Air Load Research Articles

Energy-efficient fresh air system with pressure-independent dampers for nearly zero energy buildings

Fresh air volume control is of great significance in reducing energy consumption in nearly zero energy buildings. Previous studies have shown that the operating fresh air volume often deviates significantly from the design value, resulting in unnecessary energy consumption. To overcome this problem, this study proposes an energy efficiency fresh air system for NEBs by using pressure-independent dampers to balance system resistance and control the operating fresh air volume accurately. A typical fresh air system used in a typical NZEB was tested both in laboratory and on site for a whole heating season. Based on the test data, the energy consumption model of the proposed fresh air system was established and validated. The energy performance of the proposed system was analyzed comprehensively. Results show that using the pressure-independent damper in the fresh air system to control the fresh air flow rate can significantly reduce the fresh air load by 39.2%, 49.4%, 52.3% and 45.5% in Harbin, Beijing, Shanghai and Guangzhou, respectively; The annual energy saving rates in these cities are approximately 29.3%, 28.7%, 27.0% and 19.1%, respectively. These energy saving rates are smaller than the corresponding fresh air load reductions due to the additional energy consumption caused by the pressure-independent damper; Furthermore, replacing the pressure-independent damper with an ideal variable speed ventilator for fresh air flow rate control can further increase the energy saving rate by 12%∼16%. This study identifies the energy saving potential of fresh air systems and contributes to achieving sustainable development in nearly zero energy buildings.

Effect of portable HEPA filters on COVID-19 period prevalence: an observational quasi-interventional study in German kindergartens

ObjectivesThe aim of the study was to evaluate the effect of high-efficiency particulate air (HEPA) filters on COVID-19 period prevalence in kindergartens.DesignThe observational study follows an intervention design with the...

Monitoring of Air and Water Bacterial Load in the Operation Theatres and Intensive Care Units of Selected Hospitals in Dhaka city: A Cross-Sectional Study

Background: Hospital milieu monitoring is an essential component for controlling healthcare associated infections (HCAIs) as it serves as the reservoir for pathogenic microbes. Aim of this study was to identify the bacterial load in Intensive care units (ICU) and Operation theaters (OT) air and water sources of selected tertiary care hospitals. Material & Methods: The study was organized in Microbiology department, BIRDEM General Hospital. A sum total 28 air samples & 6 water samples were collected from three selected hospitals and those were processed according to the set of protocols. Results: From air sampling, highest load of bacteria was found 480 CFU/dm²/hr in Hospital C ICU, 38.40 ± 9.99 CFU/dm²/hr in pre-OT samples & 218.2±43.35 CFU/dm²/hr in intra OT samples of Hospital C. From water sampling, unacceptable level of coliforms was found in all three hospitals. Among the non-pathogens, 24% – 37% Micrococcus spp. (normal flora) and 2% -18% Bacillus spp. (contaminants) were found in the OTs. Whereas pathogens found were Acinetobacter spp. (20.7%) followed by Pseudomonas spp. (19.4%), Klebsiella spp. (12.1%) & S. aureus (9.2%) in the ICUs. Conclusion: It could be deduced from the study that environmental sources such as air and water contaminations with multidrug resistant pathogens are an ultimate risk factor for all related to the healthcare settings, specially the indoor patients.

Comparison of fine bubble scouring, backwash, and mass air load supply for dynamic membrane maintenance and steady operation in SFD MBR for wastewater treatment

The self-forming dynamic membrane bioreactor (SFD MBR) is an evolution of the conventional ultrafiltration-based MBR where filtration occurs through a cake layer (dynamic membrane, DM) supported by a filtration net. The effluent quality levels that may be achieved through this technology are comparable to those of conventional MBR and suitable for effluent reuse, as shown in previous research. In addition, SFD MBR are more sustainable, both in terms of investment costs (filtration net materials are cheaper than UF membranes), and operation. Indeed, the typical operating pressure of these systems is below 100 mbar, thus compatible with gravity-driven operation. Nevertheless, as all membrane-based processes, also SFD MBR require periodic maintenance cleaning of the supports holding the filtering layers, in order to ensure high and constant effluent quality and steady operation. In this paper, different strategies for continuous or temporized cyclic DM maintenance aimed at limiting the frequency of on-site manual cleaning interventions are compared. In particular, five tests were performed at the bench scale adopting the same process conditions except for the type of DM maintenance strategy. Continuous fine-bubble air scouring of the membrane surface was compared with two intermittent cyclic procedures based on backwash with permeate (with and without simultaneous air scouring) and mass air load supply (with two cycles of different durations), respectively. The results have confirmed the overall high performance of this technology under all the tested conditions, with COD removal efficiencies always exceeding 86 %, effluent turbidity values normally well below 5 NTU (and often much lower), complete nitrification and partial nitrogen removal. Furthermore, the comparison among the different DM maintenance strategies has shown that the mass air load supply is the most efficient approach towards sustainable operation. In particular, shorter mass air load cycles provided the best performance in limiting the manual cleaning needs, which under this condition were as low as once every 3 weeks. The key finding of this study is the demonstration of cyclic air mass load as an effective preventive cleaning strategy allowing good performance of a bench-scale SFD MBR, strongly reducing the manual maintenance requirements. More experiments are required to confirm these results in larger scale installations.

Direct Quantitation of SARS-CoV-2 Virus in Urban Ambient Air via a Continuous-Flow Electrochemical Bioassay.

Airborne SARS-CoV-2 virus surveillance faces challenges in complicated biomarker enrichment, interferences from various non-specific matters and extremely low viral load in the urban ambient air, leading to difficulties in detecting SARS-CoV-2 bioaerosols. This workreports a highly specific bioanalysis platform, with an exceptionally low limit-of-detection (≤1 copym-3 ) and good analytical accordance with RT-qPCR, relying on surface-mediated electrochemical signaling and enzyme-assisted signal amplification, enabling gene and signal amplification for accurate identification and quantitation of low doses human coronavirus 229E (HCoV-229E) and SARS-CoV-2 viruses in urban ambient air. This workprovides a laboratory test using cultivated coronavirus to simulate the airborne spread of SARS-CoV-2, and validate that theplatform couldreliably detect airborne coronavirus and reveal the transmission characteristics. Thisbioassay conducts the quantitation of real-world HCoV-229E and SARS-CoV-2 in airborne particulate matters collected from road-side and residential areas in Bern and Zurich (Switzerland) and Wuhan (China), with resultant concentrations verified by RT-qPCR.

Shear Stress Distribution in a Fuselage of an Aircraft

The aircraft is assembled from basic components like fuselages, control surfaces, wings, and tail units. These components vary in different aircraft and have more than one specific function. The structure of an aircraft is designed to withstand two different types of loads namely the ground loads which includes landing loads, taxiing load, hoisting, and towing load. Air load is the second type which includes loads acting on the structure during flight by maneuvers and gusts. These two classes of load can be subdivided into surface forces which acts on the surface of the structure like hydrostatic pressure and aerodynamics, and body forces which is produced by inertia and gravitational effects and acts over the volume of the structure. The impact of these air loads results in bending stresses, shear stresses and torsional loads in all parts of the structure of the aircraft. The purpose of this paper is to calculate and plot the shear stress distribution as function of “a” on a cross section of an airplane fuselage made of 2014-T4 aluminum alloy. The plate thickness is 0.175a mm which is constant around the periphery and an applied torque of 200 kN.m. The radii of the fuselage are 50a mm and 32a mm respectively and it has a height of 69.5a mm. The fuselage is divided into sectors and triangles and their areas calculated. The shear flow which is a product of shear stress and thickness of the fuselage can be calculated. From the result it can be observed that as the magnitude of “a” increases the shear stress reduces. Verification and validation were carried out on solid works to test for convergence.
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PREPARATION OF NEW HARD ELASTIC POLYMERIC MATERIAL BASED ON ULTRA-HIGH MOLECULAR WEIGHT POLYETHYLENE

A novel approach for the preparation of hard elastic polymeric material based on ultra-high molecular weight polyethylene via the strategy of crazing of polymers has been proposed. This approach includes the process of deformation of the pristine films of ultra-high molecular weight polyethylene via environmental intercrystallite crazing mechanism and subsequent low-temperature spontaneous strain recovery upon stress relaxation. As a result, the material acquires new properties typical for hard elastic materials: restoration of the porous structure upon secondary loading in air up to ~20 vol. % with pore sizes in the nanometer range (up to 10 nm), high reversibility of deformation (50−85%), the effect of opening and closing pores upon cyclic loading. The mechanism of this phenomenon has been proposed and the areas of practical applications of such mechanoresponsive material have been indicated.

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.

Female crash fatality risk relative to males for similar physical impacts

Objective This paper estimates the latest trends regarding the effect of sex on driver-side or right-front passenger-side occupant fatalities in fatal crashes. The focus is on how recent model year (MY) light vehicles with advanced occupant protection technologies compare to older vehicles without these protections in terms of female fatality risk relative to males. Methods Data from the Fatality Analysis Reporting System (FARS) from 1975 to 2019 is used to calculate estimates of female fatality risk relative to males using logistic regression models and the double-pair comparison method. These estimates are calculated in various groups of MY vehicles and occupant protection systems. Occupant protection systems observed are the use of seat belts, and the availability of dual air bags, pretensioners and load limiters in the vehicles. All vehicles used include occupants age 16 to 96. Occupants studied include front-row occupants (drivers and right-front (RF) passengers). The average between drivers and RF passengers is also calculated. Results Incremental female fatality risk estimates versus males are reduced in newer MY vehicles. Incremental relative risks for female front-row occupants (average of drivers and right-front passengers) are found to be 19.9% (± 1.3) in fatal crashes in MY 1960–1999 vehicles, and 9.4% (± 2.2) percent in MY 2000–2020 vehicles. The difference in fatality risk between females and males is further reduced when looking at MY 2010–2020 vehicles (6.3 ± 5.4%) compared to MY 1960–2009 vehicles (18.3 ± 1.2%). Incremental fatality risk estimates also decrease in vehicles with newer generations of occupant protection systems regardless of MY. When occupants are belted in vehicles with the latest generation of modern occupant protection systems (dual air bags, seat belt pretensioners and load limiters), the estimated female fatality risk relative to males (average of drivers and right-front passengers) becomes 5.8% (± 3.8), which is lower than for belted occupants in vehicles without those occupant protections. Conclusions The disparity in fatality risk between males and females for the same physical impacts is reduced for later MY vehicles, as well as vehicles with more advanced occupant protection systems.

Football as a means of involving schoolchildren in health and recreational activities

The peculiarities of involving schoolchildren in health and recreational activities with the use of football are considered, as this sport is widely used in various parts of the physical education system. The aim. Defining principles, involving students in health and recreational activities using football. Methods. Analysis of scientific and methodological literature, observation, comparison. Results. The collective nature of football nurtures a sense of friendship and mutual assistance, develops such moral qualities as a sense of responsibility, respect for partners and rivals, discipline, activity. Each player can show their personal qualities: independence, initiative, creativity. However, the game requires the subordination of personal aspirations to the interests of the team. Systematic football lessons in different climatic and meteorological conditions promote physical hardening, increase resistance to disease and strengthen the body's adaptive capacity. At the same time, important habits of constant observance of domestic, labor, educational and sports regimes are nurtured. The article considers football as a type of recreational activity. The assessment of motivation to play football among children of primary school age is given. For most of them, recreational games have been shown to be a means of improving health and well-being. The health-improving effect of playing football and its availability have been determined. It is established that the feature of the game is a great variety of motor actions. Playing with the foot, head, chest requires high coordination of movements, mobility in the joints. The skill of performing techniques with the foot (part of the body, much less differentiated, and adapted to such movements than the hand) is admired by both spectators and the participants of the game. Conclusions. The article proves that the health effect of playing football is provided by dynamic work, a variety of muscular loads in the fresh air. The game is accompanied by the development of all quality aspects of motor activity. The great variety of motor actions promotes the creative reproduction of new conditioned-reflex connections, and, consequently, the mastery of new forms of movement, which enriches the motor experience of young athletes.

Community kitchen tandoors (CKT)-a potential candidate for air pollution mitigation strategies?

Community kitchen tandoor (CKT) is a clay-based hollow cylindrical device commonly used in South Asian and Middle Eastern countries for baking flatbreads and cooking meat. These CKTs, generally fuelled by charcoal or wood, contribute significantly to the pollution loads in ambient air along with occupational exposure hazards. CKTs, being a part of the informal sector, lack emissions and safety guidelines. This study surveys 139 restaurants in CKT hotspots of New Delhi, India, to understand tandoor design and operational parameters and to assess PM2.5 and CO exposure concentrations at representative field restaurants. PM2.5 and CO exposure concentrations from traditional CKT wasfound to be several-folds higher than safe indoor air quality levels. Further, the traditional CKT was evaluated for different improved fuels (like briquettes and pellets) in the laboratory for PM2.5 and CO microenvironment concentrations. It was found that the fuel improvements in traditional CKT could not improve microenvironment concentrations to the desired levels; hence, an automated pellet-fed forced-draft improved tandoor with an improved combustion chamber design is demonstrated. The results of the laboratory trial of improved tandoor were compared with traditional tandoor (using pellets) and have shown 84% and 94% reductions in PM2.5 and CO concentrations, respectively, indicating significant benefits to the environment and health. We recommend implementing such improved CKT, on a large scale, combined with other identified control options, as a potential candidate under air pollution mitigation strategies in cities' action plans under National Clean Air Programme (NCAP).

Establishment and application of test methodology demonstrating the functionality of air purification systems in reducing virus-loaded aerosol in indoor air

The global COVID-19 pandemic has resulted in a greater interest in improving the ventilation of indoor environments in order to remove aerosolized virus and thus reduce transmission. Air purification systems have been proposed as a solution to improve aerosol removal. The aim is to determine the efficacy of air purification systems in reducing the viral load in environmental air of a room. A containment room equipped with HEPA filter on air intake and exhaust was constructed. It was connected via an inlet with the BSL-2 facility. From the BSL-2, Feline Corona virus (FCoV) loaded aerosols were released into the containment room. After nebulization, air sampling was performed to determine the viral load in air prior to assessing the clean air delivery rate of the air purification systems. The infectivity of the captured viruses was also examined. The air purification systems realized a 97 to 99% reduction in viral load in air in one hour. Captured infectious FCoV was reduced by 99.9% to 99.99% by use of an ESP technology. The air purification systems, using ESP technology or HEPA filter, reduce the viral load in air. The ESP purifiers inactivate captured FCoV viruses. Therefore, air purification systems can be used as an adjunctive infection control measure.

Study on simulation of real‐time hybrid model test for offshore wind turbines

AbstractAs an emerging energy source with great potential, offshore wind power is supported by development policies in an increasing number of countries. However, the performance evaluation of floating offshore wind turbine (FOWT) structures is challenging due to the complexity of wind and wave loads and the difficulty in reproducing such loading conditions for downscaled FOWTs in laboratories. In physical model tests of FOWTs, the Froude's similarity law is adopted for the foundation, while the Reynolds similarity law is adopted for the blades, thus there is an issue with uncoordinated scaling laws. The FOWTs real‐time hybrid test uses loading device to simulate air loads, offering a new way to avoid scaling issues and reduce cost barriers. In this study, taking the 5 MW Braceless FOWT as the research object, a conceptual design of a real‐time hybrid model test system for Braceless offshore wind turbines is proposed. Six sets of working conditions are set for simulation to study the motion and force performances of the hybrid system. The performance requirements of the Braceless structure for the loading device in the real‐time hybrid test are quantified. Simulate different errors in the test to analyse the sensitivity of the response of the Braceless offshore wind turbine to various errors. The results show that the Braceless FOWT is relatively sensitive to motion and force errors. Due to the low‐frequency characteristics of offshore wind turbines and external load, the delay error has relatively little effect. The method results in this paper can provide theoretical support and design information support for the implementation of real‐time hybrid model tests in the future.

Parameter Adaptive Sliding Mode Force Control for Aerospace Electro-Hydraulic Load Simulator

The aerospace electro-hydraulic servo simulator is used to simulate the air load received during flight, and is used for the performance test and acceptance test of aerospace servo actuators on the ground. The force loading accuracy of the load simulator is an important assessment index. Because the loading system and the actuator system to be tested are coupled together, the free displacement of the system to be tested during loading will bring huge disturbance to the loading system, thus how to suppress external interference has always been a hot issue in the control field. This paper addresses this issue under the influence of nonlinear friction and uncertain external disturbance. First, the exact mathematical model of the system is derived, and the characteristics of the system are described by the state equations. Second, in order to obtain the relevant parameters in the controller, the system parameters are identified. Third, the parameter adaptive sliding mode force control based on the reaching law is proposed, and the performance of the control algorithm is analyzed theoretically. Finally, the new control method is applied in the aerospace electro-hydraulic servo simulator, and the results show that the new control algorithm can suppress the external interference by 95% or more, and the control accuracy is more than 97%, which fully demonstrates the effectiveness of the control method.

Experimental simulation for moisture damage of saturated asphalt mixture and evolution of mixture’s pore water pressure, accumulative strain

Moisture damage has significant impact on pavement’s performance and service life, researching this kind of distress’ mechanical mechanism, experimental simulation protocol or theoretical analysis method continues to be the research that should be conducted in depth for pavement researchers. But, due to the complexity of this distress’ influencing factors, there is still not a satisfactory research result by far, particularly for its experimental simulation test, the current research lack of a satisfactory apparatus or protocol that can simulate asphalt mixture’s moisture damage in lab. So then, this paper, basing on a fully mechanical analysis in advance for asphalt pavement’s moisture damage, develops an experimental apparatus being capability to simulate and investigate asphalt mixture’s moisture damage in lab by improving a dynamic triaxial tester, then utilizes this improved triaxial tester investigate moisture damage of asphalt mixture with different air void percent or applied by different confining pressure, and acquires these mixture’s characteristics regarding their pore water pressure evolution, strain cumulation, specimen deformation as well as their influencing factors, then classifies these test results into three types according to their characteristics. The test results demonstrate, this developed apparatus can comparatively satisfactorily simulate mixture’s moisture damage phenomena in lab, its simulation test results are close to field investigation results, and air void percent, confining pressure and loading frequency are the principal factors that have significant impact on mixture’s moisture damage test results. For the specimen with lower air void percent or under a higher confining pressure, their test results are primarily type 1, whose pore water pressure and cumulative strain are relatively low, deformation are pure compression. Whereas, for the specimen with larger air void percent or applied by higher confining pressure, their pore water pressure and cumulative strain are usually larger, specimen are generally observed with stripping or cracking in the end of test, even some are found with diagonal cracks, these characteristics are classified as type 3. As for type 2, their test results are primarily between that of type 1 and type 3, their pore water pressure, cumulative strain are relatively large, yet specimen’s deformation mainly attribute to compression, and only swelling in radial direction or slight stripping are found with specimens.

The role of stress-state on the low cycle fatigue resistance of non-hydrided beta-treated Zircaloy-4

Reactor operation results in cyclic stresses that produce fatigue. Increased strain to failure under monotonic loading has been observed for Zircaloy-4 under a stress-state of shear defined by a low triaxiality. Triaxiality (η) is defined as the ratio of hydrostatic stress to von Mises stress and typically ranges from values of -0.33 for compression, to 0 for torsion loading and to 0.9 for notched, axial loaded specimens. Low Cycle Fatigue (LCF) testing of Zircaloy-4 was performed under uniaxial and torsion loading in air at room-temperature. Both smooth and notched specimens were tested to vary the value of positive triaxiality. An increase in LCF resistance with less notch sensitivity is observed under torsion loading. Cyclic stress-strain curves are developed that show a higher strain to failure and lower flow stress under torsion loading. This suggests a lower triaxiality produces increased strain to failure capability under both cyclic and monotonic loading that is shown to generally follow a Rice-Tracey model for void nucleation, growth and coalescence. Fractography examinations are used to understand the mechanism for crack extension.

High-cycle fatigue behavior of IN 738LC superalloy at high temperatures

The presented study is focused on experimental results of high-cycle fatigue life of a cast polycrystalline nickel-based superalloy IN 738LC at temperatures of 800, 900, and 950°C. The absence of hot isostatic pressing (HIP) led to the occurrence of casting defects in the microstructure. The fatigue tests were performed in symmetrical loading in laboratory air. The fracture surfaces of specimens were studied by scanning electron microscopy to describe the influence of temperature on the fatigue damage mechanism and fatigue crack initiation. Change in the primary crack propagation mechanism from crystalline (stage I regime) to non-crystalline (stage II regime) mechanism was observed with increasing temperature. However, the effect of changing mechanism caused by temperature dependence was unfavorably influenced by casting defects.

Impact of thickness, void content, temperature and loading rate on tensile fracture toughness and work of fracture of asphalt mixtures- An experimental study using the SCB test

Asphaltic concrete mixtures are among the most common construction materials for the pavement of roads. As a multi-phase composite mixture with randomly distributed aggregates inside the mastic part, the mechanical properties of such materials can be influenced by different factors. Cracking and induced fracture is among the common degradation and failure modes in these construction mixtures that often takes place in cold regions. In this research, the effects of some influencing parameters including temperature, air void percentage and loading rate are investigated experimentally on the fracture toughness (KIc) and work of fracture (WIc) of hot mix asphalt material. Edge notched semi-circular bend (SCB) specimen was employed to conduct mode I fracture experiments. The thickness of SCB samples were considered as variable and the HMA mixtures were tested with two SCB thicknesses of 30 and 60 mm. The experimental results showed that both fracture toughness and fracture work are increased by increasing the thickness. However, the effect of thickness on the fracture work was much more significant than the KIc value. Also, the fracture and cracking resistance parameters were increased by decreasing the temperature and air void content. Both KIc and WIc values were also increased by increasing the loading rate in the investigated range of 1 to 8 mm/min. The most influencing parameters on the change of fracture resistance parameters were the temperature, loading rate, air void content and thickness, respectively.

Research on load characteristics of squeeze-film air bearings based on fluid–solid coupling

In order to obtain the loading capacity and its variation of the squeeze-film air bearing, taking an air bearing as the research object, the structure model and the equivalent disk model of the squeeze-film air bearing are established. The modal analysis of the designed structure is carried out, and the mode of the bearing structure in the ultrasonic frequency range and the working squeeze frequency of the bearing are obtained. At the same time, the influence of air film thickness on the load characteristics of squeeze-film air bearing is analyzed by the fluid–solid coupling method. The relationship between air film thickness and loading capacity, and the relationship between contact area and loading capacity are obtained, respectively, by the above method. The results show that reducing the gap between the bearing bush and the rotor, increasing the amplitude of the bearing bush, and increasing the contact area between the bearing bush and the rotor can improve the loading capacity of the squeeze-film air bearing.

A study on dedicated outdoor air handling unit systems regarding the widespread of ZEB

ZEB has been promoted in the building sector to realize energy conservation and carbon neutrality. This has caused changes such as a decrease in the room sensible heat load factor and an increase in the outdoor air load ratio. In this study, the systems with a dedicated outdoor air handling unit (OAHU) are evaluated as air conditioning systems that can flexibly respond to a changing heat load, and guidelines for rational design and operation are given. A case study is conducted to evaluate the indoor environment and energy performance of a conventional air handling unit (AHU) system and an OAHU system under the assumption of a reduction in internal heat gain intensity. The study results showed that the OAHU processed latent heat and reduced the number of uncomfortable hours by 78% compared to those for the AHU system during the cooling season for cases with reduced internal heat gain. Regarding system energy consumption, the OAHU system consumed 17% more energy than the AHU-system. Thus, the OAHU system maintained a better indoor environment than the AHU system at the cost of increased energy use. Based on these results, measures for reducing the energy consumption of the OAHU system are discussed.