summer cooling of a building.

Performance prediction of a new integrated central cooling plant for energy efficiency and comfort enhancement

The effective design of an energy efficient heating, ventilation and air conditioning system is reliant on multiple components. Among others, the air-handling unit cooling coil and its ability to perform efficiently directly influences heating, ventilation and air conditioning system performance. This paper investigates the energy and thermal performance of a water-cooled central cooling plant when combined with a direct evaporative cooling system located between the cooling tower and cooling coil of the air-handling unit. The evaporative cooler uses the water made by cooling tower to reduce the temperature of the 100% ambient air. The cooled air then passes through the cooling coil. This paper will demonstrate a series of mathematical models of the system components and validate them against experimental results. For this purpose, the central cooling plant is extensively equipped with a number of sensors and instrumentation devices for experimentation and data collection. The influence of the evaporative cooler on the energy saving potential and thermal comfort of the central cooling plant is evaluated. The advantages of this proposed hybrid system rests with the fact that the refrigeration effect of the chiller’s evaporator is decreased, which causes reduction of compressor power consumption. Results show that the hybrid system can provide average monthly energy savings between 11% and 24%, while enhancing the comfort level inside the building. Practical application: With traditional heating, ventilation and air conditioning systems contributing to 40% of a building’s overall energy consumption, the public’s increasing reliance on them as a necessity rather than a luxury is an issue in urgent need of attention. This together with a growing demand for cost-effective infrastructure and appliances has necessitated new installations and major retrofits in occupied buildings to achieve energy efficiency and environmental sustainability. The aim of this paper is to present a new integrated heating, ventilation and air conditioning system to meet these requirements without compromising comfort and indoor air quality.

Economic, Environmental and Health Implications of Enhanced Ventilation in Office Buildings.

Introduction: Current building ventilation standards are based on acceptable minimums. Three decades of research demonstrates the human health benefits of increased ventilation above these minimums. Recent research also shows the benefits on human decision-making performance in office workers, which translates to increased productivity. However, adoption of enhanced ventilation strategies is lagging. We sought to evaluate two of the perceived potential barriers to more widespread adoption—Economic and environmental costs. Methods: We estimated the energy consumption and associated per building occupant costs for office buildings in seven U.S. cities, representing different climate zones for three ventilation scenarios (standard practice (20 cfm/person), 30% enhanced ventilation, and 40 cfm/person) and four different heating, ventilation and air conditioning (HVAC) system strategies (Variable Air Volume (VAV) with reheat and a Fan Coil Unit (FCU), both with and without an energy recovery ventilator). We also estimated emissions of greenhouse gases associated with this increased energy usage, and, for comparison, converted this to the equivalent number of vehicles using greenhouse gas equivalencies. Lastly, we paired results from our previous research on cognitive function and ventilation with labor statistics to estimate the economic benefit of increased productivity associated with increasing ventilation rates. Results: Doubling the ventilation rate from the American Society of Heating, Refrigeration and Air-Conditioning Engineers minimum cost less than $40 per person per year in all climate zones investigated. Using an energy recovery ventilation system significantly reduced energy costs, and in some scenarios led to a net savings. At the highest ventilation rate, adding an ERV essentially neutralized the environmental impact of enhanced ventilation (0.03 additional cars on the road per building across all cities). The same change in ventilation improved the performance of workers by 8%, equivalent to a $6500 increase in employee productivity each year. Reduced absenteeism and improved health are also seen with enhanced ventilation. Conclusions: The health benefits associated with enhanced ventilation rates far exceed the per-person energy costs relative to salary costs. Environmental impacts can be mitigated at regional, building, and individual-level scales through the transition to renewable energy sources, adoption of energy efficient systems and ventilation strategies, and promotion of other sustainable policies.

Performance Assessment of Dedicated Outdoorair Systems for Office Building in Thailand

Ventilation is necessary for good indoor air quality (IAQ) in air-conditioned buildings. However, the ventilation causes a substantial load and resulting energy consumption of the air-conditioning system particularly for buildings in tropical region. To address the issue, this paper investigates the dedicated outdoor air system (DOAS) for the energy-efficient ventilation. In the study, performance of various DOAS configurations is evaluated for a typical office building under the hot and humid climate of Thailand. The results from the simulations using TRNSYS software show that the DOAS of the combination of a cooling coil, a run-around coil and an enthalpy wheel is the most energy efficient by which it offers the smallest total air-conditioning loads in obedience with the Thai's ventilation standard requirement.